Power supply unit, high-frequency circuit system and heater voltage control method

A power supply unit for supplying power to a heater provided for an electron tube, 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 the resultant DC voltage to said heater;
• a current detector for detecting the heater current flowing through said heater;
• and
• a control circuit which, at the time of power activation, determines the rate of change of the current flowing through said heater, said current being detected by said current detector for every predetermined period time, and outputs a control signal that starts the operation of said electron tube when said rate of change becomes equal to or lower than a predetermined threshold.

A heater voltage control method for use in 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;
• and a rectifying circuit for rectifying said AC voltage to supply a DC voltage to said heater, comprising the steps of:
• supplying said heater with a voltage higher than said normal voltage from said rectifying circuit 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;
• and
• supplying said normal voltage from said rectifying circuit to said heater and outputting a control signal for starting the operation of said electron tube after a lapse of a predetermined time.

A heater voltage control method for controlling a voltage to be supplied to a heater provided for an electron tube from a power supply unit 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 the resultant DC voltage to said heater;
• a current detector for detecting the heater current flowing through said heater, comprising the steps of:
• determining the rate of change of said heater current detected at the time of power activation by said current detector, for every predetermined period of time;
• and
• outputting a control signal for starting the operation of said electron tube when said rate of change falls equal to or lower than a predetermined threshold.