TW202327237A - Dual-path active damper for a resonant network - Google Patents

Abstract

A dual-path active damper reduces power losses while damping ringing waveforms in resonant circuits. One path clamps the peak value of a node voltage at less than a rated voltage of a protected device while allowing the node voltage to ring and decay naturally. Another path waits for some delay after the peak value is clamped until closing an active switch to draw a reset current through an RC snubber to actively dampen the ringing of the node voltage. The delay and on-time of the active switch are set to reduce or even minimize power losses for damping the ringing waveform within a specified period.

Description

Dual Path Active Dampers for Resonant Networks

This invention relates to damping of resonant circuits, and more particularly to dual path active dampers that reduce power loss while damping ripple oscillation waveforms.

Power conversion electronics contain circuits that can change state abruptly, resulting in rapid changes in voltage waveforms. This is especially prevalent in modern power converters utilizing high-speed switching elements based on MOSFET, SiC and GaN semiconductors. High rate-of-change voltages can excite resonant circuits inherent in the interconnections of circuit elements, causing ripple oscillations in waveforms. These ripple oscillation waveforms can cause overvoltage stress to circuit components, excessive electromagnetic interference (EMI), and damage to measurements critical to the operation of power converters.

1A and 1B show a resonant circuit 100 (eg, parallel-connected parasitic inductance Lr and parasitic resistance Rr connected in series with parasitic capacitance Cr) driven by a rapidly rising voltage waveform (eg, forcing function Vs) with arbitrary damping. When forcing function Vs 102 transitions from low to high, node voltage Vr 104 has a resulting resonant response where Vr has a peak amplitude twice that of Vs and has a resonant frequency of one of the following: (1)

A DC-DC switched power converter (SPC) has an energy storage section, a switching control circuit such as a pulse width modulator (PWM), a primary switch, and a rectifier. The energy storage section generates a current and a regulated DC output voltage in response to the selective application of the DC input voltage. The switching control circuit, primary switch and rectifier control the application of the DC input voltage to the energy storage section for setting the value of the regulated DC output voltage. "Buck", "Boost" and "Buck/Boost" are the basic SPC topologies which can be isolated to provide "Flyback" and "Forward" topologies. These can be single-ended or double-ended and single or double core.

As shown in FIGS. 2A to 2C, a buck converter 200 includes a DC voltage source 202 , an energy storage section 204 including an inductor L1 and a capacitor C1, a switching circuit 206 including switches S1 and S2 , and a control circuit that controls the One of the switches switches the control circuit (not shown). Switches S1 and S2 switch inversely to generate a square wave forcing function at node 209 from a DC voltage source. The square wave is filtered by elements L1 and C1 to generate a DC output voltage Vout. The transfer function is related to the duty cycle (D) of S1 multiplied by the source voltage Vg to obtain: (2)

In an actual implementation, the loop area of the switching circuit is non-zero and develops a parasitic inductance Lr. In addition, a parasitic capacitance Cr exists due to the layout of the circuit elements and the output capacitance (Coss) of the switches S1 and S2. When S2 opens and S1 immediately closes, a voltage step 207 at Vg occurs across Lr, causing a node voltage Vr 208 of ripple oscillation at node 209 . The ripple oscillation frequency in a well designed converter is much higher than the operating frequency of the power converter and can be on the order of 30-50 MHz.

The node voltage Vr ripples to twice the applied DC input voltage Vg. Therefore, the switches S1 and S1 must have a voltage rating (Vrated) in order to reliably withstand the applied voltage stress. Semiconductor switches generally have higher resistive losses with higher voltage ratings, so it is desirable to use switches with as low a voltage rating as possible for the application to achieve the lowest losses and costs. In addition, the ripple oscillator waveform will generate unwanted high frequency EMI. Ripple oscillations in power converters can also disrupt controlled operation. For example, if the inductor current L1 is to be controlled through a sensing component (not shown), the sensing will be negatively affected by the ripple oscillation during S1 conduction (D state) unless the ripple oscillation waveform is mitigated. .

