An adaptive startup circuit suitable for primary feedback flyback converter

Abstract

The invention relates to an adaptive starting circuit suitable for a primary side feedback flyback converter, belonging to the technical field of switching power supply. The negative input terminal ofthe error amplifier is connected with a primary side inductor current limit signal proportional to the output voltage of the primary side feedback flyback converter, the positive input terminal thereof is connected with a reference voltage, and the output terminal thereof is connected with the negative input terminal of the first comparator; A forward input terminal of the first comparator is connected with a sawtooth wave signal, and an output terminal of the first comparator outputs a pulse width modulated signal. The positive input terminal of the second comparator is connected with the primary inductor current limiting signal, the negative input terminal is connected with the primary inductor current peak signal, and the output terminal outputs the current limiting judgment signal after passing through the latch. A logic module generate an output signal according to that pulse width modulation signal and the current limit judgement signal for controlling the on / off of the switch transistor in the primary side feedback flyback converter. The invention can self-adaptively adjust the starting speed of the primary side feedback flyback converter and ensure that the primary side feedback flyback converter always works in 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 inductor 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 serie...

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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