"Bill Sloman" <bill.sloman@gmail.com> wrote in message news:a91887ad-29e7-42e4-a65b-90712b3245ff@googlegroups.com...> That sounds a bit odd. Bifilar wound transformers are famously closely > coupled, and the bifilar winding is just a single length of twisted > pair.The coupling of course is in regards to a conventional (two section "shell", or let alone bank wound) construction, which doesn't couple nearly so well.> Leakage inductance is flux that threads one coil without threading the > other, and the thing about ferrite cores and shields is that they offer > a much lower reluctance path to the flux for the path that goes through > the middle of the whole coil and returns around the outside the whole > coil.Yes, and there's plenty of space between the wires of a transmission line -- if there were none, it wouldn't transmit (or rather, it would violate causality -- no inductance means infinite speed of light). Analogously, no material has an infinite speed of sound, or stiffness (though people often say "water is incompressible", which has the same error or approximation). There are many cases where a (single element) transmission line transformer won't suffice; high frequency power conversion is an easy example. Put simply, the circuit impedance is lower than most transmission line structures or winding constructions, hence LL dominates.> At high frequencies very little of the flux gets outside the > transmission line.Correct, particularly literal in the case of coax. But it's also not mutual inductance: in the case of coax, the flux that loops around the inner conductor necessarily does not also enclose the outer conductor. Thus, fully describing leakage inductance. The external flux (corresponding to current flowing on the shield) is what's doing the transformering.> They do couple, but the sign of the coupling reverses with every twist, > so the couplings cancel pretty exactly.I may've overstated the impact. Last I recall measuring one, the leakage was consistent with the length of twisted pair used. Capacitance should be higher, given the proximity, and since the proximity is to subsequent turns, it will be dispersive, at least in the common mode.> I'm wondering about more elaborate transmission line structures. Two > parallel tracks are a transmission line, but one with a relatively large > external field. > > If you stacked two such lines, one above the other, and tied the > diagonal pairs together, the external field would fall off faster.Indeed, you go from dipole to quadrapole and so on. It would be a big transformer to have the edge-to-edge distance in the far field though (say, 100+ mils edge-to-edge spacing for a 20 mil layer-to-layer spacing), and for not much advantage (in these sorts of situations, you normally just deal with, or outright ignore, the dispersion arising from turn-to-turn coupling). Each facing pair of traces crudely looks like a parallel plate transmission line in isolation, so that a stack of N layers of alternating traces (P, S, P, S, ..) looks like N-1 transmission lines in parallel and thus N-1 times lower impedance: same as using a very wide transmission line, except not. (And also saving on edge effect, which was mentioned earlier.) The layers will inevitably couple between each other, which I think should increase the impedance slightly, but not by nearly as much as the construction reduces it to begin with.> A hexagon arrangement, spread over three layers of a multilayer board, > is even sillier. Of course, if you put in a central track, and drive > the six outside tracks together, you've just built a crude - but > possibly useful - approximation to a coax cable.Pretty neat: http://en.wikipedia.org/wiki/Radio_frequency_power_transmission#mediaviewer/File:Solec_Kujawski_longwave_antenna_feeder.jpg Though I wonder how well it performs under windy conditions. Tim -- Seven Transistor Labs Electrical Engineering Consultation Website: http://seventransistorlabs.com
PCB transmission line transformer
Started by ●June 13, 2014
Reply by ●June 14, 20142014-06-14
Reply by ●June 14, 20142014-06-14
