A synchronous rectification device and control method thereof

Abstract

A synchronous rectifier device includes a synchronous rectifier, a drive control circuit, a Vcc capacitor, and a charging circuit for charging the gate of the synchronous rectifier. The Vcc capacitor is charged via the charging circuit using a reverse voltage applied to the synchronous rectifier. When the Vcc capacitor voltage is detected to have risen to its upper limit, Vcc_H, charging of the Vcc capacitor is stopped; when the Vcc voltage is detected to have dropped to its lower limit, Vcc_L, charging of the Vcc capacitor is resumed, so that the switching tube of the charging circuit operates in an intermittent and fully conductive state. By controlling the upper and lower limits of the Vcc voltage, the present invention promotes intermittent operation of the charging circuit, significantly reducing the power consumption of the power supply circuit. In the standby mode, when the operating frequency is lower, the current consumption at the Vcc terminal is extremely low, and the intermittent operation of the charging circuit is extended, further reducing power consumption, heat generation, and standby power consumption.

Description

Technical Field

[0001] The present invention relates to the technical field of switching power supplies, and in particular to a power supply technology for a synchronous rectification device and a control method thereof. Background Art

[0002] A diode is a commonly used rectifying device. When a forward voltage is applied, it conducts, allowing current to flow in the forward direction. When a reverse voltage is applied, it cuts off, preventing reverse current flow. Because a diode has an inherent forward voltage drop when conducting, and the voltage drop increases with increasing current, diode losses are typically described as the current multiplied by the forward voltage drop. Therefore, as the current flowing through the diode increases, its losses also increase, resulting in reduced switching power supply efficiency. To address the issue of rectifier diode losses, power semiconductor devices, such as MOS transistors, can be used to replace diode rectification, a technique known as synchronous rectification. Unlike diodes, the on-state characteristics of MOS transistors are described as their internal resistance, and the on-state losses are described as the square of the effective current flowing through the MOS transistor multiplied by the internal resistance. Power semiconductors typically have very low internal resistance, especially low-voltage MOS transistors used in synchronous rectification, which can have an internal resistance in the milliohm range. This can significantly reduce losses in the rectification circuit, thereby improving the efficiency of the switching power supply. The advantage of using power semiconductor devices instead of diodes as rectifiers is that efficiency is improved. However, power semiconductor devices are controlled devices and need to detect and control the circuit signals. The detection circuit and control circuit require appropriate power supply to work properly.

[0003] U.S. Patent No. 6,060,943A, published in 1998 by NMB Corporation, discloses a diode-simulating circuit with two terminals, A and K. This circuit allows current to flow in one direction, from terminal A to K, while blocking current in the opposite direction, from K to A. The circuit also includes a comparator and a three-terminal switching device. The voltage comparator controls the control terminal of the three-terminal switching device to activate the switching device. When the voltage at terminal A is higher than the voltage at terminal K, current flows from terminal A to terminal K. When the voltage at terminal K is higher than the voltage at terminal A, the current flows from terminal K to terminal A. The control method described in the document, which enables the semiconductor device to have the same characteristics as a traditional diode, has become a well-known technology. However, the document does not mention the power supply scheme for the control unit.

[0004] Infineon Technologies AG published Chinese patent CN105846695A in 2016, which discloses a self-powered circuit for synchronous rectifiers. The circuit needs to be arranged in an isolated topology, including a primary side and a secondary side. The synchronous rectifier is arranged on the secondary side and has a synchronous rectifier transistor, a voltage regulator, an auxiliary transistor, a clamping device, and a gate driver circuit. The schematic diagram of the charging circuit is shown in FIG. Figure 1As shown, it includes a charging MOS tube, a voltage regulator tube, etc. The basic principle is to use the reverse voltage generated by the primary-side switch action of the isolation topology in the secondary-side rectifier to power the control circuit, and the Vcc voltage is clamped by the voltage regulator tube connected to the gate of the charging MOS tube. During normal operation, when the difference between the Vcc voltage and the gate voltage of the charging MOS tube is less than the turn-on threshold of the auxiliary transistor, charging of Vcc is stopped, so the Vcc voltage is clamped to a certain voltage value by the voltage regulator tube. In actual application, when the circuit reaches a steady state, the auxiliary transistor operates in a non-fully conductive state, similar to a linear regulator. Current flows through the auxiliary transistor in each cycle, causing great power loss, leading to heat, low efficiency and high standby power consumption. Summary of the Invention

[0005] In view of this, the technical problem to be solved by the present invention is to provide a synchronous rectification device and a control method thereof, which can reduce the power loss of the power supply circuit, reduce heat and standby power consumption, and improve the efficiency of the switching power supply.

