Synchronous rectification circuit

Abstract

The utility model relates to a synchronous rectification circuit, which is suitable for being connected in series between an alternating current live wire and a load, and comprises an MOSFET (Metal-Oxide-Semiconductor Field Effect Transistor) Q4, a triode Q5, a first diode D10, a second diode D9, a first resistor R15, a second resistor R14 and a voltage stabilizing diode DW7, a grid electrode of the MOSFET tube Q4 is electrically connected with a second resistor R14; the second resistor R14 is electrically connected with a cathode of a voltage stabilizing diode DW7; the anode of the first diode D10 is electrically connected with the second input / output end; the cathode of the first diode D10 is electrically connected with the first resistor R15; the collector electrode of the triode Q5 is electrically connected to a circuit where the grid electrode of the MOSFET tube Q4 is connected with the second resistor R14. The emitter of the triode Q5 is electrically connected with the first input / output end; the base electrode of the triode Q5 is electrically connected with one end of a first resistor R15; the other end of the first resistor R15 is electrically connected with the cathode of the first diode D10; the cathode of the second diode D9 is electrically connected with the second input and output end, and the anode of the second diode D9 is electrically connected to a circuit where the base electrode of the triode Q5 is connected with the first resistor R15.

Description

Technical Field

[0001] This application relates to the field of synchronous rectification technology, and more particularly to a synchronous rectification circuit. Background Technology

[0002] Switching power supplies process AC power through transformers, rectifier circuits, and filter circuits, ultimately converting it into a stable, low-ripple DC voltage for power supply. The rectifier circuit is a crucial component of a switching power supply. Existing rectifier circuits often employ synchronous rectification to convert high-frequency AC power into DC for subsequent stages. Synchronous rectification circuits typically use dedicated synchronous rectification IC chips for synchronous rectification. However, most synchronous rectification IC chips cannot operate in high-temperature environments (>85°C) because excessively high temperatures trigger the chip's high-temperature protection mode, preventing the synchronous rectification circuit from functioning properly. Summary of the Invention

[0003] In view of this, this application proposes a synchronous rectification circuit.

[0004] According to one aspect of this application, a synchronous rectification circuit is provided, which is suitable for being connected in series between an AC live wire and a load to rectify the AC current flowing out of the AC live wire, characterized in that it includes: a MOSFET Q4, a transistor Q5, a first diode D10, a second diode D9, a first resistor R15, a second resistor R14, and a Zener diode DW7.

[0005] The source of MOSFET Q4 is defined as the first input / output terminal of the synchronous rectifier circuit, and the drain of MOSFET Q4 is defined as the second input / output terminal of the synchronous rectifier circuit. Both the first and second input / output terminals are suitable for electrically connecting the AC live wire and the load, so that the synchronous rectifier circuit can be connected in series between the live wire and the load in different ways to rectify the AC power and output a positive DC voltage or a negative DC voltage.

[0006] The gate of MOSFET Q4 is electrically connected to one end of the second resistor R14, and the other end of the second resistor R14 is electrically connected to the cathode of Zener diode DW7.

[0007] The anode of the first diode D10 is electrically connected to the second input / output terminal; the cathode of the first diode D10 is electrically connected to the first resistor R15.

[0008] The collector of transistor Q5 is electrically connected to the circuit where the gate of MOSFET Q4 is connected to the second resistor R14; the emitter of transistor Q5 is electrically connected to the first input / output terminal; the base of transistor Q5 is electrically connected to one end of the first resistor R15; and the other end of the first resistor R15 is electrically connected to the cathode of the first diode D10.

[0009] The cathode of the second diode D9 is electrically connected to the second input / output terminal, and the anode of the second diode D9 is electrically connected to the circuit in which the base of the transistor Q5 is connected to the first resistor R15.

