Patent ID: 6130826
Filing Date: 2000-10-10
Classification: H02M

Abstract:
A switching power supply, comprising:a power conversion circuit for converting power supplied from a primary power supply to power a load and further comprising an auxiliary power supply;a control circuit for controlling operation of said power conversion circuit; andan auxiliary power supply circuit for supplying power to said control circuit by conducting a switching operation to supply power from said primary power supply during initialization, and to supply power from said auxiliary power supply during steady-state operation,wherein said auxiliary power supply circuit comprises:a fixed bias circuit for forming a first bias voltage from a voltage across said primary power supply and a second bias voltage having a voltage higher than said first bias voltage;a second transistor for making said first bias voltage an operation starting voltage; anda first transistor connected in series to said second transistor for making said second bias voltage an operation starting voltage;wherein said auxiliary power supply is connected to a connection point of said first transistor and said second transistor; andwherein, when a voltage difference between said second bias voltage and an output voltage of said auxiliary power supply becomes equal to or less than a switching voltage, power is supplied from said auxiliary power supply to said control circuit through said second transistor.