Control circuit capable of adjusting leading edge blanking time and power supply switching-over system

Abstract

The invention relates to a controlling circuit for adjusting the leading edge shading time, which is applied to a power conversion system. The controlling circuit comprises a changeable charging current generation circuit, a capacitor, a charging and discharging switch coupled with the capacitor, and a first comparator, wherein the changeable charging current generation circuit is used to generate charging current proportionate with the voltage valve of a feedback signal according to the feedback signal; when the power switch of the power conversion system is turned on, the charging and discharging switch is cut off, and when the power switch is cut off, the charging and discharging switch is turned on; the input terminal of the first comparator is connected with the capacitor and the charging and discharging switch, and when the charging voltage of the capacitor reaches the reference voltage of the first comparator, the output signal of the first comparator enables the power conversion system to start the current protection mechanism. The controlling circuit determines the shading time according to the relevant feedback signal of the load size of the output terminal of the power conversion system, so that the overcurrent protection mechanism is not started for the power conversion system within the shading time.

Description

technical field [0001] The invention relates to a control circuit for leading edge blanking time, in particular to a control circuit capable of adjusting the leading edge blanking time and a power conversion system including the control circuit. Background technique [0002] figure 1 A known flyback converter 10 is shown. The pulse modulation (pulsewidth modulation; PWM) control chip 100 outputs a pulse modulation signal VPWM from its output pin (pin) OUT to control the on and off of the power switch 101, so as to convert the input voltage Vin into the output voltage Vout, and in order to avoid The primary side current Ip of the flyback power converter 10 is too large to cause element damage, and the pulse modulation control chip 100 further detects the voltage level Vcs of the current sensing pin CS (Vcs=Rs×Ip, the primary side current Ip flows through the sensing resistor Rs), when Vcs reaches a preset over current protection (over current protection) reference voltage l...

AI Technical Summary

Problems solved by technology

When the pulse modulation control chip 100 enters the intermittent operation mode, if the leading-edge shielding time is too short, the energy sent into the system from the input terminal Vin will be small, so that the frequency of the feedback signal VCOMP presenting an approximate sinusoidal wave will become higher, so that It will cause a high switching loss in the system and make the power saving function of the system worse

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