| 摘要 |
PURPOSE:To equal approximately brightness on the surface of a color cathode ray tube ad amplitude of a scan line even when a variety of horizontal synchronizing signal frequencies lies by setting such that the electrostatic capacity of a horizontal blanking capacitor is increased as the frequency of the horizontal synchronizing signal drops and a high output voltage is set approximately constant. CONSTITUTION:Plural serial circuits composed of, for instance, two capacitors 49 and 50 and connection switches 48a and 48b are connected in parallel to the horizontal blanking capacitor 43b. A voltage from a frequency-voltage conversion circuit 31 is supplied to a comparator circuit for binary comparison 54, and a comparison output corresponding to respective ranges where frequencies of horizontal synchronizing signals are <=about 20kHz, 20kHz-27.5kHz and >=27.5kHz is formed. The output signal of the comparator circuit 54 controls a switch circuit 48 composed of the connection switches 48a and 48b. Namely, when the frequency of the horizontal synchronizing signal is >=27.5kHz, the switches 48a and 48b are turned off. The switches 48b and 48a are turned on and off when the frequencies are 20kHz-27.5kHz and <=20kHz, respectively. |
