A flyback power supply short circuit protection circuit

Abstract

The utility model discloses a flyback power supply short circuit protection circuit, include: signal feedback unit for providing feedback signal, feedback signal clamping unit includes power management chip and voltage limiting unit for clamping feedback signal, and the feedback pin of power management chip is connected in the output of signal feedback unit, and voltage limiting unit is connected in the feedback pin of power management chip, reference voltage source pin respectively, short circuit detection protection unit includes voltage stabilizing element, detection resistance, switch element and first electric capacity, and voltage stabilizing element and detection resistance series connection are between reference ground and the feedback pin of power management chip, one end of switch element is connected in the midpoint of voltage stabilizing element and detection resistance, and the other end is through first electric capacity and is connected in the self -feed electricity pin of power management chip, compared with relevant prior art, not only can realize short circuit detection, response and protection, and high reliability, and easy to realize, and the application prospect is good.

Description

Technical Field

[0001] This utility model relates to the field of electronic measurement technology, and in particular to a short-circuit protection circuit for a flyback power supply. Background Technology

[0002] In high-power flyback power supplies, the energy stored during a single-cycle excitation approaches the limit of the transformer's energy storage capacity. When a short circuit occurs in the transformer, the voltage of the secondary winding is pulled down to near zero. At this point, the energy stored in the secondary winding cannot be released, the transformer is prone to saturation, and the flyback power supply protection circuit is damaged.

[0003] Currently, in the event of an output short circuit, the self-feeding voltage output by the self-feedback winding of a flyback power supply decreases due to the reduced duty cycle, thanks to the good coupling between the transformer windings. When the self-feeding voltage falls below the chip's startup threshold, the chip stops operating, thus achieving short-circuit protection. However, in practical applications of flyback power supplies with wide input ranges, the normal operating duty cycle under high-voltage input conditions is already at a low level. If an output short circuit occurs under these conditions, the self-feeding voltage is unlikely to decrease further below the chip's startup threshold, causing the short-circuit protection function to fail. Furthermore, the effectiveness of the above protection mechanism is closely related to process factors such as the coupling quality of the transformer windings, making it difficult for flyback power supplies to maintain high consistency across different batches or production conditions. Utility Model Content

[0004] This invention aims to at least partially solve one of the technical problems in related technologies. To this end, this invention proposes a flyback power supply short-circuit protection circuit that is highly reliable, has a stable response, and is easy to implement.

[0005] This utility model embodiment provides a flyback power supply short-circuit protection circuit, including:

[0006] The signal feedback unit is used to provide feedback signals;

[0007] The feedback signal clamping unit includes a power management chip and a voltage limiting unit for clamping the feedback signal. The feedback pin of the power management chip is connected to the output terminal of the signal feedback unit, and the voltage limiting unit is connected to the feedback pin and the reference voltage source pin of the power management chip, respectively.

[0008] The short-circuit detection and protection unit includes a voltage regulator, a sensing resistor, a switching element, and a first capacitor. The voltage regulator and the sensing resistor are connected in series between a reference ground and the feedback pin of the power management chip. One end of the switching element is connected to the midpoint between the voltage regulator and the sensing resistor, and the other end is connected to the self-feeding pin of the power management chip through the first capacitor.

[0009] Optionally, in one embodiment of this utility model, the voltage regulator is a Zener diode, and the switching element is an NPN transistor; the negative terminal of the voltage regulator is connected to the feedback pin of the power management chip, and the positive terminal is connected to the sensing resistor and the base of the switching element respectively; the emitter of the switching element is connected to the self-feeding pin of the power management chip through the first capacitor, and the emitter of the switching element and one end of the first capacitor are connected to the reference ground.

[0010] Optionally, in one embodiment of the present invention, the short-circuit detection and protection unit further includes a current-limiting resistor and a recovery resistor. The recovery resistor is used in conjunction with the first capacitor to form a soft-start and automatic recovery circuit. The collector of the switching element is connected to one end of the current-limiting resistor. The other end of the current-limiting resistor is connected to the self-feeding pin of the power management chip and is also connected to an external input voltage through the recovery resistor.

