View Single Post
Old 08-01-2009, 10:20 PM
Harvey's Avatar
Harvey Harvey is offline
Gold Member
Join Date: Jul 2009
Posts: 1,137
Avalanche Proof vs. Avalanche Rated

Really these are just two ways of saying the same thing. The SK transistor has a breakdown voltage of 900V while the IR transistor is 1000V. Essentially, both will handle the breakdown without destruction. Naturally, they will both have limits as to how long they can handle that condition under the rated current.

The SK does not offer the Joule rating nor does it infer any recovery timing etc for an Avalanche condition. So without actually delving into the particulars of what they mean by "Proof" and "No secondary breakdown" it would be difficult to determine what this device would do with a 925V spike.

TK did raise an important point regarding the spike slope, and another poster here (sorry forgot the name) explained how the voltage of the spike is directly related to the time it takes to travel from peak to peak. The shorter the time period, the higher the voltage. Remember, an AMP is a time based unit. When you subdivide the time you trade amp for volt.

The Avalanche is only a factor in this circuit if Rosemary's original configuration was able to produce greater than 1000 volts across the HEXFET. In that case, for that brief period, extra current would flow due to the extended ON condition through the Avalanche thereby bolstering the magnetic field and slowing its total collapse. If however the voltage never reaches breakdown, and the spike and ringing is all below that limit, then the entire energy in the ringing is a result of how fully you charge the magnetic field before collapse - it can only store so much before it saturates.

Keep in mind too, that as I understand Rosemary's claim, it has to do with conserved energy in the load resistor being stored at the point of manufacture, and that it would leak into the field and add to it resulting in a breakdown of the load resistor. Please correct me if I am wrong here.