MOV time domain voltage graph - Page 1
Forum section: electronics / projects

author: coppercone2
author_rank: Super Contributor
timestamp: December 29, 2018, 09:31:05 am
content: Does anyone have a graph that shows what a MOV does when it clamps a voltage? Say like if there is a AC or DC relatively high voltage and a spike is regularly pulsed on it.Does it just flat out like a clipped rail in a op-amp, or does it have some kind of hysterisis where it takes the rail down under its regulated voltage during the end of its conduction phase when the transient decayed? I don't think I ever noticed a subsequent dip with op-amps before, but I think they are not operating correctly as they leave saturation. Does it have a dependence on supply impedance?Preferably a before and after.I can't find a good picture on line and I don't have a simulator here. I mean if its trigger voltage is really close to the rail voltage. When its way above it seems to be pretty flat but I wonder if there is a slope to the line (there are only conceptual pictures I can find in datasheets, not measured ones).

author: Rerouter
author_rank: Super Contributor
timestamp: December 29, 2018, 09:41:37 am
content: It behaves like a zener clamp, it starts conducting at a knee voltage. and shunts far more current as it continuesthis knee voltage also degrades with each conduction event and with the length of a conduction event. for mains protection this can lead to it reacting to normal mains, and collapsing down to a short / flare / thermal explosion

author: coppercone2
author_rank: Super Contributor
timestamp: December 29, 2018, 09:49:50 am
content: so say it starts conducting at 155 volts. What would it typically stop conducting at?could you make a special mov that is almost broke by design so you can trigger it with a HV pulse to act as a 1 shot crowbar?So its used as a over current triggered shunt that blows itself up or gets red hot or whatever it does.can you reliability degrade a commercial MOV to function like this (one of the big ones that is like a puck).

author: T3sl4co1l
author_rank: Super Contributor
timestamp: December 29, 2018, 10:14:50 am
content: Offhand I found a waveform here,https://www.bourns.com/data/global/pdfs/ACTP250J1BJ.pdfThe V-I curves are in the MOV datasheet from which you can calculate maximum peak voltage. You can also run a simulation with whatever SPICE models you can find, though all the ones I've seen are written terribly; maybe they still run on LTSpice.Tim

author: BravoV
author_rank: Super Contributor
timestamp: December 29, 2018, 10:53:11 am
content: Not sure the model's accuracy, claimed to be Littelfuse's MOV part no V20E175, the LTSpice model & simulation originated from ->HEREVoltage clamped at 480V and the MOV's dissipation attached below.

author: coppercone2
author_rank: Super Contributor
timestamp: December 29, 2018, 11:34:12 am
content: hmm it seems like a regular MOV is really flat.I am going to assume trying to damage it precisely is not possible?

author: T3sl4co1l
author_rank: Super Contributor
timestamp: December 29, 2018, 12:31:23 pm
content: Yeah that right there is a model that ain't working worth shit... or its parameters are completely wrong.Tim