dagmargoodboat@yahoo.com wrote...> > Winfield Hill wrote: >> >> There's very little in the signal path. And the 20ns delay to >> *the MOSFET output* is about as fast as you'll find. My only >> complaint is that the FETs are too big, too much capacitance. >> When switching a 50-ohm cable-matching output resistor, a low >> 70-milli-ohm Ron is serious overkill. > > Hey Win, here's a smaller-sized version of the same concept, > driver-plus-GaN on a chip: ><https://media.digikey.com/pdf/Data%20Sheets/Navitas%20Semi%20PDFs/NV6113%20Datasheet%20(FINAL)%208-28-18.pdf>Wow, Navitas NV6113, GaN, 200V/ns, only $3.38 at Digi-Key. And Octopart doesn't even know about them yet! It looks hard to get heat out of the package, they say limited to 2MHz switching rate. -- Thanks, - Win
Linear power FETs
Started by ●January 10, 2019
Reply by ●January 12, 20192019-01-12
Reply by ●January 12, 20192019-01-12
Winfield Hill wrote...> >dagmargoodboat@yahoo.com wrote... >> >> Winfield Hill wrote: >>> >>> There's very little in the signal path. And the 20ns delay to >>> *the MOSFET output* is about as fast as you'll find. My only >>> complaint is that the FETs are too big, too much capacitance. >>> When switching a 50-ohm cable-matching output resistor, a low >>> 70-milli-ohm Ron is serious overkill. >> >> Hey Win, here's a smaller-sized version of the same concept, >> driver-plus-GaN on a chip: >><https://media.digikey.com/pdf/Data%20Sheets/Navitas%20Semi%20PDFs/NV6113%20Datasheet%20(FINAL)%208-28-18.pdf> > > Wow, Navitas NV6113, GaN, 200V/ns, only $3.38 at Digi-Key. And > Octopart doesn't even know about them yet! It looks hard to get > heat out of the package, they say limited to 2MHz switching rate.Hah, you have to register, complete with password, just to see a product list. Well, at least Digi-Key shows three single-FET switches available now. But their two-FET half-bridge would be far more interesting to those of us who like to make HV pulsers. BTW, WRT their stated 2MHz operation spec, the Co(er) spec, which is 16pF at 400V, that's only P = C V^2 f = 5 watts at 2MHz. But, oops, with Rth-ja = 50C/W on 1-in-sq copper, that's dT = 250C. -- Thanks, - Win
Reply by ●January 12, 20192019-01-12
On Saturday, January 12, 2019 at 3:20:53 PM UTC-5, Winfield Hill wrote:> Winfield Hill wrote... > > > >dagmargoodboat@yahoo.com wrote... > >> > >> Winfield Hill wrote: > >>> > >>> There's very little in the signal path. And the 20ns delay to > >>> *the MOSFET output* is about as fast as you'll find. My only > >>> complaint is that the FETs are too big, too much capacitance. > >>> When switching a 50-ohm cable-matching output resistor, a low > >>> 70-milli-ohm Ron is serious overkill. > >> > >> Hey Win, here's a smaller-sized version of the same concept, > >> driver-plus-GaN on a chip: > >><https://media.digikey.com/pdf/Data%20Sheets/Navitas%20Semi%20PDFs/NV6113%20Datasheet%20(FINAL)%208-28-18.pdf> > > > > Wow, Navitas NV6113, GaN, 200V/ns, only $3.38 at Digi-Key. And > > Octopart doesn't even know about them yet! It looks hard to get > > heat out of the package, they say limited to 2MHz switching rate. > > Hah, you have to register, complete with password, just to see > a product list. Well, at least Digi-Key shows three single-FET > switches available now. But their two-FET half-bridge would be > far more interesting to those of us who like to make HV pulsers. > > BTW, WRT their stated 2MHz operation spec, the Co(er) spec, which > is 16pF at 400V, that's only P = C V^2 f = 5 watts at 2MHz. But, > oops, with Rth-ja = 50C/W on 1-in-sq copper, that's dT = 250C. > > > -- > Thanks, > - WinI get 16pF x 1 MHz x 400V^2 = 2.56W But, that's assuming the driver dissipates power in both directions, which isn't true. When the FET is off and something else is charging Co, the driver dissipation is essentially zero. So, the actual 2MHz / 400V dynamic dissipation, unloaded, should be about 1.3 watts, right? Cheers, James Arthur
Reply by ●January 12, 20192019-01-12
