Active variable inductor circuit

Abstract

A switched mode power supply uses a primary winding of a transformer instead of an inductor. The secondary winding of the transformer is driven by the current generated by the negative inductance circuit. When reverse current flows through, the equivalent inductance value of the primary winding can be increased. When the output voltage is maintained within a predetermined limit range, the steady-state detector activates a steady-state signal and closes a switch to turn on a reverse current from the operational amplifier to increase the inductance, thereby reducing the ripple during the steady state. When output transient jump occurs, the steady-state signal is deactivated, the switch is turned off, and current is prevented from flowing through the secondary of the transformer, so that primary inductance is reduced, and the current flows to the output faster to suppress transient. A resistor and capacitor network around the operational amplifier may be used to adjust inductance modulation.

Description

W O 2 02 6 / 08 59 10 A l IH III III III III III III III III O III III III III III IH III III I (12) INTERNATIONAL APPLICATION PUBLISHED UNDER THE PATENT COOPERATION TREATY (PCT) (19) World Intellectual Property Organization International Bureau (43) International Publication Date 30 April 2026 (30.04.2026) WIPO I PCT lll■llllllllll■IIIIIIIIHIIilllllllllllllll (10) International Publication Number WO 2026 / 085910 Al (51) International Patent Classification: H02M 3 / 335 (2006.01) H02M1 / 14 (2006.01) H02M1 / 32 (2007.01) H02H 7 / 12 (2006.01) (21) International Application Number: PCT / CN2024 / 128494 (22) International Filing Date: 30 October 2024 (30.10.2024) (25) Filing Language: English (26) Publication Language: English (30) Priority Data: 18 / 923,891 23 October 2024 (23.10.2024) US (71) Applicant: HONG KONG APPLIED SCIENCE AND TECHNOLOGY RESEARCH INSTITUTE COMPA­ NY LIMITED [CN / CN]; 5 / F, Photonics Centre, 2 Science Park East Avenue, Hong Kong Science Park, Shatin, N.T., Hong Kong (CN). (72)Inventors: XU,Danting; 7A, Tower 3, ONTOLO, 7 Fo Yin Road, Pak Shek Kok, Tai Po, N.T., Hong Kong (CN). MA, Yiie; Room 624, Innoceli, No.l Chong San Road, Tai Po, N.T., Hong Kong (CN). LI, Chengyong; Flat E 9 / F, Tower 13,18 Chong San Road, Centra Horizon Pak Shek Kok Tai PoN.T., Hong Kong (CN). (74) Agent: CHINA TRUER IP; Room 1104, Building 2, Excellence Meilin Central Plaza (North Area), No. 128 Zhongkang Road, Meidu Community, Meilin Street, Futian District, Shenzhen, Guangdong 518049 (CN). (81) Designated States (unless otherwise indicated, for every kind of national protection available): AE, AG, AL, AM, AO, AT, AU, AZ, BA, BB, BG, BH, BN, BR, BW, BY BZ, CA, CH, CL, CN, CO, CR, CU, CV, CZ, DE, DJ, DK, DM, (54) Title: ACTIVE VARIABLE INDUCTOR CIRCUIT (57) Abstract: A Switched-Mode Power Supply uses a primary winding of a transformer rather than an inductor. The secondary winding of the transformer is driven with a current generated by a negative inductance circuit. When the reversecunent flows it can increase the equivalent inductance value of the primary windings. A steady-state detector activates a steady signal and closes a switch to turn on the reverse current from an op amp when the output voltage remains within predetermined limits, causing the inductance to increase thus reducing ripple during steady state. When an output transient occurs, the steacfy signal is deactivated and the switch opened to stop the current from flowing through the transformer secondary, reducing primary inductance to allow for cunent to flow faster to the output to suppress the transient. Resistor and capacitor networks around the op amp allow fortuning the inductance modulation. [Continued on next page] WO 2026 / 085910 Al DO, DZ, EC, EE, EG, ES, FI, GB, GD, GE, GH, GM, GT, HN, HR, HU, ID, IL, IN, IQ, IR, IS, IT, JM, JO, JP, KE, KG, KH, KN, KP, KR, KW, KZ, LA, LC, LK, LR, LS, LU, LY, MA, MD, MG, MK, MN, MU, MW, MX, MY MZ, NA, NG, NI, NO, NZ, OM, PA, PE, PG, PH, PL, PT, QA, RO, RS,RU, RW, SA, SC, SD, SE, SG, SK, SL, ST, SV, SY,TH, TJ, TM, TN, TR, TT, TZ, UA, UG, US, UZ, VC, VN, WS, ZA,ZM,ZW. (84) Designated States (unless otherwise indicated, for every kind of regional protection available)'. ARIPO (BW, CV, GH, GM, KE, LR, LS, MW, MZ, NA, RW, SC, SD, SL, ST, SZ, TZ, UG, ZM, ZW), Eurasian (AM, AZ, BY, KG, KZ, RU, TJ, TM), European (AL, AT, BE, BG, CH, CY, CZ, DE, DK, EE, ES, FI, FR, GB, GR, HR, HU, E, IS, IT, LT, LU, LV, MC, ME, MK, MT, NL, NO, PL, PT, RO, RS, SE, SI, SK, SM, TR), OAPI (BF, BJ, CF, CG, CI, CM, GA, GN, GQ, GW, KM, ML, MR, NE, SN, TD, TG). Published: — with international search report (Art. 21(3)) WO 2026 / 085910 PCT / CN2024 / 128494 1 Active Variable Inductor Circuit FIELD OF THE INVENTION

[0001] This invention relates to active inductors, and more particularly to a negative inductance circuit for a Switched-Mode Power Supply (SMPS). BACKGROUND OF THE INVENTION

[0002] Power Metal Oxide Semiconductor Field Effect Transistors (MOSFETs) that switch inthe hundred kHz range have enabled light, small, and efficient Switched-Mode Power Supplies (SMPS). A typical SMPS uses two power transistors in a Buck converter arrangement. The gates of the power transistors are switched on and off by a controller than ensures that both transistors are not on at the same time. By controlling the duty cycles and other timing, a desired output voltage can be generated from an input voltage.

[0003] Figure 1 shows a prior-art SMPS. The SMPS converts input voltage VIN to output voltage VOUT that drives a load represented by load resistor 18. Controller 12 drives gate signal SI high to turn on transistor 22 to allow current to flow from VIN, through transistor 22 and inductor 10 to charge output capacitor 16. Then controller 12 turn off SI and turn on gate signal S2, which turns on transistor 24, discharging output capacitor 16. The ON times for SI and S2 generated by controller 12 determine the output voltage VOUT that is sustained in steady-state for agiven value of VIN and device sizes.

[0004] Input capacitor 14 smooths VIN, while output capacitor 16 stores charge and smooths ripples on VOUT. Inductor 10 stores energy in its magnetic field and smooths variations in inductor current IL that drives VOUT and supplies capacitor current IC to charge output capacitor 16.

[0005] Figure 2 is a waveform showing operation of the SMPS of Fig. 1. When controller drives S1 high, VIN drives current through transistor 22 and inductor 10. The voltage across inductor 10, VL, rises and falls as SI turns transistor 22 on and off. This voltage VL causes inductor current IL to rise sharply during SI high, and fall slowly when SI is low. Energy is stored in inductor 10 when IL rises, and is released as IL falls.

[0006] The AC portion of inductor current IL flows mostly to output capacitor 16, causing capacitor current IC to follow inductor current IL, but with curvature due to the RC delay. The voltage across output capacitor 16, and VOUT, rises andfalls with inductor current IL, after an RC delay.

[0007] The rising and falling of VOUT is known as ripple, and is undesirable. Ripple can be reduced by increasing the capacitance value (measured in Farads) of output capacitor 16. However, this is undesirable singe large capacitors occupy board or layout space and can be expensive and have long wiring paths that have electrical losses. Ripple can also be reduced by increasing the inductance value (measured in Henrys) of inductor 10, but again large inductors tend to be even more expensive and cumbersome than capacitors.

[0008] Increasing the capacitance or inductance also reduces the transient response of the SMPS. For example, the load may contain many transistors or other circuits that are switched on and off during normal operation. This can cause the current drawn by the load to vary. The SMPS should respond to these load current WO 2026 / 085910 PCT / CN2024 / 128494 2 variations by supplying additional or reduced current as needed.However, when output capacitor 16 is large, the current through transistor 22 is applied to charge output capacitor 16 rather than flow through load resistor 18. Likewise a larger inductor 10 also has a poor transient response. When transient response is weak, VOUT can swing to extreme levels that can trigger over-voltage or under-voltage protection circuits, which is undesirable.

[0009] There is a trade-off between increasing output capacitance and inductance to reduce ripple, while still providing enough transient response. The inventors realize that reducing output ripple and improving transient response are mutually exclusive when traditional fixed-value capacitor and inductors are used in the SMPS.

[00010] What is desired is an active inductor for use in an SMPS. An active inductor that has an increased inductance value during steady-state conditions is desirable to reduce output ripple, and that has a reduced inductance value during transients to improve transient response. Anactive inductor that has its inductance value controlled by a circuit is desired. BRIEF DESCRIPTION OF THE DRAWINGS

[00011] Figure 1 shows a prior-art SMPS.

[00012] Figure 2 is a waveform showing operation of the SMPS of Fig. 1.

[00013] Figure 3 shows an SMPS with an active inductor.

[00014] Figure 4 shows the SMPS with a capacitor-based negative inductance circuit in more detail.

[00015] Figure 5 is a graph of the primary current in the transformer with the NIC turned on and off.

[00016] Figure 6 is a graph of the output voltage VOUT with the NIC turned on and off.

[00017] Figures 7A-7B shown waveforms of the SMPS responding to a jump in load cunent with the NIC turned on and off.

[00018] Figures 8A-8B shown waveforms of the SMPS responding to a drop in load current with the NIC turned on and off.

[00019] Figure 9 shows an embodiment of the steady-state detector in more detail.

[00020] Figure 10 shows the SMPS with the NIC having a bipolar transistor switch.

[00021] Figure 11 showsthe SMPS with the NIC having an n-channel transistor switch.

[00022] Figure 12 shows the SMPS with the NIC having a diode switch.

[00023] Figure 13 shows the SMPS with the NIC with a positive inductor.

[00024] Figure 14 shows a boost converter SMPS with a NIC.

[00025] Figure 15 shows a SMPS with a NIC that only partially modulates the secondary current. DETAILED DESCRIPTION

[00026] The present invention relates to an improvement in active inductor circuits. The following description is presented to enable one of ordinary skill in the art to make and use the invention as provided in the context of a particular application and its requirements. Various modifications to the preferred embodiment WO 2026 / 085910 PCT / CN2024 / 128494 3 will be apparent to those with skill in the art, and the general principles defined herein may be applied to other embodiments. Therefore, the present invention is not intended to be limited to the particular embodiments shown and described, but is to be accordedthe widest scope consistent with the principles and novel features herein disclosed.

[00027] The inventors have realized that a variable inductor would allow a SMPS to have low ripple by increasing the inductance value, and to have faster transient response by reducing the inductance value. While variable inductors are used in older radio equipment, these variable inductors are often large coils that have magnetic cores that are physically moved to alter inductance.

[00028] The inventors realize that an active variable power inductor can be realized by replacing the inductor with a mutual inductance device such as a transformer. The primary windings of the transformer carry inductor current IL in the SMPS. The secondary windings in the transformer are connected to a Negative Inductance Circuit (NIC). The NIC can send current through the secondary windings, which then generates a magnetic field that is coupled through the magnetic core to the primary windings. The NIC can send a currentin reverse through the secondary windings to create a mutual inductance in the primary windings that resists current flow and thus increases the inductance value of the primary windings. Thus the NIC can adjust the inductance value seen by the primary windings.

[00029] Figure 3 shows an SMPS with an active inductor. Inductor 10 of Fig. 1 is replaced by transformer 20. The primary windings of transformer 20 carry inductor current IL from transistor 22 to output capacitor 16.

[00030] Controller 12 drives gate signal SI hi^i to allow current to flow through transistor 22 and the primary windings of transformer 20 to charge output capacitor 16. Controller 12 also drives gate signal S2 high to turn on transistor 24 to reduce the voltage across transformer 20 to maintain a desired output voltage VOUT. Input capacitor 14 is optional but helps to maintain VIN.

[00031] Load resistor 18 represents the load driven by VOUT which can vary during operation, creating transients. When no transientoccurs, steady-state detector 50 senses that VOUT is within predetermined limits, and drives steady signal ST high, closing switch 40. Switch 40 closes the loop with Negative Inductance Circuit NIC 30 and the secondary windings of transformer 20.

[00032] With switch 40 closed, NIC 30 can generate a reverse current that flows through the secondary windings of transformer 20. This reverse current generates a magnetic field in transformer 20 that is coupled through or enhanced by the magnetic core of transformer 20. This generated magnetic field creates an additional inductance in the primary windings of transformer 20. Thus the inductance value of the primary windings of transformer 20 is increased when switch 40 closes to enable NIC 30.

[00033] When a sufficiently large transient occurs on the output, VOUT is no longer within the predetermined limits, and steady-state detector 50 drives steady signal ST low, opening switch 40. Switch 40 opens the loop and prevents NIC 30 from drivingthe reverse current through the secondary windings of WO 2026 / 085910 PCT / CN2024 / 128494 4 transformer 20. The inductance of the primary windings of transformer 20 falls back to its nominal value. The lower inductance value through transformer 20 allows for a larger inductor current IL to flow to the output and to load 18. A faster response to the transient is possible due to the increased current flowing through transformer 20.

