Patent ID: 7009368
Filing Date: 2006-03-07
Classification: H02M

Abstract:
1. An apparatus comprising: a d.c. power source; a booster coil in which an electric current flows from the d.c. power source; a switching transistor for turning on and off a flow of the electric current in the booster coil thereby to store electric energy and boost a voltage supplied form the d.c. power source; a current detection circuit for detecting an electric current flowing in the switching transistor and turning off the switching transistor when the detected current reaches a predetermined level; an off-period control circuit for variably controlling an off-period of the switching transistor after the switching transistor is turned off; and a back-up circuit, connected to the booster coil, for storing the boosted voltage as an output voltage, wherein the off-period control circuit varies the off-period in accordance with a voltage difference between the output voltage and a predetermined reference voltage.