Isolation circuit and energy recovery circuit and method thereof

Abstract

An energy recovery circuit for an isolation circuit is disclosed. The isolation circuit comprises a transformer, a primary side switch and a secondary side synchronous rectification switch, the energy recovery circuit comprises an energy recovery branch, the energy recovery branch comprises a clamping capacitor, an auxiliary switch and a current detection resistor which are sequentially connected in series and coupled, a first end of the clamping capacitor is coupled to a first end of a primary side winding, and a second end of the auxiliary switch is coupled to a second end of a secondary side winding; the second end of the clamping capacitor is coupled to the first end of the auxiliary switch, the second end of the auxiliary switch is coupled to the first end of the current detection resistor, the second end of the current detection resistor is coupled to the second end of the primary winding, and the recovery control integrated circuit comprises a first terminal, a second terminal and a third terminal, wherein the first terminal is coupled to the second end of the primary winding, the second terminal is coupled to the first end of the current detection resistor to receive a current detection signal, and the third terminal is coupled to the control end of the auxiliary switch. Wherein the voltage between the control end and the second end of the auxiliary switch is reduced during the discharging period of the clamping capacitor.

Description

Technical Field

[0001] The present invention relates to electronic circuits, and in particular to an energy recovery circuit for an isolation circuit and a method for energy recovery thereof. Background Art

[0002] Common clamping circuits in isolation circuits include RCD clamping and active clamping. Figure 1 A conventional isolation circuit 100 using RCD clamping is shown. As Figure 1 shown, the RCD clamping is implemented by an RCD buffer 10, including a clamping capacitor Csn, a buffer resistor Rsn, and a diode Dsn. When the primary control signal GP turns off the primary switch MP coupled to the primary winding Np, the leakage inductance of the transformer T transfers its leakage inductance energy, and charges the clamping capacitor Csn through the diode Dsn. After the charging process of the clamping capacitor Csn ends, the energy stored in the clamping capacitor Csn is consumed by the buffer resistor Rsn. Although the voltage spike of the isolation circuit 100 can thus be suppressed, since the leakage inductance energy is exhausted rather than recovered, the efficiency of the isolation circuit 100 is reduced.

[0003] Active clamping overcomes the disadvantages of RCD clamping. Figure 2 A conventional isolation circuit 200 using active clamping is shown. When the primary switch QP is in the conducting state, the auxiliary switch QH remains off. Current flows through the primary winding Np and the primary switch QP to the primary reference ground, and energy is stored in the transformer T and the leakage inductance Lk accordingly. When the primary switch QP is in the off state. The leakage inductance Lk of the transformer T charges the clamping capacitor Csn through the body diode of the auxiliary switch QH to transfer and store the leakage inductance energy in the clamping capacitor Csn. Subsequently, the auxiliary switch QH is turned on, and the energy stored in the clamping capacitor Csn is not consumed, but is recovered through the auxiliary switch QH and the transformer T. The addition of the auxiliary switch QH provides a bidirectional current path, which can not only suppress the voltage spike on the primary switch QP, but also help recover Figure 1 the energy dissipated by the RCD clamping in, and completely release the recovered energy to the secondary output, thereby improving the efficiency of the isolation circuit 200.

[0004] However, in some applications, when the current oscillation after the auxiliary switch tube QH turns off is transferred to the secondary side, it will cause the problem of early turn-off of the secondary synchronous rectifier tube, thereby reducing the reliability and efficiency of the isolation circuit. Summary of the Invention

[0005] To solve the foregoing one or more problems, the present invention provides an isolation circuit, an energy recovery circuit, and an energy recovery method, which can prevent voltage spikes on the primary switch, recover leakage inductance energy, and further prevent early turn-off of the secondary synchronous rectifier switch.

[0006] According to an embodiment of the present invention, an energy recovery circuit for an isolation circuit is provided. The isolation circuit includes a transformer having a primary winding and a secondary winding, a primary switch coupled to a second end of the primary winding, and a secondary synchronous rectification switch coupled to the secondary winding. The energy recovery circuit includes an energy recovery branch and an integrated circuit. The energy recovery branch is coupled between a first end and a second end of the primary winding and includes a clamping capacitor, an auxiliary switch, and a current sensing resistor connected in series, wherein a first end of the clamping capacitor is coupled to the first end of the primary winding, a second end of the clamping capacitor is coupled to a first end of the auxiliary switch, a second end of the auxiliary switch is coupled to a first end of the current sensing resistor, and a second end of the current sensing resistor is coupled to the second end of the primary winding. The integrated circuit has a first terminal, a second terminal, and a third terminal, wherein the first terminal is coupled to the second end of the primary winding, the second terminal is coupled to the first end of the current sensing resistor to receive a current sensing signal representing the current flowing through the energy recovery branch, and the third terminal is coupled to a control end of the auxiliary switch to control the conduction and turn-off of the auxiliary switch, wherein the voltage between the control end and the second end of the auxiliary switch is reduced during the discharge of the clamping capacitor.

