Patent ID: 8212481
Filing Date: 2012-07-03
Classification: H01J

Abstract:
1. A voltage control apparatus used for an electron tube, which includes at least an anode electrode, a cathode electrode and a helix electrode, comprising: a detecting circuit for detecting a current flowing through the helix electrode; a voltage-limiting circuit for controlling a potential difference between the helix electrode and the anode electrode based on a predetermined voltage level; and a switch for connecting the helix electrode and the anode electrode through the voltage-limiting circuit and causing a short circuit between the helix electrode and the anode electrode based on an output from the detecting circuit, wherein the detecting circuit includes: a direct voltage source for outputting a predetermined direct voltage for turning on the switch when the electron tube performs a normal operation; and a current-detecting resistor for generating a potential difference according to the current flowing through the helix electrode and for decreasing the direct voltage, applied from the direct voltage source to the switch, to be smaller than an operating voltage of the switch based on the potential difference.