A snubber element can be introduced to dampen a resonant circuit. The buffer element inserts a loss element in such a way that the energy stored in the resonant element is converted into heat. As shown in FIG. 3, a buck converter 300 of the type shown in FIG. 2 is provided with a simple snubber element 302 consisting of a resistor Rsnub and a capacitor Csnub commonly referred to as an "RC snubber". Csnub is AC coupled with resistor Rsnub, in parallel with the resonant voltage node, to prevent DC losses. In practice, Csnub will be much larger than Cr (approximately 2 to 10 times), and Rsnub is usually set equal to the characteristic impedance of the resonant circuit: (3)

The operation of the RC snubber forces the capacitor Csnub to charge and discharge at each switching cycle, so that the first order power loss of the snubber resistor in this circuit is simply: (4)

Although effectively snubbing the ripple oscillations of the node voltage Vr 304 at node 306 in the resonant circuit, simple RC snubbers offer limited design modification options and can result in significant losses because the loss equation is based on the square of the applied voltage Vg.

The active snubber technique can overcome some of the limitations of simple RC snubbers by introducing an active switch whose timing is such that the RC snubber is applied to the resonant circuit in a controlled manner. As shown in FIGS. 4A to 4C , a buck converter 400 similar to that of FIG. 2 is provided with an active buffer 402 . Active snubber 402 includes an active switch S3 404 inserted in series with RC snubber 406 (eg Rsnub and Csnub connected in series) to form an active clamping function. Switch S3 is closed immediately after S1 is closed, producing node voltage Vr 408 at node 410 , and S3 is opened some time before S1 is opened. This switching pattern prevents Csnub from fully discharging, and thus the energy in the snubber is reduced to the snubber capacitor's differential voltage (eg: Vr - Vg). Since losses are related to the square of the voltage, losses in active snubbers can be significantly reduced, in contrast to simple RC snubbers.

The following is a summary of the present invention in order to provide a basic understanding of some aspects of the present invention. This summary is not intended to identify key or critical elements of the invention or to delineate the scope of the invention. Its sole purpose is to present some concepts of the invention in a simplified form as a prelude to the more detailed description that is presented later and to define the claims.

The present invention provides a dual-path active damper, which reduces power loss and at the same time reduces the ripple oscillation waveform in the resonant circuit. A path clamps the peak value of a node voltage below the rated voltage of a protected device while allowing the node voltage to naturally ripple and decay. Another path waits a certain period after the peak is clamped until the active switch is closed to draw a reset current through an RC snubber to actively slow down the ripple oscillation of the node voltage. Set the delay and on-time of the active switching to reduce or even minimize the power loss for reducing the ripple oscillation waveform within a specified period.

In one embodiment, a dual-path active damper includes a common snubber capacitor Csnub coupled to a node, a clamping path including Csnub, a diode, and a clamping voltage, and a series connection of Csnub and a snubber Resistor Rsnub and a damped path of an active switch. At each positive state change of a forcing function applied to the resonant network, a node voltage Vr increases from a steady state value Vss until it exceeds Vr+Vclamp, at which point the diode in the clamp path conducts Iclamp with Clamp the peak voltage of the node voltage Vr at Vss + Vclamp (<Vrated). After a delay from each positive state change, the active switch is closed so that the damping path conducts a reset current Ireset through an RC snubber to slow down the ripple oscillation of the node voltage Vr. The delay and closure of the active switch occurs after the clamping of the peak value of the node voltage and remains closed for at least a minimum reset period of the RC snubber.

In various embodiments, the active switch opens or remains closed before closing to overlap a negative state change under the forcing function.

In different embodiments, the "on time" (off period) of the active switch can be fixed or variable. If variable, the on-time can respond to changes in the forcing function.

In one embodiment, the damping path further includes a diode. The damping path conducts reset current through the series connected RC snubber and diode only when the diode is negatively offset.

In one embodiment, a switched power supply (SPC) supplies the forcing function and defines the resonant network. The protected device is usually located in one of the switches in the SPC.

In one embodiment, a system includes multiple different resonant networks or nodes where a waveform must be slowed to protect different devices.

