4. The circuit consists of:
Comparator A,
Comparator B,
3 Resistors of 5k ohms each Capacitor
of 0.01μF
5.
6.
7. The astable multivibrator does not require
any external trigger to change the state of the
output. Hence the name free running
oscillator.
The time during which the output is either
high or low is determined by the two resistors
and a capacitor which are externally
connected to the 555 timer.
The astable multivibrator generates a square
wave, the period of which is determined by
the circuit external to IC 555.
8. Let t1 and t2 represent the charge and
discharge times of the astable multivibrator
respectively.
were RA and RB are in ohms and C is in Farad.
9. Astable Multivibrator Duty Cycle
Time
The duty cycle is defined as
the ratio of charge time
constant (t1) to the total
cycle time (T) and for the
astable oscillator it is found
to be:
10. The simple operation and less number of external
components make the astable multivibrator using
555 IC a popular one.
The perfect square wave output from the circuit
makes it good for many applications.
Easy to design, low cost and no external triggering
are the other advantages.
The disadvantage is that we cannot achieve a duty
cycle less than or equal to 50% using this circuit.
This problem can be solved by inverting the output or
by using a diode parallel to RB.
DISADVANDAGES
