TWI523392B - Resonant converter and controlling method thereof - Google Patents

Description

Resonant converter and control method thereof

The present invention relates to a power conversion technique, and more particularly to a resonant converter and a control method therefor.

The development trend of DC converters is like most power supply products, and it is developing towards high efficiency, high power density, high reliability and low cost. Resonant converters (such as LLC resonant converters) have zero-voltage switching (ZVS) on the primary side and zero-current switching on the secondary side rectified diodes in the full load range (zero- Current switching, ZCS), etc., have been increasingly applied to DC converters in recent years.

Overcurrent protection is a relatively critical issue in the circuit design of resonant converters. In general, the resonant circuit generates a large resonant current in the event of an overload or load short circuit. If the resonant current is not limited and protected, the resonant converter is likely to fail due to excessive current.

In the current application, a feasible way to implement the overcurrent protection mechanism is A clamp circuit is added to the resonant converter to achieve current limiting by clamping the voltage across the resonant capacitor to the input voltage. The above method is simple and easy, and the cycle-by-cycle current limiting can be realized without adding an additional control circuit, which is passive control. Furthermore, the resonant converter using the above-described overcurrent protection mechanism only needs to add a plurality of diodes as a clamped diode in the circuit, and a resonant structure is used to design the resonant circuit.

However, in the resonant converter employing the above-described overcurrent protection mechanism, since the voltage across the resonant capacitor is clamped based on the input voltage, the voltage across the resonant capacitor changes as the input voltage changes, and the resonant capacitor The maximum voltage across is only the input voltage. As a result, the design of the resonant circuit is limited, and the operating range of the resonant circuit is also affected.

In addition, when the resonant converter enters the hold up time, since the voltage across the resonant capacitor is limited by the clamped diode, the stored energy of the resonant circuit is reduced, which will result in a decrease in the maximum gain of the output voltage. As a result, designers need to match larger capacitors to meet the retention time requirements, which will cause problems such as increased size and cost of the resonant converter.

The present invention provides a resonant converter, a switching power supply that allows the voltage across the resonant capacitor to be unrestricted by the clamping circuit under normal operating conditions.

The resonant converter of the present invention is adapted to provide a drive voltage to the load. The resonant converter includes a bridge switching circuit, a resonant and voltage converting circuit, and a rectifying and filtering circuit And overcurrent protection circuit. The bridge switch circuit has a power supply terminal, wherein the bridge switch circuit receives a DC input voltage via a power supply terminal. The resonant and voltage transformer circuit is coupled to the bridge switch circuit and has at least one resonant capacitor, wherein the resonant capacitor reacts to the switching of the bridge switch circuit to charge and discharge energy. The rectifying and filtering circuit is coupled to the resonant and transforming circuit for rectifying and filtering the output of the resonant and transforming circuit, and generating a driving voltage accordingly. An overcurrent protection circuit is coupled to the power supply terminal and across the ends of the resonant capacitor to form a clamp path. The overcurrent protection circuit is configured to detect a current flowing through the resonant and voltage converting circuit or the load to determine whether to turn on the clamping path to clamp the resonant capacitor across the first voltage range according to the detected result.

In an embodiment of the invention, when the overcurrent protection circuit detects that the current flowing through the resonant and transformer circuit or the load is greater than or equal to a predetermined current value, the overcurrent protection circuit turns on the clamp path to at least one resonance. The capacitor is clamped across the first voltage range, and when the overcurrent protection circuit detects that the current flowing through the resonant and transformer circuit or the load is less than the preset current value, the overcurrent protection circuit cuts off the clamp path to at least The voltage across a resonant capacitor is not limited to the first voltage range. Wherein, the upper limit of the first voltage range is a DC input voltage.

In an embodiment of the invention, the overcurrent protection circuit includes a clamp circuit, an overcurrent determination circuit, and a clamp switch circuit. Clamp circuit, coupled to the power supply terminal. The overcurrent determining circuit is configured to detect a current flowing through the resonant and voltage converting circuit or the load, and generate an overcurrent determining signal accordingly. The clamp switch circuit is coupled between the clamp circuit and the at least one resonant capacitor, and is controlled to be turned on or off by the overcurrent determination signal. Wherein, the clamp path is formed via a clamp switch circuit.

In an embodiment of the invention, the rectifying and filtering circuit includes first to fourth diodes. The cathode end of the first diode is coupled to the cathode end of the third diode, the anode end of the first diode is coupled to the cathode end of the second diode, and the anode end of the second diode is coupled to the fourth terminal The anode end of the diode and the anode end of the third diode are coupled to the cathode end of the fourth diode. The filter capacitor has a first end coupled to the cathode ends of the first and third diodes and one end of the load, and a second end coupled to the anode ends of the second and fourth diodes and the other end of the load.

In an embodiment of the invention, the bridge switch circuit includes a first switch transistor and a second switch transistor. The first switching transistor has a first end of the power supply end and a control end receiving a first control signal. The second switch transistor has a first end coupled to the second end of the first switch transistor, a second end coupled to the ground end, and a control end receiving a second control signal.

In an embodiment of the invention, the resonant and transforming circuit includes a first resonant capacitor, a first resonant inductor, and a transformer. The first resonant capacitor has a first end coupled to the ground. The first resonant inductor has a first end coupled to the second end of the first switching transistor and the first end of the second switching transistor. The transformer has a primary side winding and a secondary side winding, the same end of the primary side winding is coupled to the second end of the first resonant inductor, and the different end of the primary side winding is coupled to the second end of the first resonant capacitor, The same-name end of the secondary winding is coupled to the anode end of the first diode and the cathode end of the second diode, and the opposite end of the secondary winding is coupled to the anode end and the fourth diode of the third diode The cathode end.

In an embodiment of the invention, the clamping circuit includes a first clamping diode and a second clamping diode. a first clamp diode having a cathode end coupled to the first switch The first end of the crystal. The second clamp diode has an anode end coupled to the ground end and a cathode end coupled to the anode end of the first clamp diode.

In an embodiment of the invention, the clamp switch circuit includes a switch. The switch has a first end coupled to the anode end of the first clamp diode and a cathode end of the second clamp diode, and a second end coupled to the second end of the first resonant capacitor and a different name of the primary winding And the control end is coupled to the overcurrent determination circuit.

In an embodiment of the invention, the resonant and transforming circuit includes a first resonant capacitor, a second resonant capacitor, a first resonant inductor, and a transformer. The first resonant capacitor has a first end coupled to the ground. The second resonant capacitor has a first end coupled to the second end of the first resonant capacitor and a second end coupled to the first end of the first switching transistor. The first resonant inductor has a first end coupled to the second end of the first switching transistor and the first end of the second switching transistor. The transformer has a primary side winding and a secondary side winding, and the same end of the primary side winding is coupled to the second end of the first resonant inductor, and the different end of the primary side winding is coupled to the second end of the first resonant capacitor a first end of the second resonant capacitor, the same end of the secondary winding is coupled to the anode end of the first diode and the cathode end of the second diode, and the different end of the secondary winding is coupled to the third diode The anode end and the cathode end of the fourth diode.

