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555 Timer

555 Timer. Monostable Operation. Monostable Operation – (one-shot). External capacitor is initially held discharged by transistor inside timer.

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555 Timer

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  1. 555 Timer BAE 5413

  2. Monostable Operation BAE 5413

  3. Monostable Operation – (one-shot) • External capacitor is initially held discharged by transistor inside timer. • Upon application of a negative trigger pulse of less than 1/3 VCC to pin 2, the flip-flop is set which both releases the short circuit across the capacitor and drives the output high. • Voltage across the capacitor then increases exponentially for a period of t = 1.1 RAC, at the end of which time the voltage equals 2/3 VCC. • comparator then resets the flip-flop which in turn discharges the capacitor and drives the output to its low state BAE 5413

  4. Astable Operation (Clock) BAE 5413

  5. Astable Operation (Clock) • Same as with monostable mode except a connection is made from the threshold to reset which causes the timer to reset after each cycle. • Capacitor (0.01 uF) must be connected to control voltage to ground • Trigger must be high and dropped to less than 1/3 Vcc for short period to trigger. See datasheet note. BAE 5413

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