[sdiy] re re power supply pain

[Happy Harry]

Hi Gavin:  inline


>From: "Gavin Russom" <elmystico at earthlink.net>
>To: synth-diy at node12b53.a2000.nl
>Subject: [sdiy] re re power supply pain
>Date: Fri, 25 May 2001 14:55:28 -0400
>
>thanks for all the responses on this question,  Is it possible to take the
>voltage coming off the filter caps (after the bridge rectifier) and split 
>it
>off so it goes through all the neccessary regs but not in series?  (does
>this sentence make sense?)  Basically, to use one 3A 25VCT transformer to
>drive three separate + and three separate - voltage regulators?  Some
>responses to my original power supply question seemed to suggest yes, 
>others

Yes it is possible. Those who said "no" were thinking that if you needed a 
12V supply, the main fiter caps would have to run at a minimum of 15V...

Then the 5V regulator would have to drop 10V... multiply that drop
by the current on the 5V supply... and you have watts of heat you need
to dissipate... not good if you have an analog synth with imperfect
temp. compensation.

I put together a schematic on how it would look (using 220uF elec caps
>to filter the output of each of the regs and tapping off the voltage across
>the 1000uF elec filter caps from the bridge rectifier as I said to in put 
>to
>the regs)  possible problems occuring to me are
1. too much draw on the transformer

Yes that's possible.


  2. too much voltage going into the 7805

That's likely. It might be better to use two transformers... one for the +/- 
12 and 9V... and a second lower secondary voltage unit for the
5V.

3. some signal interaction problem resulting from all the voltage sources 
being connected together

That should NOT be a problem with regulated suplies at all, until you get to 
an overload condition.

Series connection is still possible if the combined current drain is not too 
great.

H^) harry

>Ideas??
>thanks for the tip on the 79XX pinout, unfortunately I learned that one the
>HARD way
>MYSTIC

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