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Registered Member #1210
Joined: Fri Jan 04 2008, 07:41AM
Location:
Posts: 2
Hi all.
I am about to start building a small SSTC and while digging for parts in a frequency converter I noticed that they used IGBT gate drive optocouplers. Every SSTC design i have looked at have GDT's to drive the gates. Now to my question: Can I use the optocouplers to drive the gates directly, or can I use them to drive a GDT. Link to HCNW3120 datasheet:
I am not completly new to teslacoils. For about 4 years ago I built a SGTC and managed to get 30-40 cm arcs. My interest in TC's have now come back and I have study many SSTC's and started to gather parts.
Registered Member #33
Joined: Sat Feb 04 2006, 01:31PM
Location: Norway
Posts: 971
The main problem with using optocouplers for this is their high delay times. 300-500nS rise and fall delay in this optocoupler. In SSTCs and especially DRSSTCs, it's important to minimize the total delay time to minimize hard-switching. This device is simply too slow. The 2A peak output current is also a bit low.
It isn't really that hard making a GDT, it's mostly about getting the right driver chips and the right core. Noise suppression ferrites work OK as GDT cores in my experience, not as good as a core made for the purpose, but adequately for a small SSTC.
Registered Member #15
Joined: Thu Feb 02 2006, 01:11PM
Location:
Posts: 3068
For the types of SSTCs typically built, the gate driver circuitry drives and powers the gates directly. For this, you really need a gate transformer.
There are high speed optocouplers, but they are often used in drive circuits where there is already an isolated power source floating at the gate to provide the actualy power to switch the gate and the optocoupler merely provided the "control signal."
Registered Member #1210
Joined: Fri Jan 04 2008, 07:41AM
Location:
Posts: 2
OK.
What is an ideal GDT size to look for, and do you know any equipment who has cores good for GDT's??
I have found 4 pcs of IGBT modules, 3 of them are SIEMENS BSM150GB120DN2 and 1 BSM25GD120DN2. The 3 big ones have a Turn-off delay time of 600nS, does this mean that they are to slow for TC?? (I know they are way to big for my small coil) The smaller is a 3-phase full-bridge 1200V/25A. Can it be used partially for a full bridge or half-bridge? I have the 4 above and 6-8pcs of GT8Q101 1200V/8A IGBT's. I have trouble finding Mosfets/IGBT's as i dont have so mutch $$$ to put into this project. Is the GT8Q101's good for a small SSTC? Another trouble i have is the GDT driver chip. My local store don't have 4420's or UCC37321/2's, can I use some small transistors or are they to slow for this?
My plan is to start with a coil based on Steve Wards mini SSTC, as it seems to be a good design built by many other members of this forum.
Registered Member #195
Joined: Fri Feb 17 2006, 08:27PM
Location: Berkeley, ca.
Posts: 1111
mateo to my knowlage I am the only one in the forum that uses optocuplers in there tesla circuits. It is true that there is delay in opto's and I have got it down to about 140nS delay but it has not been a serous problem with my drsstc that I'm experimenting with. By no means is this method that is cost efective and more comlpicated than transformers. I have spent a lot of efort to get to this scematic and do it for fun. If you want cost efective a prooven transformer method is your best bet
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IGBT Gate Drive Optocoupler
