OP-AMP applications

UNIT-5

Mohammad Asif IqbalAssistant Professor, Deptt of ECE,JETGI, Barabanki

MULTIVIBRATORSBISTABLEASTABLEMONOSTABLE

BISTABLE

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

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.

Performance and operation..

charging

v+=v-

discharging

Monostable Multivibraotor (one stable state)

Vp > Vn, Vo = L+

Vp < Vn, Vo = L-

L+Forward bias

Vn

=0

L-Reverse bias

=-ve & will vary

exponentially

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+

IC 555 Timer

Remember! Its your SR

Op-ampAnd output will be regarded as 1 for L+ & 0 for L-

Q: why it is known as IC

555A: Because

of these resisters.

They are of 5k ohm.

S R Q Q’

0 0 No change

0 1 Reset

1 0 Set

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+

10

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.

Implementing a Astable Multivibrator using 555 IC

0

1

OFF

Vp >

Vn >

0

1

0

1

ON

Vn >

0

Vp >

1

1

0

THANK YOU!