Patent ID: 6011365
Filing Date: 2000-01-04
Classification: H04N

Abstract:
An electromagnetic focus apparatus comprising:a focus coil;a power source for supplying power to said focus coil;a switching circuit having a plurality of switches for supplying power from said power source to said focus coil on the basis of various combinations of ON/OFF-timings of the plurality of switches, and for regenerating electric current from said focus coil to said power source;data setting means for setting a timing at which plurality of switches of said switching circuit are controlled;switch controlling means for controlling said plurality of switches in synchronization with horizontal synchronization signals on the basis of the timing set by the data setting means;a current detecting resistor, the current detecting resistor intervening between said focus coil and said power source, the current detecting resistor detecting the current flowing into the focus coil; andcurrent interrupting means, the current interrupting means comparing a current value detected by said current detecting resistor with a reference value, the current interrupting means forcibly turning off a line switch, which supplies the current to said focus coil, when said detection current value exceeds said reference value, whereinan electric current linearly increasing in proportion to time flows to said focus coil in a case of applying a constant voltage to said focus coil.