CN2842869Y - Constant voltage-current charging circuit - Google Patents

Abstract

The utility model discloses a constant voltage and constant current charging circuit, which utilizes a constant voltage circuit composed of a photocoupler commonly used in switching power supplies and a voltage stabilizing element, and adds a current sampling resistor on the positive polarity side of the secondary pole winding of a transformer. The original photocoupler achieves the purpose of constant current charging control, and achieves the charging control function of constant voltage and constant current through function combination and reuse with the least discrete components. Compared with the prior art, the utility model has the characteristics of fewer discrete elements and simple circuit structure.

Description

A constant voltage constant current charging circuit

technical field

The utility model relates to a charging circuit.

Background technique

The existing constant voltage and constant current charging circuit, such as a constant voltage switching power supply disclosed in Chinese utility model patent 01201433.8, includes an input rectification and filter circuit, a transformer, a secondary rectification and filter circuit, a surge voltage absorption circuit and a self-excited Oscillating circuit, the surge voltage absorbing circuit is connected in parallel at both ends of the primary winding of the transformer, the self-excited oscillating circuit is composed of the primary winding of the transformer, primary and secondary control circuits, the primary control circuit includes the power switch tube and its control circuit, and the power switch tube The output is connected to the primary winding in series, and the photoelectric signal output of the light-emitting tube of the photoelectric coupler in the secondary control circuit is the signal input of the receiving tube of the photocoupler in the primary control circuit. In this constant-voltage constant-current charging circuit, the current-limiting resistor is connected to the negative side of the secondary winding of the transformer, and the current-limiting control circuit is composed of a triode, two resistors and the current-limiting resistor. The discrete components used More, the circuit structure is more complicated.

Utility model content

The purpose of the utility model is to provide a constant voltage and constant current charging circuit with fewer discrete components and a simpler circuit structure.

The technical scheme of the utility model is as follows: a constant voltage constant current charging circuit, including input rectification and filter circuit, transformer, secondary rectification and filter circuit, surge voltage absorption circuit and self-excited oscillation circuit, surge voltage absorption The circuit is connected in parallel at both ends of the primary winding of the transformer TR1. The self-excited oscillation circuit is composed of the primary winding of the transformer TR1, the primary control circuit and the secondary control circuit. The primary control circuit includes the power switch tube Q1 and its resistors R4-R10, capacitor C2- C4, diode D6, photocoupler PH1B and triode Q2 are used to control the control circuit of the power switch tube Q1, the output of the power switch tube Q1 is connected in series with the primary winding of the transformer TR1; the secondary control circuit is equipped with a photocoupler PH1A , resistor R19 and the constant voltage control circuit formed by connecting the voltage regulator circuit, the photoelectric signal output of the photocoupler PH1A in the secondary control circuit is the signal input of the photocoupler PH1B in the primary control circuit; the positive terminal of the photocoupler PH1A is connected to One end of the current sampling resistor RA, and the other end of the current sampling resistor RA are connected to the negative terminal of the photocoupler PH1A through the resistor R17.

It also includes a charging indication circuit composed of charging indicator lights LED-R, LED-G, triode QA and resistors R11 and R13.

The voltage stabilizing circuit is composed of resistor R18, resistor R19, resistor R20, resistor R21, resistor R22, resistor R15, capacitor C6, resistor R23 and regulator IC2.

The utility model utilizes a constant voltage line composed of a photocoupler and a voltage stabilizing element commonly used in switching power supplies, and adds a current sampling resistor on the positive side of the secondary pole winding of the transformer, and uses the original photocoupler to achieve constant current charging control. The purpose is to achieve the charging control function of constant voltage and constant current through function combination and reuse with the least discrete components. Compared with the prior art, the utility model has the characteristics of fewer discrete elements and simple circuit structure.

Description of drawings

Fig. 1 is the circuit diagram of the utility model.

Detailed ways

The utility model is a constant voltage and constant current charging circuit, as shown in Figure 1, it contains a fuse FU1, adjustable resistance VR1, rectifier bridge D1-D4, resistance R1, inductance L1 and capacitance EC1, EC2 composed of input rectification and Filter circuit; a surge voltage absorbing circuit composed of resistors R2, R3, capacitor C1 and diode D5; transformer TR1; a receiving tube PH1B and triode composed of resistors R4-R10, capacitors C2-C4, diode D6, photocoupler A primary control circuit composed of Q2 for controlling the power switch tube Q1; a secondary rectification filter circuit composed of capacitors C5, C5. The constant voltage control circuit is connected with the voltage stabilizing circuit. The voltage stabilizing circuit is composed of resistor R18, resistor R19, resistor R20, resistor R21, resistor R22, resistor R15, capacitor C6, resistor R23 and voltage regulator IC2; the photocoupler The positive terminal of the light-emitting tube PH1A is connected to one terminal of the current sampling resistor RA, and the other terminal of the current sampling resistor RA is connected to the negative terminal of the photocoupler PH1A through the resistor R17; one is composed of the charging indicator LED-R, LED-G, triode The charging indication circuit composed of QA and resistors R11 and R13; the output of the secondary control circuit is provided with a filter circuit composed of resistor R16 and capacitor EC4, and the two ends of the secondary winding of transformer TR1 are connected in parallel with voltage regulator ZD1 as output overvoltage protection , to prevent excessive output voltage.