In an embodiment of the invention, the clamping circuit includes a first clamping diode and a second clamping diode. The first clamping diode has a cathode end coupled to the first end of the first switching transistor and the first end of the first resonant capacitor. The second clamp diode has an anode end coupled to the ground end and a cathode end coupled to the anode end of the first clamp diode.

In an embodiment of the invention, the clamp switch circuit includes a switch. switch, The first end is coupled to the anode end of the first clamp diode and the cathode end of the second clamp diode, and the second end is coupled to the second end of the first resonant capacitor and the first end of the second resonant capacitor And the control end is coupled to the overcurrent determination circuit.

In an embodiment of the invention, the resonant and voltage transformer circuit includes a first capacitor, a second capacitor, a first resonant capacitor, a first resonant inductor, and a first transformer. The first capacitor has a first end coupled to the first end of the first switching transistor. The second capacitor has a first end coupled to the second end of the first capacitor and a second end coupled to the ground end. The first resonant capacitor has a first end coupled to the second end of the first switching transistor and the first end of the second switching transistor. The first resonant inductor has a first end coupled to the second end of the first resonant capacitor. The first transformer has a primary side winding and a secondary side winding, and the same end of the primary side winding is coupled to the second end of the first resonant inductor, and the different end of the primary side winding is coupled to the second end of the first capacitor The first end of the second capacitor, the same end of the secondary winding is coupled to the anode end of the first diode and the cathode end of the second diode, and the different end of the secondary winding is coupled to the third diode The anode end and the cathode end of the fourth diode.

In an embodiment of the invention, the clamping circuit includes a second transformer, a first clamping diode, and a second clamping diode. The second transformer has a primary side winding and a secondary side winding, and the same end of the primary side winding is coupled to the first end of the first resonant capacitor, and the different end of the primary side winding is coupled to the first resonant capacitor Two ends. The first clamp diode has an anode end coupled to the same name end of the secondary winding of the second transformer. The second clamp diode has an anode end coupled to the opposite end of the secondary winding of the second transformer, and a cathode end coupled to the cathode end of the first clamp diode.

In an embodiment of the invention, the clamp switch circuit includes a switch. switch, The first end is coupled to the cathode ends of the first and second clamp diodes, the second end of which is coupled to the first end of the filter capacitor, and the control end is coupled to the overcurrent determination circuit.

In an embodiment of the invention, the bridge switch circuit includes a first switch transistor, a second switch transistor, a third switch transistor, and a fourth switch transistor. The first switching transistor has a first end of the power supply end and a control end receiving a first control signal. The second switch transistor has a first end coupled to the second end of the first switch transistor, a second end coupled to the ground end, and a control end receiving a second control signal. The third switch transistor has a first end coupled to the first end of the first switch transistor and a control end receiving a third control signal. The fourth switch transistor has a first end coupled to the second end of the third switch transistor, a second end coupled to the ground end, and a control end receiving a fourth control signal.

In an embodiment of the invention, the resonant and transforming circuit includes a first resonant capacitor, a first resonant inductor, a second resonant inductor, and a transformer. The first resonant inductor has a first end coupled to the second end of the first switching transistor and the first end of the second switching transistor. The second resonant inductor has a first end coupled to the second end of the third switching transistor and the first end of the fourth switching transistor. The transformer has a first primary side winding, a second primary side winding and a secondary side winding. The same end of the first primary side winding is coupled to the first end of the first resonant capacitor, the first primary side The different end of the winding is coupled to the second end of the first resonant inductor, the same end of the second primary winding is coupled to the second end of the second resonant inductor, and the different end of the second primary winding is coupled to the first resonant capacitor The second end of the second side winding is coupled to the anode end of the first diode and the cathode end of the second diode, and the different end of the secondary winding is coupled to the anode end of the third diode With the fourth pole The cathode end of the body.

In an embodiment of the invention, the clamping circuit includes a first clamping diode, a second clamping diode, a third clamping diode, and a fourth clamping diode. The first clamp diode has a cathode end coupled to the first end of the first switching transistor. The second clamp diode has an anode end coupled to the ground end and a cathode end coupled to the anode end of the first clamp diode. The third clamp diode has a cathode end coupled to the cathode end of the first clamp diode. The fourth clamp diode has an anode end coupled to the ground end and a cathode end coupled to the anode end of the third clamp diode.

In an embodiment of the invention, the clamp switch circuit includes a first switch and a second switch. a first switch having a first end coupled to the anode end of the first clamp diode and a cathode end of the second clamp diode, the second end coupled to the first end of the first resonant capacitor, and controlling The end is coupled to the overcurrent determination circuit. a second switch having a first end coupled to the anode end of the third clamp diode and a cathode end of the fourth clamp diode, the second end coupled to the second end of the first resonant capacitor, and controlling The end is coupled to the overcurrent determination circuit.

The control method of the resonant converter of the present invention comprises the steps of: controlling switching of the bridge switching circuit, wherein the bridge switching circuit receives the DC input voltage via a power supply terminal; and reacting at least one resonant capacitor to the switching of the bridge switching circuit Charging and discharging energy; rectifying and filtering the output of the resonant and voltage converting circuit by a rectifying and filtering circuit, and generating a driving voltage to drive a load; detecting a current flowing through the resonant and transformer circuit or the load; The result of the measurement determines whether the clamp path is turned on to clamp the voltage across the at least one resonant capacitor to a first voltage range.

In an embodiment of the invention, determining whether to turn on the forceps according to the result of the detection The bit path to clamp the cross-voltage of the at least one resonant capacitor to a first voltage range includes the steps of: determining whether a current flowing through the resonant and transformer circuit or the load is greater than or equal to a predetermined current value; The current of the voltage circuit or the load is determined to be greater than or equal to the preset current value, and the overcurrent protection circuit is turned on the clamp path to clamp the cross voltage of the at least one resonant capacitor to the first voltage range; and if the resonant and the voltage are passed through The current of the circuit or the load is determined to be less than the preset current value, and the overcurrent protection circuit cuts off the clamp path so that the voltage across the at least one resonant capacitor is not limited to the first voltage range, wherein the upper limit of the first voltage range is DC input voltage.

Based on the above, an embodiment of the present invention provides a control method for a resonant converter. The resonant converter can determine whether an overcurrent phenomenon occurs in the load by detecting the current of the primary side or the load. Wherein, the resonant converter turns on the clamp path to provide overcurrent protection when the load is overcurrent, and cuts off the clamp path when the load does not have an overcurrent phenomenon so that the resonant capacitor is not limited by the DC input voltage. . Therefore, the resonant converter does not need to be additionally limited in the design of the circuit parameters and the working range, thereby reducing the difficulty and cost of the overall circuit design.

The above described features and advantages of the invention will be apparent from the following description.

