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Is This Brick Any Good?

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Daniel Kramnik

Tue Jun 07 2011, 06:37PM

Registered Member #3885 Joined: Sun May 15 2011, 12:47AM
Location: Newton, Massachusetts, United States
Posts: 94

Hello all-

I've had the pictures PRX transistor module laying around for a long time and I'm wondering if it would be any good for a Tesla coil project. It's not an IGBT - it's very large darlington transistor rated for 500 amps at 600 volts and 1.5kW dissipation. I only have one module, so this will affect my design. Would it be possible to build an OLTC or other single transistor coil using this brick? I'm not aiming for amazing performance, just for something that works. A medium-sized Tesla coil would be just fine.

Thanks!

-Daniel

Matt Edwards

Wed Jun 08 2011, 07:41PM

Registered Member #2838 Joined: Fri Apr 30 2010, 07:55PM
Location: tehachapi, CA
Posts: 333

What's the part number?

Mads Barnkob

Wed Jun 08 2011, 08:47PM

Registered Member #1403 Joined: Tue Mar 18 2008, 06:05PM
Location: Denmark, Odense C
Posts: 1968

Oidium45 wrote ...

What's the part number?

Does it really weigh in at 6,4 kg?

Forty

Wed Jun 08 2011, 09:04PM

Registered Member #3888 Joined: Sun May 15 2011, 09:50PM
Location: Erie, PA
Posts: 649

maybe the package has gamma ray shielding, just in case

Daniel Kramnik

Thu Jun 09 2011, 03:10AM

Registered Member #3885 Joined: Sun May 15 2011, 12:47AM
Location: Newton, Massachusetts, United States
Posts: 94

I think that 6400 grams is a misprint - mine wights more like 640g. In any case, is it any good?

Gregory

Thu Jun 09 2011, 02:12PM

Registered Member #2922 Joined: Sun Jun 13 2010, 12:08AM
Location:
Posts: 226

Maybe you can use it for a BIG OLTC... It don't swicth much fast..

Daniel Kramnik

Fri Jun 10 2011, 12:30AM

Registered Member #3885 Joined: Sun May 15 2011, 12:47AM
Location: Newton, Massachusetts, United States
Posts: 94

The problem here is that because the switching speed is rather low, any coil I build with this would have to be rather large and thus expensive. Since I only have one of these bricks and since getting another one would probably be next to impossible, I don't think it makes sense for me to invest in a large coil and driver if a single transistor failure would cost me the whole project. Then again, I'm sure it's possible to design a driver that would work with multiple types of bricks, but I'm working on a mid-sized DRSSTC right now and I'd rather focus on that project because my funding is very limited.

The real question I had, however, was whether it would be possible in the first place to use this brick in a Tesla coil. I've only seen MOSFETs and IGBTs in SSTC before, never simple bipolar transistors.

Ash Small

Fri Jun 10 2011, 01:38AM

Registered Member #3414 Joined: Sun Nov 14 2010, 05:05PM
Location: UK
Posts: 4245

It's possible to use a BJT in an SGTC. I don't know about other types of coil, though.

Arcstarter

Fri Jun 10 2011, 01:56AM

Registered Member #1225 Joined: Sat Jan 12 2008, 01:24AM
Location: Beaumont, Texas, USA
Posts: 2253

A BJT will work in most sstc's but with downfalls such as current tail and base current requirements. I think an OLTC would be the best idea if you wish to make a Tesla coil. If it does not have an internal freewheeling diode you must use an external one. You should probably use an external one regardless...

The hardest part will be tuning and making the primary and secondary. The driver does not need first notch quenching or anything like that... A simple 555 oscillator with low duty cycle would work fine, though not as well as the more complicated drivers. This brick could probably handle 2000 amps without breaking a sweat with low duty cycle (like an OLTC requires).

Daniel Kramnik

Fri Jun 10 2011, 04:04AM

Registered Member #3885 Joined: Sun May 15 2011, 12:47AM
Location: Newton, Massachusetts, United States
Posts: 94

I have very little knowledge about OLTCs, but from what I've read, the switching frequency can be very low because the transistor isn't switching at the coil's resonant frequency, but at the rate that the capacitor charges and discharges. Does this mean that I can use a tank circuit with a frequency that is far above the switching speed of the transistor? In that case, I could easily cobble something together with what I have.

As for the driver, would a simple 555 timer mutivibrator work, or should I go with a CT and comparator to detect a drop in dI/dt as the capacitor charges and trigger a monostable 555?

Also, what kind of primary capacitor would be suitable for an OLTC? I have several MO capacitors and motor capacitors that are around 1 or 2 uF (about the value I've seen in some OLTCs) and I do have a 75nF 8kV bank of CDE capacitors, but I'd rather not touch it because it's supposed to be for my DRSSTC.

In terms of amplifying the 555's signal, would it be possible to just use a pair (or two pairs) of UCCs with 15V on the supply through a GDT to get 30V to the base of the transistor? Does driving the base of a BJT differ significantly from driving the gate of a MOSFET for this application (other than the fact that this particular BJT will require quite a bit more current)?

Thanks!

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