LED constant current driving system and constant current control circuit thereof

Abstract

The invention discloses a constant current control circuit of an LED constant current driving system. The constant current control circuit includes a voltage control circuit used for selecting a reference voltage and a feedback voltage from a firsts reference voltage, a second reference voltage and load sampling feedback voltages according to control of a PWM control signal and a clock signal, and modulating the reference voltage and feedback voltage to output a regulating voltage signal; a driving signal generating circuit used for comparing the regulating voltage signal and a sawtooth wave signal of a fixed frequency to obtain a driving signal with a varying duty ratio, and the voltage of a load is controlled through the driving signal, so that the current of the load is kept constant. The constant current control circuit provided by the invention overcomes the problem that traditional PWM diming is limited by frequency, also solves the problem of low analog dimming precision, the load sampling feedback voltages are direct voltage signals, variation of PWM dimming signals are embodied through variation of voltage values of the load sampling feedback voltages, the regulation range is relatively wide, and the dimming precision 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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