ULN2003 Multi Voltage

[gdenehy]

Can I control multiple volatges with a single ULN2003?
I am using 5V and 12V

I am using the ULN2003 currently to control 12V things using a picaxe.
I need to control at least one 5V relay - can I hook this up to the same ULN2003?
If so, how?

 

[MartinM57]

Yep...
..remember ULN2003 is just a set of ground side switches so it's unaware of the voltages above each load.

Just connect 12v-load-ULN-Gnd as required and 5v-load-ULN-Gnd as required.

The only question is where to connect the +v (COM) pin to - it would have to be the highest load supply voltage (or if you're not driving inductive loads, I don't believe you have to connect it to anything)

 

[hippy]

The COM pin can probably be left disconnected and 'flyback diodes' added externally for all channels which need them.

 

[gdenehy]

Yep...
The only question is where to connect the +v (COM) pin to - it would have to be the highest load supply voltage (or if you're not driving inductive loads, I don't believe you have to connect it to anything)

I am switching inductive loads, so just attaching it to the 12V will DEFINATELY work?

 

[BeanieBots]

That should work.
The purpose of the catch diode is to protect the switching transistor from the high voltage tranients when it turns off an inductive load.

With the COM connected to 12v and a relay switched from a 5v supply, the flyback voltage will be clamped to 12v which will be perfectly OK as far as the ULN2003 is concerned. However, if anything else is connected to the relay coil which could be damaged by 12v, then clamp it to the 5v line with a seperate diode.