Self-locking flyback switching power supply circuit with overcurrent and overvoltage protection

Abstract

The invention relates to the technical field of switching power supplies, in particular to a self-locking flyback switching power supply circuit with overcurrent and overvoltage protection, which comprises a primary side control circuit, a power conversion circuit, a synchronous rectification circuit and an output circuit, and is characterized in that a self-locking circuit is electrically connected with an overvoltage detection circuit and an overcurrent detection circuit; wherein the over-current detection circuit is used for detecting whether output current exceeds rated current or not; the overvoltage detection circuit is used for detecting whether the output voltage exceeds the rated voltage; and the self-locking circuit is used for pulling down the starting voltage of the primary side control circuit and the synchronous rectification circuit to a low level when the output overvoltage or overcurrent is detected, so that the power conversion circuit stops working until the input voltage is disconnected. According to the invention, the defects of response speed, protection precision, cost and adaptability in over-current and over-voltage protection of the existing flyback switching power supply are overcome.

Description

Technical Field

[0001] The present invention relates to the technical field of switching power supplies, and particularly to a self-locking flyback switching power supply circuit with over-current and over-voltage protection. Background Art

[0002] Due to its advantages such as simple structure, low cost, wide input voltage range and high conversion efficiency, the flyback switching power supply performs outstandingly in scenarios of low power, multiple outputs and electrical isolation, such as mobile phone chargers and LED driver power supplies; however, the over-current (OCP) and over-voltage (OVP) problems at the output end have always threatened the reliability and safety of the system.

[0003] Traditional flyback switching power supplies usually adopt discrete components or simple control logics in protection design, such as fuses, current-limiting resistors and voltage comparators, etc.; but these methods have problems such as slow response speed, low protection threshold accuracy and poor self-recovery ability; in addition, the existing co-protection mechanism for over-current and over-voltage is insufficient, and independent detection circuits are mostly used, increasing the circuit complexity and making it difficult to achieve fast self-locking protection.

[0004] At present, over-current protection at the output end often adopts the method of comparing the primary-side current sampling with a fixed threshold, but it is easily affected by transformer parameter drift, leakage inductance interference and load transient changes, and the protection threshold setting is inaccurate; although the traditional linear optocoupler feedback scheme can directly detect the output voltage and achieve over-voltage shutdown, the dynamic response speed is limited by the optocoupler transmission delay, and it may not be able to suppress voltage spikes in time, damaging the backend load; in addition, the adaptability of some integrated protection chips is limited, it is difficult to flexibly adapt to the requirements of different flyback topology parameters, and improper design of the peripheral circuit may introduce new failure risks. Summary of the Invention

[0005] Aiming at the deficiencies of the existing circuit, the present invention solves the deficiencies in response speed, protection accuracy, cost and adaptability in over-current and over-voltage protection of the existing flyback switching power supply.

[0006] The technical solution adopted by the present invention is: a self-locking flyback switching power supply circuit with over-current and over-voltage protection, including: a primary control circuit, a power conversion circuit, a synchronous rectification circuit, a self-locking circuit, an over-voltage detection circuit, an over-current detection circuit and an output circuit; wherein,

[0007] The over-current detection circuit is used to detect whether the output current exceeds the rated current;

[0008] The over-voltage detection circuit is used to detect whether the output voltage exceeds the rated voltage;

[0009] The self-locking circuit is used to pull down the startup voltages of the primary control circuit and the synchronous rectification circuit to a low level when detecting output over-voltage and / or over-current, so that the power conversion circuit stops working until the input voltage is disconnected.

[0010] As a preferred embodiment of the present invention, the overvoltage detection circuit includes: operational amplifier U6, resistors R26, R29, R19, R23, triode Q4, and diode D6; the 3rd pin of U6 is connected in series with resistor R29 at the output terminal of U6; the output terminal of U6 is connected to the positive electrodes of R26 and D6, the negative electrode of D6 is connected to the base of Q4, and the emitter of Q4 is connected to the common terminal of R19 and R23.

