Flyback DCM mode voltage trough detection circuit

Abstract

The utility model belongs to the technical field of detection circuits, and discloses a flyback DCM mode voltage trough detection circuit, which comprises a voltage trough detection unit, an MCU control unit and an isolation driving unit, the voltage trough detection unit comprises a resistor R1, one end of the resistor R1 is connected with the drain electrode of an MOS tube Q11 of a flyback circuit, and the other end of the resistor R1 is connected with the isolation driving unit. The other end of the resistor R1 is connected with one end of the resistor R2 and one end of the capacitor C1, and the other end of the capacitor C1 is connected with one end of the capacitor C2, the other end of the resistor R2, one end of the resistor R3, a pin 3 of the switching diode D1 and a grid electrode of the MOS tube Q1. The flyback conversion DCM voltage trough detection circuit has the advantages that accurate judgment and detection can be achieved, the voltage trough in the flyback conversion DCM mode can be detected in an advanced or lagged mode according to actual conditions, the circuit is simple, easy to understand, safe and reliable, and the circuit further has the advantages of being low in cost, real-time, efficient, convenient to achieve and the like.

Description

Technical Field

[0001] The utility model relates to the technical field of detection circuits, in particular to a flyback DCM mode voltage valley detection circuit. Background Art

[0002] With the continuous development of power electronics and new energy technologies, switching power supplies are becoming more and more diversified. Switching power supplies have almost swept the electronics industry with their advantages of low loss, high efficiency, small size and low noise. Flyback is the most common and widely used topology circuit of switching power supplies. It has stable performance, safe and reliable operation, and is widely used in the field of low power. Its efficiency is also higher than that of forward topology circuits. Flyback integrated chips have been developed accordingly, and the flyback switch tube is also integrated into the chip, but this is only suitable for low power and cannot withstand large currents. It has low efficiency and has good performance. It has voltage valley detection, but the frequency is adjusted through a closed loop and cannot be changed. There is a certain delay between detecting the valley and issuing the drive, thus missing the significance of opening the valley.

[0003] Therefore, it is necessary to provide a flyback DCM mode voltage valley detection circuit, which can accurately judge and detect and can advance or lag the voltage valley in the flyback conversion DCM mode according to actual conditions. The circuit is simple and easy to understand, safe and reliable, and has the advantages of low cost, real-time high efficiency and easy implementation. Utility Model Content

[0004] The utility model discloses a flyback DCM mode voltage valley detection circuit, which can effectively solve the technical problems involved in the background technology.

[0005] To achieve the above purpose, the technical solution of the utility model is:

[0006] A flyback DCM mode voltage valley detection circuit, comprising a voltage valley detection unit, an MCU control unit and an isolation drive unit; the voltage valley detection unit comprises a resistor R1, one end of the resistor R1 is connected to the drain of a MOS tube Q11 of a flyback circuit, the other end of the resistor R1 is connected to one end of a resistor R2 and one end of a capacitor C1, the other end of the capacitor C1 is connected to one end of a capacitor C2, the other end of the resistor R2, one end of a resistor R3, a pin 3 of a switching diode D1 and a gate of the MOS tube Q1, the drain of the MOS tube Q1 is connected to one end of a resistor R4 and One end of the resistor R5 and the other end of the resistor R4 are connected to the port SMCU_3.3V, the other end of the resistor R5 is connected to one end of the resistor R6 and the MCU control unit, the other end of the capacitor C2, the other end of the resistor R3, the pin 1 of the switching diode D1, the source of the MOS tube Q1 and the other end of the resistor R6 are connected to the port AGND, and the pin 2 of the switching diode D1 is connected to the port 12V; the MCU control unit is connected to the isolation drive unit, and the isolation drive unit is connected to the gate of the MOS tube Q11 of the flyback circuit.

[0007] The valley detection unit is composed of a voltage divider circuit unit, a MOS-FET unit, and a protection unit, and forms a closed-loop control with the MUC unit, the drive control circuit, and the flyback circuit. By detecting the valley of the oscillation voltage, that is, when the current in the loop is zero, a signal is provided to the MCU to control the opening of the flyback switch tube, thereby realizing a circuit of zero current opening. The circuit is simple and easy to control, and can improve the flyback efficiency, reduce the switching loss, and control the flyback switching frequency, thereby improving the flyback efficiency at a low cost.

