CN202043053U

CN202043053U - Switching power supply with under-voltage protection function

Info

Publication number: CN202043053U
Application number: CN2011201607988U
Authority: CN
Inventors: 李国平; 丁晓鸿; 刘国强
Original assignee: Shenzhen Zhenhua Microelectronics Co Ltd
Current assignee: Shenzhen Zhenhua Microelectronics Co Ltd
Priority date: 2011-05-18
Filing date: 2011-05-18
Publication date: 2011-11-16
Anticipated expiration: 2021-05-18

Abstract

The utility model is applicable to the field of power supply circuits and particularly relates to a switching power supply with an under-voltage protection function. When in an under-voltage state, a comparator U1 of a first under-voltage protection unit outputs low level to an input end of a comparator U2 at the same phase so as to enable the comparator U2 to output the low level and provides a signal for turning off a PMW (pulse width modulation) controller, and then an MOS (metal oxide semiconductor) tube V1 is turned off, and accordingly, an auxiliary power supplying unit consisting of a diode D1 and a capacitor C1 is turned off as well. Since a starting circuit and the auxiliary power supplying unit are turned off simultaneously in the under-voltage state, damage of a circuit of the switching power supply is avoided.

Description

A kind of Switching Power Supply that has under-voltage protection function

Technical field

The utility model belongs to the power circuit field, relates in particular to a kind of Switching Power Supply that has under-voltage protection function.

Background technology

Fig. 1 shows a kind of circuit structure that has the Switching Power Supply of under-voltage protection function, this Switching Power Supply comprises transformer TA, diode D1, diode D2, capacitor C 1, PWM controller, metal-oxide-semiconductor V1, metal-oxide-semiconductor V2 and the first under-voltage protection unit 1, wherein, metal-oxide-semiconductor V2 and diode D2 constitute start-up circuit; The second elementary winding of transformer TA, diode D1 and capacitor C 1 constitute auxiliary power unit 2.First termination power of the first elementary winding of transformer TA; the drain electrode of the second termination metal-oxide-semiconductor V1 of the first elementary winding of transformer TA; the source ground of metal-oxide-semiconductor V1; the grid of metal-oxide-semiconductor V1 connects the PWM controller; the first end ground connection of the second elementary winding of transformer TA; the positive pole of the second terminating diode D1 of the second elementary winding; the negative pole of diode D1 is by capacitor C 1 ground connection; the negative pole of diode D1 connects the power end of PWM controller; the drain electrode of the power end of the first under-voltage protection unit 1 and metal-oxide-semiconductor V2 connects power supply simultaneously; the grid of metal-oxide-semiconductor V2 connects the first under-voltage protection unit 1; the source electrode of metal-oxide-semiconductor V2 connects the positive pole of diode D2, and the negative pole of diode D2 connects the power end of PWM controller.The first under-voltage protection unit 1 comprises voltage-stabiliser tube ZD1; voltage-stabiliser tube ZD2; voltage-stabiliser tube ZD3; resistance R 1; resistance R 2; resistance R 3; resistance R 4; resistance R 5 and comparator U1; the in-phase input end of comparator U1 connects power supply by resistance R 2; the in-phase input end of comparator U1 is by resistance R 3 ground connection; the inverting input of comparator U1 connects power supply by resistance R 4; the inverting input of comparator U1 is by voltage-stabiliser tube ZD2 ground connection; the power end of comparator U1 is leaded up to voltage-stabiliser tube ZD3 ground connection; another road of the power end of comparator U1 connects power supply by resistance R 5; the earth terminal ground connection of comparator U1; the output of comparator U1 is first end of connecting resistance R1 simultaneously; the grid of the negative pole of voltage-stabiliser tube ZD1 and metal-oxide-semiconductor V2; the plus earth of voltage-stabiliser tube ZD1, second termination power of resistance R 1.

When this Switching Power Supply is in under-voltage condition, comparator U1 output low level, metal-oxide-semiconductor V2 grid voltage is dragged down, not conducting of metal-oxide-semiconductor V2, the output of metal-oxide-semiconductor V2 source electrode no-voltage, to the power supply of PWM controller, circuit does not start, and therefore plays a protective role.

But; there are some problems in this under-voltage protecting circuit scheme; supply voltage from greater than cut-in voltage when low-voltage changes; if be lower than the pass breakpoint; the first under-voltage protection unit 1 turn-offs metal-oxide-semiconductor V2; but auxiliary power unit 2 can not be turn-offed; can continue as the power end power supply of PWM controller; when supply voltage continues to descend; when exceeding the voltage stabilized range of circuit, circuit plays pendulum, and the voltage that auxiliary power unit 2 is provided can not be stable greater than Von; cause the start-up circuit instability, very easily make the circuit damage.In addition, in order to solve the little power problems of high pressure, this circuit can not directly turn-off the PWM controller from the finite energy that power supply takes out.

The utility model content

The purpose of this utility model is to provide a kind of Switching Power Supply that has under-voltage protection function, is intended to solve present under-voltage protection scheme owing to can not directly turn-off the PWM controller, can not turn-off auxiliary power unit and causes the problem of circuit damage.

