Anti-backflow control circuit and switching power supply

Abstract

The present invention relates to an anti-backfeed control circuit and a switching power supply. The anti-backfeed control circuit comprises an error voltage providing unit, an output voltage sampling unit, an error voltage feedback unit, and a constant current operation unit. When there is no backfeed voltage at the output of a product, the anti-backfeed control circuit does not affect the normal operation of the switching power supply. When a backfeed voltage suddenly appears at the output end of the product, the error voltage providing unit in the circuit obtains an error voltage according to the sampled voltage, which is then calculated by an error feedback voltage unit and transmitted to the constant current operation unit. The constant current operation unit outputs feedback information proportional to the backfeed voltage error signal, which acts on a negative feedback system of the power supply, thereby ensuring that the input voltage in the negative feedback system of the switching power supply can reflect the backfeed voltage information in real time, and timely adjusting the negative feedback effect, so that the feedback control of the power supply system is not affected by changes in the output voltage, thereby maintaining stable operation of the module.

Description

Technical Field

[0001] The present invention relates to the technical field of switching power supplies, and in particular to an anti-backfeed control circuit and a switching power supply. Background Art

[0002] A switching power supply is a power supply that uses modern power electronics technology to control the on and off time of the switch tube to maintain a stable output voltage. As the application fields of switching power supplies become wider and wider, such as in battery charging equipment, motor applications, etc., there will be a backfeed voltage at the output end of the existing switching power supply that is higher than the output voltage of the switching power supply. This backfeed voltage will cause the sampling value of the output voltage in the negative feedback regulation system of the switching power supply to rise as the voltage at the output end of the switching power supply rises, thereby shortening the on time of the switching tube of the switching power supply, or even shutting down the PWM control. Therefore, when voltage backfeed occurs at the output end of the switching power supply, it may cause the functional circuit inside the switching power supply to fail, the output voltage accuracy to be poor, the control loop protection to be abnormal, and the like. The anti-backfeed control method and circuit provided by the present invention are crucial for applications where voltage backfeed occurs at the output end of the switching power supply. Summary of the Invention

[0003] To address the above problems, the present invention provides an anti-backfeed control circuit and a switching power supply. When voltage backfeed occurs at the output end of the switching power supply, the voltage detection value of the power supply negative feedback system is adjusted to compensate and eliminate the influence of the increased external input voltage on the voltage detection value, so that the switching power supply can still operate normally and reliably.

[0004] The technical solution adopted by the present invention is:

[0005] In a first aspect, an anti-backfeed control circuit is provided, which is applied to a switching power supply, wherein the switching power supply includes a power input system, a power switch conversion system, a power output system, a power negative feedback system, and a PWM control system connected in sequence; the control circuit includes: an output voltage sampling unit, an error voltage providing unit, an error voltage feedback unit, and a constant current operation unit;

[0006] The input end of the error voltage providing unit is used to be connected to the power switch conversion system, and the output end is connected to the first input end of the error voltage feedback unit;

[0007] The input end of the output voltage sampling unit is respectively used to be connected to the power output system, and the output end is connected to the second input end of the error voltage feedback unit;

[0008] The first output terminal of the error voltage feedback unit is connected to the first input terminal of the constant current operation unit, and the second output terminal of the error voltage feedback unit is connected to the second input terminal of the constant current operation unit;

[0009] The output end of the constant current operation unit is used to connect to the power supply negative feedback system;

[0010] The error voltage providing unit is used to sample the synchronous voltage U1 and the first output voltage U2 of the power switch conversion system, and generate the error voltage U3 according to the synchronous voltage U1 and the first output voltage U2;

[0011] The output voltage sampling unit is used to collect the first output voltage U2 and the second output voltage U4 of the power output system;

[0012] The error voltage feedback unit is used to generate a feedback voltage signal U5 according to the magnitude of the error voltage U3 and the second output voltage U4;

[0013] When voltage backflow occurs at the output end of the switching power supply, the constant current operation unit is used to operate the feedback voltage signal U5 to generate a control voltage signal U6, and output it to the power supply negative feedback system to adjust the voltage detection value of the power supply negative feedback system, compensate and eliminate the influence of the external input voltage increase on the voltage detection value, wherein the control voltage signal U6 is proportional to the external input voltage.

