An LLC switching power supply and its control device and method

Abstract

This invention discloses a control device, an LLC switching power supply, and a control method thereof. The device includes: a control unit, which, when the LLC switching power supply is powered on, controls the current switching transistor in the upper and lower bridge switching transistors to turn on; and controls a set of rectifier switching transistors corresponding to the current switching transistor to turn on in advance; a control unit, which controls the current switching transistor to turn off, and controls the set of rectifier switching transistors corresponding to the current switching transistor to turn off; a detection unit, which detects the current on the resonant inductor to obtain a first detection signal, and detects the current on the magnetizing inductor to obtain a second detection signal; and a control unit, which, when the first and second detection signals are determined to be equal, outputs a control signal to control the set of rectifier switching transistors corresponding to the next switching transistor to turn on preferentially before the secondary side of the transformer is energized. This scheme reduces switching losses and improves power supply efficiency by prioritizing the switching transistors on the synchronous rectification side before the transformer conducts.

Description

Technical Field

[0001] This invention belongs to the field of LLC switching power supply technology, specifically relating to a control device for LLC switching power supply, LLC switching power supply and its control method, and particularly to a novel low-loss synchronous rectification circuit for the downstream stage of LLC switching power supply and its synchronous rectification control method, as well as an LLC switching power supply having the novel low-loss synchronous rectification circuit for the downstream stage of LLC switching power supply. Background Technology

[0002] LLC (Limited-Loop) switching power supplies, which use a resonant circuit to maintain a constant output voltage by controlling the switching frequency, are often used in medium-power applications. Therefore, LLC switching power supplies are more sensitive to switching losses than flyback switching power supplies. However, LLC switching power supplies have relatively high switching losses, which affects their efficiency.

[0003] The above content is only used to help understand the technical solution of the present invention and does not represent an admission that the above content is prior art. Summary of the Invention

[0004] The purpose of this invention is to provide a control device, an LLC switching power supply, and a control method thereof for an LLC switching power supply, in order to solve the problem that the switching losses of LLC switching power supplies are large, which affects the efficiency of LLC switching power supplies. By prioritizing the conduction of the switching transistors on the synchronous rectification side of the half-bridge LLC switching power supply before the transformer during the dead time, the switching losses of the switching transistors on the synchronous rectification side are reduced, which is beneficial to reducing the switching losses of the half-bridge LLC switching power supply and thus improving the efficiency of the half-bridge LLC switching power supply.

[0005] This invention provides a control device for an LLC switching power supply. The LLC switching power supply includes: a half-bridge circuit, a resonant circuit, a transformer, a synchronous rectifier circuit, and a drive circuit for the synchronous rectifier circuit. The half-bridge circuit and the resonant circuit are sequentially arranged on the primary side of the transformer. The synchronous rectifier circuit is arranged on the secondary side of the transformer. The half-bridge circuit includes: an upper bridge switch and a lower bridge switch. The resonant circuit has a resonant inductor and a magnetizing inductor. The synchronous rectifier circuit includes: a first set of rectifier switches and a second set of rectifier switches, wherein the first set of rectifier switches is correspondingly turned on or off with the upper bridge switch, and the second set of rectifier switches is correspondingly turned on or off with the lower bridge switch. The circuit is configured to turn on or off as needed; the driving circuit includes: a first driving unit for driving the first group of rectifier switches, and a second driving unit for driving the second group of rectifier switches; the control device of the LLC switching power supply includes: a detection unit and a control unit; wherein, the control unit is configured to, when the LLC switching power supply is powered on, control one of the upper bridge switches and the lower bridge switches to turn on, designate the selected switch as the current switch, and designate the other switch as the next switch; and control the pair of rectifier switches in the first group and the second group corresponding to the current switch. A set of driving units operates to control the first set of rectifier switches and the set of rectifier switches corresponding to the current switch in the second set of rectifier switches to turn on at a predetermined time; the control unit is also used to control the current switch to turn off when the current switch needs to be turned off, and to control the set of rectifier switches corresponding to the current switch in the first set of rectifier switches and the second set of rectifier switches to turn off; after the current switch is turned off and before the next switch is turned on, the LLC switching power supply enters a dead zone state; the detection unit is used to detect the current on the resonant inductor and the current on the magnetizing inductor, and to transmit the detected current on the resonant inductor... The current is recorded as the first detection signal, and the detected current on the magnetizing inductor is recorded as the second detection signal; the control unit is further configured to determine whether the first detection signal and the second detection signal are equal when the LLC switching power supply is in a dead zone state, so as to output a control signal when the first detection signal and the second detection signal are determined to be equal, so as to control the first group of rectifier switches and the group of rectifier switches corresponding to the next switch in the second group of rectifier switches to work, so as to control the first group of rectifier switches and the group of rectifier switches corresponding to the next switch in the second group of rectifier switches to be turned on firstly before the secondary side of the transformer is energized.

[0006] In some embodiments, the detection unit includes: a first detection resistor module and a second detection resistor module; the first detection resistor module is disposed between the upper bridge switch and the resonant inductor; the second detection resistor module is disposed between the magnetizing inductor and the primary side of the transformer.

[0007] In some embodiments, the synchronous rectification circuit is a full-bridge synchronous rectification circuit; the first group of rectifier switches includes a first switch and a second switch; the second group of rectifier switches includes a third switch and a fourth switch; the first switch, the second switch, the third switch, and the fourth switch constitute a full-bridge synchronous rectification circuit; the first group of driving units includes a first push-pull circuit; the second group of driving units includes a second push-pull circuit; the first push-pull circuit is used to drive the first switch and the second switch to turn on or off; the second push-pull circuit is used to drive the third switch and the fourth switch to turn on or off; the control signal output by the control unit includes a first control signal and a second control signal; the first control signal is used to control the operation of the first push-pull circuit; the second control signal is used to control the operation of the second push-pull circuit.

[0008] In some embodiments, a protection resistor module is further provided between the gate and drain of each of the first, second, third, and fourth switching transistors in the synchronous rectification circuit.

[0009] In some implementations, when the LLC switching power supply is operating, the upper bridge switch and the lower bridge switch are alternately turned on; wherein: if the current switch is the upper bridge switch, then when the upper bridge switch is turned on and then turned off, the control signal output by the control unit is the second control signal; if the current switch is the lower bridge switch, then when the lower bridge switch is turned on and then turned off, the control signal output by the control unit is the first control signal.

[0010] In conjunction with the above-described device, the present invention further provides an LLC switching power supply, comprising: the control device for the LLC switching power supply described above.

