Auxiliary circuit for zero voltage switching in a phase-shifted full bridge converter

Abstract

An example apparatus may include one or more of a transformer, a primary circuit that is electrically coupled to the transformer, wherein the primary circuit includes a first leg with a first pair of switches and a second leg with a second pair of switches, and a first auxiliary circuit that is electrically coupled to the first leg and a second auxiliary circuit that is electrically coupled to the second leg of the primary circuit, wherein each auxiliary circuit is configured to store energy while one switch among a respective pair of switches is turned on and another switch among the respective pair of switches is turned off, and supply the stored energy for the purpose of recharging all attached capacitance in a respective leg when both switches among the respective pair of switches are turned off.

Description

AUXILIARY CIRCUIT FOR ZERO VOLTAGE SWITCHING IN A PHASE-SHIFTED FULL BRIDGE CONVERTERBACKGROUND

[0001] Some system constraints may create a situation where modern resonant converters are less preferred within a system. For example, the constraints may include a very high peak-to- average power ratio or very wide output voltage range. In these situations, older converter types, such as phase-shifted full bridges, may provide a better solution. A phase-shifted full bridge converter is similar to a full-bridge DC-DC converter, but with the addition of phase shifting control. The phase shifting control enables the converter to achieve “soft switching”, which reduces switching loss and increases efficiency.

[0002] However, a phase-shifted full bridge converter typically suffers from loss of zero voltage switching during low power output. Furthermore, for a converter with a high peak power ratio, using large switching semiconductors (commonly found in phase-shifted full bridge converters) along with high voltage ratings can result in very high idle losses, which are not acceptable.Related circuits in use give the same basic advantage, and in particular, these circuits can suffer from problems starting up and varying charge stored depending on converter regulation.SUMMARY

[0003] One example embodiment provides an apparatus that may include at least one of a transformer, a primary circuit that is electrically coupled to the transformer, wherein the primary circuit includes a first leg with a first pair of switches and a second leg with a second pair of switches, and a first auxiliary circuit that is electrically coupled to the first leg and a second auxiliary circuit that is electrically coupled to the second leg of the primary circuit, wherein eachauxiliary circuit is configured to store energy while one switch among a respective pair of switches is turned on and another switch among the respective pair of switches is turned off, and supply the stored energy for the purpose of recharging all attached capacitance in a respective leg when both switches among the respective pair of switches are turned off.BRIEF DESCRIPTION OF THE DRAWINGS

[0004] FIG. 1A is a diagram illustrating an example of a phase-shifted full bridge converter according to example embodiments.

[0005] FIG. IB is a diagram illustrating a graph of power signals from the four switches in the phase-shifted full bridge converter of FIG. 1A, according to example embodiments.

[0006] FIG. 2A is a diagram illustrating an example of an auxiliary circuit for a ZVS phase- shifted full bridge power converter according to other example embodiments.

[0007] FIG. 2B is a diagram illustrating a view of voltage over time and current over time from different locations within the auxiliary circuit according to example embodiments.DETAILED DESCRIPTION

[0008] The example embodiments are directed to an auxiliary circuit that can be integrated into a primary circuit of a ZVS phase-shifted full bridge converter such as commonly used to power loads, for example, a loudspeaker, an amplifier, and the like. Zero voltage switching (ZVS) is a technique that turns off a switch when the voltage is zero. It’s a type of “soft switching” technique that can reduce thermal requirements, switching losses, electromagnetic interference(EMI) emissions, and the like.

[0009] A traditional ZVS phase-shifted full bridge converter struggles to perform zero voltage switching on a switch when there is no voltage over the load. The auxiliary circuit that is described herein ensures that there is enough current in the circuit to perform the zero voltage switching (ZVS) at the main switches, even when there is no power transfer through the transformer.

[0010] The primary circuit of the ZVS phase- shifted full bridge converter may include four switches (e.g., Qi, Q2, Q3, and Q4) and four capacitors with each switch being coupled to a different respective capacitor in such a way that the respective capacitor provides intrinsic and / or external capacitance in / over the switch. The primary circuit also includes a leading leg and a trailing leg which are coupled to opposing sides of a transformer that is configured to supply power to a secondary side of the ZVS phase-shifted full bridge converter.

