CN115276416A

CN115276416A - Bridge type power supply circuit

Info

Publication number: CN115276416A
Application number: CN202210925612.6A
Authority: CN
Inventors: 刘拓夫; 黎波; 周俊
Original assignee: On Bright Electronics Shanghai Co Ltd
Current assignee: On Bright Electronics Shanghai Co Ltd
Priority date: 2022-08-03
Filing date: 2022-08-03
Publication date: 2022-11-01
Also published as: TW202408142A

Abstract

There is provided a bridge power supply circuit comprising a first transistor, a second transistor, a driver transformer, and a transistor control circuit, wherein a resonant current on a first winding of the driver transformer is used to provide a drive current for the first transistor and the second transistor, a second winding of the driver transformer is connected between a base and an emitter of the first transistor, a third winding of the driver transformer is connected between a base and an emitter of the second transistor, the transistor control circuit being configured to: controlling one of the first transistor and the second transistor to change from an on state to an off state based on an output feedback signal representing an output current or an output voltage of the bridge power supply circuit; and controlling the other of the first transistor and the second transistor to change from an off state to an on state when the commutation of the resonant current is detected.

Description

Bridge type power supply circuit

Technical Field

The invention relates to the field of circuits, in particular to a bridge type power supply circuit.

Background

Bridge power circuits (e.g., half-bridge or full-bridge power circuits) are a common switching power topology that is favored for their high switching efficiency. Generally, a bridge power circuit uses a metal oxide semiconductor field effect transistor (MOSFET, abbreviated as MOS transistor) as a switch, and has the advantages of simple control and high reliability. However, since the MOS transistor is expensive, the system cost of the bridge power supply circuit using the MOS transistor as a switch is high.

A triode has a large cost advantage compared to a MOSFET, but has a high requirement for a driver and a large driving loss because a triode requires a large driving current. Fig. 1 shows a circuit schematic of a conventional electronic ballast 100 employing a transistor as a switch. In the electronic ballast 100 shown in fig. 1, once the transistor is turned on, the resonant circuit provides a driving current to the transistor through the transformer winding, causing the transistor to self-oscillate according to the natural frequency of the resonant circuit. Although the transistor driving scheme shown in fig. 1 solves the problem of the driving current of the transistor, the switching frequency of the transistor can only be kept consistent with the natural frequency of the resonant circuit and cannot be adjusted according to actual needs. In the switching power supply circuit, the switching frequency of the transistor is often adjusted according to factors such as the deviation of the parameters of the electrical elements and the load condition.

Therefore, a transistor driving scheme for a bridge power circuit is required to solve the difficulty in driving a transistor, improve the driving efficiency of the transistor, and reduce the system cost.

Disclosure of Invention

The bridge power supply circuit according to the embodiment of the invention comprises a first triode, a second triode, a driving transformer and a triode control circuit, wherein the resonant current on the first winding of the drive transformer is used to provide a drive current for the first transistor and the second transistor, a second winding of the driver transformer is connected between the base and emitter of the first transistor, a third winding of the driver transformer is connected between the base and emitter of the second transistor, and the transistor control circuit is configured to: controlling one of the first triode and the second triode to be changed into a turn-off state from a conducting state based on an output feedback signal representing the output current or the output voltage of the bridge power supply circuit; and controlling the other of the first transistor and the second transistor to change from an off state to an on state when the commutation of the resonant current is detected.

Drawings

The invention may be better understood from the following description of specific embodiments thereof taken in conjunction with the accompanying drawings, in which:

fig. 1 shows a circuit diagram of a conventional bridge power supply circuit using a transistor as a switch.

Fig. 2 shows a circuit schematic of a bridge power supply circuit according to an embodiment of the invention.

Fig. 3 is a schematic circuit diagram of a transistor driving control circuit in the control chip shown in fig. 2.

Fig. 4 shows a timing diagram of a plurality of signals associated with the triode drive control circuit shown in fig. 3.

Fig. 5 shows a circuit schematic of the current commutation detection circuit in the control chip shown in fig. 2.

