Flyback power supply control circuit

Abstract

The utility model relates to the technical field of power supplies, in particular to a flyback power supply control circuit. A main circuit comprises an input filter circuit, an intermediate rectifying circuit, a transformer (T1) and an output rectifying circuit which are connected in sequence, wherein a primary side of the transformer (T1) is connected in series with a switching tube (Q1); the control circuit comprises a PWM (Pulse Width Modulation) control chip (U1) and a feedback circuit connected with the PWM control chip (U1), and the output end of the PWM control chip (U1) is in control connection with the switching tube (Q1); the output side of the intermediate rectification circuit is also connected with an absorption circuit, and the primary side of the transformer (T1) is connected in series with a third capacitor (Coss1) and an inductor (Lkp1). The flyback power supply control circuit provided by the utility model is higher in stability and stronger in anti-interference capability.

Description

Technical Field

[0001] The utility model relates to the technical field of power supplies. More specifically, the utility model relates to a flyback power supply control circuit. Background Art

[0002] Under the condition that the environment does not meet the standards, the power supply control circuit is vulnerable to interference, resulting in poor working effect of the power supply control circuit. Moreover, the power supply control circuit may suddenly have problems such as excessive current or excessive voltage, resulting in damage to the components in the circuit. Content of the Utility Model

[0003] In order to solve the technical problems of poor anti-interference ability and low stability of the above flyback power supply control circuit, the utility model provides the following solutions.

[0004] The utility model provides a flyback power supply control circuit, including: its main circuit includes an input filter circuit, an intermediate rectifier circuit, a transformer (T1) and an output rectifier circuit connected in sequence, and a switching tube (Q1) is connected in series to the primary side of the transformer (T1); it also includes a control circuit, the control circuit includes a PWM control chip (U1) and a feedback circuit connected thereto, and the output end of the PWM control chip (U1) is connected to control the switching tube (Q1); an absorption circuit is also connected to the output side of the intermediate rectifier circuit, and the absorption circuit includes: a first voltage stabilizing diode (ZD), a first diode (D5), a first resistor (R10), a second resistor (R11), a third resistor (R13), a first capacitor (C5) and a second capacitor (C6); wherein, the first resistor (R10) is connected in parallel with the first capacitor (C5), the first voltage stabilizing diode (ZD) and the second resistor (R11) are connected in series and then connected in parallel at both ends of the first resistor (R10), the negative electrode of the first diode (D5) is connected to the second resistor (R11), the positive electrode of the first diode (D5) is connected to the series-connected third resistor (R13) and the second capacitor (C6), and the second capacitor (C6) is connected to the first voltage stabilizing diode (ZD); a third capacitor (Coss1) and an inductor (Lkp1) are connected in series to the primary side of the transformer (T1).

[0005] In one embodiment, the input filter circuit includes: a common mode inductor (L1), a fourth resistor (R1), a fifth resistor (R4), a sixth resistor (R5), a fourth capacitor (C1), a fifth capacitor (C3), and a sixth capacitor (C4); wherein, the fourth resistor (R1), the fifth resistor (R4), and the sixth resistor (R5) are connected in series in sequence and then connected to the output side of the common mode inductor (L1), the fourth capacitor (C1) is connected in parallel across the two ends of the fourth resistor (R1), the fifth resistor (R4), and the sixth resistor (R5) connected in series in sequence, the fifth capacitor (C3) and the sixth capacitor (C4) are connected in series and then connected in parallel across the two ends of the fourth capacitor (C1), and the connection point between the fifth capacitor (C3) and the sixth capacitor (C4) is connected to the AC ground (YGND).

[0006] In one embodiment, pin 8 of the PWM control chip (U1) is connected to the second diode (D3) and the seventh resistor (R12) connected in parallel.

[0007] In one embodiment, pin 6 of the PWM control chip (U1) is connected to the gate of the switching transistor (Q1) through the second zener diode (D6) and the eighth resistor (R15) connected in parallel.

[0008] In one embodiment, the output rectifier circuit includes: a third diode (D7), a fourth diode (D8), and a polarized capacitor (C15), wherein the third diode (D7) and the fourth diode (D8) are connected in parallel and then connected to the polarized capacitor (C15).

[0009] In one embodiment, the feedback circuit includes a ninth resistor (R16) and an optocoupler (U2), wherein the ninth resistor (R16) is connected in series with the optocoupler (U2), and the connection point between the ninth resistor (R16) and the optocoupler (U2) is connected to pin 1 of the PWM control chip (U1).

[0010] In one embodiment, the main circuit further includes an input protection circuit, and the input protection circuit includes a fuse (F1), a thermistor (R6), and a variable resistor (R3) connected in series in sequence.