[0011] In conjunction with the aforementioned LLC switching power supply, this invention further provides a control method for an LLC switching power supply, comprising: when the LLC switching power supply is powered on, controlling one of the upper bridge switching transistors and the lower bridge switching transistors to turn on, recording this one switching transistor as the current switching transistor, and recording the other of the upper bridge switching transistors and the lower bridge switching transistors as the next switching transistor; and controlling a set of drive units corresponding to the set of rectifier switching transistors in the first group of rectifier switching transistors and the second group of rectifier switching transistors corresponding to the current switching transistor to operate, so as to control the set of rectifier switching transistors in the first group of rectifier switching transistors and the second group of rectifier switching transistors corresponding to the current switching transistor to turn on for a predetermined time; when the current switching transistor needs to be turned off, controlling the current switching transistor to turn off, and controlling the set of rectifier switching transistors in the first group of rectifier switching transistors and the second group of rectifier switching transistors corresponding to the current switching transistor to turn off; After the current switch is turned off and before the next switch is turned on, the LLC switching power supply enters a dead zone state. The current on the resonant inductor and the current on the magnetizing inductor are detected. The detected current on the resonant inductor is recorded as the first detection signal, and the detected current on the magnetizing inductor is recorded as the second detection signal. When the LLC switching power supply is in the dead zone state, it is determined whether the first detection signal and the second detection signal are equal. If the first detection signal and the second detection signal are determined to be equal, a control signal is output to control the operation of the drive unit corresponding to the first group of rectifier switches and the second group of rectifier switches corresponding to the next switch. This ensures that the first group of rectifier switches and the second group of rectifier switches corresponding to the next switch are turned on preferentially before the secondary side of the transformer is energized.

[0012] In some embodiments, the first set of driving units includes: a first push-pull circuit; the second set of driving units includes: a second push-pull circuit; the first push-pull circuit is used to drive the first switch and the second switch to turn on or off; the second push-pull circuit is used to drive the third switch and the fourth switch to turn on or off; the control signal output by the control unit includes: a first control signal and a second control signal; the first control signal is used to control the first push-pull circuit to operate; the second control signal is used to control the second push-pull circuit to operate.

[0013] In some implementations, when the LLC switching power supply is operating, the upper bridge switch and the lower bridge switch are alternately turned on; wherein: if the current switch is the upper bridge switch, then when the upper bridge switch is turned on and then turned off, the control signal output by the control unit is the second control signal; if the current switch is the lower bridge switch, then when the lower bridge switch is turned on and then turned off, the control signal output by the control unit is the first control signal.

[0014] Therefore, the solution of the present invention addresses a half-bridge LLC switching power supply, which includes a half-bridge circuit, a resonant circuit, a transformer, a synchronous rectifier circuit, and a drive circuit for the synchronous rectifier circuit. The half-bridge circuit and the resonant circuit are sequentially arranged on the primary side of the transformer, while the synchronous rectifier circuit and its drive circuit are arranged on the secondary side of the transformer. When the upper bridge switch or the lower bridge switch in the half-bridge circuit is turned on and then turned off, the half-bridge LLC switching power supply enters a dead-time state. During the dead-time of the half-bridge LLC switching power supply, the current of the resonant inductor in the resonant circuit (i.e., the resonant current) and the current of the magnetizing inductor in the resonant circuit (i.e., the magnetizing current) are detected to be equal. When the excitation current is equal, a set of switching transistors in the synchronous rectifier circuit corresponding to the switching transistors that have been turned on and off in the half-bridge circuit are turned on. This ensures that the switching transistors in this set are turned on preferentially before the transformer secondary side receives current, avoiding voltage and current crossover losses when the switching transistors are turned on after the transformer secondary side receives current. Thus, by prioritizing the switching transistors on the synchronous rectifier side of the half-bridge LLC switching power supply to turn on before the transformer during the dead time, the switching losses of the switching transistors on the synchronous rectifier side are reduced, which helps to reduce the switching losses of the half-bridge LLC switching power supply and thus improves the efficiency of the half-bridge LLC switching power supply.

[0015] Other features and advantages of the invention will be set forth in the description which follows, and will be apparent in part from the description, or may be learned by practicing the invention.

[0016] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. Attached Figure Description

[0017] Figure 1 This is a schematic diagram of the structure of an embodiment of the control device for the LLC switching power supply of the present invention;

[0018] Figure 2 This is a schematic diagram of an embodiment of a novel low-loss synchronous rectifier circuit for the downstream stage of an LLC switching power supply.

[0019] Figure 3This is a schematic diagram of the working waveforms of a novel low-loss synchronous rectifier circuit in the downstream stage of an LLC switching power supply.

[0020] Figure 4 This is a schematic diagram of the working process of a novel low-loss synchronous rectifier circuit in the downstream stage of an LLC switching power supply.

[0021] Figure 5 A flowchart illustrating a synchronous rectification control method for a novel low-loss synchronous rectifier circuit in a LLC switching power supply.

[0022] Figure 6 This is a schematic diagram of the ideal waveform of the drive signal for a novel low-loss synchronous rectifier circuit in a LLC switching power supply.

[0023] Figure 7 This is a flowchart illustrating an embodiment of the control method for an LLC switching power supply according to the present invention.

[0024] Referring to the accompanying drawings, the reference numerals in the embodiments of the present invention are as follows:

[0025] 102 - Detection unit; 104 - Control unit. Detailed Implementation

[0026] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be clearly and completely described below in conjunction with specific embodiments and corresponding drawings. Obviously, the described embodiments are only a part of the embodiments of this invention, and not all of them. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this invention.

[0027] Considering that the resonant cavity circuit unique to LLC switching power supplies can clamp the MOSFETs (i.e., MOSFETs) of the upper and lower bridge arms to a relatively small voltage of about 0.7 volts in the dead zone, the loss problem of common hard switching is prevented. For the rectification section following the LLC switching power supply topology, some solutions use a rectifier bridge composed of diodes for full-wave rectification. However, since there is a turn-off delay time for the diodes, the corresponding current will also be large if the load is large. When the diodes reverse recover, the reverse withstand voltage of the diodes will generate a crossover loss. Specifically, when the diodes reverse recover, it is equivalent to the process of a resistor changing from large to small. Therefore, the resistance multiplied by the current generates the loss. So, if the load is large, it will cause the diode losses of the rectifier bridge to be too large, and there are also higher requirements for the reverse withstand voltage of the diodes. For example, the reverse withstand voltage of the diodes needs to be twice the output voltage of the LLC switching power supply. Therefore, relevant solutions use synchronous rectification schemes, which can reduce the conduction loss of the diodes in some solutions to a relatively low value. Even so, losses can still be further reduced.

[0028] In addition, in the relevant solutions, the losses of LLC switching power supplies mainly include turn-on losses, conduction losses, and turn-off losses. Among them, for conduction losses, once the MOSFET is selected, the conduction losses of LLC switching power supplies are determined only by the effective current flowing through the MOSFET and the equivalent internal resistance of the MOSFET, which is an unchangeable value. Therefore, reducing the losses of LLC switching power supplies can only be achieved by addressing turn-on losses and turn-off losses.

[0029] Therefore, the present invention proposes a control device for an LLC switching power supply, specifically a novel low-loss synchronous rectifier circuit for the downstream stage of an LLC switching power supply. Utilizing the characteristic that the magnetizing inductance Lm of the LLC switching power supply is clamped by the secondary coil of the transformer T during operation, the novel low-loss synchronous rectifier circuit for the downstream stage of the LLC switching power supply controls the upper and lower arms of the synchronous rectifier bridge to alternately conduct when the voltage of the magnetizing inductance reaches a certain threshold. This achieves zero-voltage turn-on and zero-current turn-off, thereby reducing the switching losses of the LLC switching power supply and improving its efficiency.

