Fixed Bench PSU

[yngndrw]

Hi,

Well I want to make a simple bench PSU which will give out: +-12V @ 1A and +-5V @ 1A.

Looking through my CPC catalogue, I've made the following design [Attached]. (Although the -12V is now limited to 0.5A, due to the limitations of CPC.

Parts list and prices:

[b]Parts list (CPC Part Numbers) - Prices in GBP, excluding VAT

[ Ref			- CPC Part #	- Description					- Price (Total) ][/b]

T1			- FF01553	- 60VA Toroidal 2x15V				- £10.85

BR1			- SC05773	- KBPC601 (50V, 6A Bridge Rectifier)		- £1.97

RG1			- SCL78S12CV	- L78S12CV (+12V, 2A Regulator)			- £0.99
RG2			- SCL7912CV	- L7912CV (-12V, 1.5A Regulator)		- £0.72
RG3			- SCMC7805CT	- MC7805CT (+5V, 1A Regulator)			- £0.26
RG4			- SC05482	- MC7905CT (-5V, 1A Regulator)			- £0.39

C1 & C2			- CA04567	- Aluminium Electrolytic 2200uF 50V		- £3.10
C3 & C7			- CA04503	- Aluminium Electrolytic 3.3uF 50V		- £0.20
C4 & C8			- CA04506	- Aluminium Electrolytic 22uF 50V		- £0.26
C5 & C9			- CA04501	- Aluminium Electrolytic 1uF 50V		- £0.20
C6 & C10		- CA04558	- Aluminium Electrolytic 10uF 50V		- £0.14

D1			- LP00348	- 12V 5mm Green LED				- £1.37

SW1

F1			- FF00394	- 3.15A TD 1 1/4" Fuse (10 Pack)		- £1.18
F2 & F4 & F5		- FF01404	- 1A QB 20mm Fuse (10 Pack)			- £0.58
F3			- FF01393	- 500mA QB 20mm Fuse (10 Pack)			- £1.13

[b]*Others:[/b]
Fuse Holders (x4)	- FF01330	- 20mm Fuse Holders (x4)			- £1.04

Mains Inlet		- CN09935	- Power Socket, Fuse Holder, Switch Module	- £3.25

Regulator Insulators	- SCW353PK	- TO-220 Insulators (10 Pack)			- £1.85

Case
Heatsink

[b]*Total Price (+Case and Heatsink):[/b]
Without VAT	= £29.48
With VAT	= £34.64

Questions:
1) Suggestions / Improvements ?
2) What size heatsink would I need for ALL the regulators AND the bridge rectifier ? Note: The regulators and bridge rectifier will be mounted to the side of a small die-cast aluminium case, with the heatsink bolted to the outside.

Thanks,
-Andrew.

 

[Sceadwian]

Why bother building it? Any old PC power supply will meet those requirements. They're easy to modify with a few binding posts and a toggle switch.

 

[yngndrw]

You have a good point, before I started designing and pricing it up, I expected it to be a LOT cheaper. The problem with a PC PSU is that the output is "noisey".

I have quite a few old PSU's lying around, guess I might just make a nice case for one.

Thanks.

 

[Gayan Soyza]

Questions:
1) Suggestions / Improvements ?

*It is better to use an 18V transformer.
*Don’t you like to put the POWER ON LED near one of the 2200uF capacitor?

But when comparing the size, price & the transformer it’s worthwhile to convert an ATX power unit for your workbench like Sceadwin points out.

Here some useful links to you.

http://www.wikihow.com/Convert-a-Computer-ATX-Power-Supply-to-a-Lab-Power-Supply

http://web2.murraystate.edu/andy.batts/ps/POWERSUPPLY.HTM

 

[yngndrw]

Never realised a PSU would need such headroom, so thanks for pointing that out.

The reason for the LED's position is it's more of a PSU Is Ok LED, so if both the +5V and -5V rails are working, you can assume that the rest of the PSU is working fine.

Thanks for the links, I would have forgotten to put a load resistor on it without them.

 

[Hero999]

You have a good point, before I started designing and pricing it up, I expected it to be a LOT cheaper. The problem with a PC PSU is that the output is "noisey".

I have quite a few old PSU's lying around, guess I might just make a nice case for one.

Thanks.

Then use a filter consisting of capacitors ferrite beads and common mode chokes.

 

[yngndrw]

True true, that sounds like the best option. A lot cheaper than building one anyway.

Thanks.