10‧‧‧ load

100, 200, 300, 400, 500‧‧‧ resonant converter

110, 210, 310, 410, 510‧‧ ‧ bridge switch circuit

120, 220, 320, 420, 520‧‧‧ resonant and transformer circuits

130, 230, 330, 430, 530‧ ‧ rectification filter circuit

140, 240, 340, 440, 540‧‧‧ overcurrent protection circuit

142, 242, 342, 442, 542‧‧ ‧ clamp circuit

144, 244, 344, 444, 544‧‧‧ overcurrent judgment circuit

146, 246, 346, 446, 546‧‧‧ clamp switch circuit

AG‧‧‧ and gate

CP‧‧‧ clamp path

C1, C2, Co‧‧‧ capacitors

Cr, Cr1, Cr2‧‧‧ resonant capacitor

D1~D4‧‧‧Clamping diode

Ds1~Ds4‧‧‧ Diode

DC‧‧‧ drive circuit

GND‧‧‧ ground terminal

I1, Io‧‧‧ current

J‧‧‧ Relay

Lr1, Lr2‧‧‧ resonant inductor

N1‧‧‧ power terminal

NP, NP1, NP2, NP'‧‧‧ primary winding

NS, NS’‧‧‧ secondary winding

P1, P2‧‧‧ nodes

Q, Q1~Q4‧‧‧Switching transistor

Rr, Rre‧‧‧ resistance

S1~S4‧‧‧ control signal

S810~S850‧‧‧Steps

S_ocd‧‧‧Overcurrent judgment signal

T1, T2, T1'‧‧‧ transformer

VCC‧‧‧Power supply voltage

VI‧‧‧Detection voltage

VREF‧‧‧reference voltage

Vcr‧‧‧ voltage

Vd‧‧‧ drive voltage

Vin‧‧‧DC input voltage

1 is a functional block diagram of a resonant converter according to an embodiment of the present invention.

2 to 5 are circuit diagrams of a resonant converter according to various embodiments of the present invention.

FIG. 6 is a functional block diagram of an overcurrent determination circuit according to an embodiment of the present invention.

FIG. 7 is a circuit diagram of an overcurrent determination circuit in accordance with the embodiment of FIG. 6. FIG.

FIG. 8 is a flow chart showing the steps of a method for controlling a resonant converter according to an embodiment of the present invention.

Embodiments of the present invention provide a control method for a resonant converter. The resonant converter can determine whether an overcurrent phenomenon occurs in the load by detecting the current of the primary side or the load. Wherein, the resonant converter turns on the clamp path to provide overcurrent protection when the load is overcurrent, and cuts off the clamp path when the load does not have an overcurrent phenomenon so that the resonant capacitor is not limited by the DC input voltage. . Therefore, the resonant converter does not need to be additionally limited in the design of the circuit parameters and the working range, thereby reducing the difficulty and cost of the overall circuit design. In order to make the disclosure of the present disclosure easier to understand, the following specific embodiments are examples that can be implemented by the present disclosure. In addition, wherever possible, the same elements, components, and steps in the drawings and embodiments are used to represent the same or similar components.

1 is a functional block diagram of a resonant converter according to an embodiment of the present invention. In the present embodiment, the resonant converter 100 is adapted to DC-DC convert the DC input voltage Vin and accordingly drive the voltage Vd to drive the load 10. Referring to FIG. 1 , the resonant converter 100 includes a bridge switching circuit 110 , a resonant and transforming circuit 120 , a rectifying and filtering circuit 130 , and an overcurrent protection circuit 140 .

The bridge switch circuit 110 has a power terminal N1, wherein the bridge switch circuit 110 The DC input voltage Vin is received via the power terminal N1. In this embodiment, the bridge switch circuit 110 can be, for example, an asymmetric half-bridge switch circuit, a symmetric half-bridge switch circuit, or a full-bridge switch circuit. The present invention is not limited thereto (the embodiments described later will further explain various differences). An embodiment of a type of bridge switch circuit 110).

The resonant and voltage transformer circuit 120 is coupled to the bridge switch circuit 110, wherein the resonant and transforming circuit 120 can have one or more resonant capacitors Cr based on the type of the corresponding resonant converter 100. More specifically, the resonant and transformer circuit 120 further includes a resonant inductor and a transformer (not shown, the embodiments described later will be further described according to different resonant converter implementations), wherein the resonant capacitor Cr will be combined with the resonant inductor. The resonant tank is charged or discharged in response to switching of the bridge switching circuit 110, so that the transformer of the subsequent stage boosts or steps down the output of the resonant tank.

The rectifying and filtering circuit 130 is coupled to the resonant and transforming circuit 120 for rectifying and filtering the output of the resonant and transforming circuit 120, and accordingly generating a driving voltage Vd. In this embodiment, the rectifying function portion of the rectifying and filtering circuit 130 can be implemented by using a bridge rectifier (not shown), and the filtering function portion can be implemented by using a filtering capacitor (not shown) connected to the load 10. However, the invention is not limited thereto.

The overcurrent protection circuit 140 is coupled to the power supply terminal N1 and across the two ends of the resonant capacitor Cr to form a clamp path CP. In this embodiment, the overcurrent protection circuit 140 can be configured to detect the current flowing through the resonant and transforming circuit 130 or the load 10, and determine whether to turn on the clamp path CP to convert the resonant capacitor Cr according to the result of the detection. The voltage across the voltage Vcr is clamped to the first voltage range.

In detail, when the overcurrent protection circuit 140 detects the flow through the resonance and the transformation When the current of the circuit 120 or the load 10 is greater than or equal to a predetermined current value, it will judge that the load 10 has an overcurrent phenomenon (that is, a phenomenon that the load current is too high due to a short circuit of the load 10 or other unintended state). At this time, the overcurrent protection circuit 140 turns on the clamp path CP, so that the overcurrent protection circuit 140 clamps the voltage across the voltage Vcr of the resonant capacitor Cr within a voltage range lower than the DC input voltage Vin (ie, the upper limit of the voltage range) The value is the DC input voltage Vin), thereby limiting the amount of current flowing through the load 10.

On the other hand, when the overcurrent protection circuit 140 detects that the current flowing through the resonance and voltage transformation circuit 120 or the load 10 is less than the preset current value, it will judge that the load 10 has not experienced an overcurrent phenomenon. At this time, the overcurrent protection circuit 140 turns off the clamp path CP so that the voltage across the voltage Vcr of the resonant capacitor Cr is not limited by the overcurrent protection circuit 140, but must be within a voltage range lower than the DC input voltage Vin. In other words, in the case where the overcurrent phenomenon does not occur in the load 10, the voltage across the resonant capacitor Cr Vcr may be greater than the direct current input voltage Vin.

In more detail, the overcurrent protection circuit 140 includes a clamp circuit 142, an overcurrent determination circuit 144, and a clamp switch circuit 146. The clamp circuit 142 is coupled to the power terminal N1. The overcurrent determining circuit 144 is configured to detect a current flowing through the resonant and voltage converting circuit or the load, and generate an overcurrent determining signal S_ocd accordingly. The clamp switch circuit 146 is coupled between the clamp circuit 142 and the resonant capacitor Cr, and is controlled to be turned on or off by the overcurrent determination signal S_ocd.

In the present embodiment, the clamp path CP is formed via the clamp switch circuit 146. Therefore, when the clamp switch circuit 146 is turned on in response to the overcurrent determination signal S_ocd, the clamp path CP is simultaneously turned on, and the clamp circuit 142 can be based on the straight The input voltage Vin is flowed to limit the magnitude of the voltage Vcr. Conversely, when the clamp switch circuit 146 is turned off in response to the overcurrent determination signal S_ocd, the clamp path CP is simultaneously turned off, and the voltage Vcr is not limited by the clamp circuit 142.

