These slides contains animated description of multivibrators, and IC-555 timers and explain the working of these circuits in detail.

1. UNIT-5
Mohammad Asif Iqbal
Assistant Professor,
Deptt of ECE,
JETGI, Barabanki

2. MULTIVIBRATORS
BISTABLE
ASTABLE
MONOSTABLE

3. BISTABLE

5. Now consider what will happen as Vi is decreased from L-

6. Astable Multivibrator(No stable state)
A square waveform can be generated by arranging for a bistable
multivibrator to switch states periodically.
This can be done by connecting the bistable multivibrator with an
RC circuit in a feedback loop.

7. Performance and operation..
charging
v+=v-
discharg
ing

8. Monostable Multivibraotor(one stable state)
Vp >Vn, Vo = L+
Vp <Vn, Vo = L-

9. L+
Forward bias
Vn
=0
L-Reverse bias
=-ve & will
vary
exponentially

10. Monostable Multivibrator
L+
=0
Vp > Vn, Vo = L+
Vp <Vn, Vo = L-
Forward bias for only
–ve triggering pulse
Diode will conduct
heavily and pull Vp
down
L-
=-ve
Vp -Vn= +ve
L+

11. IC 555 Timer
Remember!
Its your SR
Op-amp
And output
will be
regarded as
1 for L+ & 0
for L-
Q: why it is
known as IC
555
A: Because
of these
resisters.
They are of
5k ohm.
S R Q Q’
0 0 No change
0 1 Reset
1 0 Set

12. Implementing a monostable Multivibrator using 555 IC
0
1
ON
Vp <Vn, Vo = L-
0We
keep
Vtrigger
>VTL
0
Lets
trigger
1
Vp >Vn, Vo = L+
1
0
OFF
Q:How long it
will remain 1?
Just for that
much span
of time, after
that
triggering
pulse will
become
positive and
o/p of
comparator
2 goes to 0.
Vp >Vn, Vo = L+
1
0
1
0
0
Q:Justify the
difference
between
charging and
discharging
time
Q:Justify the
difference
between
charging and
discharging
time
A: Look the
difference
between the
time
constant.

13. Implementing a Astable Multivibrator using 555 IC
0
1
OFF
Vp >
Vn >
0
1
0
1
ON
Vn >
0
Vp >
1
1
0

14. THANK YOU!