Active variable inductance 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

[Technical field]

[0001] The present invention relates to active inductors, and more particularly to negative inductance circuits for switch mode power supplies (SMPS). [Background technology]

[0002] Power metal oxide semiconductor field effect transistors (MOSFETs) switch at 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 both transistors are not turned on at the same time. By controlling the duty cycle and other timing, the desired output voltage can be generated from the input voltage.

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

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

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

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

[0007] The rise and fall of VOUT is called ripple, which is a negative effect. Ripple can be reduced by increasing the capacitance value (measured in farads) of the output capacitor 16. However, this approach also has disadvantages because a single large capacitor takes up board or layout space, is expensive, and has long wiring paths that produce electrical losses. Ripple can also be reduced by increasing the inductance value (measured in henries) of the inductor 10, but large inductors tend to be more expensive and bulky than capacitors.

[0008] Adding capacitance or inductance can also degrade the transient response of the SMPS. For example, the load may contain many transistors or other circuits that switch on and off during normal operation. This causes the current consumed by the load to vary. The SMPS should provide additional or reduced current as needed to cope with these load current variations. However, when the output capacitor 16 is larger, the current through the transistor 22 charges the output capacitor 16 instead of flowing through the load resistor 18. Similarly, a larger inductor 10 will also have a poor transient response. When the transient response is weak, the VOUT spike may swing to extreme levels, triggering the overvoltage or undervoltage protection circuit, which is undesirable.

[0009] There is a trade-off between increasing output capacitance and inductance to reduce ripple while providing adequate 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.

[0010] Therefore, an active inductor for SMPS is needed. It is hoped that the active inductor increases the SMPS power inductance value under steady-state conditions to reduce output ripple, and reduces the power inductance value under transient conditions to improve transient response. An active inductor whose equivalent inductance value is controlled by a circuit is needed.

Brief Description of the Drawings

[0011] Figure 1 A switch mode power supply (SMPS) of the prior art is shown.

[0012] Figure 2 show Figure 1 Waveforms when the SMPS is running.

[0013] Figure 3 An SMPS with an active inductor is shown.

[0014] Figure 4 An SMPS with a capacitor-based negative inductance circuit (NIC) is shown in more detail.

[0015] Figure 5 Figure 2 is a schematic diagram of the primary current in the transformer when the NIC is turned on and off.

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

[0017] Figure 7A-7B The waveforms showing the SMPS response to load current jumps when the NIC is turned on and off.

[0018] Figures 8A-8B The waveforms showing the SMPS response to a load current step drop when the NIC is turned on and off.

[0019] Fig. 9 One embodiment of a steady-state detector is shown in more detail.

[0020] Fig.10 An SMPS of a NIC with bipolar transistor switches is shown.

[0021] Fig.11 An SMPS of a NIC with n-channel transistor switches is shown.

[0022] Fig.12 An SMPS of a NIC with a diode switch is shown.

[0023] Fig.13 An SMPS with a NIC topology employing a positive inductor is shown.

[0024] Fig.14 A boost converter SMPS with a NIC is shown.

[0025] Fig.15 An SMPS with a NIC that only partially modulates the secondary current is shown. [Specific implementation method]

[0026] The present invention relates to improvements to active inductor circuits. The following description is intended to enable one of ordinary skill in the art to make and use the invention in the context of a particular application and its requirements. Various modifications to the preferred embodiments will be apparent to one skilled in the art, and the general principles defined herein may also be applied to other embodiments. Therefore, the present invention is not intended to be limited to the specific embodiments shown and described, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

[0027] The inventors have realized that variable inductors can reduce the ripple of an SMPS by increasing the inductance value and speed up the transient response by decreasing the inductance value. While variable inductors are used in older radio equipment, these variable inductors are typically large coils with a magnetic core that are physically moved to change the inductance.

[0028] The inventors realized that an active variable power inductor can be realized by replacing an inductor with a mutual inductance device (e.g., a transformer). 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, which is coupled to the primary winding through the magnetic core. The NIC can send current in the reverse direction through the secondary winding, thereby generating mutual inductance in the primary winding, resisting the flow of current, thereby increasing the inductance value of the primary winding. Therefore, the NIC can adjust the inductance value of the primary winding.