[0011] Optionally, in one embodiment of the present invention, the voltage limiting unit includes a first diode and a second diode connected in series, the anode of the first diode is connected to the feedback pin of the power management chip, the cathode of the first diode is connected to the anode of the second diode, and the cathode of the second diode is connected to the reference voltage source pin of the power management chip.

[0012] Optionally, in one embodiment of this utility model, the signal feedback unit includes an optocoupler, a reference voltage source, a third resistor, a fourth resistor, and a second capacitor; the third resistor and the fourth resistor are connected in series to an external output voltage; one end of the reference voltage source is connected to the midpoint between the third resistor and the fourth resistor, and the other end is connected to the primary side of the optocoupler, so that the voltage divider signal of the output voltage is input to the optocoupler through the reference voltage source; the secondary side of the optocoupler and the second capacitor cooperate to form a feedback loop for generating a feedback signal, and the feedback loop is respectively connected to a reference ground and the feedback pin of the power management chip.

[0013] Optionally, in one embodiment of the present invention, the signal feedback unit further includes a first resistor and a second resistor that serve as current limiting components. The first resistor is disposed in the feedback loop and connected to the secondary side of the optocoupler, and the second resistor is connected in series with the reference voltage source through the primary side of the optocoupler.

[0014] Optionally, in one embodiment of this utility model, the power management chip is a UC2844 chip.

[0015] This invention proposes a flyback power supply short-circuit protection circuit. Through the cooperation of a signal feedback unit, a power management chip, and a voltage limiting unit, a stable feedback signal is provided to effectively detect flyback power supply short circuits. When the feedback signal voltage abnormally rises, the voltage regulator element will be detected as having broken down, thus confirming the output short circuit. In this case, the voltage drop across the detection resistor will drive the switching element to conduct, rapidly discharging the charge on the first capacitor. This causes the self-feeding voltage to drop below the undervoltage lockout threshold of the power management chip, forcing the chip to enter a shutdown protection state. This achieves effective protection of the power circuit. Compared to existing technologies, this circuit not only stably achieves short-circuit detection, response, and protection with high reliability, but also has minimal requirements on the flyback power supply's own process configuration, making it easy to implement and promising for future applications. Attached Figure Description

[0016] Figure 1 This is a circuit diagram of a flyback power supply short-circuit protection circuit provided in one embodiment of the present invention. Detailed Implementation

[0017] To make the objectives, technical solutions, and advantages of this utility model clearer, the present utility model will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain this utility model and are not intended to limit this utility model.

[0018] Figure 1 The circuit diagram shows a short-circuit protection circuit for a flyback power supply provided in one embodiment of this utility model. Figure 1 As shown, the flyback power supply short-circuit protection circuit includes, but is not limited to:

[0019] The signal feedback unit 100 is used to provide a feedback signal to maintain the stability of the output voltage;

[0020] The feedback signal clamping unit 200 may include, but is not limited to, a power management chip U1 and a voltage limiting unit 210 for clamping the feedback signal. The feedback pin COMP of the power management chip U1 is connected to the output terminal of the signal feedback unit 100. The voltage limiting unit 210 is connected to the feedback pin COMP and the reference voltage source pin VREF of the power management chip U1 respectively to improve the stability of short circuit detection.

[0021] The short-circuit detection and protection unit 300 may include, but is not limited to, a voltage regulator Z1, a sensing resistor R7, a switching element Q1, and a first capacitor C1. The voltage regulator Z1 and the sensing resistor R7 are connected in series between the reference ground and the feedback pin COMP of the power management chip U1. One end of the switching element Q1 is connected to the midpoint between the voltage regulator Z1 and the sensing resistor R7, and the other end is connected to the self-feeding pin VCC of the power management chip U1 through the first capacitor C1, so as to realize short-circuit detection and protection of the flyback power supply.

