Home made power supplies

[brainz2000]

I wondered if there are a few kind souls who can dispense advice and wisdom around power supplies ...

I am just getting back into electronics a bit after a long (>25 year) gap.

Remembering a long time ago at school I built a power supply using a transformer, a bridged rectifier, some smoothing caps - I thought I would research and build something simple to give me a clean 5v output for a Squeezebox classic

No messing with mains to start with so I've got myself a voltage regulator, a 78S05 and I have soldered the reference circuit with 0.33uF on the input and 0.1uF on the output.

I if have a couple of questions

1. I used 3 x 0.1uF in parallel as I didn't have a 0.33uF - will this cause any side effects? Can I use a bigger cap - will it matter?

2. How clean will the output be? I don't have an oscilloscope - it looks fine on my cheap volt meter ... Is there any other way I can check?

3. I need to put a big heat sink on... Does anyone know where I can get a small ventilated case - at 2A this is going to produce a lot of heat if the step down is from 12V (ideally I'll drive it with 9v or less if I can but it would be nice to be able to use 12v...)

Thanks in advance for any help ...

Tim

[JimC]

Those Capacitances seem a little on the small side for Reservoir/Smoothing Caps in a Power Supply.

I found this on the net.......

http://www.triumphrat.net/attachments/speed-triple-forum/40763d1314722199-5vdc-mini-circuit-board-for-speedy-power-supply-5v-2a-by-ic-78s05.gif

The input to the 7805 should be nice and big to smooth as much of the ripple from the DC presumably from a Transformer and Bridge Rectifier. The 220uF in the link would be OK but you could go larger (1000uF for example) if you wanted.
0.1uF on the output of the 7805 also seems a bit small. You don't necessarily need to go as large as the Input Cap but 10uF upwards would be a start. I'd leave the 0.1uF there too to hopefully filter out any pops and clicks (higher frequency 'noise' than the Mains ripple) there might be.

It is usually acceptable to go larger, within reason, when dealing with 50Hz, HF smoothing for Switch Mode Power Supplies is a different matter. But do remember not to go lower with the Voltage rating on any Capacitor. I was always taught ''at least twice the Voltage present across the Capacitor''. Therefore for a 5Volt supply, at least a 10V Cap should be used. You'll find this is not the case in most modern commercially available electronics but this is due to financial considerations more than anything else.

Hope all that helps,

James.

[JimC]

http://www.ebay.co.uk/itm/Professional-Quality-Aluminium-Enclosure-Project-Desk-Box-Electronic-/200970018309?pt=UK_BOI_Electrical_Components_Suppl ies_ET&var=&hash=item7475a10360

[Puffin]

Aren't 7805's only good for 1A really

http://www.fairchildsemi.com/ds/LM/LM7812.pdf

I built a PS for a Squeezebox Touch for Covenant on here. The Touch draws 2A (I believe) and I used a circuit that boosted the output of the 7805 with an additional transistor (I can find the circuit if necessary)

[JimC]

The OP quotes a 78s05 which is a 2A device.

JC

[337alant]

If you realy need 2A?, then you would be better off going for an over rated device like the LT1083
http://www.ebay.co.uk/itm/300908449963?ssPageName=STRK:MEWAX:IT&_trksid=p3984.m1423.l2649
just add a 9 or 12v transformer

Alan