Monostable circuit with 555 Timer

The integrated timer 555 is timer circuit intended for generating a rectangular pulses with voltage controlled time duration. The timer 555 can work in astable and monostable mode. The monostable circuit with timer 555 is shown on Picture 1. In order to avoid the unwanted modulation during the controlling, the controlling pin of the circuit (CV-pin) is grounded via the capacitor C3 of 10 nF.

Picture 1: Monostable circuit with integrated 555 timer

Time-domain analysis

The results of the transient analysis for this circuit in time domain is shown on Picture 2. On same picture are plotted both wave forms of the output Vo (green line plot) and the triggering voltage VT (blue line plot). As trigger voltage signal, here we use 3 rectangular pulses with amplitude of 5 V and time duration of about 50 ms, where the pause time between pulses or the duration of no trigger signal is about 150 ms. When the trigger signal is on high level (5 V), the output of the circuit is on its low level of about 4 mV, and the output high level is generated right after the input pulse. As it can be seen from the plot, when the input signal fails near the zero volts, the output starts increasing very fast to its high level of about 12 V. The first output pulse starts at about 60 ms and ends at about 81 ms, so the time duration of the output pulses is about 21 ms, and it can be varied by changing the values of the capacitor C1, through which the triggering pulse is leaded to the 555 timer circuit.

Picture 2: Transient analysis - output voltage Vo and trigger voltage VT wave forms (time-domain)