Constant voltage output: When the charging voltage output by the transformer TR1 is too high, the light-emitting tube PH1A of the photocoupler turns on and emits light, and the receiving tube PH1B of the photocoupler receives the light signal and also turns on, so that the triode Q2 turns on and controls the power switch The tube Q1 turns off the output, and the output voltage of the transformer TR1 decreases; when the charging voltage output by the transformer TR1 is too low, the light-emitting tube PH1A of the photocoupler is not turned on, and the receiving tube PH1B of the photocoupler is not turned on, so the triode Q2 If it is not conducting, the power switch tube Q1 is conducting, and the output voltage of the transformer TR1 rises, so that the cycle control achieves the purpose of constant voltage control.

Constant current output: When the charging current flows through the current sampling resistor RA, a voltage will be generated at both ends of the upper resistor RA. When the output charging current becomes larger, the voltage generated by the resistor RA will become larger, triggering the light-emitting tube PH1A of the photocoupler to conduct Lighting, the receiving tube PH1B of the photocoupler receives the light signal and is also turned on, so that the transistor Q2 is turned on, and the power switch tube Q1 is controlled to turn off the output, so that the output charging current is reduced; when the output charging current is small, the voltage at both ends of the resistor RA It is not enough to drive the light-emitting tube PH1A of the optocoupler, and the receiving tube PH1B of the optocoupler has no signal input, so the triode Q2 is not turned on, and the power switch tube Q1 is controlled to be in the on state, so that the output charging current increases. Constant current control purpose.

Charging indication: When the charging current flows through the current sampling resistor RA, a voltage will be generated at both ends of the upper resistor RA. When charging normally, the charging current is larger, the voltage on the current sampling resistor RA is larger, and the triode QA is turned on, so that there is The current flows through the charging indicator LED-R, and the charging indicator LED-R lights up, indicating that it is in the charging state; when fully charged, the current flowing through the current sampling resistor RA becomes smaller, and the voltage across the current sampling resistor RA is not enough The driving transistor QA is turned on, the charging indicator LED-R has no current, and the light is off, indicating that it is fully charged, and the indicator LED-G is always on. If the indicators LED-R and LED-G are red and green lights, the orange light will be on when charging, and the green light will be on when fully charged. This charging indication function is optional and should be set according to the requirements of consumers and cost structure.

Claims (3)

1, a kind of constant voltage constant current charging circuit, comprise input rectifying and filter circuit, transformer, secondary commutation and filter circuit, surge voltage absorbing circuit and self-maintained circuit, surge voltage absorbing circuit is connected in parallel on the two ends of the elementary winding of transformer TR1, self-maintained circuit is by the elementary winding of transformer TR1, elementary control circuit and secondary control circuit are formed, elementary control circuit comprises power supply switch tube Q1 and by resistance R 4-R10, capacitor C 2-C4, diode D6, the control circuit that is used to control power supply switch tube Q1 that photoelectrical coupler PH1B and triode Q2 constitute, the elementary winding of the output series transformer TR1 of power supply switch tube Q1; Secondary control circuit is provided with the constant-voltage control circuit that is connected and composed by photoelectrical coupler PH1A, resistance R 19 and voltage stabilizing circuit, and the photosignal of photoelectrical coupler PH1A is output as the signal input of photoelectrical coupler PH1B in the elementary control circuit in the secondary control circuit; It is characterized in that: the positive ends of photoelectrical coupler PH1A connects the end of current sampling resistor RA, and the other end of current sampling resistor RA is connected to the negative polarity end of photoelectrical coupler PH1A by resistance R 17.

2, a kind of constant voltage constant current charging circuit according to claim 1 is characterized in that: also comprise the charging indication that is made of charging indicator light LED-R, LED-G triode QA and resistance R 11, R13.

3, a kind of constant voltage constant current charging circuit according to claim 1 is characterized in that: above-mentioned voltage stabilizing circuit is made of resistance R 18, resistance R 19, capacitor C 6, resistance R 23 and voltage-stabiliser tube IC2.

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