Patent ID: 7800311

Claim:
A power supply unit for supplying a normal voltage that is a fixed voltage to a heater of an electron tube while the electron tube operates in normal mode, comprising: a DC voltage source; an inverter for converting a DC voltage output from said DC voltage source into an AC voltage; a rectifying circuit for rectifying said AC voltage to supply a DC voltage to said heater; a power failure detecting circuit for detecting occurrence of a power failure in said DC voltage source and restoration of the power supply after a power failure; and a control circuit which, when occurrence of a power failure in said DC voltage source in the normal operation mode of said electron tube and restoration of the power supply after a power failure is detected by said power failure detecting circuit, causes said rectifying circuit to supply a voltage higher than said normal voltage to said heater, causes said rectifying circuit to supply said normal voltage to said heater and outputs a control signal to start the operation of said electron tube after a lapse of a predetermined time.