[0029] Figure 3 A SMPS with an active inductor is shown. Figure 1 The inductor 10 in the embodiment 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] Controller 12 drives gate signal S1 high, causing current to flow through transistor 22 and the primary winding of transformer 20, charging output capacitor 16. Controller 12 also drives gate signal S2 high to turn on transistor 24, thereby reducing the voltage across transformer 20 to maintain the desired output voltage VOUT. Input capacitor 14 is optional, but helps maintain VIN.

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

[0032] When the switch 40 is closed, the NIC 30 can generate a reverse current that flows through the secondary winding of the transformer 20. The reverse current generates a magnetic field in the transformer 20, which is coupled or enhanced by the magnetic core of the transformer 20. The generated magnetic field generates additional inductance in the primary winding of the transformer 20. Therefore, when the switch 40 is closed to enable the NIC 30, the inductance value of the primary winding of the transformer 20 increases.

[0033] When a sufficiently large transient occurs at the output, VOUT is no longer within the predetermined limits, and the steady-state detection 50 drives the steady-state signal ST low, thereby opening the switch 40. The switch 40 opens the loop, 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 drops back to its rated value. The lower inductance value through the transformer 20 allows a larger inductor current IL to flow to the output and the load 18. Since the current flowing through the transformer 20 is increased, a faster response to the transient can be achieved.

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

[0035] Therefore, by turning the NIC 30 on and off, the equivalent inductance value in the primary 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 the transient response time when a transient is detected. For example, when the rated inductance of the transformer 20 is 1 μH (physical inductance value), the equivalent inductance value is 1 μH when the NIC 30 is turned off, and the equivalent inductance value is 1 μH when the NIC 30 is turned on.

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

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

[0038] Switch 40 and resistor value R p The positive resistor 38 is connected in series between the output node UC of the operational amplifier 32 and the non-inverting input node UB of the operational amplifier 32. When the steady-state detector 50 drives ST to a high level and closes the switch 40, the second impedance (Z p) connects the non-inverting input terminal and output terminal of the operational amplifier 32.

[0039] Since the controller 12 turns on and off the power transistors 22 and 24, the frequency of the ripple on the primary current flowing through the transformer 20 is the same as the selected switching frequency. The inductor circuit is a voltage-controlled current source, and a voltage UB is generated at the end of the secondary winding through the mutual inductance of the metal core of the transformer 20. According to the characteristics of the operational amplifier, the voltages at the non-inverting input terminal (+) and the inverting input terminal (-) of the operational amplifier 32 are equal, so the inverting input terminal voltage UA is equal to the non-inverting input terminal voltage UB. Since the feedback network generates a voltage gain through the feedback capacitor 34, the output voltage of the operational amplifier 32 after gain is UC. In this case, the voltages UC and UB across the forward resistor 38 generate a reverse AC current on the forward resistor 38. The reverse AC current is opposite in phase to the ripple part of IL, and is coupled to the primary winding of the transformer 20 through the secondary winding of the transformer 20. The coupled ripple part of IL has the same phase as the original ripple, but the ripple amplitude is reduced.

[0040] Similar ripples are generated in the secondary current by the mutual inductance through the metal core of the transformer 20. These ripples in the secondary current are applied to the inverting (+) input of the operational amplifier 32, amplified by the gain factor, and 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 that flows in the reverse direction 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, and the second impedance network is connected to the non-inverting (+) input terminal of the operational amplifier 32. The grounding resistor 36 and the feedback capacitor 34 are connected to the inverting input terminal of the operational amplifier 32 and form a first impedance network, i.e., an inverting feedback network. The forward resistor 38 is connected to the non-inverting (+) input terminal of the operational amplifier 32 to form a second impedance network.

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

[0043] In this embodiment, under the effect of the proportional factor s, the first impedance is Z 1 =1 / (sC f ), the second impedance is Zp =R p The ground resistor 36 and the forward resistor 38 may be variable resistors or fixed resistors (e.g., suitable resistance values ​​are determined by circuit analysis, simulation, or prototype testing). When the ground resistor 36 and the forward resistor 38 are variable resistors, they may be programmable, for example, the resistors in the resistor group may be selected by a programmable register, and the register may be programmable by a program.

