voltage follower?

Question

with a voltage follower, if the input draws a very small current and the output can provide a much larger current, where does the extra current come from? All my book says is that this is due to a very high input impedence and a very low output impedence. Can anybody explain this in more detail?

i've realised this question is in the wrong section.

Answer 1

Basically, current increases where there is less resistance.

See:
http://en.wikipedia.org/wiki/Ohm's_law

It's really that simple, I think. The less resistance in the output, the more current there will be there.

The above answerer is kind of wrong, since we're talking (presumably) about a constant voltage with a varied input/output impedance. That gives:

ir = IR

where lowercase is input, uppercase is output. If you know r>>R, then you know i<> and << are "very much less than" and "very much greater than."

Answer 2

The input impedance is high, so it draws a very small current. That's just what we mean by a high impedance.

Small variations in the input voltage cause small variations in the already-small input current, but the electronic trick is that these current changes can be arranged to cause HUGE changes in the output impedance. The power supply provides the current. When the output impedance is high, the current is small. When a change in the input current lowers the output impedance, it is like opening a tap; the power supply pours more and more current through the lower impedance that it sees.

Answer 3

Trying to figure out why this question is on maths page?
However as maths is used throughout electrical engineering work:-
Assume input power = output power
V i = v x I
It follows that if v < V, then I > i
ie output current , I , is greater than input current , i.