Raijuu.net

Hey folks, how are you?

So, some time ago in one of my classes we soldered a small variable power supply, I has in the need of one anyway, but unfortunately the supply had a lot of noise, I tried to use the ADC of an atmega8 and a LM35 to check the temperature of my room and the temp has varying considerable more then when the power was coming from my usb port.

And it was a pain to have to adjust the power to 5V everytime, burned a chip because I forgot to do that…

So that is why I decided to use the transformer from the old board and make a new board with a regulated 5V output and a variable output also. And since I was gonna do that, might as well do a decent enclosure.

Overview

• Single sided PCB
• +5V 1 Amp output
• Variable 1 Amp output
• Fine tuning potentiometer

Schematics

A lot of emphasis was put on making this power supply very stable, a big 4700uF cap takes care of the ripple, then come the regulators, after that a 220uF clean any noises that the regulator might have let pass. The polyester capacitors do a more subtle filtering.

Notice that for the rectifier diodes I used 1N5408 diodes, do NOT use a 1N40XX, this family of components only handle 1 A, while the 1N5408 can handle 3 A.

The LM317 is a adjustable voltage regulator that outputs 1,25*(1 + R2/R1) volts, where R2 is the resistance that you want to vary (we are keeping the R1 at 330 ohms).

I suggest you use a 2.2K pot in series with a 1K, that should give a max 13V output and the 1K resistor should make easy for you to tune the right voltage.

Board

Unfortunately as you can see, there is a jumper, I would prefer not to have one but the board would have to be a little bigger.

Anyway, the board is really simple and you shouldn’t have any problems making and soldering it.

Just be sure to solder the caps in the right position and be carefull the first time you power it up, if you see any smoke turn the damn thing off.

Transformers

On the primary side of the transformer you should find 3-wires or 4-wires and the way you connect then to the 110/220V switch is different, on the diagram below you should find the respective way to connect then, but since the color code can vary a lot, try to read the fucking manual of the transformer first, ok?

3-wire conection

4-wire conection

Download

The schematics and the board file in eagle format.
The schematics in PNG.

These are released as-is under
Creative Commons 3.0 – Attribution – Share Alike

Conclusion

Alright, that should explain everything you need to make the power supply, but now we need a enclosure since you probably don’t want this kind of project laying around.

So next time i’m gonna walk you trough on how to do a decent enclosure with a CFP-61013 box, this is a iron box with 6x10x13 cm, hence the name.

But I will try to make it generic enough so that you may use another box.

That is it for now, see you next time!