Lab Power Supplies

[AndrewT]

Originally Posted by dangus

........... the rest isn't hard. Transformer, caps and rectifiers could come from a junked hifi receiver.
...............
20 amps???!!! Doing that with a linear supply will be interesting... big transformer, big caps, lots of power transistors.

and what about dissipation when the output voltage is <<30Vdc?

A multi tapped transformer is virtually obligatory for a linear supply.

[star882]

A low voltage buck converter is pretty easy to build. And no high voltages after the transformer so it is very good for beginners.

[AndrewT]

Originally Posted by star882

A low voltage buck converter is pretty easy to build. And no high voltages after the transformer so it is very good for beginners.

I've seen some on the net but don't know if they are safe.

[Bakmeel]

Does it have to be the cheapest of the line?

I've been using Delta Power Supplies for years in the lab and I'm convinced they are the best... not the cheapest though....

They'll last you a lifetime... I have an oldie at home. (30V / 10A) linear jobbie. Weighs a ton, but still works beautifully after 20+ years

[DRC]

Buy a secondhand one made by a good manufacturer. Unless you want very high power stick to linear designs.

dave

[star882]

I've seen some on the net but don't know if they are safe.

Start with something very low power, like step down a 9v battery to 5v or 3.3v. Such a low power circuit is very safe to handle.

Unless you want very high power stick to linear designs.

Switching regulators have become much cheaper than in the past. You'll really want switching for any significant amount of power as the thermal dissipation of a linear becomes prohibitive at higher powers. In modern commercial equipment, I have seen linear only used up to about 2w or so, except LDO which is still used at higher powers as thermal dissipation is still manageable. Above that and switching is the regulator of choice. In fact, given the very low cost of switching regulator circuits, the break even point where a switcher would be cheaper is surprisingly low and continues to fall.

Note that a low voltage buck converter is only slightly more difficult to design than a linear. And it is a good learning tool for beginners. My first switcher was based on a National Semiconductor switcher-on-a-chip and I used it as my bench power supply for a few years. To give you an idea of how easy it is to build it, I built it in 5th grade. It worked perfectly the first time I turned it on.