[0011] As a preferred embodiment of the present invention, the overcurrent detection circuit includes: operational amplifier U5, resistors R10, R16, R19, R23, triode Q4, and diode D3; the inverting input terminal and the output terminal of U5 are connected in series with R16, the output terminal of U5 is connected to the positive electrodes of R10 and D3, the negative electrode of D3 is connected to the base of Q4, and the emitter of Q4 is connected to the common terminal of R19 and R23.

[0012] As a preferred embodiment of the present invention, the first self-locking circuit of the self-locking circuit includes: MOS transistor Q5, triodes Q6, Q3, resistors R7, R9, R24, R25; the gate of Q5 is connected to the left end of R19, the source and drain of Q5 are connected in parallel with the collector and emitter of Q6, R24 and R25 are connected in parallel and then connected to the base and emitter of Q6, the upper end of R24 is connected to the collector of Q3, the two ends of the parallel connection of R7 and R9 are respectively connected to the emitter and base of Q3, and the base of Q3 is connected to the collector of Q6; the upper end of R7 is connected to the output circuit and the synchronous rectification circuit.

[0013] As a preferred embodiment of the present invention, the second self-locking circuit of the self-locking circuit includes: MOS transistor Q8, triodes Q7, Q9, resistors R21, R22, R30, R31; the gate of Q8 is connected to the left end of R19, the source and drain of Q8 are connected in parallel with the collector and emitter of Q9, R30 and R31 are connected in parallel and then connected to the base and emitter of Q9, the upper end of R30 is connected to the collector of Q7, the two ends of the parallel connection of R21 and R22 are respectively connected to the emitter and base of Q7, and the base of Q7 is connected to the collector of Q9; the upper end of R21 is connected to the primary control circuit.

[0014] As a preferred embodiment of the present invention, it further includes: the voltage feedback circuit adjusts the voltage of the output circuit by adjusting the duty cycle of the primary control circuit.

[0015] As a preferred embodiment of the present invention, it further includes: a voltage regulator, which is used for the rated voltage and / or rated current of the overvoltage protection circuit and / or the overcurrent protection circuit.

[0016] As a preferred embodiment of the present invention, the control chip model of the primary control circuit is CR6885.

[0017] As a preferred embodiment of the present invention, the model of the synchronous rectification chip of the synchronous rectification circuit is UCC24612.

[0018] As a preferred embodiment of the present invention, it further includes a power supply circuit for providing a 5V voltage.

[0019] Advantages of the present invention:

[0020] 1. Compared with the protection method at the output end of the traditional flyback switching power supply, the circuit of the present invention has the ability to simultaneously detect overcurrent and / or overvoltage signals; the traditional synchronous rectification switching power supply lacks the protection design for overcurrent and overvoltage at the output end. When an abnormality occurs in the power supply, the present invention can quickly detect overcurrent and overvoltage, and use the self-locking circuit to respond quickly, effectively preventing circuit damage.

[0021] 2. Compared with the traditional flyback switching power supply, the present invention realizes instant protection for overcurrent and / or overvoltage conditions of the output circuit by designing two self-locking circuits. When overcurrent and / or overvoltage occur in the circuit, the self-locking circuit can be immediately activated, pulling down the start pins of the primary control chip and / or the synchronous rectification chip to a low level together, thereby cutting off the power output, protecting each component and the load in the circuit, and avoiding losses.