[0006] In order to solve the above technical problems, the present invention provides the following technical solutions:

[0007] A control method for a synchronous rectifier device utilizes a reverse voltage applied to the synchronous rectifier device to charge a Vcc capacitor through a charging circuit. When it is detected that the Vcc capacitor voltage rises to its upper limit value Vcc_H, charging of the Vcc capacitor is stopped; when it is detected that the Vcc voltage drops to its lower limit value Vcc_L, charging of the Vcc capacitor is started, so that a switch tube of the charging circuit operates in an intermittent and fully conductive state.

[0008] The voltage across the synchronous rectifier is detected by the drive control circuit. When it is detected that the voltage across the synchronous rectifier is forward, that is, the voltage at terminal A is higher than the voltage at terminal K, the synchronous rectifier is turned on and the current flows from terminal A to terminal K. When it is detected that the voltage across the synchronous rectifier is reverse, that is, the voltage at terminal A is lower than the voltage at terminal K, the synchronous rectifier is turned off to prevent the current from flowing from terminal K to terminal A.

[0009] A synchronous rectifier device includes a synchronous rectifier, a drive control circuit, a Vcc capacitor, and a charging circuit. The source of the synchronous rectifier serves as an anode A of the synchronous rectifier device, and the drain of the synchronous rectifier serves as a cathode K of the synchronous rectifier device. The drive control circuit is used to detect the voltage across the synchronous rectifier to control the on and off of the synchronous rectifier. The Vcc capacitor is used to provide a suitable operating voltage to the drive control circuit when the synchronous rectifier is on. The charging circuit is used to control the voltage of the Vcc capacitor and charge the Vcc capacitor using a reverse voltage applied to the synchronous rectifier. The device is characterized in that: an input end of the charging circuit is connected to the drain of the synchronous rectifier and a first input end of the drive control circuit, a first output end of the charging circuit is connected to one end of the Vcc capacitor and a second input end of the drive control circuit, a second output end of the charging circuit is connected to the other end of the Vcc capacitor, a third input end of the drive control circuit, and the source of the synchronous rectifier, and an output end of the drive control circuit is connected to the gate of the synchronous rectifier.

[0010] As a specific embodiment of the above-mentioned synchronous rectification device, the charging circuit includes a negative voltage protection circuit, a switching circuit, a charging control circuit and a current limiting circuit; the input end of the negative voltage protection circuit serves as the input end of the charging circuit and is connected to the first input end of the drive control circuit and the drain of the synchronous rectifier tube, the output end of the negative voltage protection circuit is connected to the first input end of the switching circuit, the second input end of the switching circuit is connected to the first output end of the charging control circuit, the output end of the switching circuit is connected to the input end of the current limiting circuit, the output end of the current limiting circuit is connected to the first input end of the charging control circuit and serves as the first output end of the charging circuit and is connected to one end of the Vcc capacitor and the second input end of the drive control circuit. The second output end of the charging control circuit serves as the second output end of the charging circuit and is connected to the other end of the Vcc capacitor, the third input end of the drive control circuit and the source of the synchronous rectifier tube, and the output end of the drive control circuit is connected to the gate of the synchronous rectifier tube.

[0011] As a specific embodiment of the above-mentioned synchronous rectification device, the drive control circuit includes a signal detection circuit and a drive circuit, the first input end of the signal detection circuit serves as the first input end of the drive control circuit, the second input end of the signal detection circuit is connected to the first input end of the drive circuit as the second input end of the drive control circuit, and is also connected to the Vcc capacitor as the power supply end, the third input end of the signal detection circuit is connected to the fourth input end of the signal detection circuit and is also connected to the second input end of the drive circuit as the third input end of the drive control circuit, and is also connected to GND as a signal ground; the output end of the signal detection circuit is connected to the third input end of the drive circuit, and the output end of the drive circuit is connected to the gate of the synchronous rectifier tube as the output end of the drive control circuit.

