ULN2803A multiple voltages

Thread Starter


Joined Nov 21, 2008
Hi everybody...:)

I have had a search but not really found the answer..

I am using a Pic Micro/ ULN3803A to drive 4 x 24v (approx 60mA each) Led display modules, which works fine. I have them connected as below ( common unconnected)

24V-----Led Module------collector on ULN2803A
Is it possible to the same on another output of the same IC, but at 5v?

Also, I would like to use PWM on one of the spare inputs to supply a chain of IR Leds @ 12v 60mA.

I have done all of the above at one time or another, but not all on the same IC

Any advice/previous experience greatly appreciated


Ron H

Joined Apr 14, 2005
You should be able to use different supply voltages. I would connect the common pin to the highest voltage. It will work if you leave it unconnected, but you could see some transient effects if you were running at high frequency.


Joined Jul 17, 2007
Just to qualify RonH's input...

The various voltages must all have a common ground point.

If they don't, you will have big problems.

Thread Starter


Joined Nov 21, 2008
Thx Ron n wookie :)

For sure, a common ground is important, I was wondering if anybody had problems with maybe a nearby input being pulsed along with the one I intended..
I'll knock it up on a breadboard, see what happens, and let you know.
I would have thought it would be OK, I was just trying to make use of a couple of spare outputs on the board

Thx again