Bench top power supply

[electron_misfire]

Excuse my poor articulation of words this is my first post on the forum.
As I've started making projects I've decided that I need a power supply.
My problem is that I've got a very small budget (around $50 aud) and was thinking if anyone had a way to get a cheap power supply or maybe even make one myself.
Would anyone have a simple schematic?
Thanks

[Rerouter]

You never said what voltage or current range you need,

For the cheapest you could get away with, find an old ATX power supply, and you have moderate current 3.3, 5 and 12V, (dont try using the -12 or -5 rails on older supplies there only good for a few mA at best)

if you want more control than that, then grab a transformer (remembering the rectified voltage will be about 1.4 times the AC voltage of the transformer) and make up a lm317 (or lm317/lm337 on a center tapped transformer for split rails) supply, remembering every volt not used has to be burned up as heat,

[electron_misfire]

You never said what voltage or current range you need,

if you want more control than that, then grab a transformer (remembering the rectified voltage will be about 1.4 times the AC voltage of the transformer) and make up a lm317 (or lm317/lm337 on a center tapped transformer for split rails) supply, remembering every volt not used has to be burned up as heat,

Thanks,
I think I'll need no more than 12V most of the time with around 1-3A.
I might try a transformer since I'll need 9v most commonly and an ATX power supply cannot output 9v and a battery won't provide enough current.

[han]

I build switching adjustable 0-3A , 0-12V, and power it using Laptop power supply.
it only cost about <$20 to build.
If you interesting i will upload the schematic and photo..

[electron_misfire]

I build switching adjustable 0-3A , 0-12V, and power it using Laptop power supply.
it only cost about <$20 to build.
If you interesting i will upload the schematic and photo..

Yes please,
That sounds like exactly what I need

[han]

definitely ,not the world best P/S... But it's work 

Here the pic and "handcrafted" schematic,
sorry for the crude drawing.
I build it a long time ago, so have to open and make new schematic..

[electron_misfire]

definitely ,not the world best P/S... But it's work 

Here the pic and "handcrafted" schematic,
sorry for the crude drawing.
I build it a long time ago, so have to open and make new schematic..

Thank you very much, this is perfect for my use

[Shock]

Looks really cool, but oh man that fuse holder did you have to? hehehe I would have sprung for a buck on that one and gone panel mount.

[han]

The fuse is from my old motorcycle..  Which i didn't have anymore
I didn't buy anything for that (only buy banana jack/plug)..
all is University project leftover even the used protoboard PCB..
<$20 is the cost of brand new component..but in my case, the P/S cost <$1 

[electron_misfire]

I've noticed in your photo that you have 4 trimpots but in your schematic you have only one.
which resistors are trimpots or are they just a replacement for fixed value resistors.

[han]

Actually i use 3,
The 4th is not used since i use LM2576-5 (the FB is connected to 5V directly)

[electron_misfire]

Oh, wow I must be really stupid to have missed those. Also are the diodes for the feedback area on the bottom left 1N5822's too?

[han]

the diode is for reducing voltage from Opamp pullup resistor, use regular diode (1n4148 or 1n400x (x is the voltage rating anyting will do))

- first trim pot from the left is for compensating voltage drop when the P/S is loaded
- Second one is for set the maximum output for I and V of the P/S
- Third one is for calibrating/Set voltage feed back and Voltage readout


note: the schematic is not the best one, open for improvement, like:
- Adding LC filter to output
- more smaller filtering capacitor (on input and output)
- Use 12 bit DAC digital control.(MCP4922)