5V regulator current?

Question

If I have a 5V circuit that draws 9mA.

How much current would be drawn if I use a 9V supply and a 5V regulator?

Answer 1

9mA, plus the quiescent current of the regulator. If you use the standard low current regulator, the 78L05, the quiescent current is 3mA, so your total current draw would be 12mA.

http://www.national.com/mpf/LM/LM78L05.h...

There are lower quiescent current regulators, like the LM2936, which uses about 15uA:

http://www.national.com/opf/LM/LM2936-5....