Lab style Bench power supply

I would like to build my own unit that can give variable voltage and variable amps, if possible, also to be safe and reliable, not one of the homebrew units that use an old PC unit. I could pick one up from Maplins for less than £100 but I would like it to be made by me, also it can help my son with his Design & Technology coursework at school.
Can anyone point me in the direction for a good quality home made unit, parts list, schematics etc.
I understand the safety implications of 240V, I work with 600V so am aware and follow all safety measures.

Thanks in advance.

Stewart

How many volts and amps?
Variable or fixed?
Single or dual output?
I purchased an Elenco Kit, quite basic but had three outputs. I modified it with a PICAXE 14M to include voltage and current readings, overload warning, a fan control and the ability to turn on an off all three outputs simultaneously.
Let me see what I can find, schematics, model #, etc.

Have a look at this:

http://www.tuxgraphics.org/electronics/200707/bench-power-supply-unit.shtml

Nice idea, and you could produce something similar with a picaxe, good learning curve. I used an old P2 CPU heat sink and the 30 volt SMPSU from an A3 HP Inkjet. Flat-screen monitor power supplies or laptop chargers make a good source to then regulate linearly, if you see what I mean.
Chip (Atmel) needs programming for the kit listed.

HTH

Gareth

The cheapest way I know of doing this is to take £2.50 L200 regulator (36V, 2A) put it in a metal box with a few pot, knobs, fuses and feed it with a ex laptop PC supply.

Job done you have an adjustable volts and current supply.

The laptop PC supply (plastic brick) does not need to be cased of course, unlike a ex desktop PC supply (metal box).

If you are looking for a low cost 10 - 15V power supply schematic, you may try this one -


I had built this one for loads between 0.5A and 30A.
With some changes, also works for 5-10V or 15-30V. Stable, low noise, good regulation. The Mosfet tab is ground. Current limit can be added. I use one for car battery quick charge ( the 30A one) and one for my CB radio now. Usually cheap halogen lamp transformers are OK.

Have a look at the LM723 control circuit here........

http://www.thebackshed.com/Windmill/articles/VariablePowerSupply.asp

I like to use LM723 controllers with a generic pass transistor circuit, because they are dirt cheap circuits, and will give you both adjustable voltage and adjustable current limit. The web is full of schematics for them.

Thanks guys the LM723 looks like it fits the bill, will investigate further circuit wise and report back.

Cheers

Stewart

fernando_g said:

... I modified it with a PICAXE 14M to include voltage and current readings, overload warning, a fan control and the ability to turn on an off all three outputs simultaneously.
Let me see what I can find, schematics, model #, etc.

"Will design analog circuitry for beer"

Click to expand...

I think a power supply qualifies as analogue circuitry.

For PICAXE use, a supply which provides 2V to 6V at up to 200mA is probably suitable for a lot of things and can be built quite cheaply using various LMxxx regulators without needing great circuit design skills.

It might be worth building a simpler and cheaper supply like that to get experience before moving on to something more powerful with more complexity.

While designing it, "what if my power supply fails, or I have made a design error, and it dumps its input straight into the PICAXE circuit?" and "will it keep working under all PICAXE-side fault conditions?" questions will undoubtedly arise. It makes one think, and that adds an understanding that, seemingly expensive, commercial products aren't just about component costs but in answering those questions and ensuring, as best they can, bad things won't happen. You are not paying just for the parts but paying for some guarantee that it will always work as expected under all conditions.

hippy said:

While designing it, "what if my power supply fails, or I have made a design error, and it dumps its input straight into the PICAXE circuit?" and "will it keep working under all PICAXE-side fault conditions?" questions will undoubtedly arise. It makes one think, and that adds an understanding that, seemingly expensive, commercial products aren't just about component costs but in answering those questions and ensuring, as best they can, bad things won't happen. You are not paying just for the parts but paying for some guarantee that it will always work as expected under all conditions.

Click to expand...

Totally agree with you Hippy, that's why am asking the question on here where the experience and knowledge is abundant and some seriously qualified members can guide and help us lesser mortals to a satisfactory conclusion.

OK, I have had a look at the backshed stuff and looks like what I need. I can get hold of a few good quality multi tap transformers to give me the 240v to ?v input I need and bridge rectifiers and large caps to smooth the voltage, the schematic from backshed looks simple enough to make, now I would like to have LCD displays to show voltage and amps. The next question is how to integrate these with the backshed schematic?

http://shop.tuxgraphics.org/electronic/detail_microcontroller_powersupply.html

The Tuxgraphics kit is only 24 Euros - just need display / Picaxe / DC supply then program it