Active variable inductance circuit

Abstract

A switch-mode power supply uses the primary winding of a transformer instead of an inductor. The secondary winding of the transformer is driven by a current generated by a negative inductance circuit. When a reverse current flows, it increases the equivalent inductance of the primary winding. When the output voltage is maintained within predetermined limits, a 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 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.

Description

[Technical Field]

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

[0002] Power metal-oxide-semiconductor field-effect transistors (MOSFETs) enable portable, compact, and efficient switch-mode power supplies (SMPSs) with switching frequencies in the hundreds of kilohertz range. 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 parameters, the desired output voltage can be generated from the input voltage.

[0003] Figure 1 This illustrates 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, charging output capacitor 16. Then, controller 12 turns off S1 and turns on gate signal S2, thereby turning on transistor 24 and discharging 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 It is a display Figure 1 The waveform of SMPS operation is shown below. When the controller drive S1 is high, the 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 the inductor current IL to rise sharply when S1 is high and fall slowly when S1 is low. When IL rises, energy is stored in inductor 10, and when IL falls, energy is released.

[0006] The AC portion of the inductor current IL mainly flows to the output capacitor 16, causing the capacitor current IC to closely follow the inductor current IL. However, due to the RC delay, curvature is generated. After the RC delay, the voltage and VOUT on the 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 drawbacks, as a single large capacitor occupies board or layout space, 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] Adding capacitors or inductors can also reduce the transient response of the SMPS. For example, a load may contain many transistors or other circuits that turn on and off during normal operation. This causes variations in the current consumed by the load. The SMPS should provide additional or reduced current as needed to accommodate these load current variations. However, when the output capacitor 16 is large, the current through transistor 22 will charge the output capacitor 16 instead of flowing through the load resistor 18. Similarly, a large inductor 10 will also have a poor transient response. When the transient response is weak, VOUT spikes may swing to extreme levels, triggering undesirable overvoltage or undervoltage protection circuitry.

[0009] There is a trade-off between increasing the output capacitance and inductance to reduce ripple and providing sufficient transient response. The inventors realized that reducing output ripple and improving transient response are mutually exclusive when using conventional fixed-value capacitors and inductors in SMPS.

[0010] Therefore, an active inductor for SMPS is needed. It is desirable for the active inductor to increase the SMPS power inductance value 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 a circuit is required. [Attached Image Description]

[0011] Figure 1 This demonstrates a switch-mode power supply (SMPS) based on existing technology.

[0012] Figure 2 show Figure 1 The waveform of SMPS during runtime.

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

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

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

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

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

[0018] Figures 8A-8B The waveforms of the SMPS response to the drop in load current are displayed when the NIC is turned on and off.

[0019] Figure 9 An embodiment of the steady-state detector is shown in more detail.

[0020] Figure 10 The SMPS of a NIC with bipolar transistor switches is shown.

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

[0022] Figure 12 The SMPS of the NIC with diode switches is shown.

[0023] Figure 13 The SMPS with a NIC topology employing a positive inductor is shown.

[0024] Figure 14 The SMPS boost converter with NIC is shown.

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

Detailed Implementation Methods

[0026] This invention relates to improvements to active inductor circuits. The following description is intended to enable those skilled in the art to make and use the invention in the context of specific applications and 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 realized that variable inductors could reduce ripple in SMPS by increasing the inductance value and speed up transient response by decreasing the inductance value. Although variable inductors were used in older wireless equipment, these variable inductors were typically large coils with magnetic cores, where the inductance was changed by physical movement.

[0028] The inventors realized that an active variable power inductor could be realized by replacing the inductor with a mutual inductance device (such as 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 the negative inductance circuit (NIC). The NIC can send current through the secondary winding, which then generates a magnetic field that couples to the primary winding through the core. The NIC can also send current in the reverse direction through the secondary winding, thereby creating mutual inductance in the primary winding, resisting current flow, and increasing the inductance of the primary winding. Therefore, the NIC can adjust the inductance of the primary winding.

