CN214255697U

CN214255697U - Output short-circuit protection circuit of non-optical-coupling flyback power supply

Info

Publication number: CN214255697U
Application number: CN202120436138.1U
Authority: CN
Inventors: 宫麟; 张燕燕
Original assignee: Eura Drives Electric Co ltd
Current assignee: Eura Drives Electric Co ltd
Priority date: 2021-03-01
Filing date: 2021-03-01
Publication date: 2021-09-21
Anticipated expiration: 2031-03-01

Abstract

The utility model discloses a no optical coupling flyback power supply output short-circuit protection circuit, including collection module and protection module, collection module is connected with supply circuit's output and protection circuit's control end respectively, protection module includes triode T2, soft start electric capacity C34, resistance R33 and diode D15, triode T2's base is direct to be connected with collection module or is connected with collection module through resistance R49, triode T2's projecting pole is connected with power output VNC, triode T2's collecting electrode is connected with diode D15's positive pole, diode D15's negative pole is connected with control chip's compensation end through resistance R33, soft start electric capacity C34 is connected between the collecting electrode and the projecting pole of triode. The utility model discloses a quick protection of power output short circuit, the reliability is high, simple structure, with low costs.

Description

Output short-circuit protection circuit of non-optical-coupling flyback power supply

Technical Field

The utility model relates to a switching power supply protection technical field, concretely relates to no optical coupling flyback power supply output short-circuit protection circuit.

Background

At present, a multi-output flyback power supply is adopted by a frequency converter as an auxiliary power supply, and the frequency converter is characterized by multiple output power supply loops, small power of a single-circuit power supply and small short-circuit current capable of bearing. When the output of the non-main feedback winding is short-circuited, the self-power supply voltage of the control chip is pulled down, so that short-circuit protection is realized; when the main feedback winding is short-circuited, the current detection pin of the high-voltage side control chip must exceed 1V to trigger short-circuit protection. Because the selection of the high-voltage side current detection resistor needs to meet the power requirement of the whole flyback power supply, the resistance value of the high-voltage side current detection resistor is usually small, and the short-circuit instant current is very large. The devices in the main feedback loop cannot bear the current stress at the moment of short circuit, and are very easy to damage in a short circuit state.

The flyback power supply used by the existing frequency converter is mainly isolated by a main feedback optocoupler, and has a plurality of short-circuit protection schemes aiming at the flyback power supply with the isolating optocoupler, and the principle of the flyback power supply is that whether a short circuit occurs or not is mostly judged by a main feedback output voltage value. Whether the reliability of short circuit is low is judged by using the main feedback output voltage, and a power circuit with an isolation optocoupler is complex and high in cost, and the optocoupler also has the problem of service life. The flyback power supply circuit without the optical coupler has a simple structure, but cannot be widely applied due to the lack of a reliable short-circuit protection scheme.

SUMMERY OF THE UTILITY MODEL

The utility model provides a no optical coupling flyback power supply output short-circuit protection circuit, its purpose: the quick protection of the short circuit of the main feedback output of the non-optical coupling flyback power supply is realized.

The utility model discloses technical scheme as follows:

the output short-circuit protection circuit of the non-optical-coupling flyback power supply comprises a control circuit and a power supply circuit, wherein the control circuit comprises a control chip, and the control circuit is connected with the power supply circuit and used for controlling the output of the flyback power supply. The short-circuit protection circuit comprises an acquisition module and a protection module, wherein the acquisition module is respectively connected with the output end of the power supply circuit and the control end of the protection circuit, and the acquisition module is used for acquiring the current of an output loop and obtaining the starting voltage of the protection module; the protection module comprises a triode T2, a soft start capacitor C34, a resistor R33 and a diode D15, wherein the base electrode of the triode T2 is directly connected with the acquisition module or is connected with the acquisition module through a resistor R49, the emitter electrode of the triode T2 is connected with the power output end VNC, the collector electrode of the triode T2 is connected with the anode of the diode D15, the cathode of the diode D15 is connected with the compensation end of the control chip through the resistor R33, and the protection module is used for closing the PWM output of the control chip to realize short-circuit protection; the soft-start capacitor C34 is connected between the collector and emitter of the transistor T2.

Further, the collecting module includes a shunt resistor R50 connected between the power output terminal VNC and the load.

Further, the protection module further comprises a resistor R40, and the resistor R40 is connected between the base of the transistor T2 and the cathode of the diode D15.

