Patent ID: 8659238

Claim:
A power supply comprising: a filter operable to prevent high frequency current from entering input voltage source; a protection operable to protect the power supply at over current condition; a bridge rectifier operable to rectify an alternating current (AC) voltage and generate a DC input voltage; a converter to convert an input voltage to an output voltage for an output device with constant power; a controller operable to adjust on time of main switch in the converter to keep output at constant power, the controller comprising: (i) a signal process circuit operable to generate a power feedback signal as multiplication product of voltage feedback signal and current feedback signal; (ii) a reference operable to set a voltage signal proportional to a predetermined power level; (iii) an opamp operable to compare power feedback signal with a reference signal and generate a power error signal with gain; (iv) a saw tooth generator operable to generate a saw tooth signal; (v) a comparator operable to compare power error signal with saw tooth signal and generate a pulse; and (vi) a driver operable to control on time of the main switch of the converter to keep output at constant power; a voltage feedback circuit operable to sample output voltage and send the voltage feedback signal proportional to output voltage back to the controller; and a current feedback circuit operable to sample output current and send the current feedback signal proportional to output current back to the controller.