[00034] The lower inductance value through the primary windings of transformer 20 provides for a higher bandwidth of the SMPS when a transient is detected. When no transient is detected, NIC 30 is enabled to increase the inductance value of the primary windings of transformer 20. This higher inductance during steady state reduces output ripple. [0003S] Thus by switching NIC 30 on and off, the equivalent inductance value in the primary is adjusted. High inductance is provided to reduce ripple during steady state, while low inductance is provided for fastertransient response times when a transient is detected. For example, when transformer 20 has a rated inductance of 1 pH (the physical inductance value), the equivalent inductance value is lpH when NIC 30 is off, and the equivalent inductance value is lgH when NIC 30 is on.

[00036] Figure 4 shows the SMPS with a capacitor-based negative inductance circuit in more detail. Op amp 32 is powered by power supply voltages VS+ and VS-. A midpoint voltage, such as midway between VS+ and VS-, can be used to generate a secondary ground GND2. This ground GND2 is connected to one terminal of the secondary windings of transformer 20, while the other terminal of the secondary windings is connected to the non-inverting input of op amp 32 as node UB.

[00037] The inverting input of op amp 32 is node UA, which is connected to ground GND2 by ground resistor 36 with resistance value Rg. Feedback capacitor 34 wi± capacitance value Cf connects node UA to the output of op amp 32, node UC. Feedback capacitor 34and ground resistor 36 form a dual feedback network with an impedance of Zi / Rg causing op amp 32 to provide a gain of 1+Zi / Rg.

[00038] Switch 40 and positive resistor 38 with resistance value Rp are in series between op amp 32 output node UC and the non-inverting input of op amp 32, node UB. When steady-state detector 50 drives ST high and closes switch 40, second impedance (Zp) connects the noninverting input and output of op amp 32.

[00039] Ripples are preset on the primary current through transformer 20 because controller 12 switches power transistors 22, 24 on and off. These ripples have the same frequency as the selected switching frequency. The inductor circuit is a voltage controlled current source. The mutual inductance through the metal core of the transformer 20 induces a voltage UB at the end of the secondary winding. According to the characteristics of an operational amplifier, the voltages at the non-inverting input (+) and the inverting input (-) of op amp 32 are equal,so voltage UA at the inverting input is equal to voltage UB at the non-inverting input. Due to the feedback network through feedback capacitor 34, a voltage gain is generated, and the output voltage after the gain of op amp 32 is UC. In this case, the voltages UC and UB at the two ends of positive resistor 38 create a reverse AC current on positive resistor 38. This reverse AC current is opposite in phase to the ripple portion of WO 2026 / 085910 PCT / CN2024 / 128494 5 IL and is coupled through the secondary winding of transformer 20 to the primary winding of transformer 20. The coupled ripple portion of IL has the same phase as the original ripple, but the ripple amplitude is reduced

[00040] Mutual inductance through the metal core of transformer 20 induces similar ripples in the secondary current. These ripples in the secondary current are applied to the inverting (+) input of op amp 32 and are amplified by the gain factor and converted to current flowing through positive resistor 38 whenswitch 40 is closed. Positive resistor 38 converts these ripples to a voltage difference across positive resistor 38 and provides a current that flows in reverse through the secondary windings of transformer 20, from the right terminal to the left terminal and GND2.

[00041] A first impedance network is attached to the inverting (-) input of op amp 32, while a second impedance network is attached to the non-inverting (+) input of op amp 32. Ground resistor 36 and feedback capacitor 34 connect to the inverting input of op amp 32 and form a first impedance network that is an inverting feedback network. Positive resistor 38 connects to the non-inverting (+) input of op amp 32 and forms a second impedance network.

[00042] A voltage ripple from the primary current induces an AC ripple into the secondary current because of the mutual inductance of transformer 20. This AC ripple of the secondary current is applied to the inverting (+) input of op amp 32 and causes an AC ripple in the op ampoutput current when switch 40 is closed. The reverse amplification gain of op amp 32 is 1+Zi / Rg. Impedance Zi is from feedback capacitor 34.

[00043] In this embodiment, with scaling factor s, the first impedance is Zi=l / (sCf) and the second impedance is Zp=Rp. Ground resistor 36 and positive resistor 38 can be variable resistors or can be fixed resistors once their resistance values have been set, such as by circuit analysis, simulation, or testing with a prototype. When ground resistor 36 and positive resistor 38 are variable resistors, they can be programmable, such as with a resistor bank that has resistors selectable by a programmable register that can be programmed by a program.

[00044] Scaling factor s is the complex frequency. In frequency domain analysis, the complex frequency s is a complex number denoted ass = o+jco, where g is the real part, denoting the decay or growth factor, andjco is the imaginary part, denoting the angular frequency. For ideal inductors and capacitors,a is 0. The frequency domain s is defined as the decomposition of the signal into imaginary exponential components of different frequencies and the response of the system may be obtained by Fourier inverse transformation.

[00045] The SMPS operates as described before, except that the inductance value of the primary windings of transformer 20 is boosted to reduce ripple when steady-state detector 50 determines that VOUT remains within predetermined limits. When VOUT has a transient that is not within the predetermined limits, steady-state detector 50 drives ST low to open switch 40 and turn off the current in the secondary windings. The equivalent inductance of the primary windings falls to a nominal value. The lower nominal inductance allows for a larger WO 2026 / 085910 PCT / CN2024 / 128494 6 peak-to-peak value of the ripple within a cycle to flow to the load, which has a larger current slope, allowing for faster transient response.

[00046] In practice, the inductance value of the primarywindings are adjustable and can double or triple when the reverse cunent flows through the secondary windings. The amount of inductance increase due to the NIC can be adjusted by adjusting values of resistance of ground resistor 36, positive resistor 38, the capacitance of feedback capacitor 34, and the windings ratio and magnetic core (mutual inductance) of transformer 20.

[00047] Figure 5 is a graph of the primary current in the transformer with the NIC turned on and off. The inductor primary current IL flows thorough the primary windings of transformer 20 (Fig. 4). This inductor current IL has a low value of waveform 102 when steady-state detector 50 detects steady-state and closes switch 40 to enable NIC 30. If switch 40 remains open during steady state, NIC 30 is turned off and the secondary current in transformer 20 is halted. The lower equivalent inductance allows for a higher inductor current IL to flow in the primary windings, as seen by waveform 104.

[00048] Figure 6 is agraph of the output voltage VOUT with the NIC turned on and off. There is a ripple on the output, as shown by output voltage VOUT rising and falling. The absolute value of the ripple is small, but this ripple is still undesirable.

[00049] When there are no transients steady-state detector 50 detects the steady-state and closes switch 40 to enable NIC 30. The equivalent inductance of the primary windings of transformer 20 is larger than (double or triple ) the nominal value (such as 1 micro-Henry) because of mutual inductance from the reverse current flowing through the secondary windings from op amp 32. This higher equivalent inductance acts to resist changes in inductor current and thus reduces changes in VOUT due to the normal switching on and off of transistors 22, 24 by controller 12. Waveform 112 shows the reduced ripple on VOUT when NIC 30 is turned on.

[00050] If switch 40 remains open during steady state, NIC 30 is turned off and the secondary current in transformer 20 ishalted. The lower equivalent inductance allows for a higher inductor current IL to flow in the primary windings. Since this inductor current is switched on and off by transistors 22, 24, this modulation of a higher inductor current causes larger swings in VOUT, as seen by waveform 114.

[00051] Figures 7A-7B show waveforms highlighting the effect of turning the NIC on and off on VOUT for transients with sudden increases in the SMPS load current.

[00052] In Fig, 7A, the load current ILOAD through load resistor 18 suddenly increases, such as when transistors in the load switch states and draw a large transient current. In Fig. 7B, the output voltage VOUT suddenly drops due to this sudden increase in load current. When NIC 30 is turned off, a simulation produces waveform 122, which recovers faster than waveform 124, which is from a simulation with NIC 30 turned on. Thus when steady-state detector 50 detects a transient and turns off NIC 30, transients can be recovered from more quickly. WO2026 / 085910 PCT / CN2024 / 128494 7

[00053] Even if the transient is faster than steady-state detector 50 and NIC 30 can be turned on, there may be other transients that follow that may benefit from NIC 30 being turned off by the first transient.

[00054] Figures 8A-8B show waveforms of the effect of the NIC turning on and off on VOUT for transients with sudden drops in SMPS load current. In Fig, 8A, the load current ILOAD through load resistor 18 suddenly drops, such as when transistors switch to a light load.

[00055] In Fig. 8B, the output voltage VOUT suddenly spikes higher due to this sudden decrease in load current. When NIC 30 is turned off, a simulation produces waveform 132, which recovers faster with lower ripple than waveform 134, which is from a simulation with NIC 30 turned on. Thus when steady-state detector 50 detects a transient and turns off NIC 30, both high-going and low-going transients can be recovered from more quickly.

[00056] Figure 9 shows an embodiment of thesteady-state detector in more detail. Output voltage VOUT is input to steady-state detector 50 and compared to predetermined voltage limits VMIN, VMAX that can be set to an acceptable level of ripple or may be determined by testing or simulation to best determined when to enable transient response.

[00057] Comparator 52 drives its output high when VOUT is above VMIN, or within the lower limit. Comparator 54 drives its output high when VOUT is below VMAX, or within the upper limit. Thus when both outputs are high, VOUT is within the predetermined limits. The 11 inputs applied to XNOR gate 56 drive its output, steady signal ST, high. This turns on NIC 30 for steady-state conditions of VOUT.

[00058] When VOUT is above VMAX, comparator 54 drives its output low, while comparator 52 still drives its output high. The 01 inputs to XNOR gate 56 drive its output ST low, turning off NIC 30 for better transient response.

[00059] When VOUT is below VMIN, comparator 52 drives its output low, whilecomparator 54 still drives its output high. The 10 inputs to XNOR gate 56 drive its output ST low, turning off NIC 30 for better transient response.

[00060] Figure 10 shows the SMPS with the NIC having a bipolar transistor switch. In this embodiment, switch 40 is implemented as bipolar NPN transistor 41. The transistor base is driven by steady-state signal ST that is generated by steady-state detector 50.

[00061] Figure 11 shows the SMPS with the NIC having an n-channel transistor switch. In this embodiment, switch 40 is implemented as n-channel transistor 43. The transistor gate is driven by steady-state signal ST that is generated by steady-state detector 50.

[00062] Figure 12 shows the SMPS with the NIC having a diode switch. In this embodiment, switch 40 is implemented as diode 45. Since diode 45 has no control gate, ST and steady-state detector 50 are not needed.

[00063] Diode 45 blocks reverse current flow. NIC acts as a voltage-controlled current source. In steady-state, diode45 only allows a positive current to pass through it. A small forward voltage across diode 45 is required WO 2026 / 085910 PCT / CN2024 / 128494 8 for current to flow. This results in a small DC offset. At low voltages diode 45 turns off and the current waveform is clipped at these low voltages of the AC ripple.

[00064] When a positive transient occurs, a large but low frequency current rise is sensed by op amp 32. The voltage into diode 45 rises with the low-frequency rise due to the transient. This higher voltage allows diode 45 to remain on longer and to flow more secondary current while the transient occurs. The higher secondary current increases the mutual inductance, and the higher primary inductance

[00065] Although there is no steady-state detector 50 in this embodiment, diode 45 itself can react according to the voltage applied to it, i.e. when the voltage is negative, diode 45 blocks current; when the voltage is positive, diode 45 conducts. When transient occurs, the load currentincreases in the primary circuit, and this increase is sensed through transformer 20 to node UB. Then the two terminals diode 45 also ‘sense’ a voltage change since diode 45 is connected in series with transformer 20. For a short time diode 45 is forward biased during the voltage change, so there is a low frequency transient current change induced.

[00066] Figure 13 shows the SMPS with the NIC with a positive inductor. In this embodiment, ground resistor 36 is replaced by ground inductor 39 and feedback capacitor 34 is replaced by feedback resistor 35. In this embodiment, Zi = Rf of feedback resistor 35, while Z2 = sLp, where s is the complex frequency and Lp is the inductance value of ground inductor 39. The gain generated by feedback capacitor 34 (Fig. 4) is affected by the switching frequency. However, using feedback resistor 35 produces a fixed gain that is not affected by frequency.

[00067] Figure 14 shows a boost converter SMPS with a NIC. In this embodiment, a boost converterrather than a Buck converter is used for the primary converter. Power transistor 22 is located after transformer 20 rather than before transformer 20 as in the Buck converter shown in Figs. 3, 4, 10-13. Power transistor 24 to ground is located before transformer 20 rather than after transformer 20.

[00068] Figure 15 shows a SMPS with a NIC that partially modulates the secondary current. In this embodiment, switch shunt resistor 60 in in parallel with switch 40. Some current from the output of op amp 32 passes through switch shunt resistor 60 even when switch 40 is open. Thus NIC 30 remains on even when steady-state detector 50 detects a transient and drives steady signal ST low to open switch 40. When steady­ state detector 50 detects the steady state and drives steady signal ST high, switch 40 closes and current from the output of op amp 32 passes through switch 40 and switch shunt resistor 60 in parallel. Thus closing switch 40 increases the current through positive resistor 38, andthus increases the secondary current in transformer 20.

[00069] Rather than turn NIC 30 fully on and off, NIC 30 remains on, but its current is modulated by steady­ state detector 50. Leaving NIC 30 on can be advantageous because turning op amp 32 on and off may require time to reinitialize, resulting in delays when ST is switched on and off.

[00070] The amount of current that is modulated between the two states can be adjusted by adjusting the resistance value of switch shunt resistor 60 and of switch 40. Another resistor could be added in series with WO 2026 / 085910 PCT / CN2024 / 128494 9 switch 40 to further adjust the current ratio. Thus more design flexibility is introduced with switch shunt resistor 60. ALTERNATE EMBODIMENTS

[00071] Several other embodiments are contemplated by the inventors. For example many combinations and variations of switch 40 are possible. The switch could be any kind of transistor, such as an Insulated-Gate transistor or diode, NPN or PNP or other triode, andcould have a network of transistors rather than a single transistor.

