A protection circuit for auxiliary output end based on multi-output flyback power supply

Abstract

The utility model provides a kind of protection circuit of auxiliary road output end based on multiple output flyback power supply, including overvoltage detection circuit, overcurrent detection circuit, control circuit and sampling circuit;The voltage detection input end of overvoltage detection circuit is connected with the auxiliary road output end of flyback power supply, overvoltage reference voltage input end receives reference voltage signal from reference voltage source VREF, and overvoltage protection signal output end is connected to the protection trigger input end of control circuit;The current sampling signal input end of overcurrent detection circuit is connected with the current sampling amplification signal output end of sampling circuit, and overcurrent reference voltage input end receives reference voltage signal from reference voltage source VREF, and overcurrent protection signal output end is connected with the protection trigger input end of control circuit;The current sampling signal input end of control circuit is connected with the current sampling signal input end of sampling circuit.The utility model carries out restriction and protection to the output voltage of multiple output flyback power supply, and can prevent electronic component burnout.

Description

Technical Field

[0001] This utility model belongs to the field of power supply technology, specifically relating to a protection circuit for the auxiliary output terminal of a multi-output flyback power supply. Background Technology

[0002] With the continuous development of electronic technology, multi-output flyback power supplies have been widely used in various electronic devices. Flyback power supplies have advantages such as simple circuit structure, low cost, high efficiency, and multiple output voltages. However, since only the main output is controlled by feedback, while the auxiliary output relies on the magnetic field characteristics of the transformer for energy acquisition and output, when the load on the main output increases while the load on the auxiliary output is too light, the auxiliary output load is not adjusted in time, causing the auxiliary voltage to rise too high, which can burn out the auxiliary components. The control chip of the main feedback cannot provide timely circuit protection before the burnout, leading to power supply damage or even safety accidents. Therefore, an effective protection circuit is needed to ensure the safety of the auxiliary output. Utility Model Content

[0003] To improve the functionality of a multi-output flyback power supply and protect its auxiliary circuit voltage, thereby reducing power supply damage and safety accidents, this invention proposes a protection circuit based on the auxiliary circuit output of a multi-output flyback power supply. The circuit includes: an overvoltage detection circuit, an overcurrent detection circuit, a control circuit, and a sampling circuit. The voltage detection input of the overvoltage detection circuit is connected to the auxiliary circuit output of the flyback power supply, and the overvoltage reference voltage input receives a reference voltage signal from the reference voltage source VREF. The overvoltage protection signal output is connected to the protection trigger input of the control circuit. The current sampling signal input of the overcurrent detection circuit is connected to the current sampling amplification signal output of the sampling circuit. The overcurrent reference voltage input receives a reference voltage signal from the reference voltage source VREF, and the overcurrent protection signal output is connected to the protection trigger input of the control circuit. The control signal output of the control circuit is connected to the current sampling signal input of the sampling circuit.

[0004] Furthermore, the overvoltage detection circuit includes voltage divider resistors R1 and R3, an overvoltage protection comparator U2A, and a diode D2.

[0005] Furthermore, the auxiliary output of the flyback power supply is connected to the non-inverting input of the overvoltage protection comparator U2A through a voltage divider resistor R1, and the reference voltage signal output of the reference voltage source VREF is connected to the inverting input of the overvoltage protection comparator U2A through a voltage divider resistor R3; the output of the overvoltage protection comparator U2A is connected to the protection trigger input of the control circuit through a diode D2.

[0006] Furthermore, the overcurrent detection circuit includes voltage divider resistors R2, R4, and R5, current limiting resistor R6, capacitor C1, overcurrent protection comparator U2B, and diode D3.

[0007] Furthermore, the reference voltage signal output of the reference voltage source VREF is connected to the inverting input of the overcurrent comparator U2B in sequence through voltage divider resistors R3 and R4; the non-inverting input of the overcurrent comparator U2B is connected to the current sampling amplification signal output of the sampling circuit; the output of the overcurrent protection comparator U2B is connected to the protection trigger input of the control circuit through diode D3 and current limiting resistor R6; one end of the voltage divider resistor R2 is connected to the voltage divider resistor R1 of the overvoltage detection circuit, and the other end is grounded; capacitor C1 is connected in parallel across the two ends of the voltage divider resistor R2; the other end of the voltage divider resistor R4 is grounded through the other end of the voltage divider resistor R5.