[0008] As a preferred improvement of the utility model: the flyback circuit includes a port PV+, the port PV+ is connected to the pin 4 of the transformer T4, the pin 3 of the transformer T4 is connected to the drain of the MOS tube Q11, the source of the MOS tube Q11 is connected to the port AGND, the gate of the MOS tube Q11 is connected to one end of the resistor R7, and the other end of the resistor R7 is connected to the isolation drive unit;

[0009] Pin 1 of the transformer T4 is connected to the positive end of the diode D2, the negative end of the diode D2 is connected to one end of the capacitor C3, one end of the capacitor C4 and the port VDC+, and pin 2 of the transformer T4 is connected to the other end of the capacitor C3, the other end of the capacitor C4 and the port GND.

[0010] As a preferred improvement of the present invention: one end of the resistor R7 is connected to one end of the resistor R8, the other end of the resistor R8 is connected to the positive end of the diode D3, and the negative end of the diode D3 is connected to the other end of the resistor R7.

[0011] As a preferred improvement of the present utility model: the gate of the MOS tube Q11 is connected to one end of the resistor R9, and the other end of the resistor R9 is connected to the source of the MOS tube Q11.

[0012] As a preferred improvement of the present utility model: the MCU control unit includes a controller, the controller model is IC-TM320F280023PMSR-LQFP64, and the switching diode D1 model is BAV99.

[0013] As a preferred improvement of the utility model: the isolation driving unit includes a port INV_DRVAH, the port INV_DRVAH is connected to the negative end of the diode D47 and one end of the resistor R185, the positive end of the diode D47 is connected to the other end of the resistor R185, one end of the resistor R192 and the gate of the MOS tube Q8, the source of the MOS tube Q8 is connected to the other end of the resistor R192 and the port GND, the drain of the MOS tube Q8 is connected to the pin 3 of the control chip U3, the pin 1 of the control chip U3 is connected to one end of the resistor R184, the other end of the resistor R184 is connected to the port VCCB and one end of the capacitor C109, and the other end of the capacitor C109 is connected to the port GND;

[0014] Pin 4 of the control chip U3 is connected to one end of the capacitor C133, one end of the capacitor C128, one end of the resistor R193, one end of the resistor R194 and the port AGND, pin 5 of the control chip U3 is connected to one end of the resistor R180, the other end of the resistor R180 is connected to the port DRVAL_G, and pin 6 of the control chip U3 is connected to the port VCCH, the other end of the capacitor C133, the other end of the capacitor C128, the other end of the resistor R193 and the other end of the resistor R194;

[0015] The port INV_DRVAH is connected to the MCU control unit, and the port DRVAL_G is connected to the gate of the MOS tube Q11 of the flyback circuit.

[0016] As a preferred improvement of the present invention: the control chip U3 is IC-LTV-314W-TA1-SOP6.

[0017] As a preferred improvement of the present utility model: the MCU control unit is connected to the other end of the resistor R5 through an isolation optical coupler.

[0018] The beneficial effects of the utility model are as follows:

[0019] When the voltage oscillates to the trough, the current of the flyback switch tube is zero, and the voltage drop across the tube is the smallest. At this time, the switching loss is the smallest. The voltage trough detection circuit detects the trough and sends a detection signal. The MCU control unit receives the detection signal and sends a drive pulse. The trough detection circuit can adjust the voltage divider resistor to reduce the influence of the signal transmission processing delay and achieve efficient opening. The circuit is simple and easy to understand, safe and reliable, low-cost, real-time and efficient, easy to implement, and easy to promote. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] In order to more clearly illustrate the technical solutions in the embodiments of the present utility model, the following briefly introduces the drawings required for use in the description of the embodiments. Obviously, the drawings described below are only some embodiments of the present utility model. For those skilled in the art, other drawings can be obtained based on these drawings without creative work, among which:

[0021] Figure 1 It is a schematic diagram of a flyback DCM mode voltage valley detection circuit of the utility model;

[0022] Figure 2 It is a schematic diagram of the isolation drive unit of the utility model. DETAILED DESCRIPTION

[0023] The technical solutions in the embodiments of the present invention will be described clearly and completely below in combination with the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0024] It should be noted that all directional indications in the embodiments of the present invention (such as up, down, left, right, front, back, etc.) are only used to explain the relative position relationship, movement status, etc. between the components under a certain specific posture (as shown in the accompanying drawings). If the specific posture changes, the directional indication will also change accordingly.