[0029] Figure 3 The SMPS with an active inductor is shown. Figure 1 Inductor 10 is replaced by transformer 20. The primary winding of transformer 20 conducts the inductor current IL from transistor 22 to 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] Load resistor 18 represents the load driven by VOUT, which may change during operation, resulting in transients. When no transients occur, 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 inductor 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 inductance of the primary winding of transformer 20 increases.

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

[0034] When a transient is detected, the lower inductance value of the primary winding of transformer 20 provides a wider bandwidth for 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, the higher inductance value reduces output ripple.

[0035] Therefore, the equivalent inductance value in the primary winding can be adjusted by turning NIC 30 on and off. A high inductance value is provided to reduce ripple during steady-state conditions, while a low inductance value is provided to speed up transient response time when transients are detected.

[0036] Figure 4 The SMPS with a capacitor-based negative inductor circuit is shown in more detail. Operational amplifier 32 is powered by supply voltages VS+ and VS-. A midpoint voltage (e.g., the intermediate value between VS+ and VS-) is 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 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 the grounding resistor 36 form a double feedback network with an impedance of Z1 / R. g This enables operational amplifier 32 to provide 1+Z1 / R g The gain.

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

[0039] Since controller 12 turns power transistors 22 and 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, generating 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 voltages at the non-inverting input (+) and the inverting input (-) of operational amplifier 32 are equal, therefore the voltage UA at the inverting input is equal to the voltage UB at the non-inverting input. Since the feedback network generates voltage gain through feedback capacitor 34, the output voltage of operational amplifier 32 after gain is UC. In this case, the voltages UC and UB across the forward resistor 38 generate a reverse alternating current across the forward resistor 38. This reverse alternating current is out of phase with the ripple portion of IL and is coupled to the primary winding of transformer 20 through the secondary winding. The coupled ripple portion of IL is in phase with the original ripple, but the ripple amplitude is reduced.

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

[0041] The first impedance network is connected to the inverting (-) input of operational amplifier 32, while the second impedance network is connected to the non-inverting (+) input of operational amplifier 32. Grounding resistor 36 and feedback capacitor 34 are connected to the inverting input of operational amplifier 32, forming the first impedance network, i.e., the inverting feedback network. Forward resistor 38 is connected to the non-inverting (+) input of operational amplifier 32, forming the second impedance network.

[0042] Due to the mutual inductance of transformer 20, the voltage ripple of the primary current will generate an AC ripple in the secondary current. This AC ripple of the secondary current is applied to the non-inverting (+) input of operational amplifier 32, and causes an AC ripple in the output current of the operational amplifier when switch 40 is closed. The inverting gain of operational amplifier 32 is 1 + Z1 / R. g Impedance Z1 comes from feedback capacitor 34.

[0043] In this embodiment, under the influence of the scaling factor s, the first impedance is Z1 = 1 / (sC) f The second impedance is Z. p =R pThe grounding resistor 36 and the forward resistor 38 can be variable resistors or fixed resistors (e.g., the applicable resistance values ​​are determined through circuit analysis, simulation, or prototype testing). When the grounding 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 via a programmable register, which can be programmed by 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 = 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. In the frequency domain, *s* is defined as the decomposition of the signal into imaginary exponential components of different frequencies; the system response can be obtained through inverse Fourier transform.

[0045] The SMPS operates as described previously, except that when the steady-state detector 50 determines that VOUT remains within a predetermined range, the inductance of the primary winding of transformer 20 is increased to reduce ripple. When a transient occurs where VOUT is outside the predetermined range, the steady-state detector 50 drives ST low to open switch 40 and shut off current in the secondary winding. The equivalent inductance of the primary winding drops to its rated value. This lower rated inductance allows a larger peak-to-peak ripple to flow to the load over a single cycle, while the load current slope is larger, resulting in 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 of the grounding resistor 36, the resistance of the forward resistor 38, the capacitance of the feedback capacitor 34, and the winding ratio and core (mutual inductance) value of the transformer 20.