[0022] It can be seen that the signal feedback unit 100, power management chip U1, and voltage limiting unit 210 work together to provide a stable feedback signal, which facilitates effective short-circuit detection of the flyback power supply. When the feedback signal voltage rises abnormally, the voltage regulator Z1 will be detected as broken down, thus confirming that an output short circuit has occurred. In this case, the voltage drop across the detection resistor R7 will drive the switching element Q1 to conduct, thereby quickly discharging the charge on the first capacitor C1, causing the self-feeding voltage to drop below the undervoltage lockout threshold of the power management chip U1, thus forcing the chip to enter the shutdown protection state, achieving effective protection of the power circuit. Compared with related existing technologies, it can not only stably realize short-circuit detection, response, and protection with high reliability, but also does not have too many requirements on the flyback power supply's own process configuration conditions, making it easy to implement and with good application prospects.

[0023] In one embodiment, the specifications and parameters of the power management chip U1 can be selected and set according to the actual application scenario, and there are no restrictions here. For example, it can be, but is not limited to, using the UC2844 chip. The UC2844 chip is a current-mode PWM controller chip launched by TI, mainly used for switching power supply design. It has features such as 16V / 10V undervoltage lockout and a maximum switching frequency of 500kHz, and is widely used in flyback, boost, and other topologies. Alternatively, the TL3844 chip can be used, etc. Figure 1 The embodiments shown use the UC2844 chip as an example for illustration, but should not be construed as an arbitrary limitation.

[0024] In one embodiment, such as Figure 1 As shown, the signal feedback unit 100 may include, but is not limited to, an optocoupler U2, a reference voltage source D3, a third resistor R3, a fourth resistor R4, and a second capacitor C2; the third resistor R3 and the fourth resistor R4 are connected in series to the external output voltage Vout; one end of the reference voltage source D3 is connected to the midpoint between the third resistor R3 and the fourth resistor R4, and the other end is connected to the primary side of the optocoupler U2, so that the voltage divider signal of the output voltage Vout is input to the optocoupler U2 through the reference voltage source D3; the secondary side of the optocoupler U2 and the second capacitor C2 cooperate to form a feedback loop for generating a feedback signal, and the feedback loop is connected to the reference ground and the feedback pin COMP of the power management chip U1, respectively.

[0025] In one embodiment, such as Figure 1 As shown, the signal feedback unit 100 may also include, but is not limited to, a first resistor R1 and a second resistor R2 that serve as current limiters. The first resistor R1 is set in the feedback loop and connected to the secondary side of the optocoupler U2, and the second resistor R2 is connected in series with the reference voltage source D3 through the primary side of the optocoupler U2.

[0026] Specifically, the working principle of the signal feedback unit 100 is as follows:

[0027] The output voltage from an external source (such as an auxiliary source) is divided sequentially by resistors R3 and R4 to obtain a voltage divider signal. This voltage divider signal is then input to the reference terminal of the reference voltage source D3. As a result, the output signal of the reference voltage source D3 can drive the primary-side LED of the optocoupler U2 to operate. On the secondary side of the optocoupler U2, the output signal is current-limited and filtered by resistor R1 and capacitor C2 to generate a feedback signal. This feedback signal is connected to the feedback pin COMP of the UC2844 chip, forming a closed-loop control circuit, thereby realizing automatic adjustment and stable control of the output voltage.

[0028] In one embodiment, such as Figure 1 As shown, the voltage limiting unit 210 may include, but is not limited to, a first diode D1 and a second diode D2 connected in series. The anode of the first diode D1 is connected to the feedback pin COMP of the power management chip U1, the cathode of the first diode D1 is connected to the anode of the second diode D2, and the cathode of the second diode D2 is connected to the reference voltage source pin VREF of the power management chip U1. For the UC2844 chip, the typical voltage value Vref of the reference voltage source is 5V. The voltage limiting unit 210 can limit the highest potential of the feedback pin COMP to below Vref+2×Vf, where Vf is the forward voltage drop of a single diode (first diode D1 or second diode D2). It can be seen that the voltage limiting unit 210 can effectively suppress the abnormal rise of the feedback signal caused by noise and other factors, thereby avoiding electrical stress damage to the power management chip U1, and providing a stable voltage reference for the short-circuit detection function of the entire system.

