CN212063831U

CN212063831U - Automatic bypass circuit for power-on starting of flyback power supply

Info

Publication number: CN212063831U
Application number: CN202021176277.7U
Authority: CN
Inventors: 魏继云; 高栋; 郑丹丹; 房科科
Original assignee: Shandong Windsun Electronics Science & Technology Co ltd
Current assignee: Shandong Windsun Electronics Science & Technology Co ltd
Priority date: 2020-06-23
Filing date: 2020-06-23
Publication date: 2020-12-01
Anticipated expiration: 2030-06-23

Abstract

An automatic bypass circuit for power-on starting of a flyback power supply relates to the technical field of flyback power supplies, solves the problems of power loss and heating of a power-on starting circuit, and comprises an automatic bypass circuit, an MOS (metal oxide semiconductor) switching tube charging circuit and an MOS switching tube control circuit; the working mode of the power-on starting circuit of the flyback power supply is improved, after the high-frequency transformer outputs stably, the auxiliary power supply is used for driving the triode to be in saturation conduction, and the starting circuit is automatically disconnected, so that the problems of resistance heating of the starting circuit and the overall efficiency of the power supply are effectively solved, and the reliability of the flyback power supply is improved.

Description

Automatic bypass circuit for power-on starting of flyback power supply

Technical Field

The utility model relates to a flyback power technical field especially relates to an automatic bypass circuit of going up electric start-up on flyback power.

Background

The flyback power supply refers to a switching power supply which uses a flyback high-frequency transformer to isolate an input-output loop. The working principle is that when the input switch tube is switched on, the primary winding of the high-frequency transformer is used as inductance energy storage, the diode of the secondary winding is cut off in the reverse direction and does not work, and the secondary output power supply is maintained by capacitor discharge. When the input switch tube is turned off, the energy stored in the primary winding of the high-frequency transformer is transferred to the secondary winding through electromagnetic coupling, the diode of the secondary loop is conducted in the forward direction, and the energy is supplied to the load through capacitor filtering.

As shown in fig. 1, the flyback power supply circuit includes a power-on start circuit, a switching tube control circuit, a high-frequency transformer main circuit, and a secondary output circuit. The most critical process is power-on starting, when power supply voltage is provided instantly, a power-on starting circuit is connected in series with a capacitor through a resistor to form a charging circuit, the voltage on the capacitor continuously rises until a power supply of a power supply control chip is established, a PWM signal is output, a switching tube is controlled to be switched on and switched off, and finally a stable state is achieved. At this time, the power of the power control chip is supplied by the secondary auxiliary power VF. However, the conventional resistor-capacitor charging circuit is always connected in parallel in the circuit, the current on the resistor forms heat loss, and the circuit board is more easily burnt out under the condition of poor heat dissipation in a closed environment. In addition, the working temperature rise of surrounding circuit elements is improved, the aging of the elements is accelerated, and unstable factors are generated. For the occasion with high requirement on the energy efficiency of the power supply, the part of loss reduces the working efficiency of the power supply.

Therefore, the starting circuit is improved in an innovative circuit form, so that the power supply of the power supply control chip UC2844 is switched to the automatic bypass after the power supply of the auxiliary power supply is supplied by the starting circuit, the working state of the starting circuit is closed, the starting circuit has practical significance on energy conservation and consumption reduction, and meanwhile, the stability of the flyback power supply is improved.

Disclosure of Invention

In order to solve the problem, the utility model provides a fly back automatic bypass circuit of power-on start-up on power provides a starting circuit power and switches to automatic bypass circuit behind the auxiliary unit power supply, and the starting circuit return circuit is cut off, and the resistance is opened a way and is not had current and pass through, can not produce power loss and the problem of generating heat. In order to achieve the above purpose, the utility model adopts the following technical scheme: an automatic bypass circuit for power-on start of a flyback power supply comprises an automatic bypass circuit, an MOS switch tube charging circuit and an MOS switch tube control circuit, wherein the MOS switch tube control circuit comprises an MOS switch tube VT2, the drain electrode of the MOS switch tube VT2 is connected with a flyback power supply main circuit through a multi-stage series resistor, the source electrode of the MOS switch tube VT2 is connected with a capacitor C2 in series through a diode D4, a voltage output end Vcc on the capacitor C2 is connected to a power supply pin 7 of a power supply control chip UC2844, the other end of the capacitor C2 is grounded, the MOS switch tube control circuit comprises a grid electrode of an MOS switch tube 829VT 4, the grid electrode of the MOS switch tube VT 5 is used as a control end and is connected with two paths of signals, one path is a power-on start control signal, the flyback power supply main circuit is connected with the grid electrode of the MOS switch tube VT2 through the multi-stage resistor in series for current limiting, the grid electrode of the MOS switch tube VT2 is, the other path is an output signal of an automatic bypass circuit and is connected to the grid of an MOS (metal oxide semiconductor) switching tube VT2, the automatic bypass circuit comprises a triode VT3, an auxiliary VF power output Vcc1 of a flyback power supply is connected with a diode D2 in series, a signal is generated through resistance voltage division and is connected with the base of the triode VT3, a collector output bypass signal of a triode VT3 is connected with the grid of an MOS switching tube VT2, the emitter of the triode VT3 is grounded, and the bypass action is effective when the potential of the emitter of the triode VT3 is low.

