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Registered Member #2941
Joined: Fri Jun 25 2010, 08:08AM
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Posts: 143
igbt are bipolar transistor for the power part ,some of them must have avalanche capabilities ,it's important to me as I was planing to move toward avalanche transistor for the pulser anyway ,some igbt can stand short circuit for a short time ,100 or 200 nanosecond is short on there scale, Igbt are a bad choices for high voltage ns pulse generator ,they are slow ,bulky,the same set up made with mosfet might give 10 ns rise time with out magnetic pulse compression,but it would be more expensive,probably involving staking them in series -parallel to have the same rating,the triggering system would need to be a bit more power full and sophisticated to,actually ,one thing I notice when I previously try with mosfet ,the one I use behave like if they had a zener build in(if I would go above they volt rating they would clamp the voltage) ,while according to the data sheet ,they didn't ,I suppose it was du to the fast recovery diode inside. for the tvs ,and also for the igbt it,s nice to have component from the same production line and from the same lot witch can be tested ,so you know if you can rely on them and what are there true characteristic,I ll probably come to that when I start working on a pulser ,I was just investigating magnetic pulse compression,so I build a pulser and it work,if it didn't I would have made a mark on the corner of my table.if some one have some good idea about how to make solid state switch witch is reliable ,sheep ,easy to build and who don't involve proprietary technologies I ll take them.
Registered Member #2901
Joined: Thu Jun 03 2010, 01:25PM
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Posts: 837
The only practical solid state alternative to MPC I know of are SOS diodes (a great big stack of avalanching transistors is also an option, but less practical). I have never seen them for sale.
Registered Member #30
Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706
cedric wrote ... one thing I notice when I previously try with mosfet ,the one I use behave like if they had a zener build in(if I would go above they volt rating they would clamp the voltage) ,while according to the data sheet ,they didn't
All MOSFETs and IGBTs do that. The avalanche-rated ones are just guaranteed to absorb a certain amount of energy and dissipate a certain amount of power in that mode: both values are stated in the datasheet.
Some of our members like to build series strings of SIDACs. There's no need to worry about uneven voltage sharing, because overvoltage is the very thing that triggers a SIDAC. You can also use them as "spark gaps" in a 400-volt-per-stage Marx generator.
Maybe one of those would make a good driver for a magnetic pulse compressor.
And, there are those little neon gas discharge tubes used for protection, boiler ignition and the like.
Registered Member #2901
Joined: Thu Jun 03 2010, 01:25PM
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Posts: 837
cedric wrote ... if some one have some good idea about how to make solid state switch witch is reliable ,sheep ,easy to build and who don't involve proprietary technologies I ll take them.
It looks a bit like voodoo, but if these circuits work they could be very practical :
It's similar to the method from "NANOSECOND PULSE GENERATOR USING A FAST RECOVERY DIODE" ... but it uses a slight different effect and a less complex circuit. I wonder if the effect is the same one underlying the mythical SOS diode assemblies? The diode used in this paper is dirt cheap at any rate (1n5408). They suggest it can work for most power rectifiers and in another paper "Improvement of Electromagnetic Pulse Radiation Efficiency". They write :
wrote ... if the following requirements are provided: injection time (τ+) is much more shorter than the diode’s reverse recovery time (τrr); removing time (τ−) is shorter than injection time (τ+); and removing current (I−) doesn’t exceed maximum possible current (Im).
So it might work with very long recovery time diodes giving you a little more switching time.
It looks too simple, but we will see.
PS. it's not entirely unbelievable, I've seen it said elsewhere that any diode can be driven into snappy turn off (which is what this is) with the correct current profile (although in those cases it was described as a bad thing). Still, if it's this simple/cheap why isn't it widespread?
Registered Member #2941
Joined: Fri Jun 25 2010, 08:08AM
Location:
Posts: 143
Pinky's Brain wrote ...
cedric wrote ... if some one have some good idea about how to make solid state switch witch is reliable ,sheep ,easy to build and who don't involve proprietary technologies I ll take them.