In other words, under the architecture of the resonant converter 100 of the embodiment of FIG. 1, when the overcurrent determining circuit 144 determines that an overcurrent phenomenon occurs on the secondary side of the resonant converter 100, the overcurrent protection circuit 140 can pass through the clamp circuit 142 and the clamp. The bit switching circuit 144 cooperates to clamp the voltage across the voltage Vcr of the resonant capacitor Cr to the input DC voltage Vin, thereby achieving the effect of suppressing the primary side switching current stress. Conversely, when the overcurrent determination circuit 144 determines that the resonant converter 100 is operating normally, the overcurrent protection circuit 140 can cut off the clamp path CP by cutting off the clamp switch circuit 144, so that the crossover voltage Vcr of the resonant capacitor Cr does not It is limited by the clamp circuit 142.

Therefore, compared with the conventional resonant converter with overcurrent protection mechanism, the designer does not need to additionally consider the DC input voltage Vin for resonance when designing the design parameters and working range of the resonant converter 100 of the present embodiment. The limitation and influence of the capacitor Cr can make the design parameters and the working range of the resonant converter 100 of the embodiment have more design choices, thereby reducing the difficulty of design.

In order to more clearly illustrate the embodiments of the present invention, the specific circuit architecture of the resonant converter of the embodiment of the present invention in different embodiments will be described below with reference to FIG. 2 to FIG. 2 is a schematic circuit diagram of an asymmetric half-bridge resonant converter, FIG. 3 and FIG. 4 are circuit diagrams of a symmetric half-bridge resonant converter, and FIG. 5 is a schematic circuit diagram of a full-bridge resonant converter. Here, in the embodiment of FIG. 2 to FIG. 5, the switching transistors (eg, Q1 to Q4) in the bridge switching circuit are all N-type power transistors. (N-type power transistor) is an example of implementation, but the invention is not limited thereto.

Referring first to FIG. 2, the resonant converter 200 includes a bridge switching circuit 210, a resonant and transforming circuit 220, a rectifying and filtering circuit 230, and an overcurrent protection circuit 240. In the present embodiment, the bridge switch circuit 210 includes switching transistors Q1 and Q2. The resonant and transforming circuit 220 includes a first resonant capacitor Cr1, a first resonant inductor Lr1, and a transformer T1. The rectifying and filtering circuit 230 includes diodes Ds1 to Ds4 and a filter capacitor Co. The overcurrent protection circuit 240 includes a clamp circuit 242 composed of clamp diodes D1 and D2, an overcurrent determination circuit 244, and a clamp switch circuit 246 composed of a switch SW1.

In the bridge switch circuit 210, the 汲 of the switching transistor Q1 receives the power supply terminal of the DC input voltage Vin, and the source of the switching transistor Q1 is coupled to the drain of the switching transistor Q2. The source of the switching transistor Q2 is coupled to the ground GND. The gates of the switching transistors Q1 and Q2 receive the control signals S1 and S2, respectively, wherein the control signals S1 and S2 are respectively signals having a pulse width modulation. In this architecture, the switching transistors Q1 and Q2 are turned on or off in response to the control signals S1 and S2, respectively, so that the DC input voltage Vin is supplied to the resonant and transforming circuit 220 by switching.

In the resonant and voltage converting circuit 220, the first end of the first resonant capacitor Cr1 is coupled to the ground GND. The first end of the first resonant inductor Lr1 is coupled to the source of the switching transistor Q1 and the drain of the switching transistor Q2. The transformer T1 has a primary winding NP and a secondary winding NS. The common-polarity terminal (the dot-end end) of the primary winding NP The second end of the first resonant capacitor L1 is coupled to the second end of the first resonant capacitor Cr1. The opposite end of the primary winding NP is coupled to the second end of the first resonant capacitor Cr1.

In the rectifying and filtering circuit 230, the cathode end and the anode end of the diode Ds1 are respectively coupled to the cathode end of the diode Ds3 and the cathode end of the diode Ds2, and the anode end of the diode Ds2 is coupled to the diode Ds4. The anode end, and the anode end of the diode Ds3 is coupled to the cathode end of the diode Ds4, wherein the anode end of the diode Ds1 and the cathode end of the diode Ds2 are commonly coupled to the secondary winding NS of the transformer T1 The same end, and the anode end of the diode Ds3 and the cathode end of the diode Ds4 are commonly coupled to the different end of the secondary winding NS of the transformer T1. The first end of the filter capacitor Co is coupled to the cathode ends of the diodes Ds1 and Ds3 and coupled to one end of the load 10, and the second end of the filter capacitor Co is coupled to the anode ends of the diodes Ds2 and Ds4 and coupled to The other end of the load 10.

It should be noted that, in this embodiment, the rectifying and filtering circuit 230 uses a full-bridge rectifier composed of diodes Ds1 to Ds4 as an implementation example, but the present invention is not limited thereto. . In other embodiments, the rectifying and filtering circuit 230 can also use a synchronous rectifier (SR) composed of a power transistor to separately replace the diodes Ds1 to Ds4, thereby forming a self-excited or excited synchronization. Rectifier circuit). Everything depends on the actual design/application needs.

In the overcurrent protection circuit 240, the cathode end of the clamp diode D1 is coupled to the drain of the switching transistor Q1 (ie, the power supply terminal N1). Anode end coupling of clamp diode D2 Connected to the ground GND, and the cathode end of the clamp diode D2 is coupled to the anode terminal of the clamp diode D1. The overcurrent determining circuit 244 detects the current I1 flowing through the primary winding NP of the transformer T1, and accordingly generates an overcurrent determining signal S_ocd. The first end of the switch SW1 is coupled to the anode end of the clamp diode D1 and the cathode end of the clamp diode D2. The second end of the switch SW1 is coupled to the second end of the first resonant capacitor Cr1 and the transformer T1. The control terminal of the switch SW1 is coupled to the overcurrent determination circuit 244 to receive the overcurrent determination signal S_ocd.

It should be noted that in the present embodiment, the overcurrent determining circuit 244 is configured to detect the primary current of the resonant converter 200 (ie, the current I1 flowing through the primary winding NP) as a determination of whether the load 10 is The basis of the overcurrent phenomenon occurs, but the present invention is not limited to this. In other embodiments, the overcurrent determination circuit 244 can also determine whether the load 10 has an overcurrent phenomenon by the secondary current of the resonant converter 200 (ie, the current Io flowing through the load 10).

