CN204304789U - Flyback power supply - Google Patents

Abstract

Flyback power supply, relate to power technique fields, comprise start-up circuit, transformer T1, the driver U1 of switching tube Q1 and the break-make for control switch pipe Q1, the armature winding of transformer T1 is connected between input power and ground after connecting with switching tube Q1, the secondary winding of transformer T1 externally provides power supply to export, start-up circuit is from described input power power taking and provide starting resistor to driver U1, transformer T1 is also provided with auxiliary winding, this auxiliary winding obtains electric backward driver U1 and powers, also comprise energy-saving circuit, the auxiliary winding of transformer T1 obtain electric after, energy-saving circuit is triggered thus cuts off the circuit that start-up circuit powers to driver U1.

Description

flyback power supply

technical field

The invention relates to the technical field of power supplies, in particular to a flyback power supply.

Background technique

The principle of the flyback power supply is shown in Figure 2. The IN terminal inputs the DC power supply, and the A terminal and the B terminal are the output terminals. When the switch tube Q1 is turned on, the induced voltage of the primary winding of the transformer T1 is positive and negative, and the rectifier diode D4 is in the off state, storing energy in the primary winding of the transformer T1. When the switch tube Q1 is off, the energy stored in the primary winding of the transformer T1 is rectified by the secondary winding and the rectifier diode D4 and filtered by the capacitor C9, and then output to the load, and the capacitor C9 simultaneously Charging is completed to maintain the output to the load by discharging when switch Q1 turns on again. The controller U1 sends a PWM signal with a certain duty ratio to the control terminal of the switch Q1, thereby controlling the output to the load.

In practical applications, the transformer T1 is usually equipped with an auxiliary winding, which supplies power to the controller U1 to maintain the work of the controller U1. However, when the controller U1 is not started, the flyback power supply is not in the working state, and the transformer T1 The auxiliary winding has no output. In order to start the controller U1, only one more startup circuit can be added. The startup circuit usually takes power from the input terminal of the flyback power supply, so that after the input terminal of the flyback power supply is powered, the startup circuit can provide power to the controller U1. A start voltage to start the controller U1. After the controller U1 is started, it controls the switch tube Q1 to be turned on and off, and the flyback power supply enters the working state, and the auxiliary winding of the transformer T1 is energized accordingly and supplies power to the controller U1. In the existing flyback power supply, when the auxiliary winding of the transformer T1 replaces the starting circuit to supply power to the controller U1 after it enters the working state, the starting circuit remains on and continues to work, thereby causing unnecessary loss.

Contents of the invention

Aiming at the above-mentioned technical problems in the prior art, the present invention provides a flyback power supply, which can reduce loss and save energy.

In order to achieve the above object, the present invention provides the following technical solutions.

The flyback power supply includes a start-up circuit, a transformer T1, a switch tube Q1, and a driver U1 for controlling the on-off of the switch tube Q1. The primary winding of the transformer T1 is connected in series with the switch tube Q1 and connected between the input power supply and the ground. The transformer The secondary winding of T1 provides power output to the outside, and the start-up circuit takes power from the input power supply and provides a start-up voltage to the driver U1. The transformer T1 is also provided with an auxiliary winding, which supplies power to the driver U1 after being powered, and also includes an energy-saving circuit. After the auxiliary winding of the transformer T1 is energized, the energy-saving circuit is triggered to cut off the power supply line of the starting circuit to the driver U1.

Wherein, the starting circuit includes a voltage dividing resistor R8, a voltage dividing resistor R9 and a switch tube Q2, and the voltage dividing resistor R8 and the voltage dividing resistor R9 are connected in series between the input power supply and the ground, and the control terminal of the switch tube Q2 is connected to the voltage dividing resistor The junction of R8 and the voltage dividing resistor R9, and the two controlled conduction terminals are respectively connected to the input power supply and the driver U1.

