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NNTP-Posting-Date: Sat, 08 Mar 2025 16:57:43 +0000
From: john larkin <jl@650pot.com>
Newsgroups: sci.electronics.design
Subject: dumper circuit
Date: Sat, 08 Mar 2025 08:57:43 -0800
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I'll have an isolated class-D amplifier powered by a dc/dc converter
from my big 48 volt supply. Simple push-pull, transformer, rectifier,
making maybe isolated 46.

In one situation, the class-D amp can push current uphill into the
isolated supply, and we need to dump it. This circuit acts sort of
like a 25-watt zener diode.

https://www.dropbox.com/scl/fi/98n07mnf3qokvbewuv1oy/Dumper_1.jpg?rlkey=poiep8hzhz33qecswdj50sdne&raw=1

It didn't work in simulation. It was driving me to despair. No amount
of chocolate would help.

The problem was of course that the Spice initial condition simulation
perfectly biased everything, balanced the pencil on its point.

So how can the initial conditions sim ignore the positive feedback?