[arm-allstar] 12V to 5V DC-DC Converters?

[Doug Crompton]

Sam,

 This power supply was mentioned as being good and used by several BBB owners -

http://www.ebay.com/itm/Waterproof-DC-DC-Converter-12V-Step-down-to-5V-3A-15W-Power-Supply-Module/221117981188?_trksid=p2047675.c100005.m1851&_trkparms=aid%3D222007%26algo%3DSIC.MBE%26ao%3D1%26asc%3D27538%26meid%3D988493afeb074ee58054fe9bb314e6bb%26pid%3D100005%26prg%3D11353%26rk%3D1%26rkt%3D6%26sd%3D221605016721&rt=nc

73 Doug
WA3DSP
http://www.crompton.com/hamradio


Date: Fri, 6 Feb 2015 22:58:09 -0800
From: kj6qfs at gmail.com
To: arm-allstar at hamvoip.org
Subject: Re: [arm-allstar] 12V to 5V DC-DC Converters?

David/ Everyone,
Which switching DC-DC converter should I be using for my BBB? I Have a URI and four USB-Serial adapters connected, so I'd like to come up with an adequate power supply. 
Thanks and 73

Sam Skolfield
KJ6QFS
On Thu, Nov 20, 2014 at 8:41 PM, David McGough <kb4fxc at inttek.net> wrote:


Hi Tom,



Thanks for sharing your schematic. I've noticed one area of concern, which

has personally bit me before. You should add a capacitor (perhaps 1uF or

larger) very near the input of the LM7806. These little regulators are

wonderful except when they decide to oscillate. And, that can happen, I

promise--(Hind sight: 20/20 in my case!). Even if your regulator is well

behaved, others might encounter problems if they try to duplicate your

design, due to subtle variations.



Also, note that the TIP110 transistor is rated for a maximum base-emitter

voltage of 2.8VDC. So, your results many vary from device to device.

Under variable load, the voltage regulation probably won't be perfect.



A simpler linear regulator would be to use an LM7805T directly (including

input and output bypass capacitors). They're capable of at least 1A output

directly and will power a BBB okay...They will need a heatsink with a 12v

input source.



The primary reason I bring all this up is that BBB's are VERY sensitive to

any power supply instability. The best, inexpensive, solution I've found

is a small switching DC-DC converter like those already mentioned.





73, David KB4FXC







On Thu, 20 Nov 2014, k5tra wrote:



> 'Looks like the attachment didn't make it onto the list. Here's a link:

>

>

>

> https://dl.dropboxusercontent.com/u/97484437/BBB%20Regulator%20%26%20Fan%20C

> ontrol.jpg

>

>

>

> Tom / K5TRA

>

>



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-- 
KJ6QFS
Sam Skolfield


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