Inexpensive Power Supply, Versions 1




it blew up (the rectivier)
and i dont want to repair it
the lm317 still works
i need the powersupply for my plasma speaker
i need 24 V 

Well it is so cheap that if you are handy (like me), it only will set you back 3 or 4 dollars for a nice case.

With a well stocked junk drawer, you could even make it for free.

Would you like to see what it is?  It is a low voltage, variable power supply.

V1 = from 1.5 to13 volts positive output
V2 = from 2 to 35 volts positive output

With Version 1 you cannot use the higher output because the fan can only hande 12 volts.

You can modify it to handle  the higher voltage, but I suggest you build Version 2 instead.
Version 2 starts in step 5.

Step 1: Bill of Material

Parts List:

1 - LM317 (Texas Instruments has the smd in the free sample program, the same one I used.)
1 - 10K ohm variable resistor (potentiometer) (pot)
1 - diode bridge (rectifier) or 4 fast diodes .  Watch the polarity!  Follow the schematic exactly.
1 - electrolytic capacitor 63V, 100-300uF (it doesn't matter.) ( Watch the polarity.)
1 - small heatsink for the LM317
1 - small PC fan (12V)
1 - small piece of circuit board
2 - connectors (so you can screw your wires instead of alligator clipping them)
1 - transformer (I used one that has 3 wires and 2 outputs, 13.5V and 27V)
Note:  In order to use the full power, use a transformer that can handle at least 1A because the LM317 can deliver up to 1.5A.
1 - box
1 - line cord with plug
Various lengths of wire

1 - voltage display (mine is from an old radio control (rc) transmitter)

Step 2: Assemble the Circuit

Just follow the schematic.  Tie a knot in the end of the line cord after you insert it into the case to act as a strain relief.

If you have a voltmeter you can put it on the output.

Be sure and leave room for the LM317 and some space for the heatsink.

Use 3 long pieces of wire to connect  the variable resistor to the top of the box.

I used a 10K ohm variable resistor.

Step 3: Prepare the Case and Wire the Circuit

First you will need a few holes in the case.  A knife or sissors will work fine.

1 for the power cable
1 for the fan
1 for the variable resistor
1 inlet for the fan (above the heatsink so there is better airflow)

1 for your meter

Once you make the holes you can wire all the components inside the box.
Place the fan in the exhaust hole and wire it up.

I forgot to take a picture of the inside of the lid on V1, so this is a picture of  V2.

Step 4: Plug It In

If you followed the schematic correctly, the power supply should work just fine.

Place a a multimeter on the output and turn the variable resistor.

If the fan speed changes, congratulations!   If nothing happens, recheck your wiring against the schematic.  Are the diodes placed correctly?  Is the polarity of the capacitor correct?

The voltage read-out on both meters will also change when you rotate the pot.

Step 5: Version 2

Bill of Material

1 - switch with 2 NO and 2 NC contacts (normaly open/normaly closed)
1 - LM317
1 - 10K ohm variable resistor
1 - diode bridge (the rating doesn't matter, as long as it converts AC to DC.)
1 - electrolytic capacitor 63V, 100-300uF (rating not important).
1 - piece of circuit board
1 - LED
1 - 1K ohm resistor
1 - line cord with plug
Various lengths of wire.

I asume in this part that you already made V1.



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    13 Discussions

    garrys newman

    9 years ago on Step 2

    there is a litle problem

    adj.-out resistance should be at least 220 ohms   so if you put your pot all the way up it will short adj.-out (0 ohms)  not realy good for the lm317

    1 reply
    robot797garrys newman

    Reply 9 years ago on Step 2

    ya i know
    but mine still works

    i did blow it when i powered a flyback transformer

    so the next version has some sort of protection


    9 years ago on Introduction

    OK, I made some corrections.  Version 2 needs its own schematic though.  It needs to show how to place the LED, the switch, and the resistor for the LED.  Also, you really should include a fuse on the hot side of the line cord before the transformer.  Otherwise if something happens, you have a nice little fire starter.

    3 replies

    Reply 9 years ago on Introduction

    For some reason I wasn't able to correct some of the embedded captions.  Maybe you can.  "connector" is misspelled every time (2 "n"s in the middle).  How do you like my update?  Where is the thermal fuse?


    Reply 9 years ago on Introduction

    the thermal fuse is imbeded inside the transformer

    the label shows that it can take 135 degre's celcius

    i will coorrect connector


    9 years ago on Introduction

    I always enjoy your I*, if only to try and figure out what you're saying.  I offer you encouragement - and safety!

    5 replies

    Reply 9 years ago on Introduction

    thank you

    i am corecting a lot on my grammas mistakes latly

    so i can be be understandeble for others.

    but it will never be the best


    Reply 9 years ago on Introduction


    What I was thinking was to download your I*, make some corrections, then send it back to you to post.  I don't want any credit.  I just think you have a good I* and it needs to be understand.  Or, I could just send you the corrections to make on your own. My email: mathman at comcast dot net.  Understand how to make this into an address?  I'm doing it this way so the bots don't have such an easy chance.  Glad to help.


    Reply 9 years ago on Introduction

    collaborated you into the project
    if i am correct you can now edit it

    if not you will get it via e-mail


    9 years ago on Introduction

    I did something similar as well ... 2 days ago. When I finished my dinner (china food), I was left with one bow like yours ... so I decide to put the power supply for my Proxxon there ... and it fits exactly, like the box was made for it :) ... and it is water resist as well.

    Good thinking :)