Mosfet avalanche noise in PI

[Ferric Toes]

A few years ago there was a discussion on another forum as to whether running a TX mosfet in repetitive avalanche conditions caused additional circuit noise, and that it was better to use a snubber that restricted the peak voltage to somewhat below the breakdown voltage. I have never had any evidence of this noise myself and cannot see that any such noise can extend into the OFF time. I am interested to know what the viewpoint is from members here.

Eric.

[green]

A few years ago there was a discussion on another forum as to whether running a TX mosfet in repetitive avalanche conditions caused additional circuit noise, and that it was better to use a snubber that restricted the peak voltage to somewhat below the breakdown voltage. I have never had any evidence of this noise myself and cannot see that any such noise can extend into the OFF time. I am interested to know what the viewpoint is from members here.

Eric.

I agree with you.

[homefire]

It would all be history before the samples are taken.

[6666]

I think is was member ECLIPSE that did some testing recently with adding snubbers to see what the effect on avalanche noise was.

[Xtrem]

I dont know if the noise extent to "off" time, but a possible test design, would be using a TX mosfet (irf840) , a snubber circuit (D R C) that "cut" the
voltage at 400V, and a irf740 (G to S shortcircuited) parallel to TX mosfet acting as a "zener" at 400V.
Comparing between the 2 "snubbers" maybe give us the different about noise after the TX time.
I think using snubber has many advantages at longer TX ON times, especially a "light version", cutting peak vlotage "somewhat below".

[6666]

I dont know if the noise extent to "off" time, but a possible test design, would be using a TX mosfet (irf840) , a snubber circuit (D R C) that "cut" the
voltage at 400V, and a irf740 (G to S shortcircuited) parallel to TX mosfet acting as a "zener" at 400V.
Comparing between the 2 "snubbers" maybe give us the different about noise after the TX time.
I think using snubber has many advantages at longer TX ON times, especially a "light version", cutting peak vlotage "somewhat below".

Would you like to draw it ?

[Xtrem]

[6666]

[ATTACH]38196[/ATTACH]

With my limited knowledge of spice, the sims seem to show that this works, but a bit unpredictable as to the cut off voltage
as I dont have an irf740 component in my library, but choosing other types will reduce the coil voltage