[0010] The anode of Zener diode DW7 is electrically connected to the first input / output terminal, and the cathode of Zener diode DW7 is electrically connected to the circuit in which the cathode of first diode D10 is connected to the first resistor R15 and the second resistor R14.

[0011] This is applicable when a positive voltage is applied to the first input / output terminal, the source and drain of MOSFET Q4 are connected, and current can flow from the first input / output terminal to the second input / output terminal; it is also applicable when a positive voltage is applied to the second input / output terminal, the source and drain of MOSFET Q4 are not connected, and current cannot flow from the second input / output terminal to the first input / output terminal.

[0012] In one possible implementation, it also includes: a voltage regulator resistor R13; one end of the voltage regulator resistor R13 is electrically connected to the anode of the first diode D10, and the other end of the voltage regulator resistor R13 is electrically connected to the first resistor R15 and the second resistor R14.

[0013] In one possible implementation, it also includes: a storage capacitor C19; the cathode of the first diode D10 is electrically connected to the storage capacitor C19.

[0014] In one possible implementation, the Zener diode DW7 has a stable voltage between 15 and 18V.

[0015] Beneficial Effects: In the synchronous rectification process, this application utilizes the on / off state of MOSFET Q4 to control the current flow and rectify AC power into DC power. Apart from the high-power MOSFET Q4, all other components (transistor Q5, first diode D10, second diode D9, first resistor R15, second resistor R14, and Zener diode DW7) are low-power components, allowing for a smaller overall circuit size after integration. Furthermore, the discrete component design avoids the high-temperature protection issue, enabling the circuit to operate normally even at high temperatures, as long as the temperature remains below the lower limit of transistor Q5's junction temperature. Additionally, the high-frequency switching performance and low R-value of MOSFET Q4... ds(0n) The on-resistance results in very low heat generation from MOSFET Q4 under normal rectification conditions. Therefore, this application provides a synchronous rectification circuit that can operate at high temperatures at low cost.

[0016] Other features and aspects of this application will become clear from the following detailed description of exemplary embodiments with reference to the accompanying drawings. Attached Figure Description

[0017] The accompanying drawings, which are included in and form part of this specification, illustrate exemplary embodiments, features, and aspects of this application together with the specification and serve to explain the principles of this application.

[0018] Figure 1 A circuit diagram of a synchronous rectification circuit according to an embodiment of this application is shown;

[0019] Figure 2 A schematic diagram showing the current flow of the synchronous rectification circuit according to an embodiment of this application is provided.

[0020] Figure 3 A schematic diagram showing the current flow of the synchronous rectification circuit according to an embodiment of this application is provided.

[0021] Figure 4 A schematic diagram showing the current flow of the synchronous rectification circuit according to an embodiment of this application is provided.

[0022] Figure 5 A schematic diagram showing the current flow of the synchronous rectification circuit according to an embodiment of this application is provided.

[0023] Figure 6 A circuit diagram of a switching circuit applying this application is shown. Detailed Implementation

[0024] Various exemplary embodiments, features, and aspects of this application will now be described in detail with reference to the accompanying drawings. The same reference numerals in the drawings denote elements that have the same or similar functions. Although various aspects of the embodiments are shown in the drawings, they are not necessarily drawn to scale unless specifically indicated otherwise.

[0025] It should be understood that the terms "center", "longitudinal", "lateral", "length", "width", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", "clockwise", "counterclockwise", "axial", "radial", and "circumferential" indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this utility model or simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this utility model.

[0026] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of this utility model, "a plurality of" means two or more, unless otherwise explicitly specified.

[0027] The term “exemplary” as used herein means “serving as an example, embodiment, or illustration.” Any embodiment illustrated herein as “exemplary” is not necessarily to be construed as superior to or better than other embodiments.

[0028] Furthermore, to better illustrate this application, numerous specific details are provided in the following detailed embodiments. Those skilled in the art should understand that this application can be implemented without certain specific details. In some instances, methods, means, components, and circuits well-known to those skilled in the art have not been described in detail in order to highlight the main points of this application.