[0022] 3. In terms of power supply design, there are significant differences between the present invention and the traditional flyback switching power supply. The start voltages of the operational amplifier and the voltage regulator of the present invention both come from the voltage regulation circuit. This design enables the power supply to stably output the rated voltage and / or rated current, providing reliable power support for the entire circuit; compared with the traditional power supply design, the voltage output of the present invention is more stable, less affected by external factors, and improves the overall performance and reliability of the circuit. Description of the Drawings

[0023] Figure 1 System block diagram of the overcurrent and overvoltage protection circuit at the output end of the synchronous rectification flyback switching power supply of the present invention;

[0024] Figure 2 Traditional synchronous rectification flyback switching power supply circuit;

[0025] Figure 3 Circuit diagram of the self-locking flyback switching power supply with overcurrent and overvoltage protection of the present invention;

[0026] Figure 4 Schematic diagram when the output voltage of the present invention is overvoltage;

[0027] Figure 5 Schematic diagram when the output current of the present invention is overcurrent. Detailed Embodiments

[0028] The present invention will be further described below in conjunction with the accompanying drawings and embodiments. This figure is a simplified schematic diagram, which only illustrates the basic structure of the present invention in a schematic manner. Therefore, it only shows the components related to the present invention.

[0029] In existing flyback switch power supplies, especially under special working conditions such as light load, capacitive load or short circuit, it is more difficult to detect the protection circuit; therefore, there is an urgent need for a circuit with high integration, rapid response and self-locking function, which can not only balance real-time performance and reliability, but also be easy to implement to meet the protection requirements under complex working conditions, while maintaining the structural advantages and cost-effectiveness of the flyback topology. When the present invention detects an abnormality, it can quickly cut off the power control signal to avoid mis-triggering, and comprehensively improve the stability and service life of the flyback switch power supply.

[0030] Traditional synchronous rectification flyback switch power supplies, although combining the advantages of synchronous rectification technology and flyback topology, have characteristics such as high efficiency and low cost; however, the current and voltage signals at their output terminals are relatively vulnerable and are easily affected by factors such as load changes and input voltage fluctuations; therefore, in order to ensure the stable operation of the power supply and the safety of the load, it is necessary to design additional monitoring and protection circuits.

[0031] As Figure 2 shown is a traditional flyback switch power supply. In the design of traditional flyback switch power supplies, usually only a current detection module is set at the input end, and the voltage on the detection resistor R6 is detected to judge whether the primary control circuit has an overcurrent situation; in terms of the output circuit, only the output voltage can be adjusted through an optocoupler sensor. When the output voltage is too large or too small, the duty cycle of the primary MOS tube is adjusted to adjust the output voltage, lacking a direct overcurrent and overvoltage detection mechanism for the output voltage and output current.

[0032] Specifically, traditional flyback switch power supplies usually only rely on an optocoupler sensor to indirectly judge the size of the output voltage; the optocoupler sensor adjusts the internal light emission intensity by sensing the change of the output voltage, and then transmits this signal to the primary control circuit through components such as triodes; the primary control circuit adjusts the on-off duty cycle of the primary MOS tube according to the received signal, so as to realize the adjustment of the output voltage; however, this indirect detection method has limitations because it cannot directly reflect the size of the output current, nor can it provide sufficient overcurrent protection for the output circuit, and when the voltage of the output circuit is too large, it cannot protect the load; therefore, traditional flyback switch power supplies have deficiencies in the protection of the output circuit and cannot well ensure the safe and stable operation of the output circuit.

[0033] As Figure 1As shown, a self-locking flyback switching power supply circuit with over-current and over-voltage protection includes: a primary control circuit, a power conversion circuit, a synchronous rectification circuit, a self-locking circuit, an over-current detection circuit, an over-voltage detection circuit, and an output circuit; among them,

[0034] The primary control circuit is used to control the conduction and turn-off of the primary MOS tube;

[0035] The output circuit is used to provide an output voltage and an output current to the load;

[0036] The over-current detection circuit is used to detect whether the output current exceeds the rated current;

[0037] The over-voltage detection circuit is used to detect whether the output voltage exceeds the rated voltage;

[0038] The power conversion circuit is used to convert the input voltage into a stable output voltage;

[0039] The synchronous rectification circuit is used to control the conduction and turn-off of the MOS tube in the output circuit;

[0040] The voltage feedback circuit is used to adjust the magnitude of the voltage at the output end;

[0041] The self-locking circuit is used to pull down the start-up voltage of the primary control circuit and the synchronous rectification circuit to a low level when detecting output over-voltage and / or over-current, so that the power conversion circuit stops working until the input voltage is disconnected;

[0042] The present invention realizes over-current and / or over-voltage monitoring by comparing the output current and / or output voltage, current rated value and / or voltage rated value. When the circuit is over-current and / or over-voltage, the start-up pins of the primary control chip and the synchronous rectification chip are pulled down to a low level through the self-locking circuit to protect the circuit.