[0011] In one embodiment, the PWM control chip U1 is any one of the UC384X series.

[0012] The beneficial effects of the present utility model are as follows: The power control circuit of the present utility model improves the anti-interference ability and stability of the entire circuit through the input filter circuit and the absorption circuit. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] By reading the following detailed description with reference to the accompanying drawings, the above and other objects, features, and advantages of the exemplary embodiments of the present utility model will become readily understandable. In the drawings, several embodiments of the present utility model are shown in an exemplary rather than restrictive manner, and the same or corresponding reference numerals represent the same or corresponding parts, wherein:

[0014] Figure 1 is a circuit diagram schematically showing a flyback power control circuit according to an embodiment of the present utility model. Detailed Embodiments

[0015] Next, the technical solutions in the embodiments of the present utility model will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present utility model. Obviously, the described embodiments are some, but not all, of the embodiments of the present utility model. All other embodiments obtained by those skilled in the art based on the embodiments of the present utility model without creative efforts shall fall within the protection scope of the present utility model.

[0016] Next, the detailed embodiments of the present utility model will be described in detail in conjunction with the accompanying drawings.

[0017] Figure 1 is a circuit diagram schematically showing a flyback power control circuit according to an embodiment of the present utility model.

[0018] As can be seen from Figure 1 the flyback power control circuit includes a main circuit and a control circuit. Among them, the main circuit is used to convert alternating current into direct current, perform voltage conversion, and then output the required voltage; the control circuit is used to control the main circuit to output a stable and accurate output voltage.

[0019] Specifically, the main circuit includes: an input protection circuit, an input filter circuit, an intermediate rectifier circuit, a transformer T1, and an output rectifier circuit connected in sequence. Among them, the input protection circuit is used to prevent damage to the power control circuit caused by excessive input current, etc.; the input filter circuit is used to smooth the input voltage and reduce interference, so as to obtain a more stable and processable signal; the intermediate rectifier circuit is used to convert the input alternating voltage into a direct voltage and perform filtering; the transformer T1 is used for voltage conversion and electrical isolation; the output rectifier circuit is used to provide a stable direct voltage and eliminate interference.

[0020] The input protection circuit includes: a fuse F1, a thermistor R6, and a variable resistor R3. Among them, the fuse F1 and the thermistor R6 are connected through the variable resistor R3.

[0021] Specifically, when alternating current passes through the input protection circuit, if the current is too large, the fuse F1 will blow, thus protecting the power control circuit from being burned out; the thermistor R6 is used to suppress the large inrush current impact when the power control circuit starts and provides a certain current limiting effect under normal working conditions.

[0022] By setting up the input protection circuit, the stability and reliability of the entire circuit are improved.

[0023] The input filter circuit includes: a common-mode inductor (L1), a fourth resistor (R1), a fifth resistor (R4), a sixth resistor (R5), a fourth capacitor (C1), a fifth capacitor (C3), and a sixth capacitor (C4); wherein, the fourth resistor (R1), the fifth resistor (R4), and the sixth resistor (R5) are connected in series in sequence and then connected to the output side of the common-mode inductor (L1), the fourth capacitor (C1) is connected in parallel across the series-connected fourth resistor (R1), fifth resistor (R4), and sixth resistor (R5), the fifth capacitor (C3) and the sixth capacitor (C4) are connected in series and then connected in parallel across the fourth capacitor (C1), and the connection point between the fifth capacitor (C3) and the sixth capacitor (C4) is connected to the AC ground (YGND).

[0024] Specifically, the common-mode inductor L1 is used to suppress the electromagnetic wave radiation generated by the high-speed signal line; the fourth resistor R1, the fifth resistor R4, and the sixth resistor R5 are used to release the electrical energy stored in the energy storage components in the power control circuit; the fourth capacitor C1 is used to filter out the differential-mode interference; the fifth capacitor C3 and the sixth capacitor C4 are used to filter out the common-mode interference.

[0025] Through the input filter circuit, the interference signals in the input alternating current are eliminated, thus obtaining a stable voltage, and further improving the anti-interference ability of the entire circuit.

[0026] The intermediate rectifier circuit includes: a bridge rectifier D1 and a polarized capacitor C2, wherein, the pin 1 of the bridge rectifier D1 is connected to the polarized capacitor C2 and the AC ground YGND in sequence, the pins 2 and 3 of the bridge rectifier D1 are connected to the input filter circuit, and the pin 4 of the bridge rectifier D1 is connected to the AC ground YGND.