[0011] According to various embodiments, the auxiliary circuit may include one or more inductors, one or more diodes, one or more capacitors, and the like, which can provide the necessary currents in the necessary polarity to the different switches e.g., four switches) in a full bridge power converter to achieve full zero voltage switching even during no phase shift. The circuit utilizes added diodes to create a limit of the charge and can allow for varying pulse length and / or phase shift without noticeable changing charge of the auxiliary circuit. The circuit provides operating a phase shift converter completely without load for any output voltage, which still operates with full zero voltage switching of all phase shift bridge semiconductors.

[0012] During operation, the effect of the auxiliary circuit will be nullified by the transferred current at some point, so to completely obtain zero voltage switching for the entire voltage and load range, the circuit could be supplemented with controlled transformer magnetizing inductance and / or leakage inductance to close all the gaps for all operating points. This circuitenables the design of a power supply with a very high peak power while maintaining a low idle consumption and low EMC emissions.

[0013] The auxiliary circuit may provide the necessary currents in the necessary polarity to achieve full zero voltage switching even during no phase shift. The amount of current is controlled by the size of capacitors in the auxiliary circuit to provide a limit on the charge of these capacitors and thereby limit the amount of current. Charging of capacitors happens through inductors that are included in the auxiliary circuit, and the energy charged leads to a current in the inductors. The size of the inductors and the capacitors in the auxiliary circuit will give the time it takes for re-charging the circuit to a new potential. Tuning this current to be enough to overcome the output capacitance of the switches within a reasonable time and the timing to allow for changing of the state of the auxiliary circuit well before the next switch event is set to happen.

[0014] The four switches of the primary circuit of the ZVS phase-shifted full bridge converter may operate to create voltage across the transformer. The first leg includes a first pair of switches (z.e., Qi and Q2) and the second leg includes a second pair of switches (z.e., Q3 and Q4). During operation, the four switches are turned on and off at different times thereby generating voltage across the transformer which causes power to be transferred from the primary circuit to the secondary circuit (i.e., of a load).

[0015] The components within the auxiliary circuit (e.g., the inductors, the capacitors, the diodes, etc.) in each of the legs do not participate in the power transfer process from the primary side to the secondary side. Instead, the components within the auxiliary circuit keep current within the circuit. The auxiliary circuit can continuously supply current to make sure that there is always enough current in the system to perform zero voltage switching. As a result of theauxiliary circuit, there is going to be current in the system even when there is no load on the secondary side of the circuit. The auxiliary circuit can act as a sink and a source to ensure that the zero voltage switching can always be performed. Once the capacitors are charged equal to input voltage it turns on the diode and current can flow out, preventing further charging of the capacitors and further energy storage.[00161 A standard full-bridge type of converter implementation typically uses four devices such as Metal-Oxide-Semiconductor Field-Effect Transistors (MOSFETs) as switches and a transformer as in the configuration shown in FIG. 1 A. For power to be transferred from the primary side of the transformer to the secondary side of the transformer, a voltage difference must be created across the primary side of the transformer. The voltage difference is created by altering which switches are turned on and which switches are turned off enabling a voltage differential to form across the transformer. For example, a positive transformer primary side voltage is developed when switches QI and Q4 are both turned on at roughly the same times while the switches Q2 and Q3 are turned off at roughly the same time. Meanwhile a negative transformer primary side voltage is developed when the switches QI and Q4 are turned off, and the switches Q2 and Q3 are turned on. This process may be repeated. For example, the switches Q2 and Q3 may subsequently be turned off and the switches QI and Q4 can be turned back on. By alternating the simultaneous on / off states of the switches QI and Q4 and the simultaneous off / on states of the switches Q2 and Q3 at different times and with a phase shift, power is enabled to be driven through the transformer.