Furthermore, the protection module further comprises a filter capacitor C37, wherein one end of the filter capacitor C37 is connected to the base of the transistor T2, and the other end of the filter capacitor C37 is connected to the emitter of the transistor T2 and the power output terminal VNC.

Further, the short-circuit protection circuit further comprises a loop RC, wherein the loop RC comprises a resistor R38 and a capacitor C29 which are connected in parallel, and the loop RC is connected between the compensation end and the voltage feedback end of the control chip.

Compared with the prior art, the utility model discloses following beneficial effect has: (1) the current collection is realized by connecting shunt resistors in series in an output loop, and a triode is used as a threshold switch for circuit protection, so that the quick protection of the main feedback output short circuit of the non-optical coupling flyback power supply is realized; (2) the bias resistor is arranged to provide static bias voltage for the triode, so that the voltage drop at two ends of the shunt resistor is reduced, and the voltage stabilization performance and the conversion efficiency of the power supply are improved; (3) the utility model discloses the reliability is high, circuit structure is simple, with low costs.

Drawings

Fig. 1 is a circuit diagram of the present invention.

Detailed Description

The technical scheme of the utility model is explained in detail below with the attached drawings:

as shown in fig. 1, an output short-circuit protection circuit of a non-optical-coupling flyback power supply includes a control circuit and a power supply circuit, where the control circuit includes a control chip, and the control circuit is connected to the power supply circuit and is used to control the output of the flyback power supply; the short-circuit protection circuit comprises an acquisition module and a protection module, wherein the acquisition module is respectively connected with the output end of the power supply circuit and the control end of the protection circuit, and the acquisition module is used for acquiring the current of the output loop and obtaining the starting voltage of the protection module. Specifically, the acquisition module in this embodiment includes a shunt resistor R50 connected between the power output terminal VNC and the load.

The protection module comprises a triode T2, a soft start capacitor C34, a resistor R33 and a diode D15, wherein the base electrode of the triode T2 is directly connected with the acquisition module or is connected with the acquisition module through a resistor R49, the emitter electrode of the triode T2 is connected with the power output end VNC, the collector electrode of the triode T2 is connected with the anode of the diode D15, and the cathode of the diode D15 is connected with the compensation end of the control chip through the resistor R33; the protection module is used for closing the PWM output of the control chip to realize short-circuit protection; the soft-start capacitor C34 is connected between the collector and emitter of the transistor T2.

The protection module further comprises a resistor R40, and the resistor R40 is connected between the base of the transistor T2 and the cathode of the diode D15. The resistor R49 and the resistor R40 are used for providing static bias voltage for the triode T2, the static bias voltage provided for the triode can reduce the voltage drop at two ends of the shunt resistor R50, and the voltage stabilizing performance and the conversion efficiency of the power supply are improved.

Further, the power supply circuit is further configured to provide a charging voltage for the control chip, and includes a starting resistor and a diode LED2, the power input end P is connected to the power end of the control chip through the starting resistor and the diode LED2 which are sequentially connected in series, and the current conducting direction of the diode LED2 is the power end directed to the control chip by the starting resistor. An energy storage capacitor E15 is also connected between the power supply end of the control chip and the power supply output end VNC.

The selection and parameters of the elements in this embodiment are as follows: the control chip uses UC2844, the triode T2 uses 2N5551, and the shunt resistor R50 uses 50m omega/1206. 330 omega/0805 is used for the resistor R49, 3k omega/0805 is used for the resistor R40, 1nf/0805 is used for the capacitor C37, 22uf/0805 is used for the capacitor C34, and BAV99 is used for the diode D15. The static bias voltage of the triode T2 is 200mV, and the short-circuit protection trigger current value of the main feedback loop is 4A.

