| 摘要 |
PURPOSE:To facilitate discrimination of the cause of a fault by providing a circuit to discriminate the presence/absence of a signal to the video signal input terminal of a display, and making an LED radiate when a signal is inputted. CONSTITUTION:After the DC component of an input signal is cut off by a capacitor C1, a DC bias of VA is applied to a video amplifier circuit 1 by means of a resistor R1 and diodes D1-D3. Since a voltage enough to turn on a transistor TR1 is VB=VTR1+VTR2, when the amplitude of an input signal comes to Vin=VB-VA, the transistor TR1 turns on, and a transistor TR2 also turns on simultaneously, thus the LED D5 is turned on. Therefore, when an input signal of a voltage VB-VA is inputted, the LED emits light, the presence of a signal can be confirmed. |