[0044] The scale factor s is the complex frequency. In frequency domain analysis, the complex frequency s is a complex number expressed as s = σ + jω, where σ is the real part, representing the attenuation or growth factor, and jω is the imaginary part, representing the angular frequency. For ideal inductors and capacitors, σ 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 can be obtained by inverse Fourier 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 of the primary winding of the transformer 20 is increased to reduce the ripple. When VOUT is transient and not within the predetermined range, the steady-state detector 50 drives ST to low to open the switch 40 and turn off the current in the secondary winding. The equivalent inductance of the primary winding drops to the rated value, and the lower rated inductance allows a larger ripple peak-to-peak value to flow to the load within one cycle, and the current slope of the load is larger, thereby achieving a faster transient response.

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

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

[0048] Figure 6This is the waveform of the output voltage VOUT when the NIC is turned on and off. As shown in the figure, there is ripple at the output end, that is, the output voltage VOUT rises and falls. The absolute value of the ripple is very small, but this ripple is still undesirable in the design.

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

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

[0051] Figure 7A-7B The waveforms show the effect of turning the NIC on and off on VOUT during a transient condition where the SMPS load current suddenly increases.

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

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

[0054] Figures 8A-8B The waveforms showing the effect of NIC turning on and off on VOUT under transient conditions when the SMPS load current suddenly drops. Fig. 8A In the embodiment of FIG. 1 , the load current I LOAD through the load resistor 18 suddenly drops, for example when the transistor switches to a light load.

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

[0056] Fig. 9 One embodiment of a steady state detector is shown in more detail. The output voltage VOUT is input to a steady state detector 50 and compared to predetermined voltage limits VMIN, VMAX (VMIN, VMAX may be set to acceptable ripple levels or may be determined by testing or simulation) to determine when to enable transient response.

[0057] When VOUT is above VMIN or within the lower limit, comparator 52 drives its output high. 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 the predetermined limit. The 11 input applied to XNOR logic gate 56 drives its output (steady state signal ST) high. Thus, when VOUT is in a steady state, NIC 30 is turned on.

[0058] When VOUT is above VMAX, comparator 54 drives its output low while comparator 52 still drives its output high. The 01 input of XNOR logic gate 56 drives its output ST low, shutting down NIC 30 for better transient response.

[0059] When VOUT is below VMIN, comparator 52 drives its output low, while comparator 54 still drives its output high. The 10-input of XNOR logic gate 56 drives its output ST low, shutting down NIC 30 for better transient response.

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

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

[0062] Fig.12The SMPS of the NIC with diode switch is shown. In this embodiment, the switch 40 is a diode 45. Since the diode 45 has no control gate, the ST and steady state detector 50 are not required.

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

[0064] When a forward transient occurs, operational amplifier 32 senses a larger but low frequency current rise. Due to the transient, the voltage across diode 45 rises with the low frequency rise. The higher voltage allows diode 45 to remain on longer when the transient occurs and more secondary current flows. The larger the secondary current, the larger the mutual inductance and the larger the primary equivalent inductance.

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

[0066] Fig.13 SMPS of NIC with positive inductor is shown. 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, Z 1 = R of feedback resistor 35 f , while Z 2 =sL p , where s is the complex frequency, L p is the inductance of the grounding inductor 39. The feedback capacitor 34 ( Figure 4 ) produces a gain that is affected by the switching frequency. However, using feedback resistor 35 produces a fixed gain that is not affected by frequency.

[0067] Fig.14 A boost converter SMPS with a NIC is shown. In this embodiment, the primary converter uses a boost converter instead of a buck converter. The power transistor 22 is located after the transformer 20 instead of Figure 3 , Figure 4 , Figure 10-13The grounded power transistor 24 is located before the transformer 20, rather than after the transformer 20, as shown in FIG.

[0068] Fig.15 An SMPS with a NIC that can partially modulate the secondary current is shown. In this embodiment, a switch shunt resistor 60 is connected in parallel with the switch 40. Even if the switch 40 is open, part of the current output by the operational amplifier 32 passes through the switch shunt resistor 60. Therefore, even if the steady-state detector 50 detects a transient state and drives the steady-state signal ST to a low level to open the switch 40, the NIC 30 remains in the on state. When the steady-state detector 50 detects a steady state and drives the steady-state signal ST to a high level, the switch 40 is closed, and the current output by the operational amplifier 32 passes through the switch 40 and the switch shunt resistor 60 in parallel. Therefore, closing the switch 40 increases the current through the forward resistor 38, thereby increasing the secondary current of the transformer 20.

