Bench Power Supply Recommendation

chopsuey · Post by **chopsuey** » Fri May 12, 2006 6:20 am

Can anyone recommend a reasonably affordable bench power supply? I am done dealing with batteries when working with my PIC projects. Also I am going to be looking into working on some other electronic projects so I will need variable voltage.

Sambuchi · Post by **Sambuchi** » Fri May 12, 2006 6:37 am

have you checked your local hobbie stores? Thats where you should start.

philba · Post by **philba** » Fri May 12, 2006 8:24 am

You could also check out these guys - they generally have decent stuff at ok prices. I noticed a wide range of products. maybe there is one there that meets your needs and budget:
http://www.web-tronics.com/test-equipme ... plies.html

sambuchi-san - great avatar!

Robert Reed · Post by **Robert Reed** » Fri May 12, 2006 8:25 am

Have you thought about building your own? If you have a substantial "junk Box " like most of us, with only the addition of a few purchased parts you could do this, and design it for your exat needs only. This could be any where from bare bones to the sublime. I have built approx. a dozen bench power supplys in the past and am currently designing my "ultimate "supply. Of course, a junkbox full of parts helps keep costs down. Eventually, you will need more than one supply, as the demands here cover too much ground. But it sounds like what you want for starters is a nice low power, COMPACT supply that won't take up much bench space.

Newz2000 · Post by **Newz2000** » Fri May 12, 2006 11:18 am

Robert Reed wrote:Have you thought about building your own?

here's a link to a schematic... http://www.electronickits.com/kit/compl ... e/k114.pdf

Radio shack has 25.2v center tapped transformers for $10, and adjustable voltage regulators for $4.5 and the caps and everything you need. You could have a +/- 12v power supply or a 25v power supply for $20 tonight if you wanted. Here's the datasheet for that voltage regulator... it has a ton of cool circuit ideas listed (they're close to the end)

You know, the little radio shack near my house is closing and everything is 10 - 50% off... maybe I should go buy the parts to make two of these.

chopsuey · Post by **chopsuey** » Fri May 12, 2006 12:43 pm

Thanks for the ideas guys, I might give it a shot and build my own this weekend.

Dean Huster · Post by **Dean Huster** » Sun May 14, 2006 5:55 am

Don't insist that you have a variable supply that goes from zero to +50v, triple variable supply, 10a current capability, etc. I've never found that a variable supply was that useful except for educational experiments, such as plotting diode current vs. voltage or some such thing. You'll find that 99% of your needs will be fixed voltages and that can cut down on the expense of building a supply a lot. Myself, I'd stick with simply using several fixed regulators to give a Â±5, Â±12 and Â±15. You can always add some for lower (3.3 or 3.0 voltages) for newer ICs. Usually 1a output is sufficient for most things. You can cobble together a supply like that for under $20 or $30 if you have a decently-stocked junk box.

My last foray into Radio Shack transformers left me with a bad taste in my mouth. They were so inefficient or poorly-made that they heated up to uncomfortable temperatures with no load. I'd try using transformers from junked VCRs or better yet, a junked stereo amp since they tend to be beefier.

Dean

Robert Reed · Post by **Robert Reed** » Sun May 14, 2006 9:33 am

"I've never found that a variable supply was that useful except for educational experiments, such as plotting diode current vs. voltage or some such thing"

Theres a lot of truth in what you say Dean.However I always like to be able to vary my supply somewhat above or below target levels to note the effects on new circuit design, especially with mobile or other battery operated equipment. With todays chips, adding the variable doesn't require much.

Newz2000 · Post by **Newz2000** » Sun May 14, 2006 1:54 pm

I've never owned a variable power supply but started thinking about making one. How trustworthy is the voltage output (as far as stability is concerned)?

If I set it at 3.3v with no or a very light load (.1ma for example) will it stay at 3.3v or do I have to keep checking and adjust it up once I put a load on it?

Assuming something like the LM3017T.

Robert Reed · Post by **Robert Reed** » Sun May 14, 2006 4:43 pm

Matt
I assume you meant LM317. I am in the process of completing a rather elaborate bench supply and the LM317 was chosen for various outputting. After running extensive tests on this chip, I've found that is everything the manufacture says it is--exellent! This chip equals the perfomance of my previous design which was a fairly complex discrete design. It only falls short in one respect, and that is no provision for remote sensing. If you are going to deal in voltages below 2 VDC, you may want to add an LM113 in order to adjust the supply to true zero. Also consider adding a FINE adjust for voltage control. This is merely a pot seriesed up to the normal voltage adjust control-about 10% of that value works fine.

chopsuey · Post by **chopsuey** » Mon May 15, 2006 12:34 pm

Well I would be happy with a 5v supply for right now for my PIC projects. So if I get one of the 12.6v center tapped transformers from Radio Shack, follow the schematic Newz2000 linked to in his earlier post and put a 5v voltage regulator on the output I should be all set? Thanks for all the help guys.

Engineer1138 · Post by **Engineer1138** » Mon May 15, 2006 1:53 pm

Newz2000:
My benchtop supply is about 10 years old and is rock solid to within a few 10's of mV. Putting a load will not change the output voltage unless it is over the current limit setting. That current limit is perhaps its most useful feature.

1. Need to test polarity on an unmarked batch of LEDs? set current limit to 20mA and connect LED. Voltage doesnt' matter since supply will only allow 20mA and I can see which direction the led needs to light up.

2. Bringing up new prototype board: set to safe current limit and appropriate voltage. If voltage folds over at the limit, I have a short, or a backwards chip or something, and I discover this without smoking an expensive IC.

3. Likewise I can immediately see motor current draw at various voltages by playing with the Volts knob and viewing the current consumption without needing an ammeter connected.

My supply has variable voltage & current settings with digital readouts for each and only cost $199 brand new and came with schematics (that I have since lost

But I have seen similar ones even cheaper at catalogs like Circuit Specialists & MPJA for under $100, just not with both digital readouts.

To the OP: rather than build one, I'd look on eBay for an old hp lab power supply. Those things are worth their weight in gold and I'd expect to find one with the analog meter for under $50 these days.

A good benchtop PS is one of those things you never think you need before you have one but you can't live without after you get it.
Kinda like my wife, actually

Engineer1138 · Post by **Engineer1138** » Mon May 15, 2006 2:04 pm

Replying to my own post...
I just checked ebay and found an hp6202 supply for $20 "as-is". Even if it needs work, the transformer and case/meter are worth more than that. Auction expires in 19 hours and best of all the guy lives just a few miles from me if I decide to get it and save on shipping.

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