Re: 7704A (et. al.) Inverter Regulator Question

Albert Otten

On Mon, Sep 13, 2021 at 04:09 AM, n4buq wrote:

I notice there is also a diode, a 15V zener diode, and an RC network all
connected in series between the collectors of both Q3102/Q3104 and ground. Is
this a fail-safe overvoltage protection circuit for the inverter should
Q3102/Q3104 or U3105 fail or is this a snubbing circuit to clip noise spikes
(which I don't quite understand would be necessary), or something else? The
manual doesn't seem to mention it - at least not that I've found.
Here is my interpretation. Waveform picture 3 shown at the node of C3101/C3102 and the mean voltage +9.9 V there suggests that the voltage is clamped at about +15 V immediately each cycle. The higher "hat" would be due to R3105/C3105. The open peak voltage of the 30T windings would be much higher than 15 V.

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