[0030] According to an embodiment of the present invention, a control device for an LLC switching power supply is provided. See also Figure 1The diagram shows a structural schematic of an embodiment of the device of the present invention. The LLC switching power supply is specifically a half-bridge LLC switching power supply. The half-bridge LLC switching power supply includes: a half-bridge circuit, a resonant circuit, a transformer, a synchronous rectifier circuit, and a drive circuit for the synchronous rectifier circuit. The half-bridge circuit and the resonant circuit are sequentially arranged on the primary side of the transformer. The synchronous rectifier circuit is arranged on the secondary side of the transformer. The half-bridge circuit includes: an upper bridge switch and a lower bridge switch, specifically... Figure 2 This is a schematic diagram of an embodiment of a novel low-loss synchronous rectifier circuit for the power supply stage of an LLC switching power supply. The upper bridge switching transistor is shown below. Figure 2 The switch S1 shown is a lower bridge switch as follows: Figure 2 The switch S2 shown is used for alternating switching between the upper and lower bridge switches. The resonant circuit has a resonant inductor and a magnetizing inductor, the resonant inductor being as follows... Figure 2 The resonant inductance Lr and the magnetizing inductance shown are as follows: Figure 2 The magnetizing inductor Lm is shown. The synchronous rectification circuit includes: a first group of rectifier switches and a second group of rectifier switches. The first group of rectifier switches is turned on or off correspondingly with the upper bridge switch, and the second group of rectifier switches is turned on or off correspondingly with the lower bridge switch. That is, when the upper bridge switch is turned on, the first group of rectifier switches is turned on; when the upper bridge switch is turned off, the first group of rectifier switches is turned off. Similarly, when the lower bridge switch is turned on, the second group of rectifier switches is turned on; when the lower bridge switch is turned off, the second group of rectifier switches is turned off. The driving circuit includes: a first driving unit for driving the first group of rectifier switches and a second driving unit for driving the second group of rectifier switches. The first driving unit mainly consists of, for example,... Figure 2 The driving unit shown consists of transistors Sp and Sn. The second group of driving units mainly consists of... Figure 2 The driving unit shown is composed of transistors Sp1 and Sn1. The control device of the LLC switching power supply includes: a detection unit 102 and a control unit 104. The detection unit 102 is a detection circuit composed of resistors R1 and R2, and the control unit 104 is a control IC.

[0031] The control unit 104 is configured to, when the LLC switching power supply is powered on, control one of the upper bridge switching transistors and the lower bridge switching transistors to turn on, and designate this one switching transistor as the current switching transistor, that is, designate this one switching transistor as the current switching transistor among the upper bridge switching transistors and the lower bridge switching transistors, and designate the other switching transistor among the upper bridge switching transistors and the lower bridge switching transistors as the next switching transistor. Furthermore, it controls the operation of a set of drive units corresponding to the set of rectifier switching transistors in the first group and the second group of rectifier switching transistors that correspond to the current switching transistor, so as to control the set of rectifier switching transistors in the first group and the second group of rectifier switching transistors that correspond to the current switching transistor to turn on at a predetermined time, during which no current flows through this set of rectifier switching transistors.

[0032] The control unit 104 is further configured to, based on the alternating conduction rules of the upper bridge switch and the lower bridge switch, control the current switch to turn off when the current switch needs to be turned off, and control the first group of rectifier switches and the second group of rectifier switches corresponding to the current switch to turn off. After the current switch is turned off and before the next switch is turned on, the LLC switching power supply enters a dead zone state.

[0033] The detection unit 102, disposed in the resonant circuit, is used to detect the current in the resonant inductor and the current in the magnetizing inductor. When the LLC switching power supply is in a dead-zone state, the detected current in the resonant inductor is recorded as a first detection signal, and the detected current in the magnetizing inductor is recorded as a second detection signal. The first detection signal can be a voltage signal representing the magnitude of the current in the resonant inductor, and the second detection signal can be a voltage signal representing the magnitude of the current in the magnetizing inductor.

[0034] The control unit 104 is further configured to determine whether the first detection signal and the second detection signal are equal when the LLC switching power supply is in a dead zone state, so as to output a control signal when the first detection signal and the second detection signal are determined to be equal, so as to control the drive unit corresponding to the first group of rectifier switches and the group of rectifier switches corresponding to the next switch in the second group of rectifier switches to work, so as to control the first group of rectifier switches and the group of rectifier switches corresponding to the next switch in the second group of rectifier switches to be turned on firstly before the secondary side of the transformer is energized.

[0035] Specifically, Figure 3 This is a schematic diagram of the operating waveforms of a novel low-loss synchronous rectifier circuit in the downstream stage of an LLC switching power supply. Figure 3As shown, at time t0, switch S1 is driven and ZVS is turned on (i.e., zero-voltage conduction). The resonant current Ir is greater than the current Im on the magnetizing inductor Lm, and transformer T is turned on. Switches Sw1 and Sw2 on the synchronous rectification side are turned on. The voltage reflected onto the magnetizing inductor Lm on the primary side of transformer T causes the magnetizing current Im to increase linearly. The difference between the input voltage of the LLC switching power supply and the output voltage reflected onto the primary side of transformer T is applied to the resonant chain (i.e., the resonant circuit composed of resonant inductor Lr, magnetizing inductor Lm, and resonant capacitor Cr), generating a sinusoidal resonant current Ir. At time t1, switch S1 is turned off. Because the switching frequency of switch S1 and switch S2 is equal to the resonant frequency of the resonant chain, the resonant current Ir at this moment is equal to the magnetizing current Im. The solution of this invention utilizes this equality relationship to detect the resonant current Ir and the excitation current Im, and to turn on the switch (i.e., the synchronous rectifier switch) on the secondary side of transformer T ahead of the current flowing through it. Furthermore, the low-loss synchronous rectifier circuit following the LLC switching power supply itself ensures that the switch (i.e., the synchronous rectifier switch) on the secondary side of transformer T is turned off at zero current crossing (i.e., zero-current turn-off). After the resonant current Ir becomes positive, switch S1 turns on, thus achieving ZVS turn-on (i.e., zero-voltage turn-on).

[0036] This invention proposes a novel low-loss synchronous rectification circuit for the downstream stage of an LLC switching power supply. Utilizing the characteristic that the magnetizing inductance Lm of the LLC switching power supply is clamped by the secondary coil of the transformer T during operation, the novel low-loss synchronous rectification circuit detects when the voltage of the magnetizing inductance reaches a certain threshold. It then controls the upper and lower arms of the synchronous rectifier bridge to conduct alternately, achieving zero-voltage turn-on and zero-current turn-off, thereby reducing the switching losses and improving the efficiency of the LLC switching power supply. By utilizing the operating characteristics of the LLC switching power supply and designing a driver circuit to drive the downstream synchronous rectification circuit, a driver chip is eliminated, reducing costs and providing higher stability than a driver chip. Achieving zero-voltage turn-on and zero-current turn-off in synchronous rectification reduces the rectification losses and heat generation of the switching transistors in the synchronous rectifier circuit, which is beneficial for extending the lifespan of the switching transistors and improving the operating efficiency of the LLC switching power supply.