Among them, the switching tube Q2 is an NPN triode, and the energy-saving circuit is provided with a switching tube Q3, and the two controlled conduction ends of the switching tube Q3 are respectively connected to the control terminal of the switching tube Q2 and the ground. The switch Q3 is triggered and turned on, so that the control terminal of the switch tube Q2 is grounded, and the switch tube Q2 is thus turned off.

Wherein, the starting circuit is further provided with a current limiting resistor, and the switching tube Q2 is connected to the input power supply through the current limiting resistor.

Among them, an auxiliary power supply circuit is also included. The auxiliary winding of the transformer T1 supplies power to the driver U1 through the auxiliary power supply circuit. The auxiliary power supply circuit is provided with a rectifier diode D2 and an energy storage capacitor C4. The positive pole of the rectifier diode D2 is connected to one end of the auxiliary winding of the transformer T1, and the negative pole is Connect the driver U1, one end of the energy storage capacitor C4 is connected to the cathode of the rectifier diode D2, and the other end is grounded.

Wherein, a mains rectifier is also included, and the mains rectifier outputs the input power after rectifying the mains.

Among them, a discharge circuit is also included. The discharge circuit includes a diode D1, a resistor R5, a resistor R7 and a capacitor C2. The diode D1 and the resistor R5 are connected in series to both ends of the primary winding of the transformer T1, and the resistor R7 and the capacitor C2 are connected in series. Between the junction of diode D1 and resistor R5 and the input supply.

Wherein, a capacitor CY1 is also included, and the capacitor CY1 is connected between the secondary winding and the auxiliary winding of the transformer T1.

The beneficial effect of the present invention is: add an energy-saving circuit, which is controlled by the auxiliary winding of the transformer T1. After the flyback power supply created by the present invention enters the working state, the auxiliary winding of the transformer T1 is energized, and the energy-saving circuit is triggered. In this way, the power supply line of the starting circuit to the driver U1 is cut off, so that the starting circuit stops working after the power supply enters the working state, thereby reducing loss and saving energy.

Description of drawings

Fig. 1 is a schematic circuit diagram of a flyback power supply created by the present invention.

Figure 2 is a circuit schematic diagram of a classic flyback power supply.

Reference signs include: starting circuit 1 , energy saving circuit 2 , auxiliary power supply circuit 3 , and discharge circuit 4 .

Detailed ways

The invention will be described in detail below in conjunction with specific embodiments.

Figure 1 shows the flyback power supply of this embodiment, which includes a mains rectifier BD1, a transformer T1, a switch tube Q1, a driver U1, a rectifier diode D4, a capacitor C9, a starting circuit 1, an energy-saving circuit 2, an auxiliary power supply circuit 3 and The discharge circuit 4, the mains rectifier BD1 rectifies the mains, and the DC power outputted by it is used as the input power of the flyback power supply in this embodiment.

After the mains is powered on, the current limiting resistors R1, R2 and the voltage dividing resistors R8, R9 form a loop, and the four resistors R1, R2, R8, and R9 divide the voltage of the input power supply, and the base of the NPN transistor Q2 is very high. level, the transistor Q2 is turned on, and the input power supplies the starting voltage to the VDD pin of the power supply of the driver U1 through the current limiting resistors R1, R2 and the transistor Q2, and the driver U1 is thus started and outputs a PWM signal to the gate of the switching transistor Q1 To control its on-off, the flyback power supply of this embodiment enters into a working state. Since then, both the secondary winding and the auxiliary winding of the transformer T1 are energized, the secondary winding of the transformer T1 outputs to the load from the A and B terminals through the rectifier diode D4 and the capacitor C9, and the auxiliary winding supplies power to the driver U1 through the auxiliary power supply circuit 3 The VDD pin supplies power to maintain the driver U1 to work. The auxiliary power supply circuit 3 includes a rectifier diode D2 and an energy storage capacitor C4. The rectifier diode D2 rectifies the output of the auxiliary winding of the transformer T1 and supplies it to the driver U1. The energy storage capacitor C4 has two functions of energy storage and filtering. When the winding output is reversed, the rectifier diode D2 is cut off, and at this time, the energy storage capacitor C4 supplies power to the driver U1.