Fig. 6 shows a timing diagram of a plurality of signals associated with the current commutation detection circuit shown in fig. 5.

Fig. 7 shows a circuit schematic of a bridge power supply circuit according to another embodiment of the invention.

Fig. 8 shows a circuit schematic of the current commutation detection circuit in the control chip shown in fig. 7.

Fig. 9 shows a timing diagram of a plurality of signals associated with the current commutation detection circuit shown in fig. 8.

Fig. 10 shows a timing diagram of a plurality of signals associated with the triode drive control circuit shown in fig. 3.

Detailed Description

Features and exemplary embodiments of various aspects of the present invention will be described in detail below. In the following detailed description, numerous specific details are set forth in order to provide a thorough understanding of the present invention. It will be apparent, however, to one skilled in the art that the present invention may be practiced without some of these specific details. The following description of the embodiments is merely intended to provide a better understanding of the present invention by illustrating examples of the present invention. The present invention is in no way limited to any specific configuration and algorithm set forth below, but rather covers any modification, replacement or improvement of elements, components or algorithms without departing from the spirit of the invention. In the drawings and the following description, well-known structures and techniques are not shown in order to avoid unnecessarily obscuring the present invention.

In view of the above, the bridge power supply circuit according to the embodiment of the invention is provided, in which the transistor driving scheme can turn on and off the transistor at a desired switching frequency, so as to greatly reduce the driving current required to be supplied to the transistor by a control chip (i.e., a transistor control circuit) for controlling the on and off of the transistor, improve the switching efficiency of the transistor, and greatly reduce the system cost.

Fig. 2 shows an exemplary circuit diagram of a bridge power supply circuit 200 according to an embodiment of the present invention. In the bridge power supply circuit 200 shown in fig. 2, C1 is a bus capacitor, U1 is a control chip for controlling on and off of the transistors Q1 and Q2, D1, D2, D3, and D4 are freewheeling diodes, W1 is a driving transformer for supplying a driving current to the transistors Q1 and Q2 (W1 a, W1b, and W1C are 3 different windings of the driving transformer W1, and the directions of the ends of the same name are shown in the figure), T1 is a transformer, C2 is a resonant capacitor, and C3 is an output filter capacitor. The base and emitter of the transistors Q1 and Q2 are connected to respective control pins of the control chip U1 in addition to the respective windings of the drive transformer W1. The control chip U1 can detect the working state of the system load RL through one or more of primary side sampling, secondary side sampling, voltage sampling, current sampling and the like, and controls the on and off of the triodes Q1 and Q2 according to the current working state of the system, so as to achieve the purposes of controlling the working frequency of the system and adjusting the working state of the system load RL.

In other words, in the bridge power supply circuit 200 shown in fig. 2, the resonant current ILr on the winding W1a of the driving transformer W1 is used to provide the transistors Q1 and Q2 with the driving current, the winding W1b of the driving transformer W1 is connected between the base and emitter of the transistor Q1, the winding W1c of the driving transformer W1 is connected between the base and emitter of the transistor Q2, and the control chip U1 may be configured to control one of the transistors Q1 and Q2 to change from the on state to the off state based on an output feedback signal FB (not shown in the figure) representing the output current or the output voltage of the bridge power supply circuit 200, and to control the other of the transistors Q1 and Q2 to change from the off state to the on state upon detecting the commutation of the resonant current ILr.

In the bridge power supply circuit 200 shown in fig. 2, when the transistor Q1/Q2 is just turned on, the on current is small, so the required driving current is small, and the control chip U1 only needs to provide a small driving current to turn on the transistor Q1/Q2. With the increase of the conduction current of the transistor Q1/Q2, the driving current required for driving the transistor Q1/Q2 in a conduction state also increases, and at this time, the driving transformer W1 can provide sufficient driving current for the transistor Q1/Q2 through the coupling current of the resonant current ILr. When the triode Q1/Q2 needs to be turned off, the control chip U1 correspondingly pulls down the base voltage of the triode Q1/Q2 to ensure that the triode Q1/Q2 is reliably turned off, and the conduction of the pair of transistors is controlled after the resonance current ILr is detected to be reversed.