[0025] In addition, in the present invention, descriptions such as "first", "second", etc. are only used for descriptive purposes and cannot be understood as indicating or implying their relative importance or implicitly indicating the number of the indicated technical features. Therefore, the features defined as "first" or "second" may explicitly or implicitly include at least one of the features. In the description of the present invention, the meaning of "plurality" is at least two, such as two, three, etc., unless otherwise clearly and specifically defined.

[0026] In the present invention, unless otherwise clearly specified and limited, the terms "connection", "fixation", etc. should be understood in a broad sense. For example, "fixation" can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection or an indirect connection through an intermediate medium, it can be the internal connection of two elements or the interaction relationship between two elements, unless otherwise clearly defined. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0027] In addition, the technical solutions between the various embodiments of the present invention can be combined with each other, but it must be based on the fact that ordinary technicians in the field can implement it. When the combination of technical solutions is contradictory or cannot be implemented, it should be deemed that such combination of technical solutions does not exist and is not within the scope of protection required by the present invention.

[0028] See also Figure 1 As shown, the utility model provides a flyback DCM mode voltage valley detection circuit, including a voltage valley detection unit, an MCU control unit and an isolation drive unit, wherein the voltage valley detection unit includes a resistor R1, one end of the resistor R1 is connected to the drain of the MOS tube Q11 of the flyback circuit, the other end of the resistor R1 is connected to one end of the resistor R2 and one end of the capacitor C1, the other end of the capacitor C1 is connected to one end of the capacitor C2, the other end of the resistor R2, one end of the resistor R3, the pin 3 of the switching diode D1 and the gate of the MOS tube Q1, the drain of the MOS tube Q1 is connected to one end of the resistor R4 and one end of the resistor R5, the other end of the resistor R4 is connected to the port SMCU_3.3V, the other end of the resistor R5 is connected to one end of the resistor R6 and the MCU control unit, the other end of the capacitor C2, the other end of the resistor R3, the pin 1 of the switching diode D1, the source of the MOS tube Q1 and the other end of the resistor R6 are connected to the port AGND, and the pin 2 of the switching diode D1 is connected to the port 12V. The MCU control unit is connected to the isolation driving unit, and the isolation driving unit is connected to the gate of the MOS tube Q11 of the flyback circuit.

[0029] Specifically, Figure 1The invention comprises a switching power supply flyback circuit, a voltage valley detection unit, an MCU control unit and a pulse isolation drive unit. The switching power supply flyback circuit is connected to the voltage valley detection unit. The MCU control unit drives the switch tube of the flyback circuit by controlling the pulse drive circuit. When the switch is turned on, the flyback primary side stores energy. When the switch is turned off, the energy of the primary side is transmitted to the secondary side. When the energy of the primary side is released, the voltage at both ends of the switch tube will form an oscillation. When the voltage oscillates to the bottom of the valley, the voltage valley detection unit detects and transmits the valley signal to the MCU control unit. When the MCU control unit receives the detection signal sent by the detection circuit, it sends a pulse signal to the drive circuit to control the conduction of the flyback switch tube, so as to achieve zero current opening. Among them, the switching power supply flyback circuit is used to provide working power to the voltage valley detection unit, the pulse drive circuit and the MCU control unit, and is used for power output. The pulse drive circuit is used to output a pulse signal to control the conduction and shutdown of the flyback switch tube. The voltage valley detection unit is used to collect the voltage state signal according to the switching power supply flyback circuit. The MCU control unit is used to issue an operation instruction to the pulse drive circuit according to the detection signal collected by the voltage valley detection unit.

