DIY 0-30V Regulated Power Supply
So over the weekend I saw a commercial 0-30V 3A regulated power supply with digital output, current & voltage control. The only drawback was it costs RM499 which is well over my budged. So I decided why not build my own from whatever i could scrap and save some money. Firstly I didn’t need current control and i needed something within 1A. Searching the interweb turned out many designs but they were all complex and most didn’t come with eagle schematics, then I remembered that last year i purchased a schematic book from Jalan Pasar which had a schematic for a 0-30V AC/DC Regulated Power Supply able to supply up to 1A, the schematic looked easy enough plus the parts were relatively inexpensive.
Bill of Materials
|1||Metal Case||19||19||Dimension 5 x 3.5 x 6|
|1||Transformer||25||25||15-0-15 24VA 1.6A|
|1||Bridge Rectifier||-||Supports up to 2A|
|1||LM317T||3.5||3.5||0-35V @ 1.5A|
|1||330 Ohm||0.1||0.1||1/4 W|
|1||100 uF eCap||0.2||0.2||50V|
|1||1000 uF eCap||0.5||0.5||50V|
|2||0.1 uF (104)||0.1||0.2||Ceramic NP|
|1||1.5A Fuse + Holder||1.20||1.20|
|4||PCB Plastic Stand||0.3||1.2|
|2||ETB 1303||1.5||3||Red & Black|
Designing The Schematics
D-I-Y Kit schematic from book purchased at Jalan Pasar.
Notice that the schematic recommends using a 100 ohm resistor for R1 and a 5/10K Pot for VR. I decided to follow this and my supply hit the max even before the nob hit 1/4 of a turn, had to replace R1 with 330R to fix that problem.
Schematic on Eagle
Making Improvements & Fixes
- Adding Protection Diode
Quote from National Semiconductor data-sheet for LM317T (Page
- Adding Bridge Rectifier
Adding a bridge rectifier makes it easier as there is less routing on the PCB. The bridge rectifier chosen could sustain up to 2A.
- Adding Plastic Stands
Plastic Stands would mean that my PCB would not be touching the housing. This is needed if your using a metal housing.
- Adding T-Blocks
Adding T-Blocks meant that it would be easier to replace/remove wires if there was an upgrade in the future.
- Replacing 100R with 330R
Using an LM317 Calculator from http://www.whatcircuits.com/lm317-calculator-v2/ i found that when using a 330R was more suited for a 10K Pot in order for the power supply to reach its max while having the knob turned to almost max (Using a 100R would mean turning the pot 1/4 to reach the max output of the power supply).
Etching The Board, Mounting Items & Soldering
The toner-transfer method was used to do the transfer while Ferric Chloride was used to etch the board.
A fully soldered and assembled board
Always check the polarity of the capacitors before turning on the power supply or it will pop real loud and smell like charred fish.