[0012] As a specific embodiment of the above-mentioned synchronous rectification device, the charging circuit includes a diode, a charging MOS tube, a constant current source, a hysteresis comparator, a voltage regulator, and a reference voltage; the anode of the diode serves as the input end of the charging circuit, the cathode of the diode is connected to the drain of the charging MOS tube, the source of the charging MOS tube is connected to one end of the constant current source, the other end of the constant current source is connected to the first input end of the hysteresis comparator as the first output end of the charging circuit connected to one end of the Vcc capacitor, the positive electrode of the reference voltage is connected to the second input end of the hysteresis comparator, the negative electrode of the reference voltage is connected to the anode of the voltage regulator as the second output end of the charging circuit connected to the other end of the Vcc capacitor; the cathode of the voltage regulator is connected to the gate of the charging MOS tube and is also connected to the output end of the hysteresis comparator.

[0013] As another specific embodiment of the above-mentioned synchronous rectification device, the charging circuit includes a diode, a charging MOS tube, a current limiting resistor, a hysteresis comparator, a voltage regulator, and a reference voltage; the anode of the diode serves as the input end of the charging circuit, the cathode of the diode is connected to the drain of the charging MOS tube, the source of the charging MOS tube is connected to one end of the current limiting resistor, the other end of the current limiting resistor is connected to the first input end of the hysteresis comparator as the first output end of the charging circuit connected to one end of the Vcc capacitor, the positive electrode of the reference voltage is connected to the second input end of the hysteresis comparator, the negative electrode of the reference voltage is connected to the anode of the voltage regulator tube as the second output end of the charging circuit connected to the other end of the Vcc capacitor, the cathode of the voltage regulator tube is connected to the gate of the charging MOS tube, and is also connected to the output end of the hysteresis comparator.

[0014] The working principle of the present invention will be analyzed in detail in the specific implementation method. Compared with the prior art, the present invention has the following beneficial effects:

[0015] 1. By controlling the upper and lower limits of the Vcc voltage, the charging circuit is prompted to work intermittently, greatly reducing the power consumption of the power supply circuit;

[0016] 2. In standby mode, when the operating frequency is lower, the current consumption of the Vcc terminal is extremely small, and the interval time of the charging circuit will be longer, further reducing power consumption, heat generation and standby power consumption. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 It is a schematic diagram of a charging circuit in the prior art;

[0018] Figure 2 It is a structural schematic diagram of a synchronous rectification device of the present invention;

[0019] Figure 3 This is a schematic diagram of the modular structure of a synchronous rectification device of the present invention;

[0020] Figure 4a This is a schematic diagram of a first type of device connection structure of a synchronous rectifier charging circuit of the present invention;

[0021] Figure 4b This is a schematic diagram of a second device connection structure of a synchronous rectifier charging circuit of the present invention;

[0022] Figure 5 This is a main waveform diagram of a synchronous rectification device charging circuit in operation according to the present invention. DETAILED DESCRIPTION

[0023] In order to better understand the control circuit design of the present invention, specific embodiments of the present invention will now be described in detail with reference to the accompanying drawings. Specific embodiments

[0025] like Figure 2 FIG. 1 is a schematic diagram of the structure of a synchronous rectifier device according to the present invention, comprising a synchronous rectifier 10, a charging circuit 20, a drive control circuit 30, and a Vcc capacitor 40. The synchronous rectifier 10 is an N-channel MOS transistor having three terminals: a drain, a source, and a gate. The voltage between the gate and source is represented by a drive voltage Vgs. The drain serves as the cathode K of the synchronous rectifier device, and the source serves as the anode A of the synchronous rectifier device. A diode 10a is connected between the anode A and the cathode K. The input of the charging circuit 20 is connected to the cathode K of the synchronous rectifier device and the first input of the drive control circuit 30. The first output of the charging circuit 20 is connected to one end of the Vcc capacitor 40 and the second input of the drive control circuit 30. The second output of the charging circuit 20 is connected to the other end of the Vcc capacitor 40, the third input of the drive control circuit 30, and the anode A of the synchronous rectifier device. The output of the drive control circuit 30 is connected to the gate of the synchronous rectifier 10.

