N. Thornton wrote:
Ian Stirling wrote in message ...
NT wrote...

OK, the factors stated above do not ensure no 50Hz current is present.
snip
With such a setup, if one emitter has total failure, the tube can
conduct current one way only, giving intolerably strong 50Hz flicker.

No, it can't.

An electronic ballast has a rectifier at the front of it.
The waveform after the rectifier is NOT a 50Hz sine wave.

I'd have to draw the cct and label the waveforms, and I'm too busy
today. I could sit here and assure you it can flicker at 50Hz, but
that wont convince either of us. Maybe if I get the time later I'll
draw it and we'll see what comes up.

I'm not saying it's impossible.
However, after the bridge rectifier and capacitor, the waveform
looks like (view in fixed font)



340V .. ..
. ~-_ .
240V . -~-_ .
~~




0V ----10ms---


The difference in successive crests varies by millivolts at most.
The slope of the decay, and the voltage it gets down to depends on the
load and the size of the capacitor, which varies.

What can happen with a marginal bulb or broken driver is that it may
try to restrike the tube often, and it doesn't quite work, leading to
pronounced flicker.