[0008] Furthermore, the control circuit includes current-limiting resistors R7~R9, an NPN transistor Q2, and a single-pole double-throw relay U1.

[0009] Furthermore, the IN1 pin of the single-pole double-throw relay U1 is connected to the reference voltage signal output terminal of the reference voltage source VREF through the current-limiting resistor R7, and is also connected to the collector of the NPN transistor Q2. The IN2 pin is grounded through the current-limiting resistor R8. The VIN pin is connected to the auxiliary output terminal of the flyback power supply. The VOUT1 pin is connected to the current sampling signal input terminal of the sampling circuit. The VOUT2 pin is grounded through the current-limiting resistor R9. The base of the NPN transistor Q2 is connected to the overcurrent protection signal output terminal of the overcurrent detection circuit and the overvoltage protection signal output terminal of the overvoltage detection circuit, respectively.

[0010] Furthermore, the sampling circuit includes a sampling resistor R10, a load R11, a capacitor C2, an operational amplifier comparator U2C, a current-voltage amplifier U3A, and proportional resistors R12 and R13.

[0011] Furthermore, the control signal output terminal of the control circuit is connected to the non-inverting input terminal of the operational amplifier comparator U2C, and is also connected to the inverting input terminal of the operational amplifier comparator U2C through the sampling resistor R10; the output terminal of the operational amplifier comparator U2C is connected to the non-inverting input terminal of the current-voltage amplifier U3A; the non-inverting input terminal of the operational amplifier comparator U2C is connected to the control signal output terminal of the control circuit; the inverting input terminal of the current-voltage amplifier U3A is grounded through the proportional resistor R13, and is also connected to the output terminal of the current-voltage amplifier U3A through the proportional resistor R12; the output terminal of the current-voltage amplifier U3A is connected to the current sampling signal input terminal of the overcurrent detection circuit.

[0012] Furthermore, the inverting input of the operational amplifier comparator U2C is grounded through the load R11, and the capacitor C2 is connected in parallel across the load R11.

[0013] The beneficial effects of this utility model include: addressing the problem that excessively high auxiliary output voltage of a multi-output flyback power supply can easily lead to burnout of components at the output end and the next stage circuit, this invention limits and protects the output voltage to prevent burnout of electronic components and reduce costs in the product design process. Attached Figure Description

[0014] Figure 1 This is a circuit diagram of an embodiment of the present invention;

[0015] Figure 2 This is a block diagram of a multi-output flyback power supply circuit. Detailed Implementation

[0016] The following detailed embodiments are provided to explain the technical solution of this utility model, so that those skilled in the art can understand this utility model. The protection scope of this utility model is not limited to the following specific embodiments. Any modifications or improvements made by those skilled in the art that incorporate the technical solution of this utility model but differ from the following detailed embodiments are also within the protection scope of this utility model.

[0017] This utility model relates to a protection circuit for the auxiliary output terminal of a multi-output flyback power supply, such as... Figure 1 As shown, it includes: an overvoltage detection circuit, an overcurrent detection circuit, a control circuit, and a sampling circuit; the voltage detection input terminal of the overvoltage detection circuit is connected to the auxiliary output terminal of the flyback power supply, the overvoltage reference voltage input terminal receives the reference voltage signal from the reference voltage source VREF, and the overvoltage protection signal output terminal is connected to the protection trigger input terminal of the control circuit; the current sampling signal input terminal of the overcurrent detection circuit is connected to the current sampling amplification signal output terminal of the sampling circuit, the overcurrent reference voltage input terminal receives the reference voltage signal from the reference voltage source VREF, and the overcurrent protection signal output terminal is connected to the protection trigger input terminal of the control circuit; the control signal output terminal of the control circuit is connected to the current sampling signal input terminal of the sampling circuit.

[0018] In some embodiments, the overvoltage detection circuit includes voltage divider resistors R1 and R3, an overvoltage protection comparator U2A, and a diode D2.

[0019] In some embodiments, the auxiliary output of the flyback power supply is connected to the non-inverting input of the overvoltage protection comparator U2A through a voltage divider resistor R1, and the reference voltage signal output of the reference voltage source VREF is connected to the inverting input of the overvoltage protection comparator U2A through a voltage divider resistor R3; the output of the overvoltage protection comparator U2A is connected to the protection trigger input of the control circuit through a diode D2.

[0020] In some embodiments, the overcurrent detection circuit includes voltage divider resistors R2, R4, and R5, current limiting resistor R6, capacitor C1, overcurrent protection comparator U2B, and diode D3.