[0026] The drive control circuit 30 is used to detect the voltage across the synchronous rectifier 10 and thereby control the on and off of the synchronous rectifier 10. When it is detected that there is a forward voltage across the synchronous rectifier 10, that is, the voltage at terminal A is higher than the voltage at terminal K, the synchronous rectifier 10 is controlled to be on, and the current flows from terminal A to terminal K. When it is detected that there is a reverse voltage across the synchronous rectifier 10, that is, the voltage at terminal A is lower than the voltage at terminal K, the synchronous rectifier 10 is controlled to be off, preventing the current from flowing from terminal K to terminal A.

[0027] The Vcc capacitor 40 is used to provide a suitable operating voltage to the driving control circuit 30 when the synchronous rectifier 10 is turned on, so that the driving control circuit 30 can provide a driving voltage to the synchronous rectifier 10 .

[0028] The charging circuit 20 is used to control the voltage of the Vcc capacitor 40. It uses the reverse voltage applied to the synchronous rectifier 10 to charge the Vcc capacitor. When it detects that the Vcc voltage rises to the upper limit value Vcc_H, it stops charging the Vcc capacitor. When it detects that the Vcc voltage drops to the lower limit value Vcc_L, it starts charging the Vcc capacitor.

[0029] Figure 3 This is a modular structural diagram of a synchronous rectification device of the present invention. The drive control circuit 30 includes a signal detection circuit 31 and a drive circuit 32; the first input end of the signal detection circuit 31 serves as the first input end of the drive control circuit 30, the second input end of the signal detection circuit 31 is connected to the first input end of the drive circuit 32 as the second input end of the drive control circuit 30, and is also connected to the Vcc capacitor 40 as the power supply end, the third input end of the signal detection circuit 31 is connected to the fourth input end of the signal detection circuit 31 and is also connected to the second input end of the drive circuit 32 as the third input end of the drive control circuit 30, and is also connected to GND as a signal ground; the output end of the signal detection circuit 31 is connected to the third input end of the drive circuit 32, and the output end of the drive circuit 32 serves as the output end of the drive control circuit 30.

[0030] The signal detection circuit 31 is used to detect the voltage across the synchronous rectifier. When it is detected that the voltage across the synchronous rectifier is forward, that is, the voltage at terminal A is higher than the voltage at terminal K, it outputs a high level to the drive circuit; when it is detected that the voltage across the synchronous rectifier is reverse, that is, the voltage at terminal A is lower than the voltage at terminal K, it outputs a low level to the drive circuit.

[0031] The drive circuit 32 is used to drive the synchronous rectifier tube to be turned on and off. When the signal received by the drive circuit 32 from the signal detection circuit 31 is at a high level, the synchronous rectifier tube is controlled to be turned on, and the current flows from the A terminal to the K terminal; when the signal received by the drive circuit 32 from the signal detection circuit 31 is at a low level, the synchronous rectifier tube is controlled to be turned off, preventing the current from flowing from the K terminal to the A terminal.

[0032] like Figure 3 As shown, the charging circuit 20 includes a negative voltage protection circuit 21, a switch circuit 22, a current limiting circuit 23, and a charging control circuit 24. The input end of the negative voltage protection circuit 21 serves as the input end of the charging circuit 20, the output end of the negative voltage protection circuit 21 is connected to the first input end of the switch circuit 22, the second input end of the switch circuit 22 is connected to the first output end of the charging control circuit 24, the output end of the switch circuit 22 is connected to the input end of the current limiting circuit 23, the output end of the current limiting circuit 23 is connected to the first input end of the charging control circuit 24 and serves as the first output end of the charging circuit 20, and the second output end of the charging control circuit 24 serves as the second output end of the charging circuit 20.

[0033] The negative voltage protection circuit 21 is a circuit that allows current to flow in one direction and prevents current from flowing in the reverse direction. It is used to prevent current from flowing through the charging circuit 20 when the voltage across the synchronous rectifier is in the forward direction; and to allow current to flow through the charging circuit when the voltage across the synchronous rectifier is in the reverse direction.

[0034] The switch circuit 22 is used to provide a charging path and has two states: on and off. It is controlled by the charging control circuit 24 .

[0035] The charging control circuit 24 is used to detect and control the voltage on the Vcc capacitor within a reasonable range. When it is detected that the Vcc voltage rises to the upper limit value Vcc_H, it sends a shutdown signal to the switch circuit 22 to stop charging the Vcc capacitor; when it is detected that the Vcc voltage drops to the lower limit value Vcc_L, it sends an open signal to the switch circuit 22 to start charging the Vcc capacitor.

