THE MINISUPPLY

3 - 30V / 1.5A Regulated Power Supply



INTRODUCTION

The MiniSupply was my very first DIY project, and it was a birthday present for my 11th birthday. Though even at this age I was fond of electronics, I didn't yet posess the skills and patience to properly construct the thing in a box. It ended up in a corner of my room unfinished for a very long time.

The MiniSupply Years and years later a day came where I really needed a small power supply, and I decided to finally finish the project. I bought a new enclosure, a nice new panel meter and banana connectors. It still works, and due to its size it really is a handy versatile minisupply


HOW IT WORKS

The MiniSupply is a very straightforward LM317 stabilized power supply. It is easy to understand and easy to build yourself (provided that you have some basic electronics skills)
The schematic is presented below:
<schematic>

On the left you will find the mains connected parts. Always be sure to put the correct fuse, that corresponds to the transformer rated primary current. The transformer VA rating is calculated by multiplying the "unregulated" transformer output voltage with the maximum output current plus a margin. In this case: 35V x 2A = 70VA (Volt-Ampere)

The bridge rectifier has four capacitors parallel with the diodes. These will help reducing some noise on the output voltage. The bridge rectifier feeds a large tank capacitor, which will filter the mains ripple current and acts as a buffer for power transients.

Then there is the regulator part.


INSIDE THE BOX

The MiniSupplyI don't have pictures left from the first build. But they wouldn't make a good example anyway, so I'll just stick with the second build, of which I have only 2 pictures.

The power supply is assembled in a 2-shell box made of PVC plastic. That made modifying the box to fit the heatsink, voltmeter etc really easy. All mains connected parts are located left, including the mains fuse. Since there are no metallic "touchable" mains connected parts, there is no need for grounding the case. The PCB, was designed to have the main capacitor located on top of it. That didn't fit with the box, so it's glued on the right, and connected via wires.

The LM317 regulator is mounted on the heatsink in the back. All controls are -obviously- on the front. The front was made very simple with paper glued on the box, then laminated with self-adhesive transparent foil. A few cutouts to feed the controls through, and presto!


USING THE MINISUPPLY

Is as easy as using your vacuum cleaner. Simply plug in the power, connect wires to the banana outlets, switch on the supply and adjust the voltage to your likings. Measuring voltage or current simply by selecting voltage or current on the front panel and the read the scale.

If your setup is drawing too much power, shorts out,, or for any reason the supply overheats, then the internal protections inside the LM317 will prevent damage to the supply and maybe also your setup...

This supply is soo mini, but soo handy...