[0007] According to another embodiment of the present invention, an isolation circuit is provided, including a transformer having a primary winding and a secondary winding, a primary switch coupled to the primary winding, a secondary synchronous rectification switch coupled to the secondary winding, and the energy recovery circuit as described above.

[0008] According to still another embodiment of the present invention, a method for recovering energy of an isolation circuit is provided. The isolation circuit includes a transformer having a primary winding and a secondary winding, a primary switch coupled to the primary winding, and a secondary synchronous rectification switch coupled to the secondary winding. The method includes: coupling the energy recovery branch in parallel with the primary winding, wherein the energy recovery branch includes a clamping capacitor, an auxiliary switch, and a current sensing resistor connected in series in sequence; coupling a first terminal of the integrated circuit to a connection point between the primary switch and the primary winding; receiving, through a second terminal of the integrated circuit, a current sensing signal representing the current flowing through the energy recovery branch; coupling a third terminal of the integrated circuit to a control end of the auxiliary switch to control the conduction and turn-off of the auxiliary switch; and reducing the gate-source voltage of the auxiliary switch during the discharge of the clamping capacitor.

[0009] According to an embodiment of the present invention, the energy recovery circuit proposed by the present invention can increase the efficiency of the isolation circuit. The integrated circuit of the present invention can be selectively paired with any primary controller to form an isolation circuit, which can avoid premature turn-off of the secondary synchronous rectification switch while maintaining high efficiency, thereby improving the reliability of the isolation circuit. Description of the Drawings

[0010] Refer to the following detailed description and the accompanying drawings for a further understanding of the present invention, in which like components are denoted by like reference numerals. The following drawings are for illustrative purposes only and may show only a part of the device and are not necessarily drawn to scale.

[0011] Figure 1 Fig. shows a conventional isolation circuit 100 using an RCD clamp;

[0012] Figure 2 Fig. shows a conventional isolation circuit 200 using an active clamp;

[0013] Figure 3 Fig. shows a schematic diagram of an isolation circuit 300 according to an embodiment of the present invention;

[0014] Figure 4 Fig. shows a circuit block diagram of an integrated circuit 20A for an isolation circuit 400 according to an embodiment of the present invention;

[0015] Figure 5 Fig. shows Figure 2 the operating waveform diagram of the isolation circuit 200 shown;

[0016] Figure 6 Fig. shows according to an embodiment of the present invention Figure 4 the operating waveform diagram of the isolation circuit 300 shown;

[0017] Figure 7 Fig. shows a circuit block diagram of an integrated circuit 20B for an isolation circuit 300 according to another embodiment of the present invention;

[0018] Figure 8 Fig. shows a circuit block diagram of an integrated circuit 20C for an isolation circuit 300 according to another embodiment of the present invention;

[0019] Figure 9 Fig. shows the circuit schematic diagram of an isolation circuit 400 according to another embodiment of the present invention;

[0020] Figure 10 Fig. shows the operating schematic diagram of an isolation circuit 400 according to an embodiment of the present invention;

[0021] Figure 11 Fig. shows three operating waveform diagrams of an isolation circuit 400 according to an embodiment of the present invention;

[0022] Figure 12 Fig. shows a flowchart of an energy recovery method 600 for an isolation circuit according to an embodiment of the present invention. Detailed Description of the Invention

[0023] The following describes multiple different embodiments of the present invention. In the following description, some specific details, such as exemplary circuits and exemplary values of these circuit components, are provided to give a detailed understanding of the embodiments. However, those skilled in the art can understand that it is not necessarily required to have the one or more specific details to implement the present invention, or other methods, components, materials, etc. can be used to implement the present invention. In other examples, well-known structures, materials, processes, or operations are not described or shown in detail to avoid obscuring the present invention.

[0024] Throughout the specification and claims, terms such as "left", "right", "inner", "outer", "front", "rear", "upper", "above", "on top of", "lower", "underneath", "beneath" and their like are used for descriptive purposes only and are not used to describe permanently fixed relative relationships. It should be understood that these terms are interchangeable under appropriate circumstances, so that embodiments of the technology described herein can operate, for example, in other directions than those shown or otherwise described herein. Terms such as "coupled" and "connected" as used herein are defined as being directly or indirectly connected in an electrical or non-electrical manner. Terms such as "a", "the" and "said" include plural forms. The phrase "in one embodiment" used herein does not necessarily refer to the same embodiment, but may also be the same embodiment. Those skilled in the art should understand that the meanings of the above terms do not limit these terms, but are only used to provide illustrative examples for these terms.

[0025] The present invention can be applied to any isolation circuit. In the following detailed description, for the sake of simplicity, only the flyback circuit is taken as an example to explain the specific working principle of the present invention.