[0036] As a specific implementation of the charging circuit 20, Figure 4a FIG. 1 is a schematic diagram of a first component connection structure of a charging circuit for a synchronous rectifier device according to the present invention. The charging circuit 20 includes a diode 21, a charging MOSFET 22, a constant current source 23a, a hysteresis comparator 241, a voltage regulator 242, and a reference voltage 243. The anode of the diode 21 serves as the input of the charging circuit 20. The cathode of the diode 21 is connected to the drain of the charging MOSFET 22. The source of the charging MOSFET 22 is connected to one end of the constant current source 23a. The other end of the constant current source 23a is connected to one end of the Vcc capacitor 40 and is also connected to the first input of the hysteresis comparator 241, serving as the first output of the charging circuit 20. The positive electrode of the reference voltage 243 is connected to the second input of the hysteresis comparator 241. The negative electrode of the reference voltage 243 is connected to the other end of the Vcc capacitor 40 and is also connected to the anode of the voltage regulator 242, serving as the second output of the charging circuit 20. The cathode of the voltage regulator 242 is connected to the gate of the charging MOSFET 22 and is also connected to the output of the hysteresis comparator 241.

[0037] like Figure 4bFIG2 is a schematic diagram of a second component connection structure of a charging circuit for a synchronous rectifier device according to the present invention. The charging circuit 20 includes a diode 21, a charging MOSFET 22, a current-limiting resistor 23b, a hysteresis comparator 241, a voltage regulator 242, and a reference voltage 243. The anode of the diode 21 serves as the input of the charging circuit 20, the cathode of the diode 21 is connected to the drain of the charging MOSFET 22, the source of the charging MOSFET 22 is connected to one end of the current-limiting resistor 23b, the other end of the current-limiting resistor 23b is connected to one end of the Vcc capacitor 40 and is also connected to the first input of the hysteresis comparator 241, serving as the first output of the charging circuit 20. The positive electrode of the reference voltage 243 is connected to the second input of the hysteresis comparator 241, the negative electrode of the reference voltage 243 is connected to the other end of the Vcc capacitor 40 and is also connected to the anode of the voltage regulator 242, serving as the second output of the charging circuit 20. The cathode of the voltage regulator 242 is connected to the gate of the charging MOSFET 22 and is also connected to the first output of the hysteresis comparator 241.

[0038] In the two device connection structures of the above-mentioned synchronous rectifier charging circuit, the current limiting circuit can use a constant current source or a current limiting resistor. The difference is: the use of a current limiting resistor is a low-cost application and the solution is simple. Its disadvantage is that it will cause the charging current to change with the input voltage. The lower the voltage, the smaller the charging current, and it is difficult to maintain stable power supply; the use of a constant current source is slightly more complicated and the cost is higher than that of a current limiting resistor, but the constant current source can be applied to a wide voltage range, ensuring the stability of the charging current under different voltages, thereby maintaining stable power supply.

[0039] The operating principle of the charging circuit 20 is as follows: when it is detected that the Vcc voltage is lower than Vcc_L, the hysteresis comparator 241 outputs a high level, at which point the charging MOS transistor 22 is turned on. When the voltage across the synchronous rectifier is a reverse voltage, that is, when the voltage at terminal A is lower than the voltage at terminal K, the current charges the Vcc capacitor 40 through the diode 21, the charging MOS transistor 22, and the current limiting circuit 23. When it is detected that the Vcc voltage is higher than Vcc_H, the hysteresis comparator 241 outputs a low level, at which point the charging MOS transistor 22 is turned off, and the charging current is blocked by the charging MOS transistor 22. When the voltage across the synchronous rectifier is a forward voltage, that is, when the voltage at terminal A is higher than the voltage at terminal K, the reverse current is blocked by the diode 21, and the charging circuit 20 stops operating. When the hysteresis comparator fails or the circuit is disturbed, the voltage of the Vcc capacitor 40 may exceed Vcc_H. At this time, the voltage regulator 242 clamps the gate voltage of the charging MOS transistor 22 to a certain voltage, which is a manually set safety voltage. When the voltage of the Vcc capacitor 40 exceeds Vcc_H and continues to increase, the gate-to-source voltage of the charging MOS transistor 22 will fall below its conduction threshold and turn off, effectively preventing the voltage of the Vcc capacitor 40 from being too high and damaging other circuits of the synchronous rectifier device.

