555 TV programs monitoring and timing conversion circuit

Published:2011/6/16 1:11:00 Author:TaoXi | Keyword: 555, TV programs, monitoring, timing, conversion circuit | From:SeekIC

When the switch K2 of the additional circuit is in the position 1 , the astable multivibrator is composed of the 555 and R1, R2, C1, because the charging time of the circuit tcharging=0.693(R1+R2)C1, it is larger than the discharging time td=0.693R2C1, so the duty ratio of the output pulse is small, this circuit can realize the main channel long-time display (about 10 minutes) and the vice channel short display (about 5 seconds). When the K2 is in the position 2 , the monostable timing circuit is composed of the 555 and R3, VT, RP, C2. The constant current source is composed of the MOSFET 3DJ6, this constant current source charges the C2 to improve the timing accuracy. By adjusting RP, you can pre-set the timing time (5 to 90 minutes). When this circuit is used as the timing circuit, you need to press AN to set the 555 circuit, so the timing starts.



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