The working principle of the circuit is as follows: in normal operation, when the voltage across the shunt resistor R50 exceeds 200mV, the voltage VBE =700mV between the base and the emitter of the transistor T2, the transistor T2 starts to conduct, and the voltage VCE between the collector and the emitter of the transistor T2 approaches 0V. After the VCE of the transistor T2 approaches 0V, the soft-start capacitor C34 completes discharging, and the level of the compensation terminal of the control chip IC2 is pulled down to 0V through the diode D15. The output of IC2 will stop the PWM output and the power supply will stop operating. After the power supply stops working, the voltage of the main feedback power supply end VN1 is reduced to 0V, the voltage at the two ends of the shunt resistor R50 is also reduced to 0V, the short-circuit protection process is finished, and the power supply is subjected to a starting process. The power input end P charges the energy storage capacitor E15 through the starting resistors (resistors R30, R29, R28 and R27) and the diode LED2, and when the voltage at two ends of the energy storage capacitor E15 rises to 16V, the reference voltage end of the control chip IC2 outputs 5V voltage. The control chip IC2 starts oscillation, and the reference voltage terminal of the control chip IC2 charges the soft start capacitor C34 through the resistor R33 and the diode D15. When the voltage at the compensation end charged to the control chip IC2 is higher than the voltage at the feedback end, the output end of the control chip IC2 starts to output PWM, and at the moment, the voltage at the main feedback power supply end VN1 starts to slowly rise to the rated voltage. During the voltage rising process, if the voltage across the shunt resistor R50 still exceeds 200mV, the short-circuit protection will continue until the short circuit of the main feedback output loop is eliminated.

In conclusion, the circuit realizes current collection by serially connecting the shunt resistor in the output loop, and the triode is used as a threshold switch for circuit protection. When the voltage drop at the two ends of the shunt resistor exceeds the threshold voltage of the triode, the PWM output of the control chip can be closed, and therefore power output short-circuit protection is achieved. In this embodiment, the short-circuit protection can be triggered as long as the voltage across the shunt resistor R50 exceeds 200mV, so the current value of the short-circuit protection depends on the resistance value of the resistor R50, and the current value of the short-circuit protection can be accurately controlled by changing the resistance value of the resistor R50.

The utility model discloses can trigger short-circuit protection fast, other devices in protection rectifier diode D18 and the power do not receive the damage. The current peak value on the main feedback output loop short-circuit instant rectifier diode D18 is 4.4A, the hiccup mode is entered after short-circuit protection, the current peak value on the diode D18 is smaller than 4.4A when the diode is hiccup at each time, the starting time when the diode is hiccup at each time is 20ms, the hiccup period is 2.5S, and the proportion of the working time to the non-working time when the short circuit is continued is 0.8%. The utility model discloses the reliability is high, and gives out heat very low when the main feedback output loop lasts the short circuit, can not damage the device in the circuit.

Claims

1. The utility model provides a no optical coupling flyback power supply output short-circuit protection circuit, no optical coupling flyback power supply includes control circuit and power supply circuit, control circuit includes control chip, control circuit is connected with power supply circuit for control flyback power supply's output, its characterized in that: the short-circuit protection circuit comprises an acquisition module and a protection module, wherein the acquisition module is respectively connected with the output end of the power supply circuit and the control end of the protection circuit, and the acquisition module is used for acquiring the current of an output loop and obtaining the starting voltage of the protection module; the protection module comprises a triode T2, a soft start capacitor C34, a resistor R33 and a diode D15, wherein the base electrode of the triode T2 is directly connected with the acquisition module or is connected with the acquisition module through a resistor R49, the emitter electrode of the triode T2 is connected with the power output end VNC, the collector electrode of the triode T2 is connected with the anode of the diode D15, the cathode of the diode D15 is connected with the compensation end of the control chip through the resistor R33, and the protection module is used for closing the PWM output of the control chip to realize short-circuit protection; the soft-start capacitor C34 is connected between the collector and emitter of the transistor T2.

2. The non-coupled flyback power supply output short-circuit protection circuit of claim 1, wherein: the acquisition module comprises a shunt resistor R50 connected between the power supply output VNC and the load.

3. The non-coupled flyback power supply output short-circuit protection circuit of claim 1, wherein: the protection module further comprises a resistor R40, and the resistor R40 is connected between the base of the transistor T2 and the cathode of the diode D15.

4. The non-coupled flyback power supply output short-circuit protection circuit of claim 1, wherein: the protection module further comprises a filter capacitor C37, one end of the filter capacitor C37 is connected with the base electrode of the triode T2, and the other end of the filter capacitor C37 is connected with the emitter electrode of the triode T2 and the power output end VNC.

5. The output short-circuit protection circuit of the non-optical-coupling flyback power supply of any one of claims 1 to 4, wherein: the circuit also comprises a loop RC, wherein the loop RC comprises a resistor R38 and a capacitor C29 which are connected in parallel, and the loop RC is connected between the compensation end and the voltage feedback end of the control chip.