Constant voltage constant current control circuit and control method thereof

Abstract

The invention relates to a constant voltage constant current control circuit and a constant voltage constant current control method thereof, and is applied to a flyback converter. The constant voltage constant current control circuit generates a constant voltage/constant current control signal according to an output voltage feedback signal and an output current feedback signal to control the duty ratio of a switching signal of a main switching tube in the flyback converter and further ensure that the output voltage or output current of the flyback converter is kept constant. A circuit coupling control scheme is adopted, and then constant voltage or constant current control can be realized only by one capacitor, so that the constant voltage constant current control circuit has a simple structure; and moreover, the output voltage feedback signal which precisely represents the output voltage information of a secondary side and the output current feedback signal which precisely represents the output current information of the secondary side can be obtained by a voltage feedback circuit and a current feedback circuit, so that the constant voltage constant current control circuit is high in accuracy.

Description

technical field [0001] The present invention relates to the field of switching power supplies, more specifically, to a constant voltage and constant current control circuit and a control method thereof. Background technique [0002] With the rapid development of the power supply industry, the application of switching power supplies using constant voltage and constant current control is becoming more and more extensive, and its design requirements for control circuits are also getting higher and higher. the greatest goal pursued. [0003] figure 1 Shown is a conventional constant voltage and constant current control device of a flyback converter controlled by the secondary side, which adjusts the output voltage and output current through a sampling resistor, an optocoupler 101 and a secondary side feedback control circuit 102 control, the sampling resistor (including voltage sampling resistor and current sampling resistor) is used to sample the secondary output voltage and ...

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Problems solved by technology

[0005] the above figure 2 Although the constant voltage and constant current control device shown in is reduced in size and cost, but in the working process of the flyback converter, when the secondary winding N S discharged to zero current, the auxiliary winding N T The coupled voltage on will drop sharply, therefore, by the auxiliary winding N T feedback to obtain the output voltage feedback signal V FB It cannot accurately follow the change of the actual converter output voltage, and may even have a large deviation, resulting in inaccurate feedback control

In addition, the implementation of the existing integrated circuit control unit is relatively complicated. For example, its constant voltage control loop and constant current control loop still need external compensation circuits for control and adjustment, and there are many circuit components.

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