I’ve updated my bench power supply project description with a summary of the project (as follows):
This project started as me trying to fulfil a need for a reliable and convenient power supply and wanting to learn some lessons along the way. I designed the project in sketchup and then proceeded to go through various stages of construction. There were a few design changes along the way but nothing major. I decided to add an external voltage probe and a switch to allow voltage measurements either from the ammeter or ground.
- My Adjustable Voltage Circuit
- My Panel Meter Circuit
- My Aluminium Supply Case (Labelled)
- 2x DPDT switch
- Green Binding Post
- 4x Red Binding Post
- 4x Black Binding Post
- 3mm Red LED
- 6x 3mm Green LED
- 7x 3mm LED panel clips
- 4P2T rotary switch
- Amp Panel Meter
- Voltage Panel Meter
- Red Multimeter Lead
- 2x 6mm knobs
- ~20cm of 3mm 3:1 Heatshrink
- 2x TO-220 heasinks
- ~50 Crimp terminals
- Lead Free Solder
- 3x 47 KΩ resistors
- 3x 5.6 KΩ resistors
- 3.9 KΩ resistor
- 820 Ω resistor
- 12 KΩ resistor
- 1.8 KΩ resistor
- Soldering Iron
- Crimping tool
- Snipe nosed pliers
- Wire cutters
- Glue Gun
- Phillips screwdriver
- 2mm Allen key
For most of this it should be clear how it goes together. The circuit construction just followed my power supply schematic. If there is anything that needs explaining further then feel free to ask. Unfortunately i got a bit carried away at some parts and forgot to take photos, I’m still learning to take my time.
Note: There is an updated version of this schematic here
I’ve been unable to get to the tools lately to finish off the bench power supply case, so thought i would do an update for people looking to do a similar project.
I’ve drawn up the circuit schematic for the bench power supply. I’ve given colour coded labels for the cables coming from the ATX power supply (correct according to wikipedia at time of publication) and shown all the circuits that are needed, including all component values that I’ve so far decided on. The resistors attached to the LEDs will be chosen at later date, hence those have no values in this schematic.
I hope you find it useful
edit: I should add that i have some planned upgrades to this, such as relays to switch the binding post outputs based on the state of the power good line. This should protect any equipment from unstable voltages when the supply is first turned on. Also I would like to put resettable fuses in line with the outputs to prevent over loading any of the components. These are complications that can wait though. For now i just want to get the basics working.
I’m starting out with a highly useful project.
Realising that i need a decent power supply for my projects, and a place to work from, I looked at getting myself a bench top power supply, but at £100+ for a decent one, I looked into building one and came across this instructable. It looks like i can build one for less than the cost of buying and it should give me more output options and more current. Since the whole point of this adventure is to start building stuff from scratch too, it makes sense to make it myself.
The principle looks fairly simple and the only circuits required seem quite basic so i jumped in and started ordering parts.
While i was waiting for parts, i set about designing my new power supply in google sketchup (free):
The power supply is based on an old pc ATX power supply. This is great because they are cheap, efficient and provide a huge amount of current on demand. I didn’t have any spare power supplies lying around so i asked a few friends and managed to get a nice 550w supply for free. This has a huge 12cm fan on top which will be useful for cooling my electronics as well as the supply itself.
The supply has a bundle of wires coming from it. All wires of the same colour provide the same function and so can be bundled together.
the voltages provided are:
-12v: blue wire
3.3v: orange wire
5v: red wire
12v yellow wire
as usual the black wires are ground
There are a number of other wires coming from the supply and these have special functions that i’ll explain later. If you’re curious you can look at the wikipedia page
in addition to these outputs I’m adding a variable output by using a variable low drop out, linear voltage regulator on the 12v line. This should give me from 1.4v to 11.6v with a couple of amps.
ATX power supplies have had a number of revisions and some older ones include a -5v output on a white wire. Unfortunately this one doesn’t but I don’t think I’ll miss it much.