[0026] Figure 3 A schematic diagram of an isolation circuit 300 according to an embodiment of the present invention is shown. The isolation circuit 300 includes a transformer T, a primary switch QP, a primary control circuit 10, an integrated circuit 20, an energy recovery branch 30, and an output circuit 40. The transformer T has a primary winding Np and a secondary winding Ns. The transformer T is coupled and receives an input voltage Vin, and generates an output voltage Vout supplied to the load through a secondary synchronous rectification switch SR and an output capacitor Cout of the output circuit 40. The primary switch QP is coupled between the second end of the primary winding Np and the primary reference ground, and is controlled by a primary drive signal GP provided by the primary control circuit 10. The energy recovery branch 30 includes a clamping capacitor Csn, an auxiliary switch QH, and a current detection resistor Rcs connected in series in sequence.

[0027] In Figure 3In the embodiment, the energy recovery branch 30 is coupled in parallel with the primary winding Np. Specifically, the first end of the clamping capacitor Csn is coupled to the first end of the primary winding Np, and the second end of the clamping capacitor Csn is coupled to the first end of the auxiliary switch QH. The second end of the auxiliary switch QH is coupled to the first end of the current sensing resistor Rcs, and the second end of the current sensing resistor Rcs is coupled to the second end of the primary winding Np.

[0028] The integrated circuit 20 has a plurality of terminals, including: a power supply terminal VCC, a regulated voltage terminal VDD, a ground terminal VSS, a control terminal VG, a current sensing terminal CS, and a setting terminal SET. The power supply terminal VCC receives the power supply voltage VPR of the primary control circuit 10 through the diode D0 to supply power to the integrated circuit 20, and determines whether the primary switch QP is in the on or off state based on the logic state of the power supply voltage VPR with respect to the ground terminal VSS. The power supply voltage VPR received by the power supply terminal VCC is converted into an adjusted voltage signal and output at the regulated voltage terminal VDD. The regulated voltage terminal VDD is coupled to the ground terminal VSS through the capacitor C0. The ground terminal VSS is coupled to the second ends of the primary switch QP and the primary winding Np, that is, the connection point of the primary winding Np and the primary switch Qp. The current sensing terminal CS is coupled to the first end of the current sensing resistor Rcs to receive a current sensing signal VCS representing the current flowing through the energy recovery branch 30. The control terminal VG is coupled to the control end of the auxiliary switch QH to control the on and off of the auxiliary switch QH. The SET terminal is coupled to the external resistor Rset to set the maximum conduction duration threshold of the auxiliary switch QH.

[0029] As Figure 3 shown, when the primary switch QP is on, the auxiliary switch QH remains off. Current flows through the primary winding Np and the primary switch MP, and energy is stored in the transformer T and the leakage inductance Lk. When the primary switch QP is off, the leakage inductance Lk of the transformer T transfers energy to the clamping capacitor Csn and the secondary output. Current flows from the second end of the primary winding Np through the current sensing circuit Rcs and the body diode of the auxiliary switch QH to charge the clamping capacitor Csn. Once current flows through the body diode of the auxiliary switch QH, the auxiliary switch QH will be turned on quickly.

[0030] Subsequently, the energy stored in the clamping capacitor Csn is released to the secondary output through the transformer T. The clamping capacitor Csn discharges, and current flows from the auxiliary switch QH through the current sensing resistor Rcs and the leakage inductance Lk. During the discharge of the clamping capacitor Csn, the voltage between the control end and the second end of the auxiliary switch QH will be reduced to avoid premature turn-off of the secondary synchronous rectifier switch SR caused by current oscillation. Specifically, refer to the attached Figures 4 - 6 to illustrate the working principle of the embodiment of the present invention.

[0031] Figure 4FIG. 20A shows a circuit block diagram of an integrated circuit 20A for isolating circuit 300 according to an embodiment of the present invention. As Figure 4 shown, the integrated circuit 20A includes a turn-on control circuit 201, a turn-off control circuit 202, and a gate driver 203.

[0032] In Figure 4 the embodiment shown, the turn-on control circuit 201 is configured to compare the current detection signal VCS with the turn-on threshold voltage VCS_ON, and generate a turn-on control signal DRV_ON according to the comparison result. As Figure 4 shown, the turn-on control circuit 201 includes a comparator CMP1. The comparator CMP1 has an inverting input terminal, a non-inverting input terminal, and an output terminal. Among them, the inverting input terminal of the comparator CMP1 is coupled to the current detection terminal CS to receive the current detection signal VCS representing the current flowing through the energy recovery branch 30, the non-inverting input terminal is coupled to the turn-on threshold voltage VCS_ON, and the turn-on control signal DRV_ON is provided at the output terminal. In one embodiment, the turn-on threshold voltage VCS_ON is -20 mV. In response to the current detection signal VCS decreasing to less than the turn-on threshold voltage VCS_ON, the turn-on control signal DRV_ON switches from a low level to a valid high level, and the auxiliary switch QH is turned on.

