Flyback converter and constant current control method thereof

Abstract

The invention discloses a flyback converter and a constant current control method thereof. The flyback converter comprises a transformer; a second switch tube, a first capacitor and a first inductor; a first switch tube and a sampling resistor; the control circuit is used for providing a first control signal and a second control signal to respectively control the switching states of the first switching tube and the second switching tube, and the control circuit comprises a first sampling unit used for sampling the voltage at the two ends of the primary winding to obtain a first sampling signal; the feedback unit is used for generating a feedback current signal according to the input voltage, the first sampling signal, and the positive peak voltage and the negative peak voltage at the two ends of the sampling resistor in each switching period, and generating a compensation signal according to the feedback current signal; and the first driving unit is used for controlling the turn-off of the first switching tube according to the compensation signal. Constant current control can be realized on the primary side of the converter, and the converter is high in control precision, low in cost and high in reliability.

Description

technical field [0001] The invention relates to the technical field of switching power supplies, in particular to a flyback converter and a constant current control method thereof. Background technique [0002] Power converters are essential components in electronic systems. In switching power supply applications, isolated converters are widely used, because isolated switching power converters can protect the load from high voltage shock and damage to the input bus, and have a wide range of applications in telecom wireless networks, automobiles and medical equipment. Among the various topologies of isolated converters, because the flyback converter topology does not require an output filter inductor, the circuit structure is simple, the output is isolated, and the cost is low, it occupies a high proportion in the application of terminal equipment. However, the existing traditional flyback converters are gradually not used due to low working efficiency and serious EMI proble...

AI Technical Summary

Problems solved by technology

However, in an active clamp flyback converter, the reference figure 1 , due to the resonance of the transformer leakage inductance Lk and the first capacitor C1, the output diode current of the active clamp flyback converter presents nonlinear changes, and it is difficult to obtain accurate output voltage and output current through the voltage and current signals collected by the primary side Simultaneously owing to realize the zero-voltage turn-on (ZVS) of the first switching tube Q1 of primary side, when the second switching tube Q2 was turned off, the excitation inductor current (denoted as I Lm ) is already a negative value, so from the excitation current I Lm From the point of view, the converter is not working in the critical conduction mode at this time, but in the discontinuous mode

Furthermore, the traditional method of obtaining the zero-crossing signal of the excitation inductor current based on the voltage Vaux at both ends of the auxiliary winding Na, or the drain-source voltage and gate voltage of the first switch tube Q1 is no longer applicable, so the traditional primary-side feedback current The control scheme is less accurate

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