Fig. 3 shows a schematic circuit diagram of the triode drive control circuit 300 in the control chip U1 shown in fig. 2. As shown in fig. 3, the transistor driving control circuit 300 includes switches S1, S2, S3, S4 and driving current limiting resistors RB1, RB2, wherein the supply voltages HVCC and VCC are respectively used for supplying power to the driving control circuits of the transistors Q1 and Q2, the switch S1 is connected between the supply voltage HVCC and the base of the transistor Q1, the switch S2 is connected between the base and the emitter of the transistor Q1, the switch S3 is connected between the supply voltage VCC and the base of the transistor Q2, and the switch S4 is connected between the base and the emitter of the transistor Q2. Here, it is assumed that each of the switches S1, S2, S3, and S4 is in a closed state when its control signal is at a high level, and is in an open state when its control signal is at a low level.

Fig. 4 shows a timing chart of a plurality of signals related to the transistor drive control circuit 300 shown in fig. 3, where ILr denotes a resonance current on the winding W1a of the drive transformer W1, HB denotes a voltage at a midpoint of a half bridge between the transistors Q1 and Q2, vbe (Q1) denotes a voltage difference between the base and emitter of the transistor Q1, ib (Q1) denotes a base current of the transistor Q1, ice (Q1) denotes an on current of the transistor Q1, vbe (Q2) denotes a voltage difference between the base and emitter of the transistor Q2, ib (Q2) denotes a base current of the transistor Q2, ice (Q2) denotes an on current of the transistor Q2, G1 (S1) denotes a control signal for controlling the closing and opening of the switch S1, G2 (S2) denotes a control signal for controlling the closing and opening of the switch S2, G3 (S3) denotes a control signal for controlling the closing and opening of the switch S3, and G4 (S4) denotes a control signal for controlling the closing and opening of the switch S4.

As can be seen from fig. 3 and 4, at time t0, the control chip U1 controls the switch S4 to change from the open state to the closed state and controls the switches S1, S2, and S3 to continue to be in the open state, at this time, the driving current provided by the driving transformer W1 is absorbed by the switch S4, and due to the existence of the electric charge stored in the transistor, until time t1, the transistor Q2 does not change from the on state to the off state, and at this time, both the base voltage and the base current of the transistor Q2 change to 0. At time t2, the voltage HB at the midpoint of the half bridge rises to the bus voltage, the freewheeling diode D1 is turned on, and the resonant current ILr flows through the freewheeling diode D1. At time t3, the control chip U1 detects that the resonant current ILr is commutated, the control switch S1 is changed from the open state to the closed state, the control switch S4 is changed from the closed state to the open state, and the control switches S2 and S3 are continuously in the open state, at which time the transistor Q1 is changed from the off state to the on state, and the driving current of the transistor Q1 is provided by at least one of the control chip U1 and the driving transformer W1. At the moment t4, the control chip U1 controls the switch S1 to be changed from the closed state to the open state and controls the switches S2, S3 and S4 to be continuously in the open state, at the moment, the driving transformer W1 continuously provides driving current for the triode Q1, and the control chip U1 does not need to provide driving current for the triode Q1 any more, so that the power consumption of the control chip U1 is reduced. In the time period from the time t5 to the time t9, the control chip U1 controls the transistor Q1 to change from the on state to the off state and controls the transistor Q2 to change from the off state to the on state after detecting the commutation of the resonant current ILr, and this control process is similar to the process of controlling the transistor Q2 to change from the on state to the off state and controlling the transistor Q1 to change from the off state to the on state in the time period from the time t0 to the time t4, and therefore, the description is omitted.