[0014] Furthermore, when no voltage backflow occurs at the output end of the switching power supply, the error voltage U3 is equal to the second output voltage U4; when voltage backflow occurs at the output end of the switching power supply, the error voltage U3 is less than the second output voltage U4.

[0015] Furthermore, the error voltage providing unit includes: a synchronous voltage sampling unit and an error voltage reference unit;

[0016] The input end of the synchronous voltage unit is used to be connected to the power switch conversion system, and the output end is connected to the input end of the error voltage reference unit, and is used to sample the synchronous voltage U1 and the first output voltage U2 of the power switch conversion system;

[0017] The output end of the error voltage reference unit serves as the output end of the error voltage providing unit and is connected to the first input end of the error voltage feedback unit, and is used to generate an error voltage U3 according to the synchronization voltage U1 and the first output voltage U2.

[0018] Furthermore, the output voltage sampling unit includes: resistors R12, R13 and an operational amplifier OPA1, one end of the resistor R12 serves as the input end of the output voltage sampling unit for connecting to the output end of the power output system, and the other end of the resistor R12 is connected to one end of the resistor R13 and the non-inverting input end of the operational amplifier OPA1; the other end of the resistor R13 is grounded; after the inverting input end of the operational amplifier OPA1 is connected to the output end, it serves as the output end of the output voltage sampling unit and is connected to the second input end of the error voltage feedback unit.

[0019] Furthermore, the error voltage feedback unit includes a resistor R10 and an operational amplifier POA3, the non-inverting input terminal of the operational amplifier POA3 serves as the second input terminal of the error voltage feedback unit and is connected to the output terminal of the output voltage sampling unit; after the inverting input terminal of the operational amplifier POA3 is connected to one end of the resistor R10, it serves as the second output terminal of the error voltage feedback unit and is connected to the second input terminal of the constant current voltage operation unit; the other end of the resistor R10 serves as the input terminal of the error voltage feedback unit and is connected to the output terminal of the error voltage providing unit; the output terminal of the operational amplifier POA3 serves as the first output terminal of the error voltage feedback unit and is connected to the first input terminal of the constant current voltage operation unit.

[0020] Furthermore, the constant current operation unit includes: a resistor R11, a resistor R14, a resistor R15, a resistor R16, a capacitor C4 and a transistor Q1; one end of the resistor R11 is connected to one end of the capacitor C4 and serves as the second input end of the constant current operation unit, and is connected to the second output end of the error voltage feedback unit; the other end of the resistor R11 is connected to the other end of the capacitor C4, one end of the resistor R16, and the emitter collector of the transistor Q1; the base of the transistor Q1 serves as the first input end of the constant current operation unit, and is connected to the first output end of the error voltage feedback unit, and the collector is connected to one end of the resistor R15 and one end of the resistor R14, and serves as the output end of the constant current operation unit for connecting to the power supply negative feedback system; the other end of the resistor R14 is used to be connected to the output end of the power supply output system; the other end of the resistor R15 and the other end of the resistor R16 are grounded.

[0021] Furthermore, the synchronous voltage sampling unit includes: a diode D3, a diode D4, a resistor R1, a resistor R2, a resistor R3, a resistor R6, a resistor R7 and a capacitor C1; the anode of the diode D3 is used to be connected to the first end of the secondary winding of the transformer T1 of the power switch conversion system and the anode of the diode D1, and the cathode of the diode D3 is connected to one end of the resistor R1, one end of the capacitor C1, one end of the resistor R3 and the cathode of the diode D4; the anode of the diode D4 is used to be connected to the second end of the secondary winding of the transformer T1 of the power switch conversion system and the anode of the diode D2; the other end of the resistor R1 is connected to the other end of the capacitor C1 After one end is connected, it is used to be connected to the cathode of the diode D1 and the cathode of the diode D2 of the power switch conversion system; the other end of the resistor R3 is connected to one end of the resistor R2 and serves as the first output end of the synchronous voltage sampling circuit, and is connected to the first input end of the error voltage reference unit; one end of the resistor R6 is used to be connected to the cathode of the diode D1 and the cathode of the diode D2 of the power switch conversion system, and the other end of the resistor R6 is connected to one end of the resistor R7 and serves as the second output end of the synchronous voltage sampling unit, and is connected to the second input end of the error voltage reference unit; the other end of the resistor R2 and the other end of the resistor R7 are grounded.