[0047] Figure 5 This is a schematic diagram of the primary current in the transformer when the NIC is turned on and off. The primary current IL of the inductor 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 the switch 40 to enable the NIC 30, the waveform 102 value of the inductor current IL is lower. 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 in waveform 104.

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

[0049] When there is no transient transition, the steady-state detector 50 detects a 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) its 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 cancels out 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. Because this inductor current is switched on and off by transistors 22 and 24, this modulation of the higher inductor current causes a larger fluctuation in VOUT, as shown in waveform 114.

[0051] Figures 7A-7B The waveforms showing the effect of turning the NIC on and off on VOUT during a transient situation of a sudden increase in SMPS load current are displayed.

[0052] exist Figure 7A In this case, the load current ILOAD through the load resistor 18 suddenly increases, for example, when a transistor in the load switches states and consumes a large transient current. Figure 7B In the simulation, due to a sudden increase in load current, the output voltage VOUT suddenly drops. 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 be turned on, there may be subsequent transients that may benefit from NIC 30 being turned off by the first transient.

[0054] Figures 8A-8B The waveforms showing the effect of NIC switching on and off on VOUT under transient conditions of a sudden drop in SMPS load current are displayed. Figure 8A In the case of a sudden drop in load current ILOAD through load resistor 18, for example when the transistor switches to a light load.

[0055] exist Figure 8BIn the simulation, due to the sudden decrease in load current, the output voltage VOUT suddenly increases. When NIC 30 is off, the circuit simulation produces waveform 132. Compared with the output waveform 134 when NIC 30 is on, waveform 132 recovers faster and has lower ripple. Therefore, when the steady-state detector 50 detects the transient and turns off NIC 30, both high-level and low-level transients can recover more quickly.

[0056] Figure 9 An embodiment of the steady-state detector is shown 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 to enable transient response.

[0057] When VOUT is higher than VMIN or within the lower limit, comparator 52 drives its output high. When VOUT is lower than 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 pins of XNOR gate 56 drive its output (stable-state signal ST) high. Thus, NIC 30 is enabled when VOUT is in a stable state.

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

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

[0061] Figure 11 The SMPS of a NIC with an n-channel transistor switch is shown. In this embodiment, 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] Figure 12The SMPS of a NIC with a diode switch is shown. In this embodiment, switch 40 is a diode 45. Since diode 45 has no control gate, ST and steady-state detector 50 are not required.

[0063] Diode 45 prevents 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 produces 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 increases with the low frequency rise. The 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 can react 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 The SMPS of the NIC with a positive inductor is shown. In this embodiment, the grounding resistor 36 is replaced by the grounding inductor 39, and the feedback capacitor 34 is replaced by the feedback resistor 35. In this embodiment, Z1 = R of the feedback resistor 35. f And Z2 = sL p Where s is the complex frequency, L p This is the inductance value of the grounding inductor 39. Feedback capacitor 34 ( Figure 4 The gain produced is affected by the switching frequency. However, using feedback resistor 35 will produce a fixed gain that is not affected by the frequency.

[0067] Figure 14 A boost converter SMPS with a NIC is shown. 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... Figure 3 , Figure 4 , Figure 10-13The step-down converter shown is located before transformer 20. Ground power transistor 24 is located before transformer 20, not after it.

[0068] Figure 15 A SMPS with a NIC capable of modulating a portion of its secondary current is shown. 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 if 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 switched on and off, but remains on, although 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 changing the resistance values ​​of the shunt resistor 60 and the switch 40. Another resistor can be connected in series with the switch 40 to further adjust the current ratio. Therefore, the shunt resistor 60 provides greater design flexibility.

[0071] [Alternative Embodiments]

[0072] The inventors have also envisioned several other embodiments. For example, switch 40 can have various 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.

[0073] Although most of the accompanying drawings show the buck converter arrangement of transistors 22 and 24, and Figure 14 The diagram shows a boost converter, but it can be replaced by other converters, such as buck-boost, isolated, or multiphase converters. Other SMPS converters (such as Cuk or Sepic) can also be used as alternatives.

