Custom Circuit (LED Ring Light) Requirements
 

I have an LED ring light to fit over our Axis camera on the robot, which requires 12V. For power I'll connect to the PDB with a 20 amp breaker, but I wanted to be able to use a DIO to toggle the light on and off (save power, not be distracting while testing).
To do this I want to use an NPN transistor then toggle the Base via DIO. To comply with custom circuit rules, what sort of protection do I need (if any)? I would think the LED's themselves would suffice as protection diodes.

Re: Custom Circuit (LED Ring Light) Requirements
 

Have you considered hooking it to a Spike instead of building your own circuit?

Re: Custom Circuit (LED Ring Light) Requirements
 

I'm not clear on what you mean by the LEDs being their own protection diodes.

BK's spike suggestion is your easiest option. Otherwise, consider the NPN transistor to be part of your custom electronics (not a separate power controlling element) when you review the rules.

Re: Custom Circuit (LED Ring Light) Requirements
 

Yes but a spike relay costs $35 + extra weight and a transistor costs about $1.50. This is a low current application.
The concern with transistor is back-current from a load after power-off, so in my experience with integrated circuits we always need to add a diode to prevent said back current. In this case, the LEDs would serve its own purpose I'd think, but I just wasn't sure how inspectors treat custom circuits.

Re: Custom Circuit (LED Ring Light) Requirements
 

That's only a concern with inductive loads. For controlling LEDs, don't worry about it.