The utility model is to realize like this; a kind of Switching Power Supply that has under-voltage protection function; comprise transformer TA, diode D1, diode D2, capacitor C 1, PWM controller, metal-oxide-semiconductor V1, metal-oxide-semiconductor V2 and the first under-voltage protection unit; the described Switching Power Supply that has under-voltage protection function also comprises the second under-voltage protection unit, and the described second under-voltage protection unit comprises:

Resistance R 6, resistance R 7, resistance R 8, voltage-stabilizing device, diode D3 and comparator U2;

The in-phase input end of described comparator U2 is leaded up to resistance R 6 and is connect the output of the comparator U1 of the first under-voltage protection unit; another road of the in-phase input end of described comparator U2 is by resistance R 7 ground connection; the inverting input one tunnel of described comparator U2 connects the hot end of voltage-stabilizing device; the cold end ground connection of described voltage-stabilizing device; another road of the inverting input of described comparator U2 connects the negative pole of diode D2 by resistance R 8; the negative pole of the power supply terminating diode D2 of described comparator U2; the earth terminal ground connection of described comparator U2; the negative pole of the output terminating diode D3 of described comparator U2, the positive pole of described diode D3 connects the control end of PWM controller.

In the said structure, described voltage-stabilizing device adopts voltage-stabiliser tube ZD4, and the cold end of the just very voltage-stabilizing device of described voltage-stabiliser tube ZD4, the negative pole of described voltage-stabiliser tube ZD4 are the hot end of voltage-stabilizing device.

In the utility model; when being in under-voltage condition; the comparator U1 output low level of the first under-voltage protection unit makes comparator U2 output low level to the in-phase input end of the comparator U2 of the second under-voltage protection unit, provides to turn-off the PWM controller signals; turn-off the PWM controller; and then turn-off metal-oxide-semiconductor V1, the auxiliary power unit that diode D1 and capacitor C 1 are constituted is turn-offed, when under-voltage condition; turn-off start-up circuit and auxiliary power unit simultaneously, so just avoided switching power circuit to be damaged.

Description of drawings

Fig. 1 is the existing circuit diagram that has the Switching Power Supply of under-voltage protection function;

Fig. 2 is the circuit diagram of the Switching Power Supply that has under-voltage protection function that provides of the utility model embodiment.

Embodiment

In order to make the purpose of this utility model, technical scheme and advantage clearer,, the utility model is further elaborated below in conjunction with drawings and Examples.Should be appreciated that specific embodiment described herein only in order to explanation the utility model, and be not used in qualification the utility model.

Fig. 2 shows the circuit structure of the Switching Power Supply that has under-voltage protection function that the utility model embodiment provides, and for convenience of explanation, only shows the part relevant with the utility model embodiment, and details are as follows.

A kind of Switching Power Supply that has under-voltage protection function; comprise transformer TA, diode D1, diode D2, capacitor C 1, PWM controller, metal-oxide-semiconductor V1, metal-oxide-semiconductor V2 and the first under-voltage protection unit 100; the Switching Power Supply that has under-voltage protection function comprises that also 300, the second under-voltage protection unit 300, the second under-voltage protection unit comprise:

Resistance R 6, resistance R 7, resistance R 8, voltage-stabilizing device 301, diode D3 and comparator U2;

The in-phase input end of comparator U2 is leaded up to resistance R 6 and is connect the output of the comparator U1 of the first under-voltage protection unit 100; another road of the in-phase input end of comparator U2 is by resistance R 7 ground connection; the inverting input one tunnel of comparator U2 connects the hot end of voltage-stabilizing device 301; the cold end ground connection of voltage-stabilizing device 301; another road of the inverting input of comparator U2 connects the negative pole of diode D2 by resistance R 8; the negative pole of the power supply terminating diode D2 of comparator U2; the earth terminal ground connection of comparator U2; the negative pole of the output terminating diode D3 of comparator U2, the positive pole of diode D3 connects the control end of PWM controller.

As the utility model one embodiment, voltage-stabilizing device 301 adopts voltage-stabiliser tube ZD4, and the cold end of the just very pressurizer 301 of voltage-stabiliser tube ZD4, the negative pole of voltage-stabiliser tube ZD4 are the hot end of voltage-stabilizing device 301.

In the utility model embodiment; when being in under-voltage condition; the comparator U1 output low level of the first under-voltage protection unit 100 is to the in-phase input end of the comparator U2 of the second under-voltage protection unit 300; make comparator U2 output low level; provide and turn-off the PWM controller signals; turn-off the PWM controller; and then shutoff metal-oxide-semiconductor V1; the auxiliary power unit 200 that diode D1 and capacitor C 1 are constituted is turn-offed; when under-voltage condition; turn-off start-up circuit and auxiliary power unit 200 simultaneously, so just avoided switching power circuit to be damaged.

The above only is preferred embodiment of the present utility model; not in order to restriction the utility model; all any modifications of within spirit of the present utility model and principle, being done, be equal to and replace and improvement etc., all should be included within the protection range of the present utility model.

Claims

1. Switching Power Supply that has under-voltage protection function; comprise transformer TA, diode D1, diode D2, capacitor C 1, PWM controller, metal-oxide-semiconductor V1, metal-oxide-semiconductor V2 and the first under-voltage protection unit; it is characterized in that; the described Switching Power Supply that has under-voltage protection function also comprises the second under-voltage protection unit, and the described second under-voltage protection unit comprises:

2. the Switching Power Supply that has under-voltage protection function as claimed in claim 1; it is characterized in that; described voltage-stabilizing device adopts voltage-stabiliser tube ZD4, and the cold end of the just very voltage-stabilizing device of described voltage-stabiliser tube ZD4, the negative pole of described voltage-stabiliser tube ZD4 are the hot end of voltage-stabilizing device.