In detail, in the case where the resonant converter 200 operates normally (ie, the overcurrent phenomenon occurs in the load 10), the switch SW1 is turned off in response to the overcurrent determining signal S_ocd, so that the clamp path CP formed via the switch SW1 is also Cut off accordingly. At this time, the voltage across the first resonant capacitor Cr1 is not limited by the clamped diodes D1 and D2. That is, in this state, the first resonance capacitor Cr1 can be charged to a voltage level exceeding the DC input voltage Vin. On the other hand, in the case where the overcurrent phenomenon occurs in the load 10, the switch SW1 is turned on in response to the overcurrent determination signal S_ocd, so that the clamp path CP formed via the switch SW1 is also turned on accordingly. At this time, the voltage across the first resonant capacitor Cr1 is limited by the clamped diodes D1 and D2. also That is, in this state, the maximum voltage across the first resonant capacitor Cr1 is limited to the voltage level of the DC input voltage Vin.

Compared with the conventional resonant converter which only uses the clamp circuit for overcurrent protection, since the resonant converter 200 operates normally, the voltage across the first resonant capacitor Cr1 is not clamped by the diode. D1 and D2 are limited, so the designer does not need to additionally consider the influence of the DC input voltage Vin on the first resonant capacitor Cr1 when designing the resonant circuit. In addition, since the voltage across the first resonant capacitor Cr1 is not limited by the clamped diodes D1 and D2, the energy stored in the overall resonant circuit is not reduced, so the designer does not need to specifically match the larger capacitor. It can meet the retention time requirements.

Referring to FIG. 3, the resonant converter 300 of the present embodiment is different from the resonant converter 200 of the foregoing embodiment of FIG. 2 in that the resonant converter 300 of the present embodiment has a circuit configuration of a symmetric half bridge. The resonant converter 300 includes a bridge switching circuit 310, a resonant and transforming circuit 320, a rectifying and filtering circuit 330, and an overcurrent protection circuit 340, wherein the architecture and configuration of the bridge switching circuit 310, the rectifying and filtering circuit 330, and the overcurrent protection circuit 340 The embodiment is substantially the same as the embodiment of FIG. 2, and therefore, the description of the embodiment of FIG. 2 is repeated, and details are not described herein again. The differences between the embodiments will be further explained below.

In this embodiment, the resonant and voltage converting circuit 320 further includes a second resonant capacitor Cr2, wherein the second resonant capacitor Cr2 is coupled between the power terminal N1 and the second end of the first resonant capacitor Cr1 to form a symmetric half bridge. Circuit configuration. Based on this circuit configuration, the overcurrent protection circuit 340 can also detect the primary side winding through the transformer T1. The current I1 of the resistance NP (but not limited to this) is used to determine whether or not the overcurrent phenomenon occurs in the load 10, and it is determined whether or not the switch SW1 is turned on to limit the voltage across the first resonance capacitor Cr1 and the second resonance capacitor Cr2.

Referring to FIG. 4, the resonant converter 400 of the present embodiment is another possible implementation of a symmetric half-bridge resonant converter. The resonant converter 400 includes a bridge switching circuit 410, a resonant and transforming circuit 420, a rectifying and filtering circuit 430, and an overcurrent protection circuit 440. The architecture and configuration of the bridge switching circuit 410 and the rectifying and filtering circuit 430 are substantially implemented in the foregoing FIG. For the same example, please refer to the description of the foregoing embodiment of FIG. 2, and details are not described herein again. The differences between the embodiments will be further explained below.

In the present embodiment, the resonant and transforming circuit 420 includes a first resonant capacitor Cr1, a first capacitor C1, a second capacitor C2, a first resonant inductor Lr1, and a transformer T1. The overcurrent protection circuit 440 includes a clamp circuit 442 composed of clamp diodes D1 and D2 and a transformer T2, an overcurrent determination circuit 444, and a clamp switch circuit 446 composed of a switch SW1.

In the resonant and voltage converting circuit 420, the first end of the first capacitor C1 is coupled to the drain of the switching transistor Q1 (ie, the power terminal N1). The first end of the second capacitor C2 is coupled to the second end of the first capacitor C1, and the second end of the second capacitor C2 is coupled to the ground GND. The first end of the first resonant capacitor Cr1 is coupled to the source of the switching transistor Q1 and the drain of the switching transistor Q2. The first end of the first resonant inductor Lr1 is coupled to the second end of the first resonant capacitor Cr1. The same end of the primary winding NP of the transformer T1 is coupled to the second end of the first resonant inductor Lr1, and the different end of the primary winding NP is coupled to the second end of the first capacitor C1 and the first end of the second capacitor C2. Secondary winding of transformer T1 The same-named end and the different-named end of the NS are respectively coupled to the anode ends of the diodes Ds1 and Ds3 of the rectifying and filtering circuit 430.

In the overcurrent protection circuit 440, the same-name end and the different-name end of the primary winding NP' of the transformer T2 are respectively coupled to both ends of the first resonant capacitor Cr1. The anode end of the clamp diode D1 is coupled to the terminal of the same name of the secondary winding NS' of the transformer T2. The anode end of the clamp diode D2 is coupled to the opposite end of the secondary winding NS' of the transformer T2, and the cathode ends of the clamp diodes D1 and D2 are coupled to each other. The overcurrent protection circuit 444 detects the current Io flowing through the load 10 and accordingly generates an overcurrent determination signal S_ocd. The first end of the switch SW1 is coupled to the cathode end of the clamp diodes D1 and D2, and the second end of the switch SW1 is coupled to the first end of the filter capacitor Co of the rectification filter circuit 430, and the control end of the switch SW1 is coupled The stream judging circuit 444 receives the overcurrent judging signal S_ocd.

Based on the circuit configuration, the overcurrent protection circuit 440 determines whether the load 10 has an overcurrent phenomenon by detecting the current Io flowing through the load 10 (but not limited thereto), and determines whether to turn on the switch SW1 to limit the current. The voltage across the first resonant capacitor Cr1.

Referring to FIG. 5, the resonant converter 500 of the present embodiment is different from the resonant converters 200-400 of the foregoing FIGS. 2 to 4 in that the resonant converter 500 of the present embodiment has a full-bridge circuit configuration. The resonant converter 500 includes a bridge switching circuit 510, a resonant and transforming circuit 520, a rectifying and filtering circuit 530, and an overcurrent protection circuit 540. In the present embodiment, the bridge switch circuit 510 includes switch transistors Q1 to Q4. The resonance and wall voltage circuit 520 includes a first resonance capacitor Cr1, a first resonance inductor Lr1, a second resonance inductor Lr2, and a transformer T1. Rectifier filter circuit 530 Similar to the aforementioned rectification filter circuit 230, 330 or 430. The overcurrent protection circuit 540 includes a clamp circuit 542 composed of clamped diodes D1 to D4, an overcurrent determination circuit 544, and a clamp switch circuit 546 composed of switches SW1 and SW2.

In the bridge switch circuit 510, the 汲 of the switching transistor Q1 receives the power supply terminal of the DC input voltage Vin, and the source of the switching transistor Q1 is coupled to the drain of the switching transistor Q2. The drain of the switching transistor Q3 is coupled to the drain of the switching transistor Q1, and the source of the switching transistor Q3 is coupled to the drain of the switching transistor Q4. The sources of the switching transistors Q2 and Q4 are commonly coupled to the ground GND. The gates of the switching transistors Q1~Q4 respectively receive the control signals S1~S4, wherein the control signals S1~S4 can respectively be signals with pulse width modulation. In this architecture, the switching transistors Q1~Q4 are turned on or off in response to the control signals S1~S4, respectively, so that the DC input voltage Vin is supplied to the resonant and transforming circuit 520 by switching.