These and other features and advantages of the present invention will become apparent to those of ordinary skill in the art from the following detailed description of preferred embodiments, taken together with the accompanying drawings, in which:

Although active snubbers provide improvements in losses over passive RC snubbers, they still cannot optimize losses while providing peak voltage clamping capability. In particular, it is desirable to have an active damping function that allows the node voltage Vr to ripple at a set interval as long as the peak voltage is clamped to a specific level to optimize the performance of the converter before damping the node voltage Vr change. However, due to the switching control and topology of the active snubber, the loss in the snubber versus the voltage offset of Vr cannot be independently controlled. Switch S3 can be opened or closed. Therefore, losses in the snubber configuration must come at the expense of controlling the peak voltage of Vr.

As shown in FIG. 5 , closing active switch S3 in the active snubber immediately after closing S1 results in a rapidly slowing node voltage Vr 500 . If the active switch S3 is delayed in closing, the node voltage Vr 502 is allowed to ripple and oscillate, minimizing losses. However, the peak value of the node voltage Vr climbs to twice the applied DC input voltage. An active snubber is required to provide controlled damping along with independent control of the peak voltage of the resonant circuit.

According to the present invention, a dual-path active damper reduces power loss while attenuating ripple oscillation waveforms in a resonant circuit. A path clamps the peak value of a node voltage below the rated voltage of a protected device while allowing the node voltage to naturally ripple and decay. The other path waits for some delay after the peak is clamped until closing the active switch to sink a reset current through an RC snubber to actively slow down the ripple oscillation of the node voltage. Using different voltages for clamping and clipping allows a significant reduction in snubber power losses. Set the delay and on-time of the active switching to reduce or even minimize the power loss for reducing the ripple oscillation waveform within a specified period.

As shown in FIGS. 6A and 6B , a damped resonant circuit 600 includes a source of a forcing function Vs 602 , a resonant circuit 604 , and a dual-path active damper 606 coupled to a node 608 of the resonant circuit 604 . Source 602 may be any source that changes state abruptly resulting in a rapid change in voltage waveform. Any SPC topology can be used. Resonant circuit 604 may be a discrete circuit or a circuit and node within the source, such as any type of SPC. There can be multiple nodes where the waveform ripples and must be mitigated. One option is to strategically dampen a node with dual path active dampers 606 and thereby dampen other downstream nodes. Alternatively, multiple dual-path active dampers 606 may be coupled to different nodes and resonant circuits.

In most resonant circuits, only forcing a positive state change of the function (such as from low voltage to high voltage) produces a ripple oscillation waveform that must be slowed down. Typically, a negative state change switches the node to a negative rail, such as ground or zero volts clamping it to zero volts.

Dual-path active damper 606 includes a common snubber capacitor Csnub 610 coupled to node 608 , a clamping path 612 and a damping path 614 , both of which include the common snubber capacitor Csnub 610 . The clamping path 612 includes Csnub 610 , a buffer diode Dsnub 616 and a clamping voltage Vclamp 618 connected in series. Csnub is roughly 10 times the parasitic capacitance, but is sized to maintain peak voltage and minimize power dissipation. Vclamp can be a specifically selected voltage, or a convenient voltage in the design. For example, Vclamp can be the output voltage of a power converter or an internal or external bias rail. Damping path 614 includes Csnub 610 and Rsnub 620 connected in series forming an RC snubber, and an active switch S1 622 . Rsnub is suitably set equal to the characteristic impedance of the resonant network so that the time constant of the RC snubber may be 5 to 10 times the period of the resonant network and the ripple oscillations are completely damped within 1 to 2 cycles. Optionally, the damping path 614 may include a diode, whereby only negative excursions of the node voltage Vr from a steady state value are damped. Reduction takes longer, but wear and tear will be reduced.

At each positive state change of the forcing function Vs, the node voltage Vr 624 increases from a steady state value Vss (e.g., the switched DC value of Vs) until it exceeds Vr + Vclamp, at which point the diode 616 switches Bias, and conduct a clamping current Iclamp to clamp the peak voltage 625 of the node voltage Vr at Vss+Vclamp. Depending on the natural damping nature of Vr as the ripple oscillates, the peak may only be clamped one or more times until it decays to less than Vss + Vclamp, at which point the clamping path self-blocks. For the protected device, Vss + Vclamp < Vrated. Lowering Vclamp allows the use of lower voltage ratings, and the device thus loses less. The choice of Vclamp is a trade-off between protecting the device and minimizing the loss.

