[sdiy] Power Supply Start-up Issues

[John Speth]

> The cure for each is the same. Reduce start up current. And the 
> easiest way to do that is reduce the decoupling capacitance on 
> modules. I've seen modules with a couple of 220uF connected to their 
> power headers. Perhaps it's best not to use any more than 4u7 per rail 
> per module, unless series resistors are used.
>
This design is as old as three terminal regulators, probably older. I've 
seen some similar designs with small series resistors on each regulator 
output. I always assumed they were there to limit inrush current. The 
tradeoff will be too large (too much voltage drop, negating the 
regulation that the regulator provides) vs. too low (having insufficient 
effect on inrush current).

Sizing the resistors would be a simple calculation if you know your 
current draw range. Knowing that is not always easy with a modular synth.

JJS