Multivibrator Astable Menggunakan IC 555 Multivibrator Astable Menggunakan IC 555

Multivibrator is an electronic circuit that at a certain time only one of two output voltage levels, except during the transition period. The transition (switching) between the two levels of output voltage occurs quickly. Two state level of the multivibrator output voltage, which is stable and Quasistable.

Astable multivibrator is called when the output voltage levels generated by the multivibrator circuit is quasistable. The circuit will only change the state of the output voltage level between the 2 conditions, each state has a fixed period. Multivibrator circuit will work independently and no longer need a trigger. Period of time each output voltage level is determined by the components making up the circuit.

The picture above is the astable multivibrator circuit. This circuit will work when the voltage applied to Vcc ration and ground her. This circuit has two conditions are always changing with time. Because changing the type is known as astable multivibrator. With constant changes of 0 and 1, then the multivibrator is also called a bistable multivibrator (multivibrator which has two stable state of 0 and 1).


This change in cycle length can be calculated using the following equation:

Period = t1 + t2
t1 = 0.7 x (RA + RB) XC
t2 = 0.7 xRBxC.

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Rangkaian Multivibrator Monostable IC 555 Rangkaian Multivibrator Monostable IC 555

Multivibrator Monostable IC 555

Rangkaian Multivibrator Monostable IC 555 is a pulse generator circuit in which the duration of the pulse is determined by the R-C connected to IC 555 timer. In such a vibrator, one state of output is stable while the other is quasi-stable (unstable). For auto-triggering of output from quasi-stable state to stable state energy is stored by an externally connected capaci tor C to a reference
level. The time taken in storage determines the pulse width. The transition of output from stable state to quasi-stable state is accom­plished by external triggering.

Capacitor C has to charge through resistance RA. The larger the time constant RAC, the longer it takes for the capacitor voltage to reach +2/3VCC. In other words, the RC time constant controls the width of the output pulse. The time during which the timer output remains high is given as

tp = 1.0986 RAC

where RA is in ohms and C is in farads. The above relation is derived as below. Voltage across the capacitor at any instant during charging period is given as

vc = VCC (1- e-t/RAC)

Substituting vc = 2/3 VCC in above equation we get the time taken by the capacitor to charge from 0 to +2/3VCC.

So +2/3VCC. = VCC. (1 – e-t/RAC) or t – RAC loge 3 = 1.0986 RAC

So pulse width, tP = 1.0986 RAC s 1.1 RAC

The pulse width of the circuit may range from micro-seconds to many seconds. This circuit is widely used in industry for many different timing applications.

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