Re: dumper circuit

On Sat, 08 Mar 2025 18:57:11 +0000, JM
<sunaecoNoChoppedPork@gmail.com> wrote:

On Sat, 08 Mar 2025 08:57:43 -0800, john larkin <jl@650pot.com> wrote:
>

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?

>
Use .ic together with uic.

It sims fine if I click the box to skip the initial condition
solution. That's faster too. Delaying the power supplies breaks the
tie too.

What I don't understand is how negative feedbacks work during the ic
solution, but positive feedbacks don't.