By Radu Motisan Posted on February 21st, 2010 , 17890 Views (Rate 15.07)
For this article, I'm going to show my supply, built from scratch, the design I've used (schematics) and a few safety tips.
First thing we need is a high power transformer. I've ordered a custom toroidal unit, with a primary for 220V mains, and two secondaries one of 24Volts, 10Amps max and another one of 12V, 0.5Amps max.
It's very heavy and it was quite expensive. I've also purchased a rectifier bridge, capable of handling 400V at 35A max:
For the case I opted for a computer power source metal casing: little space but eventually there was enough space to fit everything inside and keep it well organized.
An aluminum heat-sink was added to the case, with several screws so the case itself would absorb the extra heat and by so having a more efficient heat-sink.
Part of the case was cut so that I could fit a voltmeter and some power transistors directly on the aluminum heatsink:
The low power secondary would be used to obtain 12V and 5V with the L7812/L7805, to power the digital voltmeter applied on the high power secondary and also various microcontroller projects that don't require too much current.
I've soldered everything on a test board, using tick copper wire were needed (eg. for the connections to the transistors). A few holes in the front panel and I was able to place the 5k pot used to adjust the output, the LEDs, the fuse, and the black array of wire connectors for the output (The variable regulated output, the max regulated output, the non rectified alternative current output, the low power 5V and 12V output, etc).
My transformer gives 10A max at 24V, but this supply can handle up to 20A max, because of the 6 transistors. If you need more or less, simply change the number of transistors to suit your needs.
This supply is extremely reliable. I've used it for more then a year now, the initial design used 4 2n3055, but they failed quite frequently because of my high voltage experiments that produced spike backs. The TIP3055 seems to be almost indestructible, so I highly recommend it.
I've also placed a neon bulb, to protect the supply against high voltage kick backs. I'm not sure you need that if you're only doing low voltage stuff.
Here are some variants created by my readers
As a common effort of several people, this circuit diagram comes with several improvements. You can read the comments below for more details. Instead of the 2n3055 I recommend the TIP3055.
John also provided a regulated power supply that has a nice current control feature, but it uses the LM723 instead:
Here is the ready-built supply, using LM723:
Phil provided several helpful advises (see comments section) for others willing to build a power supply. He also experimented with multiple circuits, seeking for the better alternative.
For switched power supplies, see this article.