CN2847345Y

CN2847345Y - Constant current controller for switch power source

Info

Publication number: CN2847345Y
Application number: CN 200520059767
Authority: CN
Inventors: 杨义根
Original assignee: Individual
Current assignee: Individual
Priority date: 2005-06-07
Filing date: 2005-06-07
Publication date: 2006-12-13
Anticipated expiration: 2015-06-07

Abstract

The utility model discloses a constant current control circuit for a switching power supply. The utility model aims to solve the technical problem of providing a constant current control circuit for a switching power supply which has the characteristics of constant current and constant power output and reliable quality; besides, the circuit structure is simplified and the production cost is reduced. Therefore, based on the original constant current control circuit for a switching power supply which comprises a high frequency transformer, a low voltage rectifying and filtering circuit, an output voltage sampling circuit and a control IC for the switching the power supply, the utility model is additionally provided with an output current sampling circuit, the output end of the output current sampling circuit and a connection point of a voltage division resistor of the output voltage sampling circuit are simultaneously connected with the input end of the control IC for the switching the power supply.

Description

The constant-current control circuit that a kind of Switching Power Supply is used

Technical field

The utility model relates to the switch power technology field, the constant-current control circuit that particularly a kind of Switching Power Supply is used.

Background technology

In switching power circuit, for avoiding causing that because of load current is excessive the situation that Switching Power Supply is damaged takes place, often adopt the constant current control technology, work with security and stability to guarantee Switching Power Supply.

The constant-current control circuit that existing Switching Power Supply is used generally is made up of high-frequency transformer TR, lower pressure rectifier filtering circuit D1, D2, L, C1, output voltage sample circuit R1, R2 and PWM control IC, and high-frequency transformer TR secondary voltage is exported after the filtering circuit filtering that diode D1, D2 full-wave rectification and inductance L, capacitor C 1 are formed.Usually, constant-current control circuit is taken a sample to output current earlier, and promptly sample resistance Rs of series connection in output loop produces pressure drop when output current is flowed through sample resistance Rs, this pressure drop is delivered to the input end of comparer A1 as signal, with the reference voltage V that is connected to the other end _Ref1Compare, as shown in Figure 1.When output current surpassed certain certain value, the output of comparer A1 can be adjusted the gating pulse width, reduces output current, thereby reaches the purpose of constant current.In output loop, be parallel with output voltage sample circuit R1, R2, after resistance R 1, R2 dividing potential drop, signal voltage be input to comparer A2 input end, with its other end reference voltage V _Ref2Compare.When output voltage surpassed certain certain value, the output of comparer A2 can be adjusted the width of gating pulse, changed output voltage, thus constant output voltage.

But there is following problem in foregoing circuit:

(1) constant-current control circuit and mu balanced circuit respectively use comparer A1, an A2, and therefore, pwm control circuit must use the IC with two comparers, and peripheral circuit is complicated, the cost height.

(2) power consumption of sample resistance Rs is big, and thermal value is many, and circuit efficiency is not high.

Summary of the invention

The technical problems to be solved in the utility model provides a kind of constant current, the output of permanent power and Switching Power Supply constant-current control circuit of fine qualities; Simultaneously, also simplify circuit structure, reduced production cost.

