jlarkin@highlandsniptechnology.com wrote:> On Thu, 30 Dec 2021 10:22:06 -0500, Phil Hobbs > <pcdhSpamMeSenseless@electrooptical.net> wrote: > >> legg wrote: >>> On Thu, 30 Dec 2021 19:04:22 +1100, Sylvia Else <sylvia@email.invalid> >>> wrote: >>> >>>> On 30-Dec-21 4:11 pm, jlarkin@highlandsniptechnology.com wrote: >>>>> Version 4 >>>> >>>> <snip> >>>> >>>> What is the use-case for this that a conventional digital isolator >>>> wouldn't be suitable for? >>>> >>>> Sylvia. >>> >>> Sometimes used in lower frequency isolated gate drive, when minimal >>> magnetics cost is the aim. >>> >>> RL >>> >> >> Or very fast edges are needed, as in the examples JL and I posted in the >> "CML-CML level shifter" thread. Logic isolators don't go much faster >> than 40 ns AFAICT. >> >> Cheers >> >> Phil Hobbs > > Right. And most modulate/demodulate so have a lot of jitter. > > One could make a very fast low-jitter optical isolator, but it would > be a big expensive power hog.And would have crappy latency compared with a coaxial transformer. Cheers Phil Hobbs -- Dr Philip C D Hobbs Principal Consultant ElectroOptical Innovations LLC / Hobbs ElectroOptics Optics, Electro-optics, Photonics, Analog Electronics Briarcliff Manor NY 10510 http://electrooptical.net http://hobbs-eo.com
transformer coupled logic isolator
Started by ●December 30, 2021
Reply by ●December 30, 20212021-12-30
Reply by ●December 30, 20212021-12-30
jlarkin@highlandsniptechnology.com wrote:> On Thu, 30 Dec 2021 10:22:06 -0500, Phil Hobbs > <pcdhSpamMeSenseless@electrooptical.net> wrote: > >> legg wrote: >>> On Thu, 30 Dec 2021 19:04:22 +1100, Sylvia Else <sylvia@email.invalid> >>> wrote: >>> >>>> On 30-Dec-21 4:11 pm, jlarkin@highlandsniptechnology.com wrote: >>>>> Version 4 >>>> >>>> <snip> >>>> >>>> What is the use-case for this that a conventional digital isolator >>>> wouldn't be suitable for? >>>> >>>> Sylvia. >>> >>> Sometimes used in lower frequency isolated gate drive, when minimal >>> magnetics cost is the aim. >>> >>> RL >>> >> >> Or very fast edges are needed, as in the examples JL and I posted in the >> "CML-CML level shifter" thread. Logic isolators don't go much faster >> than 40 ns AFAICT.> > That circuit was just a doodle. It would need tweaking in real life. > It's most elegant when the transformer time constant matches the > Schmitt feedback time constant, and when the final RC also damps any > leakage inductance ringing. That actually gets complex. > > It really doesn't need a Schmitt gate, but it's nice.That's one place where the common-gate GaN FET trick is good--it pretty well ignores reasonable amounts of ringing. I need to try it out to see if the body diode of the EPC parts is quick enough. <https://www.ti.com/lit/an/snoaa36/snoaa36.pdf> has an interesting discussion of how third-quadrant conduction works in GaN FETs, but doesn't give any numbers. It does make the point that the reverse conduction mechanism isn't a diode as in vertical MOSFETs, but is just the channel turning on in the reverse direction (drain and source exchanged). That's all majority-carrier conduction, so there's no reverse recovery issue, and since the channel turns on due to the gate voltage and not diffusion, there should be no forward recovery delay either. Cheers Phil Hobbs -- Dr Philip C D Hobbs Principal Consultant ElectroOptical Innovations LLC / Hobbs ElectroOptics Optics, Electro-optics, Photonics, Analog Electronics Briarcliff Manor NY 10510 http://electrooptical.net http://hobbs-eo.com
Reply by ●December 30, 20212021-12-30
