POWER SUPPLY INTERRUPT ALARM CIRCUIT

摘要

PURPOSE:To eliminate the need for a metallic cable for transmitting power supply interrupt information. CONSTITUTION:A video signal immediate interrupt circuit 1 immediately stops a video signal in an output when power from a power supply 4 is interrupted. A pulse frequency demodulation circuit 2 applies pulse frequency modulation to the video signal and sends a carrier for a prescribed time when the power is interrupted. A transmitter 3 sends the modulated video signal or the carrier at power interrupt to a transmission line 5. A receiver 6 outputs a signal received from the transmission line 5. A pulse frequency demodulation circuit 7 demodulates the signal inputted from the receiver 6 and outputs the result as a received video signal. An alarm circuit 8 generates an input interrupt alarm at a terminal 11 when the received signal and the received video signal are interrupted and inhibit the production of the input interrupt alarm when the received signal level is normal and the received video signal is interrupted.