[0030] Wherein, the voltage valley detection unit includes a first resistor R1, a second resistor R2, a third resistor R3, a fourth resistor R4, a fifth resistor R5, a sixth resistor R6, a first capacitor C1, a second capacitor C2, a first switch diode D1, and a first transistor Q1. The voltage detection adopts resistance voltage division for sampling. The first resistor R1, the second resistor R2 and the third resistor R3 are connected in series for voltage division. The first resistor is connected to the drain of the switch tube of the switching power supply flyback circuit, the first capacitor C1 is connected in parallel with the second resistor R2, and the second capacitor C2 is connected in parallel with the third resistor to form a voltage division circuit. Pin 1 of the first switch diode D1 is connected to AGND, pin 2 of the first switch diode D1 is connected to 12Vdc (power supply), and pin 3 of the first switch diode D1 is connected to the connection point of the second resistor R2 and the third resistor R3 for protection of the embedded position. The gate of the first transistor Q1 is connected to the connection point of the second resistor R2 and the third resistor R3, the source of the first transistor Q1 is connected to AGND, the drain of the first transistor Q1 is connected to the connection point of the fourth resistor R4 and the fifth resistor R5, the fourth resistor R4 is connected to SMCU_3.3V, providing a high level, the fifth resistor R5 is connected to the sixth resistor R6, and is also connected to the MCU control unit, and the other end of the sixth resistor is connected to AGND. This solution is suitable for medium-power flyback and high-efficiency technical fields, and has a good effect on improving efficiency, reducing reactive power consumption, reducing costs, and controllably adjusting the valley detection point in the DC-DC conversion field. The design of this solution is in the flyback intermittent mode, and the voltage is detected at the first valley of the oscillation to give the MCU a level signal.

[0031] When the flyback works in DCM mode, the switch tube releases energy after being turned off. When the energy is released, the voltage starts to resonate. When the voltage has not oscillated to the lowest point, the voltage divider module of the voltage valley detection unit is still in the on-voltage range of the first transistor Q1. The first transistor Q1 is in the on state, and the drain voltage of the first transistor Q1 is pulled down from 3.3V to zero, and VDS-1 is in a low level state. When the voltage oscillates to the bottom of the valley, the gate voltage of the first transistor Q1 is in the off-voltage range, the first transistor Q1 is in the off state, and the drain voltage of the first transistor Q1 is 3.3V high level. When the MCU control unit receives VDS-1 (an isolation optocoupler is set between the VDS-1 connection point and the MCU control unit) as a high level, the control driving circuit turns on the flyback switch tube Q11. At the same time, due to the delay in the signal transmission process, the resistance value of the voltage divider resistor can be adjusted to realize the early opening and closing of the first transistor, thereby eliminating the influence of the signal transmission and MCU control delay, thereby improving efficiency. The circuit has the advantages of being simple to understand, safe and reliable, low cost, real-time and efficient, and easy to implement.

[0032] As an implementation mode, the flyback circuit includes a port PV+, the port PV+ is connected to the pin 4 of the transformer T4, the pin 3 of the transformer T4 is connected to the drain of the MOS tube Q11, the source of the MOS tube Q11 is connected to the port AGND, the gate of the MOS tube Q11 is connected to one end of the resistor R7, and the other end of the resistor R7 is connected to the isolation drive unit. The pin 1 of the transformer T4 is connected to the positive end of the diode D2, the negative end of the diode D2 is connected to one end of the capacitor C3, one end of the capacitor C4 and the port VDC+, and the pin 2 of the transformer T4 is connected to the other end of the capacitor C3, the other end of the capacitor C4 and the port GND. One end of the resistor R7 is connected to one end of the resistor R8, the other end of the resistor R8 is connected to the positive end of the diode D3, and the negative end of the diode D3 is connected to the other end of the resistor R7. The gate of the MOS tube Q11 is connected to one end of the resistor R9, and the other end of the resistor R9 is connected to the source of the MOS tube Q11. The MCU control unit includes a controller, the controller model is IC-TM320F280023PMSR-LQFP64, and the switching diode D1 model is BAV99.

