### Author Topic: How to convert 5V to 3.3V  (Read 7868 times)

0 Members and 1 Guest are viewing this topic.

#### Ecir Hana

• Jr. Member
• Posts: 13
##### How to convert 5V to 3.3V
« on: November 25, 2009, 01:24:10 PM »
Hello,
I have 5V of regulated voltage (USB) and I would like to get from it 3.3V. How to do it? I read that one possibility is to build "voltage divider" (2 serial resistors, maintaining voltage ratio), (Zener) diodes which drop some voltage, voltage regulators, ....
What is the best way to do it? I need quite steady voltage (to power a microcontroller), max. 1A. I would prefer some integrated circuit but I don't know which one - LM3940? LM317? L78L33ACZ? or something else? Or the simple divider would be the best option?
« Last Edit: November 25, 2009, 01:29:36 PM by Ecir Hana »

#### rollingrobot

• Jr. Member
• Posts: 13
##### Re: How to convert 5V to 3.3V
« Reply #1 on: November 25, 2009, 01:48:31 PM »
You would need a 3.3V regulator

SparkFun would have them. Just put it on a small PCB proto board. Make some pins to connect from your current source of voltage to the regulator than connect the regulator output to your board.

#### Ecir Hana

• Jr. Member
• Posts: 13
##### Re: How to convert 5V to 3.3V
« Reply #2 on: November 25, 2009, 02:11:59 PM »
Quote
You would need a 3.3V regulator
Yes, but which one? There are very many of them... Does it even matter? Just some voltage regulator which can handle enough mA?

#### Ecir Hana

• Jr. Member
• Posts: 13
##### Re: How to convert 5V to 3.3V
« Reply #3 on: November 25, 2009, 02:20:15 PM »
Also, LM3940 is more than 10x expensive than the two dividing resistors - what's the difference?

#### Soeren

• Supreme Robot
• Posts: 4,672
##### Re: How to convert 5V to 3.3V
« Reply #4 on: November 25, 2009, 02:42:31 PM »
Hi,

If you are only gonna use up to eg. 1mA, you could get away with a resistive voltage divider, but it won't have any regulation.

You need an LDO regulator (Low Drop Out), as eg. an LM317 (or the 78 series) needs to drop 3V, leaving you with only 2V at the output.
An LDO can have a drop of less than half a volt or less (down to <0.1V if a high current device is used with low current).
Regards,
Søren

A rather fast and fairly heavy robot with quite large wheels needs what? A lot of power?
Engineering is based on numbers - not adjectives

• Jr. Member
• Posts: 13