ULN2803 + Relays + Flyback Diode

A friend of mine was saying I should add flyback diodes around the coil of my relay.

If I'm using a ULN2803 with 8 relays (KEMET EC2-5NU), is this true?

ULN2803 has "flyback" diodes built in but prob'ly wouldn't hurt to have one for each coil for good measure. Just be sure of your wiring. If you will be driving all relays at the same time, be sure the ULN2803 can handle the current load without overheating.


I can live with "probably wouldn't hurt." I'm surprised I haven't seen many schems that have it included.

What do you mean by "be sure of your wiring?" Anything specific?

Well, with that many components it’s easy to make simple mistakes like getting a diode backwards that can ruin your day, just take your time & keep your eyes open (from long experience) :slight_smile:

OH! Ok. I thought there was something a bit ... "more"... than that. :) Yeah, I'll be sure my schem and PCB have the band facing the right way. :)

Thanks for the quick answers!

You could prob'ly get by without the extra diodes but think about this: All relays are energized and you lose power, all the flyback diodes on the chip take a wallop at the same instant, can it stand the stress many times?