On Saturday, January 12, 2019 at 12:42:03 PM UTC-5, dagmarg...@yahoo.com wrote:> On Saturday, January 12, 2019 at 11:00:55 AM UTC-5, George Herold wrote: > > On Saturday, January 12, 2019 at 12:58:21 AM UTC-5, dagmarg...@yahoo.com wrote: > > > On Friday, January 11, 2019 at 8:53:41 PM UTC-5, George Herold wrote: > > > > On Friday, January 11, 2019 at 3:05:14 PM UTC-5, dagmarg...@yahoo.com wrote: > > > > > On Friday, January 11, 2019 at 12:44:48 AM UTC-5, Phil Hobbs wrote: > > > > > > On 1/10/19 11:46 PM, dagmargoodboat@yahoo.com wrote: > > > > > > > RF MOSFETs. They're built for linear operation. At a glance, they seem > > > > > > > > > > > > Welcome back! You've been a bit scarce since last spring, iirc. > > > > > > > > > > > > Cheers > > > > > > > > > > > > Phil Hobbs > > > > > > > > > > Hi Phil! > > > > > > > > > > I've been doing some pretty fun things, but hobby-level > > > > > electronics, nothing I thought would be very interesting > > > > > for sed. I do still peek in to see what's happening. > > > > James!, As a tadpole here on SED I'd love to hear/see any > > > > of your hobby level 'fun' stuff. > > > > The fare has been a little thin here. > > > > > > > > I'm doing this high side switch driving a heater to ground. > > > > Looking at the circuit I got to work, I've got low pass filters > > > > everywhere, with little understanding... which happens sometimes > > > > when you're just trying to get something working. > > > > > > > > I think my circuit was missing some resistance on the inverting input. > > > > (I tried to do some asci art, but too much of a Friday night buzz. :^) > > > > > > > > High side GS resistor (on pfet) that is turned off by > > > > level sift 'grounded' base npn, with emitter resistor > > > > driven by opamp. A resistor divider senses drain/load > > > > voltage-compares that to error (in opamp) which drives > > > > emitter R. > > > > > > > > George H. > > > > > > Like this? > > > > > > Q1 > > > V+ >--+-----+-. .-------+--------. > > > | | ^ | | | > > > .-. .- - - | | > > > Rgs | | | .-. | > > > '-' | | | Rload | > > > | | '-' | > > > '----+ | | > > > | | | > > > |/ === | > > > +5v >--| Q2 | > > > |>. .-. > > > | | | R1 > > > .-. '-' > > > Re | | /| | > > > '-' /+|-----------+ > > > | / | | > > > '-----< | .-. > > > \ | | | R2 > > > \-|-- Vref '-' > > > \| | > > > === > > > > > > That looks like an oscillator. :-) > > > > > > Cheers, > > > James Arthur > > > > Prezactly! I killed the oscillation with a nF across R2(10k) and > > 100 nF! of feedback C. > > > Q1 > > > V+ >--+-----+-. .-------+---------------. > > > | | ^ | | | > > > .-. .- - - | | > > > Rgs | | | .-. | > > > '-' | | | Rload | > > > | | '-' | > > > '----+ | | > > > | | | > > > |/ === | > > > +5v >--| Q2 | > > > |>. .-. > > > | | | R1 > > > .-. '-' > > > Re | | /| | > > > '-' /+|------------------+-------. > > > | / | | | > > > +-----< | .-. ___ > > > | \ | Rcomp | | R2 ___ C2 1nF > > > | \-|--+-/\/\/-- Vrf '-' | > > > | \| | | ==== > > > '-----||-----' === > > > 100nF > > > > Is there some better way to compensate? > > It's a heater thing so slow is fine. > > > > Thanks for the nice pic, I certainly miss your presence. > > > > George H. > > C2 across R2 is anti-helpful. The problem, in lay terms, > is that your op-amp is reacting very quickly, but to old news. > > That is, it's over-reacting to feedback that is delayed in > time. So you're creating a situation where you are already > driving Q2 appropriately, but Q1's output hasn't moved yet, > and your op-amp then tries to drive Q2 even harder even though > its existing drive level was already perfect (if it had only > waited long enough to see). C2 makes that worse. > > The easy solution is to eliminate C2 and add in Rcomp. Rcomp, > sufficiently large, slows the op-amp response until the > feedback delay is inconsequential in comparison to the op-amp's > now-gradual corrections. In that way, the op-amp is reacting > to a realistic representation of the results of that op-amp's > last output, and can make appropriate new adjustments. > > Another way is to accelerate the feedback to the op-amp > so that the op-amp's information isn't so stale, such > as with feed-forward compensation. Here, that would mean > putting C2 across R1. But if you don't need the maximum > speed possible, just slow down the op-amp. It's less ticklish. > > Slowed down, the op-amp will make corrections gradually, then > have plenty of time to see the effects of those corrections, > then make even more corrections. Tada! that's also known as > 'closed-loop feedback'. :-) > > Did that make sense?Yeah thanks James. I thought I needed some inverting R. I need something for the feedback cap to 'work' against. George H.> > Cheers, > James Arthur
