Flyback circuit overcurrent protection circuit based on operational amplifier

Abstract

The present application relates to a kind of overcurrent protection circuit based on the realization of flyback circuit, including power supply drive module, output voltage module, current sampling module, current comparison module and overcurrent protection switch module.The circuit uses Hall sensor and first operational amplifier chip U2 and first comparator U3, first transistor Q2 signal transmission or processing in turn, by comparison, judge whether current exceeds threshold value, and the result is fed back to first drive chip U1, once sampling current reaches set value, quickly through first transistor Q2 the pin COMP of first drive chip U1 is pulled down, feedback to first drive chip U1 no longer output PWM wave to drive circuit operation, make system quickly reach protection purpose, instead of transferring pressure to other devices.The whole circuit structure is simple, timely for overcurrent protection, and accurate judgment, high reliability, can be widely applied to the circuit scene that needs higher stability of auxiliary power supply, such as solar inverter, smart home and other products.

Description

Technical Field

[0001] This invention relates to the field of flyback circuit technology, and more specifically to an overcurrent protection circuit for a flyback circuit based on an operational amplifier. Background Technology

[0002] In many current renewable energy inverter flyback circuit systems, the UC38XX series chips are mostly used as the driver IC. However, the current loop protection of this series of ICs only shuts down the driver chip when the IS pin reaches 1V. This approach of transferring the pressure to other components suffers from slow response, poor reliability, unreasonable design, and potential damage. Some designs use an external "short-circuit protection" circuit, but this may result in the flyback circuit falsely triggering the "short-circuit protection" during startup. This could lead to instability, with the system starting up and then losing power. This approach is clearly unsuitable for systems with high reliability requirements. Therefore, there is a need for a flyback circuit overcurrent protection solution that can address the aforementioned shortcomings. Summary of the Invention

[0003] In view of this, an overcurrent protection circuit based on an operational amplifier is provided, which is simple in structure, highly reliable, and provides timely and accurate protection.

[0004] An overcurrent protection circuit based on an operational amplifier-implemented flyback circuit includes a power drive module, an output voltage module, a current sampling module, a current comparison module, and an overcurrent protection switch module.

[0005] The power drive module includes a first drive chip U1, a ninth resistor R9 and a first MOSFET Q1. The output pin of the first drive chip U1 is connected to the gate of the first MOSFET Q1 via the ninth resistor R9.

[0006] The output voltage module includes a first transformer TX1, a first diode D1, and an output capacitor. The primary winding of the first transformer TX1 is connected to the drain of the first MOSFET Q1, and the primary winding of the first transformer TX1 is connected to the positive terminal of the DC input. The source of the first MOSFET Q1 is grounded through a first resistor R1. The secondary output winding of the first transformer TX1 is connected to the anode of the first diode D1.

[0007] The current sampling module includes a Hall sensor HCT, a first operational amplifier chip U2, a second resistor R2, and a third resistor R3. The input terminal of the Hall sensor HCT is connected to the cathode of the first diode D1, and the output terminal of the Hall sensor HCT is connected to the output load. The Hall sensor HCT also has three pins, which are respectively connected to signal ground GND, connected to the out-of-phase input terminal of the first operational amplifier chip U2 through the second resistor R2, and connected to the non-in-phase input terminal of the first operational amplifier chip U2 through the third resistor R3.

[0008] The current comparison module includes a first comparator U3 and a connection resistor. The output terminal of the first operational amplifier chip U2 is connected to the inverting input terminal of the first comparator U3 through the connection resistor, and the non-inverting input terminal of the first comparator U3 is connected to a voltage input source.

[0009] The overcurrent protection switch module includes a first transistor Q2 and an eighth resistor R8. The base of the first transistor Q2 is connected to the output of the first comparator U3 through the eighth resistor R8. The collector of the first transistor Q2 is connected to the compensation pin COMP of the first driver chip U1, and the emitter of the first transistor Q2 is connected to signal ground GND. When the actual current of the main output circuit exceeds the set value, the first comparator U3 outputs a low-level signal to turn on the first transistor Q2 and simultaneously pulls down the signal of the compensation pin COMP of the first driver chip U1 to turn off the first driver chip U1, thereby achieving overcurrent protection.