After a time delay 626 from each positive state change, the active switch S1 622 is closed to conduct a reset current Ireset to slow down the ripple oscillation of the node voltage Vr 624 . The time delay is at least about ¼ cycle through the peak 625 or resonant circuit. For example, the time delay can be two to four cycles of the resonant circuit. Latency can be "fixed" or "variable", based on changes in the forcing function to minimize losses. Changes in the forcing function can be driven, for example, by changes in a load. The delay and "on time" (closed period) 628 of the active switch S1 is set to reduce the power loss limited by the change of the node voltage Vr from each positive state to the steady state value Vss within a specified period 630 , and is less than Best to achieve the minimum. In general, the delay is as long as possible before clipping to minimize losses. The on-time is at least one of the minimum reset periods of the RC snubber. Normally, the specified period ends and the active switch S1 opens before a negative state change under the forcing function. However, in some conditions, the on-time is prolonged and overlaps the next negative state change, causing Csnub to discharge. This can occur when the input voltage is abnormally high in order to fully or partially discharge Csnub, thereby reducing the effective peak node voltage on the protected device because Cnsub must be charged every cycle. This will increase the losses, but abnormal conditions are usually rare and short-lived, so it can be a good choice for the protection device until the input voltage returns to its normal value.

As shown in FIGS. 7A and 7B , the buck converter 700 is provided with a dual-path active damper 702 . Buck converter 700 includes a DC voltage source 704 that supplies voltage Vg, an energy storage section 706 that includes inductor L1 and capacitor C1, a switching circuit 708 that includes switches S1 and S2, and a switching control that controls the switches. circuit (not shown). Switches S1 and S2 switch inversely to generate a square wave forcing function at node 710 from a DC voltage source. The square wave is filtered by elements L1 and C1 to generate a DC output voltage Vout. A parasitic inductance Lr and a parasitic capacitance Cr of the buck converter define a resonant network 712 . When S2 is opened and S1 is immediately closed, a voltage step is generated which produces a node voltage Vr 714 at node 710 . If left uncontrolled, the node voltage Vr will ripple to twice the applied DC input voltage Vg. Therefore, switch S2 will need a rated voltage Vrated > 2*Vg, which is generally undesirable.

Instead, the dual-path active damper 702 clamps the peak value of Vr to Vg + Vout (where Vclamp is Vout in this embodiment), limits the peak excursion of Vr, and allows Vr to ripple and naturally dampen the forcing function About 3 cycles. Active switch S3 is delayed for minimum loss mitigation. Thus, the dual-path active damper allows independent control of shedding and peak voltage control, minimizing losses and protecting the device (switch S2 in this case).

As shown in FIG. 7B , the node voltage Vr 714 is clamped at a specified peak value, allowing the ripple to oscillate and then slow down to a steady state value of Vss = Vg for a specified period. For a passive RC snubber of the type shown in Figures 3A-3B, a node voltage Vr 720 increases to a higher peak value and then slows down rapidly to a steady state value. For an active Rc snubber of the type shown in Figures 4A to 4C, a node voltage Vr 722 is quickly ramped down to a steady state value. Active switch S3 closes 724 immediately after the positive state change 726 of switch S1. The clamped peak of node voltage Vr 714 is actually much higher than the peak of either the passive or active buffer, which further reduces losses in the dual path active buffer. Active switch S3 closes 728 after a specified delay 730 from positive state change 726 . The dual-path active buffer allows the node voltage Vr to rise to a higher value and ripple (while clamping the peak voltage < Vrated) for a period of time. The delta V used by the dual-path active buffer is smaller than the delta V used by the known active buffer. As a result, the total power loss required to damp Vr is much lower than either passive or active RC snubbers. For a given situation, the relative power loss depends strongly on the circuit topology, resonant network, load and forcing function. That is, one-fourth to one-third the power loss of a dual-path active buffer may be expected to be that of an active buffer.

For example purposes, let's walk through one of the force functions' loops and the response of the dual-path active buffer. Assume that the circuit is in a negative state (S1 open, S2 closed, S3 open) and has reached a steady-state state where the node voltage Vr is at 0 volts to ground. Voltage VCsnub is at Vg. The voltage at the junction of Csnub, Rsnub and Dsnub is -Vg.

