Flyback switching power supply

Abstract

The utility model relates to the technical field of switching power supplies, in particular to a flyback switching power supply, which comprises a PWM (Pulse Width Modulation) control chip U1, an input loop for inputting voltage and an output loop for outputting voltage, the input loop is connected with the PWM control chip U1, the input loop and the output loop realize output voltage regulation through a transformer, and the output loop is connected with the PWM control chip U1. The output loop is connected with a feedback loop, the feedback loop is used for feeding back the output voltage to the PWM control chip U1, and the PWM control chip U1 is connected with the input voltage feedback compensation circuit and the overload stable hiccup protection circuit. And a fixed overload protection point exists in a full input voltage range.

Description

Technical Field

[0001] This utility model relates to the field of switching power supply technology, specifically to a flyback switching power supply. Background Technology

[0002] A switching power supply is a type of power supply that uses modern electronic power technology to control the on and off time ratio of a switching transistor to maintain a stable output voltage. Switching power supplies are generally composed of a pulse width modulation (PWM) control IC and a MOSFET. Flyback switching power supplies occupy an important position in the small and medium power field due to their simple structure and low cost.

[0003] However, the flyback circuit of existing PWM control ICs generally adopts single voltage loop control, which is relatively simple in terms of output current control. When the single output is overloaded, the capacitor of the current pin of the control IC is charged through the current sampling resistor. When the input voltage range is wide, the circuit is prone to failure to enter the hiccup protection. In addition, the overcurrent points of high input voltage and low input voltage are quite different. The existence of the above two problems may indirectly lead to circuit overheating failure. Utility Model Content

[0004] The purpose of this invention is to provide a flyback switching power supply that can stably enter hiccup protection state under overload conditions, and has a fixed overload protection point across the entire input voltage range.

[0005] To achieve the above objectives, this utility model provides the following technical solution:

[0006] In a first aspect, this utility model provides a flyback switching power supply, including a PWM control chip U1, comprising: an input circuit for input voltage, the input circuit being connected to the PWM control chip U1, and an output circuit for output voltage, wherein the input circuit and the output circuit are connected to a transformer to achieve output voltage regulation, the output circuit being connected to a feedback circuit, the feedback circuit being used to feed the output voltage back to the PWM control chip U1, and the PWM control chip U1 being connected to an input voltage feedback compensation circuit and an overload stability hiccup protection circuit respectively.

[0007] In conjunction with the first aspect, optionally, the PWM control chip U1 is one of UC2842, UC2843, UC2844, UC2845, UC3842, UC3843, UC3844, and UC3845.

[0008] In conjunction with the first aspect, optionally, the input voltage feedback supplement circuit includes resistor R2, resistor R3 and capacitor C1. One end of resistor R2 is connected to the input voltage VIN, and the other end of resistor R2 is connected to the third pin of PWM control chip U1. One end of resistor R3 is connected to the third pin of PWM control chip U1, and the other end of resistor R3 is grounded. Capacitor C1 is connected in parallel with resistor R3.

[0009] In conjunction with the first aspect, optionally, the overload stabilization hiccup protection circuit includes transistors Q1 and Q2. The base of transistor Q1 is connected to one end of resistor R4, and the other end of resistor R4 is connected to the first pin of PWM control chip U1. A resistor R5 is connected in series between the base and emitter of transistor Q1, and a capacitor C3 is connected in parallel across the two ends of resistor R5. A capacitor C4 is connected in series between the emitter and collector of transistor Q1. The emitter of transistor Q1 is grounded. The collector of transistor Q1 is connected to one end of resistor R6, and the other end of resistor R6 is connected to the base of transistor Q2. A resistor R7 is connected in series between the base and collector of transistor Q2. The collector of transistor Q2 is connected to a reference voltage VREF, and the emitter of transistor Q2 is connected to the third pin of PWM control chip U1.