[0010] Specifically, the current passing through the Hall sensor HCT is set to I, and the voltage value V1 converted by the Hall sensor HCT and conducted to the first operational amplifier chip U2 is V1 = 0.067 * I. When the signal of voltage value V1 passes through the first operational amplifier chip U2, the output voltage signal V2 = V1 * (8.2 / 2.2). The first comparator U3 compares the received voltage signal V2 with the reference voltage value at the non-inverting input terminal of the first comparator U3. When the received voltage signal V2 is less than the reference voltage value, the first comparator U3 transmits a high-level signal to the eighth resistor R8. When the received voltage signal V2 is greater than the reference voltage value, the first comparator U3 transmits a low-level signal to the eighth resistor R8.

[0011] Furthermore, a first filter circuit is connected between the non-inverting input terminal and the output terminal of the first operational amplifier chip U2. The first filter circuit includes a fifth resistor R5 and a second capacitor C2 connected in parallel. One end of the parallel connection of the fifth resistor R5 and the second capacitor C2 is connected to the non-inverting input terminal of the first operational amplifier chip U2, while the other end of the parallel connection of the fifth resistor R5 and the second capacitor C2 is connected to the output pin of the first operational amplifier chip U2.

[0012] Furthermore, the non-inverting input of the first operational amplifier chip U2 is connected to a second filter circuit; the second filter circuit includes a first capacitor C1 and a fourth resistor R4 connected in parallel; the non-inverting input of the first operational amplifier chip U2 is connected to one end of the parallel connection of the fourth resistor R4 and the first capacitor C1, and the other end of the parallel connection of the fourth resistor R4 and the first capacitor C1 is connected to signal ground.

[0013] Preferably, the access resistor includes a sixth resistor R6, and the out-of-phase input terminal of the first comparator U3 is connected to a third filter circuit; the third filter circuit includes a seventh resistor R7 and a third capacitor C3, and the output pin of the first operational amplifier chip U2 is connected to one end of the third capacitor C3 and the seventh resistor R7 via the sixth resistor R6, while the other end of the third capacitor C3 is connected to signal ground.

[0014] Preferably, the output terminal of the Hall sensor HCT is connected to the anode of the output capacitor; an external optocoupler isolation circuit is connected between the output terminal of the Hall sensor HCT and the output capacitor; the optocoupler isolation circuit includes a driving diode, a phototransistor, an optocoupler filter circuit, and an optocoupler resistor; the driving diode and the optocoupler resistor are connected in parallel, the substrate of the phototransistor is optocoupled with the driving diode so that its emitter is grounded, and the collector of the phototransistor is connected to the compensation pin COMP of the first driving chip U1. More preferably, the optocoupler filter circuit is connected in parallel between the emitter and collector of the phototransistor.

[0015] Furthermore, an external voltage regulator unit is connected between the output capacitor and the output terminal; the cathode of the Zener diode of the voltage regulator unit is connected to the optocoupler resistor, and the anode of the Zener diode of the voltage regulator unit is grounded. Even further, the reference terminal of the voltage regulator unit is connected between the output capacitor and the output terminal through multiple resistors; the non-inverting input terminal of the first comparator U3 is connected to the reference terminal of the voltage regulator unit or an external stable voltage source.

[0016] Preferably, the Hall sensor HCT is located on the main output line. The internal ratio of the Hall sensor HCT is adjustable so that the first operational amplifier chip U2 amplifies or reduces the signal to a predetermined value. The predetermined value output by the first operational amplifier chip U2 is used to regulate the required measured current threshold, thereby protecting against various overcurrents. The external resistor of the first operational amplifier chip U2 is an adjustable resistor, and the DC input power supply is also adjustable. By adjusting the resistance or the input power supply and using the Hall sensor with an adjustable predetermined ratio, the required measured current threshold can be regulated, thereby protecting against various overcurrents.

[0017] Furthermore, the source of the first MOSFET Q1 is grounded via the first resistor R1; the source of the first MOSFET Q1 is also connected to the detection pin IS of the first driver chip U1 via another resistor.

[0018] Preferably, the first MOSFET Q1 is an enhancement-mode N-channel MOSFET; the first driver chip U1 is a UC38XX model chip; the first comparator U3 is an LM339 model; the first transistor Q2 is a PNP type transistor; and the Zener diode is a TL431 model.