Open S2, close S1 to produce a positive state change in the forcing function. The resonant circuit of Lr and Cr starts to resonate and Vr starts at 0 V and then resonates towards 2*Vg, actuating the clamping path when the diode Dsnub is forward biased. The first peak of Vr (assuming it > Vg + Vout) is clamped. Depending on the forcing function, Vclamp and the natural slowdown of the node voltage Vr, the additional peak may or may not be clamped.

After a delay, closing S3 actuates the damping path to sink reset current through Csnub and Rsnub to slow node voltage Vr to equal Vg. The damping path picks up any additional charge placed on Csnub by the clamping path and dissipates it in Rsnub. VRsnub is the difference between Vr (now Vg) and VCsnub, which is zero at steady state. That "difference" is less than a corresponding delta for known active snubbers and represents power loss. In the stable phase, Vr = Vg, VCsnub = Vg, VRsnub = 0 and the reset current is zero, and S3 is open.

A negative state change under the forcing function, closing S2 and opening S1 (S3 remains open) drives Vr to ground potential of zero voltage. VCsnub maintains charge at +Vg. On the next positive state change, the process is repeated.

Referring now to Figures 8A and 8B, an embodiment of a switch controller 800 includes a delay 802 for receiving a positive state change command 803 , a timer 804 , and a switch driver 806 that generates a command 806 to drive the dual path active Active switch in buffer. A positive state change command 803 is an active input to the switch controller based on a positive state change of a forcing function (eg: SPC). The command can be a function of a clock signal driving a forcing function or a rising edge of node voltage Vr.

T1 is equal to the time of the command signal.

T_delay is the time to deviate from the command signal and is a function of the delay adjustment.

The delay adjustment controls the amount of delay, which may be a function of the converter's operating point (ie, input voltage, output voltage, output power).

T_timer is the time during which the active switch is commanded to conduct and is a function of the timer adjustment.

The timer adjustment controls the on-time of the active switch and may be a function of the converter's operating point (ie, input voltage, output voltage, output power).

Based on the operating point of the converter (ie input voltage, output voltage, output power), T_timer can be smaller than T1 or larger than T1.

Whether fixed or variable, T_delay and T_timer are set to reduce or minimize power loss to slow down.

Dual-path active dampers can be implemented with active switches in the reset or clamp paths, and with non-ideal switches such as MOSFETs or GaN FETs with intrinsically anti-parallel conducting elements. As shown in FIG. 9, in a damped buck converter 900 , the active switch S3 of the dual-path active damper is implemented with an N-channel MOSFET or GaN switch 902 in both the clamping and damping paths, and utilizes The anti-parallel intrinsic diode of the N-channel MOSFET, or the reverse-channel conduction mode of the GaN FET provides clamping path connection capability when S3 is open. The damping path requires a blocking diode D2 904 to prevent clamping current from flowing through Rsnub during the clamping interval. Diode D2 limits the droop to negative excursions of node voltage Vr. As shown in FIG. 10, in a damped buck converter 1000 , the active switch S3 is implemented with only one P-channel MOSFET 1002 placed in the damped path. The anti-parallel internal diodes cause the polarity of the P-channel device D2 1004 to prevent clamping current from flowing in Rsnub during the clamping interval. D2 is required for proper operation of the clamp path and also limits the clipping to negative excursions of node voltage Vr below Vg. This increases the amount of on-time required to slow Vr, but reduces losses.

In both embodiments, a MOSFET or a GaN switch can be chosen, which has an on-state resistance (Rds_on) as Rsnub. Therefore, Rsnub is incorporated into the active switch. More generally, Rsnub can be a discrete resistive element or an on-resistance of an active switch.

Dual-path active dampers are illustrated as an example on a buck converter and, for comparison, on known passive and active snubbers. It can be used to clamp and cancel any resonant network.

