CONTROL CIRCUIT AND METHOD OF A LED DRIVER

摘要

A control circuit of a LED driver utilizes a counter to acquire a cycle and a conduction time or a non-conduction time of an AC phase-cut voltage outputted by a TRIAC dimmer. A bleeding signal is determined according to the cycle and the conduction time or the non-conduction time and used for adjusting a bleeding current so as to avoid a flickering of the LED. The control circuit does not need extra pins for coupling a large capacitor, but the bleeding signal can be still acquired. Preferably, the present invention is suitable for an IC of low pin numbers.

主权项

1. A control circuit of an light emitting diode (LED) driver which is including a triode alternating current dimmer configured to operably receive an alternating current (AC) voltage and output an AC phase-cut voltage with an adjustable conduction angle, a rectifier configured to operably rectify the AC phase-cut voltage so as to generate a direct current (DC) phase-cut voltage, and a supply voltage capacitor configured to operably provide a supply voltage, the control circuit comprising:
a voltage-to-time circuit configured to operably acquire a conduction time and a non-conduction time of the DC phase-cut voltage; and a time-to-voltage circuit including:
a clock generator configured to operably provide a clock;a first counter coupled to the voltage-to-time circuit and the clock generator, configured to operably count the conduction time or the non-conduction time of the DC phase-cut voltage according to the clock so as to generate a first counting value; a second counter coupled to the voltage-to-time circuit and the
clock generator, configured to operably count a cycle of the DC phase-cut voltage according to the clock so as to generate a second counting value for adjusting a frequency of the clock; and a digital to analog circuit coupled to the first counter, configured to operably convert the first counting value into a bleeding signal so as to adjust a bleeding current, wherein the bleeding current prevents the LED from flickering caused by the DC phase-cut voltage being influenced by a holding current of the triode alternating current dimmer.