[0029] Figure 1 A circuit diagram of a synchronous rectification circuit according to an embodiment of this application is shown. Figure 1As shown, a synchronous rectifier circuit is suitable for use in series between an AC live wire and a load to rectify the AC current flowing from the AC live wire. It is characterized by comprising: a MOSFET Q4, a transistor Q5, a first diode D10, a second diode D9, a first resistor R15, a second resistor R14, and a Zener diode DW7. The source of the MOSFET Q4 is defined as the first input / output terminal of the synchronous rectifier circuit, and the drain of the MOSFET Q4 is defined as the second input / output terminal of the synchronous rectifier circuit. Both the first and second input / output terminals are electrically connected to the AC live wire and the load, so that the synchronous rectifier circuit can be connected in series between the live wire and the load in different ways to rectify the AC current and output a positive or negative DC voltage. The gate of the MOSFET Q4 is electrically connected to one end of the second resistor R14, and the other end of the second resistor R14 is electrically connected to the cathode of the Zener diode DW7. The anode of the first diode D10 is electrically connected to the second input / output terminal. The cathode of the first diode D10 is electrically connected to the first resistor R15. The collector of the transistor Q5 is electrically connected to the MOSFET Q4. The gate of FET Q4 is connected to the second resistor R14 in the circuit; the emitter of transistor Q5 is electrically connected to the first input / output terminal; the base of transistor Q5 is electrically connected to one end of the first resistor R15; the other end of the first resistor R15 is electrically connected to the cathode of the first diode D10; the cathode of the second diode D9 is electrically connected to the second input / output terminal, and the anode of the second diode D9 is electrically connected to the circuit where the base of transistor Q5 is connected to the first resistor R15; the anode of Zener diode DW7 is electrically connected to the first input / output terminal. The cathode of DW7 is electrically connected to the circuit in which the cathode of the first diode D10 is connected to the first resistor R15 and the second resistor R14; it is suitable for situations where, when a positive voltage is applied to the first input / output terminal, the source and drain of MOSFET Q4 are conducting, and current can flow from the first input / output terminal to the second input / output terminal; it is also suitable for situations where, when a positive voltage is applied to the second input / output terminal, the source and drain of MOSFET Q4 are not conducting, and current cannot flow from the second input / output terminal to the first input / output terminal.

[0030] It should be noted that since alternating current has positive and negative half-cycles, this application can be connected in series with the AC live wire or between it and the load to rectify a smooth DC negative voltage; or it can be connected in series with the AC live wire or between it and the load to rectify a smooth DC positive voltage. Depending on the application, either positive or negative voltage output can be achieved. Figure 1 As shown, the drain (D terminal) of MOSFET Q4 is defined as the second input / output terminal (PK terminal), and the source (S terminal) of MOSFET Q4 is defined as the first input / output terminal (PA terminal); this is to better illustrate this application.

[0031] Furthermore, when a positive voltage is applied to the first input / output terminal (PA terminal), the source (S terminal) and drain (D terminal) of MOSFET Q4 are connected, and current can flow from the source (S terminal) to the drain (D terminal) of MOSFET Q4. At this time, the second input / output terminal (PK terminal) is negative. When a positive voltage is applied to the second input / output terminal (PK terminal), the source (S terminal) and drain (D terminal) of MOSFET Q4 are cut off, and current cannot flow from the drain (D terminal) to the source (S terminal) of MOSFET Q4.

[0032] The cutoff principle of MOSFET Q4 is explained as follows: When the second input / output terminal (PK terminal) is positive, the first diode D10 is turned on. Because the second input / output terminal (PK terminal) is positive, current flows through the first diode D10 to the first resistor R15. The first resistor R15 provides a drive current to the base (B terminal) of transistor Q5, causing transistor Q5 to operate in a saturated conduction state, thus increasing the gate voltage V of MOSFET Q4. G Since the voltage is 0V, MOSFET Q4 remains in the off state. The source (S terminal) and drain (D terminal) of MOSFET Q4 are not connected, and current cannot flow through MOSFET Q4.

