| 摘要 |
PURPOSE:To obtain a satisfactory regulation characteristic even to the video signal of any horizontal scanning frequency by providing a control circuit to control a first voltage regulator so as to always set voltage difference between a third direct current voltage and a second direct current voltage constant as prescribed when the beam current of a cathode ray tube is fixed by adjusting the second direct current voltage even when the various horizontal synchronizing signals of different frequencies are applied. CONSTITUTION:The control circuit of a potential drop type switching regulator 6 (the first voltage regulator) is composed of a monostable multivibrator 1, pulse driving circuit 3, horizontal synchronizing signal detection circuit 8 and switch 9. The pulse width of a pulse outputted from the monostable multivibrator 1 is decided by the time constants of a capacitor C1 and of resistors R12 and R13. The horizontal synchronizing signal detection circuit 8 detects the frequency (horizontal scanning frequency fH) of an incoming horizontal synchronizing signal, and when the horizontal scanning frequency fH is 35kHz-24kHz, the switch 9 is short-circuited. Thus, the value of voltage difference HB2-HB3 between the input and output of a series regulator 7 (second voltage regulator) can be set at a prescribed constant value 40V in a TV mode and an HDTV mode. |