In the resonant and voltage converting circuit 520, the first end of the first resonant inductor Lr1 is coupled to the source of the switching transistor Q1 and the drain of the switching transistor Q2. The first end of the second resonant inductor Lr2 is coupled to the source of the switching transistor Q3 and the drain of the switching transistor Q4. The transformer T1' has a first primary side winding NP1, a second primary side winding NP2, and a secondary side winding NS. The first end of the first primary winding NP1 is coupled to the first end of the first resonant capacitor Cr1, and the different end of the first primary winding NP1 is coupled to the second end of the first resonant capacitor Lr1. The second end of the second primary winding NP2 is coupled to the second end of the second resonant inductor Lr2, and the different end of the second primary winding NP2 is coupled to the second end of the first resonant capacitor Cr1. The same-name end and the different-name end of the secondary side winding NS are respectively coupled to the anode ends of the diodes Ds1 and Ds3 of the rectifying and filtering circuit 530.

In the overcurrent protection circuit 540, the cathode ends of the clamp diodes D1 and D3 are coupled to the drain of the switching transistor Q1 (ie, the power terminal N1), and the anode terminal of the clamp diode D1 is coupled to the clamp 2 The anode end of the pole D2 is coupled to the ground end GND, and the anode end of the clamp diode D3 is coupled to the cathode end of the clamp diode D4. The overcurrent judging circuit 544 detects the current I1 flowing through the first side winding NP1 of the transformer T1', and accordingly generates an overcurrent judging signal S_ocd. The first end of the switch SW1 is coupled to the anode end of the clamp diode D1 and the cathode end of the clamp diode D2, and the second end of the switch SW1 is coupled to the first end of the first resonant capacitor Cr1. The first end of the switch SW2 is coupled to the anode end of the clamp diode D3 and the cathode end of the clamp diode D4, and the second end of the switch SW2 is coupled to the second end of the first resonant capacitor Cr1. The control terminals of the switches SW1 and SW2 are coupled to the overcurrent determination circuit 544 to receive the overcurrent determination signal S_ocd.

Based on the circuit configuration of the embodiment, the overcurrent protection circuit 540 determines whether the load 10 has an overcurrent phenomenon by detecting the current I1 flowing through the first primary winding NP1 (but not limited to this). The voltage across the first resonant capacitor Cr1 is limited to determine whether the switches SW1 and SW2 are turned on at the same time.

In order to more clearly explain the overcurrent detection and determination mechanism of the above embodiments of FIG. 2 to FIG. 5, the specific embodiment of the above-described overcurrent determination circuit will be described below with reference to the embodiment of FIG. 6 and FIG. 6 is a functional block diagram of an overcurrent determination circuit according to an embodiment of the present invention. FIG. 7 is a circuit diagram of an overcurrent determination circuit in accordance with the embodiment of FIG. 6. FIG.

Here, in order to make the present embodiment easier to understand, the present embodiment is The architecture of the overcurrent determination circuit 244 is described in conjunction with the resonant converter 200 of the embodiment of FIG. 2, but the invention is not limited thereto. More specifically, the architecture and current detection mechanism of the overcurrent determination circuit 244 described in this embodiment can be applied to the overcurrent determination circuit (such as 344, 444, 544) in any of the above embodiments.

Referring first to FIG. 6, in the present embodiment, the overcurrent determination circuit includes a sampling resistor Rr, a current sampling circuit SC, a comparison circuit COM, and a drive circuit DC. The sampling resistor Rr is connected in series in the primary side circuit of the transformer T (ie, the path from the second end of the first resonant capacitor Cr1 to the different end of the primary side winding NP). The two input ends of the current sampling circuit SC are connected across the two ends of the sampling resistor Rr. The current sampling circuit SC can determine the magnitude of the current I1 by detecting the voltage difference across the sampling resistor Rr, and generate an associated current. The detection voltage VI of the size of I1. The comparison circuit COM is coupled to the output end of the current sampling circuit SC, and is used for comparing the detection voltage VI with a reference voltage VREF, wherein the comparison result of the comparison circuit COM indicates that the magnitude between the current I1 and a preset current value is relatively relationship. The driving circuit DC is for controlling the on and off of the switch SW1 according to the comparison result of the comparison circuit COM.

In detail, when the comparison circuit COM generates a comparison result that the detection voltage VI is greater than or equal to the reference voltage VREF, it indicates that an overcurrent phenomenon may occur in the load 10 (the current I1 is greater than or equal to the preset current value). At this time, the driving circuit DC turns on the switch SW1 according to the comparison result of the comparison circuit COM to form the turned-on clamping path CP (the path of the nodes P1 to P2), so that the voltage across the first resonant capacitor Cr1 is clamped to the pole The limitation of the bodies D1 and D2, thereby suppressing the overcurrent phenomenon of the load 10.

Conversely, when the comparison circuit COM generates the detection voltage VI is less than the reference power When the comparison result of the voltage VREF is pressed, it indicates that the resonant converter 200 is in a normal operating state (the current I1 is smaller than the preset current value). At this time, the drive circuit DC turns off the switch SW1 according to the comparison result of the comparison circuit COM, so that the voltage across the first resonance capacitor Cr1 is not restricted by the clamp diodes D1 and D2.

More specifically, the comparison circuit COM, the drive circuit DC, and the switch SW1 shown in FIG. 6 can be realized by the circuit architecture of the embodiment of FIG. Referring to FIG. 7 , in the embodiment, the switch SW1 can be implemented by using a relay J, the comparator COM can be implemented by using a gate and an AG, and the driving circuit DC can utilize the current limiting resistor Rre and the transistor Q. Architecture to achieve. In this circuit configuration, when the gate AG receives the high-level detection voltage VI, it generates an enable signal to conduct the transistor Q. The turned-on transistor Q establishes a current path between the supply voltage VCC and the ground GND. The coil portion of the relay J is excited based on the current in the current path, and its switching portion is closed in response to the excitation of the coil portion, thereby electrically connecting the nodes P1 and P2 to form the clamp path CP.

It should be noted that the above embodiments of FIG. 6 and FIG. 7 are based on the detection of the primary side current I1 as an example, but those having ordinary knowledge in the art should be able to follow the description of the embodiments of FIG. 6 and FIG. 7 described above. The implementation of the overcurrent protection by detecting the secondary current (ie, the load current Io) is self-inferred.

In addition, according to the description of the above embodiments of FIG. 2 to FIG. 5, those skilled in the art should understand that the resonant converter with overcurrent protection mechanism to be protected by the embodiment of the present invention is not limited to a specific one. Under the circuit configuration. More specifically, whether it is asymmetric half-bridge, symmetric half-bridge, full-bridge or other forms The resonant converter can utilize the concept of the above-mentioned overcurrent protection mechanism, so that the voltage across the resonant capacitor can be not affected by the DC input voltage under the normal operation of the resonant converter. In other words, the resonant converter to be protected by the present invention is not limited to the circuit configuration mentioned in the above embodiments, as long as it is a resonant converter that controls whether the clamp path is turned on or off according to the occurrence or absence of an overcurrent to obtain the above advantageous effects. They do not depart from the scope of the invention to be protected.