"John Larkin" <jjlarkin@highNOTlandTHIStechnologyPART.com> wrote in message news:gfuop9dtimgrs015klrrgq8uer51m5pm0l@4ax.com...> Not to change the subject, but I've been exploring mosfets for fast > kilovolt switching. Most kilovolt-level power fets kill you from gate > charge requirements and/or source lead inductance. SiC looks like a > winner until you see the internal gate resistances, 5 ohms or so, too > much to allow you to drive the gate hard and fast.What, I thought MOSFETs were "the harder you drive them, the faster they go"? ;-) I doubt they make SiC much slower than regular types. Rg and Vgs are higher, and Qg is smaller. It all scales. Superjunction FETs are pretty amazing, at least above 20V or so. I imagine you wouldn't have a very good pulse generator using those, if you ran into the saturation region. Perhaps some sort of level-shifted pre-Cds-catastrophe active clamp thingy to make a sharp pulse without fully saturating. And plenty of opportunity for "interesting/risky" in that driver circuit thing. I take it your customer is a bit more picky than the level of, say, avalanche chains? And the voltage is higher than, say, step recovery can provide? But that's a silly limitation, because 4kV single junctions are available. And they're slow and probably have really shitty recovery. Maybe another research project. Interesting. Risky. Or if you can find SiC diodes in that range, too. The junction (not schottky) types are just as awful as silicon, for instance, the performance of SiC BJTs, or MOSFET body diodes. AFAIK, they are constructed exactly the same as their Si counterparts, just in different material. Tim -- Seven Transistor Labs Electrical Engineering Consultation Website: http://seventransistorlabs.com
Reply by ●June 14, 20142014-06-14
On Sat, 14 Jun 2014 20:07:58 -0500, "Tim Williams" <tmoranwms@charter.net> wrote:>"John Larkin" <jjlarkin@highNOTlandTHIStechnologyPART.com> wrote in message >news:gfuop9dtimgrs015klrrgq8uer51m5pm0l@4ax.com... >> Not to change the subject, but I've been exploring mosfets for fast >> kilovolt switching. Most kilovolt-level power fets kill you from gate >> charge requirements and/or source lead inductance. SiC looks like a >> winner until you see the internal gate resistances, 5 ohms or so, too >> much to allow you to drive the gate hard and fast. > >What, I thought MOSFETs were "the harder you drive them, the faster they >go"? ;-)Until you blow out the gate, yes.> >I doubt they make SiC much slower than regular types. Rg and Vgs are >higher, and Qg is smaller. It all scales.The small SiC chips make the gate resistances high, according to the appnotes. A 40 amp 1200 volt silicon mosfet may have a gate resistance of a couple tenths of an ohm, and a corresponding SiC may be 6 ohms. And the Qg advantage might be around 2:1. At nanosecond switching speeds, you can't pump the gate fast enough, through that 6 ohms.> >Superjunction FETs are pretty amazing, at least above 20V or so. I imagine >you wouldn't have a very good pulse generator using those, if you ran into >the saturation region. Perhaps some sort of level-shifted >pre-Cds-catastrophe active clamp thingy to make a sharp pulse without fully >saturating. And plenty of opportunity for "interesting/risky" in that >driver circuit thing. > >I take it your customer is a bit more picky than the level of, say, >avalanche chains?A Zetex avalanche chain would be great at 100 Hz. It would melt at 100KHz. And the voltage is higher than, say, step recovery can>provide? But that's a silly limitation, because 4kV single junctions are >available. And they're slow and probably have really shitty recovery. >Maybe another research project. Interesting. Risky.Lots of diodes are unintentional drift-step-recovery (Grehkov) diodes, and if there isn't a 4KV part somewhere, one could series some 1400 volt parts. There are some high-voltage power transistors whose c-b junctions make great DSRDs. Water-cooled 2KV 400KHz DSRD pulser: https://dl.dropboxusercontent.com/u/53724080/Gear/Imago_Pulser.jpg https://dl.dropboxusercontent.com/u/53724080/Gear/Imago_Neg_2KV_pulse.JPG> >Or if you can find SiC diodes in that range, too. The junction (not >schottky) types are just as awful as silicon, for instance, the performance >of SiC BJTs, or MOSFET body diodes. AFAIK, they are constructed exactly the >same as their Si counterparts, just in different material.Schottky diodes don't do the step-recovery thing; diffused silicon PNs seem to have the best doping profiles. What I may wind up doing is talking the customer down to something more reasonable, 2-4 ns. The sine-squared transfer function of a Pockels cell speeds up the optical risetime a bit. I guess we may as well get some SiC transistors and bang the gates until we blow them up. Then we'll know. The Cree, Rohm, and Ixys parts seem to be remarkably similar.
