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

[coolnose]

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]

What current are you going to draw from each voltage.

 

[coolnose]

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]

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

 

[coolnose]

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

 

[Minion]

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 ......