As shown in FIG. 11A, flyback converter 1100, as implemented in FIG. 10, is provided with a pair of dual path active dampers 1102 and 1104 at node 1106 on top of primary switch S1 and at node 1108 on top of output rectifier D1. . Alternatively, abatement may be provided only on the primary or only on the secondary. The flyback converter 1100 includes a DC voltage source 1110 , a converter T1, a primary switch S1, a rectifier D1 and an output capacitor C1. A primary resonant network includes the leakage inductance Lk of the converter T1 and the output capacitance (Coss) of the switch S1. The primary resonant network includes leakage inductance Lk (reflected through converter T1) and rectifier parasitic capacitance CD1.

For the primary, the dual-path active snubber 1102 includes a common snubber capacitor Csnub2, including Csnub2, a diode Dsnub2, and a clamping voltage shown as Vg (could be any other voltage, but Vg is convenient and it keeps the energy A clamping path that recirculates back to Vg), and a damping path that includes Csnub2, Rsnub2, the active switch S4 (P-channel MOSFET) and a diode D3, which is required for proper operation with a P-channel The clamping path of the MOSFET and limits the clipping to negative offsets of Vr2 at node 1106 . Clamping on the primary of a flyback is of particular interest for flyback converters operating with a passive rectifier (or an active rectifier that mimics a diode), because it provides an active clamping function that allows the magnetization of the converter The current stays in the first quadrant. This has the benefit of reducing power by keeping the converter in a forced discontinuous mode, which was not possible with prior art active clamping.

For the secondary, the dual-path active snubber 1104 includes a common snubber capacitor Csnub1, including Csnub1, a diode Dsnub1 and a clamping voltage shown as Vout (could be any other voltage, but again, it is of convenience) A clamping path, and a damping path including Csnub1, Rsnub1, active switch S3 (P-channel MOSFET) and a diode D2, diode D2 is required for proper operation of the clamping path with P-channel MOSFET, And limit the curtailment to negative offsets of Vr1 at node 1108 .

In a flyback converter, when switch S1 is closed, converter T1 acts like a coupled inductor to apply the voltage Vg + Vout across rectifier D1 (assuming a turns ratio across T1 of one). This stores energy in the air gap and magnetizing inductance of transformer T1. Vout is supported by the voltage on the output capacitor C1. When switch S1 is open, rectifier diode D1 conducts current, transfers the energy stored in converter T1 and delivers current to output capacitor C1 to support Vout and restore the charge that was used to support Vout in the previous half cycle .

As shown in Figure 11B, when S1 is switched to be at a high level (on or off) to charge converter T1, a voltage Vg is applied across converter T1, causing the secondary resonant circuit of Lk and CD1 to resonate and the node voltage Vr1 to ripple oscillation. The dual path active damper 1104 clamps Vr1 and after a delay, switches S3 high to dampen Vr1. When S1 is switched low (blocked or disconnected) to discharge T1, the primary resonant network of Lk and Coss resonates and the node voltage Vr2 ripples. The dual path active damper 1102 clamps Vr2 and after a delay, switches S4 high to dampen Vr2.

While a few illustrative embodiments of the invention have been shown and described, numerous modifications and alternative embodiments will occur to those skilled in the art. Such modifications and alternative embodiments can be contemplated and made without departing from the spirit and scope of the invention as defined by the appended claims.

100,604: resonant circuit 102,602,Vs: mandatory function 104,208,304,408,500,502,624,714,720,722: node voltage 200, 300, 400, 700: buck converter 202,704: DC voltage source 204,706: energy storage section 206,708: switching circuits 207: Voltage step 209,306,410,608,710,1106,1108: nodes 302: Simple cushioning element 402: Active Buffer 404,622,S1,S2,S3,S4: switch, active switch 406: RC buffer 600: Damping resonance circuit 606, 702, 1102, 1104: Dual Path Active Dampers 610, Csnub, Csnub1, Csnub2: Common snubber capacitors 612: clamp path 614: Damping path 616, Dsnub: snubber diode 618, Vclamp: clamping voltage 620, Rsnub, Rsnub1, Rsnub2: resistors, snubber resistors 625:Peak 626: time delay 628: Delay and "on time" (close cycle) 630: specify cycle 712: Resonant Network 724,728: Active switch S3 closed 726: Positive state change 730: specify delay 800: switch controller 802: delay 803: Positive state change command 804: timer 806: switch driver 900, 1000: Damped Buck Converter 902: N-channel MOSFET or GaN switch 904: blocking diode 1002: P channel MOSFET 1004: P channel device 1100, 1110: flyback converter C1: Capacitor Coss: output capacitance CD1, Cr: parasitic capacitance D1: rectifier D2, D3, Dsnub1, Dsnub2: Diodes Iclamp: clamping current Ireset: reset current L1: Inductor Lk: leakage inductance Lr: Parasitic inductance Rr: parasitic resistance T1: Transformer T1, T_delay, T_timer: time VCsnub, Vg: Voltage Vout: DC output voltage Vr, Vr1, Vr2: node voltage