[00072] While a Buck converter arrangement of transistors 22, 24 has been shown in most drawings, and a Boost converter shown in Fig. 14, other converters may be substituted, such as Buck-boost, isolated, or multiphase converters. Other SMPS, such as Cuk or Sepic may be substituted.

[00073] There are many possible embodiments of steady-state detector 50. The embodiment in Fig. 9 may swap inverting and non-inverting inputs to the comparators, inverters may be added or removed, and other gating may be used other than XNOR. A differentiator or a load transient detector may be used.

[00074] The output voltage may be sensed by a resistive network, and then the signal is passed directly to the buck control loop comparator for handling ,as another alternative for steady-state detector 50.

[00075] Alternately, the input voltage node of the buck converter may be used for transient detection instead of the output voltage nodefor faster detection, and an auxiliary buck converter is used to smooth the transient spike.

[00076] By using a resistive network and an improved Differential Difference Amplifier (DDA)-based Type- III compensator, such as an OTA, the load transient response could be detected and passed to the comparator in control loop.

[00077] Steady-state detector 50 could use the input node instead of the output node for sensing the load step. Alternately, steady-state detector 50 could sense current in the output capacitor or the voltage at the load side to detect the variation. Together with the comparator, the control can be realized by setting a proper threshold of the comparator.

[00078] Comparators 52, 54 can be op amps or other compare circuits. Hysteresis can be added to require that a transient last for a predetermined time period before triggering steady-state detector 50 to turn off steady­ state signal ST. XNOR 56 can be an XOR gate followed by an inverter. Rather than have twopredetermined voltage levels, providing transient response for both high and low transients, only one voltage limit could be provided, with one comparator. For example, steady-state detector 50 could turn off steady-state signal ST only for high-going transients that exceed VMAX, but not turn off ST for low-going transients. This may be useful when only high-going transients are problematic or severe.

[00079] Rather than have an active-high steady-state signal ST, and active low signal could be used. The signal may be inverted for use with certain types of switches. Rather than have just a single n-channel transistor WO 2026 / 085910 PCT / CN2024 / 128494 10 as the switch, a transmission gate with both p-channel and n-channel transistors in parallel may be used, with an inverter to generate STB for the p-channel gate.

[00080] Steady-state detector 50 may be powered by VS+, VS- or by another power supply and have voltage level shifters as needed. The secondary ground GND2 can be isolated fromthe primary ground GND, or may be coupled to it. Other power and grounding schemes could be substituted. Power and ground voltages may be shifted. GND2 may be a reference voltage of some sort and does not have to be exactly the midpoint voltage.

[00081] Other impedance networks of resistors, capacitors, and / or inductors could be added around op amp 32, and the values of these components adjusted as desired. Transformer 20 could be any kind of mutual inductance device with core energy storage, such as a PCB inductor with E core or C core, or a planar transformer. Rather than a single transformer, two or more transformers may be placed in series to obtain a desired nominal inductance. While a transformer with a metal or iron core has been described, the metal core could be removed if a sufficient mutual inductance is available. The number of turns in the primary and secondary of transformer 20 could vary, and different wire gages (cross-sectional areas) could be used for the primary andsecondary windings. These factors can affect the mutual inductance and nominal inductance values.

[00082] While the term windings has been used generically to describe the wire paths that carry the primary current or secondary current within transformer 20, these windings do not have to be uniform loops but can have various physical arrangements and configurations and shapes. The windings may each be a long wire that is wound or wrapped around a metal core, but the windings could also be a spiral pattern on a plane for a planar transformer. The primary and secondary windings could be in separate planes. Many other variations are possible. There may be intermediate terminals, such as an intermediate terminal halfway along the primary winding, between a left primary termina and a right primary terminal. There may be a third winding for a third current path through transformer 20, such as an auxiliary winding for sensing, shielding, or testing.

[00083] In general, the impedance of thesecondary loop, Z(UA-UB) = -sCfRpRg = sLeq, and can be adjusted to a design target value by adjusting or trimming the resistor and capacitor values.

[00084] Any mutual inductor with a primary loop and a secondary loop that are electrically isolated but connected magnetically by mutual inductance may be used for transformer 20. Transformer 20 has been described as having a primary winding that has primary current flowing from a left terminal (switched from VIN) to a right terminal (VOUT), and the secondary winding having a left terminal that is grounded and a right terminal that is driven by current from op amp 32 through positive resistor 38. Thus the secondary current ripple is reduced, thereby reducing the primary current ripple. So the secondary current flows in the same direction as the primary current, thus increasing primary inductance when the secondary current flows. However, other arrangements are possible, such as having primary and secondary currents flow in the oppositedirection with the primary inductance decreasing rather than increasing when switch 40 closes and secondary current increases. Various component parameters and applications may be substituted. The secondary winding orientation may be WO 2026 / 085910 PCT / CN2024 / 128494 11 changed, such as by changing the orientation of the homonymous end. After changing the homonymous end, switch 40 can be in the off state when steady state is detected. When a transient state is detected, switch 40 is on in this alternative. An inverter could be added to invert steady signal ST from steady-state detector 50 and the inverted ST applied to switch 40. Switch 40 could be a normally-closed rather than a normally-open switch.

[00085] NIC 30 and transformer 20 provide an active inductor with a variable inductance value in the primary windings. This variable inductance can be modulated to a high inductance to reduce ripples in steady state, and modulated to a low inductance to extend the bandwidth and bettersuppress or converge transient spikes. This active inductor may allow for a smaller output capacitor to be used for a target amount of ripple and transient suppression. DC copper losses can also be reduced with the smaller output capacitance and variable inductance. Trimming to meet target inductance values for switch 40 being ON and OFF can be achieved by adjusting the resistance values of ground resistor 36, positive resistor 38.

[00086] Switch 40 is in series with positive resistor 38. As an alternative order, positive resistor 38 could connect between the output of op amp 32 and the switch, while the switch connects between positive resistor 38 and the non-inverting input of op amp 32.

[00087] More complex buffers, level shifters, or other components could be substituted or added. Inversions could be added at various locations. Hysteresis of other delays and output wave shaping could be added. Other kinds of buffer circuits, selectors, or muxes may be used.

[00088] Transformer 20only affects the AC components, not the DC components, of the output VOUT. Controlling the impedance of the active inductor, transformer 20, can reduce ripple in steady state by increasing the equivalent impedance value and increasing the filtering effect of transformer 20 and output capacitor 16, and can also suppress transients and spikes by decreasing the equivalent impedance of transformer 20, allowing output current to increase or decrease faster to the load, thus increasing the bandwidth and speeding convergence. The AC components of the primary can be considered to be absorbed by the mutual inductance from the reverse current flowing in the secondary as the inductance stores energy from the primary-side AC components into the magnetic fields.

[00089] Different transistor, capacitor, resistor, inductor, transformer, and other device sizes can be used, and various layout arrangements can be used, such as multi-leg, ring, doughnut or irregular-shape transistors. Currents can bepositive or negative currents and flow in either direction. Many second and third order circuit effects may be present and may be significant, especially for smaller device sizes. A circuit simulation may be used to account for these secondary factors during design.

[00090] Switch devices may be implemented using n-channel, p-channel, or bipolar transistors, or junctions within these transistors. The gate lengths and spacings can be increased to provide better protection from damage. WO 2026 / 085910 PCT / CN2024 / 128494 12

[00091] Many variations of IC semiconductor manufacturing processes are possible. Various materials may be used. Additional process steps may be added, such as for additional metal layers or for other transistor types or modification of standard complementary metal-oxide-semiconductor (CMOS) transistors when the transistors are integrated onto a larger device. While complementary metal-oxide-semiconductor (CMOS) transistors have been described, other kinds of transistorscould be substituted for some embodiments, such as n-channel only, p-channel only when the output swing can be limited, or various alternate transistor technologies such as Bipolar or BiCMOS. The CMOS process may be a Fin Field-Effect Transistor (FinFET) process.

[00092] Terms such as up, down, above, under, horizontal, vertical, inside, outside, are relative and depend on the viewpoint and are not meant to limit the invention to a particular perspective. Devices may be rotated so that vertical is horizontal and horizontal is vertical, so these terms are viewer dependent.

[00093] The background of the invention section may contain background information about the problem or environment of the invention rather than describe prior art by others. Thus inclusion of material in the background section is not an admission of prior art by the Applicant.

[00094] Any methods or processes described herein are machine-implemented or computer-implemented and are intended to be performed by machine,computer, or other device and are not intended to be performed solely by humans without such machine assistance. Tangible results generated may include reports or other machine­ generated displays on display devices such as computer monitors, projection devices, audio-generating devices, and related media devices, and may include hardcopy printouts that are also machine-generated. Computer control of other machines is another tangible result.

[00095] Any advantages and benefits described may not apply to all embodiments of the invention. When the word "means" is recited in a claim element, Applicant intends for the claim element to fall under 35 USC Sect. 112, paragraph 6. Often a label of one or more words precedes the word "means". The word or words preceding the word "means" is a label intended to ease referencing of claim elements and is not intended to convey a structural limitation. Such means-plus-function claims are intended to cover not only the structures described herein forperforming the function and their structural equivalents, but also equivalent structures. For example, although a nail and a screw have different structures, they are equivalent structures since they both perform the function of fastening. Claims that do not use the word “means” are not intended to fall under 35 USC Sect. 112, paragraph 6. Signals are typically electronic signals, but may be optical signals such as can be carried over a fiber optic line.

