A hybrid dimming circuit and hybrid dimming method for LED

Abstract

The invention discloses a hybrid dimming circuit and a hybrid dimming method for LEDs. When the duty ratio of an external first dimming signal is greater than or equal to a preset value N, amplitude dimming is used for dimming. light; when the duty ratio of the first dimming signal is less than the preset value N, the duty ratio of the first dimming signal is converted by a duty ratio conversion circuit to obtain a second dimming signal, and then Dimming by ON‑OFF dimming. The hybrid dimming method of the present invention has good dimming accuracy when the duty ratio of the PWM1 dimming signal is large, and the output current has no optical fluctuations. When the duty ratio of the PWM1 dimming signal is small, the ON ‑OFF dimming mode to adjust the output current, thereby increasing the depth of dimming.

Description

technical field [0001] The invention relates to the field of LED dimming, and more specifically relates to a hybrid dimming circuit and a hybrid dimming method. Background technique [0002] LED lamp has 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 LED lights in different occasions. In order to adapt to different occasions, the requirements for dimming LED lights generally include: 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] Traditional LED dimming usually has an amplitude dimming method. The principle is: the PWM dimming control signal is input to the control chip through the pin, and the control chip recei...

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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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