Patent ID: 9084318
Filing Date: 2015-07-14
Classification: H05B

Abstract:
1. A primary-side controlled switch-mode power supply controller for driving LED with constant current, comprising: a multiplier circuit, configured to receive a signal indicative of an instantaneous input AC voltage, and output a reference voltage signal, wherein the reference voltage signal is in direct proportion with the instantaneous input AC voltage; a zero-crossing detection circuit, configured to receive an auxiliary winding signal, detect a conduct time of a freewheeling diode at a secondary side, and output a zero-crossing detection signal; a turn-on signal control circuit, configured to receive the zero-crossing detection signal output by the zero-crossing detection circuit and the reference voltage signal output by the multiplier circuit, control a ratio of the conduct time of the freewheeling diode at the secondary side to a switching cycle of a power switch such that the ratio is in direct proportion to the reference voltage signal output by the multiplier circuit, calculate the switching cycle of the power switch so as to control the moment when the power switch starts to turn on, and output a turn-on signal for the power switch; a comparator circuit, configured to sample a peak current at the primary side of a transformer of the switch-mode power supply and compare the peak current with the reference voltage signal, wherein when a voltage sampled from the peak current at the primary side equals the reference voltage signal output by the multiplier circuit, the comparator circuit is configured to output a turn-off signal for the power switch; and a trigger circuit, configured to receive an output control signal from the turn-on signal control circuit and a signal output from the comparator, and output a first driving signal to a driving circuit; the driving circuit, configured to receive the first driving signal from the trigger circuit, wherein when the output from the comparator is the turn-off signal for the power switch, the driving circuit controls to turn off the power switch; when the output from the turn-on signal control circuit is the turn-on signal for the power switch, the driving circuit controls to turn on the power switch.