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What does the Impulse Sparkover at 100 V/us and 1000 V/us mean?

Does it have anything to do with arcing?

How does the impulse help us decide with which GDT to choose?

Transistor
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Sam Shurp
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  • What's the application? Plasma effects involve at least 2 spatial and one time-dim of PDEs, coupled to at least 6-dim ODEs, along with radiation transport and atomic interactions. Even then, that uses global rate equations assuming spatially averaged densities for the charged particles and neutral atoms and molecules in excited and metastable states. A text by Lieberman and Lichtenberg, "*Principles of Plasma Discharges and Materials Processing*," treat the basics: discharges, global models, collisions, and DC and RF discharges. I suggest contacting technical sales and simply ask for help.. – jonk Nov 08 '19 at 07:38

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What does the Impulse Sparkover at 100 V/us and 1000 V/us mean?

What it tells you is that if you applied a fast rising surge changing at a rate of 100 volts per microsecond then the GDT would sparkover when the surge waveform reached 250 volts absolute. That's a time delay of 2.5 us.

However, if the surge was rising at 1000 volts per microsecond then sparkover wouldn't occur until the waveform reached 525 volts - that's a time delay of 0.525 us.

In other words, GDTs cannot be used (on their own) for some fast applications because they have an inherent time delay. A lot can happen to a circuit in 0.525 us!

How does the impulse help us decide with which GDT to choose?

This is sometimes why GDTs are used in parallel with MOVs. MOVs are fast but don't like being overloaded excessively. The MOV takes the initial brunt and then the GDT takes over and handles the remaining bulk energy of the surge.

Andy aka
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  • What about 75V DC Sparkover. How is that different from the impulse spark over. I assume impulse means sudden or fast rising. Also what if there is a clamping voltage components in parallel with GDT. How would the GDT react? – Sam Shurp Nov 08 '19 at 08:53
  • The 75 volts is for DC i.e. if you slowly ramped the voltage up to 75 volts (limited to 100 volts per second or less), it would sparkover at 75 volts. Devices in parallel with a GDT do not affect the operation of the GDT. Those extra devices may clamp before the GDT (as in an MOV or TVS) but that's all. – Andy aka Nov 08 '19 at 10:41
  • Just to be sure, if I have a Tvs diode with a clamping voltage of 80V in parallel with GDT, then I would not need to worry about the Impulse sparkover since the voltage will be clamped at 80V; DC Sparkover of 75V of GDT would taker over. Is that correct? – Sam Shurp Nov 11 '19 at 02:42
  • It's a little tight but theoretically would work. Check tolerance specifications - you might need to be a little higher on the TVS. – Andy aka Nov 11 '19 at 08:26