[0029] In one embodiment, the voltage regulator Z1 may be, but is not limited to, a Zener diode, and the switching element Q1 may be, but is not limited to, an open-circuit NPN transistor; such as Figure 1As shown, taking a Zener diode and an NPN transistor as examples, the negative terminal of the Zener element Z1 is connected to the feedback pin COMP of the power management chip U1, and the positive terminal is connected to the sensing resistor R7 and the base of the switching element Q1 respectively; the emitter of the switching element Q1 is connected to the self-feeding pin VCC of the power management chip U1 through the first capacitor C1, and the emitter of the switching element Q1 and one end of the first capacitor C1 are connected to the reference ground.

[0030] In one embodiment, such as Figure 1 As shown, the short-circuit detection and protection unit 300 may also include, but is not limited to, a current-limiting resistor R6 and a recovery resistor R5. The recovery resistor R5 is used in conjunction with the first capacitor C1 to form a soft-start and automatic recovery circuit. The collector of the switching element Q1 is connected to one end of the current-limiting resistor R6. The other end of the current-limiting resistor R6 is connected to the self-feeding pin VCC of the power management chip U1, and is also connected to the external input voltage Vin through the recovery resistor R5.

[0031] Specifically, the working principle of the short-circuit detection and protection unit 300 is as follows:

[0032] The Zener diode's Zener voltage (i.e., breakdown voltage) VZ satisfies the following relationship:

[0033] VZ <Vref+2×Vf-Vbe;

[0034] Where Vref is the reference voltage of power management chip U1, Vf is the forward voltage drop of a single diode (first diode D1 or second diode D2), and Vbe is the base-emitter voltage of the NPN transistor.

[0035] Therefore, when the system is working normally, the signal feedback unit 100 keeps the voltage of the feedback pin COMP at a low normal operating value (such as 2.5V). This voltage is lower than the clamping voltage of the voltage limiting unit 210 and also lower than the breakdown voltage VZ. There is no voltage drop across the Zener diode and the sensing resistor R7, the NPN transistor is in the off state, and the power management chip U1 is in the normal operating state.

[0036] When a short circuit occurs, the output voltage drops sharply. In an attempt to stabilize the output, the signal feedback unit 100 will cause the optocoupler U2 to stop working and the secondary side of the optocoupler U2 to be cut off. Since the feedback pin COMP of the power management chip U1 corresponds to a constant current source (1mA), the second capacitor C2 will be charged quickly, thereby causing the feedback voltage to be rapidly raised to 5V. Obviously, the feedback voltage will exceed the breakdown voltage VZ of the Zener diode, so the Zener diode will break down, and the current will flow from the feedback pin COMP through the Zener diode and the sensing resistor R7 to ground.

[0037] At this time, the current generates a voltage drop V_R7 across the sensing resistor R7. When V_R7 rises to the base-emitter turn-on voltage of the NPN transistor (approximately 0.7V), the NPN transistor quickly saturates and turns on, forming a low-impedance path between its collector and emitter, thereby rapidly discharging the first capacitor C1. The Vcc voltage is quickly pulled down, and when it falls below the undervoltage lockout threshold of the power management chip U1, the power management chip U1 stops working, shuts down the PWM output, and the entire power system enters a shutdown protection state, thus achieving the protection function.

[0038] In addition, the recovery resistor R5 and the first capacitor C1 together constitute a soft start and automatic recovery circuit. After the short circuit fault is eliminated, the system can automatically resume normal operation. If the short circuit continues to exist, the circuit enters an intermittent protection state.