[0043] As Figure 3 shown, the working principle of the flyback switching power supply:

[0044] By controlling the on and off of the primary MOS tube Q1, when the primary MOS tube Q1 is turned on, the electrical energy provided by the input circuit is converted into magnetic field energy stored in the primary winding of the transformer Np of the power conversion circuit; when the primary MOS tube Q1 is turned off, the magnetic field energy in the primary winding rapidly decays, and an induced electromotive force is generated in the secondary winding, thereby transmitting the energy to the secondary side, and after being processed by the output circuit, it is supplied to the load for use.

[0045] The AC-DC conversion circuit includes: an AC input terminal P1, a fuse F1, a thermistor NTC1, a variable resistor TR1, a capacitor C4, a transformer T1, a capacitor C3, a rectifier bridge BD1, and a polarized capacitor EC1; P1 is connected to 220V AC power supply, both ends of F1 and NTC1 are connected to both ends of TR1, TR1 is in parallel with C4, both ends of C4 are connected to the 1st and 3rd pins of T1, the 2nd and 4th pins of T1 are in parallel with C3, both ends of C3 are connected to the 1st and 2nd pins of BD1, the 3rd pin of BD1 is connected to the upper end of EC1, and the lower end of EC1 is connected to the 4th pin of BD1;

[0046] The primary control circuit includes: a primary control chip U4, a MOS transistor Q1, starting resistors R2, R6, and a current sampling resistor R33. U4 has a starting pin VDD, a driving pin GATE, an overcurrent detection pin CS, a feedback pin FB, and a thermal protection pin PRT;

[0047] One end of the starting resistor R2 is connected to the input voltage, and the other end is connected to the starting resistor R6. The other end of R6 is connected to the starting pin VDD of U4; the gate of the MOS transistor Q1 is connected to the common end of resistors R15 and R13. The other end of resistor R13 is connected to the positive electrode of diode D5, and the negative electrode of diode D5 is connected to the other end of resistor R15. The driving pin GATE of U4 is connected to the common end of diode D5 and resistor R15. The drain of the MOS transistor is connected to the 2nd pin of the primary winding of the transformer Np of the power conversion circuit, and the source is connected to one end of the current sampling resistor R33; one end of the current sampling resistor R33 is connected to the source of the MOS transistor Q1 and to one end of resistor R27. The other end of resistor R27 is connected to the overcurrent detection pin of U4, and the other end of R33 is grounded.

[0048] The output circuit includes: a load resistor R1, a capacitor C5, a current sampling resistor R4, a MOS transistor Q2, and a synchronous rectification chip U2. U2 has: a starting pin VCC, a driving pin VG, a device bias pin REG, a drain voltage detection pin VD, and a source voltage detection pin VS.

[0049] One end of the load resistor R1 is connected to one end of the secondary winding, and the other end is connected to the current sampling resistor R4; one end of the current sampling resistor R4 is connected to GND0 and grounded, and the other end is connected to one end of the load resistor R1;

[0050] The capacitor C5 is connected to the 5th pin of the secondary winding, and the other end is connected to GND0; the drain of Q2 is connected to the 6th pin of the secondary winding and the VD pin of U2. The gate of Q2 is connected to the driving pin VG of U2, and the source of Q2 is connected to the VS pin of U2; the starting pin VCC of U2 is connected to the 5th pin of the secondary winding.