[0033] In Figure 4 the embodiment shown, the turn-off control circuit 202 is configured to compare the current detection signal VCS with the turn-off threshold voltage VCS_ZCD, and generate a turn-off control signal DRV_OFF according to the comparison result. As Figure 4 shown, the turn-off control circuit 202 includes a comparator CMP2 and a falling-edge monostable circuit 221. The comparator CMP2 has an inverting input terminal, a non-inverting input terminal, and an output terminal. The non-inverting input terminal of the comparator CMP2 is coupled to the current detection terminal CS to receive the current detection signal VCS, and the inverting input terminal is coupled to the turn-off threshold voltage VCS_ZCD. The falling-edge monostable circuit 221 has an input terminal and an output terminal, wherein the input terminal is coupled to the output terminal of the comparator CMP2, and a falling-edge triggered pulse signal is generated at the output terminal as the turn-off control signal DRV_OFF and provided to the output terminal. In one embodiment, the turn-off threshold voltage VCS_ZCD is a value close to 0 and greater than 0. In response to the current detection signal VCS decreasing to less than the turn-off threshold voltage VCS_OFF, the turn-off control signal DRV_OFF switches from a high level to a low level, and the auxiliary switch QH is turned off.

[0034] The gate driver 203 has a first input terminal, a second input terminal, and an output terminal. The first input terminal is coupled to the turn-on control circuit 201 to receive the turn-on control signal DRV_ON. The second input terminal is coupled to the turn-off control circuit 202 to receive the turn-off control signal DRV_OFF. Based on the turn-on control signal DRV_ON and the turn-off control signal DRV_OFF, the gate driver 203 provides a drive control signal GH to the control terminal VG of the integrated circuit 20A at the output terminal.

[0035] In one embodiment, the gate driver 203 has a first driving stage and a second driving stage. In the first driving stage, the gate driver 203 controls the gate voltage VG_QH of the auxiliary switch QH to remain at a first voltage. When the gate driver 203 switches from the first driving stage to the second driving stage, the gate voltage VG_QH of the auxiliary switch QH is pulled down to reduce the voltage between the control terminal and the second terminal of the auxiliary switch QH (e.g., the gate-source voltage VGS_QH of the auxiliary switch QH).

[0036] In Figure 4 the illustrated embodiment, the integrated circuit 20A further includes a first comparison circuit 204. The first comparison circuit 204 is configured to determine whether to enable the gate driver 203 to switch to the second driving stage. As Figure 4 shown, the first comparison circuit 204 includes a comparator CMP3. The comparator CMP3 has an inverting input terminal, a non-inverting input terminal, and an output terminal. Among them, the non-inverting input terminal of the comparator CMP3 is coupled to the current detection terminal CS to receive the current detection signal VCS, the inverting input terminal is coupled to the reference threshold voltage Vref, and a first comparison signal COP1 is provided at the output terminal. In response to the current detection signal VCS increasing to the reference threshold voltage Vref, the first comparison signal COP1 changes from a low level to a high level, and the second driving stage of the gate driver 203 is enabled, and the gate driver 203 enters the second driving stage.

[0037] The gate driver 203 further includes a third input terminal, which is coupled to the output terminal of the first comparison circuit 204 to receive the first comparison signal COP1. In Figure 4 the illustrated embodiment, the gate driver 203 includes a first charging path 21, a second discharging path 22, and a third discharging path 23.

[0038] Specifically, in response to the valid level of the turn-on control signal DRV_ON, that is, in response to the current detection signal VCS decreasing to less than the turn-on threshold voltage VCS_ON, the first charging path 21 is turned on to provide a charging path from a supply voltage VS to the control terminal VG of the integrated circuit 20A. The gate driver 203 enters the first driving stage, and the gate voltage VG_QH of the auxiliary switch QH rises and remains at the first voltage.

[0039] In response to the active level of the first comparison signal COP1, that is, in response to the current detection signal VCS increasing to the reference threshold voltage Vref, the first discharge path 22 is turned on, providing a discharge path from the control terminal VG to the ground terminal VSS. The gate driver 203 switches from the first driving stage to the second driving stage, and the voltage VG_QH at the control terminal of the auxiliary switch QH is gradually decreased.

[0040] In response to the active level of the turn-off control signal DRV_OFF, that is, in response to the current detection signal VCS decreasing to be less than the turn-off threshold voltage VCS_ZCD, the second discharge path 23 is turned on to provide a fast discharge path from the control terminal VG to the ground terminal VSS, and the auxiliary switch QH is turned off accordingly.

[0041] In Figure 4 In the illustrated embodiment, the first charging path 21 includes a charging current source IS1 and a first charging transistor S1 connected in series between the supply voltage VS and the control terminal VG. In other embodiments, the first charging path 21 may include multiple series branches of a charging current source and a charging transistor to provide charging paths with different driving capabilities. The first discharge path 22 includes a discharge current source IS2 and a first discharge transistor S2 connected in series between the control terminal VG and the ground terminal VSS. The second discharge path 23 includes a second discharge transistor S3 connected in series between the control terminal VG and the ground terminal VSS. In Figure 4 In the illustrated embodiment, the second discharge path 23 has a faster discharge speed than the first discharge path 22. In Figure 4 In the illustrated embodiment, the gate driver 203 controls the conduction and turn-off of the first charging transistor S1 based on the conduction control signal DRV_ON, controls the conduction and turn-off of the first discharge transistor S2 based on the first comparison signal COP1, and controls the second discharge transistor S3 based on the turn-off control signal DRV_OFF. For example, when the first charging transistor S1 is turned on, the auxiliary switch QH is turned on. If the first discharge transistor S2 is turned on, the control terminal of the auxiliary switch QH is electrically connected to the ground terminal VSS through the discharge current source IS2, and the gate voltage of the auxiliary switch QH drops. If the second discharge transistor S3 is turned on, the gate of the auxiliary switch QH is directly electrically connected to the ground terminal VSS, and the gate voltage of the auxiliary switch QH is quickly pulled down to the zero potential of the integrated circuit 20A.

