Patent ID: 6703796
Filing Date: 2004-03-09
Classification: H05B

Abstract:
A power supply for a system with a lamp, comprising:a rectifier/filter, having an input terminal for connecting to an external alternating current (AC) power source so as to convert the input AC voltage into a direct current (DC) voltage, and an output terminal for outputting the DC voltage; a DC-DC converter, connected to the output terminal of said rectifier/filter for reducing the DC voltage to a rated DC voltage output to power the system except for the lamp; a DC-AC inverter, connected to the output terminal of said rectifier/filter for converting the DC voltage into an AC voltage output to power the lamp; and wherein said DC-AC inverter further comprises: two switches, having a common output terminal and respectively having a control input terminal; a driving circuit, electrically coupled to the respective control input terminals of the two switches, for alternatively turning on the two switches; a transformer, having a primary side electrically coupled to the common output terminal of the two switches and a secondary side electrically coupled to the lamp; a sampling circuit, electrically coupled to the lamp, for detecting the current value through the lamp and outputting a feedback signal; a modulation control circuit, electrically coupled to the sampling circuit and the driving circuit, for controlling the driving circuit according to the feedback signal; a voltage detection circuit with an input terminal, for outputting a control signal according to the voltage amplitude at the input terminal; and an impedance adjustment circuit, electrically coupled to the voltage detection circuit and the transformer, for adjusting the equivalent impedance value of the impedance adjustment circuit according to the control signal.