[0051] The voltage feedback circuit includes: optocoupler sensor U7, resistors R17, R18, R34, R35, R36, capacitors C9, C10, C11 and voltage regulator U8.

[0052] One end of resistor R17 is connected to the 5th pin of the secondary winding, and the other end is connected to one end of resistor R34 and the 1st pin of optocoupler sensor U7. The 2nd pin of U7 is connected to the 1st pin of U8. The 2nd pin of U8 is connected to the common end of R18 and R36. The 3rd pin of U8 is connected to the lower end of resistor R36 which is connected to GND0. The other end of R34 is connected to one end of C9 and the common end of R35 and the 1st pin of U8. The other end of R35 is connected to one end of C10. The other ends of C9 and C10 are connected to one end of R18. The other end of R18 is connected to the 5th pin of the secondary winding. The 4th pin of U7 is connected to the feedback pin FB of U4 and the upper end of C11. The 3rd pin of U7 and the other end of C11 are connected to GND.

[0053] When the output voltage of Np becomes higher, the sampled voltage of the 2nd pin of U8 will increase, which will cause the conduction amount of U8 to increase, so the current flowing through U8 will increase, and the current of the light-emitting diode of U7 will also increase, which will cause the current of the triode of U7 to increase as well. Then the voltage of the feedback pin FB of U4 will decrease, making the duty cycle of the output pin GATE of U4 decrease, thus reducing the output voltage of Np. When the output voltage becomes lower, then the sampled voltage of U8 will decrease, the flowing current will also decrease, which will cause the triode current of the optocoupler sensor to decrease, the voltage of the feedback pin FB of U4 will increase, and the duty cycle of the output pin GATE of U4 will be increased, thus increasing the voltage of the secondary circuit, so as to play a feedback regulation function.

[0054] The voltage regulator includes: voltage regulation chip U3, resistors R5, R8 and R14. The upper end of R5 is connected to the 5V voltage, the lower end of R5 is connected to the 1st pin of U3. The 3rd pin of U3 is connected to GDN0. The upper end of R8 is connected to the 1st pin of U3, and the lower end of R8 is connected to GDN0 after being connected to R14.

[0055] The overcurrent detection circuit includes operational amplifier U5, resistors R10, R16 and diode D3. Among them, the non-inverting input terminal of U5 is connected to the right end of sampling resistor R4 to obtain a voltage signal proportional to the output current. The inverting input terminal is connected to the reference voltage terminal after voltage division by resistors R14 and R8. R16 is connected in series between the inverting input terminal and the output terminal of U5. The output terminal of U5 is connected to the positive poles of R10 and D3. The reference voltage comes from the output of voltage regulator U3. Voltage regulator U3 provides a stable reference voltage and transmits the voltage value after voltage division to the inverting input terminal of operational amplifier U3 through a resistor voltage division network.

[0056] The overcurrent detection circuit uses operational amplifier U5 to detect whether the circuit is overcurrent. A sampling resistor R4 with a low resistance value is used for current sampling, and the magnitude of the output current is indirectly detected by detecting the voltage drop across R4. The operational amplifier U5 compares the voltages at the non-inverting input terminal and the inverting input terminal. When the voltage at the non-inverting input terminal is higher than the voltage at the inverting input terminal, it indicates that the output current exceeds the set threshold, and the operational amplifier U5 outputs the positive power supply terminal voltage to trigger the overcurrent protection mechanism. On the contrary, when the voltage at the non-inverting input terminal is lower than the voltage at the inverting input terminal, it indicates that the output current is within the normal range, and the operational amplifier U5 outputs the negative power supply terminal voltage, and the circuit operates normally.

