Controller for non-complementary active clamp flyback converter

Abstract

The invention provides a controller for a non-complementary active clamp flyback converter. The controller comprises a frequency control unit, a pulse width control unit, a sequential control unit anda driving unit, uses a multi-mode control mode, and further comprises a wave peak detecting unit and a mode a determining unit. The wave peak detecting unit detects the peaks of an oscillating voltage at the drain end of a main switching tube, and turns on a clamp tube at the troughs in the non-complementary mode of the converter. The turning off of the clamp tube is determined by internally setturn-on time. The mode determining unit, according to feedback voltage FB, gives a mode switching signal to the sequential control unit according to a mode determining result signal. By using a DCM mode, the controller prevents the clamp tube from being turned on, reduces the peak-to-peak value of the excitation current when entering a frequency hopping mode, avoids audio noise, and optimizes no-load power consumption. Since the comparison process of the mode conversion is provided with a long time delay, the influence of mode switching on a converter control loop is reduced.

Description

technical field

[0001] The invention relates to an active clamp flyback converter, in particular to a controller of a non-complementary active clamp flyback converter. Background technique

[0002] Flyback converters are widely used in small and medium power off-line switching power supplies due to their low cost and simple topology. In the actual working process, the energy of the primary side of the flyback converter cannot be completely transferred to the secondary side, and the energy left on the primary side is resonated at the switching node, that is, the drain end of the main switching tube, through the leakage inductance and the parasitic capacitance of the switching node. Very high voltage spikes. In order to reduce the voltage stress of the switch tube, a snubber circuit is needed. Conventional snubber circuits include RCD clamping circuits, LCD clamping circuits and active clamping circuits. Among them, the active clamping circuit adds an additional clamping tub...

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