Continue to Site

Welcome to EDAboard.com

Welcome to our site! EDAboard.com is an international Electronics Discussion Forum focused on EDA software, circuits, schematics, books, theory, papers, asic, pld, 8051, DSP, Network, RF, Analog Design, PCB, Service Manuals... and a whole lot more! To participate you need to register. Registration is free. Click here to register now.

Operational amplifier Current directions

Status
Not open for further replies.

paulmdrdo

Full Member level 3
Joined
Jan 17, 2014
Messages
183
Helped
1
Reputation
2
Reaction score
2
Trophy points
18
Activity points
1,394
Capture7.PNG
Hello! Can you guys explain to me why is the current in negative supply of the opamp is going in to it? I thought current goes from the negative terminal of the supply and goes out to positive terminal. TIA!
 

Hi,

it simply doesn´t matter. If the vector is in one direction then probably the sign of the value is negative...

According this picture: (assuming the bottom line is GND and all voltages are referenced to GND)
V+ is positive
IC+ is positive
(multiply both and get "positve" power, which means the OPAMP consumes power)

V- is negative
IC- is negative
(multiply both and get "positve" power, which means the OPAMP consumes power)

Io is positive and negative
Ip, In will be close to zero and may be positive as well as negative.

It´s all a question of "point of view".

Klaus
 

View attachment 144912
Hello! Can you guys explain to me why is the current in negative supply of the opamp is going in to it? I thought current goes from the negative terminal of the supply and goes out to positive terminal. TIA!

I can explain that to you. Current direction has a mathematical convention. For a voltage source, the direction is from the positive terminal, through the circuit, and into the negative terminal. That is the way an ammeter is wired to indicate, and the way all manufacturers mark their semiconductors with an arrow. For the actual physical direction, negative charge carriers (electrons) move in the opposite direction of the mathematical convention direction, and positive charge carriers like semiconductor holes, move in the same direction as the conventional direction. Usually you don't give a damn what the real direction is of the physical charge carriers. A lot of folks get wrapped around the axle by assigning current direction with respect to the charge carriers involved. Don't do that. Determine the conventional current direction first, and then if necessary, determine the real physical direction by the polarity of the charge carriers (electrons or holes).

The attachment you submitted shows the current direction going from the negative battery terminal to the op-amp. That is wrong, as an ammeter inserted into the circuit will show.

Ratch
 

Status
Not open for further replies.

Similar threads

Part and Inventory Search

Welcome to EDABoard.com

Sponsor

Back
Top