Do BRX sourcing outputs have built-in kick-back protection?

[PLCwannabe]

Do BRX sourcing outputs have built-in kick-back protection for operating small dc coil relays or is a snubber device even required? These relays will cycle up to 300 times/day.

[Garyhlucas]

Snubbers should be added, they are shown in the docs.

[Controls Guy]

I've almost never used one in 35 years and I've never, to my knowledge, worn out an output.   Killed them accidentally  switching into a dead short, but never wore one out inductively.   I'm sure it's just around the corner, though .

[Garyhlucas]

When digital Volt Ohm Meters first came out I blew out two of them in quick succession. I then realized while troubleshooting. I was checking voltage on the coil of a NEMA size 7 motor starter when it shut off.  Flyback voltage on that huge coil operating on 480vac was probably 20,000 volts or more!

[ADC Product Engineer]

It's not just the outputs that are being protected by adding snubbers.  It is also whatever else you have on that power circuit.  The CEMF spike will find the weakest link and start to eat (sic) away at the junctions for the transistors.  It may take awhile, but eventually something will fail.

Snubbers and surge protection are cheap insurance for your high dollar electronics.

[PLCwannabe]

Thanks for the info guys. I thought that with these being transistor outputs, they just might have built-in protection.

[BobO]

Thanks for the info guys. I thought that with these being transistor outputs, they just might have built-in protection.

Snubbers and high speed are mutually exclusive. There is a zener to help with inductive spikes, but it cannot be as robust as a snubber and still meet the performance requirement.

Edit: Realized that might not have been clear. Yes, there is some protection, a zener diode, which will handle small-ish amounts of inductive overvoltage. Depending on the size of the inductive load, a snubber may still be required, but is always preferred.