In short, the control chip U1 may be configured to control the transistor Q1 to change from the on state to the off state by controlling the switch S2 to change from the off state to the on state and controlling the switches S1, S3, and S4 to continue to be in the off state; and when detecting that the resonant current ILr commutates, the control switch S2 is changed from the closed state to the open state, the control switch S3 is changed from the open state to the closed state, and the control switches S1 and S4 are continuously in the open state, so that the control transistor Q2 is changed from the off state to the on state.

Further, the control chip U1 may be configured to control the transistor Q2 to change from the on state to the off state by controlling the switch S4 to change from the off state to the on state and controlling the switches S1, S2, and S3 to continue to be in the off state; and when detecting that the resonant current ILr commutates, the control switch S4 is changed from the closed state to the open state, the control switch S1 is changed from the open state to the closed state, and the control switches S2 and S3 are continuously in the open state, so that the control transistor Q1 is changed from the off state to the on state.

Fig. 5 shows a circuit schematic diagram of the current commutation detection circuit 500 in the control chip U1 shown in fig. 2. In the current commutation detection circuit 500 shown in fig. 5, the current source I1 is a mirror current source, which outputs a current I1 proportional to the current flowing through the switch S2 and generates a voltage V1 across the resistor R1, the voltage V1 being indicative of the current flowing through the switch S2. Fig. 6 shows a timing diagram of a plurality of signals associated with the current commutation detection circuit 500 shown in fig. 5, where ILr represents a resonant current across the winding W1a of the drive transformer W1, V1 represents a voltage across the resistor R1, G2 (S2) represents a control signal for controlling the closing and opening of the switch S2, and G3 (S3) represents a control signal for controlling the closing and opening of the switch S3.

The operation principle of the current commutation detection circuit 500 will be described with reference to fig. 5 and 6, taking the conduction control of the transistor Q2 as an example. As shown in fig. 5 and 6, when the switch S2 is in the closed state, the current flowing through the winding W1b will all flow through the switch S2, and the current flowing through the winding W1b is proportional to the resonant current ILr; when detecting that the voltage V1 across the resistor R1 is lower than the voltage threshold Vth _1, the control chip U1 may determine that the resonant current ILr is commutated, change the control switch S2 from the closed state to the open state, change the control switch S3 from the open state to the closed state, and control the switches S1 and S4 to continue to be in the open state, at which time the transistor Q2 changes from the off state to the on state. It should be noted that the conduction control of the transistor Q1 is similar to the conduction control of the transistor Q2, and therefore, the detailed description is omitted.

In other words, the control chip U1 may be configured to: during the period that the switch S2 is in a closed state and the switches S1, S3 and S4 are in an open state, generating a mirror current source I1 by mirroring the current flowing through the switch S2, and detecting whether the resonant current ILr is commutated or not by comparing the voltage generated on a resistor R1 by the current I1 output by the mirror current source I1 with a voltage threshold Vth _ 1; during the period that the switch S4 is in the closed state and the switches S1, S2, S3 are in the open state, the mirror current source I2 (not shown in the figure) is generated by mirroring the current flowing through the switch S4, and whether the resonant current ILr is commutated or not is detected by comparing the voltage V2 (not shown in the figure) generated by the current I2 output by the mirror current source I2 on the resistor R2 (not shown in the figure) with the voltage threshold Vth _2 (not shown in the figure).

Fig. 7 shows a circuit schematic of a bridge power supply circuit 700 according to another embodiment of the invention. The bridge power supply circuit 700 shown in fig. 7 differs from the bridge power supply circuit 200 shown in fig. 2 only in that the control chip U1' detects whether or not the resonant current ILr is commutated by detecting the voltage VCS across the current detection resistor RCS via the detection pin CS. It should be noted that, the contents of other aspects of the bridge power supply circuit 700 shown in fig. 7 are similar to the corresponding contents of the bridge power supply circuit 200 shown in fig. 2, and therefore are not described again.