After the auxiliary winding of the transformer T1 is energized, the base of the NPN transistor Q3 jumps to a high level, and the transistor Q3 is turned on, so that the base of the transistor Q2 is grounded, and the transistor Q2 is thus cut off, and the circuit 1 is started to drive U1 The power supply line is thus cut off.

The discharge circuit 4 plays the role of releasing the leakage inductance of the transformer T1. In addition, the discharge circuit 4 can also discharge the primary winding of the transformer T1 after the mains power is turned off. The capacitor CY1 is connected between the secondary winding and the auxiliary winding of the transformer T1 in order to eliminate the signal interference between the secondary winding and the auxiliary winding and prevent the auxiliary winding from affecting the output of the secondary winding to the load.

Finally, it should be noted that the above examples are only used to illustrate the technical solutions of the present invention, rather than to limit the protection scope of the present invention. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art Personnel should understand that the technical solution of the present invention can be modified or equivalently replaced without departing from the essence and scope of the technical solution of the present invention.

Claims (8)

1. A flyback power supply, including a start-up circuit, a transformer T1, a switch tube Q1, and a driver U1 for controlling the on-off of the switch tube Q1. The primary winding of the transformer T1 is connected in series with the switch tube Q1 and connected between the input power supply and ground , the secondary winding of the transformer T1 provides power output to the outside, the start-up circuit takes power from the input power and provides the start-up voltage to the driver U1, the transformer T1 is also provided with an auxiliary winding, and the auxiliary winding supplies power to the driver U1 after being powered, its characteristics Yes, it also includes an energy-saving circuit. After the auxiliary winding of the transformer T1 is energized, the energy-saving circuit is triggered to cut off the power supply line from the start-up circuit to the driver U1. 2. The flyback power supply according to claim 1, wherein the start-up circuit comprises a voltage dividing resistor R8, a voltage dividing resistor R9 and a switch tube Q2, and the voltage dividing resistor R8 and the voltage dividing resistor R9 are connected in series to the Between the input power supply and the ground, the control terminal of the switch tube Q2 is connected to the junction of the voltage dividing resistor R8 and the voltage dividing resistor R9, and the two controlled conduction terminals are respectively connected to the input power supply and the driver U1. 3. The flyback power supply according to claim 2, wherein the switch tube Q2 is an NPN triode, the energy-saving circuit is provided with a switch tube Q3, and the two controlled conducting ends of the switch tube Q3 are respectively connected to the switch tube Q2 After the auxiliary winding of the transformer T1 is energized, the switch tube Q3 is triggered and turned on, so that the control terminal of the switch tube Q2 is grounded, and the switch tube Q2 is thus turned off. 4. The flyback power supply according to claim 2, wherein the start-up circuit is further provided with a current limiting resistor, and the switching tube Q2 is connected to the input power supply through the current limiting resistor. 5. The flyback power supply according to claim 1, further comprising an auxiliary power supply circuit, the auxiliary winding of the transformer T1 supplies power to the driver U1 via the auxiliary power supply circuit, and the auxiliary power supply circuit is provided with a rectifier diode D2 and an energy storage capacitor C4, the anode of the rectifier diode D2 is connected to one end of the auxiliary winding of the transformer T1, the cathode is connected to the driver U1, one end of the energy storage capacitor C4 is connected to the cathode of the rectifier diode D2, and the other end is grounded. 6. The flyback power supply according to claim 1, further comprising a mains rectifier, which rectifies the mains and outputs the input power. 7. The flyback power supply according to claim 1, further comprising a discharge circuit, the discharge circuit includes a diode D1, a resistor R5, a resistor R7 and a capacitor C2, and the diode D1 and the resistor R5 are connected in series to the transformer Both ends of the primary winding of T1, the resistor R7 and the capacitor C2 are connected in series between the junction of the diode D1 and the resistor R5 and the input power supply. 8 . The flyback power supply according to claim 1 , further comprising a capacitor CY1 connected across the secondary winding and the auxiliary winding of the transformer T1 .