It looks a bit like voodoo, but if these circuits work they could be very practical :
It's similar to the method from "NANOSECOND PULSE GENERATOR USING A FAST RECOVERY DIODE" ... but it uses a slight different effect and a less complex circuit. I wonder if the effect is the same one underlying the mythical SOS diode assemblies? The diode used in this paper is dirt cheap at any rate (1n5408). They suggest it can work for most power rectifiers and in another paper "Improvement of Electromagnetic Pulse Radiation Efficiency". They write :
wrote ... if the following requirements are provided: injection time (τ+) is much more shorter than the diode’s reverse recovery time (τrr); removing time (τ−) is shorter than injection time (τ+); and removing current (I−) doesn’t exceed maximum possible current (Im).
So it might work with very long recovery time diodes giving you a little more switching time.
It looks too simple, but we will see.
PS. it's not entirely unbelievable, I've seen it said elsewhere that any diode can be driven into snappy turn off (which is what this is) with the correct current profile (although in those cases it was described as a bad thing). Still, if it's this simple/cheap why isn't it widespread?
I have been dinging in to it a bit and I also think it might work ,probably not as good as sos but it's worse trying ,the beauty of it is that using those component it might be possible to use the diode as un opening switch from some sort of boost converter and get a nice voltage rise on the way,my guess would be to use big disk shaped normal recovery diode rated for 6kv or more as a physically large diode may hold bigger charge and promote a better snap than a string of small one,one of the problem with this technic is that some diode might behave much better than some other regardless of the producer so the best way to go would be to by a big stack of it and try them all ,but those diode are not really sheep. Some time a go I run in some paper explaining how they modify the recovery behavior of diode using a specific type of ionization radiation in order to create recombination holes in one of the semiconductor layer,I didn't understand most of it but it's look interesting .
Registered Member #2901
Joined: Thu Jun 03 2010, 01:25PM
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Posts: 837
The circuit in the paper already is a boost converter ... the moment the diodes switches off it forms a RLC series circuit with the load with an initial current, the higher the load resistance the higher the voltage (running it unloaded is a good way of blowing it up).
The voltage rise time is supposedly dependent on the the breakdown voltage of the diode (that's in the paper I didn't link, it's not freely available). So a stack of lower voltage diodes should work better than one high voltage one ... dunno how simultaneous the snap off of the diodes is though, with avalanche diodes it wouldn't matter but that increases cost, maybe put a string of MOVs in parallel?
1n5062 seems the best bang for buck for avalanche diodes and 1n5408 and P600M the best for non avalanche diodes. To pump a decent amount of energy into a low ohmic load with a short pulse you will need very large currents of course ... given that the paper says a 1n5408 is limited to around 11A that means quite a lot of diodes.
Registered Member #2941
Joined: Fri Jun 25 2010, 08:08AM
Location:
Posts: 143
Pinky's Brain wrote ...
The circuit in the paper already is a boost converter ... the moment the diodes switches off it forms a RLC series circuit with the load with an initial current, the higher the load resistance the higher the voltage (running it unloaded is a good way of blowing it up).
The voltage rise time is supposedly dependent on the the breakdown voltage of the diode (that's in the paper I didn't link, it's not freely available). So a stack of lower voltage diodes should work better than one high voltage one ... dunno how simultaneous the snap off of the diodes is though, with avalanche diodes it wouldn't matter but that increases cost, maybe put a string of MOVs in parallel?
1n5062 seems the best bang for buck for avalanche diodes and 1n5408 and P600M the best for non avalanche diodes. To pump a decent amount of energy into a low ohmic load with a short pulse you will need very large currents of course ... given that the paper says a 1n5408 is limited to around 11A that means quite a lot of diodes.
I don't think sos diode work through an avalanche process...
Registered Member #2901
Joined: Thu Jun 03 2010, 01:25PM
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Posts: 837
All diodes can avalanche, the major difference with an avalanche rated rectifier is that you know it can survive it :) It's just so you can stack them without worrying too much about whether they snap off at exactly at the same time.
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magnetic pulse compression
