Power Supply Question Part II, distributing

[mikael__]

Ok, so i have probobly come a cross a suitible power supply.
Anybody know some schematics for distribution boards ?

[bugbrand]

Hi mikael

Hey, I'm doing similar things at the moment - trying to make a test-array of various voltage controlled modules. Things are starting to give great sounds....

I wanted to do synth modules for ages, but not knowing much about power supplies put me off. Then I saw a couple of mentions of using AC - AC wall wart adaptors followed by voltage regulators to give bopolar supplies. This method is certainly used by the new Paia ribbon controller module (Paia article)and i think its also used for the cheap'n'simple doepfer power supply unit.

There's still some things I'm not entirely sure on - - so I'd appreciate any comments...

I'm using a 25v AC supply (from 240v UK supply), but I think you can use down to 12v - does this change how much current the circuit can supply?

The two input resistors - the Paia article says 1K, but I tried this and the supply didn't work properly - I changed these to more like 60ohms (i think).. do these set the maximum current? The 1st prototype I left them out & it all overheated badly...

Caps C1&C2 - smoothing - I'm using 220u

Voltage regs - using LM7812 & LM7912 plus heatsinks

C3,C4 - 10u or 100u

I then use 4 pins for distributing the power - see the board layout for the rough idea - AC in on the left, then diodes, smoothing caps and vregs on the side (I thought to bolt them onto the side of the enclosure), then the pin distributors with plenty of space.

This power supply has made my recent testing so much quicker and easier! I've had up to about 4 modules at a time running, but haven't yet measured the current draw .. thats something I really ought to do..

So....here's the schematic]http://www.bugbrand.co.uk/schems/bipolar_power_supply_uses_ac_transformer.jpg[/img]

& the board layout (in eagle):

[dach]

Hiya,
  I've been doing some work on power supplies. I dont have modular synth stuff so I have little use for 12v, but I find that 3,5 and 9 are useful for general electronics, effect pedals and powering some circuit bent gear.

At the moment I use a simple AD-DC 9v wall wart transformer. Although it says 9v, they often put out 12v. Connect this to some big capacitors and a regulator. You can use two transformers, and a 7805/7905 pair of regulators to get a bipolar supply, great if you have lots of op amp projects.

Something to measure the current is really useful on a table full of bent gear, and where you are connecting and disconnecting devices all the time. The transformer I have at the moment is rated to 300mA, which is more than I usually need. It seems to be ok drawing twice as much for short periods, it gets hot though. This isnt recommended



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[spivkurl]

Bugbrand... if you used a transformer that outputs 12v AC, then you would be starving +/- 12v regulators, but it would be okay for +/- 5v.  A 24v center tapped transformer would be about the lowest you could go for a +/1 12v DC supply.

[bugbrand]

Bugbrand... if you used a transformer that outputs 12v AC, then you would be starving +/- 12v regulators, but it would be okay for +/- 5v.  A 24v center tapped transformer would be about the lowest you could go for a +/1 12v DC supply.

Yeah, that does seem to be correct.. I was basing this part of my assumptions on the Paia ribbon controller schematic (http://www.paia.com/LabNotes/ribbon%20ckt.jpg) that I'd seen recently - it takes a 12VAC (wall wart) to supply +/- 12v Regulators.. Strange? ? Well, I've stuck to using 25vAC adaptors and they're working FINE!