Reply by piglet March 25, 20202020-03-25
On 22/03/2020 11:40 pm, klaus.kragelund@gmail.com wrote:
> Switching that fast at 100V then I hope you are doing ZVS and ZCS swithing > > Otherwise you need super junction part or GAN > > Cheers > > Klaus >
Wasn't the OP trying to make a sinewave at a few MHz? Perhaps he'd have more luck building it as a RF PA with LC tanks and all? piglet
Reply by March 22, 20202020-03-22
On Sun, 22 Mar 2020 16:40:19 -0700 (PDT), klaus.kragelund@gmail.com
wrote:

>Switching that fast at 100V then I hope you are doing ZVS and ZCS swithing
It's a pulse generator. Totem pole, 50 ohm DPAK resistor, output connector. And maybe the cosmetics lowpass filter.
> >Otherwise you need super junction part or GAN
I'm using the EPC GaN fets. -- John Larkin Highland Technology, Inc The cork popped merrily, and Lord Peter rose to his feet. "Bunter", he said, "I give you a toast. The triumph of Instinct over Reason"
Reply by March 22, 20202020-03-22
klaus.kragelund@gmail.com wrote in
news:8dffc872-f146-4255-a01e-297af46eef4c@googlegroups.com: 

> Switching that fast at 100V then I hope you are doing ZVS and ZCS > swithing > > Otherwise you need super junction part or GAN > > Cheers > > Klaus >
Isn't anything at those levels GAN nowadays?
Reply by March 22, 20202020-03-22
Switching that fast at 100V then I hope you are doing ZVS and ZCS swithing

Otherwise you need super junction part or GAN

Cheers

Klaus 
Reply by March 22, 20202020-03-22
On 22 Mar 2020 10:19:12 -0700, Winfield Hill <winfieldhill@yahoo.com>
wrote:

>jlarkin@highlandsniptechnology.com wrote... >> >> EPC has some dynamite 100 and 200 volt parts in that >> current range. (2A) They are cheap and have amazing >> performance, the downside being the horrible BGA packages. >> >>https://www.dropbox.com/s/7247chxsr5iqi5s/T577B_30-volt_pulse.jpg?raw=1 > > Yes, good to far beyond 2 MHz. For example, EPC2012 has > gate charge < 2nC at 5V, so P_drive = f Q Vgs = 0.1W at > 10MHz, and with Coss = 73pF, P_loss = f Coss V^2 = 7W.
What's stunning is the Crss of 0.4 pF. That makes all sorts of dumb-looking circuits work. I've got a GaN totem-pole making 10 volt pulses with rise/fall below 250 ps. From dirt-cheap parts. The circuit works to at least 80 volts, but slows down a bit. The pulses do look a little ratty at that speed, so I'll lowpass them to make prettier edges around 1 ns. I've tested the EPC GaN parts. They die at just about 2x rated voltage. I kinda miss the Avago phemts, but the EPC GaNs are really better. -- John Larkin Highland Technology, Inc The cork popped merrily, and Lord Peter rose to his feet. "Bunter", he said, "I give you a toast. The triumph of Instinct over Reason"
Reply by Winfield Hill March 22, 20202020-03-22
jlarkin@highlandsniptechnology.com wrote...
> > EPC has some dynamite 100 and 200 volt parts in that > current range. (2A) They are cheap and have amazing > performance, the downside being the horrible BGA packages. > >https://www.dropbox.com/s/7247chxsr5iqi5s/T577B_30-volt_pulse.jpg?raw=1
Yes, good to far beyond 2 MHz. For example, EPC2012 has gate charge < 2nC at 5V, so P_drive = f Q Vgs = 0.1W at 10MHz, and with Coss = 73pF, P_loss = f Coss V^2 = 7W. -- Thanks, - Win
Reply by Winfield Hill March 21, 20202020-03-21
bitrex wrote...
> > Need to go fairly fast but not ridiculously fast; the > 2A ADuM4120 seems up to the task with FETs with gate > charges in that range ...
Yes, the ADuM4120 is an amazing part. It's 150kV/us slew rating is one of the best specs out there. That would be 150V/ns, or a 4ns risetime with a 600V pulse. But its 2pF in-to-out capacitance implies i = C dV/dt = 300mA i/o current during the 4ns swing. Worrisome. Better stick to slower edges. -- Thanks, - Win
Reply by bitrex March 21, 20202020-03-21
On 3/21/2020 12:02 PM, Winfield Hill wrote:
> bitrex wrote... >> >> Looking for a MOSFET with a 100 or 150-200 Vds >> N-channel - switch a couple amps at a couple MHz, >> preferably in D-pak ... > > You should avoid the temptation to go big, with > low Rds(on). Instead go for low Qg and low Coss. > Power dissipation terms are f Qg Vg, f Coss Vd^2, > and i^2 Rds(on). It'd be good to keep Coss under > 50pF. Looking in my giant MOSFET spreadsheet, an > FQD5N20L looks good, Qg = 5nC with 5V gate drive, > Coss = 40pF, and Rds = 1-ohm, oops, a little high. > Or maybe FDD7N20TM, Rds = 0.58 ohms, Coss = 45pF. > >
Yes that sounds the ballpark of what I need. It's driving about a 100 ohm load thru an LC with the N-fets sources hooked to four different rails like an interleaved buck, with bootstrapping on the top FET driver to drive the gate of that one high enough. one node switches e.g. +25/-25 and the other e.g. +12/-12 gates driven in sequence with some dead-time. Need to go fairly fast but not ridiculously fast; the 2A ADuM4120 seems up to the task with FETs with gate charges in that range. with the standard MOSFET gate-circuit of diode, small resistor in parallel in line and pull-down at the gate the waveforms look very clean in the sim.
Reply by March 21, 20202020-03-21
On 21 Mar 2020 09:56:03 -0700, Winfield Hill <winfieldhill@yahoo.com>
wrote:

>jlarkin@highlandsniptechnology.com wrote... >> >> Winfield Hill wrote: >> >>> bitrex wrote... >>>> >>>> Looking for a MOSFET with a 100 or 150-200 Vds >>>> N-channel - switch a couple amps at a couple MHz, >>>> preferably in D-pak ... >>> >>> You should avoid the temptation to go big, with >>> low Rds(on). Instead go for low Qg and low Coss. >>> Power dissipation terms are f Qg Vg, f Coss Vd^2, >>> and i^2 Rds(on). It'd be good to keep Coss under >>> 50pF. Looking in my giant MOSFET spreadsheet, an >>> FQD5N20L looks good, Qg = 5nC with 5V gate drive, >>> Coss = 40pF, and Rds = 1-ohm, oops, a little high. >>> Or maybe FDD7N20TM, Rds = 0.58 ohms, Coss = 45pF. >> >> Or maybe GaN. Many times better numbers. Easy to drive. > > Most of the GaN and SiC parts in my spreadsheet are > aimed at higher-power applications. They start with > higher voltage ratings (600 or 1200V), and actually > have higher Qg and Coss values than conventional low- > voltage FETs. But then, my spreadsheet is certainly > incomplete.
EPC has some dynamite 100 and 200 volt parts in that current range. They are cheap and have amazing performance, the downside being the horrible BGA packages. https://www.dropbox.com/s/7247chxsr5iqi5s/T577B_30-volt_pulse.jpg?raw=1 -- John Larkin Highland Technology, Inc The cork popped merrily, and Lord Peter rose to his feet. "Bunter", he said, "I give you a toast. The triumph of Instinct over Reason"
Reply by Winfield Hill March 21, 20202020-03-21
jlarkin@highlandsniptechnology.com wrote...
> > Winfield Hill wrote: > >> bitrex wrote... >>> >>> Looking for a MOSFET with a 100 or 150-200 Vds >>> N-channel - switch a couple amps at a couple MHz, >>> preferably in D-pak ... >> >> You should avoid the temptation to go big, with >> low Rds(on). Instead go for low Qg and low Coss. >> Power dissipation terms are f Qg Vg, f Coss Vd^2, >> and i^2 Rds(on). It'd be good to keep Coss under >> 50pF. Looking in my giant MOSFET spreadsheet, an >> FQD5N20L looks good, Qg = 5nC with 5V gate drive, >> Coss = 40pF, and Rds = 1-ohm, oops, a little high. >> Or maybe FDD7N20TM, Rds = 0.58 ohms, Coss = 45pF. > > Or maybe GaN. Many times better numbers. Easy to drive.
Most of the GaN and SiC parts in my spreadsheet are aimed at higher-power applications. They start with higher voltage ratings (600 or 1200V), and actually have higher Qg and Coss values than conventional low- voltage FETs. But then, my spreadsheet is certainly incomplete. -- Thanks, - Win