[0074] There are many possible embodiments of the steady-state detector 50. Figure 9 The embodiments described can interchange the inverting and non-inverting inputs of the comparator, add or remove inverters, and use gating other than XNOR. Differentiators or load transient detectors can also be used.

[0075] The output voltage can be sensed by a resistor network and then the signal can be directly passed to the buck control loop comparator for processing, which is another option for the steady-state detector 50.

[0076] In addition, the input voltage node of the buck converter can replace 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.

[0077] By using a resistor network and an improved Type III compensator based on a differential amplifier (DDA), such as an OTA, the transient response of the load can be detected and passed to a comparator in the control loop.

[0078] 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, in conjunction with the comparator.

[0079] Comparators 52 and 54 can be operational amplifiers or other comparator circuits. A hysteresis can be added before triggering the steady-state detector 50 to shut down the steady-state signal ST, requiring the transient to persist for a predetermined period. XNOR 56 can be an XOR gate followed by an inverter. Besides using two predetermined voltage levels to provide transient response for both high and low transients, a single comparator can be used to provide a voltage limit. For example, the steady-state detector 50 could shut down the steady-state signal ST only 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.

[0080] 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 for use with certain types of switches. Besides 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.

[0081] The steady-state detector 50 can be powered by VS+, VS-, or other power supplies and may be 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 supply and grounding schemes may also be used. The power supply and grounding voltages can be shifted. GND2 can be some kind of reference voltage, not necessarily the exact midpoint voltage.

[0082] 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 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 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 affect the mutual inductance and rated inductance values.

[0083] While 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. Windings can be long conductors wound around a metal core, but for planar transformers, windings can also be a helical pattern on a plane. 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, or between the left and right primary terminals. Transformer 20 may also contain a third winding for a third current path, such as an auxiliary winding for sensing, shielding, or testing.

[0084] Typically, the impedance of the secondary circuit is Z(UA-UB) = -sC f R p R g =sL eq The design target values ​​can be adjusted or fine-tuned by adjusting or fine-tuning the resistance and capacitance values.

[0085] Transformer 20 can use any current transformer with a primary and secondary circuit, electrically isolated but magnetically connected. Transformer 20 is described as having a primary winding with primary current flowing from the left end (switching from VIN) to the right end (VOUT), and a secondary winding with the left end grounded and the right end driven by the current from operational amplifier 32 through positive resistor 38. Therefore, secondary current ripple is reduced, thereby reducing primary current ripple. Thus, the secondary current flows in the same direction as the primary current, increasing the primary inductance as the secondary current flows. However, other arrangements are possible, such as primary and secondary currents flowing in opposite directions, where 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 same-name terminals, 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 from the steady-state detector 50 and apply the inverted ST to the switch 40. The switch 40 can be a normally closed switch, rather than a normally open switch.

[0086] 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 for the use of a smaller output capacitor to achieve the target amounts 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 ​​for on and off states by adjusting the resistance values ​​of grounding resistor 36 and positive resistor 38.

[0087] Switch 40 is connected in series with positive resistor 38. As an alternative, 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.

[0088] More complex buffers, level shifters, or other components can be replaced or added. Inverters can be added in different locations. Additional delays and output waveform shaping hysteresis can also be added. Other types of buffer circuits, selectors, or multiplexers can also be used.

[0089] 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-side AC component in the magnetic field.

[0090] Different transistors, capacitors, resistors, inductors, transformers, and other devices of various sizes can be used, as well as various layouts, such as multi-pin, toroidal, donut-shaped, or irregularly shaped transistors. Current can be positive or negative and can flow in either direction. Many second- and third-order circuit effects may exist and can be quite pronounced, especially for smaller devices. These secondary factors can be accounted for using circuit simulation during the design process.

[0091] Switching devices can be implemented using n-channel, p-channel, or bipolar transistors or junctions within these transistors. Gate length and spacing can be increased to provide better protection against damage.