Fig. 8 shows a circuit schematic of the current commutation detection circuit 800 in the control chip U1' shown in fig. 7. In the current commutation detection circuit 800 shown in fig. 8, when it is necessary to control the transistor Q1 from the on state to the off state and control the transistor Q2 from the off state to the on state, the control chip U1' performs the following processing: controlling the switch S2 to be changed from an open state to a closed state and controlling the switches S1, S3 and S4 to be in an off state continuously, so that the triode Q1 is changed from a conducting state to an off state; when the current detection voltage VCS is detected to be lower than a voltage threshold VCS _ TH1, the resonant current ILr is judged to be commutated, the control switch S3 is changed from an open state to a closed state, the control switch S2 is changed from the closed state to the open state, and the control switches S1 and S4 are continuously in a turn-off state, so that the triode Q2 is changed from the turn-off state to a conduction state; after the transistor Q2 is in the on state for a period of time, the switch S3 is controlled to be turned off, so that the driving transformer W1 supplies a driving current to the transistor Q2. The delay module may generate the delay signal through a delay circuit, or may generate the delay signal by determining that the current detection voltage VCS reaches a certain threshold, and the like, which is not limited herein.

Fig. 9 illustrates a timing diagram of a plurality of signals associated with the current commutation detection circuit 800 shown in fig. 8. As can be seen from fig. 9, when the current detection voltage VCS decreases to the voltage threshold VCS _ TH1, the control chip U1' determines that the resonant current ILr is commutated, the control switch S2 is changed from the closed state to the open state, the control switch S3 is changed from the open state to the closed state, and the control switches S1 and S4 are continuously in the open state, so that the transistor Q2 is changed from the off state to the on state; when the current detection voltage VCS rises to the voltage threshold VCS _ TH2, the control chip U1' determines that the resonant current ILr is commutated, the control switch S4 is changed from a closed state to an open state, the control switch S1 is changed from the open state to the closed state, and the control switches S2 and S3 are continuously in the open state, so that the triode Q1 is changed from the closed state to the conductive state.

In other words, the control chip U1' may be configured to detect whether or not the resonant current ILr commutates by comparing the current sensing voltage VCS characterizing the resonant current ILr with the voltage threshold CS _ TH1 during the time when the switch S2 is in the closed state and the switches S1, S3, and S4 are in the open state; and detects whether the resonant current ILr commutates by comparing a current sense voltage VCS characterizing the resonant current ILr with a voltage threshold CS _ TH2 during the time that the switch S4 is in a closed state and the switches S1, S2, and S3 are in an open state.

Further, as shown in fig. 8, the control chip U1' may be configured to: generating a control signal G3 for controlling the switch S3 to be turned on and off based on a first commutation characterizing signal for characterizing whether or not the resonant current ILr commutates and a control signal G2 for controlling the switch S2 to be turned on and off, wherein the switch S3 becomes an open state after being in a closed state for a predetermined time or when the current sensing voltage VCS reaches a threshold voltage VTH _ CS1 (not shown in the figure); generating a control signal G1 for controlling the switch S1 to be turned on and off based on a second commutation characterizing signal for characterizing whether or not the resonant current ILr commutates and a control signal G4 for controlling the switch S4 to be turned on and off, wherein the switch S1 becomes an open state after being in a closed state for a predetermined time or when the current sensing voltage VCS reaches a threshold voltage VTH _ CS2 (not shown in the figure); generating a control signal G2 based on the clock control signal and the control signal G3; and generating a control signal G4 based on the clock control signal and the control signal G1, wherein the clock control signal is generated based on the output feedback signal FB.

Because there is usually a certain time delay in the current commutation detection circuit 500/800 in practical application, in order to ensure that the switching tube Q1/Q2 can be reliably turned on immediately after the resonant current ILr is commutated, it can be detected that the resonant current ILr is commutated in advance by adjusting the current commutation detection thresholds Vth _1, vth _2, VCS _ TH1, VCS _ TH2, and the like. However, since the resonant current ILr is not yet commutated, the switch S2/S4 is released to pull down the transistor Q1/Q2, which may turn off, to turn on again. In order to ensure reliable switching of the transistors Q1/Q2, the overlap time of the switches S1 and S4 in the closed state and the overlap time of the switches S2 and S3 in the closed state may be increased appropriately.