[0022] Furthermore, the error voltage reference unit includes: a resistor R4, a resistor R5, a resistor R8, a resistor R9 and an operational amplifier OPA2; one end of the resistor R4 is connected to the first output end of the synchronous voltage sampling unit as the first input end of the error voltage reference unit, and the other end of the resistor R4 is connected to one end of the resistor R5 and then to the non-inverting input end of the operational amplifier OPA2; the other end of the resistor R5 is grounded; one end of the resistor R8 is connected to the second input end of the error voltage reference unit as the second input end of the error voltage reference unit and to the second output end of the synchronous voltage sampling unit, and the other end of the resistor R8 is connected to the inverting input end of the operational amplifier OPA2 and one end of the resistor R9; the other end of the resistor R9 is connected to the output end of the operational amplifier OPA2 and then connected to the first input end of the error voltage feedback unit as the output end of the error voltage reference unit.

[0023] In a second aspect, a switching power supply is provided, comprising the anti-backfeed control circuit as described above and a power input system, a power switch conversion system, a power output system, a power negative feedback system and a PWM control system connected in sequence, wherein the input end of the anti-backfeed control circuit is respectively connected to the power switch conversion system and the power output system, and the output end is connected to the power negative feedback system.

[0024] Compared with the prior art, the present invention has the following beneficial effects:

[0025] The anti-backfeed control circuit of the present invention is arranged between the switching power supply and the load. By generating a corresponding control signal based on the detected synchronous voltage, output voltage and output voltage of the power supply output system of the power switch conversion system, the voltage detection value of the power supply negative feedback system is adjusted. When a backfeed voltage higher than the steady-state rated output voltage of the system appears at the output end of the switching power supply, the anti-backfeed control circuit plays a role in real-time adjustment of the voltage feedback system, so that the power supply feedback system follows the change of the output voltage in real time, and the working state of the switching power supply is not affected or protection occurs due to excessively high backfeed voltage, thereby ensuring that all performance of the power supply operates stably. When no backfeed voltage appears at the output end of the switching power supply, the anti-backfeed control circuit does not act on the power supply negative feedback system, so that the switching power supply operates normally and the reliability of the switching power supply is improved. The present invention has a simple structure, is practical and convenient, and has reliable performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 This is a principle block diagram of the anti-backfeed control circuit described in the embodiment applied to a switching power supply;

[0027] Figure 2 This is a circuit schematic diagram of the anti-backfeed control circuit described in the embodiment applied to a switching power supply. DETAILED DESCRIPTION

[0028] The following is a more clear and complete description of the technical solution of the present invention in conjunction with the accompanying drawings of the embodiments of the present invention. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0029] like Figure 1 As shown, Figure 1 This is a principle block diagram of the anti-backfeed control circuit described in this embodiment applied to a switching power supply. In this embodiment, an anti-backfeed control circuit is provided, which is applied to a switching power supply. The switching power supply includes a power input system, a power switch conversion system, a power output system, a power negative feedback system, and a PWM control system connected in sequence; the control circuit includes: an output voltage sampling unit, an error voltage providing unit, an error voltage feedback unit, and a constant current operation unit;

[0030] The input end of the error voltage providing unit is used to be connected to the power switch conversion system, and the output end is connected to the first input end of the error voltage feedback unit;

[0031] The input end of the output voltage sampling unit is respectively used to be connected to the power output system, and the output end is connected to the second input end of the error voltage feedback unit;

[0032] The first output terminal of the error voltage feedback unit is connected to the first input terminal of the constant current operation unit, and the second output terminal of the error voltage feedback unit is connected to the second input terminal of the constant current operation unit;

[0033] The output end of the constant current operation unit is used to connect to the power supply negative feedback system;

[0034] The error voltage providing unit is used to sample the synchronous voltage U1 and the first output voltage U2 of the power switch conversion system, and generate the error voltage U3 according to the synchronous voltage U1 and the first output voltage U2;

