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Current Protection Circuit
Current Protection Circuit
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The protection shutdown circuit is designed to monitor for a short or loss of the SUB_9V, SOUND_VCC,
BT30V, and the Panel VCC sources. If any of these voltage sources goes low, Q7210 turns on. As a result, the collector of
Q7210 goes high to signal a shutdown condition to IC1100 on the A board. The TV_SUB_ON pin of IC4002 goes low to de-
activate the AC relay on the P board.
During standby operation, the 24 volt output of the P board biases the transistor Q7208 into conduction,
causing its collector to become “low”. The low at the collector of Q7208 causes the transistors Q7450 to turn off. As a result,
IC7233 goes into conduction to immediately provide the HQ 3.3V output. When the 24 drops below the reverse breakdown
voltage of D7206, transistor Q7208 turns off and transistor Q7450 turns on. IC7233 ceases to operate causing Q7451 to turn
off and Q7452 to turn on. Consequently, the SUV_9V line is now grounded. Diode D7220 becomes forward biased and
Q7210 outputs a high to trigger the shutdown of the unit.
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