The position of the rail supply for Opamps

M

muashr

Member

• Mar 20, 2014

• #1

Hi,

I read different material about opamps and in some I found +ve rail supply on the same side of the non-inverting input & -ve rail supply on the inverting input side. On some other places, a came accross a different scenario where I found +ve rail supply on the inverting input side and -ve rail supply on the noninverting input side.
What I want to know is which representation is the correct one. If the both were correct, then does it mean that changing the position of rail supply has no effect on the overall functionality of the opamp?

Thanks

 

crutschow

Well-Known Member

Most Helpful Member

• Mar 20, 2014

• #2

It's not the position of the rails with respect to the input that matters, it's the connection of the rails to the opamp power pins. The polarity of the rail must always match the polarity of the power pin it's connected to.

 

K

KeepItSimpleStupid

Well-Known Member

Most Helpful Member

• Mar 20, 2014

• #3

I did read SOMEWHERE that the positioning of the power pins like the 741 isn't optimal and whatever that OP amp was designed for, they changed the location of the pins. Power has to match.

 

audioguru

Well-Known Member

Most Helpful Member

• Mar 20, 2014

• #4

Why don't you look at the datasheet of the opamp you are using?
Most single opamps in an 8-pins case use pin1 for offset null, pin2 is the inverting input, pin 3 is the non-inverting input, pin4 is the negative supply (or ground if there is a single supply), pin5 is offset null, pin6 is the output, pin 7 is the positive supply and pin 8 is not used.

 

atferrari

Well-Known Member

Most Helpful Member

• Mar 20, 2014

• #5

He's talking about how they are drawn, not the physical location in the chip.

C. Jung always has the +V at the top and the inverting input above the non-inverting one.

 

alec_t

Well-Known Member

Most Helpful Member

• Mar 20, 2014

• #6

What I want to know is which representation is the correct one.

Click to expand...

Both are valid.

 

D

Dean Huster

Well-Known Member

• Mar 30, 2014

• #7

Schematic drawing varies to keep things looking as clean and simple as possible. I prefer to keep the inverting input on the "bottom" of the symbol but will swap the convention in a heartbeat if the seem looks cleaner. Autorouting drawing programs are sometimes locked into certain conventions and will rat's-nest the wiring to get around it.