Have a Arduino.. controlling other devices, using digital pin to turn on a transistor or something like that for higher current control(electronic switch).
Wondering..what device would I use that has the absolute lowest quiescent current draw when I'm not using it..i.e. on the digital output pins when they are low, there is no current draw at all..?

The goal is to only be using battery power when the circuit is active. The uC itself will go into ultra low poeet mode and draw bigger all when sleeping.

The devices I'll control (enable) with the Arduino are 12v/max 20amps.

 

A MOSFET switch can be configured to draw essentially only leakage current when off.
Below is an example circuit:
12V is on when the Arduino output is 5V and off otherwise.
M2 can be any P-MOSFET with an ON resistance of ≤2mΩ (to avoid having to put it on a heatsink when carrying 20A current).

 

Cool..so when the Arduino digital output is low.. what current levels would that CCT use..that's leakage current?

 

so when the Arduino digital output is low.. what current levels would that CCT use..that's leakage current?

Yes, the OFF leakage current of the two MOSFETs, which is generally a microamp or less at room ambient.
That's less than the self-discharge current of most batteries.

 

How could it be done for less.? Trying to engineer for absolute minimum. I have a uC which can go down to 1uA so if I had a few FETS like that their leakage would be significant in contrast..?

 

How could it be done for less.? Trying to engineer for absolute minimum. I have a uC which can go down to 1uA so if I had a few FETS like that their leakage would be significant in contrast..?

Why are you worried about a few microamps?
As I stated that's well below the self-discharge rate of most batteries.
And note that a microamp per MOSFET is worst-case.
Typically it will be much less.
It's fine to engineer for the absolute minimum, but only if that minimum has an advantage over what is readily obtainable.

 

By the way, that circuit is good for another reason - it protects from polarity reversal. Plug the wrong wall wart in and it DOESNT fry your circuits.

 

By the way, that circuit is good for another reason - it protects from polarity reversal.

That would be great if it did, but alas, it doesn't.
If you apply a negative voltage to the source of a P-MOSFET, the substrate diode will conduct between the source and drain.
For reverse protection, you would need to add another P-MOSFET in series, but with the drain connected to the 12V and the gate connected to ground.