[0027] The primary side of transformer T1 is successively connected in series with inductor Lkp1, capacitor Coss1, switching transistor Q1, and resistor R22. Among them, switching transistor Q1 is used to control the magnitude of the output voltage at the output end, resistor R22 is a sampling resistor, and inductor Lkp1 and capacitor Coss1 form an LC filter. The secondary side of transformer T1 is connected to an output rectification circuit, which is used to rectify and filter the output voltage. Further, the output rectification circuit includes: a third diode (D7), a fourth diode (D8), and a polarized capacitor (C15), where the third diode (D7) and the fourth diode (D8) are connected in parallel and then connected to the polarized capacitor (C15).

[0028] In addition, a load resistor RL1 is connected in parallel across the two ends of the polarized capacitor C15. When the output rectification circuit is unloaded, the energy generated by transformer T1 can be released through the load resistor RL1, thereby avoiding damage to the switching transistor Q1 caused by this energy.

[0029] Further, an absorption circuit is also connected to the output side of the intermediate rectification circuit. Specifically, the absorption circuit includes: a first zener diode (ZD), a first diode (D5), a first resistor (R10), a second resistor (R11), a third resistor (R13), a first capacitor (C5), and a second capacitor (C6); where the first resistor (R10) is connected in parallel with the first capacitor (C5), the first zener diode (ZD) and the second resistor (R11) are connected in series and then connected in parallel across the two ends of the first resistor (R10), the negative electrode of the first diode (D5) is connected to the second resistor (R11), the positive electrode of the diode is connected to the series-connected third resistor (R13) and the second capacitor (C6), and the second capacitor (C6) is connected to the first zener diode (ZD).

[0030] Through the spike absorption circuit, the spike voltage generated between the transformer T1 and the switching transistor Q1 when the switching transistor Q1 stops conducting can be absorbed, thereby clamping the spike voltage to a fixed voltage value, and further avoiding damage to components such as the switching transistor Q1 caused by the spike voltage, thus improving the stability of the entire circuit.

[0031] The control circuit includes a PWM control chip U1 and a feedback circuit connected thereto. Among them, the PWM control chip U1 is used to control the on and off of the switching transistor Q1, thereby realizing the voltage stabilization control of the power supply control circuit; the feedback circuit is used to collect the change of the output voltage and feedback it to the PWM control chip U1, so as to realize precise voltage stabilization control by controlling the on and off of the switching transistor Q1 through the PWM control chip U1.

[0032] In this embodiment, the selected PWM control chip is UC3844E in the UC384X series. In other alternative embodiments, those skilled in the art can select other chips in the UC384X series to achieve the control of switching power.

[0033] Specifically, the PWM control chip U1 has 8 pins. Among them, pin 1 (i.e., COMP) is the output terminal of the error amplifier; pin 2 (i.e., VFB) is the feedback voltage input terminal; pin 3 (i.e., CURRENT SENSE) is the current detection input terminal; pin 4 (i.e., RT / CT) is the timing terminal; pin 5 (i.e., GND) is the common ground terminal; pin 6 (i.e., OUTPUT) is the push-pull output terminal; pin 7 (i.e., Vi) is the DC voltage power supply terminal; and pin 8 (i.e., Vref) is the 5V reference voltage output terminal.

[0034] Furthermore, the external connection relationships of each pin of the PWM control chip U1 are as follows:

[0035] Pin 1 of the PWM control chip U1 is connected to the feedback circuit. The feedback circuit includes: the ninth resistor (R16) and the optocoupler (U2). Among them, the ninth resistor (R16) is in series with the optocoupler (U2), and the connection point between the ninth resistor (R16) and the optocoupler (U2) is connected to pin 1 of the PWM control chip U1. In addition, pin 1 of the PWM control chip U1 is also connected to the capacitor C9. Among them, the resistor R16 and the capacitor C9 are used to improve the gain and frequency characteristics of the error amplifier inside the PWM control chip U1, and the optocoupler U2 is used to feedback the change of the output voltage.

[0036] Pin 2 of the PWM control chip U1 is connected to the series-connected resistor R17 and the thermistor NTC. Specifically, pin 2 is connected to the connection point between the resistor R17 and the thermistor NTC. Among them, the thermistor NTC is used to suppress the large inrush current impact when the power control circuit starts and provide a certain current limiting effect under normal working conditions.

