Monostable 555 Multivibrator Working Principle and Circuit diagram with Animation

Posted on Feb 6, 2014

Monostable 555 timer multivibrator circuit (one shot monostable multivibrator) is a retriggerable mono shot pulse generator. The name Mono stable` indicates that it has only one stable state. The unstable state is called Quasi stable state`. The duration of stable state or the pulse width is determined by the charging time constant of the RC netwo

Monostable 555 Multivibrator Working Principle and Circuit diagram with Animation
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rk. We can transfer the multivibrator from stable state to quasi stable state by using push button trigger switch. The animated (simulated) working of the mono stable 555 multivibrator is shown in this article. You can use our monostable 555 timer calculator tool to find the duration of pulse(width) easily. As we know, when the voltage at the second pin of 555 IC goes below 1/3 Vcc, the output becomes high. This high state is known as Quasi stable state`. (Refer Astable multivibrator using NE 555 ) Then the discharge transistor is cut off and capacitor starts charging towards Vcc (Refer the internal circuit below). Charging of capacitor is through the resistor R1 with a time constant R1C1. As the capacitor voltage increases and finally exceeds 2/3 Vcc, it will reset the internal control flip flop, there by turning off the 555 timer IC (more than 2/3 voltage at the threshold pin (6th pin) causes IC to reset).

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