On Thu, 30 Dec 2021 10:22:06 -0500, Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> wrote:>legg wrote: >> On Thu, 30 Dec 2021 19:04:22 +1100, Sylvia Else <sylvia@email.invalid> >> wrote: >> >>> On 30-Dec-21 4:11 pm, jlarkin@highlandsniptechnology.com wrote: >>>> Version 4 >>> >>> <snip> >>> >>> What is the use-case for this that a conventional digital isolator >>> wouldn't be suitable for? >>> >>> Sylvia. >> >> Sometimes used in lower frequency isolated gate drive, when minimal >> magnetics cost is the aim. >> >> RL >> > >Or very fast edges are needed, as in the examples JL and I posted in the >"CML-CML level shifter" thread. Logic isolators don't go much faster >than 40 ns AFAICT. > >Cheers > >Phil HobbsThe drive function allowed low frequency modulation using cheap small pulse transformer with minimal VT. Many issues with this technique, but it had it's day. RL
Reply by ●December 30, 20212021-12-30
On Thu, 30 Dec 2021 10:20:57 -0800, John Larkin <jlarkin@highland_atwork_technology.com> wrote:>On Thu, 30 Dec 2021 09:08:03 -0500, legg <legg@nospam.magma.ca> wrote: > >>On Thu, 30 Dec 2021 19:04:22 +1100, Sylvia Else <sylvia@email.invalid> >>wrote: >> >>>On 30-Dec-21 4:11 pm, jlarkin@highlandsniptechnology.com wrote: >>>> Version 4 >>> >>><snip> >>> >>>What is the use-case for this that a conventional digital isolator >>>wouldn't be suitable for? >>> >>>Sylvia. >> >>Sometimes used in lower frequency isolated gate drive, when minimal >>magnetics cost is the aim. >> >>RL > >It's faster than most isolators, and is DC-coupled, after a powerup >priming shot.you hope. . . . In circuits that can go boom, the issues aren't just speed and data integrity. In a two-transistor forward converter, there's a second series switch that can police the circuit, without magnetics and restoration issues. Bridge circuits not so lucky. RL
Reply by ●December 30, 20212021-12-30
legg wrote:> On Thu, 30 Dec 2021 10:22:06 -0500, Phil Hobbs > <pcdhSpamMeSenseless@electrooptical.net> wrote: > >> legg wrote: >>> On Thu, 30 Dec 2021 19:04:22 +1100, Sylvia Else <sylvia@email.invalid> >>> wrote: >>> >>>> On 30-Dec-21 4:11 pm, jlarkin@highlandsniptechnology.com wrote: >>>>> Version 4 >>>> >>>> <snip> >>>> >>>> What is the use-case for this that a conventional digital isolator >>>> wouldn't be suitable for? >>>> >>>> Sylvia. >>> >>> Sometimes used in lower frequency isolated gate drive, when minimal >>> magnetics cost is the aim. >>> >>> RL >>> >> >> Or very fast edges are needed, as in the examples JL and I posted in the >> "CML-CML level shifter" thread. Logic isolators don't go much faster >> than 40 ns AFAICT. >> >> Cheers >> >> Phil Hobbs > > The drive function allowed low frequency modulation > using cheap small pulse transformer with minimal VT. > > Many issues with this technique, but it had it's day. > > RL >Did you check out the LTspice file I posted with the common-gate GaN FET? With a better transformer that looks like a pretty sweet solution. Cheers Phil Hobbs -- Dr Philip C D Hobbs Principal Consultant ElectroOptical Innovations LLC / Hobbs ElectroOptics Optics, Electro-optics, Photonics, Analog Electronics Briarcliff Manor NY 10510 http://electrooptical.net http://hobbs-eo.com
Reply by ●December 30, 20212021-12-30