[0033] See also Figure 2As shown, the isolation driving unit includes a port INV_DRVAH, the port INV_DRVAH is connected to the negative end of the diode D47 and one end of the resistor R185, the positive end of the diode D47 is connected to the other end of the resistor R185, one end of the resistor R192 and the gate of the MOS tube Q8, the source of the MOS tube Q8 is connected to the other end of the resistor R192 and the port GND, the drain of the MOS tube Q8 is connected to the pin 3 of the control chip U3, the pin 1 of the control chip U3 is connected to one end of the resistor R184, the other end of the resistor R184 is connected to the port VCCB and one end of the capacitor C109, and the other end of the capacitor C109 is connected to the port GND. Pin 4 of the control chip U3 is connected to one end of capacitor C133, one end of capacitor C128, one end of resistor R193, one end of resistor R194 and port AGND, pin 5 of the control chip U3 is connected to one end of resistor R180, the other end of resistor R180 is connected to port DRVAL_G, pin 6 of the control chip U3 is connected to port VCCH, the other end of capacitor C133, the other end of capacitor C128, the other end of resistor R193 and the other end of resistor R194. Port INV_DRVAH is connected to the MCU control unit, port DRVAL_G is connected to the gate of MOS tube Q11 of the flyback circuit, and the control chip U3 is IC-LTV-314W-TA1-SOP6. It should be further explained that the use of other components to achieve the above-mentioned effects should all belong to the inventive concept of the utility model and should belong to the protection scope of the utility model.

[0034] Embodiment 1

[0035] The voltage valley detection unit includes a first resistor R1, a second resistor R2, a third resistor R3, a fourth resistor R4, a fifth resistor R5, a sixth resistor R6, a first capacitor C1, a second capacitor C2, a first switch diode D1, and a first transistor Q1. The first resistor R1, the second resistor R2, and the third resistor R3 are connected in series for voltage division. The first resistor R1 is 200Ω, which is convenient for charging and discharging the first capacitor C1. The first capacitor is selected to be 100PF. The other end of the first resistor R1 is connected to the drain of the switch tube Q11 of the switching power supply flyback circuit. The first capacitor C1 is connected in parallel with the second resistor R2. The second resistor is selected to be 240kΩ. The second capacitor C2 is connected in parallel with the third resistor R3 to form a voltage division circuit. The second capacitor C2 is 100PF, and the resistance value of the third resistor R3 is 3.6kΩ.

[0036] The first switch diode D1 adopts BAV99, pin 1 of the first switch diode D1 is connected to AGND, pin 2 of the first switch diode D1 is connected to a 12Vdc power supply, and pin 3 of the first switch diode D1 is connected to a connection point of the second resistor R2 and the third resistor R3 for protection of the embedded position.

[0037] The first transistor Q1 adopts cj2310, the gate of the first transistor Q1 is connected to the connection point of the second resistor R2 and the third resistor R3, the source of the first transistor Q1 is connected to AGND, the drain of the first transistor Q1 is connected to the connection point of the fourth resistor R4 and the fifth resistor R5, the fourth resistor is 5.1kΩ, which is used to protect against 3.3V short circuit, the fifth resistor R5 has a resistance of 2KΩ, the other end of the fourth resistor R4 is connected to SMCU_3.3V to provide a high level, the fifth resistor R5 is connected to the sixth resistor R6, and is also connected to the MCU control unit, the connection point is VDS-1, the other end of the sixth resistor is connected to AGND, the sixth resistor has a resistance of 10kΩ, which is used to pull down to ground.

[0038] The connection point VDS-1 is connected to the 51st pin of the MCU control unit, and the 48th pin of the MCU control unit is connected to the driving pulse circuit to control the on and off of the flyback switch tube Q11. In the above flyback valley detection circuit, when the voltage oscillates to the valley, the current of the flyback switch tube is zero, and the voltage drop across the tube is the minimum, and the switch loss is the minimum. The voltage valley detection unit detects the valley and sends a detection signal, and the MCU control unit receives the detection signal and sends a driving pulse. The valley detection circuit can realize the influence of signal transmission processing delay by adjusting the voltage divider resistor to achieve efficient opening. The circuit is simple and easy to understand, safe and reliable, and has low cost, real-time and high efficiency, and is easy to implement and easy to promote.

[0039] Although the implementation scheme of the utility model has been disclosed as above, it is not limited to the applications listed in the specification and the implementation scheme. It can be fully applied to various fields suitable for the utility model. For those familiar with the art, additional modifications can be easily implemented. Therefore, without departing from the general concept defined by the claims and the scope of equivalents, the utility model is not limited to the specific details and the illustrations shown and described herein.

