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Is it possible for the mains to stutter up and down again? (eg in EU, USA, Aus/NZ)

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treez

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Hello,
We have an offline 40V LED driver with the attached input stage.
It comprises a current clamp whose FET takes up voltage during transient spikes.
However, if the mains stutters down and back up as shown, then the mains wiring inductance, in conjunction with the capacitor C20, causes a spike of 1000V across the current clamp FET. (this is due to the clamp FET momentarily switching off as it tries to clamp the current inrushing into C20)
The attached LTspice simulation shows the 1000V spike across the clamp FET.
Do you think this kind of mains stuttering can occur?
What would cause it?
 

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  • Mains stuttering.txt
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  • Offline LED driver input stage.pdf
    14.4 KB · Views: 89
  • Mains stuttering waveform.pdf
    18.9 KB · Views: 91

Tell me you are not really using two 1M and one 33K in series to make 2.033M Ohms.
If it's to make up sufficient voltage rating across the resistors, why not use three 680K resistors and share the voltage equally.

Brian.
 
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Do you mean?

Can you have a power switch with contact bounce exactly during the peak voltage for a fraction of a millisecond?

Possibly .... with Murphy's Law... Probably...
...
 
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thanks, sorry the 2.033M is a part of somthimg else in the cct thats not relevant here. I forgot to delete it.

Contact bounce is the one that we thought of, but we thought that things like contactors couldnt bounce like that?.. only cheap relays could bounce like that.

We think there may well be contactors in the mains system.

Some kind of glitch on the power system could also cause it.?
 

I do not think the waveform seen in the first file (Mains stuttering waveform.pdf) is realistic; the source of power is some local distribution transformer and there will be lots of capacitance on the way.

There should be some reasonable time constants and the "stuttering" should be more realistic. You cannot switch on and off modern circuit breakers like that. A loose contact? Perhaps. But that is probably produce lots of grass...
 
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