[0057] The overvoltage detection circuit includes: operational amplifier U6, resistors R26, R29, and diode D6; the non-inverting input terminal of U5 is connected to the common terminal of R12 and R28, the inverting input terminal of U6 is connected to the common terminal of the first and second pins of U3, and the third pin of U6 is in series with resistor R29 to its output terminal; the output terminal of U6 is connected to the positive electrodes of R26 and D6; the lower end of R28 is connected to the right end of R4;

[0058] The operational amplifier U6 compares the voltages at the non-inverting input terminal and the inverting input terminal. When the voltage at the non-inverting input terminal is higher than the voltage at the inverting input terminal, it indicates that the output voltage exceeds the set threshold, and the operational amplifier U6 outputs a high-level signal to trigger the overvoltage protection mechanism; the overvoltage detection circuit of U6 detects whether the circuit is overvoltage, and the output voltage is divided by resistors R12 and R28, and the magnitude of the output voltage is detected by sampling the voltage flowing through R28;

[0059] U5, U6, and U3 are all powered by the voltage regulator chip U1 of the voltage regulator circuit; U1 can provide a stable 5V voltage, and its output voltage will not be affected by the voltage signal of the output circuit; in this way, even if there are voltage fluctuations or abnormal conditions in the output circuit, it will not affect the normal operation of the detection circuit, thus ensuring the stability and reliability of the entire flyback switching power supply.

[0060] When the circuit detects an overcurrent and / or overvoltage situation, the operational amplifier in the corresponding overvoltage and / or overcurrent detection circuit will output a voltage close to its positive power supply terminal; when the circuit simultaneously detects an overcurrent and overvoltage situation, the two operational amplifiers in the circuit will also output the voltage of their positive power supply terminals; the output voltage signals of U5 and U6 are divided by resistors R10 and / or R26 and then transmitted to the base of transistor Q4, prompting Q4 to enter the saturation state, that is, its collector and emitter are conducting; at this time, the 5V voltage can flow through, and it first passes through resistor R19 for voltage division.

[0061] The first self-locking circuit includes: MOS transistor Q5, bipolar transistors Q6, Q3, resistors R7, R9, R24, R25; the gate of Q5 is connected to the left end of R19, the source and drain of Q5 are connected in parallel with the collector and emitter of Q6, R24 and R25 are connected in parallel and then connected to the base and emitter of Q6, the upper end of R24 is connected to the collector of Q3, the two ends of R7 and R9 in parallel are respectively connected to the emitter and base of Q3, the base of Q3 is connected to the collector of Q6; the upper end of R7 is connected to the VCC pin of U2 and the 5th pin of the secondary winding of the secondary circuit;

[0062] Before the first self-locking circuit is triggered, the voltage across R7 is high level, so the startup pin voltage VCC of the synchronous rectification chip U2 is also high level, and U2 is in a normal working state. When the first self-locking circuit is completed, due to the continuous conduction of Q3 and Q6, the voltage across R7 will be pulled down to low level, and at the same time, it will cause the startup pin of U2 to be pulled down to low level, so that U2 will stop working.

[0063] The second self-locking circuit includes: MOS transistor Q8, bipolar transistors Q7, Q9, resistors R21, R22, R30, R31; the gate of Q8 is connected to the left end of R19, the source and drain of Q8 are connected in parallel with the collector and emitter of Q9, R30 and R31 are connected in parallel and then connected to the base and emitter of Q9, the upper end of R30 is connected to the collector of Q7, the two ends of R21 and R22 in parallel are respectively connected to the emitter and base of Q7, the base of Q7 is connected to the collector of Q9; the upper end of R21 is connected to the VDD pin of U4.

[0064] The voltage signal after voltage division is then sent to the gates of MOS transistor Q5 and MOS transistor Q8; since the MOS transistor is a voltage-controlled device, when the gate receives a sufficient voltage signal, the source and drain of MOS transistor Q5 will conduct, and this conduction state then triggers a self-locking circuit mechanism.