[00096] The foregoing description of the embodiments of the invention has been presented for the purposes of illustration and description. It is not intended to be exhaustive or to limit the invention to the precise form disclosed. Many modifications and variations are possible in light of the above teaching. It is intended that the scope of the invention be limited not by this detailed description, but rather by the claims appended hereto. WO 2026 / 085910 PCT / CN2024 / 128494 13 Claims: 1. An active inductor circuit comprising: a mutualinductor device having primary windings between primary tenninals and having secondary windings between secondary terminals, wherein the primary windings and the secondary windings are electrically isolated from each other and are magnetically coupled together by mutual inductance generated by currents flowing through the primary windings and the secondary windings; an op amp having a first input connected to a first of the secondary terminals; a ground resistor connected between a second of the secondary terminals and a second input of the op amp; a feedback device connected between an output of the op amp and the second input of the op amp; a modulation network connected between the output of the op amp and the first input of the op amp; a switch in the modulation network, the switch modulating a secondary current flowing through the secondary windings of the mutual inductor device, the modulation network modulating an output current generated at the output of the op amp and applyinga modulated current to the second of the secondary terminals of the mutual inductor device; wherein when the switch is in a first state, the secondary current has a first current value; wherein when the switch is in a second state, the secondary current has a second current value that is greater than the first current value; wherein when the switch is in the first state, the secondary current flowing through the secondary windings increases a primary equivalent inductance value of the first windings by mutual inductance through the mutual inductor device; wherein when the switch is in the second state and the secondary current has the second current value, the primary equivalent inductance value is greater than the primary equivalent inductance value when the switch is in the first state, whereby the primary equivalent inductance value is switched between two values by the switch that modulates the secondary current. 2. The active inductor circuit of claim 1 wherein the mutual inductordevice is a transformer; wherein a primary current and the secondary current flow in a same direction within the transformer. 3. The active inductor circuit of claim 2 wherein the feedback device is a capacitor; wherein the modulation network further comprises a positive resistor connected in series with the switch between the output of the op amp and the first input of the op amp. 4. The active inductor circuit of claim 2 wherein the feedback device is a resistor; WO 2026 / 085910 PCT / CN2024 / 128494 14 wherein the modulation network further comprises a positive inductor connected in series with the switch between the output of the op amp and the first input of the op amp. 5. The active inductor circuit of claim 2 wherein the switch is a diode. 6. The active inductor circuit of claim 3 further comprising: a steady-state detector that compares a primary output voltage generated by the primary current flowing through the primary windings of the mutual inductor device to a predeterminedvoltage range and activates a switch signal when the primary output voltage is within the predetermined voltage range; wherein the switch signal from the steady-state detector is applied to open and close the switch. 7. The active inductor circuit of claim 6 wherein the switch is a transistor having a control gate that receives the switch signal from the steady-state detector; wherein the transistor is a bipolar transistor or a Metal Oxide Semiconductor Field Effect Transistor (MOSFET). 8. The active inductor circuit of claim 7 further comprising: a first power transistor connected in series with the first windings of the mutual inductor device to generate the primary output voltage, the first power transistor having a gate driven by a controller that switches the first power transistor on and off at a selected switching frequency that creates a ripple in the primary output voltage; wherein the ripple is reduced by the switch closing to increase the secondary current and to increasethe primary equivalent inductance value; wherein the primary equivalent inductance value increases when the steady-state detector detects that the primary output voltage is outside the predetermined voltage range and the switch is opened to reduce the secondary current; whereby transients are suppressed by a lower primary equivalent inductance value when a transient is detected while ripple is reduced by a higher primary equivalent inductance value when the transient is not detected at steady-state. 9. The active inductor circuit of claim 8 wherein the first power transistor is connected in series with the first windings of the mutual inductor device between an input power voltage and an output capacitance having the primary output voltage; further comprising: a second power transistor connected between a primary terminal of the mutual inductor device and a primary ground, and having a gate driven by the controller; wherein the controller generates non-overlapping gate signals to thefirst power transistor and to the second power transistor to prevent both the first and second power transistor from being on at a same time; wherein the active inductor circuit modulates primary inductance of a Switched-Mode Power Supply (SMPS). WO 2026 / 085910 PCT / CN2024 / 128494 15 10. The active inductor circuit of claim 9 wherein the switch is open when the switch is in the first state to block current flow; wherein the switch is closed when the switch is in the second state to conduct current; wherein the switch turns off the secondary current when the switch is open. 11. The active inductor circuit of claim 10 wherein the primary equivalent inductance value when the switch is closed is at least double the primary equivalent inductance value when the switch is open; wherein equivalent inductance in the primary windings is doubled by the modulation network closing the switch. 12. The active inductor circuit of claim 9 further comprising: a switch shunt resistor connected in parallelwith the switch; wherein the secondary current continues to flow when the switch is open. 13. A variable equivalent inductance circuit comprising: a transformer having a primary path and a secondary path that are electrically isolated from each other and magnetically coupled together by mutual inductance; wherein a primary cunent flows through the primary path of the transformer to charge an output capacitance to generate a primary output voltage; wherein a secondary current flows through the secondary path from an input secondary terminal to an output secondary terminal; wherein the primary current flows in a same direction as the secondary current within the transformer; an op amp having an inverting input and a non-inverting input and an output; a first resistor connected between the output secondary terminal of the transformer and the inverting input of the op amp; a feedback impedance device connected between the inverting input of the op amp and the output of the op amp; a switchand a second impedance device connected in series between the output of the op amp and the non­ inverting input of the op amp; wherein the non-inverting input of the op amp is connected to the input secondary terminal of the transformer. 14. The variable equivalent inductance circuit of claim 13 wherein the second impedance device is a resistor; wherein the feedback impedance device is a capacitor. 15. The variable equivalent inductance circuit of claim 14 wherein the op amp is powered by an upper supply voltage and a lower supply voltage; wherein a midpoint voltage between the upper supply voltage and the lower supply voltage is connected to the output secondary terminal of the transformer. 16. The variable equivalent inductance circuit of claim 15 further comprising: a steady-state detector that compares the primary output voltage to a voltage limit and activates a switch signal when the primary output voltage does not exceed the voltage limit; WO 2026 / 085910 PCT / CN2024 / 128494 16wherein the switch signal closes the switch to increase current flow through the second impedance device and increase a primary inductance along the primary path through the transformer when the switch signal is activated when small voltage ripples occur on the primary output voltage that are less than the voltage limit; wherein the switch signal opens the switch to decrease current flow through the second impedance device and decrease the primary inductance along the primary path through the transformer when the switch signal is not activated when large voltage transients occur on the primary output voltage that are more than the voltage limit, whereby the switch closing causes the primary inductance to increase during steady-state to reduce ripples and the switch opens to cause the primary inductance to decrease during transients to increase bandwidth and reduce transient response time. 17. The variable equivalent inductance circuit of claim 16 wherein the switch is a Metal OxideSemiconductor Field Effect Transistor (MOSFET) having a gate receiving the switch signal from the steady­ state detector or the switch is a bipolar transistor having a base receiving the switch signal from the steady-state detector. 18. The variable equivalent inductance circuit of claim 16 further comprising: a controller that generates a first gate signal and a second gate signal that are non-overlapping and switching at a frequency that is within an order of a magnitude of 100 kHz; a power voltage input; a first power transistor having a gate receiving the first gate signal, connected between the power voltage input and an input primary terminal to the primary path of the transformer; a second power transistor having a gate receiving the second gate signal, connected between the input primary terminal to the primary path of the transformer and a primary ground; wherein an output terminal of the primary path of the transformer is connected to the output capacitance to generate theprimary output voltage; wherein the first power transistor, the second power transistor, and the primary path of the transformer form a Buck converter Switched-Mode Power Supply (SMPS). 19. The variable equivalent inductance circuit of claim 17 further comprising: a controller that generates a first gate signal and a second gate signal that are non-overlapping and switching at a frequency that is within an order of a magnitude of 100 kHz; a power voltage input; a first power transistor having a gate receiving the first gate signal, connected between the output primary terminal of the primary path of the transformer and the output capacitance that generates the primary output voltage; WO 2026 / 085910 PCT / CN2024 / 128494 17 a second power transistor having a gate receiving the second gate signal, connected between the input primary terminal to the primary path of the transformer and a primary ground; wherein an input terminal of the primary path of the transformer is connected to the powervoltage input; wherein the first power transistor, the second power transistor, and the primary path of the transformer form a Boost converter Switched-Mode Power Supply (SMPS). 20. A switchable-inductance power-supply circuit comprising: a transformer having a primary path and a secondary path that are electrically isolated from each other and magnetically coupled together by mutual inductance; wherein a primary current flows through the primary path of the transformer to charge an output capacitance to generate a primary output voltage; wherein a secondary current flows through the secondary path from an input secondary terminal to an output secondary terminal; wherein the primary current flows in a same direction as the secondary current within the transformer; an op amp having an inverting input and a non-inverting input and an output; a first resistor connected between the output secondary terminal of the transformer and the inverting input of the op amp; a feedback capacitorconnected between the inverting input of the op amp and the output of the op amp; a switch transistor and a second resistor connected in series between the output of the op amp and the non­ inverting input of the op amp; wherein the non-inverting input of the op amp is connected to the input secondary terminal of the transformer; a controller that generates a first gate signal and a second gate signal that are non-overlapping and switching at a selected frequency; a power voltage input; a first power transistor having a gate receiving the first gate signal, connected between the power voltage input and an input primary terminal to the primary path of the transformer; a second power transistor having a gate receiving the second gate signal, connected between the input primary terminal to the primary path of the transformer and a primary ground; wherein an output terminal of the primary path of the transformer is connected to the output capacitance to generate the primary output voltage;wherein the first power transistor, the second power transistor, and the primary path of the transformer form a Buck converter Switched-Mode Power Supply (SMPS); a steady-state detector that compares the primary output voltage to a voltage limit and activates a switch signal to the switch transistor when the primary output voltage does not exceed the voltage limit; WO 2026 / 085910 PCT / CN2024 / 128494 18 wherein the switch signal closes the switch transistor to increase current flow through the second impedance device and increase primary inductance along the primary path through the transformer when the switch signal is activated when small voltage ripples occur on the primary output voltage that are less than the voltage limit; wherein the switch signal opens the switch transistor to decrease current flow through the second impedance device and decrease primary inductance along the primary path through the transformer when the switch signal is not activated when large voltage transientsoccur on the primary output voltage that are more than the voltage limit; whereby the switch transistor closing causes primary inductance to increase during steady-state to reduce ripples and the switch transistor opens to cause the primary inductance to decrease during transients to increase bandwidth and reduce transient response time. WO 2026 / 085910 PCT / CN2024 / 128494 Z) O z > 0 iZ 1 / 15 PR IO R AR T N IA WO 2026 / 085910 PCT / CN2024 / 128494 LU1 2 / 15 PR IO R A R T WO 2026 / 085910 PCT / CN2024 / 128494 3 / 15 G N D 2 =M ID ( VS +, VS -) WO 2026 / 085910 PCT / CN2024 / 128494 4 / 15 FI G . 4 IN D U C TO F PR IM AR Y C U R R EN T (IL , A M PS ) WO 2026 / 085910 PCT / CN2024 / 128494 CM CD UJ in 0 5 / 15 VO U T WO 2026 / 085910 PCT / CN2024 / 128494 cn LU 2 CD 0 z 6 / 15 IL O AD WO 2026 / 085910 PCT / CN2024 / 128494 7 / 15 ► T IM E( U S) IL O AD WO 2026 / 085910 PCT / CN2024 / 128494 cn UJ 0 0 8 / 15 >T IM E( U S) VM IN WO 2026 / 085910 PCT / CN2024 / 128494 o> I— cn 9 / 15 FI G . 9 WO 2026 / 085910 PCT / CN2024 / 128494 10 / 15 FI G . 1 0 WO2026 / 085910 PCT / CN2024 / 128494 11 / 15 FI G . 11 G N D 2 WO 2026 / 085910 PCT / CN2024 / 128494 I- =) O> oo —“ CD I > 12 / 15 FI G . 1 2 WO 2026 / 085910 PCT / CN2024 / 128494 13 / 15 FI G . 1 3 WO 2026 / 085910 PCT / CN2024 / 128494 > 14 / 15 G N D 2 =M ID (V S+ ,V S- ) WO 2026 / 085910 PCT / CN2024 / 128494 15 / 15 FI G . 1 5 F INTERNATIONAL SEARCH REPORT International application No. PCT / CN2024 / 128494 A. CLASSIFICATION OF SUBJECT MATTER H02M3 / 335(2006.01)i; H02Ml / 32(2007.01)i; H02Ml / 14(2006.01)i; H02H7 / 12(2006.0l)i According to International Patent ClassiHcation (IPC) or to both national classification and IPC B. FIELDS SEARCHED Minimum documentation searched (classification system followed by classification symbols) IPC:H02M,H02H Documentation searched other than minimum documentation to die extent that such documents are included in the fields searched Electronic data base consulted during the international search (name of data base and, where practicable, search terms used)VEN,CNABS,CNTXT,EPTXT,WOTXT,USTXT,CNKI,IEEE:inductor,inductance,adjustablej-egulable,alterable,variable,p rimary,first, winding,transformer,converter,buck,boost,dc / dc C. DOCUMENTS CONSIDERED TO BE RELEVANT Category* Citation of dcxmment, with indication, where appropriate, of the relevant passages Relevant to claim No. A JP H10172840 A (NISSIN HIGH VOLTAGE KK) 26 June 1998 (1998-06-26) description, paragraphs

[0006] -

[0028] , figure 1 1-19 A US 2023016789 Al (AES GLOBAL HOLDINGS PTE LTD.) 19 January 2023 (2023-01-19) description, paragraphs