[0035] The output voltage sampling unit is used to collect the first output voltage U2 and the second output voltage U4 of the power output system;

[0036] The error voltage feedback unit is used to generate a feedback voltage signal U5 according to the magnitude of the error voltage U3 and the second output voltage U4;

[0037] When voltage backflow occurs at the output end of the switching power supply, the constant current operation unit is used to operate the feedback voltage signal U5 to generate a control voltage signal U6, and output it to the power supply negative feedback system to adjust the voltage detection value of the power supply negative feedback system, compensate and eliminate the influence of the external input voltage increase on the voltage detection value, wherein the control voltage signal U6 is proportional to the external input voltage.

[0038] Specifically, when no voltage backflow occurs at the output end of the switching power supply, the error voltage U3 is equal to the second output voltage U4; when voltage backflow occurs at the output end of the switching power supply, the error voltage U3 is less than the second output voltage U4.

[0039] Specifically, the input of the error voltage providing unit is connected to the power switching conversion system and is used to sample the synchronous voltage U1 of the power switching conversion system and the first output voltage U2 of the output terminal of the power switching conversion system. The error voltage providing unit then performs a difference calculation on the synchronous voltage U1 and the first output voltage U2, and then performs a proportional calculation to obtain an error voltage U3. The error voltage U3 is used as the reference voltage for the error voltage feedback unit. Based on the sampling principle of the error voltage providing unit, the difference between the synchronous voltage U1 and the first output voltage U2 is inherent to the power output system. Therefore, the error voltage U3 does not change with changes in the feedback voltage at the output terminal of the switching power supply. In other words, the error voltage U3 is always proportional to the absolute value of the steady-state output voltage of the power supply. When the on-off time of the switching transistor of the switching power supply remains unchanged, the error voltage signal U3 also remains unchanged. The error voltage feedback unit receives the error voltage U3 and the second output signal U4 from the output sampling voltage sampling unit as inputs, performs error calculations, and amplifies or reduces the difference ΔU between the error voltage U3 and the second output voltage U4 by a certain ratio. This generates a feedback voltage signal U5, which is then input into the constant current calculation unit. This feedback voltage signal U5 is proportional to the difference between the real-time voltage at the output of the power supply system and the system's steady-state output voltage. The constant current calculation unit then outputs a proportional control voltage signal U6, which is then input into the power supply's negative feedback system. This controls the current in the pull-up resistor of the negative feedback system in real time, creating a stable voltage drop. Because the feedback voltage signal U5 is proportional to the difference between the real-time output voltage and the steady-state voltage, the control voltage signal U6 controls the power supply's negative feedback system in direct proportion to the difference between the real-time output voltage and the system's steady-state output voltage. This enables real-time feedback and loop adjustment of the output external voltage, maintaining the synchronization and stability of the power supply output and the external voltage.

[0040] As a specific implementation of the error voltage providing unit, the error voltage providing unit includes: a synchronous voltage sampling unit and an error voltage reference unit;

[0041] The input end of the synchronous voltage unit is used to be connected to the power switch conversion system, and the output end is connected to the input end of the error voltage reference unit, and is used to sample the synchronous voltage U1 and the first output voltage U2 of the power switch conversion system;

[0042] The output end of the error voltage reference unit serves as the output end of the error voltage providing unit and is connected to the first input end of the error voltage feedback unit, and is used to generate an error voltage U3 according to the synchronization voltage U1 and the first output voltage U2.

[0043] like Figure 2 As shown in the figure, the anti-backfeed control circuit of this embodiment is applied to the circuit principle diagram of the switching power supply. The power switch conversion system includes a switch tube S1, a switch tube S2, a transformer T1, a capacitor Cr, a diode D1 and a diode D2. Among them, the first end of the switch tube S1 is connected to the input voltage, the second end is connected to the first end of the switch tube S2 and the first end of the primary winding of the transformer T1, and the third end is connected to the input end of the power supply negative feedback system; the third end of the switch tube S2 is connected to the input end of the power supply negative feedback system; the second end of the switch tube S2 and one end of the capacitor Cr are grounded; the other end of the capacitor Cr is connected to the primary winding of the transformer T1. The second end is connected, the first end of the secondary winding of the transformer T1 is connected to the anode of the diode D1, the second end is connected to the cathode of the diode D2, and the third end is grounded; the cathode of the diode D1 and the cathode of the diode D2 are connected and serve as the output end of the power switch conversion system and the input end of the power output system; the power output system includes a capacitor C2, a capacitor C3 and an inductor L1, one end of the capacitor C2 is connected to one end of the inductor L1 and serves as the input end of the power output system, the other end of the inductor L1 is connected to one end of the capacitor C3 and serves as the output end of the power output system, and the other end of the capacitor C2 and the other end of the capacitor C3 are grounded.

