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ScotchTapeLord

Thu Mar 11 2010, 03:15PM

Registered Member #1875 Joined: Sun Dec 21 2008, 06:36PM
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Posts: 635

I've been doing a lot of searching around looking for the fastest (general purpose) MOSFET, the fastest IGBT, etc... mostly out of curiosity, but also because breaking current frequency barriers may shed light onto the next type of solid state tesla coil... or something like that, maybe?

The fastest mosfet I've ever used was the IRF740. I used them because I learned the sstc basics from Richie Burnett's excellent site, and he used them in his earliest designs.
I didn't know how to interpret datasheets at the time (I didn't even know about them at the time), but now, looking back, they are some of the fastest FETs around. With rise and fall times like those, I know they can be used for frequencies past a MHz.

I was exploring random threads in the 4hv archives, and I came across these IGBTs:

It seems those, too, can be operated into the extremely high frequencies! I definitely want to get my hands on a bridge of those. Super high frequency DRSSTC, anyone?

Are there any bricks that are particularly fast that I don't know about? Does anyone know of faster FETs and IGBTs than the ones I've shown?

Steve Conner

Thu Mar 11 2010, 03:26PM

Registered Member #30 Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706

You can get metal gate RF MOSFETs that work up into the 100s of MHz.

Most power MOSFETs can be forced up to 4MHz, maybe even 8 or 10, in a properly tuned Class-E amplifier. I think 14MHz is the SSTC record for you to beat.

I had some of the FGH50N6S2D driving my induction heater with about 1kW at 250kHz.

IGBTs probably won't ever make it into the MHz because of minority carrier effects. (Not to mention lack of demand for RF IGBTs.) MOSFETs on the other hand, are majority carrier devices and will turn on and off as fast as you can change the gate voltage. So it's purely the time constant of the gate electrode that limits their speed. That's why the metal gate ones go faster than the regular kind.

Myke

Thu Mar 11 2010, 04:08PM

Registered Member #540 Joined: Mon Feb 19 2007, 07:49PM
Location: MIT
Posts: 969

I've seen some papers talking about MESFET class E amplifiers going into the GHz range but the aren't very high power. They are all pretty much under 20W output. There are other switching devices that can operate in the 100s of MHz but sadly, their output power is fairly low which is a trade off for reduced device capacitance and low switching times.
The IRF510 might be able to be pushed up to a fairly high freq with a fair amount of power output.

Proud Mary

Thu Mar 11 2010, 05:45PM

Registered Member #543 Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992

ScotchTapeLord wrote ...

I've been doing a lot of searching around looking for the fastest (general purpose) MOSFET, the fastest IGBT, etc... mostly out of curiosity, but also because breaking current frequency barriers may shed light onto the next type of solid state tesla coil... or something like that, maybe?

The viable frequency window in which Tesla coils can operate is not determined by switching devices (electro-mechanical interruptors, thermionic valves, transistors &c) but by the fact that the voltage gain of a TC is proportional to the square root of the ratio of secondary to primary inductance.

ShawnLG

Thu Mar 11 2010, 06:32PM

Registered Member #286 Joined: Mon Mar 06 2006, 04:52AM
Location:
Posts: 399

I've been doing a lot of searching around looking for the fastest (general purpose) MOSFET, the fastest IGBT, etc... mostly out of curiosity, but also because breaking current frequency barriers may shed light onto the next type of solid state tesla coil... or something like that, maybe?

This 'next type' of tesla coil is nothing new. It is a Class-E tesla coil. Someone here has made a 13.56Mhz Class-E coil.

The only way to get many Mhz from general purpous MOSFETs without using expensive RF MOSFETs would be to use low power MOSFETs. low power MOSFETs can be switch faster.

Someone has made a 50Mhz 500 watt PA using cheap IRF510 MOSFETs.

MinorityCarrier

Thu Mar 11 2010, 06:38PM

Registered Member #2123 Joined: Sat May 16 2009, 03:10AM
Location: Bend, Oregon
Posts: 312

Check out what Microsemi's up to with silicon carbide RF transistors (1500W 450MHz)

Sulaiman

Thu Mar 11 2010, 06:41PM

Registered Member #162 Joined: Mon Feb 13 2006, 10:25AM
Location: United Kingdom
Posts: 3140

For my radio hobby I'm using a couple of fets for >100W CW at >2 GHz.
There is no point considering such a high frequency for a TC as 1/4 wavelength is 35mm.
EDIT P.S. just experimenting, not transmitting.

ScotchTapeLord

Thu Mar 11 2010, 08:13PM

Registered Member #1875 Joined: Sun Dec 21 2008, 06:36PM
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It ain't over til someone uses the ESL of a capacitor as the primary and a 40 gauge strand of wire for the secondary =P

Mattski

Thu Mar 11 2010, 09:07PM

Registered Member #1792 Joined: Fri Oct 31 2008, 08:12PM
Location: University of California
Posts: 527

I think LDMOS devices are the fastest power devices available in Silicon. They can be used in the power amplifiers of base stations even. Infineon's CoolMOS is an LDMOS line designed for switching power supplies. They operate at pretty high power levels because of the 500V+ ratings. A random example of one intended for an RF amplifier this.

Steve Conner

Thu Mar 11 2010, 10:21PM

Registered Member #30 Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706

Sulaiman wrote ...

For my radio hobby I'm using a couple of fets for >100W CW at >2 GHz.
There is no point considering such a high frequency for a TC as 1/4 wavelength is 35mm.

Yes there is! Just stick 70mm of wire in a microwave oven, streamers burst from both ends, et voila a microwave VTTC.

I've seen foolhardy people on Youtube run a magnetron removed from the oven with a sharp point attached to the antenna, and it really does break out and make a plasma flame.

Silicon carbide power JFETs recently became available, I wonder how fast they go?

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