Data sheets, op amps 1

[mankydog]

Trying to work out the current being drawn from an op amp.

What is the I/P offset current and the i/p bias current?

 

[Lewish]

Is this for a class assignment?

 

[mankydog]

Nope, work. If you don't want tell me, could you give me some sort of pointers of where to find this information.
When you are not in an educational circle it is harder to learn/teach yourself.

I have read the rules, I understand the conditions.

 

[cbarn24050]

Hi, input bias is the sum of the ip currents/2, offset is the difference betwwen these currents. Both values apply when the op voltage is zero. Note that these are signal currents not power supply current.

 

[Lewish]

Sorry, for the question mankydog, but there have been so many students trying to get us working engineers to do their homework for them, that it has driven me up to wall.

cbarn correctly answered your question. One thing to note, however, is that there must be a DC signal path to supply these currents. Or in other words, you can't have only capacitors hanging on your 2 inputs.

 

[mankydog]

Thats OK.

Cheers guys for the help. Is there any other advice that you could give me on how to look at these data sheets/learn how to translate the information on them? Or is it just something that I will have to pick up with experience?

It is interesting to look at things in this kind of depth I must say though.

 

[Lewish]

If you really want to get into the guts of opamps, I can't think of any better book than "Intuitive IC OP AMPS" by Thomas Frederiksen. It was put out by National Semiconductor as part of their Technology Series. (C) 1984.
It may be hard to find, but it really gives a good insight into why opamps are designed the way they are, and what some of the trade-offs in design are dependant on.
I like it also, because all of the math is in algebra, no integral calculus like some references.

 

[ve7brz]

Another good reference is this one:

http://vig.pearsoned.com/store/product/1,3498,store-562_isbn-0138896011,00.html