[0042] Figure 5 Shows Figure 2 The working waveform diagram of the illustrated existing isolation circuit 200. As Figure 5As shown, from top to bottom, they are: the voltage Vsw at the connection point of the primary winding Np and the primary switch Qp, the current detection signal VCS1 representing the current flowing through the clamping capacitor Csn, the current iLm flowing through the excitation inductor Lm, the current iSR1 flowing through the secondary synchronous rectifier switch SR, the gate voltage VG_QH of the auxiliary switch QH, and the gate voltage VG_SR of the secondary synchronous rectifier switch SR. It should be noted that in Figure 5 In the schematic diagram shown, the waveform of the voltage Vsw at the connection point is drawn with the primary reference ground of the isolation circuit 200 as the reference ground potential, and the current detection signal VCS1, the current iLm flowing through the excitation inductor Lm, and the gate voltage VG_QH of the auxiliary switch QH are drawn with the connection point of the primary winding Np and the primary switch Qp as the reference ground potential. The current iSR1 flowing through the secondary synchronous rectifier switch SR and the gate voltage VG_SR of the secondary synchronous rectifier switch SR are drawn with the secondary reference ground of the isolation circuit 200 as the reference ground potential.

[0043] The current iSR1 of the secondary synchronous rectifier switch SR has two sources, one is the magnetizing inductor Lm of the transformer T, and the other is the clamping capacitor Csn. As Figure 5 shown, after the primary switch QP is turned off, the secondary synchronous rectifier switch SR is turned on, and the current iLm flowing through the magnetizing inductor Lm starts to linearly decrease. In addition, after the primary switch QP is turned off, the current flows from the second end of the primary winding Np through the body diode of the auxiliary switch QH and the clamping capacitor Csn, and then the auxiliary switch QH is turned on, as Figure 5 shown at point 101 in. When the current detection signal VCS1 decreases to the turn-off threshold voltage VCS_ZCD, the auxiliary switch QH is turned off, as Figure 5 shown at point 102 in. The current flowing through the clamping capacitor Csn (current detection signal VCS1) first increases and then decreases, and then the clamping capacitor Csn continues to charge and discharge, and the current detection signal VCS1 oscillates. Therefore, for the energy transferred to the secondary side, the current iSR1 also oscillates. Figure 5 The dotted line in the waveform of VG_SR in shows the normal gate voltage of the secondary synchronous rectifier switch SR. Since the secondary current iSR1 oscillates downward, resulting in the secondary current being less than a certain threshold voltage in advance, the system determines that the secondary current iSR1 crosses zero in advance, and the secondary synchronous rectifier switch SR is turned off earlier, as Figure 5 shown at point 103 in. In order to avoid the premature turn-off of the secondary synchronous rectifier switch SR, the inventors have proposed various embodiments of the present invention.

[0044] Figure 6 shows the Figure 4 working waveform diagram of the isolation circuit 300 shown according to an embodiment of the present invention. As Figure 6As shown, from top to bottom, they are: the voltage Vsw at the connection point of the primary winding Np and the primary switch Qp, the gate voltage VG_QH of the auxiliary switch QH, the current detection signal VCS representing the current flowing through the energy recovery branch 30, the current iLm flowing through the magnetizing inductor Lm, the current iSR flowing through the secondary synchronous rectifier switch SR, and the gate voltage VG_SR of the secondary synchronous rectifier switch SR. It should be noted that in Figure 6 In the schematic diagram shown, the waveform of the voltage Vsw at the connection point is drawn with the primary reference ground of the isolation circuit 300 as the reference ground potential, the current detection signal VCS, the current iLm flowing through the magnetizing inductor Lm, and the gate voltage VG_QH of the auxiliary switch QH are drawn with the ground terminal VSS as the reference ground potential, and the current iSR1 flowing through the secondary synchronous rectifier switch SR and the gate voltage VG_SR of the secondary synchronous rectifier switch SR are drawn based on the secondary reference ground of the isolation circuit 300 as the reference ground potential.

