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

David McGough kb4fxc at inttek.net
Thu Nov 20 23:41:10 EST 2014

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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