[0037] Pin 3 of the PWM control chip U1 is respectively connected to the DC ground HGND through the resistor R18 and the capacitor C10. In addition, this pin 3 is also connected to the source electrode of the switching transistor Q1 through the resistor R19. Further, pin 3 of the PWM control chip U1 is used to implement the overcurrent protection function. Specifically, the resistor R22 detects the current of the switching transistor Q1 and feeds it back to pin 3 of the PWM control chip U1 through the resistor R19. When the voltage of pin 3 exceeds 1V, the PWM signal output by pin 6 of the PWM control chip U1 stops, thereby achieving overcurrent protection.

[0038] Pin 4 of the PWM control chip U1 is connected to the series-connected capacitor C12 and resistor R14, and the capacitor C12, resistor R14 and the internal circuit of the PWM control chip U1 form an oscillation circuit. Among them, the capacitor C12 and resistor R14 determine the operating frequency of this oscillation circuit.

[0039] Pin 6 of the PWM control chip U1 is connected to the gate of the switching transistor Q1 through the parallel-connected second zener diode (D6) and the eighth resistor (R15). Among them, the second zener diode D6 is used to protect or adjust the voltage. In addition, the gate of the switching transistor Q1 is connected to the DC ground HGND through the resistor R21. This resistor R21 is used to clamp the gate of the switching transistor Q1 at a low level when pin 6 of the PWM control chip U1 is in an uncertain state, that is, to turn off the switching transistor Q1. By setting the resistor R21 at the gate of the switching transistor Q1, the stability of the entire system is improved.

[0040] Pin 7 of the PWM control chip U1 is connected to the intermediate rectifier circuit through the series-connected resistor R2, resistor R7, and resistor R8 in sequence. A series-connected zener diode D2 and resistor R9 are connected in parallel across both ends of the resistor R8. Further, a connection point between the resistor R8 and pin 7 of the PWM control chip U1 is connected to the capacitor C11, and this capacitor C11 is used for energy storage.

[0041] Pin 8 of the PWM control chip U1 is connected to the parallel-connected second diode (D3) and the seventh resistor (R12). Among them, the second diode (D3) and the seventh resistor (R12) play a protective role.

[0042] Further, when the voltage at pin 7 reaches the compliance value (10V - 16V), pin 8 will output a 5V reference voltage, and this reference voltage is applied to the capacitor C12 and resistor R14. Since the reference voltage output by pin 8 is a stable value, the operating frequency of the above oscillation circuit is also stable.

[0043] Further, the PWM control chip U1 is also connected to a triode Q2. Specifically, the base of the triode Q2 is connected to pin 4 of the PWM control chip U1, the emitter of the triode Q2 is connected to pin 3 of the PWM control chip U1 through the resistor R20, and the collector of the triode Q2 is connected to pin 8 of the PWM control chip U1. Since a ramp signal is added to the triode Q2, oscillations under light load conditions are avoided, ensuring the stable operation of the circuit within the entire load range and improving the stability of the entire circuit.

[0044] In addition, the entire circuit is also provided with a capacitor C13 and a capacitor C14, and both the capacitor C13 and the capacitor C14 play a role in isolation protection.

[0045] The PWM control chip U1 also has an over-temperature protection function: a temperature sensor is built into the PWM control chip U1 to monitor the chip temperature. Once the temperature of the PWM control chip U1 exceeds the safe range, the PWM control chip U1 will reduce the duty cycle of the PWM signal output at pin 6 or even completely turn off to prevent damage caused by overheating of the PWM control chip U1.

[0046] The startup process of this power control circuit is as follows: the input alternating current passes through the input protection circuit, input filter circuit, and output rectifier filter circuit in sequence and then enters the startup circuit. Specifically, the filtered direct current charges the capacitor C11 through the resistors R2, R7, and R8. When the voltage of the capacitor C11 reaches 16V, it supplies power to the PWM control chip U1 through pin 7 of the PWM control chip U1, and then the PWM control chip U1 starts to work. Among them, the PWM control chip U1 outputs a PWN signal to the switching transistor Q1 at pin 6, and the switching transistor Q1 starts to conduct. At this time, the filtered direct current can enter the ground through the switching transistor Q1 and the resistor R22, thus realizing the startup of the entire circuit.

[0047] Since the PWM control chip U1 will not start when the voltage of the capacitor C11 does not reach 16V, it can prevent operations under unstable conditions and avoid potential damage.

