This is a video fading circuit. This circuit has signal that is as simple as attenuating the whole signal, since there will be a point where the sync amplitude becomes too small. One solution for this can be as complex as running a separate sync signal into the monitor, but this is not a low cost solution. This is the figure of the circuit.
Here we present a simple video “volume control” that is fades the picture to black while maintaining a good video fidelity. LT1360 (U1) and its associated components form an elementary sync separator. R1, D1 and C1 clamp the composite video signal. To compensate for the drop across D1, D2 is employed to bias the input of U1. The sync information that occupy the most negative portion is amplified by U1 when D1 conducts. In the feedback network of U1, the clamp circuit (D4 to D8) prevents the amplifier from saturating. The shape of the sync waveform is improved by D3 and CMOS inverter U4. [Circuit schematic diagram source: Linear Technology Application Notes]
Here we present a simple video “volume control” that is fades the picture to black while maintaining a good video fidelity. LT1360 (U1) and its associated components form an elementary sync separator. R1, D1 and C1 clamp the composite video signal. To compensate for the drop across D1, D2 is employed to bias the input of U1. The sync information that occupy the most negative portion is amplified by U1 when D1 conducts. In the feedback network of U1, the clamp circuit (D4 to D8) prevents the amplifier from saturating. The shape of the sync waveform is improved by D3 and CMOS inverter U4. [Circuit schematic diagram source: Linear Technology Application Notes]
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