Monday, 30 July 2012


Monostable multivibrator is also called one shot. It has a tsable state and a quasi stable state . The circuit remains in the stable state until triggering signal causes a transition to quasi stable state after a time intervell , it returns to the stable state so a single pulse is generated when a trigger is applied.
consider the instant at which the output Vo=Vsat . Now the diode D1 clamps the capacitor voltage Vc at 0.7V feed back voltage available at nin inverting terminal is +betaVsat . When the negative going triger is applied   such that the potential of non inverting terminal become less than 0.7V , the output switch to -Vsat . Now the capacitor charges through R towards -Vsat , because the diode become reverse biased. When the capacitor voltage become more negtive than -betaVsat , the comparator switches back to +Vsat , and capacitor C starts charging to +Vsat through R until Vc reaches 0.7V and C become clamped to 0.7V . The pulse width is given by T=RCln(1/1-beta) approximately. If beta=0.5 T=0.69RC . The time period of a trigger must be larger than the output pulse width T. The circuit does not respond to a trigger that appears before the specified output pulsewidth and hence it is called non-retriggerable monoshot .
Components for wiring the circuit
IC 741
D1=D2 = 1N4001
R1 = 10K
R2 =10K
Cd = 0.01μF
R = 15K
Rd = 100K
C = 0.1μF
Vin = 2Vpp

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