[sdiy] Best way to get a +3.3V rail from +15V?

BRUCE DUNCAN modcan at sympatico.ca
Fri Mar 8 23:53:16 CET 2013

One thing I wonder about is using say 10+ small SMPS sub regulators in a modular environment is what 
the cumulative effect on main transformer based power supply on startup.
I read somewhere that SMPS look like a dead short on startup. Could this cause
over current tripping on say Power One supplies with current limiting?
Having a lot of modules in a system resulting in many input caps in parallel has often been a problem
with power supply startup and just wondering if could cause similar issues.


> Date: Thu, 7 Mar 2013 22:51:53 +0100
> From: spr at spridley.freeserve.co.uk
> To: synth-diy at dropmix.xs4all.nl
> CC: synth-diy at dropmix.xs4all.nl
> Subject: Re: [sdiy] Best way to get a +3.3V rail from +15V?
> > And this is much simpler than a switching solution.
> Simpler? Try Traco TSR series or XP Power SR range devices.
> - Similar footprint to a TO220 (not smd - old folks can see them)
> - Small part count - add two caps and a small inductor
> - >90% efficient so barely warm - no more "ouch! (insert expletive here) moments when you touch it.
> - no clumsy heatsink cluttering up your development board
> - At 200mA out it'll draw less than 50mA from the 15v.
> Complicated? Linear:
> - Juggling heat dissipation across two devices in non-free space
> - Mounting heatsinks so they don't get in the way, burn you or take up acres of space
> - Deal with uneven load your +/-15v supply
> etc.
> Worth a try?
> Steve
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