[0010] In conjunction with the first aspect, optionally, the input circuit includes a capacitor C11, a transformer primary winding T19-A, a MOSFET Q10, and a resistor R1. One end of the transformer primary winding T19-A is connected to the input voltage VIN, and the other end of the transformer primary winding T19-A is connected to the drain of the MOSFET Q10. The positive terminal of the capacitor C11 is connected to the input voltage VIN, and the negative terminal of the capacitor C11 is grounded. The gate of the MOSFET Q10 is connected to one end of the resistor R10, and the other end of the resistor R10 is connected to the sixth pin of the PWM control chip U1. The source of the MOSFET Q10 is connected to the third pin of the PWM control chip U1. The source of the MOSFET Q10 is also connected to one end of the resistor R1, and the other end of the resistor R1 is grounded.

[0011] In conjunction with the first aspect, optionally, the output circuit includes a transformer secondary winding T19-B, one end of which is connected to the anode of diode D1, the cathode of diode D1 is the voltage output VOUT terminal, the cathode of diode D1 is connected to the positive terminal of capacitor C12, the negative terminal of capacitor C12 is connected to the other end of transformer secondary winding T19-B, and the negative terminal of capacitor C12 is grounded.

[0012] In conjunction with the first aspect, optionally, the feedback loop includes an optocoupler OT1, the first pin of which is connected to the cathode of diode D1, the first pin of which is connected in series with capacitor R9 and resistor R8 and then grounded, the second pin of which is connected to the cathode of three-terminal voltage regulator chip U2, the anode of which is grounded, the reference pin of which is connected to the non-grounded terminal of resistor R8, the fourth pin of which is connected in series with resistor R11 and connected to the first pin of PWM control chip U1, and the third pin of which is grounded.

[0013] In conjunction with the first aspect, optionally, a power supply circuit for powering the PWM control chip U1 is also included. The power supply circuit includes a resistor R12, one end of which is connected to the input voltage VIN, and the other end of which is connected to the seventh pin of the PWM control chip U1. The other end of the resistor R12 is also connected to the cathode of a diode D2, the anode of which is connected to one end of the secondary winding T19-C of the transformer, and the other end of the secondary winding T19-C of the transformer is grounded. The cathode of the diode D2 is also connected to one end of a capacitor C2, and the other end of the capacitor C2 is grounded.

[0014] The beneficial effects of this invention are as follows: By connecting a voltage feedback compensation circuit to the PWM control chip, the voltage is compensated to the current detection pin of the PWM control chip. When the input voltage is higher, the voltage compensation circuit compensates for the higher voltage, thus achieving a stable overload point across the entire input voltage range under wide input voltage conditions. By connecting an overload stabilization hiccup protection circuit to the PWM control chip, the circuit can stably enter the hiccup protection state across the entire input voltage range, indirectly avoiding the problem of overheating failure of the circuit. Attached Figure Description

[0015] The accompanying drawings are provided to further illustrate the present invention and form part of the specification. They are used together with the embodiments of the present invention to explain the present invention, but do not constitute a limitation thereof. In the drawings:

[0016] Figure 1 This is the circuit diagram of this utility model;

[0017] Figure 2 This is a waveform diagram of each interface in the circuit of this utility model;

[0018] The markings in the diagram are: 1 for the input circuit, 2 for the output circuit, 3 for the power supply circuit, and 4 for the feedback circuit. Detailed Implementation

[0019] The technical solution of this utility model will be described in detail below with reference to the accompanying drawings and specific embodiments. It should be understood that the embodiments and specific features in the embodiments are detailed descriptions of the technical solution of this application, rather than limitations thereof.

[0020] In the description of this utility model, the terms "first" and "second" are used only to distinguish technical features and should not be construed as indicating or implying relative importance, or implicitly indicating the number of technical features or the order of the technical features.

