Diff btw Supply Current and Bias Current of an Op Amp?

[baig_anora]

Hi,

Can any one help me out in understanding the difference between Supply Current (ICC) and Bias Current(IIB+ , IIB-) of Op Amp?
On What factors Supply Current of Op Amp depends? Can Supply current can be called as Bias Current?

Thanks.

 

[milesguidon]

The supply current is the current that the OpAmp draws from the positive and negative supplies, VCC and VEE, or VCC and GND--it's the current that the OpAmp requires to do its job, just like anything else has a supply current.

The input bias current is the current that the OpAmp draws into the Vin+ and Vin- ports--usually a very small amount, and usually a smaller bias current is better.

Two completely different things.

 

[ahsan_i_h]

milesguidon is rigt. Lets explain bias current more.....
During opamp calculation we say that current into its inputs(inverting and non inverting) is zero. But actually it is not zero. It is negligible. This negligible current is the input bias current. Why there is a input bias current? Because when you see the opamp's internal circuit you will see that the inputs(noninverting and inverting) go directly to the base of bipolar junction transistors(for bjt input opamp like 741). We know that bjt needs some base current to work properly.