Fig. 10 shows a timing diagram of a plurality of signals associated with the triode drive control circuit 300 shown in fig. 3. As can be seen from fig. 3 and 10, when the switch S4 is changed from the closed state to the open state, the driving current induced in the winding W1c flows through the switch S4. At time t0, the control chip U1/U1 'detects the zero crossing state of the resonant current ILr in advance, and at this time, the control switch S1 changes from the open state to the closed state and provides the driving current, but since the winding W1c is short-circuited by the switch S4 at this time, the current flowing out from the switch S1 is coupled via the winding of the driving transformer W1 and then flows into the switch S4, and the current flowing into the switch S4 at this time is the sum of the coupling current generated by the resonant current ILr via the driving transformer W1 and the coupling current generated by the driving current provided by the control chip U1/U1' via the driving transformer W1. At the time t1, the control chip U1/U1' controls the switch S4 to change from the closed state to the open state, at this time, the driving current provided by the control chip U1/U1' will flow to the base of the transistor Q1, at this time, the base current of the transistor Q1 is the sum of the driving current provided by the control chip U1/U1' and the coupling current generated by the resonant current ILr via the driving transformer W1, and although the coupling current of the resonant current ILr is negative, because the resonant current ILr is already low at this time, the sum of the currents is still a positive value, so that the base of the transistor Q1 is biased positively, and the base of the transistor Q2 is biased negatively, so the transistor Q2 can still maintain a reliable off state. At time t2, the resonant current ILr commutates, and the coupling current supplied to the transistor Q1 by the driving transformer W1 becomes positive, and at this time, the base current of the transistor Q1 is the sum of the driving current supplied by the control chip U1/U1' and the coupling current generated by the resonant current ILr via the driving transformer W1, so that the transistor Q1 can be reliably turned from the off state to the on state. In the time period from the time t3 to the time t5, the control chip U1/U1' controls the transistor Q1 to change from the on state to the off state and controls the transistor Q2 to change from the off state to the on state after detecting the commutation of the resonant current ILr, and the control process is similar to the process of controlling the transistor Q2 to change from the on state to the off state and controlling the transistor Q1 to change from the off state to the on state in the time period from the time t0 to the time t2, and therefore, the description is omitted.

In summary, according to the bridge power supply circuit of the embodiment of the invention, the reliability of the switching operation of the transistor is improved, the driving current provided to the transistor by the control chip for controlling the on and off of the transistor is greatly reduced, and the driving efficiency of the transistor is improved. Compared with a bridge power supply circuit adopting an MOS tube as a switch, the system cost can be greatly reduced.

The present invention may be embodied in other specific forms without departing from its spirit or essential characteristics. For example, the algorithms described in the specific embodiments may be modified without departing from the basic spirit of the invention. The present embodiments are therefore to be considered in all respects as illustrative and not restrictive, the scope of the invention being indicated by the appended claims rather than by the foregoing description, and all changes which come within the meaning and range of equivalency of the claims are therefore intended to be embraced therein.

Claims

1. A bridge power circuit comprising a first transistor, a second transistor, a driver transformer, and a transistor control circuit, wherein a resonant current on a first winding of the driver transformer is used to provide a drive current for the first transistor and the second transistor, a second winding of the driver transformer is connected between a base and an emitter of the first transistor, a third winding of the driver transformer is connected between a base and an emitter of the second transistor, the transistor control circuit configured to:

controlling one of the first transistor and the second transistor to change from an on state to an off state based on an output feedback signal indicative of an output current or an output voltage of the bridge power supply circuit; and

and when the resonant current is detected to be commutated, controlling the other one of the first triode and the second triode to be changed from an off state to a conducting state.