[0021] In the description of this utility model, the terms "one embodiment," "some embodiments," "illustrative embodiment," "example," "specific example," or "some examples," etc., refer to specific features, structures, materials, or characteristics described in connection with that embodiment or example, which are included in at least one embodiment or example of this utility model. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0022] like Figure 1 As shown, this utility model provides a flyback switching power supply, including a PWM control chip U1, and further including: an input circuit 1 for input voltage, the input circuit 1 being connected to the PWM control chip U1, and an output circuit 2 for output voltage. The input circuit 1 and the output circuit 2 are connected to a transformer to achieve output voltage regulation. The output circuit 2 is also connected to a feedback circuit 4, which is used to feed the output voltage back to the PWM control chip U1. The PWM control chip U1 is also connected to an input voltage feedback compensation circuit and an overload stability hiccup protection circuit.

[0023] In some embodiments, the PWM control chip U1 is one of UC2842, UC2843, UC2844, UC2845, UC3842, UC3843, UC3844, and UC3845.

[0024] In one embodiment, the PWM control chip U1 is model UC2843, wherein the first pin of the PWM control chip U1 is the COM terminal, the second pin is the FB terminal, the third pin is the CS terminal, the fourth pin is the RT / CT terminal, the fifth pin is the GND terminal, the sixth pin is the OUTPUT terminal, the seventh pin is the VCC terminal, and the eighth pin is the VREF terminal.

[0025] The input voltage feedback compensation circuit includes resistors R2 and R3 and capacitor C1. One end of resistor R2 is connected to the input voltage VIN, and the other end of resistor R2 is connected to the third pin of PWM control chip U1. One end of resistor R3 is connected to the third pin of PWM control chip U1, and the other end of resistor R3 is grounded. Capacitor C1 is connected in parallel with resistor R3.

[0026] The input voltage VIN is divided by resistors R2 and R3 and compensated to the third pin of the PWM control chip U1, so as to achieve a stable overload point across the entire input voltage range when the input voltage is wide.

[0027] The overload stabilization hiccup protection circuit includes transistors Q1 and Q2. The base of transistor Q1 is connected to one end of resistor R4, and the other end of resistor R4 is connected to the first pin of PWM control chip U1. Resistor R5 is connected in series between the base and emitter of transistor Q1, and capacitor C3 is connected in parallel across resistor R5. Capacitor C4 is connected in series between the emitter and collector of transistor Q1. The emitter of transistor Q1 is grounded. The collector of transistor Q1 is connected to one end of resistor R6, and the other end of resistor R6 is connected to the base of transistor Q2. Resistor R7 is connected in series between the base and collector of transistor Q2. The collector of transistor Q2 is connected to the reference voltage VREF, and the emitter of transistor Q2 is connected to the third pin of PWM control chip U1.

[0028] The voltage level on the first pin of the PWM control chip U1 increases with the increase of the output load. Therefore, based on this characteristic, the conduction of transistor Q1 is controlled by resistors R4 and R5. The conduction of transistor Q1 controls the conduction of transistor Q2, forcibly injecting the reference voltage VREF to the third pin of the PWM control chip U1, forcibly turning off the pulse width. After that, the voltage level on the first pin of the PWM control chip U1 decreases, transistor Q1 turns off, and the reference voltage VREF charges capacitor C4 through resistors R6 and R7. As the voltage of capacitor C4 increases, the base voltage of transistor Q2 increases, transistor Q2 turns off, and capacitor C1 discharges through resistor R3. After capacitor C1 finishes discharging, the PWM control chip U1 turns the pulse width back on to achieve hiccup protection. The hiccup interval can be controlled by adjusting the parameters of capacitors C1 and C4.

[0029] Input circuit 1 includes capacitor C11, transformer primary winding T19-A, MOSFET Q10, and resistor R1. One end of transformer primary winding T19-A is connected to the input voltage VIN, and the other end of transformer primary winding T19-A is connected to the drain of MOSFET Q10. The positive terminal of capacitor C11 is connected to the input voltage VIN, and the negative terminal of capacitor C11 is grounded. The gate of MOSFET Q10 is connected to one end of resistor R10, and the other end of resistor R10 is connected to the sixth pin of PWM control chip U1. The source of MOSFET Q10 is connected to the third pin of PWM control chip U1. The source of MOSFET Q10 is also connected to one end of resistor R1, and the other end of resistor R1 is grounded.