[0033] The conduction principle of MOSFET Q4 is explained as follows: When the first input / output terminal (PA terminal) is positive, the second input / output terminal (PK terminal) is negative. At this time, the second diode D9 conducts, and the drive current of the base (B terminal) of transistor Q5 is diverted by the negative voltage through the second diode D9, thus transistor Q5 quickly switches to the cutoff state. Since transistor Q5 is cut off, the current at the first input / output terminal (PA terminal) flows through the Zener diode DW7 to the second resistor R14. At this time, a positive voltage is applied to the gate (G terminal) of MOSFET Q4 through the second resistor R14, and the gate (G terminal) voltage V of MOSFET Q4 is... G The higher the on-resistance R of MOSFET Q4 ds(0n) The smaller the value, the better to reduce conduction losses. At this time, MOSFET Q4 turns into saturated conduction state, and conduction is carried out between the source (S terminal) and the drain (D terminal) of MOSFET Q4. Current can flow from the first input / output terminal (PA terminal) through MOSFET Q4 to the second input / output terminal (PK terminal).

[0034] In summary, when the second input / output terminal (PK terminal) is positive, the second diode D9 is cut off and the first diode D10 is turned on, causing transistor Q5 to enter saturation again, and MOSFET Q4 to be cut off again. During synchronous rectification, the on / off state of MOSFET Q4 is used to control the current flow, thereby determining the final required current (positive DC voltage or negative DC voltage).

[0035] In one possible implementation, a Zener diode DW7 is also included. The anode of the Zener diode DW7 is electrically connected to the first input / output terminal, and the cathode of the Zener diode DW7 is electrically connected to the circuit in which the cathode of the first diode D10 is connected to the first resistor R15 and the second resistor R14. That is, the anode of the Zener diode DW7 is electrically connected to the circuit in which the source (S terminal) of the MOSFET Q4 is connected to AC power or to a load, and the cathode of the Zener diode DW7 is electrically connected to the second resistor R14 and the first resistor R15. When the first input / output terminal (PA terminal) is positive and the second input / output terminal (PK terminal) is negative, the Zener diode DW7 is turned on, and the current flows from the Zener diode DW7 to the second resistor R14 and the first resistor R15. Since the second diode D9 is turned on, the current flows from the second resistor R14 to the gate (G terminal) of the MOSFET Q4, thereby turning on the MOSFET Q4.

[0036] In one possible implementation, the Zener diode DW7 has a stabilizing voltage between 15 and 18V. It should be noted that the positive voltage applied to the gate (G) of MOSFET Q4 through the second resistor R14 depends on the Zener diode DW7's stabilizing voltage. The function of the Zener diode DW7 is to provide a stable drive voltage to the gate (G) of MOSFET Q4. Therefore, the stabilizing voltage of the Zener diode DW7 must be lower than the gate (G) breakdown voltage of MOSFET Q4 to prevent damage to MOSFET Q4. However, this voltage should not be chosen too low, because if the gate (G) voltage of MOSFET Q4 is too low, MOSFET Q4 will not easily enter saturation, resulting in low synchronous rectification efficiency and excessive heat generation.

[0037] In one possible implementation, the circuit further includes: a voltage regulator resistor R13; one end of the voltage regulator resistor R13 is electrically connected to the cathode of the first diode D10, and both the first resistor R15 and the second resistor R14 are electrically connected to the cathode of the first diode D10 through the voltage regulator resistor R13. It should be noted that the voltage regulator resistor R13, the voltage regulator diode DW7, and the storage capacitor C19 together form a voltage regulator circuit. Simultaneously, the voltage regulator resistor R13 can also limit the current flowing through the voltage regulator diode DW7, enabling the voltage regulator diode DW7 to provide a stable operating voltage to the second resistor R14 and the first resistor R15.