[0005] -

[0076] , figure 1 20 A CN 101534047 A (GENERAL ELECTRIC CO.) 16 September 2009 (2009-09-16) the whole document 1-20 A JP 2005168157 A (SEIKO INSTR. INC.) 23 June 2005 (2005-06-23) the whole document 1-20 A JP 2016163381 A (HITACHI APPLIANCES INC.) 05 September 2016 (2016-09-05) the whole document 1-20 A US 6140808 A (INTEL CORPORATION) 31 October 2000 (2000-10-31) the whole document 1-20 A WO 2006115223 Al (NATIONAL UNIVERSITY CORPORATION GUNMAUNIVERSITY) 02 November 2006 (2006-11-02) the whole document 1-20 1 1 Further documents are listed in the continuation of Box C. See patent family annex. * Special categories of cited documents: “T” later document published after the international filing date or priority “A” document defining the general state of the ait which is not considered date and not in conflict with the application but cited to understand the to be of particular relevance principle or theory underlying the invention “D” document cited by the applicant in the international application “X” document of particular televance; the claimed invention cannot be “E” earlier application or patent but published on or after the international COTtsiderad novel or cannot be considered to involve an inventive step filing date when the document is taken alone “L” document which may throw doubts on priority claim(s) ar which is “Y” document of particular relevance; the claimed invention cannot be cited to establish thepublication date of another citation or other considered to involve an inventive step when the document is special reason (as spectfled) combined with one or more other such documents, such combination “O” document referring to an oral disclosure, use, exhibition or other being obvious to a person skilled in the art means document member of the same patent family “P” document published prior to the international filing date but later than the priority date claimed Date of the actual completion of the international search 14 July 2025 Date of mailing of the international search report 18 July 2025 Name and mailing address of the ISA / CN CHINA NATIONAL INTELLECTUAL PROPERTY ADMINISTRATION 6,Xitucheng Rd., Jimen Bridge, Haidian District, Beijing 100088, China Authorized officer JIANG,Nuo Telephone No. (+86) 010-53961260 Form PCT / ISA / 210 (second sheet) (July 2022) J INTERNATIONAL SEARCH REPORT Information on patent family members International application No. PCT / CN2024 / 128494 Patentdocument cited in search report Publication date (day / month / year) Patent family members) Publication date (day / month / year) JP H10172840 A 26 June 1998 None US 2023016789 Al 19 January 2023 US 11722049 B2 08 August 2023 TW 202320459 A 16 May 2023 TWI 856343 B 21 September 2024 EP 4371226 Al 22 May 2024 WO 2023287354 Al 19 January 2023 WO 2023287354 A9 19 October 2023 CN 101534047 A 16 September 2009 AU 2009200697 Al 01 October 2009 EP 2101399 A1 16 September 2009 US 2009231890 A1 17 September 2009 JP 2005168157 A 23 June 2005 None JP 2016163381 A 05 September 2016 None US 6140808 A 31 October 2000 US 6285175 B1 04 September 2001 WO 2006115223 A1 02 November 2006 JPWO 2006115223 A1 18 December 2008 JP 4644826 B2 09 March 2011 Form PCT / ISA / 210 (patent family annex) (July 2022) (19) State Intellectual Property Office (12) Invention Patent Application (10) Application Publication Number CN 119678357 A (43) Publication date 2025.03.21 (21) Application number 202480002899.2 (22) Application date 2024.10.30 (30) Priority data 18 / 923,891 2024.10.23 US (51) Int.CI . H02M 3 / 555(2006.01) H02M ) / 32(2007.01) H02M 1 / 14(2006.01) H02H 7 / ?2(2006.01) (85) PCT International Application Enters National Phase Date 2024.12.04 (86) Application Data for PCT International Application PCT / CN2024 / 128494 2024.10.30 (71) Applicant: Hong Kong Applied Science and Technology Research Institute Limited Address: 5 / F, Optoelectronics Centre, 2 Science Avenue East, Hong Kong Science Park, Shatin, New Territories, Hong Kong (72) Inventors: Xu Danting, Ma Yue, Li Chengyong (74) Patent Agency: Shenzhen Xinchuangyou Intellectual Property Agency Co., Ltd. 44223 Patent Attorney: Xie Linhong Claims: 4 pages Specification: 9 pages Drawings: 8 pages (54) Invention Title: Active Variable Inductor Circuit (57) Abstract: A switch-mode power supply that uses the primary winding of a transformer instead of an inductor. The secondary winding of the transformer is driven by the current generated by the negative inductor circuit. When a reverse current flows, the equivalent inductance value of the primary winding can be increased. When the output voltage remains within predetermined limits, the steady-state detector activates a steady-state signal and closes a switch to allow reverse current to flow from the operational amplifier, increasing the inductance and thus reducing ripple during steady-state operation. When a transient output change occurs, the steady-state signal is deactivated, the switch opens, and current flows through the transformer secondary winding, reducing the primary inductance and allowing current to flow to the output more quickly to suppress the transient. A network of resistors and capacitors around the operational amplifier can be used to adjust the inductance modulation. VZ LQ CO8 Z 9 6 1 I 6 CN 119678357 A Claims 1 / 4 M 1 • An active inductor circuit, comprising: a mutual inductor having a primary winding between primary terminals and a secondary winding between secondary terminals, wherein the primary winding and the secondary winding are electrically isolated from each other and magnetically coupled together by mutual inductance generated by current flowing through the primary winding and the secondary winding; an operational amplifier having a first input connected to the first secondary terminal; a grounding resistor connected between the second secondary terminal and a second input of the operational amplifier; a feedback device connected between the output of the operational amplifier and the second input of the operational amplifier; a modulation network connected between the output of the operational amplifier and the first input of the operational amplifier; a switch in the modulation network that modulates the secondary current flowing through the secondary winding of the mutual inductor, the modulation network modulating the output current generated at the output of the operational amplifier and applying the modulated current to the second secondary terminal of the mutual inductor; Wherein, when the switch is in the first state, the secondary current has a first current value; wherein, when the switch is in the second state, the secondary current has a second current value, the second current value being greater than the first current value; wherein, when the switch is in the first state, the secondary current flowing through the secondary winding passes through the mutual inductance.The mutual inductance of the devices increases the primary equivalent inductance of the first winding; wherein, when the switch is in the second state and the secondary current has a second current value, the primary equivalent inductance is greater than the primary equivalent inductance when the switch is in the first state, thereby the primary equivalent inductance switches between two values ​​by modulating the secondary current through the switch. 2. The active inductor circuit according to claim 1, wherein the mutual inductance device is a transformer; wherein the primary current and the secondary current flow in the same direction within the transformer. 3. The active inductor circuit according to claim 2, wherein the feedback device is a capacitor; wherein the modulation network further includes a forward resistor connected in series with the switch between the operational amplifier output and the first input of the operational amplifier. 4. The active inductor circuit according to claim 2, wherein the feedback device is a resistor; wherein the modulation network further includes a forward inductor connected in series with the switch between the operational amplifier output and the first input of the operational amplifier. 5. The active inductor circuit according to claim 2, wherein the switch is a diode. 6. The active inductor circuit of claim 3, further comprising: a steady-state detector that compares the primary output voltage generated by the primary current flowing through the primary winding of the mutual inductance device with a predetermined voltage range, and activates a switching signal when the primary output voltage is within the predetermined voltage range; wherein the switching signal of the steady-state detector is used to turn the switch on and off. 7. The active inductor circuit of claim 6, wherein the switch is a transistor with a control gate capable of receiving the switching signal from the steady-state detector; wherein the transistor is a bipolar transistor or a metal-oxide-semiconductor field-effect transistor (MOSFET). 8. The active inductor circuit of claim 7, further comprising: a first power transistor connected in series with a first winding of the mutual inductance device to generate a primary output voltage, the first power transistor having a gate driven by a controller that turns the first power transistor on and off at a selected switching frequency to generate ripple in the primary output voltage; wherein, by closing the switch to increase the secondary current and increase the primary equivalent inductance value, the ripple is reduced; wherein, when the steady-state detector detects that the primary output voltage exceeds a predetermined voltage range, the switch is opened to reduce the secondary current, and the primary equivalent inductance value increases; therefore, when a transient is detected, the transient is suppressed by a lower primary equivalent inductance value, while when no transient is detected in the steady state, the ripple is reduced by a higher primary equivalent inductance value. 9. The active inductor circuit of claim 8, wherein the first power transistor is connected in series with the first winding of the mutual inductance device between the input power supply voltage and the output capacitor having the primary output voltage; further comprising:A second power transistor, connected between the primary terminal and primary ground of the mutual inductor, has its gate driven by the controller; wherein the controller generates non-overlapping gate signals for the first and second power transistors to prevent the first and second power transistors from conducting simultaneously; wherein the active inductor circuit modulates the primary inductance of the switching power supply (SMPS). 10. The active inductor circuit of claim 9, wherein when the switch is in a first state, the switch is open to prevent current flow; wherein when the switch is in a second state, the switch is closed to conduct current; wherein when the switch is open, the switch turns off the secondary current. 11. The active inductor circuit of claim 10, wherein the primary equivalent inductance value when the switch is closed is at least twice the primary equivalent inductance value when the switch is open; wherein the equivalent inductance in the primary winding is doubled by closing the switch through the modulation network. 12. The active inductor circuit of claim 9, further comprising: a switching shunt resistor connected in parallel with the switch; wherein when the switch is open, the secondary current continues to flow. 13. A variable equivalent inductance circuit, comprising: a transformer, wherein its primary and secondary paths are electrically isolated from each other and magnetically coupled together by mutual inductance; wherein a secondary current flows through the primary path of the transformer to charge an output capacitor, generating a primary output voltage; wherein the secondary current flows through the secondary path from an input secondary terminal to an output secondary terminal; wherein the primary current flows in the same direction as the secondary current within the transformer; an operational amplifier having an inverting input, a non-inverting input, and an output; a first resistor connected between the output secondary terminal of the transformer and the inverting input of the operational amplifier; a feedback impedance device connected between the inverting input of the operational amplifier and the output of the operational amplifier; a switch and a second impedance device connected in series between the output of the operational amplifier and the non-inverting input of the operational amplifier; wherein the non-inverting input of the operational amplifier is connected to the input secondary terminal of the transformer. 14. The variable equivalent inductance circuit according to claim 13, wherein the second impedance device is a resistor; wherein the feedback impedance device is a capacitor. 15. The variable equivalent inductance circuit of claim 14, wherein the operational amplifier is powered by an upper supply voltage and a lower supply voltage; wherein the midpoint voltage between the upper supply voltage and the lower supply voltage is connected to the output secondary terminal of the transformer. 16. The variable equivalent inductance circuit of claim 15, further comprising: a steady-state detector that compares the primary output voltage to a voltage limit and activates a switching signal when the primary output voltage does not exceed the voltage limit;Wherein, when a small voltage ripple occurs on the primary output voltage less than the voltage limit, the switch signal is activated, and the switch signal closes the switch to increase the current flowing through the second impedance device and increase the primary inductance along the primary path through the transformer; wherein, when a large voltage transient occurs on the primary output voltage greater than the voltage limit, the switch signal is not activated, and the switch signal opens the switch to reduce the current flowing through the second impedance device and reduce the primary inductance along the primary path through the transformer, wherein closing the switch increases the primary inductance during the steady state to reduce ripple, while opening the switch decreases the primary inductance during the transient state to increase bandwidth and reduce transient response time. 17. The variable equivalent inductance circuit of claim 16, wherein the switch is a metal-oxide-semiconductor field-effect transistor (MOSFET) whose gate receives the switch signal from the steady-state detector, or the switch is a bipolar transistor whose base receives the switch signal from the steady-state detector. 18. The variable equivalent inductance circuit according to claim 16, further comprising: a controller that generates non-overlapping first gate signals and second gate signals and switches them at frequencies in the order of 100 kHz; a power supply voltage input; a first power transistor whose gate receives the first gate signal and is connected between the power supply voltage input and the input primary terminal of the transformer primary path; a second power transistor whose gate receives the second gate signal and is connected between the input primary terminal of the transformer primary path and primary ground; wherein the output terminal of the transformer primary path is connected to the output capacitor to generate the primary output voltage; wherein the first power transistor, the second power transistor, and the transformer primary path form a buck converter switch-mode power supply (SMPS). 19. The variable equivalent inductance circuit according to claim 17, further comprising: a controller that generates non-overlapping first gate signals and second gate signals and switches them at frequencies in the order of 100 kHz; a power supply voltage input; a first power transistor whose gate receives the first gate signal and is connected between the output primary terminal of the transformer primary path and the output capacitor that generates the primary output voltage. A second power transistor, whose gate receives a second gate signal, is connected between the input primary terminal of the transformer primary path and primary ground; wherein the input terminal of the transformer primary path is connected to the power supply voltage input; wherein the first power transistor, the second power transistor, and the transformer primary path form a boost converter switch-mode power supply (SMPS). 20. A switchable inductor power supply circuit, comprising: a transformer, wherein its primary path and secondary path are electrically isolated from each other and magnetically coupled together by mutual inductance;Wherein, the primary current flows through the primary path of the transformer, charging the output capacitor and generating a primary output voltage; 4 CN 119678357 A Claims 4 / 4 pages Wherein, the secondary current flows through the secondary path, from the input secondary terminal to the output secondary terminal; Wherein, the primary current flows in the same direction as the secondary current in the transformer; Operational amplifier having an inverting input, a non-inverting input, and an output; A first resistor connected between the output secondary terminal of the transformer and the inverting input of the operational amplifier; A feedback capacitor connected between the inverting input of the operational amplifier and the output of the operational amplifier; A switching transistor and a second resistor connected in series between the output of the operational amplifier and the non-inverting input of the operational amplifier; Wherein, the non-inverting input of the operational amplifier is connected to the input secondary terminal of the transformer; A controller generating a non-overlapping first gate signal and a second gate signal that switch at a selected frequency; A power supply voltage input; A first power transistor whose gate receives the first gate signal and is connected between the power supply voltage input and the input primary terminal of the primary path of the transformer; A second power transistor, whose gate receives a second gate signal, is connected between the input primary terminal and primary ground of the transformer primary path; wherein the output terminal of the transformer primary path is connected to an output capacitor to generate a primary output voltage; wherein the first power transistor, the second power transistor, and the transformer primary path form a buck converter switch-mode power supply (SMPS); a steady-state detector compares the primary output voltage with a voltage limit and activates a switching signal when the primary output voltage does not exceed the voltage limit, outputting it to the switching transistor; wherein when a small voltage ripple occurs on the primary output voltage below the voltage limit, the switching signal is activated, closing the switching transistor to increase the current flowing through the second impedance device and increase the primary inductance along the primary path through the transformer; wherein when a large voltage transient occurs on the primary output voltage above the voltage limit, the switching signal is not activated, opening the switching transistor to reduce the current flowing through the second impedance device and reduce the primary inductance along the primary path through the transformer; Wherein, the closing of the switching transistor causes the primary inductance to increase during the steady state to reduce ripple, while the opening of the switching transistor causes the primary inductance to decrease during the transient state to increase bandwidth and reduce transient response time. 5 CN 119678357 A Specification 1 / 9 Frame Active Variable Inductor Circuit [Technical Field]

[0001] This invention relates to active inductors, and particularly to a negative inductor circuit for switch-mode power supplies (SMPS). [Background Art]

[0002] Power metal-oxide-semiconductor field-effect transistors (MOSFETs) have switching frequencies in the hundreds of kilohertz range, enabling lightweight, compact, and efficient switch-mode power supplies (SMPS). A typical SMPS uses two power transistors in a buck converter. The gates of the power transistors are switched by a controller to ensure that the two transistors do not conduct simultaneously. By controlling the duty cycle and other timing, the desired output voltage can be generated from the input voltage.

[0003] Figure 1 shows a prior art SMPS. The SMPS converts the input voltage VIN to an output voltage VOUT to drive a load represented by load resistor 18. Controller 12 drives gate signal S1 high, turning on transistor 22, allowing current to flow from VIN through transistor 22 and inductor 10 to charge output capacitor 16. Then, controller 12 turns off S1 and turns on gate signal S2, thereby turning on transistor 24 to discharge output capacitor 16. The on-time of S1 and S2 generated by controller 12 determines the steady-state output voltage VOUT maintained at a given VIN value and device size.

[0004] Input capacitor 14 smooths VIN, while output capacitor 16 stores charge and smooths VOUT ripple. Inductor 10 stores energy in its magnetic field and smooths changes in inductor current IL, thereby driving VOUT and providing capacitor current IC to charge output capacitor 16.

[0005] Figure 2 is a waveform showing the operation of the SMPS of Figure 1. When controller drive S1 is high, VIN drive current flows through transistor 22 and inductor 10. The voltage VL on inductor 10 rises and falls as transistor 22 is turned on and off by S1. This voltage VL causes inductor current IL to rise sharply when S1 is high and fall slowly when S1 is low. As IL rises, energy is stored in inductor 10, and as IL falls, energy is released.

[0006] The AC portion of inductor current IL mainly flows to output capacitor 16, causing capacitor current IC to follow inductor current IL, but curvature is generated due to RC delay. After RC delay, the voltage and VOUT on output capacitor 16 rise and fall with the inductor current IL.

[0007] The rise and fall of VOUT is called ripple, which has a negative impact. Ripple can be reduced by increasing the capacitance value of output capacitor 16 (in farads). However, this method also has disadvantages, as a single large capacitor occupies board or layout space and is expensive, has long wiring paths, and generates electrical losses. Ripple can also be reduced by increasing the inductance value of inductor 10 (in henries), but large inductors are often more expensive and bulkier than capacitors.

[0008] Increasing capacitance or inductance will also reduce the transient response of SMPS. For example, the load may contain many transistors or other transistors.Other circuits, which are switched on and off during normal operation. This causes the current consumed by the load to change. The SMPS should provide additional or reduced current as needed to cope with these load current changes. However, when the output capacitor 16 is large, the current through the transistor 22 will charge the output capacitor 16 instead of flowing through the load resistor 18. Similarly, a larger inductor 10 will also have a poorer transient response. When the transient response is weak, the VOUT spike may swing to extreme levels, triggering overvoltage or undervoltage protection circuits, which is undesirable.

