From: <hvanesce@comcast.net>
To: <rsgb_lf_group@blacksheep.org>
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Date: Mon, 27 Nov 2017 17:31:57 -0500
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Subject: RE: LF: RE: Todmorden receiver
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Hello Paul,

Based on the those additional details, it might be worth a quick check of the voltage-loop stability margin: if for example your load draws 50 ma, briefly add a 390 ohm 2W resistor across a 15V output (I = 50 ma + 38 ma = 88 ma, well below any overcurrent limit on the 100 ma module)  and quickly release it. If the output voltage doesn’t ring (i.e. if the step-load response is overdamped), no problem, stability margin with the 47 uF capacitor is fine.  The instability-relevant ring time constant would likely be 10 us < t < 1 us; any faster features would be irrelevant to voltage-loop stability. Success with this test could rule out a narrow stability margin that could otherwise at some later date (with aging and temperature) add noise.  

73,

Jim AA5BW           

-----Original Message-----
From: owner-rsgb_lf_group@blacksheep.org [mailto:owner-rsgb_lf_group@blacksheep.org] On Behalf Of Paul Nicholson
Sent: Monday, November 27, 2017 2:27 PM
To: rsgb_lf_group@blacksheep.org
Subject: Re: LF: RE: Todmorden receiver


Jim wrote:

 > Considerably reducing DC-DC converter output filter  > capacitance and/or load current can almost always solve  > the problem of erratic power supply startup related to  > high source resistance,

When I checked the data sheet for the IP1215S isolating DC-DC converter I spotted that it said max 47uF load capacitance - and I had 100uF hanging on each rail.

Hopefully that's the answer.  For some reason I can't reproduce the start-up problem in the office even though I've got slightly higher cable resistance.

I like these XP power IP series converters, good isolation and they have a large input voltage range.

--
Paul Nicholson
--