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Is it possibel for the mains to stutter down and up?

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Flyback

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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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dknguyen

Well-Known Member
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Can't you just scope the mains?

EDIT: Oh you did. What in god's name is that?

EDIT: No, wait you didn't. That's just a simulation.
 

dknguyen

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Did that actually happen? I guess a power outage would do the same thing. Those definitely happen.
 
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alec_t

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I would think a brief drop in voltage could well occur during operation of breakers at power stations, or if a negative interference voltage spike occurred during a positive half cycle. I've experienced domestic incandescent and CFL lights flickering on occasions.
 

Pommie

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When I worked for a firm making HV switches we were informed that a short would result in a breaker tripping. The breaker would try and reset 3 "loops" (half cycles) later (30mS). It would attempt this with increasing delays until the third attempt would be at 3 seconds and then it would give up. This obviously wouldn't cause what you see but a very brief lived short might. Maybe a birds wingspan between overhead lines - not enough to trip the breaker but enough to cause a dip. Edit, and obviously, very short lived.

Mike.
 
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