2. The bridge power supply circuit of claim 1, wherein the transistor control circuit comprises a first switch connected between a first supply voltage of the transistor control circuit and a base of the first transistor, a second switch connected between the base and an emitter of the first transistor, a third switch connected between a second supply voltage of the transistor control circuit and a base of the second transistor, and a fourth switch connected between the base and an emitter of the second transistor, the transistor control circuit configured to:

controlling the first triode to be changed from a conducting state to a switching-off state by controlling the second switch to be changed from a switching-off state and controlling the first switch, the third switch and the fourth switch to be continuously in a switching-off state; and

when the resonant current is detected to be commutated, the second triode is controlled to be changed from the off state to the on state by controlling the second switch to be changed from the on state to the off state, the third switch is controlled to be changed from the off state to the on state, and the first switch and the fourth switch are controlled to be continuously in the off state, so that the second triode is controlled to be changed from the off state to the on state.

3. The bridge power supply circuit of claim 2, wherein the triode control circuit is further configured to:

controlling the second triode to be changed from a conducting state to a disconnecting state by controlling the fourth switch to be changed from a disconnecting state to a closing state and controlling the first switch, the second switch and the third switch to be continuously in a disconnecting state; and

when the resonant current is detected to be commutated, the fourth switch is controlled to be changed from a closed state to an open state, the first switch is controlled to be changed from the open state to the closed state, the second switch and the third switch are controlled to be continuously in the open state, and the first triode is controlled to be changed from the off state to the conducting state.

4. A bridge power supply circuit as claimed in claim 3, wherein there is an overlap between the duration of the fourth switch being in the closed state and the duration of the first switch being in the closed state, and there is an overlap between the duration of the third switch being in the closed state and the duration of the second switch being in the closed state.

5. The bridge power supply circuit of claim 2, wherein the triode control circuit is further configured to, during a time when the second switch is in a closed state and the first, third, and fourth switches are in an open state:

generating a first mirrored current source by mirroring the current flowing through the second switch;

whether the resonant current is commutated or not is detected by comparing a first voltage generated on a first resistor by a first current output by the first mirror current source with a first voltage threshold value.

6. The bridge power supply circuit of claim 2, wherein the triode control circuit is further configured to, during a period when the fourth switch is in a closed state and the first, second, and third switches are in an open state:

generating a second mirrored current source by mirroring the current flowing through the fourth switch;

and detecting whether the resonant current is commutated or not by comparing a second voltage generated on a second resistor by a second current output by the second mirror current source with a second voltage threshold value.

7. The bridge power supply circuit of claim 2, wherein the triode control circuit is further configured to, during the second switch being in a closed state and the first, third, and fourth switches being in an open state:

detecting whether the resonant current commutates by comparing a current sense voltage characterizing the resonant current with a third voltage threshold.

8. The bridge power supply circuit of claim 2, wherein the triode control circuit is further configured to, during a period when the fourth switch is in a closed state and the first, second, and third switches are in an open state:

detecting whether the resonant current commutates by comparing a current sense voltage characterizing the resonant current with a fourth voltage threshold.

9. The bridge power supply circuit of claim 7, wherein the triode control circuit is further configured to:

generating a third control signal for controlling the on and off of the third switch based on a first commutation characterization signal characterizing whether or not the resonant current commutates and a second control signal for controlling the on and off of the second switch, wherein

The third switch becomes an open state after being in a closed state for a predetermined time or when the current sensing voltage reaches a fifth threshold voltage.

10. The bridge power supply circuit of claim 7, wherein the triode control circuit is further configured to:

generating a first control signal for controlling the on and off of the first switch based on a second commutation characterization signal characterizing whether or not the resonant current commutates and a fourth control signal for controlling the on and off of the fourth switch, wherein

The first switch becomes an open state after being in a closed state for a predetermined time or when the current sensing voltage reaches a sixth threshold voltage.

11. The bridge power supply circuit of claim 9, wherein the triode control circuit is further configured to:

generating the second control signal based on a clock control signal and the third control signal, wherein the clock control signal is generated based on the output feedback signal.

12. The bridge power supply circuit of claim 10, wherein the triode control circuit is further configured to:

generating the fourth control signal based on a clock control signal and the first control signal, wherein the clock control signal is generated based on the output feedback signal.