Reply by ●June 14, 20142014-06-14
On Sat, 14 Jun 2014 18:58:21 -0500, "Tim Williams" <tmoranwms@charter.net> wrote:>"Bill Sloman" <bill.sloman@gmail.com> wrote in message >news:a91887ad-29e7-42e4-a65b-90712b3245ff@googlegroups.com... >> That sounds a bit odd. Bifilar wound transformers are famously closely >> coupled, and the bifilar winding is just a single length of twisted >> pair. > >The coupling of course is in regards to a conventional (two section "shell", >or let alone bank wound) construction, which doesn't couple nearly so well. > >> Leakage inductance is flux that threads one coil without threading the >> other, and the thing about ferrite cores and shields is that they offer >> a much lower reluctance path to the flux for the path that goes through >> the middle of the whole coil and returns around the outside the whole >> coil. > >Yes, and there's plenty of space between the wires of a transmission line -- >if there were none, it wouldn't transmit (or rather, it would violate >causality -- no inductance means infinite speed of light). Analogously, no >material has an infinite speed of sound, or stiffness (though people often >say "water is incompressible", which has the same error or approximation). > >There are many cases where a (single element) transmission line transformer >won't suffice; high frequency power conversion is an easy example. Put >simply, the circuit impedance is lower than most transmission line >structures or winding constructions, hence LL dominates. > >> At high frequencies very little of the flux gets outside the >> transmission line. > >Correct, particularly literal in the case of coax. But it's also not mutual >inductance: in the case of coax, the flux that loops around the inner >conductor necessarily does not also enclose the outer conductor. Thus, >fully describing leakage inductance. > >The external flux (corresponding to current flowing on the shield) is what's >doing the transformering. > >> They do couple, but the sign of the coupling reverses with every twist, >> so the couplings cancel pretty exactly. > >I may've overstated the impact. Last I recall measuring one, the leakage >was consistent with the length of twisted pair used. Capacitance should be >higher, given the proximity, and since the proximity is to subsequent turns, >it will be dispersive, at least in the common mode. > >> I'm wondering about more elaborate transmission line structures. Two >> parallel tracks are a transmission line, but one with a relatively large >> external field. >> >> If you stacked two such lines, one above the other, and tied the >> diagonal pairs together, the external field would fall off faster. > >Indeed, you go from dipole to quadrapole and so on. It would be a big >transformer to have the edge-to-edge distance in the far field though (say, >100+ mils edge-to-edge spacing for a 20 mil layer-to-layer spacing), and for >not much advantage (in these sorts of situations, you normally just deal >with, or outright ignore, the dispersion arising from turn-to-turn >coupling). > >Each facing pair of traces crudely looks like a parallel plate transmission >line in isolation, so that a stack of N layers of alternating traces (P, S, >P, S, ..) looks like N-1 transmission lines in parallel and thus N-1 times >lower impedance: same as using a very wide transmission line, except not. >(And also saving on edge effect, which was mentioned earlier.) > >The layers will inevitably couple between each other, which I think should >increase the impedance slightly, but not by nearly as much as the >construction reduces it to begin with. > >> A hexagon arrangement, spread over three layers of a multilayer board, >> is even sillier. Of course, if you put in a central track, and drive >> the six outside tracks together, you've just built a crude - but >> possibly useful - approximation to a coax cable. > >Pretty neat: >http://en.wikipedia.org/wiki/Radio_frequency_power_transmission#mediaviewer/File:Solec_Kujawski_longwave_antenna_feeder.jpg >Though I wonder how well it performs under windy conditions.Cool, big airline coax.
Reply by ●June 15, 20142014-06-15