Figures 1A and 1B, as above, illustrate a basic resonant circuit subject to a forcing function that produces a rapidly rising voltage with arbitrary damping; Figures 2A to 2C, as above, illustrate the use of a buck converter to provide forcing functions and ripple oscillations with naturally slowing node voltages; Figures 3A and 3B, as above, show a buck converter with a passive RC snubber and moderated node voltage; Figures 4A to 4C, as above, illustrate a buck converter with an active RC snubber and moderated node voltages; Figure 5 shows a pair of switching patterns for an active RC snubber, where in one condition the active switch is closed immediately to slow the node voltage, and in the other condition the active switch is delayed to allow the node voltage to Slow down the previous ripple oscillation to reduce power loss; Figures 6A and 6B illustrate one embodiment of a resonant circuit with a dual-path active damper that immediately clamps the peak node voltage and allows the node voltage to ripple before activating the RC snubber to minimize power loss ; 7A and 7B illustrate an embodiment of a buck converter with a dual-path active damper that immediately clamps the peak node voltage and allows the node voltage to ripple before damping to minimize power loss; 8A and 8B are block and timing diagrams of a switch controller for controlling the delay and on-time of active switches; Figures 9 and 10 are embodiments of a buck converter with a dual-path active damper showing different implementations of the active switch; and 11A and 11B illustrate an embodiment of a flyback converter with a dual-path active damper that immediately clamps the peak node voltage and allows the node voltage to ripple before damping to minimize power loss.

600: Damping resonance circuit

602,Vs: Mandatory function

604: Resonant circuit

606: Dual Path Active Damper

608: node

610, Csnub: capacitor: public snubber capacitor

612: clamp path

614: Damping path

616, Dsnub: snubber diode

618, Vclamp: clamping voltage

620, Rsnub: resistor, buffer resistor

622, S1: switch, active switch

Cr: parasitic capacitance

Iclamp: clamping current

Ireset: reset current

Lr: Parasitic inductance

Rr: parasitic resistance

VCsnub: Voltage

Vr: node voltage

Claims (21)