[0038] In one possible implementation, the system also includes: a storage capacitor C19; the cathode of the first diode D10 is electrically connected to one terminal of the storage capacitor C19 through a voltage regulator resistor R13, and the other terminal of the storage capacitor C19 is electrically connected to the anode of the voltage regulator diode DW7. The storage capacitor C19 stores charge, and when fully charged, it can ensure the continuous power supply to the MOSFET Q4 for 2-3 operating cycles. It should be noted that because the switching power supply operates at a relatively high frequency, the capacitance of the storage capacitor C19 can be very small. The storage capacitor C19 can store charge and release it when the MOSFET Q4 is turned on or off, thus maintaining the continuous stability of the output current. This application uses a MOSFET Q4 to replace the diode. Driving the MOSFET Q4 requires DC power. Therefore, when the second input / output terminal (PK terminal) is positive, the first diode D10 conducts, charging the energy storage capacitor C19. When the first input / output terminal (PA terminal) is positive, the energy storage capacitor C19 provides the driving voltage to the MOSFET Q4 through the Zener diode DW7. As the AC power changes from positive to negative, the energy storage capacitor C19 can continuously supply power to the MOSFET Q4.

[0039] It should be noted that the Zener resistor R13 serves as a voltage regulator and current limiter, and the second resistor R14 serves as the gate (G) power supply resistor for the MOSFET Q4; the resistance values ​​should not be too large, and should be selected between 2K and 10K, depending on the voltage of the actual circuit. The first resistor R15 serves as the base resistor for the transistor Q5. When the second input / output terminal (PK terminal) is positive, it provides base current to the base (B terminal) of the transistor Q5, causing the transistor Q5 to enter saturation. Its resistance value should be selected between 10K and 20K.

[0040] This application provides a detailed description of the process by which alternating current is rectified into direct current:

[0041] like Figure 2 As shown, when the drain (D terminal) of MOSFET Q4 is connected to AC power and the source (S terminal) of MOSFET Q4 is electrically connected to the load, that is, the second input / output terminal (PK terminal) is connected to AC power through the transformer, and the first input / output terminal (PA terminal) is electrically connected to the load. When the AC power is in the negative half-cycle, the current flows from the other end of the transformer through the load to the first input / output terminal (PA terminal). The first input / output terminal (PA terminal) has a positive voltage, and the second input / output terminal (PK terminal) has a negative voltage. At this time, MOSFET Q4 is turned on, and the current flows from the first input / output terminal (PA terminal) to the second input / output terminal (PK terminal) and finally to the transformer, thus forming a current loop. The negative voltage in the AC power can flow. Figure 3As shown, when the AC current is in the positive half-cycle, the current flows from the transformer to the second input / output terminal (PK terminal). The second input / output terminal (PK terminal) has a positive voltage, the MOSFET Q4 is cut off, and the current cannot flow from the second input / output terminal (PK terminal) to the first input / output terminal (PA terminal). The rectifier circuit is not open, thus cutting off the positive voltage in the AC current. Therefore, only a pulsating negative voltage is obtained at the load end, which becomes a smooth DC negative voltage after filtering.

[0042] like Figure 4 As shown, when the source (S) of MOSFET Q4 is connected to AC power and the drain (D) is electrically connected to the load, the first input / output terminal (PA) is connected to AC power through a transformer, and the second input / output terminal (PK) is electrically connected to the load. When the AC power is in its positive half-cycle, current flows from the other end of the load through the transformer to the first input / output terminal (PA), where the voltage is positive and the voltage is negative. At this time, MOSFET Q4 is turned on, and current flows from the first input / output terminal (PA) to the second input / output terminal (PK) and finally to the load, forming a current loop. The positive voltage within the AC power can flow at this point. Figure 5 As shown, when the AC current is in the negative half-cycle, the current flows from the other end of the transformer through the load to the second input / output terminal (PK terminal). The second input / output terminal (PK terminal) is at a positive voltage, the MOSFET Q4 is cut off, and the current cannot flow from the second input / output terminal (PK terminal) to the first input / output terminal (PA terminal). The rectifier circuit is not open, thus achieving the cut-off when the AC current is at a negative voltage. Therefore, only a pulsating positive voltage is obtained at the load terminal, which becomes a smooth DC positive voltage after filtering.

