Re: [Phys-l] 5v power supply

[Dan Beeker <debeeker@comcast.net>]

Don,

You need to ask how much output current you will need along with the 
voltage requirement.

You can buy good single output variable power supplies for $100 to $200. 
Less if you look hard.

0-5V power supplies are not very common and are somewhat expensive.

Here is something close. Is 0 to 15V at 300ma:
http://www.scientificsonline.com/build-a-power-supply-kit.html?&cm_mmc=Mercent-_-Google-_-NULL-_-3101500&mr:trackingCode=06721735-DB81-DE11-8C0A-000423C27502&mr:referralID=NA

Or go to a higher voltage output:
http://www.canakit.com/electronic-kits/power-supplies
One of these might actually work for you with a wallwart (see comments 
below).

If you really must make them I would use an LM317 ic. Start with a kit 
as you then get a pc board to build it on (usually). It is straight 
forward to build a 1.2V to 5V variable supply. If you need to go to zero 
volts then you will need a negative voltage to reference the 723 to zero 
volts. There is an example circuit on the National emiconductor data 
sheet you can work from. There are also many inexpensive kits that you 
can start from though they all take the easier 1.2 to 5V approach.

For the negative voltage you might try a Maxim 680. I haven't used it 
but it looks like it might work. You may need to buffer the output 
rather than directly connect it to the 723 as the output will change 
with the current drawn. I haven't crunched the numbers - just something 
to consider. Or just buy a fixed power supply with positive and negative 
outputs. But then the cost is probably too high.

I absolutely  would not build the ac supply/transformer circuit for the 
input to the regulator. Too many liability issues. Rather purchase a UL 
listed wallwart of the appropriate ac voltage and current rating. This 
helps you avoid a myriad of legal problems and much simplifies your 
efforts. As long as the output voltage of the wallwart is below 25V or 
so you should not have to worry (much) about someone getting electrocuted.

Dan Beeker

On 11/17/10 6:38 PM, phys-l-request@carnot.physics.buffalo.edu wrote:
> From: "Don McQuarrie"<mcquarrd@comcast.net>
> Subject: [Phys-l] 5v power supply
> To:<phys-l@carnot.physics.buffalo.edu>
> Message-ID:<FB657916A68D4345A062E3B6C30D22E2@dadpc>
> Content-Type: text/plain;	charset="us-ascii"
>
> I'm looking ahead to some new lab work in my physics class and have found a
> need for several adjustable 5volt power supplies. Were I to attempt to buy
> them commercially, I'd be out my budget for the next decade (ok - a bit
> exaggerated), but building them would be a cool project, especially if I
> could get some perf boards pre done. Does anyone have a suggestion for a low
> end 5v adjustable (down) power supply schematic? Cheap is an operative word
> right now in the state of Washington. It would be much appreciated.

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