A dual-path active damper for a resonant network in which a forcing function Vs generates a node voltage Vr for a device which ripples about a steady-state value Vss at each positive state change of the forcing function, This dual path active damper consists of: a snubber capacitor Csnub coupled to the node; a clamping path comprising a clamping voltage Vclamp coupled to Csnub, the clamping path conducting a clamping current Iclamp at each positive state change to clamp a peak value of the node voltage Vr at Vss+Vclamp; as well as A damping path comprising a snubber resistor Rsnub and an active switch coupled to Csnub which is turned off after a delay from each positive state change so that the damping path conducts a reset current Ireset to slow down Ripple oscillation of node voltage Vr. The dual-path active damper as claimed in claim 1, wherein a switching power supply (SPC) supplies the forcing function, and the device is located at a switch in the SPC. The dual-path active damper as claimed in claim 1, wherein the clamping path further includes a diode in series with Csnub and Vclamp, wherein at each positive state change, the node voltage Vr increases from the steady-state value Vss until it exceeds Vr At this point, the diode conducts Iclamp to clamp the peak voltage of the node voltage Vr at Vss+Vclamp. The dual-path active damper according to claim 1, wherein the device has a rated voltage Vrated, wherein Vss + Vclamp < Vrated. The dual-path active damper according to claim 1, wherein the damping path conducts the reset current Ireset through Csnub and Rsnub connected in series to slow down the ripple oscillation of the node voltage Vr. The dual-path active damper as claimed in item 5, wherein the damping path includes a diode, and wherein the damping path only conducts through Csnub and Rsnub connected in series and the diode when the node voltage Vr is negatively shifted relative to Vss The reset current Ireset slows down the ripple oscillation of the node voltage Vr. The dual-path active damper of claim 5, wherein the delay and closing of the active switch occurs after clamping the peak value of the node voltage. The dual-path active damper as claimed in claim 7, wherein the active switch remains closed for at least a minimum reset period of the serially connected Csnub and Rsnub. The dual-path active damper of claim 8, wherein the active switch is turned off before a negative state change under the forcing function. The dual-path active damper of claim 8, wherein the active switch remains closed to overlap a negative state change under the forcing function. The dual-path active damper as claimed in claim 8, wherein the delay and a turn-on time of the active switch are set to reduce the charge stored in Csnub to reduce the limited node voltage Vr at a specified time from each positive state change The damping loss that reaches this steady-state value Vss in a cycle. The dual-path active damper of claim 11, wherein the on-time is variable and responds to changes in the forcing function. The dual-path active snubber of claim 1, wherein the active switch comprises a MOSFET or GaN switch having an on-state resistance providing a snubber resistor Rsnub. A dual-path active damper for a resonant network in which a forcing function Vs generates a node voltage Vr for a device which ripples about a steady-state value Vss at each positive state change of the forcing function, This dual path active damper consists of: a snubber capacitor Csnub coupled to the node; a clamping path comprising a clamping voltage Vclamp coupled to Csnub, the clamping path conducting a clamping current Iclamp at each positive state change to clamp a peak value of the node voltage Vr at Vss+Vclamp; as well as A damping path comprising a snubber resistor Rsnub and an active switch coupled to Csnub to form an RC snubber during which the node voltage Vr naturally ramps from its peak value after a delay from each positive state change Attenuation, the active switch is closed for a turn-on time, so that the damping path conducts a reset current Ireset through the RC buffer to slow down the ripple oscillation of the node voltage Vr, wherein the delay and turn-on time are set to reduce the voltage stored in Csnub charge to reduce damping losses limited by node voltage Vr reaching the steady-state value Vss within a specified time from one of each positive state change. The dual-path active damper as claimed in claim 14, wherein the device has a rated voltage Vrated, wherein Vss + Vclamp < Vrated. The dual path active damper of claim 14, wherein the damping path includes a diode, wherein the damping path conducts the RC snubber and the diode only when the node voltage Vr is negatively shifted relative to Vss The reset current Ireset slows down the ripple oscillation of the node voltage Vr. The dual-path active damper of claim 14, wherein the on-time of the active switch is variable and responds to changes in the forcing function. A damped switched power converter (SPC) comprising: An SPC comprising an energy storage section (ESS) responsive to selective application of a DC input voltage Vin to produce a forcing function, and at least switches S1 and S2 which switch inversely to selectively apply The DC input voltage Vin; Wherein a parasitic inductance Lpar and a parasitic capacitance Cpar of the SPC form a resonant network; wherein the forcing function is applied to the resonant network to produce a node voltage Vr across switch S2 that ripples about a steady state value Vss at each positive state change of the forcing function; and A dual-path active damper that includes a snubber capacitor Csnub coupled to the node; a clamping path comprising a clamping voltage Vclamp coupled to Csnub, the clamping path conducting a clamping current Iclamp at each positive state change to clamp a peak value of the node voltage Vr at Vss+Vclamp; as well as a damping path comprising a snubber resistor Rsnub and an active switch coupled to Csnub to form an RC snubber which is closed for an on-time after a delay from each positive state change such that The damping path conducts a reset current Ireset through the RC snubber to slow down the ripple oscillation of the node voltage Vr. The damped SPC of claim 18, wherein the device has a rated voltage Vrated, wherein Vss + Vclamp < Vrated. The damped SPC of claim 18, wherein the damped path includes a diode, wherein the damped path conducts the reset current through the RC snubber and diode only when node voltage Vr is negatively offset relative to Vss Ireset to slow down the ripple oscillation of the node voltage Vr. The damped SPC of claim 18, wherein the on-time of the active switch is variable and responds to changes in the forcing function.

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