On 21 Feb 2017 11:55:32 -0800, Winfield Hill <hill@rowland.harvard.edu> wrote:>Tim Williams wrote... >> >> Intended application: gate drive V_cm testing. > > Why not simplify by using two 1.5kV MOSFETs? > Or 1.7kV SiC parts, C2M1000170D, for $5 each. > Skip the transformers, use one TI UCC21520.DEI/IXYS makes truly insane low-inductance-packaged HV mosfets and gate drivers. They also have some smaller, affordable gate drivers. I like to use transmission-line transformers to step up fast edges, to avoid stacking fets. -- John Larkin Highland Technology, Inc picosecond timing precision measurement jlarkin att highlandtechnology dott com http://www.highlandtechnology.com
These transistors sure do scream...
Started by ●February 20, 2017
Reply by ●February 21, 20172017-02-21
Reply by ●February 21, 20172017-02-21
On 21 Feb 2017 11:47:50 -0800, Winfield Hill <hill@rowland.harvard.edu> wrote:>Tim Williams wrote... >> >>Circuit, for posterity: >>https://www.seventransistorlabs.com/Images/High%20Voltage%20Bridge.pdf > > You should have two sets of drivers and gate > transformers, one each for high and low sides. > Then you can create an adjustable deadtime. > > Another attractive idea: pos/neg pulsing to > turn a set of MOSFETs on or off, with the gate > capacitance storing the state. Combine fast > on/off times with low switching frequencies.The old RadLab radar pulsers were cool. They used the stored energy in a transmission line to make rectangular pulses, with a single switch. I've made some very pretty pulses with a coax line and avalanche transistors: very small and simple circuit. I'm thinking one could merge the pulse storage line with the step-up-transformer function. I asked about the RadLab books in a technical bookstore near the MIT campus. They'd never heard of them. -- John Larkin Highland Technology, Inc picosecond timing precision measurement jlarkin att highlandtechnology dott com http://www.highlandtechnology.com
Reply by ●February 21, 20172017-02-21
John Larkin wrote...> > I asked about the RadLab books in a technical bookstore > near the MIT campus. They'd never heard of them.Yes, out of print. I bought the complete set from a guy at Flea at MIT, and gave them to the Institute. One book specializes in high-power radar pulses. -- Thanks, - Win
Reply by ●February 21, 20172017-02-21
On 21/02/17 21:11, John Larkin wrote:> On 21 Feb 2017 11:47:50 -0800, Winfield Hill > <hill@rowland.harvard.edu> wrote: > >> Tim Williams wrote... >>> >>> Circuit, for posterity: >>> https://www.seventransistorlabs.com/Images/High%20Voltage%20Bridge.pdf >> >> You should have two sets of drivers and gate >> transformers, one each for high and low sides. >> Then you can create an adjustable deadtime. >> >> Another attractive idea: pos/neg pulsing to >> turn a set of MOSFETs on or off, with the gate >> capacitance storing the state. Combine fast >> on/off times with low switching frequencies. > > The old RadLab radar pulsers were cool. They used the stored energy in > a transmission line to make rectangular pulses, with a single switch. > I've made some very pretty pulses with a coax line and avalanche > transistors: very small and simple circuit. I'm thinking one could > merge the pulse storage line with the step-up-transformer function.That's what a Blumlein pulse forming network does, sort-of. The load gets to see the full charging voltage, rather than half of it.> > I asked about the RadLab books in a technical bookstore near the MIT > campus. They'd never heard of them. > >Glasoe & Lebacqz, "Pulse generators" has a nice chapter on the synthesis of PFNs. Jeroen Belleman
Reply by ●February 21, 20172017-02-21
On Monday, February 20, 2017 at 2:31:09 AM UTC-8, Tim Williams wrote:> Playing with a switching circuit, yet I seem to have made the observation > that these things are fantastic for linear. > > Infineon SPA07N60C3, but everyone has their line of SuperJunction MOSFETs. > > Circuit, for posterity: > https://www.seventransistorlabs.com/Images/High%20Voltage%20Bridge.pdf > > Intended load is high impedance, capacitive. It can easily source 5A peak > though. > > Since the load is capacitive, it operates in hard switching. The > transistors start singing as soon as they get into the Miller plateau. > Which in this circuit, I've intentionally exaggerated (27pF D-G), to help > keep the transistor voltages matched. > > A word about SuperJunction transistors: Coss tanks by two decades, over the > 5 to 20V range. Very nonlinear, brutal. This is fantastic for switching > converters, because it "cushions" the switching edge, doing a better job of > snubbing than an external network ever could. By pushing all the Miller > effect to the low voltage end, switching loss can be very low. > > With stacked transistors, that works against me, because they'll probably be > mismatched in the low-capacitance region. So the switching times, and > voltages, probably won't be matched, forcing much more voltage across just > one over-performing transistor. > > So I increase Miller capacitance, so the rise is slower, and more linear. > > And to protect against accidental turn-on or damage, due to opposite side > hard-switching or output sparks, I put zener diodes on G-S. (Back-to-back > pairs, since the drive is transformer coupled.) > > I think between the zeners and the Miller cap, I've got a particularly nasty > loop that makes a wonderful oscillator. In the 200 to 400MHz region, > depending on which transistor you ask. > > (Ferrite beads on the gate leads solves the oscillation, more or less.) > > I'm definitely going to try an RF amplifier with these, soon. I can't do > very much power, because of thermal limitations, and bandwidth won't be > fantastic because of the high load resistance versus Coss (note that the > load resistance has to be high, i.e. the supply voltage high, and because of > power limits, the current relatively low, to stay in the low-Coss range). > The useful frequency range seemingly should be worthy of vacuum tubes, > though! Assuming lead parasitics don't trash it first, which is likely. :) > > Tim > > -- > Seven Transistor Labs, LLC > Electrical Engineering Consultation and Contract Design > Website: http://seventransistorlabs.comNice! Did you draw this with Autodesk's Inventor? Michael
Reply by ●February 21, 20172017-02-21
On 21 Feb 2017 13:16:14 -0800, Winfield Hill <hill@rowland.harvard.edu> wrote:>John Larkin wrote... >> >> I asked about the RadLab books in a technical bookstore >> near the MIT campus. They'd never heard of them. > > Yes, out of print. I bought the complete set from > a guy at Flea at MIT, and gave them to the Institute. > One book specializes in high-power radar pulses.It took me years to collect the full set, not cosmetically matched. Great stuff. -- John Larkin Highland Technology, Inc picosecond timing precision measurement jlarkin att highlandtechnology dott com http://www.highlandtechnology.com
Reply by ●February 21, 20172017-02-21
"Winfield Hill" <hill@rowland.harvard.edu> wrote in message news:o8i5vk0m79@drn.newsguy.com...> Why not simplify by using two 1.5kV MOSFETs? > Or 1.7kV SiC parts, C2M1000170D, for $5 each. > Skip the transformers, use one TI UCC21520.1. Had 'em on hand. 2. Hadn't done a stack before. Seems to work pretty well, even with the crappy drive! Tim -- Seven Transistor Labs, LLC Electrical Engineering Consultation and Contract Design Website: http://seventransistorlabs.com
Reply by ●February 21, 20172017-02-21
"John Larkin" <jjlarkin@highlandtechnology.com> wrote in message news:3tnoacd1vfrgrlgb6l5gcf7tiqr7eoejma@4ax.com...> Another way to get insane edge speeds is avalanche transistors. A > modest stack of the Zetex SOT23 parts could switch a couple of KV in a > couple of ns.Yup, though not too much current before life expectancy plummets. I can't imagine it's too easy connecting them in parallel either (yes, they can be triggered, with reasonable jitter, but that's a lot more bother). I did a minor study of transistors I have laying around; few did not exhibit latching avalanche discharge, but many were finicky (the region of base resistance vs. collector current for pulsing behavior was small, and inconsistent between samples). None really seemed to be more powerful and faster than the usual tiny suspects (like 2N3904). Avalanche also spreads out poorly -- so a very large transistor (like a 15A 1500V HOT) only 'ignites' in some random spot location, and becomes damaged at basically the same surge current as a 2N3904. (Afterwards, instead of collector leakage, there's C-E resistance, usually on the order of 40kohms. Characteristic of a microscopic burn hole.) Tim -- Seven Transistor Labs, LLC Electrical Engineering Consultation and Contract Design Website: http://seventransistorlabs.com
Reply by ●February 21, 20172017-02-21
<mrdarrett@gmail.com> wrote in message news:21c519f7-9b06-4b72-b950-94a3a4cea273@googlegroups.com...> Nice! Did you draw this with Autodesk's Inventor? >GAH! Choke! No, Altium. The real deal. ;-) (You might recognize some shapes and default colors from Win's drawings as well; he uses an old copy of Protel, IIRC. The ground symbols haven't changed a pixel!) Tim -- Seven Transistor Labs, LLC Electrical Engineering Consultation and Contract Design Website: http://seventransistorlabs.com
Reply by ●February 22, 20172017-02-22
"John Larkin" <jjlarkinxyxy@highlandtechnology.com> wrote in message news:ic7pacphaoie5kcv79k4e5vbj7pp1d692e@4ax.com...> The old RadLab radar pulsers were cool. They used the stored energy in > a transmission line to make rectangular pulses, with a single switch. > I've made some very pretty pulses with a coax line and avalanche > transistors: very small and simple circuit. I'm thinking one could > merge the pulse storage line with the step-up-transformer function.A friend of mine has been taking apart some modest-vintage radar equipment (civil, ATC I think). He's got a handful of hydrogen thyratrons and hard glass modulators (transmitter tetrodes, with fucking huge cathodes) from it. We've been thinking about pulse generator applications, like making a retro-high-tech Tesla coil. I suspect they use hydrogen thyratrons in EFT generators, but I've not taken one apart. Some day, I'd like to design and build an EFT tester, just because. But getting a hydrogen thyratron would be too easy, and not really all that helpful. I'd rather do it with an IGBT and shock line: could be very cheap and highly available, only needing custom wound inductors (saturable reactors, really). Don't know how easy it will be to adjust to make a clean pulse, though... Tim -- Seven Transistor Labs, LLC Electrical Engineering Consultation and Contract Design Website: http://seventransistorlabs.com