[0040] like Figure 5Figure 2 shows the main waveforms of the charging circuit of a synchronous rectifier device according to the present invention during operation. At time t0, the system begins operation, and positive and negative voltages begin to appear across the synchronous rectifier. At this time, the Vcc voltage is zero, and the charging circuit 20 begins charging the Vcc capacitor 40 at maximum current. The drive control circuit 30 is inactive, and the synchronous rectifier 10 is in the off state. When the voltage across the synchronous rectifier device is forward, that is, the voltage at terminal A is higher than the voltage at terminal K, current flows through diode 10a, and its forward voltage drop is VF.

[0041] At time t1, the Vcc voltage rises to Vth, reaches the working threshold of the drive control circuit 30, and starts working. At this time, when it is detected that the two ends of the synchronous rectifier are in a forward direction, that is, the voltage at the A end is higher than the voltage at the K end, the drive control circuit 30 controls the synchronous rectifier 10 to turn on, and the current flows from the A end to the K end through the synchronous rectifier 10; when it is detected that the two ends of the synchronous rectifier device are in a reverse direction, that is, the voltage at the A end is lower than the voltage at the K end, the drive control circuit 30 controls the synchronous rectifier 10 to turn off, preventing the current from flowing from the K end to the A end; as the Vcc voltage rises, the charging current of the charging circuit 20 gradually decreases, and the drive voltage Vgs output by the drive control circuit 30 follows the Vcc voltage, and its conduction voltage drop is Vds_on.

[0042] At time t2, the Vcc voltage rises to Vcc_H, reaching the voltage upper limit controlled by the charging control circuit 24. The charging circuit 20 stops charging the Vcc capacitor 40, and the Vcc voltage stops rising. At this time, only the Vcc capacitor 40 maintains the normal operation of the drive control circuit 30. As the circuit continues to consume, the Vcc voltage gradually decreases.

[0043] At time t3 , the Vcc voltage drops to Vcc_L, reaching the voltage lower limit controlled by the charging control circuit 24 . The charging circuit 20 restarts charging the Vcc capacitor 40 , and the Vcc voltage starts to rise again, maintaining the normal operation of the driving control circuit 30 .

[0044] At time t4, the Vcc voltage rises due to failure or interference of the hysteresis comparator and exceeds Vcc_H. Although the charging circuit 20 stops charging the Vcc capacitor 40, its voltage still rises. When it rises to Vcc_max, the Zener diode 242 starts to work and clamps the Vcc voltage to Vcc_max to protect other circuits.

[0045] Since the charging circuit works intermittently and in a fully conductive state, the loss of the charging circuit is greatly reduced compared to continuously working in a non-fully conductive state. Especially in the standby state, when the operating frequency is low, the current consumption of the Vcc terminal is extremely small, so the intermittent time of the charging circuit will be longer, further reducing power consumption, thereby achieving the purpose of reducing heat and standby power consumption and improving the efficiency of the switching power supply.

[0046] The above are only preferred embodiments of the present invention. It should be pointed out that the above preferred embodiments should not be regarded as limiting the present invention. For ordinary technicians in this technical field, several improvements and modifications can be made without departing from the spirit and scope of the present invention. Improvements and modifications to the transformer structure should also be regarded as within the scope of protection of the present invention. No further examples will be used here. The scope of protection of the present invention should be based on the scope defined by the claims.

Claims

1. A control method for a synchronous rectifier device, utilizing a reverse voltage applied to the synchronous rectifier device to charge a capacitor through a charging circuit. The capacitor is used to provide an operating voltage for a drive control circuit in the synchronous rectifier device. When it is detected that the capacitor voltage Vcc rises to its upper limit Vcc_H, a switch in the charging circuit is turned off, and the charging circuit stops charging the capacitor. When it is detected that the Vcc voltage drops to its lower limit Vcc_L, the switch in the charging circuit is turned on, and the charging circuit output begins charging the capacitor, so that the switch in the charging circuit operates in an intermittent and fully on state.