[0045] In Figure 6 In the embodiment shown, after the primary switch QP is turned off, when the current detection signal VCS decreases to the conduction threshold voltage VCS_ON, the auxiliary switch QH is turned on, as shown at point 101 in Figure 6 . The gate driver 203 enters the first driving stage, and the gate voltage VG_QH of the auxiliary switch QH is maintained at the first voltage. When the current detection signal VCS increases to the reference threshold voltage Vref, the gate driver 203 switches from the first driving stage to the second driving stage, as shown at point 104 in Figure 6 . The gate voltage VG_QH of the auxiliary switch QH is decreased, so the gate-source voltage VGS_QH of the auxiliary switch QH also decreases accordingly. The current oscillation flowing through the energy recovery branch 30 is suppressed. When the current detection signal VCS decreases to the turn-off threshold voltage VCS_ZCD, the auxiliary switch QH is turned off. After that, the magnetizing current iLm continues to linearly decrease. Since the current oscillation flowing through the energy recovery branch 30 is suppressed, the secondary current iSR no longer oscillates either. Until the secondary current iSR truly crosses zero, the secondary synchronous rectifier switch SR is turned off, as shown at point 105 in Figure 6 .

[0046] Figure 7 shows a circuit block diagram of an integrated circuit 20B for an isolation circuit 400 according to another embodiment of the present invention. As shown in Figure 7As shown, the gate driver 203A includes a first input terminal for receiving the turn-on control signal DRV_ON, a second input terminal for receiving the turn-off control signal DRV_OFF, a third input terminal for receiving the first comparison signal COP1, an output terminal for providing the drive control signal GH, a first charging path 21A from the supply voltage VS to the control terminal VG, a first discharging path 22A from the control terminal VG to the ground terminal VSS, and a second discharging path 23A from the control terminal VG to the ground terminal VSS.

[0047] In Figure 7 the embodiment shown, the first charging path 21A includes a gate resistor RG1 and a first charging transistor S1 connected in series. The first discharging path 22A includes a gate resistor RG2 and a first discharging transistor S2 connected in series. The second discharging path 23A includes a gate resistor RG3 and a second discharging transistor S3 connected in series. The gate resistors RG1 to RG3 are used as a setting unit for the gate drive condition to adjust the turn-on or turn-off speed of the auxiliary switch QH. For example, if the gate resistance value of RG3 is smaller than that of RG2, the turn-off speed of the auxiliary switch QH in the second discharging path 23A will be greater than that in the first discharging path 22A. In Figure 7 the embodiment shown, the second discharging path 23A further includes an acceleration capacitor C1. The acceleration capacitor C1 is connected in parallel with the gate resistor RG3 to accelerate the turn-off of the auxiliary switch QH.

[0048] In response to the valid level of the turn-on control signal DRV_ON, the first charging transistor S1 is turned on, the first charging path 21A is turned on, and the auxiliary switch QH is turned on. In response to the valid level of the first comparison signal COP1, the first discharging transistor S2 is turned on, the first discharging path 22A is turned on, and the gate voltage of the auxiliary switch QH is pulled down. In response to the valid level of the turn-off control signal DRV_OFF, the second discharging transistor S3 is turned on, the second discharging path 23A is turned on, and the auxiliary switch QH is quickly turned off.

[0049] Figure 8 The circuit diagram of the integrated circuit 20C for the isolation circuit 400 according to another embodiment of the present invention is shown. Compared with Figure 4 the integrated circuit 20A shown, Figure 8 the integrated circuit 20C shown further includes a maximum conduction duration control circuit 205. Compared with Figure 4 the gate driver 203 shown, Figure 8 the gate driver 203B shown further includes an OR gate circuit OR.

[0050] In Figure 8In the illustrated embodiment, the maximum conduction duration control circuit 205 has a first input terminal, a second input terminal, and an output terminal. The first input terminal is coupled to the control terminal VG or the conduction control circuit 201 to receive the drive control signal GH or the conduction control signal DRV_ON. The second input terminal is coupled to the setting terminal SET, and the maximum conduction duration control signal OFF1 is provided at the output terminal. The OR gate circuit OR has a first input terminal, a second input terminal, and an output terminal. The first input terminal receives the turn-off control signal DRV_OFF, the second input terminal receives the maximum conduction duration control signal OFF1, and the output terminal is coupled to the control terminal of the second discharge transistor S3. After the auxiliary switch QH is turned on, the maximum conduction duration control circuit 205 starts timing. After passing the maximum conduction duration threshold, the maximum conduction duration control circuit 205 generates the maximum conduction duration control signal OFF1 at its output terminal, controls the second discharge path to conduct through the OR gate circuit OR, and quickly turns off the auxiliary switch QH to ensure that the maximum conduction duration of the auxiliary switch QH does not exceed the maximum conduction duration threshold. The maximum conduction duration threshold is set by the resistor Rset coupled to the setting terminal SET.

[0051] Figure 9 FIG. shows a circuit schematic diagram of an isolation circuit 400 according to another embodiment of the present invention. Compared with Figure 4 the energy recovery branch 30 shown, Figure 9 the energy recovery branch 30A shown further includes a resistor R1 coupled between the second terminal of the auxiliary switch QH and the first terminal of the current detection resistor Rcs. The following is an example of the present invention through Figure 10 to illustrate.