[0017] The ZVS phase-shifted full bridge converter may include logic that controls when the switches turn on and off. For example, the logic may control the switches such that voltage is driven through the transformer in both polarities. The target result is that the flux and magneticfields are kept in balance. It switches in a phase-shifted manner, and both switches are on half of the time. The first pair of switches (leading edge) are typically alternating on and off based on a fixed clock signal. Furthermore, the second pair of switches (trailing edge) are switching on and off at different times than the first pair. Meanwhile, the auxiliary circuit enables a switch to be turned on even when there is zero voltage at the switch.[00181 The auxiliary circuit is implemented within the primary circuit side and is separate circuitry connected to each respective point in the leg. The auxiliary circuit may be run on 50 percent high and 50 percent low. It will alternate the charging of the capacitors to high and low. Since there is an inductor it will take a bit of time to recharge the capacitors. If the system is moving capacitors from zero volts to a particular input voltage it will take some time. The system may transfer the charge through the inductors. The charge required to charge the capacitor will remain in the inductor as magnetic flux. Whenever there is time to switch, the logic can be used to pre-program how much current (e.g., at least a minimum threshold level of current, etc.) is running in this network when it comes time to switch from high to low or low to high.

[0019] FIG. 1A illustrates an example of a zero voltage switching (ZVS) phase-shifted full bridge converter 100A according to example embodiments, and FIG. IB illustrates a graph 100B of pulse signals from the four switches in the circuit of FIG. 1 A, according to example embodiments. Referring to FIGS. IA and IB, the ZVS phase-shifted full bridge converter 100A described herein is able to provide isolation between a primary circuit 120 and a secondary circuit 130 of the ZVS phase-shifted full bridge converter 100A through a transformer 125. The primary circuit 120 includes a voltage source 110 as an input, and four electronic switches (e.g.. MOSFETs, insulated-gate bipolar transistors (IGBTs), etc.) The four electronic switches includean upper left switch 121 , a lower left switch 122, an upper right switch 123, and a lower right switch 124.

[0020] In this example, the transformer 125 may be a high-frequency transformer. It also provides isolation between the primary circuit 120 (primary side) and the secondary circuit 130 (secondary side) and any required voltage gain. The secondary circuit 130 also includes an inductor 132 which is used to limit the output current ripple, and a capacitor 134 which is used as a filter to stabilize the output voltage to a load 136, such as an amplifier, or the like. To create power transfer from the primary circuit 120 to the secondary circuit 130 (and power the load 136), the four electronic switches are alternated between on and off states.

[0021] In this example, a left leg of the primary circuit 120 includes a first pair of switches (i.e., QI and Q2). The first pair of switches are also labelled as the upper left switch 121 (QI) and the lower left switch 122 (Q2). To prevent shoot-through, a short-circuit of voltage source 110 via the upper left switch 121 (QI) and the lower left switch 122 (Q2), the upper left switch 121 and the lower left switch 122 may be modulated with a 180 degree difference such that neither of the upper left switch 121 and the lower left switch 122 are turned “on” at the same time. An example of the phase shift of the upper left switch 121 (QI) is shown as a pulse signal 141 in the example of FIG. IB. Meanwhile, an example of the pulse signal of the lower left switch 122 is shown as a pulse signal 142 in FIG. IB.

[0022] A right leg of the primary circuit 120 includes a second pair of switches (i.e., switches Q3 and Q4, etc.). The second pair of switches are also labelled as the upper right switch 123 (Q3) and the lower right switch 124 (Q4). To prevent shoot-through, the upper right switch 123 and the lower right switch 124 may be modulated with a 180 degree difference (e.g., inverted, etc.) such that neither of the upper right switch 123 (Q3) and the lower right switch 124 (Q4) areturned “on” at the same time. Therefore, the shape of the pulses of the upper right switch 123 (Q3) and the lower right switch 124 (Q4) are not turned on at the same time.

[0023] Furthermore, in order to create voltage over the transformer 125, the right leg and the left leg of the primary circuit 120 need to be out of phase with respect to each other. To achieve this, the pulse signal of the upper right switch 123 (Q3) is phase-shifted with respect to the upper left switch 121 (QI) as shown in pulse signal 143 in the example of FIG. IB. Likewise, the pulse signal of the lower right switch 124 (Q4) is phase-shifted with respect to the lower left switch 122 (Q2) as shown in pulse signal 144 in the example of FIG. IB.