Reply by ●January 12, 20192019-01-12
On Saturday, January 12, 2019 at 1:38:33 PM UTC-5, John Larkin wrote:> On Sat, 12 Jan 2019 10:17:47 -0800 (PST), dagmargoodboat@yahoo.com > wrote: > > >On Saturday, January 12, 2019 at 11:57:16 AM UTC-5, John Larkin wrote: > >> On Fri, 11 Jan 2019 21:58:18 -0800 (PST), dagmargoodboat@yahoo.com > >> wrote: > >> > >> >On Friday, January 11, 2019 at 8:53:41 PM UTC-5, George Herold wrote: > >> >> On Friday, January 11, 2019 at 3:05:14 PM UTC-5, dagmarg...@yahoo.com wrote: > >> >> > On Friday, January 11, 2019 at 12:44:48 AM UTC-5, Phil Hobbs wrote: > >> >> > > On 1/10/19 11:46 PM, dagmargoodboat@yahoo.com wrote: > >> >> > > > RF MOSFETs. They're built for linear operation. At a glance, they seem > >> >> > > > >> >> > > Welcome back! You've been a bit scarce since last spring, iirc. > >> >> > > > >> >> > > Cheers > >> >> > > > >> >> > > Phil Hobbs > >> >> > > >> >> > Hi Phil! > >> >> > > >> >> > I've been doing some pretty fun things, but hobby-level > >> >> > electronics, nothing I thought would be very interesting > >> >> > for sed. I do still peek in to see what's happening. > >> >> James!, As a tadpole here on SED I'd love to hear/see any > >> >> of your hobby level 'fun' stuff. > >> >> The fare has been a little thin here. > >> >> > >> >> I'm doing this high side switch driving a heater to ground. > >> >> Looking at the circuit I got to work, I've got low pass filters > >> >> everywhere, with little understanding... which happens sometimes > >> >> when you're just trying to get something working. > >> >> > >> >> I think my circuit was missing some resistance on the inverting input. > >> >> (I tried to do some asci art, but too much of a Friday night buzz. :^) > >> >> > >> >> High side GS resistor (on pfet) that is turned off by > >> >> level sift 'grounded' base npn, with emitter resistor > >> >> driven by opamp. A resistor divider senses drain/load > >> >> voltage-compares that to error (in opamp) which drives > >> >> emitter R. > >> >> > >> >> George H. > >> > > >> >Like this? > >> > > >> > Q1 > >> > V+ >--+-----+-. .-------+--------. > >> > | | ^ | | | > >> > .-. .- - - | | > >> > Rgs | | | .-. | > >> > '-' | | | Rload | > >> > | | '-' | > >> > '----+ | | > >> > | | | > >> > |/ === | > >> > +5v >--| Q2 | > >> > |>. .-. > >> > | | | R1 > >> > .-. '-' > >> > Re | | /| | > >> > '-' /+|-----------+ > >> > | / | | > >> > '-----< | .-. > >> > \ | | | R2 > >> > \-|-- Vref '-' > >> > \| | > >> > === > >> > > >> >That looks like an oscillator. :-) > >> > > >> >Cheers, > >> >James Arthur > >> > >> Is that a linear voltage regulator? There was mention of a highside > >> switch. > > > >I took it as a linear system but you're right, George said "switch." > > > >If he literally meant hard-switching Q1, that's a different kettle > >of fish. A PWM scheme with a slow feedback loop might make more > >sense for that. > > > >Cheers, > >James > > Driving heaters from linear amps is messy. There's the square-law > linearity issue, and general inefficiency. > > PWM is better for heater control.Right, this is going to run at a constant temp against a mostly constant background... So only some limited power range. (at least that's my hope. :^) George H.> > > -- > > John Larkin Highland Technology, Inc > > lunatic fringe electronics
Reply by ●January 13, 20192019-01-13
On 13/1/19 6:55 am, Winfield Hill wrote:> dagmargoodboat@yahoo.com wrote... >> >> Winfield Hill wrote: >>> >>> There's very little in the signal path. And the 20ns delay to >>> *the MOSFET output* is about as fast as you'll find. My only >>> complaint is that the FETs are too big, too much capacitance. >>> When switching a 50-ohm cable-matching output resistor, a low >>> 70-milli-ohm Ron is serious overkill. >> >> Hey Win, here's a smaller-sized version of the same concept, >> driver-plus-GaN on a chip: >> <https://media.digikey.com/pdf/Data%20Sheets/Navitas%20Semi%20PDFs/NV6113%20Datasheet%20(FINAL)%208-28-18.pdf> > > Wow, Navitas NV6113, GaN, 200V/ns, only $3.38 at Digi-Key. And > Octopart doesn't even know about them yet! It looks hard to get > heat out of the package, they say limited to 2MHz switching rate.50C/W - ugly. That would practically limit you to about 2 amps average, at 300mOhm. That's just not... special.
