| 摘要 |
PURPOSE:To lower a black level and to obtain a higher contrast by providing a start voltage control circuit in a start voltage impressing circuit and maintaining the start voltage lower during the period when video signals are sent than during a start delay period. CONSTITUTION:An AC power source AC is boosted by using a boosting transformer TR and a voltage multiplying rectifier is connected via a switching element S 4 controlled by the start voltage control circuit 6 to the output of the boosting transformer TR. Capacitors C 1, C 2 are connected respectively at one end to one end of the switching element S 4. A pair of diodes D 1, D 2 are connected at one end respectively in opposite directions to the other end of the output of the boosting transformer TR. DC high-voltage sources are obtd. between the connection points of the capacitor C 1 and the diode D 1 and the connection points of the capacitor C 2 and the diode D 2. The start voltage control circuit 6 is constituted by building two timer circuits therein and the switching element S 4 is controlled by the output thereof and is so operated that the switching element S 4 is turned off only between the time T0 and the time t2. |