[0044] As a specific embodiment of the synchronous voltage sampling unit, the synchronous voltage sampling unit includes: a diode D3, a diode D4, a resistor R1, a resistor R2, a resistor R3, a resistor R6, a resistor R7 and a capacitor C1; the anode of the diode D3 is used to be connected to the first end of the secondary winding of the transformer T1 of the power switch conversion system and the anode of the diode D1, and the cathode of the diode D3 is connected to one end of the resistor R1, one end of the capacitor C1, one end of the resistor R3 and the cathode of the diode D4; the anode of the diode D4 is used to be connected to the second end of the secondary winding of the transformer T1 of the power switch conversion system and the anode of the diode D2; the other end of the resistor R1 is connected to the cathode of the diode D4. After being connected to the other end of the capacitor C1, the resistor R3 is used to be connected to the cathode of the diode D1 and the cathode of the diode D2 of the power switch conversion system; the other end of the resistor R3 is connected to one end of the resistor R2 and serves as the first output end of the synchronous voltage sampling circuit, and is connected to the first input end of the error voltage reference unit; one end of the resistor R6 is used to be connected to the cathode of the diode D1 and the cathode of the diode D2 of the power switch conversion system, and the other end of the resistor R6 is connected to one end of the resistor R7 and serves as the second output end of the synchronous voltage sampling unit, and is connected to the second input end of the error voltage reference unit; the other end of the resistor R2 and the other end of the resistor R7 are grounded.

[0045] As a specific implementation of the error voltage reference unit, the error voltage reference unit includes: a resistor R4, a resistor R5, a resistor R8, a resistor R9 and an op amp OPA2; one end of the resistor R4 is connected to the first output end of the synchronous voltage sampling unit as the first input end of the error voltage reference unit, and the other end of the resistor R4 is connected to one end of the resistor R5 and then to the non-inverting input end of the op amp OPA2; the other end of the resistor R5 is grounded; one end of the resistor R8 is connected to the second input end of the error voltage reference unit as the second output end of the synchronous voltage sampling unit, and the other end of the resistor R8 is connected to the inverting input end of the op amp OPA2 and one end of the resistor R9; the other end of the resistor R9 is connected to the output end of the op amp OPA2 and then connected to the first input end of the error voltage feedback unit as the output end of the error voltage reference unit.

[0046] As a specific embodiment of the output voltage sampling unit, the output voltage sampling unit includes: resistors R12, R13 and an operational amplifier OPA1, one end of the resistor R12 serves as the input end of the output voltage sampling unit for connecting to the output end of the power output system, and the other end of the resistor R12 is connected to one end of the resistor R13 and the non-inverting input end of the operational amplifier OPA1; the other end of the resistor R13 is grounded; after the inverting input end of the operational amplifier OPA1 is connected to the output end, it serves as the output end of the output voltage sampling unit and is connected to the second input end of the error voltage feedback unit.

[0047] As a specific embodiment of the error voltage feedback unit, the error voltage feedback unit includes a resistor R10 and an operational amplifier POA3, the non-inverting input terminal of the operational amplifier POA3 serves as the second input terminal of the error voltage feedback unit and is connected to the output terminal of the output voltage sampling unit; after the inverting input terminal of the operational amplifier POA3 is connected to one end of the resistor R10, it serves as the second output terminal of the error voltage feedback unit and is connected to the second input terminal of the constant current voltage operation unit; the other end of the resistor R10 serves as the input terminal of the error voltage feedback unit and is connected to the output terminal of the error voltage providing unit; the output terminal of the operational amplifier POA3 serves as the first output terminal of the error voltage feedback unit and is connected to the first input terminal of the constant current voltage operation unit.

