I have a 5 volt circuit running a flashing led. What do I need to drop the voltage to run 2 1.5 volt light bulbs off of this circuit. Its in a RMT caboose that uses the 1.5 bulbs for the side marker lights.
Original Post
Replies sorted oldest to newest
LED or incandescent?
If they're incandescent, I'd wire them in series and then use three diodes to drop the voltage from 5V to 3V.
Thanks Gunrunner, Incandescent. I have two diodes wired in already and didn't think that was enough. Didn't think about wiring them in series either.
Each diode will drop .6 to .7 volts, depending on the current. With them in series, that gets you to the right place.
The problem with series wiring is if one goes they both go out. So parallel wiring with proper drop, or just using 2 diodes and wiring each bulb across those, would give you about 1.2 to 1.4 Volts for the bulbs. G
I can't imagine the horror if a bulb goes out. 
You're going to be working on it anyway, and you'll use half the current wiring them in series.
You can't just put diodes across the bulbs and connect to the 5V supply, that will drag it down to the same 1.2-1.4 volts! Suddenly, you're getting into series resistance for each bulb, etc.
I still recommend the series connection, much simpler, lower current, and fewer parts.
