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Registered Member #1025
Joined: Sun Sept 23 2007, 07:53PM
Location: Czech Rep.
Posts: 566
Hi guys, After my double IGBT death while pulling plasma from the top load of my tesla coil I came with an idea of additional protection of expensive transistors. The point is to connect a strong diode (made form a bridge which is cheap and can stand almost anything) in series with the transistors and put big cap (3.3uF) parallel to this diode. (check the scheme)
I think it could help the transistors in many ways: First the diode works like non-inductive resistor protecting the short-circuit situations. Next the diode is slower allowing the transistor to be fully open before the energy goes through it. And finally in combination with a big cap it should help to keep the deadly spikes down.
Registered Member #1025
Joined: Sun Sept 23 2007, 07:53PM
Location: Czech Rep.
Posts: 566
Shaun wrote ...
How will the diode act like a resistor?
Diode is not an ideal conductor - I don't know what is the total resistance but it must be significant (hopefully it is more than the open transistor but honestly I don't know)
Shaun wrote ...
And why from a bridge rectifier? I know there are single diodes more than capable of this.
Bridge is cheap, easy to work with (usually isolated) and you can get it from every old electronic device (I have tens of them at home). But otherwise you right...
Shaun wrote ...
Plus, I'm pretty sure a cap in series with the IGBT will not stop spikes; parallel smoothing caps do this.
The point is that the cap should stop the spikes already to protect the diode. No further spikes should appear behind the diode (the diode must be very close to the transistor to make sense). But right, there could be another decoupling caps paralel to the transistors to be double sure...
Registered Member #690
Joined: Tue May 08 2007, 03:47AM
Location: New Jersey, USA
Posts: 616
Okay I understand now. The only thing I think is still worth mentioning is that most diodes have essentially negligible resistance; they mainly dissipate by way of their forward voltage drop. So do IGBTs, which is a big part of why IGBTs and not MOSFETs are used for DRSSTCs.
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protection of IGBT (FET) ?
