The World's Smallest Bench Power Supply!
How would you like to build the world's smallest bench power supply (well, probably, anyway)? You can build one, as shown at right, with an ECROS Technology Mini-PSU kit, some parts from your spares drawer and a little creativity.
Note that not all the parts necessary are included in the kit - which is part of the fun!
(Use the menu on the left hand side to go back to the Mini-PSU introduction and for information about adjustable output voltage PSU kits.)
You can easily buy an enclosure for the Mini-PSU, but where's the challenge in that? Take a look in your basement and you'll probably find you have some sheet aluminum down there. Or, pick up a piece of roof flashing from your do-it-yourself store for less than a dollar.
With a bit of patience and, preferably, a bench vice, you can cut and form a small sheet of aluminum into a bracket as shown in the picture (click for a larger one). Use the Mini-PSU printed circuit board, before you assemble it, to mark the position of the mounting holes. Make a hole for the shaft of a potentiometer from your spares box, also a switch and some kind of output terminals, according to your preference and what's on hand. Make all holes before folding the aluminum. You may want to make a mock-up out of card first.
Mount the assembled Mini-PSU board to the bracket with suitable machine screws (4-40 in the USA, for example). Thread the screw down through the PCB, using insulating washers on both the top and bottom. You can use a nut next as a spacer and finally put a nut on underneath the base of the bracket. Threading the screw up from the bottom doesn't work so well as there is no room to tighten the nuts.
Wire the output from the GND and VOUT pads of the PCB to your terminals via the switch. You will not have put a trimmer, R1, on the board, so wire from its pads to the potentiometer on the bracket. The pad of R1 closest to C1 is the wiper. To have the voltage increase as you turn the knob clockwise, wire pin 1 of R1, the square pad, to the side of your potentiometer that the wiper reaches when you turn the knob fully counter-clockwise.
You will want to stick some rubber feet on the bottom to give your power supply some stability. The knob of the potentiometer may be the heaviest part, making the whole thing a bit front-heavy, so put feet at the very front edge. You can make a nice front panel decal with an ink-jet printer by printing on self-adhesive paper. Figuring out where the voltage markings go will involve some trial and error. You will see in the pictures that I stiffened up the bend between the front and base with epoxy.
If you want your power supply to provide high currents and/or drop a high input voltage to a low output voltage, you will probably need to use a larger heatsink than the one in the kit. You can adapt the ideas on this page to a larger housing and use a heatsink that does not mount on the board. This sort of thing is often available at surplus electronics stores. Don't forget that the mounting tab of the regulator is not isolated from the circuit. Either use an insulating kit to electrically isolate the regulator from the heatsink or use an insulating mounting arrangement for the heatsink in the housing. If the housing is enclosed, make sure there are holes for the heat to get out!
Starting with my tiny bench power supply and the ideas on this page, you will be able to come up something much better and exactly suited to your needs.