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### Topic: Convert USB 5V to 3.7V. Does this device exist? (Read 15481 times)previous topic - next topic

#### vanakaru

##### Jul 13, 2013, 09:13 pm
I need to power a camera connecting to battery pins from USB(or similar 5V) power. Battery rates 3.7V. What do i need to achieve this?

#### fungus

#1
##### Jul 13, 2013, 09:19 pm
A voltage regulator.

#### larryd

#2
##### Jul 13, 2013, 10:04 pm
You may be able to use 2 silicon diodes and a capacitor on the o/p drive.
No technical PMs.
If you need clarification, ask for help.

#### vanakaru

#3
##### Jul 13, 2013, 11:08 pm
Honestly, I do not know how to design this. What size resistors...

#### Grumpy_Mike

#4
##### Jul 13, 2013, 11:18 pm
Quote
What size resistors...

Who said anything about a resistor?

http://en.wikipedia.org/wiki/Voltage_regulator

#### bigred1212

#5
##### Jul 14, 2013, 01:10 am
How much current?  Is a camera a lot?

There are lots of logic level translators that might work if you can accept 3.3v instead of 3.7 and aren't sinking a ton of current.

Like these:
https://www.sparkfun.com/products/8745
http://www.freetronics.com/products/logic-level-converter-module#.UeHei6y0RBo

Just an idea.

#6

#### fungus

#7
##### Jul 14, 2013, 10:20 am

How much current?  Is a camera a lot?

There are lots of logic level translators that might work if you can accept 3.3v instead of 3.7 and aren't sinking a ton of current.

Logic level translators are for signal lines, not power lines.

#### Grumpy_Mike

#8
##### Jul 14, 2013, 12:14 pm

Quote
resistors

http://www.circuitstoday.com/few-lm317-voltage-regulator-circuits

It says on that page how to calculate it:-
Quote
The output voltage of the regulator circuit depends on the equation, Vout = 1.25V (1 + (R2/R1)) + I adj R2.

#### fungus

#9
##### Jul 14, 2013, 12:23 pm

Quote
The output voltage of the regulator circuit depends on the equation, Vout = 1.25V (1 + (R2/R1)) + I adj R2.

There's also thousands of web pages with tables of resistors for various voltages, eg.

http://electronicendeavors.blogspot.com.es/2011/09/lm317-voltage-table.html

#### bigred1212

#10
##### Jul 15, 2013, 12:34 am

Logic level translators are for signal lines, not power lines.

If OP wants to send a signal to a camera, might work fine.
If OP actually really wants to power things up, might not.

#### pbrouwer

#11
##### Jul 16, 2013, 10:22 am
You can get a dc-dc step-down converter from various websites for a few dollars. I got one from dx.com that has an adjustable output voltage and can handle up to 1.5 A. It has screw terminals, so it's easy to connect. Only downside is that it isn't very compact (due to the screw terminals).

Pieter

#### Vitruvius

#12
##### Feb 12, 2015, 06:13 pm
I have the same issue. I want to power my DSLR from a USB port. Did some research and does not look it will work. Camera needs 3.7V @ 3A.

1. not enough juice. USB port 5V @ 2.1A = 10.5W. Even at 100% efficiency, converted to 3.7V @ 10.5W = 2.838A. Camera will be looking for minimum 3A.

2. USB ports are now 'smart' to prevent power surges. So this intelligence might make it a no-go from the start since it is not just straight power tap.

3. There are external power pack with 110V AC inverters. So I could just plug my standard 110V AC adapter for my DSLR into this. Double inversion but no big deal. and safe. And 85W is plenty of power.

http://www.memoryexpress.com/Products/MX55400

4. There are some external power packs coming out now with multi-voltage power ports like 9V / 12V., not USB. This should work with an inline voltage regulator. Max output between all 4 ports is 4.5A.

http://www.ebay.com/itm/111594062498?_trksid=p2055119.m1438.l2649&ssPageName=STRK%3AMEBIDX%3AIT

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