[sdiy] Power Supply Start-up Issues

Oren Leavitt obl64 at ix.netcom.com
Thu Aug 27 06:47:44 CEST 2020

If you're doing a power supply for a whole synth cabinet, I'd just spend 
a little extra for a good ready-made power supply like the Power-One 
HAA, HBB or HCC series power supplies.

The 3-terminal regulators are not the best choice where you're going to 
have several modules and the cumulative inrush currents they impose.

- Oren

On 8/26/20 6:24 AM, ackolonges fds wrote:
> Hi All,
> I've been having issues with a very standard +/- 12V power supply 
> design for a modular synth. Every once in a while when powering up, 
> the positive rail doesn't rise, and it needs to be reset to work. 
> After some trial and error, and research, I found mention of this 
> issue in Douglas Self's 'Small Signal Audio Design' book, where he 
> shows a circuit almost identical to my power supply. A screen grab of 
> the related page can be found here: https://pasteboard.co/Jo8PuIu.png
> This paragraph from that page describes the issue I'm having perfectly : /
> /
> /
> /
> /"//D2, D4 will prevent damage in this case, but leave the power 
> supply vulnerable to start-up problems; if its output is being pulled 
> down by the 15 V regulator, the15 V regulator may refuse to start. 
> This is actually a very dangerous situation, because it is quite easy 
> to come up with a circuit where start-up willonly fail one time in 20 
> or more, the incidence being apparently completely random, 
> butpresumably controlled by the exact point in the AC mains cycle 
> where the supply is switched on, and other variables such as 
> temperature, the residual charge left on the reservoir capacitors, and 
> the phase of the moon. If even one start-up failure event is 
> overlooked or dismissed asunimportant. then there is likely to be 
> serious grief further down the line.Every power supplystart-up failure 
> must be taken seriously.//"/
> Unfortunately after stressing how important it is to fix such an 
> issue, no solutions are mentioned...  I've tried removing all of the 
> protection diodes, increasing and decreasing the value of the 
> smoothing caps, tried many different makes of voltage regulators, and 
> also tried an NTC thermistor to slow the in-rush current, all to no 
> avail.
> I'm starting to run out of ideas, so if anyone on the list has come 
> across a fix it would be great to hear about it.
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