# Simple voltage reduction question

#### thevoodoochild

Joined Jan 14, 2011
21
Hi forem, A simple question. I have 6.3v off a regulator, I need to drop the voltage to 5v, but if i use 2 resistors to devide it then the resistors have to be very small values & thus gets hot. whats the best way around this?

The Voodoo Child

#### #12

Joined Nov 30, 2010
18,223
Put (2) 1N4001 diodes in series with where you want 5 volts. They will use up about 1.2 to 1.3 volts and their current limit is 1 amp DC.

#### SgtWookie

Joined Jul 17, 2007
22,227
Resistors will only divide voltage, not regulate it.

What is your output current requirement at 5v?

If it is small, you might be able to use a low-dropout linear regulator without a terrible loss in efficiency. You may also be able to use just a couple of diodes in series with the positive supply and a minimum load resistor.

If your current requirement is heavy or your efficiency requirements are high, you will need some kind of switching regulator or DC-DC converter.

#### NLightNMe

Joined Apr 20, 2011
16
A resistor divider is not the best solution for your problem. A regulator would be better, as others have mentioned.

However, to answer the heart of your question... it is only the ratio of the resistors that determine the voltage in the middle. Two 1MOhm resistors will give you 1/2 the voltage the same as two 0.1Ohm resistors will. On the other hand, the power is dictated by the current going through the resistors. Ohm's law says that 6.3 V / 2 MOhms is 3.15 uA, but 6.3 V / 0.2 Ohms is 31.5 A. Power scales with the square of the current and directly to resistance. Thus, the 0.2 Ohms divider will get much hotter than the 2 MOhm divider, and will probably melt.