Mixed light dimming circuit and mixed light dimming method used for LED

Abstract

The invention discloses a mixed light dimming circuit and mixed light dimming method used for an LED. When the duty ratio of an external first light dimming signal is larger than or equal to a preset value N, light dimming is performed in an amplitude light dimming mode; when the duty ratio of the first light dimming signal is smaller than the preset value N, the duty ratio of the first light dimming signal is converted through a duty ratio conversion circuit so that a second light dimming signal can be acquired, and then light dimming is performed in an ON-OFF light dimming mode. According to the mixed light dimming method, when a PWM1 light dimming signal is large in duty ratio, light dimming precision is good, output current has light fluctuation, output current is adjusted in an ON-OFF light dimming mode by means of conversion under the condition that the duty ratio of the PWM1 light dimming signal is very small, and therefore the light dimming depth can be increased.

Description

technical field [0001] The invention relates to the field of LED dimming, and more particularly, to a hybrid dimming circuit and a hybrid dimming method. Background technique [0002] LED lights have the characteristics of small size, high mechanical strength, low power consumption, long life, easy adjustment and control, and no pollution. It is a new type of light source product with great development prospects. There are different requirements for dimming of LED lights in different occasions. In order to adapt to different occasions, the requirements for dimming of LED lights are generally: good linearity, wide dimming range, high stability, high power factor, Low electromagnetic interference, low cost, etc., so LED drivers with excellent dimming performance are very important. [0003] The traditional LED dimming usually has an amplitude dimming method. The principle is: the PWM dimming control signal is input into the control chip through the pins, and the control chip ...

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Problems solved by technology

[0004] However, the disadvantages of the above-mentioned dimming method are: 1) Due to the inherent bias of the operational amplifier, there is a fixed deviation (assuming 20mV) between the current feedback signal and the reference amplitude signal. When the duty cycle D is very small, the proportion is very large (for example, the reference voltage signal Vreference=1V, then when the duty cycle D of the PWM dimming control signal is 5%, the obtained reference amplitude signal is: D×Vreference= 50mV, 20mV has a large proportion to 50mV), that is, the accuracy of the lowest point of dimming is very poor

[0005] 2) Due to the large bias of the op amp, the dimming depth cannot generally be made very low. At this time, the output current is still relatively large, and the brightness of the LED light cannot be made very dim.

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