[0048] As a specific embodiment of the constant current operation unit, the constant current operation unit includes: a resistor R11, a resistor R14, a resistor R15, a resistor R16, a capacitor C4 and a transistor Q1; one end of the resistor R11 is connected to one end of the capacitor C4 and serves as the second input end of the constant current operation unit, and is connected to the second output end of the error voltage feedback unit; the other end of the resistor R11 is connected to the other end of the capacitor C4, one end of the resistor R16, and the emitter collector of the transistor Q1; the base of the transistor Q1 serves as the first input end of the constant current operation unit and is connected to the first output end of the error voltage feedback unit, and the collector is connected to one end of the resistor R15 and one end of the resistor R14, and serves as the output end of the constant current operation unit for connecting to the power supply negative feedback system; the other end of the resistor R14 is used to be connected to the output end of the power supply output system; the other end of the resistor R15 and the other end of the resistor R16 are grounded.

[0049] The following combination Figure 2 The specific circuit of the anti-backfeed circuit is described in detail: When the circuit is operating, the secondary of the switching power supply transformer T1 is full-wave rectified by diodes D1 and D2 to obtain an output voltage Vout2. The output voltage Vout2 is divided by resistors R6 and R7 in series to obtain the voltage signal at the connection point A between resistors R6 and R7, which is also the first output voltage U2. Node A is connected to one end of resistor R8, and the other end of resistor R8 is connected to the inverting input terminal of op amp OPA2. The voltage signal at connection point A indirectly serves as the inverting input signal of op amp OPA2. The secondary of the switching power supply transformer T1 is full-wave rectified by diodes D3 and D4 to charge capacitor C1. One end of capacitor C1 is connected to the anode terminals of diodes D3 and D4, and the other end is connected to the anode terminals of diodes D1 and D2. Due to the same winding rectification, the terminal voltage of capacitor C1 (the voltage at point B) is the output voltage Vout2. The voltage at point B is divided by resistors R2, R3, R4, and R5 to obtain the voltage at node C, also known as the synchronous sampling voltage U1. This voltage serves as the non-inverting input signal to op amp OPA2. Op amp OPA2 performs a differential operation on the input voltage signals at the non-inverting and inverting terminals to obtain the error voltage U3 at node D. Due to the non-mutational nature of capacitor C1's voltage, this error voltage U3 does not change with changes in the feedback voltage at the switching power supply output. This means that the steady-state output voltage of the power supply system is fed back.

[0050] The switching power supply's output voltage Vout1 is divided by resistors R12 and R13. The voltage at the connection point E between resistors R12 and R13 (and the second output voltage U4) is fed through op amp OPA1 and then to the non-inverting input of op amp OPA3. Op amp OPA1 functions as a real-time voltage sampling and follower. The voltage signal at the non-inverting input of op amp OPA3 can reflect changes in the switching power supply's output voltage Vout1 in real time. Op amp OPA3 performs a differential operation on the voltage signals at its non-inverting and inverting inputs to generate feedback voltage U5. Feedback voltage U5 is the output voltage signal of the error voltage feedback unit. This feedback voltage U5 directly controls transistor Q1. By controlling the voltage at node F, the collector current of transistor Q1 can be controlled. The collector of transistor Q1 is directly connected to the power supply's negative feedback system, thereby transmitting the difference signal between the external input voltage and the steady-state output voltage to the feedback system, adjusting the feedback system's sampling value and achieving system output stability.

[0051] When there is no backfeed at the output of the switching power supply, the voltage difference between the non-inverting input and the inverting input of the operational amplifier OPA3 is small, so that the feedback voltage U5 output by the operational amplifier OPA3 is small, the voltage at the output point F of the operational amplifier OPA3 is low, the transistor Q1 is not turned on, and it will not affect the normal operation of the switching power supply. When voltage backfeed occurs at the output end of the switching power supply, the voltage difference between the non-inverting input and the inverting input of the operational amplifier OPA3 increases synchronously, the voltage at the output point F of the operational amplifier OPA3 increases synchronously, and the collector current of the transistor Q1 increases synchronously. This ensures that the voltage at point G of the input voltage signal of the negative feedback system of the switching power supply will not rise due to the backfeed voltage, thereby ensuring the reliable operation of the switching power supply.