[0092] IC semiconductor manufacturing processes can vary widely. A variety of materials can be used. Additional process steps can be added when integrating transistors onto larger devices, such as for additional metal layers or other transistor types, or modifications to standard complementary metal-oxide-semiconductor (CMOS) transistors. While CMOS transistors have been described, other types of transistors can be used instead for certain embodiments, such as using only n-channel transistors, only p-channel transistors when output swing is limited, or various alternative transistor technologies such as bipolar or BiCMOS. CMOS processes can also be FinFET (Fin Field-Effect Transistor) processes.

[0093] Terms such as up, down, above, below, horizontal, vertical, inside, and outside are relative and depend on the viewpoint, and do not imply that the invention is limited to a specific viewpoint. The device can be rotated so that vertical becomes horizontal and horizontal becomes vertical, therefore these terms depend on the observer.

[0094] The background section of this invention may include background information about the problem or environment of the invention, rather than a description of prior art. Therefore, the material included in the background section is not an admission of prior art by the applicant.

[0095] Any methods or processes described herein are machine-implemented or computer-implemented and are intended to be performed by machines, computers, or other devices, and not necessarily 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.

[0096] Any advantages and benefits described herein may not necessarily apply to all embodiments of the invention. When the word "device" appears in a claim element, the applicant intends that the claim element fall within the provisions of Section 112, Subsection 6 of 35 USC. Typically, one or more words precede the word "device." These words preceding "device" are a label intended to facilitate reference to the claim element, not to express structural limitations. Such device-plus-function claims must cover not only the structure described herein for performing that 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 word "device" do not fall within the provisions of Section 112, Subsection 6 of 35 USC. Signals are typically electronic signals, but can also be optical signals, for example, transmitted via fiber optic lines.

[0097] The above description of embodiments of the invention is provided for illustrative and descriptive purposes. 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.

Claims

1. An active inductor circuit, comprising: A mutual inductor has 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 the current flowing through the primary winding and the secondary winding. An operational amplifier whose first input is connected to the first stage terminal; A grounding resistor is connected between the second stage terminal and the second input of the operational amplifier; A feedback device is connected between the output of the operational amplifier and the second input of the operational amplifier; A modulation network is connected between the output of the operational amplifier and the first input of the operational amplifier; A switch in a modulation network modulates the secondary current flowing through the secondary winding of the mutual inductor. The modulation network modulates the output current generated at the output terminal of the operational amplifier and applies the modulated current to the secondary terminal of the mutual inductor. Wherein, when the switch is in the first state, the secondary current has a first current value; When the switch is in the second state, the secondary current has a second current value, which is greater than the first current value. When the switch is in the first state, the secondary current flowing through the secondary winding increases the primary equivalent inductance of the primary winding through the mutual inductance of the mutual inductance device. Specifically, 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 that modulates 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 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 according to claim 3 further includes: A steady-state detector compares the primary output voltage generated by the primary current flowing through the primary winding of the mutual inductor with a predetermined voltage range, and activates a switching signal when the primary output voltage is within the predetermined voltage range. 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 having a control gate that can receive a switching signal from the steady-state detector; The transistors mentioned therein are bipolar transistors or metal-oxide-semiconductor field-effect transistors (MOSFETs).

8. The active inductor circuit according to claim 7, further comprising: A first power transistor is connected in series with the primary winding of the mutual inductor to generate a primary output voltage. The first power transistor has a gate driven by a controller that turns the first power transistor on and off at a selected switching frequency, thereby generating ripple in the primary output voltage. In this method, the ripple is reduced by closing the switch to increase the secondary current and the primary equivalent inductance. Specifically, when the steady-state detector detects that the primary output voltage exceeds the predetermined voltage range, and the switch is opened to reduce the secondary current, 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 steady state, the ripple is reduced by a higher primary equivalent inductance value.

9. The active inductor circuit according to claim 8, wherein the first power transistor is connected in series with the primary winding of the mutual inductance device between the input power supply voltage and the output capacitor having the primary output voltage; Also includes: The second power transistor is connected between the primary terminal of the mutual inductor and the primary ground, and its gate is driven by the controller. 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 simultaneously; 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 the first state, the switch is open to prevent current flow; When the switch is in the second state, the switch is closed to conduct current; When the switch is open, the switch shuts 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, The equivalent inductance in the primary winding is doubled by closing the switch through the modulation network.