FIG. 8 is a flow chart showing the steps of a method for controlling a resonant converter according to an embodiment of the present invention. The control method of the present embodiment is suitable for controlling the resonant converter 100, 200, 300, 400 or 500 as shown in FIGS. 1 to 5. Referring to FIG. 8, the control method of the resonant converter of the present embodiment includes the following steps: controlling switching of the bridge switching circuit (such as 110, 210, 310, 410, 510) (step S810); and making the resonant capacitor (such as Cr1). Cr2) reacts to the switching of the bridge switching circuit to charge and discharge energy (step S820); by means of a rectifying and filtering circuit (such as 130, 230, 330, 430, 530) for the resonant and transformer circuits (such as 120, 220, 320, 420) The output of 520) is rectified and filtered, and generates a driving voltage to drive the load (such as 10) (step S830); detecting a current flowing through the resonant and transformer circuit or the load (step S840); and detecting The result determines whether or not the clamp path is turned on to clamp the voltage across the resonant capacitor to the first voltage range (step S850).

Further, the above step S850 can also be implemented by: determining whether the current flowing through the resonant and transformer circuit or the load is greater than or equal to a preset current; if the current flowing through the resonant and transformer circuit or the load is judged For the preset current greater than or equal to, the overcurrent protection circuit (such as 140, 240, 340, 440, 540) is turned on. Clamping the path to clamp the voltage across the resonant capacitor to the first voltage range; and if the current flowing through the resonant and transformer circuit or the load is determined to be less than the preset current, the overcurrent protection circuit cuts off the clamp path to The voltage across the resonant capacitor is not limited to the first voltage range.

The control methods described in the embodiment of FIG. 8 can be sufficiently supported and taught according to the foregoing description of FIG. 1 to FIG. 8. Therefore, similarities or repetitions are not described herein again.

In summary, the embodiment of the present invention provides a resonant converter and a control method thereof. The resonant converter can determine whether an overcurrent phenomenon occurs in the load by detecting the current of the primary side or the load. Wherein, the resonant converter turns on the clamp path to provide overcurrent protection when the load is overcurrent, and cuts off the clamp path when the load does not have an overcurrent phenomenon so that the resonant capacitor is not limited by the DC input voltage. . Therefore, the resonant converter does not need to be additionally limited in the design of the circuit parameters and the working range, thereby reducing the difficulty and cost of the overall circuit design.

Although the present invention has been disclosed in the above embodiments, it is not intended to limit the present invention, and any one of ordinary skill in the art can make some changes and refinements without departing from the spirit and scope of the present invention. The scope of the invention is defined by the scope of the appended claims.

10‧‧‧ load

100‧‧‧Resonance converter

110‧‧‧Bridge Switch Circuit

120‧‧‧Resonance and transformer circuits

130‧‧‧Rectifier filter circuit

140‧‧‧Overcurrent protection circuit

142‧‧‧Clamp circuit

144‧‧‧Overcurrent judgment circuit

146‧‧‧Clamp switch circuit

CP‧‧‧ clamp path

Cr‧‧‧Resonance Capacitor

N1‧‧‧ power terminal

S_ocd‧‧‧Overcurrent judgment signal

Vcr‧‧‧ voltage

Vd‧‧‧ drive voltage

Vin‧‧‧DC input voltage

Claims (20)