[0069] Rather than fully switching on and off, NIC 30 remains on but its current is regulated by steady state detector 50. Keeping NIC 30 on may be advantageous because switching op amp 32 on and off may require time to reinitialize, resulting in a delay when ST is switched on and off.

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

[0071] The inventors have also contemplated other embodiments. For example, the switch 40 may have multiple combinations and variations. The switch may be any type of transistor, such as an insulated gate transistor or a diode, an NPN or PNP or other triode, and may have a transistor network instead of a single transistor.

[0072] Although most of the figures show a buck converter arrangement of transistors 22, 24, and Fig.14 A boost converter is shown, but other converters such as buck-boost, isolation or multiphase converters can be substituted. Other SMPS such as Cuk or Sepic can also be substituted.

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

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

[0075] In addition, the input voltage node of the buck converter can be used for transient detection instead of the output voltage node to speed up the detection and use an auxiliary buck converter to smooth the transient spike.

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

[0077] The steady state detector 50 may use the input node instead of the output node to detect the load step. Alternatively, the steady state detector 50 may sense the current in the output capacitor or the voltage at the load terminal to detect the change. Together with the comparator, control is achieved by setting an appropriate comparator threshold.

[0078] Comparators 52, 54 may be operational amplifiers or other comparison circuits. Hysteresis may be added requiring a transient to persist for a predetermined period of time before the steady-state detector 50 is triggered to shut down the steady-state signal ST. XNOR 56 may be an XOR gate followed by an inverter. Rather than using two predetermined voltage levels to provide a transient response for both high and low transients, only one comparator may be used to provide one voltage limit. For example, the steady-state detector 50 may shut down the steady-state signal ST only for high level transients exceeding VMAX, but not for low level transients. This may be useful when only high level transients are problematic or severe.

[0079] Instead of using an active high steady-state signal, ST, you can use an active low signal. You can invert the signal for use with certain types of switches. Instead of using a single n-channel transistor as a switch, you can use a transmission gate that connects p-channel and n-channel transistors in parallel and use an inverter 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 converter as needed. The secondary ground GND2 can be isolated from the primary ground GND or coupled to it. Other power and ground schemes can also be used. The power and ground voltages can be shifted. GND2 can be some reference voltage and does not have to be exactly the midpoint voltage.

[0081] Other impedance networks of resistors, capacitors and / or inductors can be added around the operational amplifier 32, and the values ​​of these components can be adjusted as needed. The transformer 20 can be any type of mutual inductance device with a magnetic core 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, the metal core can also be removed if there is sufficient mutual inductance. The number of turns of the primary and secondary windings of the transformer 20 can vary, and different wire gauges (cross-sectional areas) can be used for the primary and secondary windings. These factors will affect the mutual inductance and the rated inductance value.

[0082] Although the term "winding" is generally used to describe the wire paths within the transformer 20 that carry the primary or secondary current, these windings are not necessarily uniformly ring-shaped and can have a variety of physical arrangements, configurations, and shapes. The windings can be long wires wrapped around a metal core, but for planar transformers, the windings can also be a spiral pattern on a plane. The primary and secondary windings can be on different planes. There can be many other variations. There can be an intermediate terminal, such as an intermediate terminal in the middle of the primary winding, between the left primary terminal and the right primary terminal. There may also be a third winding in the transformer 20 for a third current path, such as an auxiliary winding for sensing, shielding, or testing.

[0083] Usually, the impedance of the secondary circuit is Z(UA-UB) = -sC f R p R g =sL eq , which can be adjusted to the design target value by adjusting or fine-tuning the resistance and capacitance values.