The technical solution that the utility model proposed is such: the constant-current control circuit that a kind of Switching Power Supply is used, comprise high-frequency transformer TR, the lower pressure rectifier filtering circuit, the control IC of output voltage sample circuit and Switching Power Supply, described lower pressure rectifier filtering circuit is by diode D1, D2, filter inductor L and filter capacitor C1 form, diode D1 wherein, the tie point of two negative poles of D2 is connected with the end of filter inductance L, the other end of filter inductance L is connected with power supply output cathode Vo+ with the positive pole of filter capacitor C1, described output voltage sample circuit is made up of resistance R 1 and R2, one end of resistance R 1 is connected with power supply output cathode Vo+, the tie point of resistance R 1 and R2 is connected with the input end of the control IC of Switching Power Supply, be provided with the output current sample circuit, the divider resistance R1 of its output terminal and output voltage sample circuit, the R2 tie point is connected with the input end of Switching Power Supply control IC together simultaneously.Described output current sample circuit comprises current transformer M1, the current signal current rectifying and wave filtering circuit, isolating diode D5 and current-limiting resistance R4, the end of the primary coil N4 of current transformer M1 is connected with high-frequency transformer TR one output terminal, its other end is connected with commutation diode D1 or D2, the secondary coil N5 of the input end of current signal current rectifying and wave filtering circuit and current transformer M1, N6 is connected, its output terminal is connected with the positive pole of isolating diode D5, the end of current-limiting resistance R4 is connected with the negative pole of isolating diode D5, its other end and output voltage sample circuit divider resistance R1, the R2 tie point connects and receives the control IC input end of Switching Power Supply.Described current signal current rectifying and wave filtering circuit has various ways, the 1st kind of form is by full wave rectifier D3, D4 and pull-up resistor R3, filter capacitor C2 forms, the positive pole of described diode D3 is connected with the end of the secondary coil N5 of current transformer M1, the positive pole of diode D4 is connected with the end of another secondary coil N6 of current transformer M1, twice level coil N5, the tie point of N6 be connected publicly, diode D3, the negative pole of D4 joins afterwards and pull-up resistor R3 one end, filter capacitor C2 positive pole is connected, the pull-up resistor R3 other end, filter capacitor C2 negative pole connects public ground simultaneously The 2nd kind of form of current signal current rectifying and wave filtering circuit is made up of half-wave rectifier D3 and pull-up resistor R3, filter capacitor C2, and the end of described current transformer M1 secondary coil N5 is connected with the positive pole of diode D3, its other end and public ground Be connected, the negative pole of diode D3 is connected with pull-up resistor R3, filter capacitor C2 positive pole, and the pull-up resistor R3 other end, filter capacitor C2 negative pole connect public ground simultaneously The 3rd kind of form of current signal current rectifying and wave filtering circuit is made up of bridge rectifier BD and pull-up resistor R3, filter capacitor C2, the input end of described bridge rectifier BD is connected with the two ends of the secondary coil N5 of current transformer M1 respectively, bridge rectifier BD output negative terminal with publicly

Be connected, bridge rectifier BD output plus terminal is connected with pull-up resistor R3, filter capacitor C2 positive pole, and the pull-up resistor R3 other end, filter capacitor C2 negative pole connect public ground simultaneously

Compared with prior art, the utlity model has following beneficial effect:

(1) owing to adopted the output current sample circuit, can accomplish constant current, the output of permanent power, improve the reliability of Switching Power Supply greatly.

(2) owing to need only use the PWM control IC with a comparer, thereby circuit structure is simple, and production cost is lower.

Description of drawings

Fig. 1 is the schematic circuit of the constant-current control circuit used of existing Switching Power Supply.

Fig. 2 is the schematic circuit of the constant-current control circuit that a kind of Switching Power Supply is used among the utility model embodiment.

Fig. 3 is the schematic circuit of the constant-current control circuit that another kind of Switching Power Supply is used among the utility model embodiment.

Fig. 4 is the schematic circuit of the constant-current control circuit that the third Switching Power Supply is used among the utility model embodiment.

Fig. 5 is the schematic circuit of the constant-current control circuit of the 4th kind of Switching Power Supply among the utility model embodiment.

Embodiment

By following embodiment the utility model is further elaborated.

Embodiment 1

Fig. 2 is the schematic circuit of the constant-current control circuit that a kind of Switching Power Supply is used among the utility model embodiment.Used PWM-IC is the Switching Power Supply control IC that TIX produces in this example, and model is TL494, and its first pin is a comparator input terminal.During Switching Power Supply work, secondary winding N2, the N3 of high-frequency transformer TR produces induced voltage, through diode D1, D2 full-wave rectification, after 1 filtering of inductance L capacitor C, provides electric current to load.

When load current was flowed through current transformer M1, the secondary N5 of this mutual inductor, N6 produced induced voltage, after diode D3, D4 rectification, and the current signal V1 that formation one and load current are in proportion on pull-up resistor R3.Meanwhile, output voltage V o+ produces one and the proportional voltage signal V2 of output voltage after sample resistance R1, R2 dividing potential drop, directly is added to the input end of comparer A1 among the PWM control IC (TL494).

When load current was less than or equal to ratings, the current signal V1 that current sampling circuit produces was less than the voltage signal V2 of output voltage V o+, and isolating diode D5 is in cut-off state.At this moment, the signal that acts on Switching Power Supply control IC input end only has only output voltage signal V2, and circuit is in the constant voltage duty.

But after load current surpassed rated current, current signal V1 was greater than voltage signal V2, isolating diode D5 conducting.This moment, current signal V1 and voltage signal V2 acted on the input end of Switching Power Supply control IC simultaneously, and circuit is in constant current, permanent power rating.

Constant-current control circuit of the present utility model mainly contains three kinds of forms, and above-mentioned is first kind of form, promptly adopts diode D3, D4 full-wave rectification; Second kind of form is to adopt diode D3 half-wave rectification, sees shown in Figure 3; The third form is to adopt bridge rectifier BD, sees shown in Figure 4.

