A LED constant current drive system and its constant current control circuit

Abstract

The invention discloses a constant current control circuit of an LED constant current drive system. The constant current control circuit includes: a voltage control circuit, used for controlling the voltage between the first reference voltage and the second reference voltage according to the PWM control signal and the clock signal. And the reference voltage and the feedback voltage are selected from the load sampling feedback voltage, and the reference voltage and the feedback voltage are modulated to output an adjustment voltage signal; the driving signal generation circuit is used to perform the adjustment according to the adjustment voltage signal and the fixed-frequency sawtooth wave signal. A driving signal with a changed duty ratio is obtained by comparison, and the voltage of the load is controlled through the driving signal to keep the current of the load constant. The present invention overcomes the frequency-limited problem of traditional PWM dimming, and also solves the problem of low analog dimming accuracy. The load sampling feedback voltage of the present invention is a DC voltage signal, and the change of the PWM dimming signal is reflected in the voltage of the load sampling feedback voltage. The change of the value, the adjustment range is wider, and the dimming accuracy is high.

Description

technical field [0001] The invention relates to the technical field of LED constant current drive, in particular to an LED constant current drive system and a constant current control circuit thereof. Background technique [0002] Now, the energy problem and the environmental protection problem have become the two main problems faced by human beings. LED has many advantages such as high efficiency, low consumption, environmental protection, small size and long life, and has been paid more and more attention in the lighting field. Because LED is limited by its optical and electrical characteristics, it must be supplemented with a dedicated constant current drive circuit to work properly. [0003] At present, in the integrated circuit system, the dimming modes of the LED driving system include PWM digital dimming mode, pure analog voltage dimming mode, and a mode including both PWM digital dimming and analog dimming. However, in the mode including PWM digital dimming and ana...

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Problems solved by technology

[0004] 1. Single dimming mode, PWM digital dimming mode and analog dimming mode, the control mode can only choose one, which has certain limitations;

[0005] 2. The PWM dimming method can only adjust the frequency or duty cycle of the output signal. Although the implementation is relatively simple, it is limited by the frequency. Usually, when the frequency is too high or too low, the dimming effect is poor and the linearity is poor;

[0006] 3. The analog dimming method is greatly affected by the reference voltage, which is affected by factors such as temperature and process on the reference voltage, and the dimming accuracy is low

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