Reply by ●January 13, 20192019-01-13
On Sunday, January 13, 2019 at 6:13:19 PM UTC-5, Clifford Heath wrote:> On 13/1/19 6:55 am, Winfield Hill wrote: > > dagmargoodboat@yahoo.com wrote... > >> > >> Winfield Hill wrote: > >>> > >>> There's very little in the signal path. And the 20ns delay to > >>> *the MOSFET output* is about as fast as you'll find. My only > >>> complaint is that the FETs are too big, too much capacitance. > >>> When switching a 50-ohm cable-matching output resistor, a low > >>> 70-milli-ohm Ron is serious overkill. > >> > >> Hey Win, here's a smaller-sized version of the same concept, > >> driver-plus-GaN on a chip: > >> <https://media.digikey.com/pdf/Data%20Sheets/Navitas%20Semi%20PDFs/NV6113%20Datasheet%20(FINAL)%208-28-18.pdf> > > > > Wow, Navitas NV6113, GaN, 200V/ns, only $3.38 at Digi-Key. And > > Octopart doesn't even know about them yet! It looks hard to get > > heat out of the package, they say limited to 2MHz switching rate. > > 50C/W - ugly. That would practically limit you to about 2 amps average, > at 300mOhm. That's just not... special.Au contraire! Two amps is way more than I need, and I much appreciate the reduced capacitances. (Not all of us are trying to drive big metal all the time, or launch EMI out into space. :) There are lots of big wide-gap devices for big-power stuff. But we don't have many choices yet when it comes to making a dinky lil' signal generator. Cheers, James Arthur
Reply by ●January 13, 20192019-01-13
On Mon, 14 Jan 2019 10:13:11 +1100, Clifford Heath <no.spam@please.net> wrote:>On 13/1/19 6:55 am, Winfield Hill wrote: >> dagmargoodboat@yahoo.com wrote... >>> >>> Winfield Hill wrote: >>>> >>>> There's very little in the signal path. And the 20ns delay to >>>> *the MOSFET output* is about as fast as you'll find. My only >>>> complaint is that the FETs are too big, too much capacitance. >>>> When switching a 50-ohm cable-matching output resistor, a low >>>> 70-milli-ohm Ron is serious overkill. >>> >>> Hey Win, here's a smaller-sized version of the same concept, >>> driver-plus-GaN on a chip: >>> <https://media.digikey.com/pdf/Data%20Sheets/Navitas%20Semi%20PDFs/NV6113%20Datasheet%20(FINAL)%208-28-18.pdf> >> >> Wow, Navitas NV6113, GaN, 200V/ns, only $3.38 at Digi-Key. And >> Octopart doesn't even know about them yet! It looks hard to get >> heat out of the package, they say limited to 2MHz switching rate. > >50C/W - ugly. That would practically limit you to about 2 amps average, >at 300mOhm. That's just not... special.It might make sense thermally to parallel a few smaller parts, EPC GaNs or these things. -- John Larkin Highland Technology, Inc lunatic fringe electronics
Reply by ●January 17, 20192019-01-17
Am 12.01.19 um 06:39 schrieb dagmargoodboat@yahoo.com:> One of my problems, currently, is that most of the high-voltage fancy > FETs are monstrous compared to my needs, so even though their figures- > of-merit Ron vs. Qg are worlds better than the older tech stuff, the > fact that they're 20x over-sized for my application makes them slower > than an appropriately-sized MOSFET. > > Even the most nimble GaN garbage truck FET still isn't as gamely as a > silicon itty bitty unicycle FET.A bit smaller than the other transistors that were mentioned, but nevertheless DC to 6 GHz: < https://www.mouser.de/datasheet/2/90/ghv27030s-947886.pdf > A nice driver, at least :-) Cheers, Gerhard
Reply by ●January 30, 20192019-01-30
On Thursday, January 17, 2019 at 4:52:13 PM UTC-5, Gerhard Hoffmann wrote:> Am 12.01.19 um 06:39 schrieb dagmargoodboat@yahoo.com: > > > One of my problems, currently, is that most of the high-voltage fancy > > FETs are monstrous compared to my needs, so even though their figures- > > of-merit Ron vs. Qg are worlds better than the older tech stuff, the > > fact that they're 20x over-sized for my application makes them slower > > than an appropriately-sized MOSFET. > > > > Even the most nimble GaN garbage truck FET still isn't as gamely as a > > silicon itty bitty unicycle FET. > > A bit smaller than the other transistors that were mentioned, > but nevertheless DC to 6 GHz: > > < https://www.mouser.de/datasheet/2/90/ghv27030s-947886.pdf > > > A nice driver, at least :-) > > Cheers, > GerhardWow, that's one beast of a driver ;-) Cheers, James Arthur