2. A synchronous rectifier device comprising a synchronous rectifier, a drive control circuit, a capacitor, and a charging circuit, wherein the source of the synchronous rectifier serves as an anode A of the synchronous rectifier device, and the drain of the synchronous rectifier serves as a cathode K of the synchronous rectifier device. The drive control circuit is used to detect the voltage across the synchronous rectifier to control the on and off of the synchronous rectifier. The capacitor is used to provide a suitable operating voltage to the drive control circuit when the synchronous rectifier is turned on. The charging circuit is used to control the capacitor voltage and charge the capacitor using a reverse voltage applied to the synchronous rectifier. The device is characterized in that: The input end of the charging circuit is connected to the drain of the synchronous rectifier and the first input end of the drive control circuit, the first output end of the charging circuit is connected to one end of the capacitor and the second input end of the drive control circuit, the second output end of the charging circuit is connected to the other end of the capacitor, the third input end of the drive control circuit and the source of the synchronous rectifier, and the output end of the drive control circuit is connected to the gate of the synchronous rectifier; wherein, when it is detected that the capacitor voltage Vcc drops to the lower limit value Vcc_L, the charging circuit starts to charge the capacitor, and the switch tube of the charging circuit works intermittently and operates in a fully on state.

3. A synchronous rectification device according to claim 2, characterized in that: The charging circuit includes a negative voltage protection circuit, a switch circuit, a charging control circuit and a current limiting circuit; the input end of the negative voltage protection circuit serves as the input end of the charging circuit and is connected to the first input end of the drive control circuit and the drain of the synchronous rectifier tube; the output end of the negative voltage protection circuit is connected to the first input end of the switch circuit, the second input end of the switch circuit is connected to the first output end of the charging control circuit, the output end of the switch circuit is connected to the input end of the current limiting circuit, the output end of the current limiting circuit is connected to the first input end of the charging control circuit and serves as the first output end of the charging circuit to connect one end of the capacitor and the second input end of the drive control circuit; the second input end of the charging control circuit serves as the second output end of the charging circuit and is connected to the other end of the capacitor, the third input end of the drive control circuit and the source of the synchronous rectifier tube; the output end of the drive control circuit is connected to the gate of the synchronous rectifier tube.

4. The synchronous rectification device according to claim 2, wherein: The drive control circuit includes a signal detection circuit and a drive circuit; the first input end of the signal detection circuit serves as the first input end of the drive control circuit, the second input end of the signal detection circuit is connected to the first input end of the drive circuit as the second input end of the drive control circuit, and is also connected to a capacitor as a power supply end, the third input end of the signal detection circuit is connected to the fourth input end of the signal detection circuit and is also connected to the second input end of the drive circuit as the third input end of the drive control circuit, and is also connected to GND as a signal ground; the output end of the signal detection circuit is connected to the third input end of the drive circuit, and the output end of the drive circuit serves as the output end of the drive control circuit and is connected to the gate of the synchronous rectifier tube.

5. The synchronous rectification device according to claim 3, wherein: The charging circuit includes a diode, a charging MOS tube, a constant current source, a hysteresis comparator, a voltage regulator, and a reference voltage; the anode of the diode serves as the input end of the charging circuit, the cathode of the diode is connected to the drain of the charging MOS tube, the source of the charging MOS tube is connected to one end of the constant current source, the other end of the constant current source is connected to the first input end of the hysteresis comparator as the first output end of the charging circuit connected to one end of the capacitor, the positive electrode of the reference voltage is connected to the second input end of the hysteresis comparator, the negative electrode of the reference voltage is connected to the anode of the voltage regulator tube as the second output end of the charging circuit connected to the other end of the Vcc capacitor; the cathode of the voltage regulator tube is connected to the gate of the charging MOS tube and is also connected to the output end of the hysteresis comparator.

6. The synchronous rectification device according to claim 3, characterized in that: The charging circuit includes a diode, a charging MOS tube, a current-limiting resistor, a hysteresis comparator, a voltage regulator, and a reference voltage; the anode of the diode serves as the input end of the charging circuit, the cathode of the diode is connected to the drain of the charging MOS tube, the source of the charging MOS tube is connected to one end of the current-limiting resistor, the other end of the current-limiting resistor is connected to the first input end of the hysteresis comparator as the first output end of the charging circuit and connected to one end of the capacitor, the positive electrode of the reference voltage is connected to the second input end of the hysteresis comparator, the negative electrode of the reference voltage is connected to the anode of the voltage regulator tube as the second output end of the charging circuit and connected to the other end of the capacitor, the cathode of the voltage regulator tube is connected to the gate of the charging MOS tube, and is also connected to the output end of the hysteresis comparator.

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