A circuit and corresponding method for reducing standby power and improving no-load to full-load regulation for ringing choke converters by maintaining a reduced duty cycle, with longer off time at no-load, while maintaining the output voltage swing closer to the full-load level. This reduced duty cycle prevents the output voltage from swinging high with respect to the full-load level, thereby providing good no-load and full-load output regulation in open feedback loop systems. The circuit and method provides very low no-load switching frequency and duty cycle by increasing the off time of the main switch through use of a turn off transistor driven by a zener diode, thereby maintaining conduction even with a very small control current and prolonging the off time of the main switch. The circuit and method achieves the benefits preferably using only less costly basic discrete converter components instead of more costly integrated circuits.
CROSS REFERENCE TO RELATED APPLICATION
This application claims the benefit of U.S. Provisional Application No. 60/491,176, filed Jul. 29, 2003, which is incorporated by reference herein.
A power factor correction circuit used for regulating the phase of a DC current outputted from a rectifier unit in a power supply includes an energy inductor, an output diode, a switch unit, a pulse width modulation unit, a sensing resistor, and a converter transformer. The converter transformer utilizes the DC current outputted from the rectifier unit to generate an induced current, which will pass through the two ends of the sensing resistor to produce a reference voltage, thereby the pulse width modulation unit can produce the duty cycle for the switch unit according to the reference voltage, so that the switch unit can regulate the phase of the DC current through controlling the flowing direction of the DC current.