On 2014-06-14, John Larkin <jjlarkin@highNOTlandTHIStechnologyPART.com> wrote:> On 14 Jun 2014 04:11:16 GMT, Jasen Betts <jasen@xnet.co.nz> wrote: > >>On 2014-06-13, John Larkin <jjlarkin@highNOTlandTHIStechnologyPART.com> wrote: >>> >>> >>> We've used transmission-line transformers to drive mosfet gates. We've wound >>> them from micro-coax on ferrite toroids, with the shield being the primary and >>> the inner conductor the secondary. Sub-ns speed and low leakage inductance. But >>> it's labor intensive. >>> >>> So I was thinking about doing it on a multilayer PCB, like a 6-layer. Layers >>> 1/3/5 could be one to three layers of spiral trace, primary, and 2/4/6 ditto, >>> secondary. I'm not sure how to think about the impedances, but it ought to have >>> wide traces and thin dielectrics, I guess. >>> >>> Maybe one layer, one turn, per winding? That takes no vias. >> >>one layer will be better, with 6 interleaved layers you have the L2-L3 and the >>L4-L5 parasitic capacitance working against your goal, >> >>> It needs a ferrite core. Who makes the sorts of cores that work for PCB >>> inductors? >> >>with the coax transformer how much coax does it take before you don't >>need a core? > > The coax would have to be really long to sustain wide pulses, and the > the prop delay becomes a problem.ok. you said how fast in the original post, but not how slow. as for delay: what if you do this .------> gate | drive >-------------(|) | | | | \/\ coax longer than shown. \/\ | | | | --------(|) __|_ | //// `-----> souce What if you put a diac in series with the gate - would that make a latching mosfet? -- umop apisdn https://public-wifi.ccc.govt.nz/login.html
Reply by ●June 15, 20142014-06-15
On Sat, 14 Jun 2014 18:58:21 -0500, "Tim Williams" <tmoranwms@charter.net> wrote:>Pretty neat: >http://en.wikipedia.org/wiki/Radio_frequency_power_transmission#mediaviewer/File:Solec_Kujawski_longwave_antenna_feeder.jpg >Though I wonder how well it performs under windy conditions.Only works at low frequencies. A large diameter open wire "ladder" transmission line would probably work equally well, but would require very big baluns at both ends. I'm also wondering about the losses. At low RF frequencies, skin depth and resistive losses predominate. I don't think there's enough copper in the wires to be really low loss. I've built broadband wire cage dipoles where such losses almost became a problem. At megawatt power levels, any transmission line losses can be a serious problem. I wouldn't worry (much) about the wind. The wires should all swing in unison. For wide gaps, spreaders can be added. However, I suspect the real danger is some bird landing inside the cage, resulting in an RF arc barbequed bird. Flying branches might also be a problem, but it looks like they've cleared all the trees for miles. Rain would not be a problem, unless the insulators get both dirty and wet. -- Jeff Liebermann jeffl@cruzio.com 150 Felker St #D http://www.LearnByDestroying.com Santa Cruz CA 95060 http://802.11junk.com Skype: JeffLiebermann AE6KS 831-336-2558
Reply by ●June 15, 20142014-06-15
On Sunday, June 15, 2014 1:58:21 AM UTC+2, Tim Williams wrote:> "Bill Sloman" <bill.sloman@gmail.com> wrote in message =20 > news:a91887ad-29e7-42e4-a65b-90712b3245ff@googlegroups.com... > ><snip> >=20 > > That sounds a bit odd. Bifilar wound transformers are famously closely > > coupled, and the bifilar winding is just a single length of twisted > > pair. >=20 > The coupling of course is in regards to a conventional (two section "shel=l", =20> or let alone bank wound) construction, which doesn't couple nearly so wel=l.> =20 > > Leakage inductance is flux that threads one coil without threading th==20> > other, and the thing about ferrite cores and shields is that they offer==20> > a much lower reluctance path to the flux for the path that goes through > > the middle of the whole coil and returns around the outside the whole > > coil.=20 >=20 > Yes, and there's plenty of space between the wires of a transmission line=--=20 if there were none, it wouldn't transmit (or rather, it would violate caus= ality -- no inductance means infinite speed of light). Analogously, no ma= terial has an infinite speed of sound, or stiffness (though people often = say "water is incompressible", which has the same error or approximation).> =20 > There are many cases where a (single element) transmission line transform=er =20> won't suffice; high frequency power conversion is an easy example. Put==20> simply, the circuit impedance is lower than most transmission line =20 > structures or winding constructions, hence LL dominates.You can build transmission lines from printed circuit traces with a rather = wider range of impedances than you can get with coaxial cable and twisted p= air. Since the transmission line is the transformer at high frequencies, the lea= kage inductance simply doesn't the kind of problem that you seem to be imag= ining. You do have to be careful about the lead dress as you enter and leave the t= ransformer structure - that was the area where I managed to tell Tony Willi= ams something that he didn't already know about transformers, much to my su= rprise and gratification.