[0021] In some embodiments, the reference voltage signal output of the reference voltage source VREF is connected to the inverting input of the overcurrent comparator U2B in sequence through voltage divider resistors R3 and R4; the non-inverting input of the overcurrent comparator U2B is connected to the current sampling amplification signal output of the sampling circuit; the output of the overcurrent protection comparator U2B is connected to the protection trigger input of the control circuit in sequence through diode D3 and current limiting resistor R6; one end of the voltage divider resistor R2 is connected to the voltage divider resistor R1 of the overvoltage detection circuit, and the other end is grounded; capacitor C1 is connected in parallel across the two ends of the voltage divider resistor R2; the other end of the voltage divider resistor R4 is grounded through the other end of the voltage divider resistor R5.

[0022] In some embodiments, the control circuit includes current-limiting resistors R7~R9, an NPN transistor Q2, and a single-pole double-throw relay U1.

[0023] In some embodiments, the IN1 pin of the single-pole double-throw relay U1 is connected to the reference voltage signal output terminal of the reference voltage source VREF through the current-limiting resistor R7, and is also connected to the collector of the NPN transistor Q2. The IN2 pin is grounded through the current-limiting resistor R8. The VIN pin is connected to the auxiliary output terminal of the flyback power supply. The VOUT1 pin is connected to the current sampling signal input terminal of the sampling circuit. The VOUT2 pin is grounded through the current-limiting resistor R9. The base of the NPN transistor Q2 is connected to the overcurrent protection signal output terminal of the overcurrent detection circuit and the overvoltage protection signal output terminal of the overvoltage detection circuit, respectively.

[0024] In some embodiments, the sampling circuit includes a sampling resistor R10, a load R11, a capacitor C2, an operational amplifier comparator U2C, a current-voltage amplifier U3A, and proportional resistors R12 and R13.

[0025] In some embodiments, the control signal output terminal of the control circuit is connected to the non-inverting input terminal of the operational amplifier comparator U2C, and is also connected to the inverting input terminal of the operational amplifier comparator U2C through a sampling resistor R10; the output terminal of the operational amplifier comparator U2C is connected to the non-inverting input terminal of the current-voltage amplifier U3A; the non-inverting input terminal of the operational amplifier comparator U2C is connected to the control signal output terminal of the control circuit; the inverting input terminal of the current-voltage amplifier U3A is grounded through a proportional resistor R13, and is also connected to the output terminal of the current-voltage amplifier U3A through a proportional resistor R12; the output terminal of the current-voltage amplifier U3A is connected to the current sampling signal input terminal of the overcurrent detection circuit.

[0026] In some embodiments, the inverting input of the operational amplifier comparator U2C is grounded through the load R11, and the capacitor C2 is connected in parallel across the load R11.

[0027] The working principle of this utility model is as follows:

[0028] The flyback power supply auxiliary output is connected to one end of the voltage divider resistor R1 in the overvoltage detection circuit via diode D1. The other end of the voltage divider resistor R1 is connected to the voltage divider resistor R2 in the overcurrent detection circuit and the non-inverting input of the overvoltage protection comparator U2A. The voltage Vo output from the flyback power supply auxiliary output provides a detection voltage to the non-inverting input of the overvoltage protection comparator U2A through the voltage divider resistors R1 and R2. The detection voltage value is set according to the rated value of the voltage Vo output from the flyback power supply auxiliary output. For example, when Vo is 5V, the overvoltage threshold and undervoltage threshold can be set to 6V and 4V respectively. Protection is triggered when the voltage is outside the 4V-6V range. Capacitor C1 is connected in parallel across the voltage divider resistor R2 to prevent false triggering of the protection due to excessive instantaneous surge voltage of the output voltage Vo. Voltage divider resistors R3, R4, and R5 are connected to the reference voltage source. VREF, in conjunction with the current amplifier, provides a reference voltage for the overcurrent protection comparator U2B; R6, R7, R8, and R9 are all current-limiting resistors to prevent direct short circuits; R10 is a sampling resistor, and the operational amplifier comparator U2C samples the current from the sampling resistor R10 and connects it to the non-inverting input of the current-voltage amplifier U3A; capacitor C2 is connected in parallel across the load R11 to filter out high-frequency noise in the sampling circuit, making the operating voltage of the operational amplifier comparator U2C more stable; on the other hand, it uses its own charging and discharging characteristics to help stabilize the voltage during voltage surges, ensuring the normal operation of the sampling circuit; R12 and R13 are proportional resistors for adjusting the current-voltage amplifier U3A, so that the voltage of the set maximum current is amplified to the set value (such as half of Vo) and input to the non-inverting input of the overcurrent protection comparator U2B as a comparison signal for overcurrent detection;