[0039] As can be seen, the embodiments of the present invention are based on the collaborative technology of "clamping setting reference → precise detection of Zener diode → discharge execution of switching transistor", which ultimately provides a highly reliable, fast-response, low-cost and easy-to-implement short-circuit protection solution, effectively solving the short-circuit protection problem faced by wide-range input and high-power auxiliary power sources.

[0040] It should be noted that the flyback power supply short-circuit protection circuit and application scenarios described in this utility model embodiment are for the purpose of more clearly illustrating the technical solution of this utility model embodiment, and do not constitute a limitation on the technical solution provided by this utility model embodiment. Those skilled in the art will know that with the evolution of flyback power supply short-circuit protection circuits and the emergence of new application scenarios, the technical solution provided by this utility model embodiment is also applicable to similar technical problems.

[0041] The above-described embodiments are only used to illustrate the technical solutions of this utility model, and are not intended to limit it. Although this utility model has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of this utility model, and should all be included within the protection scope of this utility model.

Claims

1. A flyback power supply short-circuit protection circuit, characterized in that, include: The signal feedback unit is used to provide feedback signals; The feedback signal clamping unit includes a power management chip and a voltage limiting unit for clamping the feedback signal. The feedback pin of the power management chip is connected to the output terminal of the signal feedback unit, and the voltage limiting unit is connected to the feedback pin and the reference voltage source pin of the power management chip, respectively. The short-circuit detection and protection unit includes a voltage regulator, a sensing resistor, a switching element, and a first capacitor. The voltage regulator and the sensing resistor are connected in series between a reference ground and the feedback pin of the power management chip. One end of the switching element is connected to the midpoint between the voltage regulator and the sensing resistor, and the other end is connected to the self-feeding pin of the power management chip through the first capacitor.

2. The flyback power supply short-circuit protection circuit according to claim 1, characterized in that, The voltage regulator is a Zener diode, and the switching element is an NPN transistor. The negative terminal of the voltage regulator is connected to the feedback pin of the power management chip, and the positive terminal is connected to the sensing resistor and the base of the switching element. The emitter of the switching element is connected to the self-feeding pin of the power management chip through the first capacitor. The emitter of the switching element and one end of the first capacitor are connected to the reference ground.

3. The flyback power supply short-circuit protection circuit according to claim 2, characterized in that, The short-circuit detection and protection unit further includes a current-limiting resistor and a recovery resistor. The recovery resistor is used in conjunction with the first capacitor to form a soft-start and automatic recovery circuit. The collector of the switching element is connected to one end of the current-limiting resistor. The other end of the current-limiting resistor is connected to the self-feeding pin of the power management chip and is also connected to the external input voltage through the recovery resistor.

4. The flyback power supply short-circuit protection circuit according to claim 1, characterized in that, The voltage limiting unit includes a first diode and a second diode connected in series. The anode of the first diode is connected to the feedback pin of the power management chip, the cathode of the first diode is connected to the anode of the second diode, and the cathode of the second diode is connected to the reference voltage source pin of the power management chip.

5. The flyback power supply short-circuit protection circuit according to claim 1, characterized in that, The signal feedback unit includes an optocoupler, a reference voltage source, a third resistor, a fourth resistor, and a second capacitor. The third and fourth resistors are connected in series to an external output voltage. One end of the reference voltage source is connected to the midpoint between the third and fourth resistors, and the other end is connected to the primary side of the optocoupler, so that the voltage divider signal of the output voltage is input to the optocoupler through the reference voltage source. The secondary side of the optocoupler and the second capacitor cooperate to form a feedback loop for generating a feedback signal. The feedback loop is connected to a reference ground and the feedback pin of the power management chip, respectively.

6. The flyback power supply short-circuit protection circuit according to claim 5, characterized in that, The signal feedback unit further includes a first resistor and a second resistor that limit current. The first resistor is disposed in the feedback loop and connected to the secondary side of the optocoupler, and the second resistor is connected in series with the reference voltage source through the primary side of the optocoupler.

7. The flyback power supply short-circuit protection circuit according to any one of claims 1 to 6, characterized in that, The power management chip used is the UC2844 chip.

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