200V N-channel FET 200V with nsec speed?

I don't know what happens today, but Zetex used to just second source the Supertex line

They certainly have parts that can switch 180V, in of the order of

10nsec - the speed that you can get does depend on the current sinking and source capacity of your driver.

Back when I was interested - a long time ago now - Supertex were about twice as fast as the competition. They'd found some different way of doing things, which has probably long since lost patent protection.

--
Bill Sloman, Nijmegen

Hello Bill,

That picture seems to have changed quite significantly. Nowadays Zetex builds parts that are hardly rivaled by anyone else.

--
Regards, Joerg

http://www.analogconsultants.com

Joerg a écrit :

How much current do you need? Otherwise, an obvious and really fast way would be going cascode.

--
Thanks,
Fred.

Hi Joerg -

Have you verified the ZXMN10 in a practical design?

Generally speaken, I think the problem is not the FET. A FET should switch in under 1ns. The problem is how to control current spread across the die in value and time. The die is large for PowerMOSFET and the gate is made of silicon and not thick metal - i think. Additional you have a big case with much inductance.

I would like to make a Class E amplifier in the 100 to 200MHz range. 100V would be enough.

Good olle Siliconix.

Maybe you find one at

regards - Henry

"Joerg" schrieb im Newsbeitrag news:R8f6h.25003$ snipped-for-privacy@newssvr21.news.prodigy.com...

My gues is its the gate spreading resistance v capacitance that holds the key. (just like in a bjt)

Colin =^.^=

I'm not sure cascode would be useful for fast turnoff.

We need to know more to better answer Joerg's question, for example, is he thinking of completely switching the MOSFET in 4ns, or is he thinking of obtaining a say 180V swing in 5ns, say not including the last 20V of a 200V load? Is he doing this once every now and then, or is he seeking to repeat this every 5 to 10ns, as Henry would like to do? Joerg, tell us, what are you working on?

I'll venture the observation that many, if not most, high-voltage MOSFETs can be made to switch ON in 5 to 10ns if enough gate current is applied. At least the near portion of the die will switch; there may be issues getting all of the MOSFET's area to rapidly turn on, and it may not achieve its low long-term Rds(on) value until many more ns have passed. If you look at a typical spice MOSFET model, you'll usually see a series gate "spreading" resistor, often 50 ohms. I have found these apparently arbitrarily-picked values to be far too high when compared to the performance of an actual part on the bench. A better model would divide the MOSFET into several portions, with a very low gate spreading resistor for one portion, etc.

With respect to fast turn-on, for small output load-current swings the gate scene described above is the issue, but for high currents, driving capacitive loads, etc, where a high dV/dt means a high I/C, the raw current capability of the MOSFET can become the determining issue. For example, I just completed a fast 1.2kV cable pulser in which I used a single FET switch to drive a 50-ohm coax through a 50-ohm source resistor. My MOSFET needed to sink I = 1kV/100 = 10A in driving the 50-ohm resistor in series with the 50-ohm coax. I observed that even though it could sink 5A to make a 500V pulse in 10ns, when making a 1kV 10A pulse it slowed to about 15ns. There's a set of electrodes at the far end of the coax, which sees a nice -1kV pulse with 15ns risetime. Happily that was good enough for us.

Joerg mentioned fast rise and fall time. While it's easy to rapidly turn off a portion of the area in a typical power MOSFET, portions that have high series gate resistance will stay on until later, so that a gradual rather than abrupt complete turnoff is experienced. This can last as long as 50ns or even 100ns in severe cases. This is assuming the turn-on gate drive lasted long enough to reach the far parts of the MOSFET. I've found wide variations in this effect from one manufacturer's part to another, and in one type to another. Joerg, you'll need to experiment with many different MOSFETs to see how they fare. Sadly, these issues are not covered in the datasheet.

--
 Thanks,
    - Win

Zetex ZVN4525

--

    Boris Mohar

I think the current delaying within the die is a typical device failure mechanism. I've seen a MOSFET making cracking noise every time I switched on the device at 400V and about 300A discharching a flashbulb. That was a more experimental device made by Harris in 1997 but nether reached market penetration. Lost my memory what exactly part number.

BTW: The maximum drain current is bounded to V(GS)! So, if you think of having the die made of thousands of small MOSFETs, all switching at different time, you never can go beyound a specific drain current saturation. The RC-lowpass delay across the die gives f(t) max. The die structure is very different between manufacturers AND R-gate too.

Interesting to see the difference between devices.

- Henry

Hello Win,

Fred, it's around 4A peaks. Very short pulses (less than 50nsec) and a duty cycle under 0.1%.

Win, I can't disclose the application but it would be ok if the FET leaves the last 10-20V "on the table". There could be a few pulses in a row, like 10nsec on, 10nsec off and so on but the total duty cycle would be next to nothing. Also, it's ok if the FET cannot stomach the full 4A since we can parallel some. Cost is not the critical parameter here (isn't that nice for a change?).

I am thinking of using a bank of lower voltage devices like the ZXMN10 that can do these speeds and transform up. But ferrite core transformers are often frowned upon because they become custom devices.

That sounds quite impressive. We will order HV FETs this morning so we can give it a shot despite of what the datasheets say.

Yeah, those datasheets. Sometimes it doesn't seem to make sense. One FET was listed with just a couple nsec turn-on but over 10nsec turn off. That appears to be too extreme but sez so on the datasheet. I wish they had a wee bit more detail. Let's see how those devices fare when Fedex brings them.