On Thu, 30 Dec 2021 13:40:47 -0500, Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> wrote:>jlarkin@highlandsniptechnology.com wrote: >> On Thu, 30 Dec 2021 10:22:06 -0500, Phil Hobbs >> <pcdhSpamMeSenseless@electrooptical.net> wrote: >> >>> legg wrote: >>>> On Thu, 30 Dec 2021 19:04:22 +1100, Sylvia Else <sylvia@email.invalid> >>>> wrote: >>>> >>>>> On 30-Dec-21 4:11 pm, jlarkin@highlandsniptechnology.com wrote: >>>>>> Version 4 >>>>> >>>>> <snip> >>>>> >>>>> What is the use-case for this that a conventional digital isolator >>>>> wouldn't be suitable for? >>>>> >>>>> Sylvia. >>>> >>>> Sometimes used in lower frequency isolated gate drive, when minimal >>>> magnetics cost is the aim. >>>> >>>> RL >>>> >>> >>> Or very fast edges are needed, as in the examples JL and I posted in the >>> "CML-CML level shifter" thread. Logic isolators don't go much faster >>> than 40 ns AFAICT. >>> >>> Cheers >>> >>> Phil Hobbs >> >> Right. And most modulate/demodulate so have a lot of jitter. >> >> One could make a very fast low-jitter optical isolator, but it would >> be a big expensive power hog. > >And would have crappy latency compared with a coaxial transformer.2 ns maybe could be done with a laser diode and a fast photodiode.> >Cheers > >Phil HobbsI was idly musing about making a dc-coupled optical link from SFP modules. The trick would be to get the jitter below the data clock period limit. FM or PWM or something. -- I yam what I yam - Popeye
Reply by ●December 30, 20212021-12-30
On Thu, 30 Dec 2021 13:54:42 -0500, Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> wrote:>jlarkin@highlandsniptechnology.com wrote: >> On Thu, 30 Dec 2021 10:22:06 -0500, Phil Hobbs >> <pcdhSpamMeSenseless@electrooptical.net> wrote: >> >>> legg wrote: >>>> On Thu, 30 Dec 2021 19:04:22 +1100, Sylvia Else <sylvia@email.invalid> >>>> wrote: >>>> >>>>> On 30-Dec-21 4:11 pm, jlarkin@highlandsniptechnology.com wrote: >>>>>> Version 4 >>>>> >>>>> <snip> >>>>> >>>>> What is the use-case for this that a conventional digital isolator >>>>> wouldn't be suitable for? >>>>> >>>>> Sylvia. >>>> >>>> Sometimes used in lower frequency isolated gate drive, when minimal >>>> magnetics cost is the aim. >>>> >>>> RL >>>> >>> >>> Or very fast edges are needed, as in the examples JL and I posted in the >>> "CML-CML level shifter" thread. Logic isolators don't go much faster >>> than 40 ns AFAICT. > >> >> That circuit was just a doodle. It would need tweaking in real life. >> It's most elegant when the transformer time constant matches the >> Schmitt feedback time constant, and when the final RC also damps any >> leakage inductance ringing. That actually gets complex. >> >> It really doesn't need a Schmitt gate, but it's nice. > >That's one place where the common-gate GaN FET trick is good--it pretty >well ignores reasonable amounts of ringing. I need to try it out to see >if the body diode of the EPC parts is quick enough. > ><https://www.ti.com/lit/an/snoaa36/snoaa36.pdf> has an interesting >discussion of how third-quadrant conduction works in GaN FETs, but >doesn't give any numbers. > >It does make the point that the reverse conduction mechanism isn't a >diode as in vertical MOSFETs, but is just the channel turning on in the >reverse direction (drain and source exchanged). > >That's all majority-carrier conduction, so there's no reverse recovery >issue, and since the channel turns on due to the gate voltage and not >diffusion, there should be no forward recovery delay either. > >Cheers > >Phil HobbsOur lamented ATF-50189 made a fabulous diode in a couple of modes. D+G against source, S+G against drain. 