[0019] In the aforementioned overcurrent protection circuit based on operational amplifiers, a Hall sensor is used in sequence to transmit or process signals with the first operational amplifier chip U2, the first comparator U3, and the first transistor Q2. Through comparison, it determines whether the current exceeds the threshold and feeds the result back to the first driver chip U1. Once the sampled current reaches the set value, the compensation pin COMP of the first driver chip U1 is quickly pulled to ground through the first transistor Q2, preventing the first driver chip U1 from outputting a PWM wave to drive the circuit. This allows the system to quickly achieve its protection purpose, rather than transferring the pressure to other devices. Furthermore, using a Hall sensor as the main sampling device offers the following advantages: ① High precision: Accuracy is better than 1% within the operating temperature range, suitable for various complex working environments, ensuring high-precision sampling measurement and control; ② Fast response speed: It can detect current changes in the output circuit in real time, thereby achieving rapid protection; ③ Good electrical isolation and strong anti-interference capability: The primary and secondary circuits have good electrical isolation performance, enabling them to operate in complex electromagnetic environments to ensure system safety and stability. Meanwhile, the Hall sensor itself has electrical isolation capabilities, eliminating the need for optocoupler isolation.

[0020] Furthermore, the overcurrent protection circuit for the flyback circuit based on operational amplifiers described above can also precisely achieve overcurrent protection for the flyback circuit by adjusting the values ​​of resistors, capacitors, and DC input sources in the circuit, as well as selecting specific types of Hall sensors, the first operational amplifier chip U2, the first comparator U3, and the first transistor Q2. This circuit is suitable for use in circuit scenarios requiring high-stability auxiliary power supply, such as solar inverters and smart home products. Attached Figure Description

[0021] Figure 1 This is a schematic diagram of the overcurrent protection circuit of the flyback circuit based on the operational amplifier in an embodiment of the present invention. Detailed Implementation

[0022] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0023] Please see Figure 1 This illustration shows an overcurrent protection circuit based on an operational amplifier implemented in a flyback circuit according to an embodiment of the present invention. The circuit includes a power drive module, an output voltage module, a current sampling module, a current comparison module, and an overcurrent protection switch module.

[0024] As shown in the figure, the power drive module includes a first driver chip U1, a ninth resistor R9, and a first MOSFET Q1. The output pin of the first driver chip U1 is connected to the gate of the first MOSFET Q1 via the ninth resistor R9. The output voltage module includes a first transformer TX1, a first diode D1, and an output capacitor. The first transformer TX1 has a primary winding and a secondary winding. In the example shown, one primary winding corresponds to two secondary windings, but it can also correspond to multiple secondary windings to form multiple outputs. The primary terminal of the first transformer TX1 is connected to the drain of the first MOSFET Q1, and the primary terminal of the first transformer TX1 is connected to the positive terminal of the DC input. A primary filter module is also connected between the primary terminals of the first transformer TX1 and the primary terminal of the first transformer TX1. The primary filter module includes a resistor and a capacitor connected in parallel. One end of the primary filter module is connected to the DC input or the primary terminal of the first transformer TX1, and the other end is connected to the drain of the first MOSFET Q1 through a reverse diode to protect the circuit. The secondary output winding of the first transformer TX1 is connected to the anode of the first diode D1 for rectification, and then connected to the output capacitor and the load. In the diagram, each output capacitor is also connected in parallel with a resistor. The maximum current is 10A in the example.

[0025] The current sampling module includes a Hall sensor HCT, a first operational amplifier chip U2, a second resistor R2, and a third resistor R3. The input terminal of the Hall sensor HCT is connected to the cathode of a first diode D1, and the output terminal of the Hall sensor HCT is connected to the output load, i.e., connected to the main output circuit, and connected to the front end of the output capacitor. The Hall sensor HCT also has three pins, which are respectively connected to signal ground GND, connected to the non-inverting input terminal of the first operational amplifier chip U2 through the second resistor R2, and connected to the non-inverting input terminal of the first operational amplifier chip U2 through the third resistor R3. Preferably, the second resistor R2 and the third resistor R3 are resistors with the same resistance value, and are preferably adjustable resistors or easily replaceable resistors.

[0026] The current comparison module includes a first comparator U3 and a connection resistor. The output terminal of the first operational amplifier chip U2 is connected to the inverting input terminal of the first comparator U3 via the connection resistor. The non-inverting input terminal of the first comparator U3 is connected to a voltage input source; this voltage input source has a fixed voltage value and serves as a reference voltage for comparison. Preferably, the connection resistor includes a sixth resistor R6. The out-of-phase input terminal of the first comparator U3 is connected to a third filter circuit; the third filter circuit includes a seventh resistor R7 and a third capacitor C3. The output pin of the first operational amplifier chip U2 is connected to one end of the third capacitor C3 and the seventh resistor R7 via the sixth resistor R6, while the other end of the third capacitor C3 is connected to signal ground. More preferably, the sixth resistor R6 and the seventh resistor R7 are connected in series and use resistors with the same resistance value, for example, 100Ω as shown in the figure. The first transistor Q2 is preferably a PNP transistor.