[0052] In summary, the anti-backfeed control circuit provided by the present invention ensures that the switching power supply can still operate reliably and the switching transistor of the switching power supply can still be turned on and off normally when a backfeed voltage appears at the output terminal of the switching power supply. In actual applications, this solution can be slightly improved according to actual conditions to achieve the same purpose.

[0053] The above-described embodiments of the present invention are merely examples for illustrating the present invention and are not intended to limit the embodiments of the present invention. Those skilled in the art will appreciate that other variations and modifications can be made based on the above description. It is not possible to enumerate all embodiments here. Any obvious variations or modifications arising from the technical solution of the present invention remain within the scope of protection of the present invention.

Claims

1. A backfeed control circuit for use in a switching power supply comprising a power input system, a power switch conversion system, a power output system, a power negative feedback system, and a PWM control system connected in sequence; characterized in that: The control circuit includes: an output voltage sampling unit, an error voltage providing unit, an error voltage feedback unit and a constant current operation unit; The input end of the error voltage providing unit is used to be connected to the power switch conversion system, and the output end is connected to the first input end of the error voltage feedback unit; The input end of the output voltage sampling unit is respectively used to be connected to the power output system, and the output end is connected to the second input end of the error voltage feedback unit; The first output terminal of the error voltage feedback unit is connected to the first input terminal of the constant current operation unit, and the second output terminal of the error voltage feedback unit is connected to the second input terminal of the constant current operation unit; The output end of the constant current operation unit is used to connect to the power supply negative feedback system; The error voltage providing unit is used to sample the synchronous voltage U1 and the first output voltage U2 of the power switch conversion system, and generate the error voltage U3 according to the synchronous voltage U1 and the first output voltage U2; The output voltage sampling unit is used to collect the first output voltage U2 and the second output voltage U4 of the power output system; The error voltage feedback unit is configured to generate a feedback voltage signal U5 based on the magnitude of the error voltage U3 and the second output voltage U4; the feedback voltage signal U5 is obtained by amplifying or reducing the difference ∆U between the error voltage U3 and the second output voltage U4 by a certain proportion; when no voltage backflow occurs at the output end of the switching power supply, the error voltage U3 and the second output voltage U4 are equal; when voltage backflow occurs at the output end of the switching power supply, the error voltage U3 is less than the second output voltage U4; When voltage backflow occurs at the output end of the switching power supply, the constant current operation unit is used to operate the feedback voltage signal U5 to generate a control voltage signal U6, and output it to the power supply negative feedback system to adjust the voltage detection value of the power supply negative feedback system, compensate and eliminate the influence of the external input voltage increase on the voltage detection value, wherein the control voltage signal U6 is proportional to the external input voltage.

2. The anti-backfeed control circuit according to claim 1, characterized in that: The error voltage providing unit includes: a synchronous voltage sampling unit and an error voltage reference unit; The input end of the synchronous voltage unit is used to be connected to the power switch conversion system, and the output end is connected to the input end of the error voltage reference unit, and is used to sample the synchronous voltage U1 and the first output voltage U2 of the power switch conversion system; The output end of the error voltage reference unit serves as the output end of the error voltage providing unit and is connected to the first input end of the error voltage feedback unit, and is used to generate an error voltage U3 according to the synchronization voltage U1 and the first output voltage U2.

3. The anti-backfeed control circuit according to claim 1, characterized in that: The output voltage sampling unit includes: resistors R12, R13 and an operational amplifier OPA1, one end of the resistor R12 serves as the input end of the output voltage sampling unit and is connected to the output end of the power output system, and the other end of the resistor R12 is connected to one end of the resistor R13 and the non-inverting input end of the operational amplifier OPA1; the other end of the resistor R13 is grounded; after the inverting input end of the operational amplifier OPA1 is connected to the output end, it serves as the output end of the output voltage sampling unit and is connected to the second input end of the error voltage feedback unit.