[0037] In the topology of LLC switching power supplies used in medium-power applications, some schemes still employ synchronous rectification modes. When the load requirements at the output of the LLC switching power supply are relatively large, the turn-on loss of the LLC switching power supply is quite significant. The solution of this invention can replace the synchronous rectification drive circuit in some synchronous rectification modes, and can achieve zero-voltage turn-on and zero-current turn-off, thereby reducing the switching losses of the LLC switching power supply and improving its efficiency. This invention cleverly utilizes the operating characteristics of the LLC switching power supply; specifically, when the upper transistor of the rectifier bridge of the LLC switching power supply is turned off, the resonant cavity circuit of the LLC switching power supply enters internal loop operation. At this time, the excitation current Im equals the resonant current, optimizing the subsequent synchronous rectification circuit, improving the efficiency of the LLC switching power supply, and reducing the heat generation of the switching transistors.

[0038] In some embodiments, the detection unit 102 includes: a first detection resistor module and a second detection resistor module, wherein the first detection resistor module is as follows: Figure 2 The resistor R1 shown, the second detection resistor module as follows Figure 2 The resistor R2 is shown. The first detection resistor module is disposed between the upper bridge switch and the resonant inductor. The second detection resistor module is disposed between the magnetizing inductor and the primary side of the transformer.

[0039] exist Figure 2 In the example shown, the control IC acts as a threshold comparison circuit or comparator. Resistors R1 and R2 serve as detection resistors, forming a detection circuit. Resistor R1 detects the current Ir in the resonant inductor Lr. Resistor R2 detects the current Im in the magnetizing inductor Lm. The resonant current Ir detected by the detection circuit is input to the first input terminal of the control IC, and the magnetizing current Im detected by the detection circuit is input to the second input terminal of the control IC. The control IC compares the input resonant current Ir and magnetizing current Im, outputs a first control signal CS from its first output terminal, and a second control signal CS1 from its second output terminal.

[0040] In some embodiments, the synchronous rectification circuit is a full-bridge synchronous rectification circuit. The first group of rectifier switches includes a first switch and a second switch. The second group of rectifier switches includes a third switch and a fourth switch. The first switch, the second switch, the third switch, and the fourth switch constitute a full-bridge synchronous rectification circuit. That is, the synchronous rectification circuit includes a first group of rectifier switches composed of the first and second switches, and a second group of rectifier switches composed of the third and fourth switches, wherein the first switch is as follows: Figure 2The shown switching transistor Sw1, the second switching transistor is as follows Figure 2 The shown switching transistor Sw2, the third switching transistor is as follows Figure 2 The fourth switching transistor is shown as Sw3. Figure 2 The switch shown is Sw4.

[0041] The first group of driving units includes a first push-pull circuit. The second group of driving units includes a second push-pull circuit. The first push-pull circuit is used to drive the first and second switching transistors to turn on or off. The second push-pull circuit is used to drive the third and fourth switching transistors to turn on or off.

[0042] The control signals output by the control unit 104 include: a first control signal and a second control signal, wherein the first control signal is as follows: Figure 2 The first control signal Cs is shown, and the second control signal is as follows: Figure 2 The second control signal Cs1 is shown. The first control signal is used to control the operation of the first push-pull circuit. The second control signal is used to control the operation of the second push-pull circuit.

[0043] exist Figure 2 In the example shown, capacitor C1 is the bus capacitor, connected in series with resonant capacitor Cr. Its function is to ensure the reset of resonant inductor Lr to prevent circuit damage. Switches S1 and S2 form a half-bridge, and voltage and current are transferred to the next stage by controlling the alternating conduction of switches S1 and S2. The four switches after transformer T, namely switches Sw1 to Sw4, are synchronous rectification switches. MOSFETs Sw1, Sw2, Sw3, and Sw4, along with resistors R3, R4, R5, and R6, constitute the synchronous rectification circuit. Transistors Sp, Sn, Sp1, and Sn1, along with resistors R7, R8, R9, and R10, constitute the drive circuit of the synchronous rectification circuit. The drive circuit mainly consists of two parts. In the first part, transistors Sn and Sp are connected to form a push-pull circuit to drive the synchronous rectification switches Sw1 and Sw2. In the second part, transistors Sn1 and Sp1 are connected to form a push-pull circuit to drive the synchronous rectification switches Sw3 and Sw4.

[0044] In some embodiments, a protection resistor module is further provided between the gate and drain of each of the first, second, third, and fourth switching transistors in the synchronous rectification circuit.

[0045] Specifically, such as Figure 2The low-loss synchronous rectification circuit of the LLC switching power supply shown includes: capacitors C0, C1, resonant capacitor Cr, and C2; MOSFETs S1 and S2 with body diodes and capacitors; resonant inductor Lr and magnetizing inductor Lm; transformer T; MOSFETs Sw1, Sw2, Sw3, and Sw4 for synchronous rectification; transistors Sp, Sn, Sp1, and Sn1; resistors R1, R2, R3, R4, R5, R6, R7, R8, R9, and R10; and a control IC.

[0046] In this configuration, capacitor C0 is located at the output of the power supply. The first terminal of capacitor C0 is connected to the source of MOSFET S1, and is also grounded via capacitor C1 and resonant capacitor Cr. The drain of MOSFET S1 is connected to the source of MOSFET S2, and the second terminal of capacitor C0 is connected to the drain of MOSFET S2 and grounded. The drain of MOSFET S1, via resistor R1, resonant inductor Lr, magnetizing inductor Lm, and resistor R2, is connected to the common terminal of capacitor C1 and resonant capacitor Cr. The common terminal of MOSFET S1 and resistor R1 serves as the sampling terminal for the first detection signal and is connected to the first input terminal of the control IC. The common terminal of magnetizing inductor Lm and resistor R2 serves as the sampling terminal for the second detection signal and is connected to the second input terminal of the control IC. The first output terminal of the control IC outputs the first control signal CS, and the second output terminal outputs the second control signal CS1. The common terminal of resonant inductor Lr and magnetizing inductor Lm is connected to the same-name terminal of the primary coil of transformer T. The common terminal of resistor R2 and resonant capacitor Cr is connected to the opposite-name terminal of the primary winding of transformer T. The secondary winding of transformer T includes a primary winding and a secondary winding. The opposite-name terminal of the primary winding is connected to the source of MOSFET Sw3, and the same-name terminal of the primary winding is grounded via capacitor C2. The opposite-name terminal of the secondary winding is connected to the same-name terminal of the primary winding, and the same-name terminal of the secondary winding is connected to the source of MOSFET Sw1, and the same-name terminal of the secondary winding is grounded via MOSFET Sw1, Sw2, Sw3, and Sw4. The drains of MOSFETs Sw1, Sw2, Sw3, and Sw4 are all grounded. A resistor R3 is connected between the gate and drain of MOSFET Sw1; a resistor R4 is connected between the gate and drain of MOSFET Sw2; a resistor R5 is connected between the gate and drain of MOSFET Sw3; and a resistor R6 is connected between the gate and drain of MOSFET Sw4. The resistors connected between the gate and drain of the MOSFETs are pull-down resistors, ensuring the circuit operates in two states: either high or low, preventing it from operating in a high-impedance state. The gates of MOSFETs Sw1 and Sw2 are also connected to the emitters of transistors Sp and Sn, respectively, via resistor R8. The gates of MOSFETs Sw3 and Sw4 are also connected to the emitters of transistors Sp1 and Sn1, respectively, via resistor R10. The first control signal CS, after passing through resistor R7, is connected to the bases of transistors Sp and Sn, respectively. The DC power supply VCC is connected to the collector of transistor Sp. The collector of transistor Sn is grounded. The second control signal CS1, after passing through resistor R9, is connected to the bases of transistors Sp1 and Sn1, respectively.The DC power supply VCC is connected to the collector of transistor Sp1. The collector of transistor Sn1 is grounded.