[0043] In summary, this application requires a total of nine components. Apart from a high-power MOSFET Q4, the other components are all low-power, allowing for a relatively small overall circuit size. Because it uses a discrete component design, the high-temperature protection issue is avoided, enabling the circuit to operate normally even at high temperatures, as long as the temperature remains below the lower limit of the junction temperature of transistor Q5. Furthermore, the high-frequency switching performance and low RO of MOSFET Q4... ds(0n) The on-resistance results in very low heat generation from MOSFET Q4 under normal rectification conditions. Therefore, this application provides a synchronous rectification circuit that can operate at high temperatures at low cost.

[0044] This application replaces diodes for rectifying high-frequency AC power into DC power for subsequent stages. Currently, the switching frequency of switching power supplies ranges from 20kHz to 1MHz, depending on design requirements. Common fast recovery diodes (which also have a recovery time from conduction to cutoff) experience increasing switching losses with higher operating frequencies during high-frequency switching rectification. However, this application uses a synchronous rectification MOSFET Q4, which operates at a higher frequency than diodes and has no recovery time limitation, resulting in significantly lower switching losses. Due to their internal structure, diodes typically have a saturation voltage drop of 0.7–1V (the higher the current flowing through the diode, the higher the voltage drop). Schottky diodes also have a voltage drop between 0.5 and 1V. Synchronous rectification uses a high-power MOSFET Q4 as the switch, and the saturation voltage of MOSFET Q4 depends on its on-resistance R. ds(0n) and the current flowing through it (the on-resistance R of a typical MOSFET Q4). ds(0n) The on-resistance (between 0.1-0.02Ω) is much lower than that of a diode, therefore the on-state voltage of MOSFET Q4 is lower than that of a diode.

[0045] Furthermore, the MOSFET Q4 can be a 5N10 (100V 5A) model.

[0046] The specific model selection, such as IRF610, should be based on the power, voltage, and output current requirements of the power supply design.

[0047] like Figure 6 The diagram shown is a circuit diagram of a switching power supply applying this application. This switching power supply includes: a transformer T1-1, an AC-DC conversion chip U1-1, two synchronous rectifier circuits 100, and a voltage regulator circuit 200. The primary winding of the transformer T1-1 is connected to AC power, and the secondary winding of the transformer T1-1 is electrically connected to the two synchronous rectifier circuits 100. The two synchronous rectifier circuits 100 respectively rectify the AC power into a +12V DC power and a -12V DC power, achieving ±12V dual power supply output. The two output DC power supplies are electrically connected to the load through the voltage regulator circuit 200, thereby achieving regulated output.

[0048] The AC-DC converter chip U1-1 is electrically connected to the primary winding of transformer T1-1. When the AC-DC converter chip U1-1 is on, high voltage is applied to the transformer T1-1 winding to magnetize it. When it is off, the magnetic energy is released to the secondary winding and then rectified by the synchronous rectifier circuit to the load. The AC-DC converter chip U1-1 controls the voltage output to the secondary winding of the transformer by controlling the duty cycle of the switch. The AC-DC converter chip U1-1 is also electrically connected to optocoupler U1-2, which is connected to the voltage regulator circuit. Optocoupler U1-2 couples the output voltage change to the AC-DC converter chip U1-1. Since the primary winding of the transformer is high voltage and the secondary winding is low voltage, the voltage change of the secondary winding is coupled to the primary winding through optocoupler U1-2.

