Introduction: 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
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.