Patent ID: 7675725
Filing Date: 2010-03-09
Classification: G05F

Abstract:
1. A constant voltage output circuit comprising: an output power transistor having a first electrode supplied with electric power from a first input power source; a control circuit supplied with electric power from a second input power source and feeding a control signal to a control electrode of the output power transistor to control driving thereof; an output terminal connected to a second electrode of the output power transistor; and a first protection circuit operating by being supplied with electric power from the first input power source and protecting the output power transistor when a voltage supplied from the first input power source is equal to or higher than a predetermined level, wherein the constant voltage output circuit further comprises: a second protection circuit making the control circuit stop the driving of the output power transistor when the voltage supplied from the first input power source is lower than the predetermined level in order to thereby prevent a current larger than a predetermined level from flowing through the output power transistor.