Compared with the prior art, the utility model discloses following beneficial effect has: the working mode of the power-on starting circuit of the flyback power supply is improved, after the high-frequency transformer outputs stably, the auxiliary power supply is used for driving the triode to be in saturation conduction, and the starting circuit is automatically disconnected, so that the problems of resistance heating of the starting circuit and the overall efficiency of the power supply are effectively solved, and the reliability of the flyback power supply is improved.

Drawings

The present invention will be described in further detail with reference to the accompanying drawings.

FIG. 1 is a schematic diagram of a general starting circuit of a flyback power supply;

fig. 2 is a schematic structural diagram of the present invention.

Detailed Description

In order to make those skilled in the art better understand the technical solution of the present invention, the present invention will be further described with reference to fig. 2 and the specific embodiment.

As shown in fig. 2, an automatic bypass circuit for power-on start of a flyback power supply includes an automatic bypass circuit, an MOS switch tube charging circuit and an MOS switch tube control circuit, where the main circuit of the flyback power supply provides a dc power supply from the outside, and generates a stable dc operating voltage after smoothing filtering by a capacitor C1 to supply the dc operating voltage to the main circuit of the flyback power supply, and for the MOS switch tube charging circuit, after the dc power supply is powered on, a positive bus is connected in series with a drain of an MOS switch tube VT2 through a resistor string R1, a source of the MOS switch tube VT2 is connected in series with a capacitor C2, and the other end of the capacitor C2 is connected to; when the grid of the MOS switch tube VT2 provides a high-level signal, the drain-source of the VT2 forms a path, the dc power supply charges the capacitor C2 through the resistor R2, the voltage on the capacitor C2 continuously rises until the voltage output terminal Vcc of the capacitor C2 reaches the operating voltage of the power control chip UC2844B, and the charging is completed at this time.

After a direct-current power supply is powered on, a positive bus forms a voltage division circuit through a resistor string R2 and R3, a connection point of R2 and R3 is connected with a grid electrode of an MOS switch tube VT2, the grid electrode of the MOS switch tube VT2 is grounded and connected with a voltage stabilizing diode D3, the breakdown of the grid electrode due to overhigh voltage is prevented, a grid signal is immediately established after the direct-current power supply, the drain-source electrode of the MOS switch tube VT2 is controlled to be conducted to work, and therefore the MOS switch tube VT2 establishes a charging loop for a capacitor C2.

The automatic bypass circuit is used for controlling the base electrode of the triode VT3 through a voltage signal generated by voltage division of the resistors R3 and R4 after the output voltage Vcc1 of the auxiliary winding of the high-frequency transformer of the flyback power supply is stably established, the collector and emitter of the triode VT3 form a conducting state, and a grid signal of the MOS switching tube VT2 is pulled down to the ground; thereby turn off MOS switch tube VT2, MOS switch tube control circuit and MOS switch tube charging circuit all open a way, and the power-on starting circuit is by-passed.

In an auxiliary power supply VF circuit of a flyback power supply, when an MOS switching tube charging circuit works, the voltage of a capacitor C2 rises until a power supply of a power supply control chip UC2844 is established, and the auxiliary power supply VF circuit starts to work; vgs signals output by the chip control a main circuit MOS switch tube VT1 to switch, pulse current is output by a flyback power supply high-frequency transformer secondary winding and is output by an auxiliary power supply after being processed by a diode D1 single tube and filtered by a capacitor, output voltage is divided into two branches, one branch is directly used for supplying power to a power supply pin of a power supply control chip UC2844, and the other branch is connected with a diode in series and is output out of an automatic bypass circuit to control the connection and disconnection of a base electrode of a triode VT 3.

Utilize technical scheme, or technical personnel in the field are in the utility model discloses under technical scheme's the inspiration, design similar technical scheme, and reach above-mentioned technological effect, all fall into the utility model discloses a protection scope.

Claims

1. An automatic bypass circuit for power-on start of a flyback power supply comprises an automatic bypass circuit, an MOS switch tube charging circuit and an MOS switch tube control circuit, and is characterized in that the MOS switch tube control circuit comprises an MOS switch tube VT2, the drain electrode of an MOS switch tube VT2 is connected with a flyback power supply main circuit through a multi-stage series resistor, the source electrode of the MOS switch tube VT2 is connected with a capacitor C2 in series through a diode D4, the voltage output end Vcc on the capacitor C2 is connected to a power supply pin of a power supply control chip UC2844, the other end of the capacitor C2 is grounded, the MOS switch tube control circuit comprises the grid electrode of an MOS switch tube VT2, the grid electrode of an MOS switch tube VT2 is used as a control end and is connected with two paths of signals, one path is a power-on start control signal, the flyback power supply main circuit is connected with the grid electrode of an MOS switch tube VT2 through a multi-stage resistor in, the grid of the MOS switch tube VT2 is connected with a voltage stabilizing tube, the other path is the output signal of an automatic bypass circuit and is connected to the grid of the MOS switch tube VT2, the automatic bypass circuit comprises a triode VT3, an auxiliary VF power output Vcc1 of a flyback power supply is connected in series with a diode D2, the signal is generated by resistance voltage division and is connected with the base electrode of a triode VT3, a collector electrode output bypass signal of the triode VT3 is connected with the grid of the MOS switch tube VT2, the emitter electrode of the triode VT3 is grounded, and the bypass action is effective when the potential of the collector electrode of the triode VT3 is low.