[0009] A trade-off needs to be made between increasing the output capacitor and inductor to reduce ripple and providing sufficient transient response. The inventors realized that when using conventional fixed-value capacitors and inductors in SMPS, reducing output ripple and improving transient response are mutually exclusive. 6 CN 119678357 A Specification 2 / 9 pages

[0010] Therefore, an active inductor for SMPS is needed. It is desirable for the active inductor to increase the power inductance value of the SMPS under steady-state conditions to reduce output ripple, and to decrease the power inductance value under transient conditions to improve transient response. An active inductor whose equivalent inductance value is controlled by the circuit is needed. [Figure Descriptions]

[0011] Figure 1 shows a prior art switch-mode power supply (SMPS).

[0012] Figure 2 shows the waveforms of the SMPS of Figure 1 during operation.

[0013] Figure 3 shows an SMPS with an active inductor.

[0014] Figure 4 shows an SMPS with a capacitor-based negative inductor circuit (NIC) in more detail.

[0015] Figure 5 is a schematic diagram of the primary current in the transformer when the NIC is turned on and off.

[0016] Figure 6 is a schematic diagram of the output voltage VOUT when the NIC is turned on and off.

[0017] Figures 7A-7B show the response waveforms of the SMPS to load current jumps when the NIC is turned on and off.

[0018] Figures 8A-8B show the response waveforms of the SMPS to the load current jump when the NIC is turned on and off.

[0019] Figure 9 shows an embodiment of the steady-state detector in more detail.

[0020] Figure 10 shows the SMPS of a NIC with a bipolar transistor switch.

[0021] Figure 11 shows the SMPS of a NIC with an n-channel transistor switch.

[0022] Figure 12 shows the SMPS of a NIC with a diode switch.

[0023] Figure 13 shows the SMPS with a NIC topology employing a positive inductor.

[0024] Figure 14 shows the SMPS of a boost converter with a NIC.

[0025] Figure 15 shows the SMPS with a NIC that only partially modulates the secondary current.

Detailed Description

[0026] The present invention relates to improvements to active inductor circuits. The following description is intended to enable those skilled in the art to...The invention can be made and used in the context of specific applications and their requirements. Various modifications to the preferred embodiments will be apparent to those skilled in the art, and the general principles defined herein may also be applied to other embodiments. Therefore, the invention is not intended to be limited to the specific embodiments shown and described, but is to be given the broadest scope consistent with the principles and novel features disclosed herein.

[0027] The inventors have realized that variable inductors can reduce the ripple of SMPS by increasing the inductance value and accelerate the transient response speed by decreasing the inductance value. Although variable inductors are used in older wireless devices, these variable inductors are typically large coils with magnetic cores, and the inductance is changed by physical movement.

[0028] The inventors have realized that active variable power inductors can be realized by replacing inductors with mutual inductance devices (e.g., transformers). The primary winding of the transformer carries the inductor current IL in the SMPS. The secondary winding of the transformer is connected to a negative inductance circuit (NIC). The NIC can send current through the secondary winding and then generate a magnetic field that is coupled to the primary winding through the magnetic core. The NIC can send current in reverse through the secondary winding, thereby creating mutual inductance in the primary winding, resisting current flow, and thus increasing the inductance value of the primary winding. Therefore, the NIC can adjust the inductance value of the primary winding. [(X)29] Figure 3 shows an SMPS with an active inductor. The inductor 10 in Figure 1 is replaced by a transformer 20. The primary winding of the transformer 20 conducts the inductor current IL from the transistor 22 to the output capacitor 16.

[0030] The controller 12 drives the gate signal S1 high, causing current to flow through the transistor 22 and the primary winding of the transformer 20 to charge the output capacitor 16. The controller 12 also drives the gate signal S2 high to turn on the transistor 24, thereby reducing the voltage across the transformer 20 to maintain the desired output voltage VOUT. The input capacitor 14 is optional but helps to maintain VIN.

[0031] Load resistor 18 represents a load driven by VOUT, which may change during operation, resulting in transients. When no transient occurs, steady-state detector 50 detects that VOUT is within a predetermined range and drives the steady-state signal ST high, thereby closing switch 40. Switch 40 closes the loop between the negative inductance circuit NIC 30 and the secondary winding of transformer 20.

[0032] When switch 40 is closed, NIC 30 can generate a reverse current flowing through the secondary winding of transformer 20. This reverse current generates a magnetic field in transformer 20, which is coupled or amplified through the core of transformer 20. The generated magnetic field produces additional inductance in the primary winding of transformer 20. Therefore, when switch 40 is closed to enable NIC 30, the primary winding of transformer 20...The inductance value will increase.

[0033] When a sufficiently large transient occurs at the output, VOUT is no longer within the predetermined limit range, and the steady-state detection 50 will drive the steady-state signal ST low, thereby turning on the switch 40. The switch 40 disconnects the circuit, preventing the NIC 30 from driving reverse current through the secondary winding of the transformer 20. The inductance value of the primary winding of the transformer 20 falls back to its rated value. The lower inductance value through the transformer 20 allows a larger inductance current IL to flow to the output and the load 18. Due to the increased current flowing through the transformer 20, a faster response to transients can be achieved.

[0034] When a transient is detected, the lower inductance value through the primary winding of the transformer 20 provides a wider bandwidth for SMPS. When no transient is detected, the NIC 30 is enabled to increase the inductance value of the primary winding of the transformer 20. During steady state, a higher inductance value reduces output ripple.

[0035] Therefore, by turning the NIC 30 on and off, the equivalent inductance value in the primary winding can be adjusted. A high inductance value is provided to reduce ripple during steady state, while a low inductance value is provided to speed up transient response time when transients are detected. For example, when the rated inductance of transformer 20 is 1gH (physical inductance value), the equivalent inductance value of NIC 30 is 1mg when it is off, and the equivalent inductance value of NIC 30 is 1gH when it is on.

[0036] Figure 4 shows the SMPS with a capacitor-based negative inductance circuit in more detail. Operational amplifier 32 is powered by supply voltages VS+ and VS-. The midpoint voltage (e.g., the intermediate value between VS+ and VS-) can be used to generate secondary ground GND2. This ground GND2 is connected to one terminal of the secondary winding of transformer 20, while the other terminal of the secondary winding is connected as node UB to the non-inverting input of operational amplifier 32.

[0037] The inverting input of operational amplifier 32 is node UA, which is connected to ground GND2 through a grounding resistor 36 with a resistance value of Rg. A feedback capacitor 34 with a capacitance of Cf connects node UA to the output node UC of operational amplifier 32. The feedback capacitor 34 and grounding resistor 36 form a double feedback network with an impedance of Z / Rg, allowing operational amplifier 32 to provide a gain of 1+Z / Rg.

[0038] Switch 40 and a positive resistor 38 with a resistance of Rp are connected in series between the output node UC of operational amplifier 32 and the non-inverting input node UB of operational amplifier 32. When steady-state detector 50 drives ST high and closes switch 40, a second impedance (Zp) connects the non-inverting input and output of operational amplifier 32.

[0039] Because controller 12 turns power transistor 22.24 on and off, the frequency of the ripple in the primary current flowing through transformer 20 is the same as the selected switching frequency. The inductor circuit is a voltage-controlled current source that generates a voltage UB at the end of the secondary winding through the mutual inductance of the metal core of transformer 20. According to the characteristics of the operational amplifier, the non-inverting input of operational amplifier 32...The voltages at the non-inverting input terminal (+) and the inverting input terminal (-) are equal. Therefore, the voltage UA at the inverting input terminal is equal to the voltage UB at the non-inverting input terminal. Since the feedback network generates a voltage gain through the feedback capacitor 34, the output voltage UC after the gain of the operational amplifier 32 is obtained. In this case, the voltages UC and UB across the forward resistor 38 generate a reverse alternating current on the forward resistor 38. This reverse alternating current is opposite in phase to the ripple portion of IL and is coupled to the primary winding of the transformer 20 through the secondary winding of the transformer 20. The coupled ripple portion of IL is the same in phase as the original ripple, but the ripple amplitude is reduced.

[0040] The mutual inductance through the metal core of the transformer 20 generates a similar ripple in the secondary current. These ripples in the secondary current are applied to the inverting (+) input terminal of the operational amplifier 32. After being amplified by the gain factor, they are converted into a current flowing through the forward resistor 38 when the switch 40 is closed. The forward resistor 38 converts these ripples into a voltage difference across the forward resistor 38 and provides a current flowing reversely through the secondary winding of the transformer 20, flowing from the right terminal to the left terminal and GND2.

[0041] The first impedance network is connected to the inverting (-) input terminal of the operational amplifier 32, while the second impedance network is connected to the non-inverting (+) input terminal of the operational amplifier 32. The ground resistor 36 and the feedback capacitor 34 are connected to the inverting input terminal of the operational amplifier 32 and form the first impedance network, that is, the inverting feedback network. The forward resistor 38 is connected to the non-inverting (+) input terminal of the operational amplifier 32 to form the second impedance network.

[0042] Due to the mutual inductance of the transformer 20, the voltage ripple of the primary current generates an alternating ripple in the secondary current. The alternating ripple of the secondary current is applied to the inverting (+) input terminal of the operational amplifier 32 and causes an alternating ripple in the output current of the operational amplifier when the switch 40 is closed. The reverse amplification gain of the operational amplifier 32 is 1 + Z / Rg. The impedance 21 comes from the feedback capacitor 34.

[0043] In this embodiment, under the action of the scaling factor s, the first impedance is Zf1 / (GCf), and the second impedance is Zp = Rp. The ground resistor 36 and the forward resistor 38 can be variable resistors or fixed resistors (for example, the applicable resistance values are determined through circuit analysis, simulation, or prototype testing). When the ground resistor 36 and the forward resistor 38 are variable resistors, they can be programmable. For example, the resistors in the resistor bank can be selected through a programmable register, and the register can be programmed through a program.

[0044] The scaling factor s is a complex frequency. In frequency domain analysis, the complex frequency s is a complex number, expressed as s = <T + jw, where a is the real part, representing the attenuation or growth factor, and jW is the imaginary part, representing the angular frequency. For ideal inductors and capacitors, a is 0. The frequency domain s is defined as decomposing a signal into different frequency imaginary exponential components, and the response of the system can be obtained through the Fourier inverse transform.

[0045] The working principle of SMPS is as described above, except that when the steady-state detector 50 determines that VOUT remains within a predetermined range, the inductance value of the primary winding of transformer 20 is increased to reduce ripple. When VOUT occurs in a transient state outside the predetermined range, the steady-state detector 50 drives ST low to open switch 40 and shut off the current in the secondary winding. The equivalent inductance of the primary winding drops to its rated value. The lower rated inductance value allows a larger peak-to-peak ripple to flow to the load within one cycle, while the current slope of the load is larger, thus achieving a faster transient response.

[0046] In practical applications, the inductance value of the primary winding is adjustable. When reverse current flows through the secondary winding, the inductance value of the primary winding can be doubled or tripled. The increase in inductance due to NIC can be adjusted by adjusting the resistance value of grounding resistor 36, the resistance value of forward resistor 38, the capacitance of feedback capacitor 34, and the winding ratio and core (mutual inductance) value of transformer 20.

[0047] Figure 5 is a schematic diagram of the primary current in the transformer when the NIC is turned on and off. The inductor primary current IL flows through the primary winding of transformer 20 (Figure 4). When the steady-state detector 50 detects that the output is in a steady state and closes switch 40 to enable NIC 30, the waveform 102 value of the inductor current IL is lower. If switch 40 remains open during the steady state, NIC 30 is turned off, and the secondary current in transformer 20 stops. The lower equivalent inductance allows a higher inductor current IL to flow through the primary winding, as shown in waveform 104.

[0048] Figure 6 is a waveform diagram of the output voltage VOUT when the NIC is turned on and off. As can be seen from the figure, there is ripple at the output terminal, that is, the output voltage VOUT rises and falls. The absolute value of the ripple is small, but this ripple is still undesirable in the design.

[0049] When there is no transient transition, the steady-state detector 50 detects the steady state and closes switch 40 to enable NIC 30. The equivalent inductance of the primary winding of transformer 20 is greater than (two or three times) the rated value (e.g., 1 microhenry) because mutual inductance is generated when reverse current from operational amplifier 32 flows through the secondary winding. This higher equivalent inductance can offset changes in inductor current, thereby reducing VOUT changes caused by the normal switching of transistors 22 and 24 by controller 12. Waveform 112 shows that the ripple on VOUT is reduced when NIC 30 is turned on.

[0050] If switch 40 remains open during steady state, NIC 30 is turned off, and the secondary current in transformer 20 stops. The lower equivalent inductance allows a higher inductor current IL to flow through the primary winding. This modulation of the higher inductor current by transistors 22 and 24 causes larger fluctuations in VOUT, as shown in waveform 114.

[0051] Figures 7A-7B show the waveforms of the effect of turning the NIC on and off on VOUT in a transient situation where the SMPS load current suddenly increases.

[0052] In Figure 7A, the load current IL0AD through the load resistor 18 suddenly increases, for example, when the transistor in the load switches states and consumes a large transient current. In Figure 7B, the output voltage VOUT suddenly drops due to the sudden increase in load current. When NIC 30 is off, the circuit simulation results show that the output waveform 122 when NIC 30 is off recovers faster than the output waveform 124 when NIC 30 is on. Therefore, when the steady-state detector 50 detects the transient and turns off NIC 30, it can recover from the transient more quickly.

[0053] Even if the transient is faster than the steady-state detector 50 and NIC 30 can turn on, there may be subsequent transients that may benefit from NIC 30 being turned off by the first transient.

[0054] Figures 8A-8B show the waveforms of the effect of turning the NIC on and off on VOUT in a transient situation where the SMPS load current suddenly decreases. In Figure 8A, the load current ILOAD through load resistor 18 suddenly drops, for example, when the transistor switches to a light load.

