Tech / Special Interest → Electronics > Resistor vs. voltage reg

Resistor vs. voltage reg

If I have something that outputs 5v at 50ma, and I want to run something that needs 3v (normally it uses qty.2 AA batteries) what resistor is appropriate, or am I better off using a voltage regulator?

I only have 50ma to work with, as this is the output of a POE module

What sort of device are we talking about here? How much current does it require?

A simple resistor will not work unless the load current is absolutely constant. For any kind of electronic device, it's going to be fluctuating.

It's one of those LED road flares, it took 2 AAA batteries. Every time you press the on button it does a different blink pattern, unfortunately some of the modes are "blinking all LEDs together" or "half the LEDs on then the other half" ...so I see what you mean about current requirements varying.

you can put 2 1N4007 diodes in series for a quick fix. each one will drop about .7 volts.

looks very much like this unit: »www.evin.ca/tutorials but mine operated off 2 AAA batteries.
would I kill it if I just operated it on 5V direct? or is 50ma not enough you're thinking?

Many of these devices use high current. See »32 LED 18V 240 lumen flashlight project.. Since they are blinking it will be difficult to tell. You could put a 39 ohm resistor in series with the supply and try it. Maybe you'll get lucky.

A 3 pin LDO regulator is almost as easy as a 2-pin resistor and you eliminate the risk.

Here is a $0.33 TI part which will provide your LED toy fixed 3V output (matching 2x AAA) from 5V to 24V PoE voltage. Current is limited to 100mA max.

»www.newark.com/texas-instruments···/41K6543

Thank you all for the insight, I think I'm going to play it safe and use the LP2950CZ-3.0

I was simply referring to the supply @50mA. The device, he said was similar, had 16 LEDS all of which could flash simultaneously. Since it is flashing they may keep the average current lower than 50. Won't know until it's measured or tried.