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

13. A variable equivalent inductance circuit, comprising: A transformer has a primary path and a secondary path that are electrically isolated from each other and are magnetically coupled together by mutual inductance. The secondary current flows through the primary path of the transformer, charging the output capacitor and generating the primary output voltage. The secondary current flows through the secondary path from the input secondary terminal to the output secondary terminal; the primary current flows in the same direction as the secondary current in the transformer. An operational amplifier has inverting input, non-inverting input, and output; A first resistor is connected between the secondary output terminal of the transformer and the inverting input of the operational amplifier; A feedback impedance device is connected between the inverting input of the operational amplifier and the output of the operational amplifier; A switch and a second impedance device are connected in series between the operational amplifier output and the operational amplifier non-inverting input; 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 power supply voltage and a lower power supply voltage; wherein the midpoint voltage between the upper power supply voltage and the lower power supply voltage is connected to the output secondary terminal of the transformer.

16. The variable equivalent inductance circuit according to claim 15, further comprising: 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. When a small voltage ripple occurs on the primary output voltage which is less than the voltage limit, the switch signal is activated and closes the switch to increase the current flowing through the second impedance device and increase the primary inductance of the transformer along the primary path. Specifically, when a large voltage transient occurs on the primary output voltage exceeding the voltage limit, and the switching signal is not activated, the switching signal disconnects the switch to reduce the current flowing through the second impedance device and to reduce the primary inductance of the transformer along the primary path. The closing of the switch increases the primary inductance during the steady state to reduce ripple, while the opening of 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 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: The controller generates non-overlapping first and second gate signals and switches them at frequencies in the order of 100 kHz. Power supply voltage input; A first power transistor, whose gate receives the first gate signal, is connected between the power supply voltage input and the input primary terminal of the transformer primary path; The second power transistor, whose gate receives the second gate signal, is connected between the input primary terminal and the primary ground of the transformer primary path; The output terminal of the primary path of the transformer is connected to the output capacitor to generate the primary output voltage; The first power transistor, the second power transistor, and the primary path of the transformer form a buck converter switch-mode power supply (SMPS).

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

20. A switchable inductive power supply circuit, comprising: A transformer has a primary path and a secondary path that are electrically isolated from each other, but are magnetically coupled together through mutual inductance; The primary current flows through the primary path of the transformer, charging the output capacitor and generating the primary output voltage. The secondary current flows through the secondary path from the input secondary terminal to the output secondary terminal; The primary current and the secondary current in the transformer flow in the same direction; the operational amplifier has an inverting input, a non-inverting input, and an output; A first resistor is connected between the output secondary terminal of the transformer and the inverting input of the operational amplifier; A feedback capacitor is connected between the inverting input of the operational amplifier and the output of the operational amplifier; A switching transistor and a second resistor are connected in series between the output of the operational amplifier and the non-inverting input of the operational amplifier; The non-inverting input of the operational amplifier is connected to the input secondary terminal of the transformer; A controller that generates a first gate signal and a second gate signal that do not overlap and are switched at a selected frequency; Power supply voltage input; A first power transistor, whose gate receives the first gate signal, is connected between the power supply voltage input and the input primary terminal of the transformer primary path; The second power transistor, whose gate receives the second gate signal, is connected between the input primary terminal and the primary ground of the transformer primary path; The output terminals of the primary path of the transformer are connected to the output capacitor to generate the primary output voltage; The first power transistor, the second power transistor, and the primary path of the transformer 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 the signal to the control terminal of the switching transistor. When a small voltage ripple occurs on the primary output voltage which is less than the voltage limit, the switching signal is activated. The switching signal closes the switching transistor to increase the current flowing through the second resistor and increase the primary inductance of the transformer along the primary path. When a large voltage transient occurs on the primary output voltage exceeding the voltage limit, and the switching signal is not activated, the switching signal disconnects the switching transistor to reduce the current flowing through the second resistor and reduce the primary inductance of the transformer along the primary path. 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.

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