[0052] Figure 10 FIG. shows a working schematic diagram of the isolation circuit 400 according to an embodiment of the present invention. As shown in FIG. (a), when the primary side switch QP is turned off, the current ics flows from the second terminal of the primary side winding Np through the current detection circuit Rcs, the resistor R1, and the body diode of the auxiliary switch QH to charge the clamping capacitor Csn. Once the current ics flows through the body diode of the auxiliary switch QH, the auxiliary switch QH will be quickly turned on. At this time, the gate-source voltage of the auxiliary switch QH is expressed by formula (1):

[0053] V GS_QH =V G_QH +i cs (R1+R cs ) (1)

[0054] Subsequently, as shown in FIG. (b), during the discharge period of the clamping capacitor Csn, the current ics reverses and flows from the auxiliary switch QH through the resistor R1, the current detection resistor Rcs, and the leakage inductance Lk. At this time, the gate-source voltage of the auxiliary switch QH is expressed by formula (2):

[0055] V GS_QH = V G_QH - i cs (R1 + R cs ) (2)

[0056] As can be seen from Formulas (1) and (2), during the discharge of the clamping capacitor Csn, the gate-source voltage of the auxiliary switch QH is reduced. The oscillation of the voltage Vsw at the connection point between the primary winding Np and the primary switch QP will also be reduced accordingly, which can prevent the premature turn-off of the secondary synchronous rectifier switch SR caused by current oscillation. Specifically, with reference to Appendix Figure 11 to illustrate the effects of the embodiments of the present invention.

[0057] Figure 11 shows three working waveform diagrams of the isolation circuit 400 according to an embodiment of the present invention. As Figure 11 shown, from left to right are the working conditions of the isolation circuit 400 when R1 = 0Ω, R1 = 2Ω, and R1 = 4Ω respectively. Among them, when R0 = 0Ω, the voltage Vsw at the connection point oscillates the most, and the secondary synchronous rectifier switch SR is prematurely turned off. As the resistance value of the resistor R1 increases, for example, when it increases to R1 = 4Ω, the voltage oscillation of the voltage Vsw at the connection point is significantly suppressed, ensuring the normal conduction of the secondary synchronous rectifier switch SR.

[0058] Figure 12 shows a flowchart of an energy recovery method 600 for an isolation circuit according to an embodiment of the present invention. The isolation circuit includes a transformer having a primary winding and a secondary winding, a primary switch coupled to the primary winding, and a secondary synchronous rectifier switch coupled to the secondary winding. The method 600 includes steps 601 to 605.

[0059] Among them, in step 601, an energy recovery branch is coupled in parallel with the primary winding. The energy recovery branch includes a clamping capacitor, an auxiliary switch, and a current detection resistor connected in series in sequence.

[0060] In one embodiment, the energy recovery branch further includes a first resistor coupled between the auxiliary switch and the current detection resistor.

[0061] In step 602, it is coupled to the connection point between the primary switch and the primary winding through the first terminal of the integrated circuit.

[0062] In step 603, a current detection signal representing the current flowing through the energy recovery branch is received through the second terminal of the integrated circuit.

[0063] In step 604, it is coupled to the control terminal of the auxiliary switch through the third terminal of the integrated circuit to control the conduction and turn-off of the auxiliary switch.

[0064] In step 605, the gate-source voltage of the auxiliary switch is decreased during the discharge of the clamping capacitor. In one embodiment, during the first driving stage, the gate voltage of the auxiliary switch is controlled to maintain a first voltage, and when switched to the second driving stage, the gate voltage of the auxiliary switch is pulled down. Among them, when the current detection signal increases to be greater than the reference threshold voltage, the switch is switched from the first driving stage to the second driving stage.

[0065] In this document, relative terms such as first, second and similar terms are only used to distinguish multiple entities or actions, and do not limit or indicate that these entities or actions have any actual relationship or order. Ordinal numbers such as "first", "second", "third", etc. only represent different ones among several, and do not limit or indicate any order unless the claims have a special definition. Unless the words of the claims have a special definition, the word order of the claims does not indicate that the process steps must be executed in chronological order or logical order. Without departing from the scope of the present invention, not conflicting with the description of the claims and being logically reasonable, the order of the operation steps can be exchanged or adjusted.

[0066] Those skilled in the art will appreciate that the present invention is not limited to the specific illustrations and descriptions above. On the contrary, the protection scope of the present invention is defined by the claims, and includes combinations and partial combinations of the various different features described above, and also includes combinations and partial combinations of the variations and modifications of these features that those skilled in the art can obtain from reading the above description and that do not belong to the prior art.

Claims

1. An energy recovery circuit for an isolation circuit, the isolation circuit including a transformer having a primary winding and a secondary winding, a primary switch coupled to a second end of the primary winding, and a secondary synchronous rectification switch coupled to the secondary winding, the energy recovery circuit including: An energy recovery branch, coupled between a first end and a second end of a primary winding, includes a clamping capacitor, an auxiliary switch, and a current sensing resistor connected in series, wherein a first end of the clamping capacitor is coupled to the first end of the primary winding, a second end of the clamping capacitor is coupled to a first end of the auxiliary switch, a second end of the auxiliary switch is coupled to a first end of the current sensing resistor, and a second end of the current sensing resistor is coupled to the second end of the primary winding; and An integrated circuit, having a first terminal, a second terminal, and a third terminal, wherein the first terminal is coupled to the second end of the primary winding, the second terminal is coupled to the first end of the current sensing resistor to receive a current sensing signal representative of a current flowing through the energy recovery branch, and the third terminal is coupled to a control end of the auxiliary switch to control conduction and turn-off of the auxiliary switch, wherein a voltage between the control end of the auxiliary switch and a second end of the auxiliary switch is reduced during discharge of the clamping capacitor.

