PWM dimming circuit used for high-power-factor primary-side-feedback LED driving power supply

Abstract

The invention discloses a PWM dimming control circuit used for a high-power-factor primary-side-feedback LED driving power supply. The PWM dimming control circuit comprises a voltage reference generation unit, a PWM processing unit, a current sampling unit, an error amplification unit, a constant current control unit, a zero-crossing detection unit, a transformer secondary winding idle time control unit and a logical and driving unit, wherein the transformer secondary winding idle time control unit is used for controlling the duration of the transformer secondary winding idle time in PWM dimming to output a signal for controlling conduction of a power switch tube; and the logical and driving unit is used for performing logical control on the constant current control unit and the output signal of the transformer secondary winding idle time control unit, so as to further drive the power switch tube and control the transformer secondary winding idle time control unit.

Description

technical field [0001] The invention relates to a PWM dimming circuit, in particular to a PWM dimming circuit used for a high power factor primary side feedback LED driving power supply. Background technique [0002] With the development of LED driving power and the requirements of green energy saving and environmental protection, LED driving power generally has a dimming function at present. Among various dimming methods, PWM dimming is the most common and abundant one. The PWM dimming circuit of the LED drive power supply uses the PWM signal output by the external MCU to control the output current of the LED drive power supply, thereby adjusting the brightness of the LED to achieve the purpose of PWM dimming. [0003] For the high power factor primary side feedback LED drive power supply, in terms of PWM signal control of the output current of the LED drive power supply, the traditional solution is to convert the PWM signal output by the external MCU into a corresponding ...

AI Technical Summary

Problems solved by technology

[0006] The traditional PWM dimming circuit used for high power factor primary side feedback LED driving power has the following disadvantages: the traditional PWM dimming circuit increases the duty cycle of the LED driving power with the decrease of the duty cycle of the PWM signal during the dimming process. working frequency

As a result, PWM dimming has poor dimming linearity at low duty ratios, thus limiting the range of PWM dimming duty ratios

[0007] In the design of high power factor primary side feedback LED drive power supply that pays attention to cost and pursues high-quality PWM dimming performance, this traditional PWM dimming control circuit has more and more limitations.

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