[0047] In some embodiments, when the LLC switching power supply is operating, the upper bridge switch and the lower bridge switch are alternately turned on. Specifically, if the current switch is the upper bridge switch, then when the upper bridge switch is turned on and then turned off, the control signal output by the control unit 104 is the second control signal. If the current switch is the lower bridge switch, then when the lower bridge switch is turned on and then turned off, the control signal output by the control unit 104 is the first control signal.

[0048] Specifically, Figure 4 This is a schematic diagram illustrating the working process of a novel low-loss synchronous rectifier circuit in the downstream stage of an LLC switching power supply. Figure 4 As shown, the working process of the low-loss synchronous rectification circuit after the LLC switching power supply includes:

[0049] Step 11: When the entire circuit of the low-loss synchronous rectifier circuit after the LLC switching power supply just starts to work, the front-end AC-DC circuit (i.e., AC-DC conversion circuit) uses a full-wave bridge uncontrolled rectifier circuit to rectify AC power into DC power as the power supply bus, and then proceed to step 12.

[0050] Step 12: The power supply bus transmits energy to the downstream LLC switching power supply. At this time, the upper MOSFET of the half-bridge LLC switching power supply, i.e. the switching transistor S1, is turned on. It is assumed that the current flow direction is positive, the resonant current Ir flows in the positive direction, the excitation current Im rises, and the resonant current Ir is greater than the excitation current Im. At this time, the current flows in the positive direction to the secondary side of the transformer T, and transmits energy to the secondary coil of the transformer T. Then, step 13 is executed.

[0051] Step 13: In the half-bridge LLC switching power supply, the upper MOSFET (switching transistor S1) and the lower MOSFET (switching transistor S2) are alternately turned on. After the upper MOSFET (switching transistor S1) of the half-bridge LLC switching power supply is turned on and then turned off, the half-bridge LLC switching power supply enters the dead time. At this time, the resonant current Ir is equal to the magnetizing current Im, and then step 14 is executed.

[0052] Step 14: Resistors R1 and R2 detect that the resonant current Ir is equal to the excitation current Im, and transmit the sampled voltage of resistor R1 for the resonant current Ir and the sampled voltage of resistor R2 for the excitation current Im to the control IC, and then execute step 15.

[0053] Step 15: The control IC determines that the sampling voltage of the resonant current Ir by resistor R1 is equal to the sampling voltage of the excitation current Im by resistor R2, i.e., the resonant current Ir is equal to the excitation current Im. Then, it outputs either the first control signal Cs or the second control signal Cs1 to control the corresponding synchronous rectification side switch to turn on, and then executes step 16. For example: if the control IC outputs the first control signal Cs, it controls the synchronous rectification side switches Sw1 and Sw2 to turn on. If the control IC outputs the second control signal Cs1, it controls the synchronous rectification side switches Sw3 and Sw4 to turn on.

[0054] In the synchronous rectification mode of the relevant scheme, switching transistors Sw3 and Sw4 are turned on, while switching transistors Sw1 and Sw2 are turned off. In the present invention, since the secondary side of transformer T clamps the magnetizing inductance Lm of the primary side, the magnetizing inductance Lm begins to charge. The current of the magnetizing inductance Lm, i.e., the magnetizing current Im, rises at a certain slope until the resonant current Ir equals the magnetizing current Im. The voltage is then sampled by two sampling resistors (i.e., resistors R1 and R2) and transmitted to the control IC for comparison. If the sampling voltage of resistor R1 for the resonant current Ir is equal to the sampling voltage of resistor R2 for the magnetizing current Im, a corresponding high or low level is applied to drive the corresponding synchronous rectification side switch. For example, when the upper MOSFET of the half-bridge LLC switching power supply, i.e., switch S1, is turned on and then turned off, the corresponding synchronous rectification side switches SW3 and SW4 are driven. When the upper MOSFET of the half-bridge LLC switching power supply, i.e., switch S2, is turned on and then turned off, the corresponding synchronous rectification side switches SW1 and SW2 are driven. Therefore, the corresponding synchronous rectifier switch can be turned on during the dead time of the half-bridge LLC switching power supply, while the current has not yet been transmitted to the secondary side of transformer T. This avoids the voltage and current overlap loss when the switch on the synchronous rectifier side is turned on. In the synchronous rectification mode of related schemes, the switch on the synchronous rectifier side is turned on only after the current on the secondary side of transformer T is transmitted. Obviously, the solution of this invention is more effective in controlling the loss of the switch on the synchronous rectifier side.

[0055] Step 16: After the dead time of the half-bridge LLC switching power supply, the lower MOSFET, i.e. the switching transistor S2, of the half-bridge LLC switching power supply is turned on and transfers energy to the subsequent stage. Since the corresponding synchronous rectification side switching transistor has been turned on in advance, no current flows through the synchronous rectification side switching transistor, which can achieve low-loss turn-on of the synchronous rectification side switching transistor.

[0056] Figure 5 This is a flowchart illustrating a synchronous rectification control method for a novel low-loss synchronous rectifier circuit in a novel LLC switching power supply. Figure 6This is a schematic diagram of the ideal waveform of the drive signal for a novel low-loss synchronous rectifier circuit in a novel LLC switching power supply. Figure 5 and Figure 6 As shown, the synchronous rectification control method for the low-loss synchronous rectifier circuit in the downstream stage of an LLC switching power supply includes:

[0057] Step 21: When the low-loss synchronous rectifier circuit of the LLC switching power supply is initially powered on (i.e., before it is powered on), the synchronous rectifier side switches Sw1 and Sw2 need to be turned on in advance during the positive half-cycle. This advance, for example, turning on the synchronous rectifier side switches before the upper MOSFET turns on, only needs to ensure that the synchronous rectifier side switches have enough time to obtain the voltage required for their turn-on. This provides the initial conditions for the steady-state operation of the low-loss synchronous rectifier circuit of the LLC switching power supply. The specific operation process is as follows: Upon initial power-on, assuming the upper MOSFET of the half-bridge LLC switching power supply, i.e., switch S1, is turned on, the current flows in the forward direction. At this time, the resonant current Ir is greater than the magnetizing current Im, and the current I transferred to the secondary side of transformer T is... 次级 The relationship between the resonant current Ir and the magnetizing current Im is shown in the formula: Ir = Im + I 次级 Since the switching transistors Sw1 and Sw2 on the synchronous rectification side are turned on in advance, the magnetizing inductor Lm on the primary side of the transformer T is charged. The current of the magnetizing inductor Lm, i.e. the magnetizing current Im, rises until it is equal to the resonant current Ir. At this time, the upper MOSFET of the half-bridge LLC switching power supply, i.e. the switching transistor S1, is turned off, and then step 22 is executed.

