# Current Limiting

I have a battery supplying 15V 10A to a voltage regulator that takes an input voltage of 15V and drops it to 12V. However, the output current of the voltage regulator is so high that it fried the regulator. How could I drop the current from 10A to 4A so the regulator won't be damaged?

P.S. I'm using LM338T voltage regulator

• Looks your load is high Commented Mar 7, 2020 at 4:19
• what are you powering? Commented Mar 7, 2020 at 5:32
• Use a DCDC buck converter to reduce current efficiently or half-bridge PWM into an inductive load Commented Mar 7, 2020 at 6:20

It sounds like the regulator is getting damaged because of the Power Loss, if I'm understanding this correctly.

The power consumed by a Linear Regulator is P = (Vin-Vout) *Iout.

In your case, if your Vout is 12V, and your load is drawing 10A, then your power consumption on the regulator is (15V - 12V) × 10A = 30W. This amount of power is waaay too high for a device like this. Linear regulators are an easy way to step down voltage, but they aren't efficient since the input current is the same as the output current. Which is why here, you are getting a power loss of 30W.

That said, the reason you are drawing 10A of current is because of your load. I don't know what your circuit looks like, but you can't limit the input current without also limiting the output current.

• I edited your answer to add parenthesis into the formulas because, without, they were misleading. It looked to me like a typo, but actually is something more, so I want you know about. Commented Mar 7, 2020 at 6:24
• Thank you. I tried adding parenthesis to the formula, but everything became italicized. But looking at your edit, I see that they can be used to submit answers.
– Jay
Commented Mar 7, 2020 at 12:07
• Any ideas of how to to limit the output current? I’m trying to power a 12V 6A motor Commented Mar 8, 2020 at 7:42