4. The anti-backfeed control circuit according to claim 1, characterized in that: The error voltage feedback unit includes a resistor R10 and an operational amplifier POA3, wherein the non-inverting input terminal of the operational amplifier POA3 serves as the second input terminal of the error voltage feedback unit and is connected to the output terminal of the output voltage sampling unit; after the inverting input terminal of the operational amplifier POA3 is connected to one end of the resistor R10, it serves as the second output terminal of the error voltage feedback unit and is connected to the second input terminal of the constant current operation unit; the other end of the resistor R10 serves as the input terminal of the error voltage feedback unit and is connected to the output terminal of the error voltage providing unit; the output terminal of the operational amplifier POA3 serves as the first output terminal of the error voltage feedback unit and is connected to the first input terminal of the constant current operation unit.

5. The anti-backfeed control circuit according to claim 1, characterized in that: The constant current operation unit includes: a resistor R11, a resistor R14, a resistor R15, a resistor R16, a capacitor C4 and a transistor Q1; one end of the resistor R11 is connected to one end of the capacitor C4 and serves as the second input end of the constant current operation unit, and is connected to the second output end of the error voltage feedback unit; the other end of the resistor R11 is connected to the other end of the capacitor C4, one end of the resistor R16, and the emitter collector of the transistor Q1; the base of the transistor Q1 serves as the first input end of the constant current operation unit and is connected to the first output end of the error voltage feedback unit, and the collector is connected to one end of the resistor R15 and one end of the resistor R14, and serves as the output end of the constant current operation unit for connecting to the power supply negative feedback system; the other end of the resistor R14 is used to be connected to the output end of the power supply output system; the other end of the resistor R15 and the other end of the resistor R16 are grounded.

6. The anti-backfeed control circuit according to claim 2, characterized in that: The synchronous voltage sampling unit includes: a diode D3, a diode D4, a resistor R1, a resistor R2, a resistor R3, a resistor R6, a resistor R7 and a capacitor C1; the anode of the diode D3 is used to be connected to the first end of the secondary winding of the transformer T1 of the power switch conversion system and the anode of the diode D1, and the cathode of the diode D3 is connected to one end of the resistor R1, one end of the capacitor C1, one end of the resistor R3 and the cathode of the diode D4; the anode of the diode D4 is used to be connected to the second end of the secondary winding of the transformer T1 of the power switch conversion system and the anode of the diode D2; the other end of the resistor R1 is connected to the other end of the capacitor C1 After being connected, it is used to be connected to the cathode of the diode D1 and the cathode of the diode D2 of the power switch conversion system; the other end of the resistor R3 is connected to one end of the resistor R2 and serves as the first output end of the synchronous voltage sampling circuit, and is connected to the first input end of the error voltage reference unit; one end of the resistor R6 is used to be connected to the cathode of the diode D1 and the cathode of the diode D2 of the power switch conversion system, and the other end of the resistor R6 is connected to one end of the resistor R7 and serves as the second output end of the synchronous voltage sampling unit, and is connected to the second input end of the error voltage reference unit; the other end of the resistor R2 and the other end of the resistor R7 are grounded.

7. The anti-backfeed control circuit according to claim 2, characterized in that: The error voltage reference unit includes: resistor R4, resistor R5, resistor R8, resistor R9 and operational amplifier OPA2; one end of resistor R4 is connected to the first output end of the synchronous voltage sampling unit as the first input end of the error voltage reference unit, and the other end of resistor R4 is connected to one end of resistor R5 and then to the non-inverting input end of operational amplifier OPA2; the other end of resistor R5 is grounded; one end of resistor R8 is connected to the second input end of the error voltage reference unit as the second input end of the error voltage reference unit and the second output end of the synchronous voltage sampling unit, and the other end of resistor R8 is connected to the inverting input end of operational amplifier OPA2 and one end of resistor R9; the other end of resistor R9 is connected to the output end of operational amplifier OPA2 and then connected to the first input end of the error voltage feedback unit as the output end of the error voltage reference unit.

8. A switching power supply, characterized in that: It comprises the anti-backfeed control circuit according to any one of claims 1 to 7 and a power input system, a power switch conversion system, a power output system, a power negative feedback system and a PWM control system connected in sequence, wherein the input end of the anti-backfeed control circuit is respectively connected to the power switch conversion system and the power output system, and the output end is connected to the power negative feedback system.

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