[0058] Step 22: With the upper MOSFET (i.e., the switching transistor S1) of the half-bridge LLC switching power supply turned off, the half-bridge LLC switching power supply enters the dead-time operating state. At this time, no current flows through the secondary side of the transformer T. Since the excitation current Im is equal to the resonant current Ir during the dead time of the half-bridge LLC switching power supply, the voltages sampled by the sampling resistors R1 and R2 are equal. The voltage signals sampled by resistors R1 and R2 are transmitted to the control IC for comparison to determine whether the excitation current Im and the resonant current Ir are equal. If they are equal, proceed to step 23; otherwise, continue to step 22.

[0059] Step 23: When the upper MOSFET (switching transistor S1) of the half-bridge LLC switching power supply is turned on and then turned off, the half-bridge LLC switching power supply enters a dead-time operating state. If this is a positive half-cycle waveform (i.e., the situation where the upper MOSFET (switching transistor S1) of the half-bridge LLC switching power supply is turned on and then turned off), and the control IC detects that the magnetizing current Im and the resonant current Ir are equal, then a certain time delay is applied. Figure 6The delay time shown is from time T2 to time T1 to avoid short circuit on the secondary side of transformer T. After that, the switching transistors Sw3 and Sw4 on the synchronous rectification side of the secondary side of transformer T are turned on, and the driving signal is the second control signal Cs1.

[0060] Conversely, when the lower MOSFET (switching transistor S2) of the half-bridge LLC switching power supply is turned on and then turned off, the half-bridge LLC switching power supply enters a dead-time operating state. If this is a negative half-cycle waveform (i.e., the situation where the lower MOSFET (switching transistor S2) of the half-bridge LLC switching power supply is turned on and then turned off), and the control IC detects that the magnetizing current Im and the resonant current Ir are equal, then a certain time delay will occur, such as... Figure 6 The delay time shown is from time T2 to time T1 to avoid short circuit on the secondary side of transformer T. After that, the switching transistors Sw1 and Sw2 on the synchronous rectification side of the secondary side of transformer T are turned on, and the driving signal is the first control signal Cs.

[0061] Since the conducting switches Sw1 and Sw2, or Sw3 and Sw4, are all synchronous rectification-side switches that are turned on during the dead-time operation of the half-bridge LLC switching power supply, and since no current flows through the secondary side of transformer T during the dead-time operation of the half-bridge LLC switching power supply, the conduction losses of the conducting switches Sw1 and Sw2, or Sw3 and Sw4, are close to zero. This reduces the losses of the synchronous rectification-side switches and improves power supply efficiency.

[0062] The technical solution of this invention addresses a half-bridge LLC switching power supply, which includes a half-bridge circuit, a resonant circuit, a transformer, a synchronous rectifier circuit, and a drive circuit for the synchronous rectifier circuit. The half-bridge circuit and the resonant circuit are sequentially arranged on the primary side of the transformer, while the synchronous rectifier circuit and its drive circuit are arranged on the secondary side of the transformer. When the upper or lower bridge switch in the half-bridge circuit is turned on and then turned off, the half-bridge LLC switching power supply enters a dead-time state. During the dead-time of the half-bridge LLC switching power supply, the current of the resonant inductor (resonant current) and the current of the magnetizing inductor (magnetizing current) in the resonant circuit are detected to be equal. If the resonant current and the magnetizing current are equal, a set of switches in the synchronous rectifier circuit corresponding to the switch that was turned on and off in the half-bridge circuit is controlled to turn on. This ensures that this set of switches turns on preferentially before receiving current on the secondary side of the transformer, avoiding voltage and current crossover losses when the set of switches turns on after receiving current on the secondary side of the transformer. Therefore, by enabling the switching transistors on the synchronous rectification side of the half-bridge LLC switching power supply to conduct before the transformer during the dead time of the half-bridge LLC switching power supply, the switching losses of the switching transistors on the synchronous rectification side are reduced, which helps to reduce the switching losses of the half-bridge LLC switching power supply and thus improve the efficiency of the half-bridge LLC switching power supply.

[0063] According to an embodiment of the present invention, an LLC switching power supply corresponding to a control device for an LLC switching power supply is also provided. This LLC switching power supply may include the control device for the LLC switching power supply described above.

[0064] Since the processing and functions implemented by the LLC switching power supply in this embodiment are basically the same as those in the embodiments, principles and examples of the device, any details not covered in this embodiment can be found in the relevant descriptions in the foregoing embodiments, and will not be repeated here.

[0065] The technical solution of this invention addresses a half-bridge LLC switching power supply, which includes a half-bridge circuit, a resonant circuit, a transformer, a synchronous rectifier circuit, and a drive circuit for the synchronous rectifier circuit. The half-bridge circuit and the resonant circuit are sequentially arranged on the primary side of the transformer, while the synchronous rectifier circuit and its drive circuit are arranged on the secondary side of the transformer. When the upper or lower bridge switch in the half-bridge circuit is turned on and then turned off, the half-bridge LLC switching power supply enters a dead-time state. During the dead time of the half-bridge LLC switching power supply, the current of the resonant inductor in the resonant circuit (i.e., the resonant current) and the current of the magnetizing inductor in the resonant circuit (i.e., the magnetizing current) are checked to see if they are equal. If the resonant current and the magnetizing current are equal, a set of switching transistors in the synchronous rectifier circuit corresponding to the switching transistors that have been turned on and off in the half-bridge circuit are controlled to turn on. This allows the set of switching transistors to turn on preferentially before receiving current on the secondary side of the transformer, avoiding the voltage and current crossover loss on the set of switching transistors when they turn on after receiving current on the secondary side of the transformer. This reduces the loss of the switching transistors on the synchronous rectifier side and improves the power supply efficiency.

[0066] According to embodiments of the present invention, a control method for an LLC switching power supply corresponding to an LLC switching power supply is also provided, such as... Figure 7 The diagram shows a flowchart of an embodiment of the method of the present invention. The control method for this LLC switching power supply may include steps S110 to S140.

[0067] In step S110, when the LLC switching power supply is powered on, one of the upper bridge switch and the lower bridge switch is turned on, and this switch is recorded as the current switch. That is, this switch is recorded as the current switch among the upper bridge switch and the lower bridge switch, and the other switch among the upper bridge switch and the lower bridge switch is recorded as the next switch. Additionally, the drive units corresponding to the set of rectifier switches in the first group and the second group that correspond to the current switch are controlled to operate, so as to control the set of rectifier switches in the first group and the second group that correspond to the current switch to turn on at a predetermined time.

[0068] In step S120, based on the alternating conduction rule of the upper bridge switch and the lower bridge switch, when the current switch needs to be turned off, the current switch is controlled to turn off, and the first group of rectifier switches and the second group of rectifier switches corresponding to the current switch are also controlled to turn off. After the current switch is turned off and before the next switch is turned on, the LLC switching power supply enters a dead zone state.

[0069] In step S130, the current in the resonant inductor and the current in the magnetizing inductor are detected. When the LLC switching power supply is in a dead-time state, the detected current in the resonant inductor is recorded as a first detection signal, and the detected current in the magnetizing inductor is recorded as a second detection signal. The first detection signal can be a voltage signal representing the magnitude of the current in the resonant inductor, and the second detection signal can be a voltage signal representing the magnitude of the current in the magnetizing inductor.