Embodiment 2

Referring to shown in Figure 5, used the IC2 of accurate adjustable reference voltage in this example, model is TL431.TL431 is a three terminal device, and when regulating the input voltage of control utmost point R end, the electric current that flows through negative electrode K end can change thereupon, and its anode A connects public ground.

The full wave rectifier of forming by diode D3, D4 that current signal rectification circuit in this example adopts.Equally, also can adopt the circuit of half-wave rectifier D3 and bridge rectifier BD, as shown in Figure 3, Figure 4.The current sampling circuit output terminal is connected to the divider resistance R1 of output voltage sample circuit, the tie point of R2 through isolating diode D5 and current-limiting resistance R4 in this example, and together is connected with the R end of IC2.

The K end of IC2 is connected to photoelectrical coupler U1 negative pole, and the positive pole of photoelectrical coupler U1 is connected to power output end Vo+ through current-limiting resistance R5.

When load current when normally and only output voltage changes, voltage signal V2 is added to the R end of IC2, and the electric current that flows through photoelectrical coupler U1 changes, thereby the size of regulating output voltage reaches the effect of constant voltage.

And after the load current overrate, current signal V1 then can be added on the voltage signal V2, and acting in conjunction is in the R of IC2 end, and circuit enters constant current, permanent power rating.

Claims

1, the constant-current control circuit that a kind of Switching Power Supply is used, comprise high-frequency transformer TR, the lower pressure rectifier filtering circuit, the control IC of output voltage sample circuit and Switching Power Supply, described lower pressure rectifier filtering circuit is by diode D1, D2, filter inductor L and filter capacitor C1 form, diode D1 wherein, the tie point of two negative poles of D2 is connected with the end of filter inductance L, the other end of filter inductance L is connected with power supply output cathode Vo+ with the positive pole of filter capacitor C1, described output voltage sample circuit is made up of resistance R 1 and R2, one end of resistance R 1 is connected with power supply output cathode Vo+, the tie point of resistance R 1 and R2 is connected with the input end of the control IC of Switching Power Supply, it is characterized in that: be provided with the output current sample circuit, the resistance R 1 of its output terminal and output voltage sample circuit, the R2 tie point is connected with the input end of Switching Power Supply control IC together simultaneously.

2, constant-current control circuit according to claim 1, it is characterized in that: described output current sample circuit comprises current transformer M1, the current signal current rectifying and wave filtering circuit, isolating diode D5 and current-limiting resistance R4, the end of the primary coil N4 of described current transformer M1 is connected with high-frequency transformer TR one output terminal, its other end is connected with commutation diode D1 or D2, the secondary coil N5 of the input end of current signal current rectifying and wave filtering circuit and current transformer M1, N6 is connected, its output terminal is connected with the positive pole of isolating diode D5, the end of current-limiting resistance R4 is connected with the negative pole of isolating diode D5, its other end and output voltage sample circuit resistance R 1, the R2 tie point connects and receives simultaneously the control IC input end of Switching Power Supply.

3, constant-current control circuit according to claim 2, it is characterized in that: described current signal current rectifying and wave filtering circuit is by full wave rectifier D3, D4 and pull-up resistor R3, filter capacitor C2 forms, the positive pole of described diode D3 is connected with the end of the secondary coil N5 of current transformer M1, the positive pole of diode D4 is connected with the end of another secondary coil N6 of current transformer M1, twice level coil N5, the tie point of N6 be connected publicly, diode D3, the negative pole of D4 joins afterwards and pull-up resistor R3 one end, filter capacitor C2 positive pole is connected, the pull-up resistor R3 other end, filter capacitor C2 negative pole connects public ground simultaneously.

4, constant-current control circuit according to claim 2, it is characterized in that: described current signal current rectifying and wave filtering circuit is made up of half-wave rectifier D3 and pull-up resistor R3, filter capacitor C2, the end of described current transformer M1 secondary coil N5 is connected with the positive pole of diode D3, its other end be connected publicly, the negative pole of diode D3 is connected with pull-up resistor R3, filter capacitor C2 positive pole, and the pull-up resistor R3 other end, filter capacitor C2 negative pole connect public ground simultaneously.

5, constant-current control circuit according to claim 2, it is characterized in that: described current signal current rectifying and wave filtering circuit is made up of bridge rectifier BD and pull-up resistor R3, filter capacitor C2, the input end of described bridge rectifier BD is connected with the two ends of the secondary coil N5 of current transformer M1 respectively, bridge rectifier BD exports negative terminal and is connected publicly, bridge rectifier BD output plus terminal is connected with pull-up resistor R3, filter capacitor C2 positive pole, and the pull-up resistor R3 other end, filter capacitor C2 negative pole connect public ground simultaneously.