[0027] The overcurrent protection switch module includes a first transistor Q2 and an eighth resistor R8. The base of the first transistor Q2 is connected to the output of the first comparator U3 through the eighth resistor R8. The collector of the first transistor Q2 is connected to the compensation pin COMP of the first driver chip U1, and the emitter of the first transistor Q2 is connected to signal ground GND. The resistance value of the eighth resistor R8 is preferably equal to the resistance values ​​of the sixth resistor R6 and the seventh resistor R7, for example, 100Ω as shown in the figure.

[0028] Specifically, the current passing through the Hall sensor HCT is set to I, and the voltage value V1 converted by the Hall sensor HCT and conducted to the first operational amplifier chip U2 is V1 = 0.067 * I. When the signal of this voltage value V1 passes through the first operational amplifier chip U2, the output voltage signal V2 = V1 * (8.2 / 2.2). The first comparator U3 compares the received voltage signal V2 with the reference voltage value at the non-inverting input terminal of the first comparator U3. When the received voltage signal V2 is less than the reference voltage value, the reference voltage value is, for example, 2.5V. The first comparator U3 transmits a high-level signal to the eighth resistor R8; when the received voltage signal V2 is greater than the reference voltage value, the first comparator U3 transmits a low-level signal to the eighth resistor R8.

[0029] When the actual current of the main output circuit exceeds the set value, for example, exceeding 10A, the voltage signal V2 is calculated to be greater than 2.5V. The first comparator U3 outputs a low-level signal, turning on the first transistor Q2, and simultaneously pulling down the signal on the compensation pin COMP of the first driver chip U1 to turn off the first driver chip U1, thus achieving overcurrent protection.

[0030] Furthermore, a first filter circuit is connected between the non-inverting input terminal and the output terminal of the first operational amplifier chip U2. The first filter circuit includes a fifth resistor R5 and a second capacitor C2 connected in parallel. One end of the parallel connection of the fifth resistor R5 and the second capacitor C2 is connected to the non-inverting input terminal of the first operational amplifier chip U2, while the other end of the parallel connection of the fifth resistor R5 and the second capacitor C2 is connected to the output pin of the first operational amplifier chip U2.

[0031] Furthermore, a second filter circuit is connected to the non-inverting input of the first operational amplifier chip U2. This second filter circuit is connected between the third resistor R3 and the non-inverting input of the first operational amplifier chip U2. The second filter circuit includes a first capacitor C1 and a fourth resistor R4 connected in parallel; the non-inverting input of the first operational amplifier chip U2 is connected to one end of the parallel connection of the fourth resistor R4 and the first capacitor C1, and the other end of the parallel connection of the fourth resistor R4 and the first capacitor C1 is connected to signal ground.

[0032] Preferably, the output terminal of the Hall sensor HCT is connected to the anode of the output capacitor. Specifically, an external optocoupler isolation circuit is connected between the output terminal of the Hall sensor HCT and the output capacitor; the optocoupler isolation circuit includes a driving diode, a phototransistor, an optocoupler filter circuit, and an optocoupler resistor. The driving diode and the optocoupler resistor are connected in parallel, the substrate of the phototransistor is optocoupled with the driving diode so that its emitter is grounded, and the collector of the phototransistor is connected to the compensation pin COMP of the first driving chip U1. More preferably, the optocoupler filter circuit is connected in parallel between the emitter and collector of the phototransistor. The front end of the parallel connection between the driving diode and the optocoupler resistor is connected to the output terminal of the Hall sensor HCT through a resistor.