[0065] Specifically, the conduction of MOS transistor Q5 causes the base voltage of the bipolar transistor Q3 connected to it to be pulled down. When the base voltage of bipolar transistor Q3 drops to a certain extent, bipolar transistor Q3 enters the saturation state, and its collector and emitter conduct; subsequently, the voltage signal flows through bipolar transistor Q3 and reaches the base of bipolar transistor Q6, causing Q6 to also enter the saturation state, and its collector and emitter conduct; when bipolar transistor Q6 conducts, it will maintain the base of bipolar transistor Q3 at a low level through the low-impedance path between its collector and emitter; this is because the conduction of Q6 pulls down the voltage of the node connected to the base of Q3, thus ensuring the continuous conduction of Q3; in this way, Q3 will continuously maintain the conduction state, and further make the voltage signal always pass through Q3, ensuring that the base of bipolar transistor Q6 is always at a sufficient level to maintain its conduction state. This series of actions completes the self-locking process of the first self-locking circuit.

[0066] Similarly, since the driving signals of MOS transistors Q5 and Q8 come from the same voltage signal segment, Q5 and Q8 can be turned on simultaneously; the gate of MOS transistor Q8 also receives the voltage signal after voltage division, and it will turn on and trigger the second self-locking circuit composed of transistor Q7 and transistor Q9; the working principle of this self-locking circuit is similar to that of the first self-locking circuit: the conduction of MOS transistor Q8 causes the base voltage of transistor Q7 to be pulled down, and Q7 enters the saturation state; subsequently, the voltage signal flows through transistor Q7 and reaches the base of transistor Q9, causing Q9 to also enter the saturation state; the conduction of Q9 in turn maintains the base of Q7 at a low level state, thus completing the self-locking process of the second self-locking circuit; when the second self-locking circuit is completed, the start pin VDD of U4 will also change from the original high level state to the low level state, and U4 will stop working.

[0067] After the circuit is self-locked, the start pins of U2 and U4 are pulled down from high level to low level; since these chips do not have sufficient voltage input, they will stop working; the result of the chips stopping working is that the MOS transistors Q1 and Q2 at the input and output ends cannot be turned on and off normally; therefore, the transformer of the power conversion circuit will no longer store energy and convert energy, and there will no longer be voltage and current flowing out of the output circuit, thus effectively protecting the load at the output end and preventing it from being damaged due to overvoltage or overcurrent.

[0068] Figure 4 It shows the comparison of the output voltage changes between the traditional flyback switching power supply and the flyback switching power supply of the present invention when there is an overvoltage situation in the output circuit; Figure 2 In the traditional flyback switching power supply, when an overvoltage situation occurs, usually only the output voltage feedback circuit can be used to gradually reduce the output voltage, but this process may be slow, and during the period of continuous high voltage, the load is easily damaged; in contrast, when the protection circuit of the present invention detects an overvoltage situation, it can immediately pull down the start pins of the synchronous rectification chip and the primary control chip, causing these chips to stop working quickly, thus effectively protecting the load at the output end and preventing it from being damaged due to overvoltage.

[0069] Figure 5 It shows the comparison of the output current changes between the traditional flyback switching power supply and the circuit of the present invention when the output circuit is overcurrent; in the traditional flyback switching power supply, due to the lack of overcurrent protection mechanism at the output end, when an overcurrent situation occurs, the circuit will always maintain a high current state, which is likely to cause serious consequences such as overheating, damage of the load and even fire; while the circuit of the present invention will quickly pull down the start pins of the synchronous rectification chip and the primary control chip when detecting an overcurrent situation, causing the circuit to immediately stop outputting current, thus effectively protecting the load in the circuit and preventing it from being damaged due to overcurrent; until the fault is eliminated and the circuit is restarted, the circuit can resume normal operation.

[0070] Inspired by the above-described ideal embodiments of the present invention, through the above description, relevant staff can completely make various changes and modifications without departing from the technical idea of this invention. The technical scope of this invention is not limited to the content in the specification, and its technical scope must be determined according to the scope of the claims.