[0055] In Figure 8B, the output voltage VOUT suddenly rises due to the sudden decrease in load current. When NIC 30 is off, the circuit simulation results produce waveform 132, which recovers faster and has lower ripple compared to the output waveform 134 when NIC 30 is on. Therefore, both high-level and low-level transients recover faster when the steady-state detector 50 detects a transient and turns off NIC 30.

[0056] Figure 9 shows an embodiment of the steady-state detector in more detail. The output voltage VOUT is input to the steady-state detector 50 and compared with predetermined voltage limits VMIN and VMAX (VMIN and VMAX can be set to acceptable ripple levels or determined by testing or simulation) to determine when transient response is enabled.

[0057] When VOUT is higher than VMIN or within the lower limit, comparator 52 drives its output to a high level. When VOUT is below VMAX or within the upper limit, comparator 54 drives its output high. Therefore, when both outputs are high, VOUT is within a predetermined limit. The I / O input of XNOR gate 56 drives its output (steady-state signal ST) high. Thus, NIC 30 is turned on when VOUT is in a steady state.

[0058] When VOUT is above VMAX, comparator 54 drives its output low, while comparator 52 still drives its output high. The O / I input of XNOR gate 56 drives its output ST low, thereby turning off NIC 30 to obtain a better transient response.

[0059] When VOUT is lower than VMIN, comparator 52 drives its output low, while comparator 54 still drives its output high. The 10 inputs of XNOR logic gate 56 drive its output ST low, thereby turning off NIC 30 to obtain better transient response.

[0060] Figure 10 shows the SMPS of a NIC with a bipolar transistor switch. In this embodiment, switch 40 uses a bipolar NPN transistor 41. The transistor base is driven by the steady-state signal ST generated by the steady-state detector 50.

[0061] Figure 11 shows the SMPS of a NIC with an n-channel transistor switch. In this embodiment, switch 40 uses an n-channel transistor 43. The transistor gate is driven by the steady-state signal ST generated by the steady-state detector 50.

[0062] Figure 12 shows the SMPS of a NIC with a diode switch. In this embodiment, switch 40 uses a diode 45. Since diode 45 does not have a control gate, ST and steady-state detector 50 are not required.

[0063] Diode 45 blocks reverse current flow. NIC acts as a voltage-controlled current source. In steady state, diode 45 only allows positive current to flow. A small forward voltage is required for current to flow through diode 45. This results in a small DC offset. At low voltages, diode 45 is off, and the current waveform is clipped at these low voltages due to AC ripple.

[0064] When a positive transient occurs, operational amplifier 32 senses a large but low-frequency current rise. Due to the transient, the voltage across diode 45 rises with the low frequency. A higher voltage allows diode 45 to remain on for a longer period during the transient and allows more secondary current to flow. The larger the secondary current, the greater the mutual inductance and the larger the primary equivalent inductance.

[0065] Although there is no steady-state detector 50 in this embodiment, diode 45 itself reacts to the voltage applied to it; that is, when the voltage is negative, diode 45 blocks the current; when the voltage is positive, diode 45 conducts. When a transient occurs, the load current in the primary circuit increases, and this increase is transmitted to node UB through transformer 20. Since diode 45 is connected in series with transformer 20, the two terminals of diode 45 can also "sense" the voltage change. During the voltage change, diode 45 is forward biased for a short time, thus inducing a low-frequency transient current change.

[0066] Figure 13 shows the SMPS of the NIC with a positive inductor. In this embodiment, grounding resistor 36 is replaced by grounding inductor 39, and feedback capacitor 34 is replaced by feedback resistor 35. In this embodiment, Z1 = Z2 of feedback resistor 35, and Z2 = sLp, where s is the complex frequency and Lp is the inductance value of grounding inductor 39. The gain generated by feedback capacitor 34 (4) is affected by the switching frequency. However, using feedback resistor 35 produces a fixed gain that is not affected by frequency.

[0067] Figure 14 shows a boost converter SMPS with a NIC. In this embodiment, a boost converter is used instead of a buck converter for the primary converter. Power transistor 22 is located after transformer 20, instead of before transformer 20 as in the buck converters shown in Figures 3, 4, and 10-13. Ground power transistor 24 is located before transformer 20, instead of after transformer 20.

[0068] Figure 15 shows an SMPS with a NIC that can modulate a portion of the secondary current. In this embodiment, a switching shunt resistor 60 is connected in parallel with switch 40. Even when switch 40 is open, a portion of the current output from operational amplifier 32 flows through switching shunt resistor 60. Therefore, even when steady-state detector 50 detects a transient and drives the steady-state signal ST low to open switch 40, NIC 30 remains on. When steady-state detector 50 detects a steady state and drives the steady-state signal ST high, switch 40 closes, and the current output from operational amplifier 32 flows in parallel through switch 40 and switching shunt resistor 60. Therefore, closing switch 40 increases the current through forward resistor 38, thereby increasing the secondary current of transformer 20.

[0069] NIC 30 is not fully on and off, but remains on, but its current is regulated by steady-state detector 50. Keeping NIC 30 on may be advantageous because turning operational amplifier 32 on and off may require time to reinitialize, resulting in a delay when ST turns on and off.

[0070] The current magnitude between the two states can be adjusted by adjusting the resistance values ​​of switch shunt resistor 60 and switch 40. Another resistor can also be connected in series with switch 40 to further adjust the current ratio. Therefore, switch shunt resistor 60 provides greater design flexibility. [Alternative Embodiments]

[0071] The inventors have also envisioned several other embodiments. For example, switch 40 can have a variety of combinations and variations. The switch can be any type of transistor, such as an insulated gate transistor or diode, NPN or PNP or other triodes, and can have a transistor network instead of a single transistor.

[0072] Although the buck converter arrangement of transistors 22, 24 is shown in most of the figures, and a boost converter is shown in Figure 14, other converters may be used instead, such as buck-boost, isolated, or multiphase converters. Other SMPSs (e.g., Cuk or Sepic) may also be used instead. 11 CN 119678357 A Specification 7 / 9

[0073] There are many possible embodiments of the steady-state detector 50. The embodiment in Figure 9 may interchange the inverting and non-inverting inputs of the comparator, may add or remove inverters, and may use gating other than XNOR. Differentiators or load transient detectors may also be used.

[0074] The output voltage may be sensed by a resistor network and then the signal may be passed directly to the buck control loop comparator for...This is another option for the steady-state detector 50.

[0075] Alternatively, the input voltage node of the buck converter can be used instead of the output voltage node for transient detection to speed up the detection process and an auxiliary buck converter can be used to smooth transient spikes.

[0076] By using a resistor network and an improved Type III compensator (e.g., OTA) based on a differential amplifier (DDA), the load transient response can be detected and passed to a comparator in the control loop.

[0077] The steady-state detector 50 can use an input node instead of an output node to detect load steps. Alternatively, the steady-state detector 50 can sense the current in the output capacitor or the voltage at the load terminal to detect changes. Control is achieved by setting an appropriate comparator threshold along with the comparator.

[0078] Comparators 52, 54 can be operational amplifiers or other comparator circuits. A hysteresis can be added before triggering the steady-state detector 50 to turn off the steady-state signal ST, requiring the transient to last for a predetermined period of time. XN0R 56 can be an XOR gate followed by an inverter. In addition to using two predetermined voltage levels to provide transient response for high and low transients, a single comparator can be used to provide a voltage limit. For example, the steady-state detector 50 can only shut down the steady-state signal ST for high-level transients exceeding VMAX, but not for low-level transients. This can be useful when only high-level transients are problematic or severe.

[0079] In addition to using a high-level active steady-state signal ST, a low-level active signal can also be used. The signal can be inverted to work with certain types of switches. In addition to using a single n-channel transistor as a switch, a transmission gate with parallel P-channel and n-channel transistors can be used, and an inverter can be used to generate STB for the p-channel gate.

[0080] The steady-state detector 50 can be powered by VS+, VS-, or other power supplies and equipped with a voltage level shifter as needed. The secondary ground GND2 can be isolated from or coupled to the primary ground GND. Other power and ground schemes can also be used. The power and ground voltages can be shifted. GND2 can be some kind of reference voltage and does not have to be exactly the midpoint voltage.

[0081] Additional impedance networks of resistors, capacitors, and / or inductors can be added around operational amplifier 32, and the values ​​of these components can be adjusted as needed. Transformer 20 can be any type of mutual inductance device with a magnetic core for energy storage, such as a PCB inductor with an E-core or a C-core, or a planar transformer. In addition to a single transformer, two or more transformers can be connected in series to obtain the desired rated inductance. Although transformers with metal or iron cores have been described, metal cores can also be omitted if sufficient mutual inductance is available. The number of turns in the primary and secondary windings of transformer 20 can be varied, and different wire gauges (cross-sectional areas) can be used for the primary and secondary windings. These factors will affect the mutual inductance and rated inductance values.

[0082] Although the term “winding” is generally used to describe the conductor path within transformer 20 that carries primary or secondary current, these windings are not necessarily uniform loops and can have various physical arrangements, configurations, and shapes. A winding can be a long conductor wound around a metal core, but for a planar transformer, the winding can also be a helical pattern on a plane. The primary and secondary windings can be on different planes. Many other variations are also possible. There can be intermediate terminals, such as an intermediate terminal in the middle of the primary winding, between the left and right primary terminals. A third winding for a third current path may also be present in transformer 20, such as an auxiliary winding for sensing, shielding, or testing.

[0083] Typically, the impedance of the secondary circuit Z(UA-UB) = sCfRpRg = sLeq can be adjusted to the design target value by adjusting or fine-tuning the resistance and capacitance values.

[0084] Transformer 20 can use any current transformer with a primary and a secondary circuit, electrically isolated but connected by mutual inductance magnetic connection 12 CN 119678357 A specification page 8 / 9. Transformer 20 has been described as having a primary winding with primary current flowing from the left end (C^VIN switch) to the right end (VOUT), the left end of the secondary winding grounded, and the right end driven by the current of operational amplifier 32 through positive resistor 38. Therefore, the secondary current ripple is reduced, thereby reducing the primary current ripple. Therefore, the flow direction of the secondary current is the same as the flow direction of the primary current, thereby increasing the primary inductance when the secondary current flows. However, other arrangements are also possible, for example, where the flow directions of the primary and secondary currents are opposite, and the primary inductance decreases instead of increases when switch 40 is closed and the secondary current increases. Various component parameters and applications can be substituted. The direction of the secondary winding can be changed, for example, by changing the direction of the same-name terminals. After changing the terminal, switch 40 can be in the ON state when a steady state is detected. When a transient state is detected, switch 40 is in the OFF state in this alternative. An inverter can be added to invert the steady-state signal ST of steady-state detector 50 and apply the inverted ST to switch 40. Switch 40 can be a normally closed switch instead of a normally open switch.

[0085] NIC 30 and transformer 20 provide an active inductor with a variable inductance value in the primary winding. This variable inductor can be modulated to a high inductance value to reduce ripple in steady state, or to a low inductance value to extend bandwidth and better suppress or converge transient spikes. This active inductor allows the use of a smaller output capacitor to achieve the target amount of ripple and transient suppression. The smaller output capacitor and variable inductor also reduce DC copper losses. Switch 40 can be fine-tuned to meet the target inductance values ​​when turned on and off by adjusting the resistance values ​​of grounding resistor 36 and positive resistor 38.

[0086] Switch 40 is connected in series with positive resistor 38. As an alternative sequence, positive resistor 38 can be connected between the output of operational amplifier 32 and the switch, while the switch is connected between positive resistor 38 and the non-inverting input of operational amplifier 32.

[0087] More complex buffers, level shifters, or other components can be replaced or added. Inverters can be added in different locations. Other delays and output waveform shaping hysteresis can also be added. Other types of buffer circuits, selectors, or multiplexers can also be used.

[0088] Transformer 20 only affects the AC component of the output VOUT, not the DC component. Controlling the impedance of the active inductor transformer 20 can reduce steady-state ripple by increasing the equivalent impedance value and improving the filtering effect of transformer 20 and output capacitor 16. It can also suppress transients and spikes by reducing the equivalent impedance of transformer 20, allowing the output current to increase or decrease to the load more quickly, thereby increasing bandwidth and accelerating convergence. The primary AC component can be considered as being absorbed by the mutual inductance of the secondary reverse current, because the inductor stores the energy of the primary AC component in the magnetic field.

[0089] Different transistors, capacitors, resistors, inductors, transformers, and other devices of various sizes can be used, as well as various layout arrangements, such as multi-pin, toroidal, donut-shaped, or irregularly shaped transistors. The current can be positive or negative and can flow in either direction. Many second- and third-order circuit effects may exist and may be quite pronounced, especially for smaller devices. These secondary factors can be accounted for using circuit simulation during the design process.

[0090] Switching devices can be implemented using n-channel, p-channel, or bipolar transistors or junctions in these transistors. Gate length and spacing can be increased to provide better damage protection.

[0091] IC semiconductor manufacturing processes can vary widely. A variety of materials can be used. Additional process steps can be added, such as for additional metal layers or other transistor types, or modifications can be made to standard complementary metal-oxide-semiconductor (CMOS) transistors when integrating transistors into larger devices. Although complementary metal-oxide-semiconductor (CMOS) transistors have been described, other types of transistors may be used instead for certain embodiments, such as using only n-channel, only p-channel when output swing is limited, or various alternative transistor technologies such as bipolar or BiCMOS. CMOS process may be FinFET process.

[0092] Terms such as up, down, above, below, horizontal, vertical, inside, outside, etc., are relative and depend on the viewing angle, and do not mean that the invention is limited to a specific viewing angle. Devices can be rotated such that vertical is horizontal and horizontal is vertical, so these terms depend on the observer. 13 CN 119678357 A Specification 9 / 9 pages

[0093] The background section of this invention may contain background information about the problem or environment of the invention, rather than describing the prior art of others. Therefore, the material included in the background section is not an admission by the applicant of prior art.