[0033] Furthermore, an external voltage regulator unit is connected between the output capacitor and the output terminal; the cathode of the Zener diode of the voltage regulator unit is connected to the optocoupler resistor, and the anode of the Zener diode is grounded. Even further, the reference electrode of the voltage regulator unit is connected between the output capacitor and the output terminal through multiple resistors; the voltage is stepped down to the required reference voltage value through these resistors. The non-inverting input terminal of the first comparator U3 is connected to the reference electrode of the voltage regulator unit or an external stable voltage source to provide a stable reference voltage, such as 2.5V, to the non-inverting input terminal of the first comparator U3. The Zener diode is preferably a TL431. The voltage regulator unit also includes filter capacitors and resistors connected in parallel or series. Additionally, the first transformer TX1 has a primary-secondary common-mode filter capacitor C10, one end of which is connected to the main output circuit and at the output end of the Hall sensor HCT, and the other end is connected to the first resistor R1; the common-mode filter capacitor C10 is preferably rated at voltage rating Y1 or higher.

[0034] More preferably, the Hall sensor HCT is located on the main output line. The internal ratio of the Hall sensor HCT is adjustable so that the first operational amplifier chip U2 amplifies or reduces the signal to a predetermined value. The predetermined value output by the first operational amplifier chip U2 is used to regulate the required measured current threshold, thereby protecting against various overcurrents. The external resistor of the first operational amplifier chip U2 is an adjustable resistor, and the DC input power supply is also adjustable. By adjusting the resistance or the input power supply and using the Hall sensor with an adjustable predetermined ratio, the required measured current threshold can be regulated according to different needs, such as different current threshold requirements, thereby protecting against various overcurrents.

[0035] Furthermore, the source of the first MOSFET Q1 is grounded via a first resistor R1; the source of the first MOSFET Q1 is also connected to the detection pin IS of the first driver chip U1 via another resistor to trigger a protection mechanism, such as causing the first driver chip U1 to shut down due to overcurrent. Preferably, the first MOSFET Q1 is an enhancement-mode N-channel MOSFET; the first driver chip U1 is a UC38XX model chip; and the first comparator U3 is an LM339 model.

[0036] The above circuit is suitable for applications requiring stable auxiliary power supply, such as solar inverters and smart home products. In operation, the Hall sensor of the current sampling module is connected to the main output circuit, converting the current signal into a voltage signal. This voltage signal is amplified by the first operational amplifier chip U2 and then output, completing the entire circuit's sampling module's working logic. The amplified voltage signal is compared by the first comparator U3, which outputs a high or low level, thus completing the comparator module's operation. This signal is then fed back to the first driver chip U1 via the first MOSFET Q1 to determine overcurrent and control whether to shut down the circuit. It is worth noting that in this embodiment, the preferred DC source is the 2.5V reference voltage already present in the circuit, rather than an external DC input source. In practical applications, users can replace this source as needed.

[0037] The working principle of the flyback circuit overcurrent protection circuit in this embodiment is illustrated below:

[0038] 1. Initial state: The first driver chip U1 has not yet received power, and the entire system is in a "shutdown" state. That is, U1 is unable to provide PWM pulses to the first MOSFET Q1 at this time, so the entire system is in an off state.

[0039] 2. Output Start-up: When an external voltage sufficient for startup is provided, such as 50Vdc, the first driver chip U1 will receive power and start outputting PWM pulses. These pulses will then drive the first MOSFET Q1 through the ninth resistor R9. Once the first MOSFET Q1 is driven, an output voltage will be obtained on the secondary side of the first transformer TX1. This voltage will be rectified by the first diode D1 to form a DC source, and then conducted to the output terminal through the Hall sensor HCT. The energy will be stored in the output capacitor. When the output terminal is loaded and needs to consume energy, it can obtain energy from the capacitor, and the system will continuously supply power to the output capacitor.

[0040] 3. Current Sampling Operation: When there is energy consumption at the output terminal, that is, when current flows through the Hall sensor HCT, let's assume the current is I (the maximum current is set to 10A, and protection will be triggered if it exceeds 10A). At this time, a voltage signal is converted by the Hall sensor HCT (assuming the ratio of the Hall sensor is 1:0.067) and transmitted to the first operational amplifier chip U2. The value of the voltage signal is V1 = 0.067 * I. After the voltage signal V1 passes through the first operational amplifier chip U2, the output voltage signal V2 = V1 * (8.2 / 2.2). At this time, the current sampling closed loop is completed, and the current I flowing through the Hall sensor HCT is sampled. The output value of the current sampling, i.e., the voltage signal V2, is received at the sixth resistor R6.