[0048] The voltage stabilization control process of this power control circuit: when it is detected that the output voltage of the output terminal changes, the change of the output voltage is fed back to the PWM control chip U1 through the optocoupler U2 via the feedback circuit, and the PWM control chip U1 controls the duty cycle of the output PWM signal according to the change. Specifically, when the output voltage increases, the triode inside the optocoupler conducts more strongly, and then pulls down the voltage at pin 1 of the PWM control chip U1 through the resistor R19. At this time, the PWM control chip U1 reduces the duty cycle of the PWM signal output at pin 6, thereby reducing the conduction time of the switching transistor Q1 to achieve a decrease in the output voltage, thus realizing the voltage stabilization control of the output terminal; similarly, when the output voltage of the output terminal decreases, the PWM control chip U1 increases the duty cycle of the PWM signal output at pin 6, thereby increasing the conduction time of the switching transistor Q1 to achieve an increase in the output voltage and finally realizing the voltage stabilization control.

[0049] In this embodiment, the switching frequency selected for this power control circuit is 48.2KHz, and the power conversion efficiency reaches 80%.

[0050] Although this specification has shown and described multiple embodiments of the present utility model, it will be apparent to those skilled in the art that such embodiments are provided by way of example only. Those skilled in the art will think of many changes, alterations, and alternative ways without departing from the spirit and idea of the present utility model. It should be understood that various alternative solutions to the embodiments of the present utility model described herein may be adopted in the practice of the present utility model.

Claims

1. A flyback power supply control circuit, characterized in that: include: The main circuit comprises an input filter circuit, an intermediate rectification circuit, a transformer (T1) and an output rectification circuit connected in sequence, wherein a switch tube (Q1) is connected in series to the primary side of the transformer (T1); and a control circuit is also included, wherein the control circuit comprises a PWM control chip (U1) and a feedback circuit connected thereto, wherein the output end of the PWM control chip (U1) is controlled to be connected to the switch tube (Q1); The output side of the intermediate rectifier circuit is also connected to an absorption circuit, and the absorption circuit includes: a first voltage regulator tube (ZD), a first diode (D5), a first resistor (R10), a second resistor (R11), a third resistor (R13), a first capacitor (C5) and a second capacitor (C6); wherein the first resistor (R10) is connected in parallel with the first capacitor (C5), the first voltage regulator tube (ZD) and the second resistor (R11) are connected in series and then connected in parallel at both ends of the first resistor (R10), the cathode of the first diode (D5) is connected to the second resistor (R11), the anode of the first diode (D5) is connected to the third resistor (R13) and the second capacitor (C6) connected in series, and the second capacitor (C6) is connected to the first voltage regulator tube (ZD); The primary side of the transformer (T1) is connected in series with a third capacitor (Coss1) and an inductor (Lkp1).

2. A flyback power supply control circuit according to claim 1, characterized in that: The input filter circuit comprises: a common mode inductor (L1), a fourth resistor (R1), a fifth resistor (R4), a sixth resistor (R5), a fourth capacitor (C1), a fifth capacitor (C3) and a sixth capacitor (C4); wherein the fourth resistor (R1), the fifth resistor (R4) and the sixth resistor (R5) are sequentially connected in series and connected to the output side of the common mode inductor (L1); the fourth capacitor (C1) is connected in parallel to both ends of the fourth resistor (R1), the fifth resistor (R4) and the sixth resistor (R5) which are sequentially connected in series; the fifth capacitor (C3) and the sixth capacitor (C4) are connected in series and then connected in parallel to both ends of the fourth capacitor (C1); and the connection point between the fifth capacitor (C3) and the sixth capacitor (C4) is connected to an AC ground (YGND).

3. A flyback power supply control circuit according to claim 1, characterized in that: Pin 8 of the PWM control chip (U1) is connected to a second diode (D3) and a seventh resistor (R12) connected in parallel.

4. A flyback power supply control circuit according to claim 3, characterized in that: Pin 6 of the PWM control chip (U1) is connected to the gate of the switch tube (Q1) via a second voltage regulator tube (D6) and an eighth resistor (R15) connected in parallel.

5. A flyback power supply control circuit according to claim 1, characterized in that: The output rectifier circuit comprises: a third diode (D7), a fourth diode (D8) and a polarity capacitor (C15), wherein the third diode (D7) and the fourth diode (D8) are connected in parallel and then connected to the polarity capacitor (C15).

6. A flyback power supply control circuit according to claim 1, characterized in that: The feedback circuit comprises a ninth resistor (R16) and an optocoupler (U2), wherein the ninth resistor (R16) is connected in series with the optocoupler (U2), and a connection point between the ninth resistor (R16) and the optocoupler (U2) is connected to pin 1 of the PWM control chip (U1).

7. The flyback power supply control circuit according to claim 1, characterized in that: The main circuit also includes an input protection circuit, which includes a fuse (F1), a thermistor (R6) and a variable resistor (R3) connected in series in sequence.

8. The flyback power supply control circuit according to claim 1, characterized in that: The PWM control chip U1 is any one of the UC384X series.

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