[0094] Any methods or processes described herein are implemented by machines or computers and are intended to be performed by machines, computers or other devices, and are not intended to be performed by humans alone without machine assistance. Tangible results may include reports or other machine-generated displays on display devices such as computer monitors, projection devices, audio generation devices and related media devices, and may include hard copy printouts that are also machine-generated. Computer control of other machines is another tangible result.

[0095] Any advantages and benefits described are not necessarily applicable to all embodiments of the invention. When the word “apparatus” appears in a claim element, the applicant intends that the claim element falls under the provisions of Section 112, paragraph 6 of 35 USC. Typically, one or more words precede the word “apparatus.” One or more words preceding the word “apparatus” are a label intended to facilitate reference to the claim element and not to express structural limitation. Such device-plus-function claims shall cover not only the structure described herein for performing the function and its structural equivalents, but also equivalent structures. For example, although nails and screws have different constructions, they are equivalent structures because they both perform the fastening function. Claims that do not use the term "device" do not fall under the provisions of Section 112, paragraph 6 of 35 USC. Signals are typically electronic signals, but can also be optical signals, for example, transmitted via fiber optic lines.

[0096] The above description of embodiments of the invention is provided for purposes of illustration and description. It is not intended to be exhaustive, nor is it intended to limit the invention to the precise forms disclosed. Many modifications and variations are possible based on the above teaching. The purpose is that the scope of the invention is not limited by this detailed description, but rather by the appended claims. 14 CN 119678357 A Specification Figure 1 / 8 Page IL Prior Art Figure 1 IL .. IC- ♦ Time Prior Art Figure 2 VIN S11 nnnn VOUT* VL1 nn n.. .......n 15 Specification Figure CN 119678357 A 2 / 8 Page VIN Figure 3 Figure 4 16 CN 119678357 A Specification Figure 3 / 8 Page Inductor Primary Current (IL, AMPS) Figure 5 Figure 6 17 CN 119678357 A Specification Figure 4 / 8 Page Figure 7A Figure 7B Figure 8A 18 CN 119678357 A Specification Figure 5 / 8 Page Figure 8B 50 Figure 9 19 CN 119678357 A Specification FigurePage 6 / 8 Figure 11 20 Specification Drawings Page 7 / 8 CN 119678357 A VOUT Figure 13 21 CN 119678357 A Specification Drawings Page 8 / 8 RG CF Figure 14 Figure 15 22 Active Variable Inductor Circuit China application no.: 202480002899.2 Abstract: A Switched-Mode Power Supply uses a primary winding of a transformer rather than an inductor. The secondary winding of the transformer is driven with a current generated by a negative inductance circuit. When the reverse current flows it can increase the equivalent inductance value of the primary windings. A steady-state detector activates a steady signal and closes a switch to turn on the reverse current from an op amp when the output voltage remains within predetermined limits, causing the inductance to increase thus reducing ripple during steady state. When an output transient occurs, the steady signal is deactivated and the switch opened to stop the current from flowing through the transformer secondary, reducing primary inductance to allow for current to flow faster to the output to suppress thetransient. Resistor and capacitor networks around the op amp allow for tuning the inductance modulation. China application no.: 202480002899.2 Abstract: A Switched-Mode Power Supply uses a primary winding of a transformer rather than an inductor. The secondary winding of the transformer is driven with a current generated by a negative inductance circuit. When the reverse current flows it can increase the equivalent inductance value of the primary windings. A steady-state detector activates a steady signal and closes a switch to turn on the reverse current from an op amp when the output voltage remains within predetermined limits, causing the inductance to increase thus reducing ripple during steady state. When an output transient occurs, the steady signal is deactivated and the switch opened to stop the current from flowing through the transformer secondary, reducing primary inductance to allow for current to flow faster to the output to suppress the transient. Resistor and capacitornetworks around the op amp allow for tuning the inductance modulation. Abstract

Claims

1. An active inductor circuit, comprising: A mutual inductor having a primary winding between primary terminals and a secondary winding between secondary terminals, wherein the primary winding and the secondary winding are electrically isolated from each other and magnetically coupled together by mutual inductance generated by current flowing through the primary winding and the secondary winding; an operational amplifier having a first input connected to the first secondary terminal; a grounded resistor connected between the second secondary terminal and the second input of the operational amplifier; a feedback device connected between the output of the operational amplifier and a second input of the operational amplifier; a modulation network connected between the output of the operational amplifier and the first input of the operational amplifier; a switch in a modulation network, wherein the switch modulates a secondary current flowing through a secondary winding of the mutual inductance device, The modulation network modulates the output current generated by the output terminal of the operational amplifier and applies the modulated current to the second secondary terminal of the mutual inductance device; Wherein, when the switch is in a first state, the secondary current has a first current value; Wherein, when the switch is in the second state, the secondary current has a second current value, and the second current value is greater than the first current value; Wherein, when the switch is in the first state, the secondary current flowing through the secondary winding increases the primary equivalent inductance value of the first winding through the mutual inductance of the mutual inductance device; Wherein, when the switch is in the second state and the secondary current has a second current value, the primary equivalent inductance value is greater than the primary equivalent inductance value when the switch is in the first state, Thus, the primary equivalent inductance value is switched between two values ​​by the switch modulating the secondary current.

2. The active inductor circuit according to claim 1, wherein the mutual inductance device is a transformer; wherein the primary current and the secondary current flow in the transformer in the same direction.

3. The active inductor circuit of claim 2, wherein the feedback device is a capacitor; wherein the modulation network further comprises a forward resistor connected in series with the switch between the operational amplifier output and the operational amplifier first input.

4. The active inductor circuit of claim 2, wherein the feedback device is a resistor; wherein the modulation network further comprises a forward inductor connected in series with the switch between the operational amplifier output and the operational amplifier first input.

5. The active inductor circuit of claim 2, wherein the switch is a diode.

6. The active inductor circuit of claim 3, further comprising: a steady-state detector that compares a primary output voltage generated by a primary current flowing through a primary winding of the mutual inductor with a predetermined voltage range and activates a switch signal when the primary output voltage is within the predetermined voltage range; The switch signal of the steady-state detector is used to turn on and off the switch.

7. The active inductor circuit of claim 6, wherein the switch is a transistor having a control gate that receives a switch signal from the steady-state detector; The transistor is a bipolar transistor or a metal oxide semiconductor field effect transistor (MOSFET).

8. The active inductor circuit of claim 7, further comprising: a first power transistor connected in series with the first winding of the mutual inductance device to generate a primary output voltage, the first power transistor having a gate driven by a controller that turns the first power transistor on and off at a selected switching frequency to generate ripple in the primary output voltage; Among them, the ripple is reduced by closing the switch to increase the secondary current and increase the primary equivalent inductance value; Wherein, when the steady-state detector detects that the primary output voltage exceeds a predetermined voltage range and the switch is disconnected to reduce the secondary current, the primary equivalent inductance value increases; Therefore, when a transient is detected, the transient is suppressed by the lower primary equivalent inductance value, and when a transient is not detected in a steady state, the ripple is reduced by the higher primary equivalent inductance value.

9. The active inductor circuit according to claim 8, wherein the first power transistor and the first winding of the mutual inductance device are connected in series between an input power supply voltage and an output capacitor having a primary output voltage; Also includes: a second power transistor connected between the primary terminal of the mutual inductance device and the primary ground, the gate of the second power transistor being driven by the controller; wherein the controller generates non-overlapping gate signals for the first power transistor and the second power transistor to prevent the first and second power transistors from being turned on at the same time; Wherein, the active inductor circuit modulates the primary inductance of a switching power supply (SMPS).

10. The active inductor circuit of claim 9, wherein when the switch is in the first state, the switch is open to prevent current flow; wherein when the switch is in the second state, the switch is closed to conduct current; When the switch is turned off, the switch cuts off the secondary current.

11. The active inductor circuit according to claim 10, wherein the primary equivalent inductance value when the switch is closed is at least twice the primary equivalent inductance value when the switch is open; in, Closing the switches by the modulation network doubles the equivalent inductance in the primary winding.

12. The active inductor circuit of claim 9, further comprising: a switch shunt resistor connected in parallel with the switch; When the switch is turned off, the secondary current continues to flow.

13. A variable equivalent inductance circuit, comprising: A transformer, whose primary and secondary paths are electrically isolated from each other and magnetically coupled together by mutual inductance; Wherein, the secondary current flows through the primary path of the transformer to charge the output capacitor and generate a primary output voltage; wherein the secondary current flows through the secondary path from the input secondary terminal to the output secondary terminal; wherein the primary current flows in the same direction as the secondary current in the transformer; an operational amplifier, which has an inverting input, a non-inverting input, and an output; a first resistor connected between the transformer output secondary terminal and the operational amplifier inverting input; a feedback impedance device connected between the operational amplifier inverting input and the operational amplifier output; A switch and a second impedance device are connected in series between the operational amplifier output and the non-inverting input of the operational amplifier; Wherein, the non-inverting input of the operational amplifier is connected to the input secondary terminal of the transformer.

14. The variable equivalent inductance circuit of claim 13, wherein the second impedance device is a resistor; and wherein the feedback impedance device is a capacitor.

15. The variable equivalent inductance circuit of claim 14, wherein the operational amplifier is powered by an upper power supply voltage and a lower power supply voltage; wherein a midpoint voltage between the upper power supply voltage and the lower power supply voltage is connected to an output secondary terminal of the transformer.

16. The variable equivalent inductance circuit according to claim 15, further comprising: a steady-state detector that compares the primary output voltage with a voltage limit and activates a switching signal when the primary output voltage does not exceed the voltage limit; wherein when a small voltage ripple appears on the primary output voltage that is less than the voltage limit, the switch signal, when activated, closes the switch to increase the current flowing through the second impedance device and increase the primary inductance along the primary path through the transformer; wherein when a large voltage transient occurs on the primary output voltage that is greater than the voltage limit, the switch signal, when not activated, opens the switch to reduce current flowing through the second impedance device and to reduce primary inductance along the primary path through the transformer, The switch is closed so that the primary inductance increases during steady state to reduce ripple, while the switch is open so that the primary inductance decreases during transient state to increase bandwidth and reduce transient response time.

17. The variable equivalent inductance circuit of claim 16, wherein the switch is a metal oxide semiconductor field effect transistor (MOSFET) whose gate receives the switching signal from the steady-state detector, or the switch is a bipolar transistor whose base receives the switching signal from the steady-state detector.

18. The variable equivalent inductance circuit according to claim 16, further comprising: a controller that generates a first gate signal and a second gate signal that are non-overlapping and switched at a frequency in the order of 100 kHz; Power supply voltage input; a first power transistor, a gate of which receives the first gate signal, connected between the supply voltage input and an input primary terminal of the transformer primary path; a second power transistor, a gate of which receives the second gate signal and is connected between an input primary terminal of the primary path of the transformer and a primary ground; wherein the output terminal of the primary path of the transformer is connected to the output capacitor to generate the primary output voltage; Wherein, the first power transistor, the second power transistor and the transformer primary path form a buck converter switch mode power supply (SMPS).

19. The variable equivalent inductance circuit according to claim 17, further comprising: a controller that generates a first gate signal and a second gate signal that are non-overlapping and switched at a frequency in the order of 100 kHz; Power supply voltage input; a first power transistor, a gate of which receives the first gate signal and is connected between an output primary terminal of the primary path of the transformer and an output capacitor generating a primary output voltage; a second power transistor, a gate of which receives the second gate signal and is connected between an input primary terminal of the primary path of the transformer and a primary ground; wherein an input terminal of the transformer primary path is connected to the supply voltage input; wherein the first power transistor, the second power transistor and the transformer primary path form a boost converter switch mode power supply (SMPS).

20. A switchable inductive power supply circuit, comprising: A transformer whose primary and secondary paths are electrically isolated from each other and magnetically coupled together by mutual inductance; Wherein, the primary current flows through the primary path of the transformer, charges the output capacitor, and generates a primary output voltage; wherein the secondary current flows through the secondary path from the input secondary terminal to the output secondary terminal; wherein the primary current flows in the same direction as the secondary current in the transformer; an operational amplifier having an inverting input, a non-inverting input and an output; a first resistor connected between the output secondary terminal of the transformer and the inverting input of the operational amplifier; a feedback capacitor connected between the inverting input of the operational amplifier and the output of the operational amplifier; a switching transistor and a second resistor connected in series between the output of the operational amplifier and the non-inverting input of the operational amplifier; wherein the non-inverting input of the operational amplifier is connected to the input secondary terminal of the transformer; a controller that generates first and second gate signals that are non-overlapping and switched at a selected frequency; Power supply voltage input; a first power transistor, a gate of which receives the first gate signal, connected between the supply voltage input and an input primary terminal of the transformer primary path; a second power transistor, a gate of which receives the second gate signal and is connected between an input primary terminal of the primary path of the transformer and a primary ground; wherein the output terminal of the primary path of the transformer is connected to an output capacitor to generate a primary output voltage; wherein the first power transistor, the second power transistor and the transformer primary path form a buck converter switch mode power supply (SMPS); a steady-state detector that compares the primary output voltage with a voltage limit and activates a switching signal to the switching transistor when the primary output voltage does not exceed the voltage limit; wherein when a small voltage ripple appears on the primary output voltage that is less than the voltage limit, the switching signal, when activated, closes the switching transistor to increase the current flowing through the second impedance device and increase the primary inductance along the primary path through the transformer; wherein when a large voltage transient occurs on the primary output voltage that is greater than the voltage limit, the switching signal turns off the switching transistor when the switching signal is not activated to reduce the current flowing through the second impedance device and reduce the primary inductance along the primary path through the transformer; The closing of the switching transistor causes the primary inductance to increase during a steady state to reduce ripple, while the opening of the switching transistor causes the primary inductance to decrease during a transient state to increase bandwidth and reduce transient response time.

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