[0070] In step S140, when the LLC switching power supply is in a dead zone state, it is determined whether the first detection signal and the second detection signal are equal. If it is determined that the first detection signal and the second detection signal are equal, a control signal is output to control the operation of a set of drive units corresponding to the first set of rectifier switches and the set of rectifier switches in the second set that correspond to the next switch. This is to control the first set of rectifier switches and the set of rectifier switches in the second set that correspond to the next switch to be turned on first before the secondary side of the transformer is energized.

[0071] The present invention utilizes the characteristic that the magnetizing inductance Lm of an LLC switching power supply is clamped by the secondary coil of a transformer T during operation. By detecting when the voltage of the magnetizing inductance reaches a certain threshold, a novel low-loss synchronous rectifier circuit in the subsequent stage of the LLC switching power supply is designed to control the upper and lower arms of the synchronous rectifier bridge to conduct alternately, achieving zero-voltage turn-on and zero-current turn-off. This reduces the switching losses of the LLC switching power supply and improves its efficiency. By utilizing the operating characteristics of the LLC switching power supply, a driver circuit is designed to drive the subsequent synchronous rectifier circuit, eliminating the need for a driver chip, reducing costs, and providing higher stability than a driver chip. Achieving zero-voltage turn-on and zero-current turn-off in synchronous rectification reduces the rectification losses of the synchronous rectifier circuit and the heat generation of the switching transistors in the synchronous rectifier circuit, which is beneficial for extending the lifespan of the switching transistors in the synchronous rectifier circuit and improving the operating efficiency of the LLC switching power supply.

[0072] In some embodiments, the first set of driving units includes a first push-pull circuit. The second set of driving units includes a second push-pull circuit. The first push-pull circuit is used to drive the first and second switching transistors to turn on or off. The second push-pull circuit is used to drive the third and fourth switching transistors to turn on or off.

[0073] The control signals output by the control unit 104 include: a first control signal and a second control signal, wherein the first control signal is as follows: Figure 2 The first control signal Cs is shown, and the second control signal is as follows: Figure 2The second control signal Cs1 is shown. The first control signal is used to control the operation of the first push-pull circuit. The second control signal is used to control the operation of the second push-pull circuit.

[0074] Specifically, the corresponding synchronous rectification side switches SW3 and SW4 are driven when the upper MOSFET (switching transistor S1) of the half-bridge LLC switching power supply is turned on and then turned off. Conversely, the corresponding synchronous rectification side switches SW1 and SW2 are driven when the upper MOSFET (switching transistor S2) of the half-bridge LLC switching power supply is turned on and then turned off. For example, if the control IC outputs a first control signal Cs, then the synchronous rectification side switches Sw1 and Sw2 are turned on. If the control IC outputs a second control signal Cs1, then the synchronous rectification side switches Sw3 and Sw4 are turned on.

[0075] In some embodiments, when the LLC switching power supply is operating, the upper bridge switch and the lower bridge switch are alternately turned on. Specifically, if the current switch is the upper bridge switch, then when the upper bridge switch is turned on and then turned off, the control signal output by the control unit 104 is the second control signal. If the current switch is the lower bridge switch, then when the lower bridge switch is turned on and then turned off, the control signal output by the control unit 104 is the first control signal.

[0076] In the present invention, sampling resistors (such as resistors R1 and R2) are added to the resonant circuit and the magnetizing inductor Lm circuit of the LLC switching power supply to collect the voltage signals of the resonant current Ir and the magnetizing current Im. When the magnetizing current Im is detected to be equal to the resonant current Ir, the corresponding synchronous rectification side switching transistors, such as the conducting switching transistors Sw1 and Sw2 or the conducting switching transistors Sw3 and Sw4, are controlled to turn on before the secondary side of the transformer T. This avoids the turn-on loss of the conducting switching transistors Sw1 and Sw2 or the conducting switching transistors Sw3 and Sw4, that is, it avoids the voltage and current crossover loss on the corresponding switching transistors on the synchronous rectification side when the switching transistors Sw1 and Sw2 or the switching transistors Sw3 and Sw4 receive current on the secondary side of the transformer T before turning on.

[0077] Since the processing and functions implemented by the method in this embodiment are basically the same as the embodiments, principles and examples of the aforementioned LLC switching power supply, any details not covered in this embodiment can be found in the relevant descriptions in the aforementioned embodiments, and will not be repeated here.

[0078] The technical solution of this embodiment addresses a half-bridge LLC switching power supply, which includes a half-bridge circuit, a resonant circuit, a transformer, a synchronous rectifier circuit, and a drive circuit for the synchronous rectifier circuit. The half-bridge circuit and the resonant circuit are sequentially arranged on the primary side of the transformer, while the synchronous rectifier circuit and its drive circuit are arranged on the secondary side of the transformer. When the upper bridge switch or the lower bridge switch in the half-bridge circuit is turned on and then turned off, the half-bridge LLC switching power supply enters a dead-time state. During the dead time of the half-bridge LLC switching power supply, the current of the resonant inductor in the resonant circuit (i.e., the resonant current) and the current of the magnetizing inductor in the resonant circuit (i.e., the magnetizing current) are checked for equality. If the resonant current and the magnetizing current are equal, a set of switching transistors in the synchronous rectifier circuit corresponding to the switching transistors that have been turned on and off in the half-bridge circuit are controlled to turn on. This ensures that the set of switching transistors turns on preferentially before receiving current on the secondary side of the transformer, avoiding the voltage and current crossover loss on the set of switching transistors when they turn on after receiving current on the secondary side of the transformer. This optimizes the subsequent synchronous rectifier circuit, improves the efficiency of the LLC switching power supply, and reduces the heat generation of the switching transistors in the LLC switching power supply.

[0079] In summary, it is readily understood by those skilled in the art that, without conflict, the aforementioned advantageous methods can be freely combined and superimposed.

[0080] The above description is merely an embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of the claims of the present invention.

