An Adaptive Start-up Circuit for Primary Side Feedback Flyback Converter

Abstract

The invention relates to an adaptive starting circuit suitable for a primary-side feedback flyback converter, which belongs to the technical field of switching power supplies. The negative input of the error amplifier is connected to the primary inductor current limit signal proportional to the output voltage of the primary feedback flyback converter, its positive input is connected to the reference voltage, and its output is connected to the negative input of the first comparator ; The positive input terminal of the first comparator is connected to the sawtooth wave signal, and its output terminal outputs a pulse width modulation signal; the positive input terminal of the second comparator is connected to the primary inductor current limit signal, and its negative input terminal is connected to the primary inductor The current peak signal, the output end of which passes through the latch and then outputs the current limiting judgment signal; the logic module generates an output signal according to the pulse width modulation signal and the current limiting judgment signal to control the opening and closing of the switching tube in the primary side feedback flyback converter broken. The invention can adaptively adjust the start-up speed of the primary-side feedback flyback converter and ensure that it always works in the DCM mode.

Description

technical field [0001] The invention belongs to the technical field of switching power supplies and relates to an adaptive start-up circuit suitable for primary-side feedback flyback converters. Background technique [0002] The primary-side feedback flyback converter has the advantages of natural input and output electrical isolation, no need for optocoupler devices, and easy expansion of multiple outputs. It is a popular product in switching power supplies. In the primary side feedback flyback converter, the degaussing speed of the secondary side inductance depends on the size of the output voltage. During the start-up process, the output voltage rises slowly from zero, causing the degaussing speed of the secondary inductance to be small for a long time, the transformer cannot be completely reset, and the system continues to work in CCM mode (continuous conduction mode), which may lead to system instability , power tube overcurrent damage, sampling voltage error and a ser...

AI Technical Summary

Problems solved by technology

[0005] Aiming at the problems that it is difficult to control the operation in DCM mode during the start-up process of the above-mentioned primary side feedback flyback converter, and the use of off-chip large capacitors in the traditional soft start method consumes too much PCB board area and increases the cost and accuracy is difficult to control, the present invention A self-adaptive start-up circuit suitable for primary-side feedback flyback converter is proposed, without additional design of soft-start, and the start-up speed can be dynamically adjusted according to the output voltage of the primary-side feedback flyback converter, ensuring that the primary-side feedback The exciter always works in DCM mode

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