> > At high frequencies very little of the flux gets outside the > > transmission line. > =20 > Correct, particularly literal in the case of coax. But it's also not mut=ual=20> inductance: in the case of coax, the flux that loops around the inner=20 > conductor necessarily does not also enclose the outer conductor. Thus,==20> fully describing leakage inductance. > =20 > The external flux (corresponding to current flowing on the shield) is wha=t's=20> doing the transformering.Wrong. It's the internal flux - in the region between the inner and the out= er - that's doing most of the work. Induced voltage is L.di/dt and at high = frequencies, di/dt is very high, so you don't need much L. =20> > They do couple, but the sign of the coupling reverses with every twist==20> > so the couplings cancel pretty exactly. > =20 > I may've overstated the impact. Last I recall measuring one, the leakage==20> was consistent with the length of twisted pair used. Capacitance should =be =20> higher, given the proximity, and since the proximity is to subsequent tur=ns, =20> it will be dispersive, at least in the common mode.Again, the capacitative currents alternate and largely cancel. =20> > I'm wondering about more elaborate transmission line structures. Two > > parallel tracks are a transmission line, but one with a relatively larg=e> > external field.=20 > > > > If you stacked two such lines, one above the other, and tied the > > diagonal pairs together, the external field would fall off faster. > =20 > Indeed, you go from dipole to quadrapole and so on. It would be a big ==20> transformer to have the edge-to-edge distance in the far field though (sa=y, =20> 100+ mils edge-to-edge spacing for a 20 mil layer-to-layer spacing), and =for=20> not much advantage (in these sorts of situations, you normally just deal==20> with, or outright ignore, the dispersion arising from turn-to-turn =20 > coupling).With transmission lines there shouldn't be a lot. Threading the structure w= ith occasional - spiral - ground lines might help a lot. Low frequency tran= sformers make use of screens to minimise inter-winding capacitances. One standard technique - albeit expensive - for minimising cross-talk in pa= rallel data cables is just to ground every second wire at each end of the c= able. It lowers the characteristic impedance and makes the cables harder to= drive, but what comes out at the receiver end is a lot cleaner. =20> Each facing pair of traces crudely looks like a parallel plate transmissi=on=20> line in isolation, so that a stack of N layers of alternating traces (P, =S,=20> P, S, ..) looks like N-1 transmission lines in parallel and thus N-1 time=s=20> lower impedance: same as using a very wide transmission line, except not.==20> (And also saving on edge effect, which was mentioned earlier.) > =20 > The layers will inevitably couple between each other, which I think shoul=d =20> increase the impedance slightly, but not by nearly as much as the =20 > construction reduces it to begin with.This coupling will be strictly second order - current flowing in screen cre= ating resistive voltage drop in screen which then induces current in adjace= nt screen. It's a real - but not usually detectable - effect in transmissio= n line transformers.> > A hexagon arrangement, spread over three layers of a multilayer board, > > is even sillier. Of course, if you put in a central track, and drive=20 > > the six outside tracks together, you've just built a crude - but=20 > > possibly useful - approximation to a coax cable. =20 >=20 > Pretty neat: >=20 > http://en.wikipedia.org/wiki/Radio_frequency_power_transmission#mediaview=er/File:Solec_Kujawski_longwave_antenna_feeder.jpg>=20 > Though I wonder how well it performs under windy conditions.Not a problem if you are putting all the traces on a multilayer printed cir= cuit board stack. --=20 Bill Sloman, Sydney
Reply by ●June 15, 20142014-06-15
On Saturday, June 14, 2014 7:05:04 PM UTC+2, John Larkin wrote:> On 14 Jun 2014 04:11:16 GMT, Jasen Betts <jasen@xnet.co.nz> wrote:=20 > >On 2014-06-13, John Larkin <jjlarkin@highNOTlandTHIStechnologyPART.com> =wrote:=20> >> =20 > >> We've used transmission-line transformers to drive mosfet gates. We've=wound them from micro-coax on ferrite toroids, with the shield being the p= rimary and the inner conductor the secondary. Sub-ns speed and low leakage = inductance. But it's labor intensive.> >>=20 > >> So I was thinking about doing it on a multilayer PCB, like a 6-layer. =Layers 1/3/5 could be one to three layers of spiral trace, primary, and 2/4= /6 ditto, secondary. I'm not sure how to think about the impedances, but it= ought to have wide traces and thin dielectrics, I guess.=20> >> > >> Maybe one layer, one turn, per winding? That takes no vias.one layer w=ill be better, with 6 interleaved layers you have the L2-L3 and the L4-L5 p= arasitic capacitance working against your goal.