[arm-allstar] power up

Sat Dec 6 00:57:54 EST 2014

There are data sheets on all these parts. I attached one for the LM3xx/78xx parts. Typically the spec is .2 to .3 uf on the input and .1 on the output.  These are mounted as close to the pins as possible. I suppose it would not hurt to put an electrolytic on the input but you want to filter higher frequencies and electrolytics are poor at that thus the small .22 or .33 on the input.  It is also not a good idea to put a larger value electrolytic on the output. These regulators can be damaged by reverse voltages - input at a lower voltage than output - which could happen if you had a large charged electrolytic on the output and the input went low. Often you see a diode from input to output of the regulator, cathode towards the input, to limit any reverse voltages but this is usually not necessary.  

There is plenty of data on the Internet on these regulators. Google  lm7805  -  both fairchild and TI data sheets are out there in entirety. 

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

Date: Fri, 5 Dec 2014 22:37:33 -0600
From: asylthe at kc9ona.com
To: arm-allstar at hamvoip.org
Subject: Re: [arm-allstar] power up

That's good information. I'll have to rework my circuit if if isn't correct. I've never had an issue and it puts out a stable 5V, but I can't argue with the manufacturer specs.
Thanks!
On Dec 5, 2014 10:33 PM, "David McGough" <kb4fxc at inttek.net> wrote:

Most data sheets recommend a value of 1uF to 10uF on the INPUT side of the

LM78xx regulators. This needs to be a good quality capacitor (low ESR),

just as Bob mentioned. I typically use a 10uF, 50V tantalum cap on the

input--I've got a big bag of them!

73, David KB4FXC

On Fri, 5 Dec 2014, Andrew Sylthe wrote:

> I typically use a 22 picofarad on the input, and a 10 microfarad on the

> output of the 7805. Is that not the correct way to do things?

>

> Thanks!

> On Dec 5, 2014 8:29 PM, "Bob" <Bob at fot.com.au> wrote:

>

> > Hi All

> > When using a 7805 Regulator male sure you put  low ESR capacitors

> > (10microfarad) right on the input and output terminals to ensure it doesn't

> > oscillate

> >

> > Bob

> >

> >

> >

> > On 6 December 2014 10:12:45 "Mark Herson, N2MH" <n2mh at n2mh.net> wrote:

> >

> >  I'm running a pair of BBB's each from its own 7805 voltage regulator with

> >> no problems. One BBB is an Element14 card (which is the Chinese version,

> >> problably what comes from MicroCenter) and the other is the USA version

> >> from Beaglebone.org. No startup problems have been noted at all.

> >>

> >> Of course, when using a 7805 voltage regulator, one must use a good

> >> heatsink. I measured the current draw at 350 mA or so. With an 8 volt

> >> voltage drop, that comes out to about 2.5 to 3 watts that the voltage

> >> regulator must dissapate. This requires a pretty good heatsink.

> >>

> >> 73, Mark, N2MH

> >>

> >> > To: arm-allstar at hamvoip.org

> >> > From: ke2n at cs.com

> >> > Date: Thu, 4 Dec 2014 06:57:55 -0500

> >> > Subject: [arm-allstar] power up

> >> >

> >> >

> >> > Any one else have a BBB Rev C power up problem?

> >> >

> >> >

> >> >

> >> >

> >> > http://elinux.org/Beagleboard:BeagleBoneBlack#Improper_

> >> Power_Down....All_

> >> > Rev

> >> > isions

> >> >

> >> >

> >> >

> >> > I got two units from Micro Center and they both have a really hard time

> >> > getting started.

> >> >

> >> > One unit I got from Spark Fun works fine every time.

> >> >

> >> >

> >> >

> >> >

> >> > Ken

> >>

> >>

> >> _______________________________________________

> >>

> >> arm-allstar mailing list

> >> arm-allstar at hamvoip.org

> >> http://lists.hamvoip.org/cgi-bin/mailman/listinfo/arm-allstar

> >>

> >> Visit the BBB web page - http://www.crompton.com/hamradio/

> >> BeagleBoneBlackAllstar/

> >>

> >

> >

> >

> > _______________________________________________

> >

> > arm-allstar mailing list

> > arm-allstar at hamvoip.org

> > http://lists.hamvoip.org/cgi-bin/mailman/listinfo/arm-allstar

> >

> > Visit the BBB web page - http://www.crompton.com/hamradio/

> > BeagleBoneBlackAllstar/

> >

>

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