Dimming control circuit, control chip, power conversion device and dimming method

Abstract

The invention relates to a dimming control circuit, a control chip of a switching power supply, a power conversion device for driving an LED, and a dimming method. The dimming control circuit is used for controlling the output of a low-PF switching power supply, the switching power supply comprises a power switch, the received input voltage comprises a power frequency component, and the dimming control circuit comprises a low-pass filtering module and an output current modulation module, wherein the low-pass filtering module is connected with a PWM dimming signal and a sampling signal, generates a filtering modulation voltage and outputs the filtering modulation voltage, the output current modulation module is electrically connected with the low-pass filtering module, the switching power supply is modulated by using the filtering modulation voltage output by the low-pass filtering module at least in a DCM mode, and when the input voltage is changed due to ripple waves of power frequency components, in a plurality of switching periods under the current PWM dimming signal, the average current value output by the switching power supply corresponding to each switching period is not changed. By utilizing the dimming control circuit, ripples introduced by power supply input voltage can be suppressed, and stroboflash can be eliminated.

Description

technical field [0001] The invention relates to the field of electronic circuits, in particular to a dimming control circuit, a control chip, a power conversion device and a dimming method. Background technique [0002] LED has the advantages of small size, high brightness, low power consumption, less heat generation, long service life and rich and colorful colors, and has been widely used in many fields such as lighting and display. At present, in LED driving, a switching power supply with low power factor (for example, less than 0.7) is often used to drive the LED to work, wherein, the power switch is periodically turned on / off to obtain a stable output on the load. In order to adjust the brightness of the load LED, the on / off of the power switch is controlled by a dimming control circuit. [0003] Among many LED dimming technologies, PWM dimming has been widely researched and applied because of its high efficiency, long-distance transmission support, and strong compatibi...

AI Technical Summary

Problems solved by technology

[0004] 1. Dimming dead zone problem, this problem is especially obvious when the PWM dimming signal is used to directly chop the output current. It is observed that if the falling edge of the PWM dimming signal happens to be within the off time of the power switch, the PWM duty The change of the ratio has no effect on the switch of the power switch, that is, the PWM dimming signal at this position has no effect on the output current, resulting in a step-shaped part (called dimming dead zone) on the cycle variation curve of the output current with the dimming signal. affect user experience;

[0005] 2. The problem of stroboscopic flicker. The research found that when the PWM dimming signal is used to directly chop the output current for dimming, the current on the load LED has a ripple whose frequency is the frequency of the PWM dimming signal. After RC filtering and then input to the control chip to avoid the dead zone of dimming, but because the input load voltage is usually obtained by direct rectification and filtering of AC voltage, the output current often has power frequency ripple, so there is still a flicker problem

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