> >> > >> It needs a ferrite core. Who makes the sorts of cores that work for PC=B inductors?=20> > > >With the coax transformer how much coax does it take before you don't > >need a core? > =20 > The coax would have to be really long to sustain wide pulses, and the the=prop delay becomes a problem. I don't entirely understand this, but it see= ms to me that the output impedance becomes the Zo of the coax when the coax= is long relative to the pulse rise time. The coax doesn't have to be long to sustain wide pulses. The joy of the tra= nsmission line transformer is that the ferrite cores make it a conventional= transformer for the low frequency content. In fact the transmission line transformer stops being a flat, frequency-ind= ependent coupling when the pulse width gets down to close to equalling the = length of the transmission line. Winfield Hill rubbed my nose in that here = many years ago - much to my delight. I'd been puzzled as to why my twisted = pair transmission line transformer had been falling over at 150MHz when the= coax version was good to 500MHz, and the difference was just the length of= the winding. =20> Here's a version we did, but only for 200 ns 5-volt pulses.=20 >=20 > https://dl.dropboxusercontent.com/u/53724080/Parts/Inductors/Xfmrs.JPG ==20>=20 > We've also done some 2:1 step-up versions, to put 100 volts into 50 ohms,=worked fine.> =20 > This is fun, a picosecond speed pulse inverter. > =20 > https://dl.dropboxusercontent.com/u/53724080/CoaxInverter/MVC-229X.JPG >=20 > https://dl.dropboxusercontent.com/u/53724080/CoaxInverter/MVC-232X.JPG >=20 > https://dl.dropboxusercontent.com/u/53724080/CoaxInverter/MVC-234X.JPG >=20 > https://dl.dropboxusercontent.com/u/53724080/CoaxInverter/MVC-235X.JPG ==20>=20 > The step response is flat for about a ns, until the generator wakes up=20 > and realizes that it's shorted. If you slip a ferrite over the coax,=20 > it handles much longer pulses. PSPL sells this in a box, for some=20 > kilobucks.I published the same idea - in this case for level-shifting - back in 1979 Ghiggino, K.P., Phillips, D., and Sloman, A.W. "Nanosecond pulse stretcher"= ,Journal of Physics E: Scientific Instruments, 12, 686-687 (1979). I didn't think the circuit was worth publishing, but Ken Ghiggino wanted th= e publication, and wrote the first version of the paper. I had to revise it= extensively to get it published. Ken was a chemist - now professor of Phys= ical Chemistry at Melbourne, where I did my Ph.D. - and he hadn't touched a= ll the bases. --=20 Bill Sloman, Sydney
Reply by ●June 15, 20142014-06-15
On Saturday, June 14, 2014 12:50:47 PM UTC-4, John Larkin wrote:> I guess I could float the gate driver electronics on the mosfet source > (and power that somehow, kilovolts off ground) and run the transformer > at signal levels. That's less interesting (aka less risky.) > > Not to change the subject, but I've been exploring mosfets for fast > kilovolt switching. Most kilovolt-level power fets kill you from gate > charge requirements and/or source lead inductance. SiC looks like a > winner until you see the internal gate resistances, 5 ohms or so, too > much to allow you to drive the gate hard and fast. > > GaN is nice, but too low voltage. Maybe a GaN gate driver into one of > those planar Ixys mosfets is the best one can do. My customer wants > 4000 volts in 1 ns, at 100 KHz, but maybe he can't have it.GaN cascoded into a MOSFET = fast, HV MOSFET? Cheers, James
Reply by ●June 15, 20142014-06-15
On Sun, 15 Jun 2014 06:44:58 -0700 (PDT), dagmargoodboat@yahoo.com wrote:>On Saturday, June 14, 2014 12:50:47 PM UTC-4, John Larkin wrote: > >> I guess I could float the gate driver electronics on the mosfet source >> (and power that somehow, kilovolts off ground) and run the transformer >> at signal levels. That's less interesting (aka less risky.) >> >> Not to change the subject, but I've been exploring mosfets for fast >> kilovolt switching. Most kilovolt-level power fets kill you from gate >> charge requirements and/or source lead inductance. SiC looks like a >> winner until you see the internal gate resistances, 5 ohms or so, too >> much to allow you to drive the gate hard and fast. >> >> GaN is nice, but too low voltage. Maybe a GaN gate driver into one of >> those planar Ixys mosfets is the best one can do. My customer wants >> 4000 volts in 1 ns, at 100 KHz, but maybe he can't have it. > >GaN cascoded into a MOSFET = fast, HV MOSFET? > >Cheers, >JamesMaybe. At the point that the peak gate current approaches the peak drain current, somewhere south of 2 ns maybe, the GaN will have to sink twice the drain current. It might be better to just ground the mosfet source and use the GaN as the gate driver. A 7 AM, not having had any coffee yet, I could well be wrong.
