JPS5555670A - Input circuit for horizontal synchronizing signal - Google Patents

Abstract

PURPOSE:To prevent the destruction of horizontal output transistor due to noise in horizontal blanking period in advance, by providing the noise suppression means at the direct drive circuit. CONSTITUTION:The noise suppression means 1 is constituted with the AND gate 2, inverter 3, and monostable multi-vibrators 4 and 5. Further, when the horizontal synchronizing signal (a) is fed to the input terminal 13, the both input terminal of the gate 2 is of high level, the monostable multivibrator 4 is triggered to produce the voltage of the waveform (b) at the terminal 14, to turn on the horizontal drive transistor 6 and to produce the drive signal. Further, when the output time of the monostable multivibrator 5 is set with a given condition, this output is fed to the gate 2 via inverter 3, and at the high level time of the voltage at the waveform (c), the gate 2 is closed. Accordingly, the monostable multivibrators 4 and 5 are not triggered with the noise mixed to the input waveform (a). The horizontal output transistor 8 is OFF for the blanking period, but since the output time of the monostable multivibrator 4 is longer than the blanking period, the transistor 8 is not turned on to prevent the destruction due to noise.