Op-amp Que

A

alizee

New Member

• Jan 7, 2010

• #1

Why it is necessary to keep supply vtg of op- amp greater than input voltage? (eg if input signal is near abt 10V and supply to opamp is 15V) And why we can't keep exactly 10V only?

 

crutschow

Well-Known Member

Most Helpful Member

• Jan 7, 2010

• #2

It's not always. The input voltage can be greater than the supply voltage if the op amp is configured as an inverter with a gain less than one.

 

R

rahul.sadtm

New Member

• Jan 7, 2010

• #3

alizee said:

Why it is necessary to keep supply vtg of op- amp greater than input voltage? (eg if input signal is near abt 10V and supply to opamp is 15V) And why we can't keep exactly 10V only?

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hi alizee

well it depands upon the application and not always true. if you have any circuit like this then put it on the thread.

 

A

alizee

New Member

• Jan 11, 2010

• #4

Thnks
Yes this is ok that its not compulsory but why it is better means what is reason it is always better to keep it like that?

 

audioguru

Well-Known Member

Most Helpful Member

• Jan 11, 2010

• #5

The inputs of an LM358 dual opamp and an LM324 quad opamp have a maximum allowed voltage of +32V and the supply voltage of the IC doesn't affect the max allowed input voltage.

Most other opamps would have their input transistors damaged or destroyed if their voltage is higher than the supply voltage for the IC.

 

Roff

Well-Known Member

• Jan 11, 2010

• #6

Audioguru gave you one reason. For the other reason, look at the Input Voltage Range or Input Common Mode Range specification in the datasheet of the op amp.