[0029] When the voltage Vo and current output from the auxiliary output terminal of the flyback power supply are both normal, the overvoltage protection comparator U2A outputs a low level, and diode D2 does not conduct; the overcurrent protection comparator U2B outputs a low level, and diode D3 does not conduct; at this time, NPN transistor Q2 does not conduct because there is no driving signal at its base, and the normally closed contact of single-pole double-throw relay U1 is closed. The voltage Vo output from the auxiliary output terminal of the flyback power supply is directly connected to the VOUT1 pin of single-pole double-throw relay U1 through the internal contacts of the relay. The VOUT1 pin outputs a normal voltage Vo2, which enables the subsequent circuits to be powered normally.

[0030] When the voltage Vo output from the auxiliary output terminal of the flyback power supply is abnormal, but the current output is normal, the overvoltage protection comparator U2A outputs a high level, and the diode D2 connected to its output terminal conducts. The overcurrent protection comparator U2B still outputs a low level, and the diode D3 connected to its output terminal does not conduct. The current after the corresponding NPN transistor Q2 conducts flows into the base of the NPN transistor Q2 through the current limiting resistor R6, causing Q2 to saturate and conduct. The coil of the corresponding single-pole double-throw relay U1 is energized, and the contacts switch to the normally open state, disconnecting from the VOUT1 pin. The voltage Vo output from the auxiliary output terminal of the flyback power supply is directly connected to the VOUT2 pin through the internal contacts of the single-pole double-throw relay U1. The VOUT2 pin is an invalid output terminal because its output Vo2 has no output voltage, thus de-energizing its subsequent circuits and providing timely protection.

[0031] When the voltage Vo output from the auxiliary output terminal of the flyback power supply is normal but the current output is abnormal, the overvoltage protection comparator U2A outputs a low level, which prevents the corresponding diode D2 from conducting. The overcurrent protection comparator U2B outputs a high level, which turns on the diode D3 connected to it. At this time, the current after D3 conducts flows into the base of the NPN transistor Q2 through the current limiting resistor R6. The corresponding NPN transistor Q2 is saturated and conducts, and the coil of the corresponding single-pole double-throw relay U1 is energized. The contacts switch to the VOUT2 pin, and the voltage Vo output from the auxiliary output terminal of the flyback power supply is directly connected to the VOUT2 pin. Since the VOUT2 pin is an invalid output terminal, Vo2 has no output voltage, which de-energizes its subsequent circuits and provides timely protection.

[0032] When the voltage Vo output from the auxiliary output terminal of the flyback power supply is abnormal and the current output is also abnormal, both the overvoltage protection comparator U2A and the overcurrent protection comparator U2B output a high level. The overvoltage protection comparator U2A turns on the corresponding diode D2, and the overcurrent protection comparator U2B turns on the corresponding diode D3. The current flows through the current-limiting resistor R6 into the base of the NPN transistor Q2. The corresponding single-pole double-throw relay U1 contacts switch to the VOUT2 pin, and the voltage Vo output from the auxiliary output terminal of the flyback power supply is directly connected to the VOUT2 pin. However, the VOUT2 pin is an invalid output terminal. Therefore... Figure 1 The output Vo2 shown has no output voltage, which de-energizes its subsequent circuits and provides timely protection.

Claims

1. A protection circuit based on the auxiliary output terminal of a multi-output flyback power supply, characterized in that, It includes an overvoltage detection circuit, an overcurrent detection circuit, a control circuit, and a sampling circuit; the voltage detection input terminal of the overvoltage detection circuit is connected to the auxiliary output terminal of the flyback power supply, the overvoltage reference voltage input terminal receives the reference voltage signal from the reference voltage source, and the overvoltage protection signal output terminal is connected to the protection trigger input terminal of the control circuit. The current sampling signal input terminal of the overcurrent detection circuit is connected to the current sampling amplification signal output terminal of the sampling circuit. The overcurrent reference voltage input terminal receives the reference voltage signal from the reference voltage source. The overcurrent protection signal output terminal is connected to the protection trigger input terminal of the control circuit. The control signal output terminal of the control circuit is connected to the current sampling signal input terminal of the sampling circuit.

