Dimming Control Circuit for LEDs

Posted on Feb 7, 2014

A dimming control circuit generates a dimming control signal for determining brightness of at least one light-emitting diode. The dimming control signal has a plurality of bright-dark cycles, each of which consists of a bright phase and a dark phase. The bright phase starts with an adaptive rising portion. The adaptive rising portion restricts the

Dimming Control Circuit for LEDs
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brightness of the at least one light-emitting diode to increase gradually from zero. The present invention relates to a dimming control circuit and, more particularly, to a dimming control circuit applied to a drive circuit for driving light-emitting diodes. FIG. 1 is a circuit diagram showing a conventional light-emitting diode drive circuit 10. In the example of FIG. 1, the light-emitting diode drive circuit 10 is implemented by a boost-type switching voltage regulator for converting an input voltage V. sub. in into an output voltage V. sub. out desired for driving one or more series-connected light-emitting diodes LED. In accordance with a current I. sub. L flowing through an inductor L and a feedback voltage V. sub. fb from a resistor R, a switching control circuit 11 generates a fixed-duty pulse drive signal FS for turning on/off a switching transistor Q. The duty ratio of the switching transistor Q determines the proportional relationship between the output voltage V. sub. out and the input voltage V. sub. in. The brightness of the light-emitting diodes LED varies depending on the diode current I. sub. LED flowing through themselves. From FIG. 1 is derived an equation regarding to the diode current I. sub. LED: I. sub. LED=V. sub. fb/R=(V. sub. out-N*V. sub. d)/R, where N is the number of the light-emitting diodes and V. sub. d is a voltage drop of one single conductive light-emitting diode. Since the voltage drop V....

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