Now if I was allowed to design in a tube I'd be home already :-)))

--
Regards, Joerg

http://www.analogconsultants.com

Hello Henry,

Yes. Works like a champ but won't take more than 100V.

Make sure this won't get you into trouble with the Federales (FCC)...

Tried them, as well as all the other cutting-edge manufacturers. No luck but we'll try actual devices now because the datasheet values seem to be a bit arbitrary in some areas.

--
Regards, Joerg

http://www.analogconsultants.com

Hello Colin,

But that wouldn't explain a more than 5:1 ratio between tdoff and tdon, with tdoff being the larger value.

--
Regards, Joerg

http://www.analogconsultants.com

"Joerg" schrieb im Newsbeitrag news:80m6h.10299$ snipped-for-privacy@newssvr12.news.prodigy.com...

Interesting. I stored the datasheet in the high-speed folder immediately...

switch

die in

with

100V

Class E uses a resonance circuit at the output. At least in my circuit.

Hm. Seems that money is of no problem? Hey, give me a project job. You can reach me at snipped-for-privacy@gmx.net (No joke) I like analog-digital-software mixed systems and speak german.

What is about using an avalanche device? Should be possible because of the very low duty-cycle. Zetex makes such devices. I heard they bought them in russia. Ordinary small bjt should also work in avalanche mode. But that should you try first and is far beyond the datasheet. Gold-doped transistors have a extremely short carrier-lifetime. I guess carrier-lifetime is the reason for your larger toff?? MOSFET includes intrinsic BJTs.

- Henry

the

Thats a good point but wait a minute, it might do for low voltage turn on devices where the test gate drive is from 0-12v. If you drove the gate symetricaly about the turn on point maybe tdoff would get closer to tdon ? It obviously has An effect, Win elaborated on it brilliantly (as with most things).

Maybe parallel lower current mosfets would be better ? presumably they have smaller dies so less far for the gate drive to travel accros the chip. could you use a differential set up ? so you would only need 100v devices, and time would be average of tdon/tdoff?

Of course there are probably other mechanisms wich limit the speed than just the gate drive voltage propogating accors the die but im far from being a semiconductor expert;

Colin =^.^=

It's been my experience you can rapidly finesse the MOSFET on and off, well beyond the ordinary rules, for a time or two, using care for the turn-on charge, and turnoff charge, but things add up and its hard to do as well repeatedly, even for a short time.

I used a MTW6n100E, capable of 18A at 1kV for a short time, and drove its Ciss = 3nF gate with a TC4429, capable of delivering 6A, through a 1-ohm 1/2W carbon resistor. If we say the gate current is 4A, that'd only take 4.5ns to move the gate by 6 volts.

High gate drive is important - apply more and more until your desired speed is obtained. But remove the gate drive rapidly as well, to minimize charging and allow faster shutoff later. You may need to use negative voltage to obtain a fast shutoff.

I like to use the smallest MOSFET that can handle the current spike, to keep the capacitance down.

--
 Thanks,
    - Win

Joerg a écrit :

Hmm, I assumed this was inductive switching, but now 4A-200V and short current pulses is closer to 50R. So, what's your load?

--
Thanks,
Fred.

Joerg wrote: ...

...

FWIW...

Back during the early days of power mosfets, I used one in essentially a forward-mode switching supply to drive a load that varied with time (well, really with heating...a filament whose resistance increased considerably as it got hot). I blew up quite a few mosfets figuring out what was going on right at turn-on: that is, when the power to the filament was turned on, not when the FET turned on each cycle. This was before the time of digital scopes, and the fastest available storage scope had some trouble keeping up. I was getting about 200V in WELL under 10 nanoseconds on turnoff: it turned out to be because the load, a transformer that drove the filament, was storing quite a bit of inductive energy that wanted to come back out quickly. It was NOT because of inductive kickback overvoltage driving the FET into avalanche.

Might it be possible to use some inductance in the net load, to help out?

Warning: at least with older power mosfet designs, too high a dv/dt could cause failure of the mosfet.

Beware g-d capacitance: 50pF*100V/nsec = 5 amps, and that has to come out of the gate. There may be some advantage to cascode. Also: if you can account for delay time externally and only need a fast rise time, it seems like that should be easier.

I'd hate to add capacitance to the output node you're driving, but could a P-channel (or N-channel) pullup help? How about a current from a higher voltage, with a clamp diode to keep it limited to whatever you want?

Have you looked into power mosfets used in RF amplifiers? That's not an area I'm very familiar with, but I think you can find them with 200V ratings. Clearly a mosfet driving a load at 150MHz must be able to deal with cycles shorter than your application. Normal power mosfets as you'd use in a 100kHz to 1MHz switching power supply don't work well for VHF power amplification, as compared with RF power mosfets designed for the job. They'll be pricier.

Cheers, Tom

"Tom Bruhns" schrieb im Newsbeitrag news: snipped-for-privacy@h48g2000cwc.googlegroups.com...

He already played with

RF-MOSFETs.

- Henry

This jarred loose a stone in my memory: to quickly charge/discharge a MOSFET gate there was a trick using a ferrite bead as a saturating transformer, connected in positive feedback, primary in series with FET source and secondary in series with the gate drive. It was only capable of a limited charge output before the small bead saturated, but the effect was to pull the gate off very rapidly because (until the protection diodes start conducting) the gate wasn't just grounded, it was pulled negative.

Modern drivers are better, but the trick might still work. As for getting nanosecond wiring into a suitable saturating ferrite, that's something an engineer could probably do...

What about the BSS131 by Infineon? rather small die size, rated to

240V and N-channel SOT-23 package).