[0041] 4. Comparator Operation: When the first comparator U3 is connected to the output of the first operational amplifier chip U2 via the sixth resistor R6 and the seventh resistor R7, when it receives the output value corresponding to the current sampling signal of its output, i.e., the voltage signal V2, the comparator will compare the received voltage signal V2 with the 2.5V reference value at the non-inverting input terminal of the first comparator U3. When V2 < 2.5, the first comparator U3 will transmit a high-level signal to the eighth resistor R8; when V2 > 2.5, the first comparator U3 will transmit a low-level signal to the eighth resistor R8.

[0042] By calculation, i.e., by substituting the conversion formulas for V1 and V2, when I>10A, V2>2.5.

[0043] Special note: Since the TL431 is used in the voltage loop of the output voltage feedback, it has a 2.5V reference voltage. In this case, the 2.5V reference is sampled as the comparison value, and no additional DC input source is used as the comparator.

[0044] 5. Overcurrent Protection Switch Control: When the first comparator U3 sends a high-level signal to the eighth resistor R8, the first transistor Q2 remains off because its base is high, meaning the compensation pin COMP of the first driver chip U1 maintains its original state. When the first comparator U3 sends a low-level signal to the eighth resistor R8, the first transistor Q2 turns on because its base is low, meaning the compensation pin COMP of the first driver chip U1 is pulled to GND. This achieves the purpose of feeding back the current sample to the first driver chip U1 and turning it off to stop emitting PWM waves to drive the circuit. After U1 is turned off, the entire system is in a shut-down state, thus completing the closed-loop control of overcurrent protection from current sampling to feedback to the first driver chip.

[0045] Meanwhile, since the Hall sensor itself has electrical isolation, optocoupler isolation is no longer required. Instead, starting from the Hall sensor, the output current is converted into a voltage signal V1 according to the Hall sensor's ratio. Then, the operational amplifier chip converts V1 into V2. V2 is then compared with the 2.5V reference of the TL431 in the voltage loop. When V2 is greater than 2.5V, it is fed back to U1 through the first transistor Q2, causing it to shut down the PWM wave, thereby shutting down the entire circuit.

[0046] It should be noted that the present invention is not limited to the above-described embodiments. Based on the inventive spirit of the present invention, those skilled in the art can make other changes, and these changes made in accordance with the inventive spirit of the present invention should be included within the scope of protection claimed by the present invention.

Claims

1. A flyback circuit overcurrent protection circuit based on an operational amplifier implementation, characterized in that, The power supply driving module, the output voltage module, the current sampling module, the current comparison module and the over-current protection switch module are included. The power supply driving module includes a first driving chip U1, a ninth resistor R9 and a first MOS tube Q1, and the output pin of the first driving chip U1 is connected with the gate of the first MOS tube Q1 through the ninth resistor R9. The output voltage module includes a first transformer TX1, a first diode D1 and an output capacitor, the primary homonymic end of the first transformer TX1 is connected with the drain of the first MOS tube Q1, and the primary heteronymic end of the first transformer TX1 is connected with the positive pole of the direct current input; the homonymic end of the secondary output winding of the first transformer TX1 is connected with the anode of the first diode D1. The current sampling module includes a Hall sensor HCT, a first operational amplifier chip U2, a second resistor R2 and a third resistor R3, the input end of the Hall sensor HCT is connected with the cathode of the first diode D1, the output end of the Hall sensor HCT is connected with the load of the output, and the Hall sensor HCT has three pins which are respectively connected with the signal ground GND, the non-inverting input end of the first operational amplifier chip U2 through the second resistor R2 and the inverting input end of the first operational amplifier chip U2 through the third resistor R3. The current comparison module includes a first comparator U3 and an access resistor, the output end of the first operational amplifier chip U2 is connected with the inverting input end of the first comparator U3 through the access resistor, and the inverting input end of the first comparator U3 is connected with the voltage input source. The over-current protection switch module includes a first triode Q2 and an eighth resistor R8, the base of the first triode Q2 is connected with the output end of the first comparator U3 through the eighth resistor R8, the collector of the first triode Q2 is connected with the compensation pin COMP of the first driving chip U1, and the emitter of the first triode Q2 is connected with the signal ground GND; when the actual current of the main output loop exceeds the set value, the first comparator U3 outputs a low level signal to make the first triode Q2 work in the on state, and the signal of the compensation pin COMP of the first driving chip U1 is pulled down to turn off the first driving chip U1, so that the over-current protection is realized.

