[sdiy] Linear PSU Power Sequencing Issue

ackolonges fds ackolonges at hotmail.com
Thu Oct 31 13:57:39 CET 2019


Thanks so much for the insight Florian and Tom, that makes perfect sense. I suppose then, that I should try things like reducing the bulk capacitance on the +5V line when it's derived from the +12V (and keep the bulk capacitance if I'm supplying the +5V line separately), or try putting a low value, high current series resistor between the +12V and +5V supplies to limit the in-rush current.

Of course these two potential solutions involve less ripple rejection, or some power wastage, so if anyone else has any other ideas, please feel free to pipe up 🙂

Thanks again.

From: Synth-diy <synth-diy-bounces at synth-diy.org> on behalf of Tom Wiltshire <tom at electricdruid.net>
Sent: Friday, November 1, 2019 1:22 AM
To: Florian Anwander <fanwander at mnet-online.de>
Cc: Synth-Diy mailing list <synth-diy at synth-diy.org>
Subject: Re: [sdiy] Linear PSU Power Sequencing Issue

> On 31 Oct 2019, at 10:50, Florian Anwander <fanwander at mnet-online.de> wrote:
> Hi Jason
> Am 31.10.2019 um 06:17 schrieb ackolonges fds:
>> and +5V (derived from the +12V line)
> Even without load at the +5V rail the +12V regulator has to provide current for loading the capacitors of the +5V-supply. This effect may become even worse, if some modules have +5V regulators on board, which use the 12V for supply.
> So, my first try would be: remove the +5V supply from the +12V rail.

+1 agree with Florian. It sounds like the extra capacitance on the +12V is causing a in-rush that shuts the regulator down. This won’t happen when the caps are part-charged, so it works fine once you’ve got it started.

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