[0024] During operation of the primary circuit 120, the primary circuit 120 may include control logic (not shown) to control when the switches open, and for how long. When the upper left switch 121 (QI) and the lower right switch 124 (Q4) are turned on at the same time, and the lower left switch 122 (Q2) and the upper right switch 123 (Q3) are turned off, a positive voltage flows through the transformer as shown in pulse signal 145 in the example of FIG. IB. Meanwhile, when the upper left switch 121 (QI) and the upper right switch 123 (Q3) are on at the same time, and the lower left switch 122 (Q2) and the lower right switch 124 (Q4) are turned off, the transformer 125 is short-circuited resulting in no voltage (zero voltage) across the transformer 125 as shown in the pulse signal 145.

[0025] Furthermore, when the lower left switch 122 (Q2) and the upper right switch 123 (Q3) are on at the same time, and the upper left switch 121 (QI) and the lower right switch 124 (Q4) are turned off, a negative voltage is created across the transformer 125 as shown in the pulse signal 145 in the example of FIG. IB. The phase-shifted pattern of switches being turned on and off in alternating and phase-shifted fashion may continue on an iterative basis creating power which is then transferred to the secondary circuit 130 by the transformer 125.

[0026] FIG. 2A illustrates a view 200A of an auxiliary circuit for a ZVS phase-shifted full bridge power converter according to other example embodiments. Referring to FIG. 2A, the auxiliary circuit may be integrated within the primary circuit of the ZVS phase-shifted full bridge power converter. In this example, the primary circuit is shown, with four switches including an upper left switch 210, a lower left switch 211, an upper right switch 212, and a lower right switch 213. The primary circuit also includes a voltage source 202 and a transformer 208. Furthermore, the primary circuit includes a leading leg output 204 which is electrically coupled to the right leg of the primary circuit and a trailing leg output 206 which is electrically coupled to the left leg of the primary circuit.

[0027] In the example of FIG. 2A, a capacitor 214 is located over the upper left switch 210, a capacitor 215 is located over the lower left switch 211, a capacitor 216 is located over the upper right switch 212, and a capacitor 217 is located over the lower right switch 213. Here, the capacitors 214, 215, 216, and 217 store energy which allows the respective upper left switches to turn on at near zero voltage over the switch.

[0028] Electrically coupled between the right leg and the left leg of the primary circuit are the components of the auxiliary circuit. In this example, the auxiliary circuit includes a first auxiliary circuit (e.g., an inductor 220, a diode 224, a diode 225, a capacitor 222, and a capacitor 223) and a second auxiliary circuit (e.g., an inductor 230, a diode 234, a diode 235, a capacitor 232, and a capacitor 233) , however, the combination of these circuits may also be referred to as an auxiliary circuit. The first auxiliary circuit includes a left-side inductor 220 and the second auxiliary circuit includes a right-side inductor. The first auxiliary circuit also includes a diode 224 that is electrically coupled to the left- side inductor 220 and the upper left switch 210, a diode225 that is electrically coupled to the left- side inductor 220 and the lower left switch 211. Thefirst auxiliary circuit also includes a capacitor 222 that is located over the diode 224, and a capacitor 223 that is located over the diode 225.

[0029] In this example, the second auxiliary circuit includes a diode 236 that is electrically coupled to the right-side inductor 230 and the upper right switch 212, a diode 235 that is electrically coupled to the right-side inductor 230 and the lower right switch 213. The second auxiliary circuit also includes a capacitor 232 that is located over the diode 236, a capacitor 233 that is located over the diode 235.

[0030] In this example, a cross-sectional area 270 of the first auxiliary circuit depicts a point 240 which represents voltage pulse, a point 250 which represents current over the left-side inductor 220, and a point 260 which represents voltage with respect to the capacitors 222 and 223.

[0031] In some embodiments, both bridge legs may operate at a fixed frequency and a fixed duty cycle. This is true in the general sense but maybe not all specific cases and not necessarily a requirement (i.e., a design could be made to switch frequency or duty cycle which may restrain this circuit operation but it does not mean it cannot be used). One of the advantages of the auxiliary circuit in this design is that even in a situation where power transfer is not occurring and voltage over the transformer primary is zero, there will be pulses with relevant length on each bridge legs which may fuel this circuit to operate reliably regardless of operating point. In contrast, traditional converters (e.g., full bridge converter, half bridge, push-pull, single switch topologies, etc.) all stop producing pulses during no power.