Claims

1. A control device for an LLC switching power supply, characterized in that, The LLC switching power supply includes: a half-bridge circuit, a resonant circuit, a transformer, a synchronous rectifier circuit, and a drive circuit for the synchronous rectifier circuit; the half-bridge circuit and the resonant circuit are sequentially arranged on the primary side of the transformer; the synchronous rectifier circuit is arranged on the secondary side of the transformer; the half-bridge circuit includes: an upper bridge switch and a lower bridge switch; the resonant circuit has a resonant inductor and a magnetizing inductor; the synchronous rectifier circuit includes: a first set of rectifier switches and a second set of rectifier switches, wherein the first set of rectifier switches is correspondingly turned on or off with the upper bridge switch, and the second set of rectifier switches is correspondingly turned on or off with the lower bridge switch; the drive circuit includes: a first set of drive units for driving the first set of rectifier switches and a second set of drive units for driving the second set of rectifier switches; the control device of the LLC switching power supply includes: a detection unit and a control unit; wherein... The control unit is configured to, when the LLC switching power supply is powered on, control one of the upper bridge switching transistors and the lower bridge switching transistors to turn on, record the one switching transistor as the current switching transistor, and record the other of the upper bridge switching transistors and the lower bridge switching transistors as the next switching transistor; and control a set of drive units corresponding to the set of rectifier switching transistors in the first group of rectifier switching transistors and the second group of rectifier switching transistors corresponding to the current switching transistor to operate, so as to control the set of rectifier switching transistors in the first group of rectifier switching transistors and the second group of rectifier switching transistors corresponding to the current switching transistor to turn on at a predetermined time; The control unit is further configured to control the current switching transistor to turn off when the current switching transistor needs to be turned off, and to control the first group of rectifier switching transistors and the second group of rectifier switching transistors corresponding to the current switching transistor to turn off; after the current switching transistor is turned off and before the next switching transistor is turned on, the LLC switching power supply enters a dead zone state; The detection unit is used to detect the current on the resonant inductor and the current on the magnetizing inductor, and to record the detected current on the resonant inductor as a first detection signal and the detected current on the magnetizing inductor as a second detection signal. The control unit is further configured to determine whether the first detection signal and the second detection signal are equal when the LLC switching power supply is in a dead zone state, so as to output a control signal when the first detection signal and the second detection signal are determined to be equal, so as to control the operation of a set of drive units corresponding to the first set of rectifier switches and the set of rectifier switches corresponding to the next switch in the second set of rectifier switches, so as to control the first set of rectifier switches and the set of rectifier switches corresponding to the next switch in the second set of rectifier switches to be turned on firstly before the secondary side of the transformer is energized.

2. The control device for the LLC switching power supply according to claim 1, characterized in that, The detection unit includes: a first detection resistor module and a second detection resistor module; the first detection resistor module is disposed between the upper bridge switch and the resonant inductor; the second detection resistor module is disposed between the magnetizing inductor and the primary side of the transformer.

3. The control device for an LLC switching power supply according to claim 1 or 2, characterized in that, in, The synchronous rectifier circuit is a full-bridge synchronous rectifier circuit; The first group of rectifier switches includes a first switch and a second switch; the second group of rectifier switches includes a third switch and a fourth switch; the first switch, the second switch, the third switch and the fourth switch constitute a full-bridge synchronous rectifier circuit. The first group of driving units includes: a first push-pull circuit; the second group of driving units includes: a second push-pull circuit; the first push-pull circuit is used to drive the first switch and the second switch to turn on or off; the second push-pull circuit is used to drive the third switch and the fourth switch to turn on or off. The control signals output by the control unit include: a first control signal and a second control signal; the first control signal is used to control the operation of the first push-pull circuit; the second control signal is used to control the operation of the second push-pull circuit.

4. The control device for the LLC switching power supply according to claim 3, characterized in that, In the synchronous rectification circuit, a protection resistor module is also provided between the gate and drain of each of the first, second, third, and fourth switching transistors.

5. The control device for the LLC switching power supply according to claim 3, characterized in that, When the LLC switching power supply is operating, the upper bridge switch and the lower bridge switch are alternately turned on; wherein: If the current switch is the upper bridge switch, then when the upper bridge switch is turned on and then turned off, the control signal output by the control unit is the second control signal. If the current switch is the lower bridge switch, then when the lower bridge switch is turned on and then turned off, the control signal output by the control unit is the first control signal.

6. An LLC switching power supply, characterized in that, include: The control device for an LLC switching power supply as described in any one of claims 1 to 2.

7. A control method for an LLC switching power supply as described in claim 6, characterized in that, include: When the LLC switching power supply is powered on, one of the upper bridge switch and the lower bridge switch is turned on, and this switch is recorded as the current switch, and the other switch is recorded as the next switch; and a set of drive units corresponding to the set of rectifier switches in the first group of rectifier switches and the second group of rectifier switches corresponding to the current switch are controlled to work, so as to control the set of rectifier switches in the first group of rectifier switches and the second group of rectifier switches corresponding to the current switch to be turned on in advance for a set time; When the current switch needs to be turned off, the current switch is controlled to turn off, and the first group of rectifier switches and the second group of rectifier switches corresponding to the current switch are also controlled to turn off; after the current switch is turned off and before the next switch is turned on, the LLC switching power supply enters a dead zone state; The current in the resonant inductor and the current in the magnetizing inductor are detected. The detected current in the resonant inductor is recorded as the first detection signal, and the detected current in the magnetizing inductor is recorded as the second detection signal. When the LLC switching power supply is in a dead zone state, it is determined whether the first detection signal and the second detection signal are equal. If the first detection signal and the second detection signal are equal, a control signal is output to control the operation of the drive unit corresponding to the first group of rectifier switches and the group of rectifier switches in the second group that corresponds to the next switch. This controls the first group of rectifier switches and the group of rectifier switches in the second group that corresponds to the next switch to be turned on first before the secondary side of the transformer is energized.

8. An LLC switching power supply, characterized in that, include: The control device for an LLC switching power supply as described in any one of claims 3 to 5.

9. A control method for an LLC switching power supply as described in claim 8, characterized in that, include: When the LLC switching power supply is powered on, one of the upper bridge switch and the lower bridge switch is turned on, and this switch is recorded as the current switch, and the other switch is recorded as the next switch; and a set of drive units corresponding to the set of rectifier switches in the first group of rectifier switches and the second group of rectifier switches corresponding to the current switch are controlled to work, so as to control the set of rectifier switches in the first group of rectifier switches and the second group of rectifier switches corresponding to the current switch to be turned on in advance for a set time; When the current switch needs to be turned off, the current switch is controlled to turn off, and the first group of rectifier switches and the second group of rectifier switches corresponding to the current switch are also controlled to turn off; after the current switch is turned off and before the next switch is turned on, the LLC switching power supply enters a dead zone state; The current in the resonant inductor and the current in the magnetizing inductor are detected. The detected current in the resonant inductor is recorded as the first detection signal, and the detected current in the magnetizing inductor is recorded as the second detection signal. When the LLC switching power supply is in a dead zone state, it is determined whether the first detection signal and the second detection signal are equal. If the first detection signal and the second detection signal are equal, a control signal is output to control the operation of the drive unit corresponding to the first group of rectifier switches and the group of rectifier switches in the second group that corresponds to the next switch. This controls the first group of rectifier switches and the group of rectifier switches in the second group that corresponds to the next switch to be turned on first before the secondary side of the transformer is energized.

10. The control method for an LLC switching power supply according to claim 9, characterized in that, The first group of driving units includes: a first push-pull circuit; the second group of driving units includes: a second push-pull circuit; the first push-pull circuit is used to drive the first switch and the second switch to turn on or off; the second push-pull circuit is used to drive the third switch and the fourth switch to turn on or off. The control signals output by the control unit include: a first control signal and a second control signal; the first control signal is used to control the operation of the first push-pull circuit; the second control signal is used to control the operation of the second push-pull circuit.

11. The control method for an LLC switching power supply according to claim 10, characterized in that, When the LLC switching power supply is operating, the upper bridge switch and the lower bridge switch are alternately turned on; wherein: If the current switch is the upper bridge switch, then when the upper bridge switch is turned on and then turned off, the control signal output by the control unit is the second control signal. If the current switch is the lower bridge switch, then when the lower bridge switch is turned on and then turned off, the control signal output by the control unit is the first control signal.

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