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-   -   small PSU using 2 reg. 7808 and LT 3080 (5V) (http://www.diyaudio.com/forums/power-supplies/208272-small-psu-using-2-reg-7808-lt-3080-5v.html)

coolnose 6th March 2012 08:00 PM

small PSU using 2 reg. 7808 and LT 3080 (5V)
 
Hi folks,

I need to rig up a small PSU giving 8V using a 7808 and giving 5V using a LT3080.

I was wondering if I should take the V+ from the 7808 to feed the LT3030, using the 7808 as a pre-regulator or rather feed them both from the unregulated 12V supply.

Benefits / Drawbacks ?

I don't feel like doing a sim on it, so any advice is appreciated.

TIA,

Max

epicyclic 6th March 2012 08:11 PM

What current are you going to draw from each voltage.

coolnose 6th March 2012 08:32 PM

Well, I'd say almost nothing... if I can say so.

5V will be feeding 2 TORX Toslink receivers and 1 TOTX Toslink emitter, 8V will be used for switchig a source selection relais...

I expect the total current drawn to be under 100mA. If the values are crucial I can dig out the datasheets.

Cheers,

Max

epicyclic 7th March 2012 09:59 AM

Suggest running LT3030 from 12V to share the heat dissipation between the 2 regulators and give max isolation from relay switching .

coolnose 7th March 2012 06:10 PM

Thanks a lot for the input.. will proceed further.

Minion 7th March 2012 11:42 PM

I just tried running a Preamp(12vDC regulated with LM317) and a Channel switching curcuit that uses relays (5vDC regulated with LM7805)) from the same 12v AC Transformer and ran into problems right off the bat ...... When I enganged Relay curcuit I would get a pop in the Audio of the pre amp , When I used a seperate transformer for each the pop went away ......

Hopefully you don"t have the same problem ......


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