[0032] The energy stored is the charge it takes to charge the capacitors over the diodes 224 and 225. This charge will translate into a current in the left-side inductor 220. Depending on the size of the components, this could go fast (if small) or slow (if large). The current needs to be high enough for the commutation of the switches to be within the reasonable time and optimally itshould complete well before the next switch cycle. Even though each bridge leg operates at fixed frequency and duty cycle, as the phase between the legs changes with regulation pulses needs to be longer or shorter to shift the bridge leg commutations in time. Proper design of these components will make the circuit immune against these changes as long as they are kept moderate. In the example the circuit is fully charged about 75% into the pulse, which leaves 25% for pulse to be shorted by the regulation without affecting the charged currents. As the final currents are clamped there is virtually no limit on how much longer the pulse can be.

[0033] According to various embodiments, each auxiliary circuit is configured to store energy while one switch among a respective pair of switches is turned on and another switch among the respective pair of switches is turned off. Furthermore, each auxiliary circuit is configured to supply the stored energy for the purpose of recharging all attached capacitance in a respective leg when both switches among the respective pair of switches are turned off. The auxiliary circuit can hold the switches (e.g., MOSFETs, etc.) in an energized state that reduces some of their parasitic characteristics such as intrinsic non-linear capacitance. Furthermore, the auxiliary circuit can reduce both electromagnetic interface (EMI), noise, etc., issues and power loss at operating levels where the circuit is outputting small amounts of power.

[0034] FIG. 2B illustrates a view 200B of voltage over time and current over time from different locations of the auxiliary circuit during operation of the ZVS phase-shifted full bridge converter shown in FIG. 2A, according to example embodiments. Referring to FIG. 2B, a graph 272 of voltages and current over time is shown. Here, a signal 242 corresponds to a value of voltage over time at the point 240 of the cross-sectional area 270, a signal 252 corresponds to a value of current over time at the point 250 of the cross-sectional area 270, and a signal 262 corresponds to a value of voltage over time at the point 260 of the cross-sectional area 270.

[0035] At tl in the graph 272, current at the inductor is 0 as shown in signal 252. Meanwhile, switch Q2 is on, causing the voltage at point 240 to be 0V as shown in signal 242. Due to the previous pulse, the voltage at point 260 is Vs as shown in the signal 262 where Vs refers to a steady-state voltage. As a result, there is -significant voltage difference over the left-side inductor 220. This voltage will make the current in the inductor increase while at the same time, the capacitors 222 and 223 over the diodes 224 and 225, respectively, will carry the same currents so they will change their charge, leading to a decay in voltage at the point 260. As the voltage at point 260 goes down, the voltage over the left-side inductor 220 goes down and the current will increase at a rate that decreases over time as shown in the signal 252. As time approaches t2, the voltage over the left-side inductor 220 will approach 0 and the current will approach steady state.

[0036] At t2 in the graph 272, the left-side inductor 220 has been charged to a steady state level of current (-As) in this example, and both voltages at the points 240 and 260 are zero as indicated by the signals 242 and 262. As the left-side inductor 220 has charged current it wants to continue to charge the capacitors 222 and 223 over the diodes 224 and 225, respectively, but at this point the diode 225 will prevent the voltage at the point 260 from becoming negative and when this happens the diode 225 will solely take over the current from the capacitors 222 and 223. The charged current will now flow through diode 225 and Q2 and could remain constant for a relatively long time. Due to various losses in the system the current will slowly decay but for the short period of time until the next switch cycle it will remain almost constant.