A resonant converter adapted to provide a driving voltage to a load, the resonant converter comprising: a bridge switching circuit having a power supply terminal, wherein the bridge switching circuit receives a DC input voltage via the power supply terminal; And a transformer circuit coupled to the bridge switch circuit, having at least one resonant capacitor, wherein the at least one resonant capacitor reacts with charging and discharging of the bridge switching circuit; and a rectifying and filtering circuit coupled to the resonant and variable a voltage circuit for rectifying and filtering the output of the resonant and voltage converting circuit, and generating the driving voltage; and an overcurrent protection circuit coupled to the power terminal and connected to the at least one resonant capacitor Forming a clamping path, wherein the overcurrent protection circuit is configured to detect a current flowing through the resonant and voltage converting circuit or the load to determine whether to turn on the clamping path according to the result of the detecting to The voltage across at least one resonant capacitor is clamped to a first voltage range. The resonant converter of claim 1, wherein the overcurrent protection circuit detects when the current flowing through the resonant and voltage converting circuit or the load is greater than or equal to a predetermined current value. The circuit turns on the clamp path to clamp the voltage across the at least one resonant capacitor to the first voltage range, and when the overcurrent protection circuit detects that the current flowing through the resonant and transformer circuit or the load is less than the When the current value is preset, the overcurrent protection circuit cuts off the clamp path so that the voltage across the at least one resonant capacitor is not limited to the first voltage range. The upper limit of the first voltage range is the DC input voltage. The resonant converter of claim 1, wherein the overcurrent protection circuit comprises: a clamp circuit coupled to the power terminal; and an overcurrent determination circuit for detecting the flow and the voltage change a current of the circuit or the load, and an overcurrent determination signal is generated; and a clamp switch circuit coupled between the clamp circuit and the at least one resonant capacitor and controlled by the overcurrent determination signal Turning on or off, wherein the clamp path is formed via the clamp switch circuit. The resonant converter of claim 3, wherein the rectifying and filtering circuit comprises: a first to a fourth diode, wherein a cathode end of the first diode is coupled to the third diode a cathode end, an anode end of the first diode is coupled to a cathode end of the second diode, an anode end of the second diode is coupled to an anode end of the fourth diode, and the third The anode end of the diode is coupled to the cathode end of the fourth diode; and a filter capacitor having a first end coupled to the cathode end of the first and third diodes and one end of the load, and The two ends are coupled to the anode ends of the second and fourth diodes and the other end of the load. The resonant converter of claim 4, wherein the bridge switching circuit comprises: a first switching transistor, the first end of which is the power terminal, and the control terminal receives a first control signal; A second switch transistor has a first end coupled to the second end of the first switch transistor, a second end coupled to the ground end, and a control end receiving a second control signal. The resonant converter of claim 5, wherein the resonant and transforming circuit comprises: a first resonant capacitor having a first end coupled to the ground; a first resonant inductor having a first end coupled a second end of the first switching transistor and a first end of the second switching transistor; and a transformer having a primary winding and a secondary winding, the same end of the primary winding being coupled to the same a second end of the first resonant inductor, the opposite end of the primary winding is coupled to the second end of the first resonant capacitor, the same end of the secondary winding is coupled to the anode end of the first diode and the first a cathode end of the diode, and the opposite end of the secondary winding is coupled to the anode end of the third diode and the cathode end of the fourth diode. The resonant converter of claim 6, wherein the clamping circuit comprises: a first clamping diode having a cathode end coupled to the first end of the first switching transistor; and a second The clamp diode has an anode end coupled to the ground end and a cathode end coupled to the anode end of the first clamp diode. The resonant converter of claim 7, wherein the clamp switch circuit comprises: a switch having a first end coupled to the anode end of the first clamp diode and the second clamp diode a cathode end of the body, the second end of which is coupled to the second end of the first resonant capacitor The opposite end of the primary side winding, and the control end thereof is coupled to the overcurrent determination circuit. The resonant converter of claim 5, wherein the resonant and transforming circuit comprises: a first resonant capacitor having a first end coupled to the ground; a second resonant capacitor coupled to the first end Connected to the second end of the first resonant capacitor, and the second end of the first resonant capacitor is coupled to the first end of the first switching transistor; the first resonant inductor has a first end coupled to the second end of the first switching transistor And a first end of the second switching transistor; and a transformer having a primary winding and a secondary winding, wherein the same end of the primary winding is coupled to the second end of the first resonant inductor, The second end of the first resonant capacitor is coupled to the first end of the first resonant capacitor and the first end of the second resonant capacitor, and the same end of the secondary winding is coupled to the anode end of the first diode and the first end a cathode end of the diode, and the opposite end of the secondary winding is coupled to the anode end of the third diode and the cathode end of the fourth diode. The resonant converter of claim 9, wherein the clamping circuit comprises: a first clamping diode, the cathode end of which is coupled to the first end of the first switching transistor and the first resonance a first end of the capacitor; and a second clamping diode having an anode end coupled to the ground end and a cathode end coupled to the anode end of the first clamping diode. The resonant converter of claim 10, wherein the clamp switch circuit comprises: a switch having a first end coupled to the anode end of the first clamp diode and a cathode end of the second clamp diode, and a second end coupled to the second end of the first resonant capacitor The first end of the second resonant capacitor, and the control end thereof is coupled to the overcurrent determining circuit. The resonant converter of claim 5, wherein the resonant and transforming circuit comprises: a first capacitor having a first end coupled to the first end of the first switching transistor; a second capacitor, The first end is coupled to the second end of the first capacitor, and the second end is coupled to the ground end; a first resonant capacitor having a first end coupled to the second end of the first switch transistor and the first end a first end of the second switching transistor; a first resonant inductor having a first end coupled to the second end of the first resonant capacitor; and a first transformer having a primary side winding and a secondary side winding The second end of the first side winding is coupled to the second end of the first resonant inductor, and the second end of the first side winding is coupled to the second end of the first capacitor and the first end of the second capacitor, the second The same end of the side winding is coupled to the anode end of the first diode and the cathode end of the second diode, and the opposite end of the secondary winding is coupled to the anode end of the third diode and the first The cathode end of the quadrupole. The resonant converter of claim 12, wherein the clamping circuit comprises: a second transformer having a primary winding and a secondary winding, wherein the same end of the primary winding is coupled to the first a first end of a resonant capacitor a different end is coupled to the second end of the first resonant capacitor; a first clamp diode having an anode end coupled to the same end of the secondary winding of the second transformer; and a second clamp diode The anode end is coupled to the opposite end of the secondary winding of the second transformer, and the cathode end thereof is coupled to the cathode end of the first clamping diode. The resonant converter of claim 13, wherein the clamp switch circuit comprises: a switch having a first end coupled to the cathode ends of the first and second clamp diodes, and a second end The first end of the filter capacitor is coupled, and the control end is coupled to the overcurrent determination circuit. The resonant converter of claim 4, wherein the bridge switch circuit comprises: a first switch transistor, the first end of which is the power terminal, and the control end receives a first control signal; a second switching transistor having a first end coupled to the second end of the first switching transistor, a second end coupled to a ground end, and a control end receiving a second control signal; a third switching transistor The first end is coupled to the first end of the first switch transistor, and the control end thereof receives a third control signal; and a fourth switch transistor, the first end of which is coupled to the third switch transistor The second end is coupled to the ground end, and the control end receives a fourth control signal. The resonant converter of claim 15, wherein the resonant and transforming circuit comprises: a first resonant capacitor having a first end coupled to the second end of the first switching transistor and a first end of the second switching transistor; a second resonant inductor having a first end a second end of the third switching transistor and a first end of the fourth switching transistor; and a transformer having a first primary winding, a second primary winding, and a secondary winding The first end of the first primary winding is coupled to the first end of the first resonant capacitor, and the different end of the first primary winding is coupled to the second end of the first resonant inductor, the second one The second end of the second side winding is coupled to the second end of the second resonant inductor, and the second end of the second side winding is coupled to the second end of the first resonant capacitor, and the same end of the secondary winding is coupled An anode end of the first diode and a cathode end of the second diode, and a different end of the secondary winding is coupled to the anode end of the third diode and the cathode end of the fourth diode . The resonant converter of claim 16, wherein the clamping circuit comprises: a first clamping diode, the cathode end of which is coupled to the first end of the first switching transistor; and a second clamp a diode having an anode end coupled to the ground and a cathode end coupled to the anode end of the first clamp diode; a third clamp diode having a cathode end coupled to the first clamp a cathode end of the diode; and a fourth clamp diode having an anode end coupled to the ground and a cathode end coupled Connect to the anode end of the third clamp diode. The resonant converter of claim 17, wherein the clamp switch circuit comprises: a first switch having a first end coupled to the anode end of the first clamp diode and the second clamp a cathode end of the diode, the second end of which is coupled to the first end of the first resonant capacitor, and the control end is coupled to the overcurrent determining circuit; and a second switch, the first end of which is coupled to the third end The anode end of the clamp diode and the cathode end of the fourth clamp diode have a second end coupled to the second end of the first resonant capacitor, and a control end coupled to the overcurrent determining circuit. A control method for a resonant converter, wherein the resonant converter includes a bridge switching circuit, a resonant and voltage converting circuit, a rectifying and filtering circuit, and an overcurrent protection circuit, the resonant and transforming circuit having at least one resonant capacitor, An overcurrent protection circuit is connected across the at least one resonant capacitor to form a clamping path. The control method includes: controlling switching of the bridge switching circuit, wherein the bridge switching circuit receives a DC input via a power terminal a voltage; causing the at least one resonant capacitor to react to the switching of the bridge switching circuit to charge and discharge energy; and the rectifying and filtering circuit is used for rectifying and filtering the output of the resonant and voltage converting circuit, and generating a driving voltage to drive a load; detecting a current flowing through the resonant and voltage converting circuit or the load; and determining whether to turn on the clamp path according to the result of the detecting, to at least one harmonic The voltage across the capacitor is clamped to a first voltage range. The control method of claim 19, wherein the step of determining whether to turn on the clamp path according to the result of the detecting to clamp the cross-voltage of the at least one resonant capacitor to the first voltage range comprises: determining a flow Whether the current through the resonant and transformer circuit or the load is greater than or equal to a predetermined current value; if the current flowing through the resonant and transformer circuit or the load is determined to be greater than or equal to the preset current value, the overcurrent is The protection circuit turns on the clamp path to clamp the voltage across the at least one resonant capacitor to the first voltage range; and if the current flowing through the resonant and transformer circuit or the load is determined to be less than the preset current value The overcurrent protection circuit is used to cut off the clamp path so that the voltage across the at least one resonant capacitor is not limited to the first voltage range, wherein an upper limit of the first voltage range is the DC input voltage.