2. The over-current protection circuit for flyback circuit based on operational amplifier according to claim 1, wherein, The current passing through the Hall sensor HCT is set as I, the voltage value V1 converted by the Hall sensor HCT and transmitted to the first operational amplifier chip U2 is V1=0.067*I; after the voltage value V1 is transmitted to the first operational amplifier chip U2, the output voltage signal V2=V1* (8.2 / 2.2); the first comparator U3 compares the received voltage signal V2 with the reference voltage value of the inverting input end of the first comparator U3; when the received voltage signal V2 is less than the reference voltage value, the first comparator U3 transmits a high level signal to the eighth resistor R8; when the received voltage signal V2 is greater than the reference voltage value, the first comparator U3 transmits a low level signal to the eighth resistor R8.

3. The over-current protection circuit for flyback circuit based on operational amplifier according to claim 1, wherein, The non-inverting input end of the first operational amplifier chip U2 is connected with a first filter circuit, the first filter circuit comprises a fifth resistor R5 and a second capacitor C2 in parallel, one end of the fifth resistor R5 and the second capacitor C2 in parallel is connected with the non-inverting input end of the first operational amplifier chip U2, and the other end of the fifth resistor R5 and the second capacitor C2 in parallel is connected with the output pin of the first operational amplifier chip U2.

4. The over-current protection circuit for flyback circuit based on operational amplifier according to claim 1, wherein, The inverting input end of the first comparator U3 is connected with a third filter circuit, the third filter circuit comprises a seventh resistor R7 and a third capacitor C3, the output pin of the first operational amplifier chip U2 is connected with one end of the third capacitor C3 and the seventh resistor R7 through the sixth resistor R6, and the other end of the third capacitor C3 is connected with the signal ground.

5. The over-current protection circuit for flyback circuit based on operational amplifier according to claim 1, wherein, The output end of the Hall sensor HCT is connected with the anode of the output capacitor, an optocoupler isolation circuit is connected between the output end of the Hall sensor HCT and the output capacitor, the optocoupler isolation circuit comprises a drive diode, a photoelectric triode, an optocoupler filter circuit and an optocoupler resistor, the drive diode is connected with the optocoupler resistor in parallel, the base plate of the photoelectric triode is coupled with the drive diode to emit the anode to the ground, the collector of the photoelectric triode is connected with the compensation pin COMP of the first drive chip U1, and the optocoupler filter circuit is connected between the emitter and the collector of the photoelectric triode in parallel.

6. The over-current protection circuit for flyback circuit based on operational amplifier implementation according to claim 1, wherein, A voltage stabilizing unit is connected between the output capacitor and the output end, the cathode of the stabilizing tube of the voltage stabilizing unit is connected with the optocoupler resistor, the anode of the stabilizing tube of the voltage stabilizing unit is connected with the ground, the reference electrode of the voltage stabilizing unit is connected with the output capacitor and the output end through a plurality of resistors, and the non-inverting input end of the first comparator U3 is connected with the reference electrode of the voltage stabilizing unit or an external stable voltage source.

7. The over-current protection circuit for flyback circuit based on operational amplifier according to claim 6, wherein, The Hall sensor HCT is arranged in the main output end circuit, the internal ratio of the Hall sensor HCT is adjustable, so that the first operational amplifier chip U2 amplifies or reduces the signal to a predetermined value, the predetermined value output by the first operational amplifier chip U2 is used for regulating the required measured current threshold, and a plurality of overcurrents are protected, the peripheral resistor of the first operational amplifier chip U2 is an adjustable resistor, and the direct current input power source is adjustable, the required measured current threshold is regulated by adjusting the resistance value or the input power source and matching the adjustable predetermined ratio of the Hall sensor, and a plurality of overcurrents are protected.

8. The over-current protection circuit for flyback circuit based on operational amplifier implementation according to claim 1, wherein, The source of the first MOS tube Q1 is connected with the ground through the first resistor R1, and the source of the first MOS tube Q1 is also connected with the detection pin IS of the first drive chip U1 through another resistor.

9. The over-current protection circuit for flyback circuit based on operational amplifier implementation according to claim 1, wherein, ​ 10. The over-current protection circuit for flyback circuit based on operational amplifier according to claim 7, wherein, The first MOS Q1 is an enhancement type N channel MOS; the first drive chip U1 is a UC38XX type chip; the first comparator U3 is an LM339 type; the first transistor Q2 is a PNP type transistor; and the voltage stabilizing tube is a TL431 type.

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