[0037] At t3 in the graph 272, a regulation system (not shown) decides it is time to open the lower left switch 211. There is a short time where both the upper left switch 210 and the lower left switch 211 are off, commonly referred to as dead-time. When lower left switch 211 turns off,the current cannot go that path anymore, instead it will go through the capacitor 215 over the lower left switch 211. Naturally, the voltage at point 240 cannot change without recharging both the capacitors 214 and 215 so the current will split between the capacitors 214 and 215. The current distribution between the capacitors 214 and 215 will depend on the size of these capacitors.[00381 If the capacitors 214 and 215 are intrinsic in the semiconductor switch it will be highly non-linear and the voltage will start to change slowly at first as the capacitance in the lower left switch 211 is much larger when there are little voltage over it, then change more rapidly as the voltage increases as the capacitance goes down, until you start to get close to the supply voltage and the capacitance in the upper left switch 210 gets larger. The current will distribute itself according to capacitance. If the capacitors 214 and 215 are discrete or linear’ the current will distribute equally and the rate of change in voltage will be more constant. Most useful is to use a combination of intrinsic non-linear capacitors, as they help turning off the lower left switch 211 quickly without voltage building up (thus achieving ZVS) with external, linear capacitors that slows down the transition during the mid-way to reduce EMC. As the voltage at the point 240 is increasing as shown in the signal 242, so is the voltage over the inductor as shown in the signal 252, but now with a different polarity than before. As the voltage transitions the current will star! to change with a rate equal to the voltage which is why it is on its way towards 0 voltage already when the voltage transition completes.

[0039] At time t4 in the graph 272, the regulation system determines the dead-time to be complete by some means (could be pre-programmed, fixed or varying based on application current, or sensed by voltage sensing). In response, the upper left switch 210 is turned on without any voltage over it, thus achieving ZVS. At this time, the current at the point 250 hasalready started to decay but now the voltage over the inductor is fixed as the voltage at point 260 is held to zero volts by the diode 224, as it is conducting current, and the voltage at the point 240 is fixed at a steady-state voltage (Vs) which means the left-side inductor 220 will see a fixed voltage almost equal to the input voltage over it, but with a different polarity from the current in it. Based on this, the current will move towards 0 at a fixed rate. roo4oi At time t5 in the graph 272, the current in the inductor has reached 0A. But there is still a voltage over the left-side inductor 220 but now the diode 222 is not conducting anymore, so there is nothing keeping the potential at the point 260 other than the capacitors 214 and 215 over the upper left switch 210 and the lower left switch 211. The capacitors 214 and 215 will carry the current as they are charging. The voltage at the point 260 will start to move from 0V towards the input voltage. Initially the inductor current is low so the voltage changes slowly but as the current increases so will the rate of voltage change. As the voltage at the point 260 increases, the voltage over the left-side inductor 220 decreases so when the voltage at the point 260 approaches input voltage, the inductor current will stop changing.

[0041] At time t6 in the graph 272, when the voltage at the point 260 has increased to or slightly above input voltage the diode 224 will prevent the voltage at the point 260 from increasing by taking over the current previously going through the capacitors 222 and 223 over the diodes 224 and 225, respectively. Now the current in the left- side inductor 220 has charged up to a desired current level and the voltage over the left-side inductor 220 is close to 0 the current will decay very slowly but for the short time until the next switch cycle it will remain virtually constant. The current at the point 250 will now go through diode 224 and the upper left switch 210.

[0042] At time t7 in the graph 272, the control system determines it is time to open the upper left switch 210, and both the upper left switch 210 and the lower left switch 221 will be off for abrief time, again referred to as dead-time. During this dead-time, the current at the point 250 cannot go through the upper left switch 210 anymore, thus it starts to go through capacitor 214 and the capacitor 215 causing charge to accumulate in the capacitors 214 and 215. As the capacitors 214 and 215 charge, the voltage at the point 240 will start to move towards 0V. the current will distribute itself over the capacitors 214 and 215 at each time depending on their capacitance which could be voltage dependent. As the voltage does not change instantly if the upper left switch 210 is turned off fast enough, intrinsic highly non-linear capacitance will help the voltage to not build up instantly, thus the upper left switch 210 is turned off without voltage over it. As the voltage at the point 240 is changing, so is the voltage over the left-side inductor 220 at the point 250, and the current at the point 250 will start to change towards 0.

