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.