[0030] Output circuit 2 includes transformer secondary winding T19-B. One end of transformer secondary winding T19-B is connected to the anode of diode D1. The cathode of diode D1 is the voltage output VOUT terminal. The cathode of diode D1 is connected to the positive terminal of capacitor C12. The negative terminal of capacitor C12 is connected to the other end of transformer secondary winding T19-B. The negative terminal of capacitor C12 is grounded.

[0031] Feedback loop 4 includes optocoupler OT1. The first pin of optocoupler OT1 is connected to the cathode of diode D1. The first pin of optocoupler OT1 is connected to ground after capacitor R9 and resistor R8 in series. The second pin of optocoupler OT1 is connected to the cathode of three-terminal voltage regulator chip U2. The anode of three-terminal voltage regulator chip U2 is grounded. The reference pin of three-terminal voltage regulator chip U2 is connected to the non-grounded pin of resistor R8. In some embodiments, the three-terminal voltage regulator chip U2 is model TL431. The fourth pin of optocoupler OT1 is connected to the first pin of PWM control chip U1 in series with resistor R11. The third pin of optocoupler OT1 is grounded.

[0032] It also includes a power supply circuit 3 for powering the PWM control chip U1. The power supply circuit 3 includes a resistor R12. One end of the resistor R12 is connected to the input voltage VIN, and the other end of the resistor R12 is connected to the seventh pin of the PWM control chip U1. The other end of the resistor R12 is also connected to the cathode of the diode D2. The anode of the diode D2 is connected to one end of the secondary winding T19-C of the transformer, and the other end of the secondary winding T19-C of the transformer is grounded. The cathode of the diode D2 is also connected to one end of the capacitor C2, and the other end of the capacitor C2 is grounded. The PWM control chip U1 starts working by charging the capacitor C2 through the resistor R12. After the circuit starts working, the capacitor C2 is charged through the rectification of the diode D2.

[0033] The cathode of diode D1 is the voltage output terminal VOUT, such as... Figure 2As shown, a high value at the voltage output VOUT terminal indicates normal output, and a low value indicates output off; IOUT is the output current. The normal output current is during the T0-T1 time period. An increase in current during the T1-T2 time period indicates output overload. Periodic high and low changes after T2 indicate the hiccup protection stage after triggering overload protection; Vg represents the PWM waveform generated by the PWM control chip U1, used to control the switching of MOSFET Q10; Cs is the level of the third pin of the PWM control chip U1, i.e., the current sampling pin. When MOSFET Q10 is turned on, current flows through the sampling resistor R1. At this time, the third pin of the PWM control chip U1 detects a triangular wave, as shown in the figure. Figure 2 As shown, the T0-T1 time period is the Cs pin waveform during normal output, and the time period after T1 is the Cs pin waveform during overload. Com represents the voltage waveform of the first pin of the PWM control chip U1, i.e., the Com pin. When the output is overloaded, the voltage at this point rises. The overload stabilization hiccup protection circuit realizes the overload protection function by identifying the voltage at this point.

[0034] The above description is merely a preferred embodiment of the present utility model and is not intended to limit the present utility model. Although the present utility model has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present utility model should be included within the protection scope of the present utility model.

Claims

1. A flyback switching power supply, comprising a PWM control chip U1, characterized in that, include: The system includes an input circuit for input voltage, which is connected to the PWM control chip U1, and an output circuit for output voltage. The input circuit and the output circuit are connected to a transformer to regulate the output voltage. The output circuit is also connected to a feedback circuit, which is used to feed the output voltage back to the PWM control chip U1. The PWM control chip U1 is also connected to an input voltage feedback compensation circuit and an overload stability hiccup protection circuit.

2. The flyback switching power supply according to claim 1, characterized in that, The PWM control chip U1 is one of the following models: UC2842, UC2843, UC2844, UC2845, UC3842, UC3843, UC3844, and UC3845.