[0043] At time t8 in the graph 272, the regulation system determines the dead-time to be complete by some means (could be pre-programmed, fixed or varying based on application current, or sensed by voltage sensing). Here, the lower left switch 211 is turned on without any voltage over it, thus achieving ZVS. At this time, the current at the point 250 has already started to decay towards 0 but now the voltage over the left-side inductor 220 is fixed as the voltage at the point 260 is held to the input voltage by the diode 225, as it is conducting current, and the voltage at the point 240 is fixed at 0V which means the left-side inductor 220 will see a fixed voltage almost equal to the input voltage over it, but with a different polarity from the current in it. Based on this, the current will move towards 0 at a fixed rate.

[0044] At time t9 in the graph 272, the current in the left-side inductor 220 will have reached 0A. At this time, there is still a voltage over the left-side inductor 220 but now the diode 224 is not conducting anymore, so there is nothing keeping the potential at the point 260 other than the capacitors 222 and 223 over the diodes 224 and 225. The capacitors 222 and 223 will carry thecurrent as they are charging. The voltage at the point 260 will start to move from input voltage towards 0V.

[0045] It will be readily understood that the components of the application, as generally described and illustrated in the figures herein, may be arranged and designed in a wide variety of different configurations. Thus, the detailed description of the embodiments is not intended to limit the scope of the application as claimed but is merely representative of selected embodiments of the application.

[0046] One having ordinary skill in the art will readily understand that the above may be practiced with steps in a different order and / or with hardware elements in configurations that are different from those which are disclosed. Therefore, although the application has been described based upon these preferred embodiments, it would be apparent to those of skill in the art that certain modifications, variations, and alternative constructions would be apparent.

[0047] While preferred examples of the present instant solution have been described, it is to be understood that the examples described are illustrative only, and the scope of the instant solution is to be defined solely by the appended claims when considered with a full range of equivalents and modifications (e.g., protocols, hardware devices, software platforms, etc.) thereto.

Claims

WHAT IS CLAIMED IS:

1. A phase-shifted full-bridge apparatus comprising: a transformer; a primary circuit that is electrically coupled to the transformer, wherein the primary circuit includes a first leg with a first pair of switches and a second leg with a second pair of switches; and a first auxiliary circuit that is electrically coupled to the first leg and a second auxiliary circuit that is electrically coupled to the second leg of the primary circuit, wherein each auxiliary circuit is configured to store energy while one switch among a respective pair of switches is turned on and another switch among the respective pair of switches is turned off, and supply the stored energy for the purpose of recharging all attached capacitance in a respective leg when both switches among the respective pair of switches are turned off.

2. The apparatus of claim 1, wherein each auxiliary circuit is further configured to reduce parasitic characteristics of the respective pa ' of switches when the transformer is outputting power to a secondary circuit.

3. The apparatus of claim 1, wherein the first auxiliary circuit comprises an inductor which is coupled to the first pair of switches, a diode which is coupled to the inductor and a first switch among the first pair of switches, a second diode which is coupled to the inductor and a second switch among the first pair of switches, a capacitor coupled to the first diode, and a second capacitor coupled to the second diode.

4. The apparatus of claim 3, wherein the inductor is configured to store energy therein while the first switch is turned on and the second switch is turned off, and discharge stored energy when the first switch among the first pair of switches is turned off and the second switch among the first pair of switches is still off.

5. The apparatus of claim 3, wherein the second auxiliary circuit comprises a second inductor which is coupled to the second pair of switches, a third diode which is coupled to the second inductor and a first switch among the second pair of switches, a fourth diode which is coupled to the second inductor and a second switch among the second pair of switches, a third capacitor coupled to the third diode, and a fourth capacitor coupled to the fourth diode.

6. The apparatus of claim 5, wherein the second inductor is configured to store energy therein while the first switch among the second pair of switches is turned on and the second switch among the second pair of switches is turned off, and discharge stored energy when the first switch among the second pair of switches is turned off and the second switch among the second pair of switches is still off.

7. The apparatus of claim 1, wherein each auxiliary circuit is integrated into the primary circuit of the phase-shifted full bridge apparatus.

8. The apparatus of claim 1 , further comprising a secondary circuit that is electrically coupled to the transformer and that is configured to receive power from the primary circuit via the transformer.

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