Homemade power-supply for beagleboard

asaf_ebgi · February 20, 2011, 9:18pm

i have a 14V powersupply--connected it as input to the 7805regulator --
connected 100uF shunt capacitors on input and output of 7805--output
is 5V--does the beagleboard ever draw more than 1A?

Gerald_Coley1 · February 20, 2011, 10:37pm

Which Beagleboard are you referring to, BeagleBoard or BeagleBoard -xM. If you read the System Reference Manuals they indicate the recommended size of the power supply. If you have a BeagleBoard, then as long as you do not load down the USB Host port, 1A should be OK. If you are referring to the BeagleBoard-xM, then your homemade power supply will not work as I recmmend a 2A power supply due ot the oinboard HUB…Also kKeep in mind that you are dropping 9V across the 7805 which generates a lot of heat. I would be surprised to see you get 500mA out of such an arrangement whiteout a real big heat sink.

Gerald

Dave_Higton · February 21, 2011, 8:05am

Quoting Gerald Coley <gerald@beagleboard.org>:

Which Beagleboard are you referring to, BeagleBoard or BeagleBoard -xM. If
you read the System Reference Manuals they indicate the recommended size of
the power supply. If you have a BeagleBoard, then as long as you do not load
down the USB Host port, 1A should be OK. If you are referring to the
BeagleBoard-xM, then your homemade power supply will not work as I recmmend
a 2A power supply due ot the oinboard HUB..Also kKeep in mind that you are
dropping 9V across the 7805 which generates a lot of heat. I would be
surprised to see you get 500mA out of such an arrangement whiteout a real
big heat sink.

Gerald

I would just add one more thing: when a 7805 fails because it has become
too hot, it's common for it to fail in such a way that there is a short
between input and output - which would apply 14 volts to your BB, which
must certainly result in further damage. By applying such a high input
voltage to your 7805, you are almost certainly going to make it get very
hot.

It would be far cheaper to get a more appropriate supply.

Dave

mark_hubrich · February 21, 2011, 1:44pm

I’m about to start making one of these too. I’m going to take a stab at using a pwm chip from a laptop pc. I have one from Maxim (couldn’t say what # till I get home) that according to the datasheets is designed to take a range up to 24v from a battery or another DC source and provide steady adjustable voltage for cpu’s and such. I believe the one I recovered from an old laptop has 2 adjustable outputs and its supposed to handle 6amps.
I’ll be able to provide more details more accurate in about 10 hours or so. The chips are small but once you mate them to a SchmartBoard size doesn’t matter.

I like this idea because:

you can use wide range of batteries or other DC supply up to 24v.
since it’s a switching power supply,PWM, it only produces what it needs to to maintain set voltage level. it would save power and not waste it with heat as the 7805 does.
the dual voltage control would allow you to take the battery voltage to 5v and generate 3.3v off the generated 5v.
6amps
adjustable, possibly other chips have more channels and beagle’s gpio or i2c can control other voltage levels.

I’ll rummage through the 10 or so laptop motherboards I have to see what else laptops use to meter and distribute their power.

Mark

djlewis · February 21, 2011, 2:39pm

7805's are over rated. I find they operate best at about 7.5 to 9vDC
input.
Even 12vDC makes them dissipate too much heat. Unlike the mention
I have never had one short input to output. Though it might happen.
There are much better regulators to use. The 7805 is way dated. But
then I have a bunch around my design bench
Failsafe is very important with the tight voltage specs of the
BeagleBoards.
If you are designing your own, do plan in protection for all
possibilities
as you can.

djlewis

Nils_Pipenbrinck1 · February 21, 2011, 5:15pm

Just a word of warning:

If you draw 1A at 14V from the 7805 the regulator has to convert 9 watt
of energy into heat. This is a lot and the regulator will overheat
within seconds. Either you need a good heatsink or better use a power
supply with a lower voltage. 9V would be a lot better.

Oh - And you can buy a cheap switch mode power supply "wallwart"-style
for just a few bucks. These can supply plenty of power at 5V, don't
require any regulation and thus don't have the heat problem.

Dave_Higton · February 21, 2011, 5:35pm

Quoting Nils Pipenbrinck <np@planetarc.de>:

mark_hubrich · February 21, 2011, 11:33pm

It is the MAX8743

Howard_Harte · February 22, 2011, 5:43am

If you really want to make your own power supply, you can use WebBench on the National Semi website to design some very nice switching supplies. For some regulators, you can even order a kit from National including PCB and all the components that WebBench recommends. It is fun, but not practical from a cost perspective unless you really want to learn about switching power supplies, or have more unique requirements than the $10 5v@2.5A supplies.

I used it to design a 12-15v to 6V-7V adjustable @10A dc-dc switcher, and used some LDO’s to get 5.0V, 3.3V and 1.8V, and I needed all four voltages and some adjustability on the 6V rail. But now there are even switchers that can do multiple output voltages, and can handle fancy stuff like power sequencing.

-Howard

Daanii · February 22, 2011, 5:23pm

"the $10 5v@2.5A supplies"

Can you steer me towards one of those? DigiKey no longer has their
BeagleBoard power supplies listed on the BeagleBoard.org parts page.
And the Sparkfun wallwart is only 1A. (I noticed that only after I
already bought it.) I haven't been able to find anything bigger.

Thanks.

Caius_Chance · February 23, 2011, 9:13pm

I bought this from digikey along with my bbxm:

T1058-P5P-ND

It is a 2.5A power supply and I tested working with the BBxM.

K410

Rgds, Caius ‘kaio’ Chance - http://fedoraproject.org/wiki/user:kaio (sent from mobile device)

Caius_kaio_Chance · February 23, 2011, 9:20pm

I bought this from digikey along my bbxm:

T1058-P5P-ND

It is a 5V 2.5A power supply which I tested working on the bbxm.

K410

Rgds, Caius ‘kaio’ Chance - http://fedoraproject.org/wiki/user:kaio (sent from mobile device)

Daanii · February 25, 2011, 3:21pm

Hey, thanks. That's exactly what I was looking for, but never found.

Caius_kaio_Chance · February 25, 2011, 6:49pm

I think we need to update the link on the webpage for convenience of buyers.

Naveen_Dhawan · February 26, 2011, 6:36pm

YES please do! I bought a power supply that switches between voltages
between 3 V to 7 V from radioshack. It had the 5V @ 2amps I was
looking for but the price is three times the amount of the one digikey
sells. I would gladly save the money I spent to buy that one.

Sid_Boyce · February 26, 2011, 9:08pm

I just came across this on the HPSDR forum - $13.00 US.
http://cgi.ebay.co.uk/ws/eBayISAPI.dll?ViewItem&item=130417466390

Others I didn't look at.
http://cgi.ebay.co.uk/ws/eBayISAPI.dll?ViewItem&item=280584969393

http://cgi.ebay.co.uk/ws/eBayISAPI.dll?ViewItem&item=290509371602

http://cgi.ebay.co.uk/ws/eBayISAPI.dll?ViewItem&item=390103502122
Regards
Sid.

Ted_Larson · February 26, 2011, 10:43pm

I have used one of these to power my Beagleboard, and it works super.

http://www.pololu.com/catalog/product/2110

-Ted

Specialcomp · February 26, 2011, 11:41pm

Here's a cheap AC Power Adapter tested for Beagleboard with US prongs
and universal input range

http://specialcomp.com/beagleboard/xm.htm#5VPwr

Special Computing