3. The flyback switching power supply according to claim 2, characterized in that, The input voltage feedback supplement circuit includes resistors R2 and R3 and capacitor C1. One end of resistor R2 is connected to the input voltage VIN, and the other end of resistor R2 is connected to the third pin of PWM control chip U1. One end of resistor R3 is connected to the third pin of PWM control chip U1, and the other end of resistor R3 is grounded. Capacitor C1 is connected in parallel with resistor R3.

4. The flyback switching power supply according to claim 2, characterized in that, The overload stabilization hiccup protection circuit includes transistors Q1 and Q2. The base of transistor Q1 is connected to one end of resistor R4, and the other end of resistor R4 is connected to the first pin of PWM control chip U1. A resistor R5 is connected in series between the base and emitter of transistor Q1, and a capacitor C3 is connected in parallel across resistor R5. A capacitor C4 is connected in series between the emitter and collector of transistor Q1. The emitter of transistor Q1 is grounded. The collector of transistor Q1 is connected to one end of resistor R6, and the other end of resistor R6 is connected to the base of transistor Q2. A resistor R7 is connected in series between the base and collector of transistor Q2. The collector of transistor Q2 is connected to a reference voltage VREF, and the emitter of transistor Q2 is connected to the third pin of PWM control chip U1.

5. The flyback switching power supply according to claim 2, characterized in that, The input circuit includes a capacitor C11, a transformer primary winding T19-A, a MOSFET Q10, and a resistor R1. One end of the transformer primary winding T19-A is connected to the input voltage VIN, and the other end of the transformer primary winding T19-A is connected to the drain of the MOSFET Q10. The positive terminal of the capacitor C11 is connected to the input voltage VIN, and the negative terminal of the capacitor C11 is grounded. The gate of the MOSFET Q10 is connected to one end of the resistor R10, and the other end of the resistor R10 is connected to the sixth pin of the PWM control chip U1. The source of the MOSFET Q10 is connected to the third pin of the PWM control chip U1. The source of the MOSFET Q10 is also connected to one end of the resistor R1, and the other end of the resistor R1 is grounded.

6. The flyback switching power supply according to claim 2, characterized in that, The output circuit includes a transformer secondary winding T19-B. One end of the transformer secondary winding T19-B is connected to the anode of diode D1. The cathode of diode D1 is the voltage output VOUT terminal. The cathode of diode D1 is connected to the positive terminal of capacitor C12. The negative terminal of capacitor C12 is connected to the other end of the transformer secondary winding T19-B. The negative terminal of capacitor C12 is grounded.

7. The flyback switching power supply according to claim 6, characterized in that, The feedback loop includes an optocoupler OT1. The first pin of the optocoupler OT1 is connected to the cathode of diode D1. The first pin of the optocoupler OT1 is connected to ground after being connected in series with resistors R9 and R8. The second pin of the optocoupler OT1 is connected to the cathode of a three-terminal voltage regulator chip U2. The anode of the three-terminal voltage regulator chip U2 is grounded. The reference pin of the three-terminal voltage regulator chip U2 is connected to the non-grounded end of resistor R8. The fourth pin of the optocoupler OT1 is connected to the first pin of the PWM control chip U1 in series with resistor R11. The third pin of the optocoupler OT1 is grounded.

8. The flyback switching power supply according to claim 2, characterized in that, It also includes a power supply circuit for powering the PWM control chip U1. The power supply circuit includes a resistor R12. One end of the resistor R12 is connected to the input voltage VIN, and the other end of the resistor R12 is connected to the seventh pin of the PWM control chip U1. The other end of the resistor R12 is also connected to the cathode of the diode D2. The anode of the diode D2 is connected to one end of the secondary winding T19-C of the transformer. The other end of the secondary winding T19-C of the transformer is grounded. The cathode of the diode D2 is also connected to one end of the capacitor C2. The other end of the capacitor C2 is grounded.

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