Claims

1. A self-locking flyback switching power supply circuit with over-current and over-voltage protection, comprising: The primary side control circuit, power conversion circuit, synchronous rectification circuit and output circuit, characterized in that the self-locking circuit is electrically connected to the overvoltage detection circuit and the overcurrent detection circuit; wherein, The overcurrent detection circuit is used to detect whether the output current exceeds the rated current; The overvoltage detection circuit is used to detect whether the output voltage exceeds the rated voltage; The self-locking circuit is used to pull down the start-up voltage of the primary side control circuit and the synchronous rectification circuit to a low level when detecting output overvoltage or overcurrent, so that the power conversion circuit stops working until the input voltage is disconnected.

2. The self-locking flyback switching power supply circuit with over-current and over-voltage protection according to claim 1, wherein The overvoltage detection circuit includes: operational amplifier U6, resistors R26, R29, R19, R23, triode Q4 and diode D6; the 3rd pin of U6 is in series with resistor R29 at the output terminal of U6; the output terminal of U6 is connected to the positive electrodes of R26 and D6, the negative electrode of D6 is connected to the base of Q4, and the emitter of Q4 is connected to the common terminal of R19 and R23.

3. The self-locking flyback switching power supply circuit with over-current and over-voltage protection according to claim 1, wherein The overcurrent detection circuit includes: operational amplifier U5, resistors R10, R16, R19, R23, triode Q4 and diode D3; the inverting input terminal and the output terminal of U5 are in series with R16, the output terminal of U5 is connected to the positive electrodes of R10 and D3, the negative electrode of D3 is connected to the base of Q4, and the emitter of Q4 is connected to the common terminal of R19 and R23.

4. The self-locking flyback switching power supply circuit with over-current and over-voltage protection according to claim 1, characterized in that, The first self-locking circuit of the self-locking circuit includes: MOS tube Q5, triodes Q6, Q3, resistors R7, R9, R24, R25; the gate of Q5 is connected to the left end of R19, the source and drain of Q5 are in parallel with the collector and emitter of Q6, R24 and R25 are in parallel and then connected to the base and emitter of Q6, the upper end of R24 is connected to the collector of Q3, the two ends of R7 and R9 in parallel are respectively connected to the emitter and base of Q3, and the base of Q3 is connected to the collector of Q6; the upper end of R7 is connected to the output circuit and the synchronous rectification circuit.

5. The self-locking flyback switching power supply circuit with over-current and over-voltage protection according to claim 1, characterized in that, The second self-locking circuit of the self-locking circuit includes: MOS tube Q8, triodes Q7, Q9, resistors R21, R22, R30, R31; the gate of Q8 is connected to the left end of R19, the source and drain of Q8 are in parallel with the collector and emitter of Q9, R30 and R31 are in parallel and then connected to the base and emitter of Q9, the upper end of R30 is connected to the collector of Q7, the two ends of R21 and R22 in parallel are respectively connected to the emitter and base of Q7, and the base of Q7 is connected to the collector of Q9; the upper end of R21 is connected to the primary side control circuit.

6. The self-locking flyback switching power supply circuit with over-current and over-voltage protection according to claim 1, characterized in that, It also includes: The voltage feedback circuit adjusts the voltage of the output circuit by adjusting the duty cycle of the primary side control circuit.

7. The self-locking flyback switching power supply circuit with over-current and over-voltage protection according to claim 1, wherein, It also includes: A voltage regulator, which is used for the rated voltage and / or rated current of the overvoltage protection circuit and / or the overcurrent protection circuit.

8. The self-locking flyback switching power supply circuit with over-current and over-voltage protection according to claim 1, characterized in that, The control chip model of the primary side control circuit is CR6885.

9. The self-locking flyback switching power supply circuit with over-current and over-voltage protection according to claim 1, characterized in that, The model of the synchronous rectification chip of the synchronous rectification circuit is UCC24612.

10. The self-locking flyback switching power supply circuit with over-current and over-voltage protection according to claim 1, characterized in that, It also includes a power supply circuit for providing 5V voltage.

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