2. The energy recovery circuit according to claim 1, wherein the integrated circuit further includes: A conduction control circuit, compares the current sensing signal with a conduction threshold voltage, and generates a conduction control signal according to a comparison result; A turn-off control circuit, compares the current sensing signal with a turn-off threshold voltage, and generates a turn-off control signal according to a comparison result; and A gate driver, receives the conduction control signal and the turn-off control signal to provide a drive control signal to the third terminal of the integrated circuit, wherein in a first driving stage, the gate driver controls the gate voltage of the auxiliary switch to remain at a first voltage, and when the gate driver switches from the first driving stage to a second driving stage, the gate voltage of the auxiliary switch is pulled down.

3. The energy recovery circuit according to claim 2, wherein the integrated circuit further includes a first comparison circuit that compares a current detection signal with a reference threshold voltage and generates a first comparison signal according to the comparison result to determine whether to switch the gate driver into a second driving stage.

4. The energy recovery circuit according to claim 3, wherein the gate driver includes: A first charging path from a supply voltage to the third terminal of the integrated circuit, wherein in response to an active level of the conduction control signal, the first charging path is turned on; A first discharging path from the third terminal of the integrated circuit to the first terminal of the integrated circuit, wherein in response to an active level of a first comparison signal, the first discharging path is turned on; and A second discharging path from the third terminal of the integrated circuit to the first terminal of the integrated circuit, wherein in response to an active level of the turn-off control signal, the second discharging path is turned on.

5. The energy recovery circuit according to claim 4, wherein the first discharge path includes a current source and a first discharge transistor connected in series between a third terminal and a first terminal of the integrated circuit, and the second discharge path includes a second discharge transistor coupled between the third terminal and the first terminal of the integrated circuit.

6. The energy recovery circuit according to claim 4, wherein the first discharge path includes a second gate resistor and a first discharge transistor connected in series between a third terminal and a first terminal of the integrated circuit, and the second discharge path includes a first circuit branch and a second discharge transistor connected in series between the third terminal and the first terminal of the integrated circuit, wherein the first circuit branch includes a second gate resistor and a capacitor connected in parallel.

7. The energy recovery circuit according to claim 2, wherein the integrated circuit further includes: A maximum conduction duration control circuit, generates a maximum conduction duration control signal when a conduction duration of the auxiliary switch reaches a maximum conduction duration threshold, and controls the auxiliary switch to turn off.

8. The energy recovery circuit according to claim 1, further including a first resistor coupled between a second end of the auxiliary switch and a first end of the current detection resistor.

9. An isolation circuit, including: A transformer, having a primary winding and a secondary winding; A primary switch, coupled between the primary winding and a primary reference ground; A secondary synchronous rectification switch, coupled to the secondary winding; and The energy recovery circuit according to any one of claims 1 to 7.

10. A method for recovering energy of an isolation circuit, the isolation circuit including a transformer having a primary winding and a secondary winding, a primary switch coupled to the primary winding, and a secondary synchronous rectification switch coupled to the secondary winding, the method comprising: Couple the energy recovery branch in parallel with the primary winding, wherein the energy recovery branch includes a clamping capacitor, an auxiliary switch, and a current sensing resistor connected in series in sequence; Couple to a connection point between the primary switch and the primary winding through a first terminal of an integrated circuit; Receive a current sensing signal representative of a current flowing through the energy recovery branch through a second terminal of the integrated circuit; Couple to a control end of the auxiliary switch through a third terminal of the integrated circuit to control conduction and turn-off of the auxiliary switch; and Reduce the gate-source voltage of the auxiliary switch during discharge of the clamping capacitor.

11. The method according to claim 9, wherein in the first driving stage, the gate voltage of the auxiliary switch is controlled to maintain a first voltage, and when switching to the second driving stage, the gate voltage of the auxiliary switch is pulled down.

12. The method according to claim 9, wherein: Switch from the first driving stage to the second driving stage in response to detecting that the current sensing signal is greater than a reference threshold voltage.

13. The method according to claim 9, further comprising: Providing a first discharge path from a third terminal to a first terminal of the integrated circuit in response to detecting that the current detection signal is greater than a reference threshold voltage; and Providing a second discharge path from the third terminal to the first terminal of the integrated circuit in response to detecting that the current detection signal is less than a turn-off threshold voltage.

14. The method according to claim 9, wherein the energy recovery branch further includes a first resistor coupled between the auxiliary switch and the current sensing resistor.

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