[0049] Diodes D1-11 and D1-10, along with resistor R1-12, together form a voltage regulator circuit 200. The emitter of transistor Q1-5 is connected to diode D1-10, the base of transistor Q1-5 is connected to a voltage divider circuit, and the collector of transistor Q1-5 is electrically connected to optocoupler U1-2. Thus, when the output voltage changes, transistor Q1-5 amplifies the change in reverse phase and feeds it back to AC-DC converter chip U1-1 through optocoupler U1-2 for adjustment. When the coupled signal changes, the duty cycle of AC-DC converter chip U1-1 also adjusts accordingly, thereby stabilizing the output voltage.

[0050] The various embodiments of this application have been described above. These descriptions are exemplary and not exhaustive, nor are they limited to the disclosed embodiments. Many modifications and variations will be apparent to those skilled in the art without departing from the scope and spirit of the described embodiments. The terminology used herein is chosen to best explain the principles, practical application, or improvement of the technology in the market, or to enable others skilled in the art to understand the embodiments disclosed herein.

Claims

1. A synchronous rectifier circuit, suitable for connection in series between an AC live wire and a load to rectify the AC current flowing from the AC live wire, characterized in that, include: MOSFET Q4, transistor Q5, first diode D10, second diode D9, first resistor R15, second resistor R14, and Zener diode DW7; The source of the MOSFET Q4 is defined as the first input / output terminal of the synchronous rectification circuit, and the drain of the MOSFET Q4 is defined as the second input / output terminal of the synchronous rectification circuit. Both the first input / output terminal and the second input / output terminal are suitable for electrically connecting the AC live wire and the load, so that the synchronous rectification circuit can be connected in series between the live wire and the load in different ways to rectify the AC power and output a positive DC voltage or a negative DC voltage. The gate of the MOSFET Q4 is electrically connected to one end of the second resistor R14, and the other end of the second resistor R14 is electrically connected to the cathode of the Zener diode DW7. The anode of the first diode D10 is electrically connected to the second input / output terminal; the cathode of the first diode D10 is electrically connected to the first resistor R15. The collector of transistor Q5 is electrically connected to the circuit in which the gate of MOSFET Q4 is connected to the second resistor R14; the emitter of transistor Q5 is electrically connected to the first input / output terminal; the base of transistor Q5 is electrically connected to one end of the first resistor R15; and the other end of the first resistor R15 is electrically connected to the cathode of the first diode D10. The cathode of the second diode D9 is electrically connected to the second input / output terminal, and the anode of the second diode D9 is electrically connected to the circuit in which the base of the transistor Q5 is connected to the first resistor R15. The anode of the Zener diode DW7 is electrically connected to the first input / output terminal, and the cathode of the Zener diode DW7 is electrically connected to the circuit in which the cathode of the first diode D10 is connected to the first resistor R15 and the second resistor R14. When a positive voltage is applied to the first input / output terminal, the source and drain of the MOSFET Q4 are connected, and current can flow from the first input / output terminal to the second input / output terminal. When a positive voltage is applied to the second input / output terminal, the source and drain of the MOSFET Q4 cannot conduct, and current cannot flow from the second input / output terminal to the first input / output terminal.

2. The synchronous rectifier circuit according to claim 1, characterized in that, Also includes: Zener resistor R13; One end of the voltage regulator resistor R13 is electrically connected to the anode of the first diode D10, and the other end of the voltage regulator resistor R13 is electrically connected to the first resistor R15 and the second resistor R14.

3. The synchronous rectifier circuit according to claim 2, characterized in that, Also includes: Energy storage capacitor C19; The cathode of the first diode D10 is electrically connected to the energy storage capacitor C19.

4. The synchronous rectifier circuit according to claim 3, characterized in that, The Zener diode DW7 has a stable voltage between 15 and 18V.

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