Claims

1. A flyback DCM mode voltage valley detection circuit, characterized in that: It includes a voltage valley detection unit, an MCU control unit and an isolation drive unit; The voltage valley detection unit includes a resistor R1, one end of the resistor R1 is connected to the drain of the MOS tube Q11 of the flyback circuit, the other end of the resistor R1 is connected to one end of the resistor R2 and one end of the capacitor C1, the other end of the capacitor C1 is connected to one end of the capacitor C2, the other end of the resistor R2, one end of the resistor R3, the pin 3 of the switch diode D1 and the gate of the MOS tube Q1, the drain of the MOS tube Q1 is connected to one end of the resistor R4 and one end of the resistor R5, the other end of the resistor R4 is connected to the port SMCU_3.3V, the other end of the resistor R5 is connected to one end of the resistor R6 and the MCU control unit, the other end of the capacitor C2, the other end of the resistor R3, the pin 1 of the switch diode D1, the source of the MOS tube Q1 and the other end of the resistor R6 are connected to the port AGND, and the pin 2 of the switch diode D1 is connected to the port 12V; The MCU control unit is connected to the isolation driving unit, and the isolation driving unit is connected to the gate of the MOS tube Q11 of the flyback circuit.

2. The flyback DCM mode voltage valley detection circuit according to claim 1, characterized in that: The flyback circuit includes a port PV+, the port PV+ is connected to the pin 4 of the transformer T4, the pin 3 of the transformer T4 is connected to the drain of the MOS tube Q11, the source of the MOS tube Q11 is connected to the port AGND, the gate of the MOS tube Q11 is connected to one end of the resistor R7, and the other end of the resistor R7 is connected to the isolation drive unit; Pin 1 of the transformer T4 is connected to the positive end of the diode D2, the negative end of the diode D2 is connected to one end of the capacitor C3, one end of the capacitor C4 and the port VDC+, and pin 2 of the transformer T4 is connected to the other end of the capacitor C3, the other end of the capacitor C4 and the port GND.

3. The flyback DCM mode voltage valley detection circuit according to claim 2, characterized in that: One end of the resistor R7 is connected to one end of the resistor R8, the other end of the resistor R8 is connected to the positive end of the diode D3, and the negative end of the diode D3 is connected to the other end of the resistor R7.

4. The flyback DCM mode voltage valley detection circuit according to claim 2, characterized in that: The gate of the MOS transistor Q11 is connected to one end of the resistor R9, and the other end of the resistor R9 is connected to the source of the MOS transistor Q11.

5. The flyback DCM mode voltage valley detection circuit according to claim 1, characterized in that: The MCU control unit includes a controller, the controller model is IC-TM320F280023PMSR-LQFP64, and the switching diode D1 model is BAV99.

6. The flyback DCM mode voltage valley detection circuit according to claim 1, characterized in that: The isolation driving unit includes a port INV_DRVAH, wherein the port INV_DRVAH is connected to the negative end of the diode D47 and one end of the resistor R185, the positive end of the diode D47 is connected to the other end of the resistor R185, one end of the resistor R192 and the gate of the MOS tube Q8, the source of the MOS tube Q8 is connected to the other end of the resistor R192 and the port GND, the drain of the MOS tube Q8 is connected to the pin 3 of the control chip U3, the pin 1 of the control chip U3 is connected to one end of the resistor R184, the other end of the resistor R184 is connected to the port VCCB and one end of the capacitor C109, and the other end of the capacitor C109 is connected to the port GND; Pin 4 of the control chip U3 is connected to one end of the capacitor C133, one end of the capacitor C128, one end of the resistor R193, one end of the resistor R194 and the port AGND, pin 5 of the control chip U3 is connected to one end of the resistor R180, the other end of the resistor R180 is connected to the port DRVAL_G, and pin 6 of the control chip U3 is connected to the port VCCH, the other end of the capacitor C133, the other end of the capacitor C128, the other end of the resistor R193 and the other end of the resistor R194; The port INV_DRVAH is connected to the MCU control unit, and the port DRVAL_G is connected to the gate of the MOS tube Q11 of the flyback circuit.

7. The flyback DCM mode voltage valley detection circuit according to claim 6, characterized in that: The control chip U3 is IC-LTV-314W-TA1-SOP6.

8. The flyback DCM mode voltage valley detection circuit according to claim 1, characterized in that: The MCU control unit is connected to the other end of the resistor R5 via an isolation optical coupler.

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