2. The protection circuit based on the auxiliary output terminal of a multi-output flyback power supply as described in claim 1, characterized in that, The overvoltage detection circuit includes voltage divider resistors R1 and R3, an overvoltage protection comparator U2A, and a diode D2.

3. The protection circuit based on the auxiliary output terminal of a multi-output flyback power supply as described in claim 2, characterized in that, The auxiliary output of the flyback power supply is connected to the non-inverting input of the overvoltage protection comparator U2A through a voltage divider resistor R1. The reference voltage signal output of the reference voltage source is connected to the inverting input of the overvoltage protection comparator U2A through a voltage divider resistor R3. The output of the overvoltage protection comparator U2A is connected to the protection trigger input of the control circuit through a diode D2.

4. The protection circuit based on the auxiliary output terminal of a multi-output flyback power supply as described in claim 2 or 3, characterized in that, The overcurrent detection circuit includes voltage divider resistors R2, R4, and R5, current limiting resistor R6, capacitor C1, overcurrent protection comparator U2B, and diode D3.

5. The protection circuit based on the auxiliary output terminal of a multi-output flyback power supply as described in claim 4, characterized in that, The reference voltage signal output of the reference voltage source is connected to the inverting input of the overcurrent comparator U2B via voltage divider resistors R3 and R4 in sequence; the non-inverting input of the overcurrent comparator U2B is connected to the current sampling amplification signal output of the sampling circuit; the output of the overcurrent protection comparator U2B is connected to the protection trigger input of the control circuit via diode D3 and current limiting resistor R6; one end of the voltage divider resistor R2 is connected to the voltage divider resistor R1 of the overvoltage detection circuit, and the other end is grounded; capacitor C1 is connected in parallel across the two ends of the voltage divider resistor R2; the other end of the voltage divider resistor R4 is grounded via the other end of the voltage divider resistor R5.

6. The protection circuit based on the auxiliary output terminal of a multi-output flyback power supply as described in claim 1, characterized in that, The control circuit includes current-limiting resistors R7~R9, an NPN transistor Q2, and a single-pole double-throw relay U1.

7. The protection circuit based on the auxiliary output terminal of a multi-output flyback power supply as described in claim 6, characterized in that, The IN1 pin of the single-pole double-throw relay U1 is connected to the reference voltage signal output terminal of the reference voltage source through the current-limiting resistor R7, and is also connected to the collector of the NPN transistor Q2. The IN2 pin is grounded through the current-limiting resistor R8. The VIN pin is connected to the auxiliary output terminal of the flyback power supply. The VOUT1 pin is connected to the current sampling signal input terminal of the sampling circuit. The VOUT2 pin is grounded through the current-limiting resistor R9. The base of the NPN transistor Q2 is connected to the overcurrent protection signal output terminal of the overcurrent detection circuit and the overvoltage protection signal output terminal of the overvoltage detection circuit, respectively.

8. The protection circuit based on the auxiliary output terminal of a multi-output flyback power supply as described in claim 1, characterized in that, The sampling circuit includes a sampling resistor R10, a load R11, a capacitor C2, an operational amplifier comparator U2C, a current-voltage amplifier U3A, and proportional resistors R12 and R13.

9. The protection circuit based on the auxiliary output terminal of a multi-output flyback power supply as described in claim 8, characterized in that, The control signal output terminal of the control circuit is connected to the non-inverting input terminal of the operational amplifier comparator U2C, and is also connected to the inverting input terminal of the operational amplifier comparator U2C through sampling resistor R10; the output terminal of the operational amplifier comparator U2C is connected to the non-inverting input terminal of the current-voltage amplifier U3A; the non-inverting input terminal of the operational amplifier comparator U2C is connected to the control signal output terminal of the control circuit; the inverting input terminal of the current-voltage amplifier U3A is grounded through proportional resistor R13, and is also connected to the output terminal of the current-voltage amplifier U3A through proportional resistor R12; the output terminal of the current-voltage amplifier U3A is connected to the current sampling signal input terminal of the overcurrent detection circuit.

10. The protection circuit based on the auxiliary output terminal of a multi-output flyback power supply as described in claim 9, characterized in that, The inverting input of the op-amp comparator U2C is grounded through the load R11, and the capacitor C2 is connected in parallel across the load R11.

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