[0084] Transformer 20 can use any mutual inductor having a primary loop and a secondary loop, which are electrically isolated but magnetically connected by mutual inductance. Transformer 20 has been described as having a primary winding, the primary current flows from the left end (switched from VIN) to the right end (VOUT), the left end of the secondary winding is grounded, and the right end is 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, there may be other arrangements, such as the flow directions of the primary current and the secondary current are opposite, and when the switch 40 is closed and the secondary current increases, the primary inductance decreases instead of increasing. Various component parameters and applications can be replaced. The direction of the secondary winding can be changed, for example, by changing the direction of the same-name terminal. After changing the same-name terminal, when a steady state is detected, switch 40 can be in an on state. When a transient state is detected, switch 40 is in an off state in this alternative. An inverter may be added to invert the steady-state signal ST of the steady-state detector 50 and apply the inverted ST to the switch 40. The switch 40 may 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. The 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. The active inductor allows the use of a smaller output capacitor to achieve the target amount of ripple and transient suppression. Smaller output capacitors and variable inductors can also reduce DC copper losses. By adjusting the resistance values ​​of ground resistor 36 and positive resistor 38, switch 40 can be fine-tuned to meet the target inductance value when turned on and off.

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

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

[0088] The transformer 20 only affects the AC component of the output VOUT, but not the DC component. Controlling the impedance of the active inductor transformer 20 can reduce the ripple in steady state by increasing the equivalent impedance value and improving the filtering effect of the transformer 20 and the output capacitor 16. It can also suppress transients and spikes by reducing the equivalent impedance of the transformer 20, so that the output current increases or decreases to the load faster, thereby increasing the bandwidth and accelerating the convergence speed. The primary AC component can be regarded as being absorbed by the mutual inductance of the secondary reverse current, because the inductor stores the energy of the primary side AC component in the magnetic field.

[0089] Different transistor, capacitor, resistor, inductor, transformer, and other device sizes can be used, as well as various layout arrangements, such as multi-pin, ring, donut, or irregular shaped transistors. Current can be positive or negative and can flow in either direction. Many second- and third-order circuit effects are possible and can be significant, especially for smaller device sizes. Circuit simulation can be used during the design process to account for these secondary factors.

[0090] The switching device can be implemented using n-channel, p-channel or bipolar transistors or junctions in these transistors. The gate length and spacing can be increased to provide better protection against damage.

[0091] There are many variations of IC semiconductor manufacturing processes. Various materials can be used. When integrating transistors into larger devices, additional process steps can be added, such as for additional metal layers or other transistor types, or modifications to standard complementary metal oxide semiconductor (CMOS) transistors. Although complementary metal oxide semiconductor (CMOS) transistors have been described, for some embodiments, other types of transistors can be used instead, such as only using n-channel, only using p-channel when the output swing is limited, or using various alternative transistor technologies, such as bipolar or BiCMOS. The CMOS process can be a fin field effect transistor (FinFET) process.

[0092] Terms such as up, down, above, below, horizontal, vertical, inside, outside, etc. are relative and depend on the viewing angle and are not meant to limit the invention to a particular viewing angle. The device can be rotated so that vertical is horizontal and horizontal is vertical, so these terms depend on the observer.

[0093] The background section of the present invention may contain background information about the problem or environment of the present invention, rather than describing the prior art of others. Therefore, the materials contained in the background section are not an admission by the applicant that the prior art is available.

[0094] Any method or process described herein is machine-implemented or computer-implemented, intended to be performed by a machine, computer or other device, and is not intended to be performed solely by humans without machine assistance. Tangible results produced 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 hard copy printouts that are also machine-generated. Computer control of other machines is another tangible result.

[0095] Any advantages and benefits described do not necessarily apply to all embodiments of the invention. When the word "means" appears in a claim element, applicant intends that the claim element fall within 35 USC § 112(6). Typically, the word "means" is preceded by a label of one or more words. The one or more words preceding the word "means" are a label for the purpose of facilitating reference to the claim element and are not intended to express a structural limitation. Such a means-plus-function claim is intended to cover not only the structures described herein for performing the function and their structural equivalents, but also equivalent structures. For example, although a nail and a screw have different constructions, they are equivalent structures because they both perform the function of fastening. Claims that do not use the word "means" do not fall within 35 USC § 112(6). Signals are typically electronic signals, but can also be optical signals, such as those that can be transmitted over fiber optic lines.

[0096] The above description of the embodiments of the present invention is presented for the purpose of illustration and description. It is not intended to be exhaustive, nor is it intended to limit the invention to the precise form disclosed. Many modifications and variations are possible in light of the above teachings. It is intended that the scope of the present invention is not limited by this detailed description, but rather by the limitations of the claims appended hereto.

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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