400 mV drop, 1 amp, 1 pF. https://www.dropbox.com/s/4ql98sfpm6oarnd/Ephemt_Diode.JPG?raw=1 The SAV parts could be useful as diodes. Sims look promising, but I haven't tried it for real. (fix the wrap!) Version 4 SHEET 1 1220 680 WIRE 224 -96 -96 -96 WIRE 528 -96 224 -96 WIRE -96 -64 -96 -96 WIRE 224 -48 224 -96 WIRE 528 -48 528 -96 WIRE -96 64 -96 16 WIRE 224 80 224 32 WIRE 272 80 224 80 WIRE 304 80 272 80 WIRE 528 80 528 32 WIRE 576 80 528 80 WIRE 608 80 576 80 WIRE 224 128 224 80 WIRE 528 128 528 80 WIRE 176 208 144 208 WIRE 480 208 432 208 WIRE 144 256 144 208 WIRE 224 256 224 224 WIRE 224 256 144 256 WIRE 432 256 432 208 WIRE 528 256 528 224 WIRE 528 256 432 256 WIRE 224 272 224 256 WIRE 528 272 528 256 FLAG 224 272 0 FLAG -96 64 0 FLAG 528 272 0 FLAG 272 80 D1 FLAG 576 80 D2 SYMBOL mesfet 176 128 R0 WINDOW 0 90 32 Left 2 WINDOW 3 67 62 Left 2 SYMATTR InstName Z1 SYMATTR Value SAV551 SYMBOL voltage -96 -80 R0 WINDOW 0 68 58 Left 2 WINDOW 3 59 97 Left 2 WINDOW 123 0 0 Left 0 WINDOW 39 0 0 Left 0 SYMATTR InstName Vd SYMATTR Value SINE(0 20 1 0 0 8) SYMBOL res 208 -64 R0 WINDOW 0 54 46 Left 2 WINDOW 3 53 77 Left 2 SYMATTR InstName R1 SYMATTR Value 5K SYMBOL res 512 -64 R0 WINDOW 0 55 44 Left 2 WINDOW 3 56 73 Left 2 SYMATTR InstName R2 SYMATTR Value 5K SYMBOL mesfet 480 128 R0 WINDOW 0 86 36 Left 2 WINDOW 3 62 64 Left 2 SYMATTR InstName Z2 SYMATTR Value SAV541 TEXT -168 328 Left 2 !.MODEL SAV551 NMF(vto=0.08, Beta=0.3,\n+ Lambda=0.07, Alpha=4 B=0.8, Pb=0.7,\n+ Cgs=0.997E-12, Cgd=0.176E-12, Rd=0.084,\n+ Rs=0.054, Kf=5e-11, Af=2) TEXT -48 272 Left 2 !.tran 5 TEXT 344 328 Left 2 !.MODEL SAV541 NMF(vto=0.08, Beta=0.6,\n+ Lambda=0.07, Alpha=4 B=0.8, Pb=0.7,\n+ Cgs=0.997E-12, Cgd=0.176E-12, Rd=0.084,\n+ Rs=0.054, Kf=5e-11, Af=2) TEXT -120 144 Left 2 ;SAV-541 and SAV-551 TEXT -64 176 Left 2 ;As Diodes TEXT -104 224 Left 2 ;JL May 10 2021 -- I yam what I yam - Popeye
Reply by ●December 30, 20212021-12-30
On Friday, December 31, 2021 at 4:20:09 AM UTC+11, jla...@highlandsniptechnology.com wrote:> On Thu, 30 Dec 2021 10:22:06 -0500, Phil Hobbs > <pcdhSpamM...@electrooptical.net> wrote: > >legg wrote: > >> On Thu, 30 Dec 2021 19:04:22 +1100, Sylvia Else <syl...@email.invalid> > >> wrote: > >> > >>> On 30-Dec-21 4:11 pm, jla...@highlandsniptechnology.com wrote: > >>>> Version 4 > >>> > >>> <snip> > >>> > >>> What is the use-case for this that a conventional digital isolator > >>> wouldn't be suitable for? > >> > >> Sometimes used in lower frequency isolated gate drive, when minimal > >> magnetics cost is the aim. > > > >Or very fast edges are needed, as in the examples JL and I posted in the > >"CML-CML level shifter" thread. Logic isolators don't go much faster > >than 40 ns AFAICT. > > That circuit was just a doodle. It would need tweaking in real life.The transformer was very much a doodle. Every winding always has parallel capacitance, and even that didn't get into the LT Spice .asc file. Since the test signal is just 50kHz. and the receiver is a generic LT Spice Schmitt trigger, it's not even much of a doodle.> It's most elegant when the transformer time constant matches the Schmitt feedback time constant, and when the final RC also damps any leakage inductance ringing. That actually gets complex.Elegance doesn't come into it> It really doesn't need a Schmitt gate, but it's nice.It probably does. The number of volt.seconds you can get through a transformer is limited by saturation. If you haven't put any thought into the transformer at all, you may not realise this. -- Bill Sloman, Sydney
Reply by ●December 30, 20212021-12-30
On Friday, December 31, 2021 at 5:21:07 AM UTC+11, John Larkin wrote:> On Thu, 30 Dec 2021 09:08:03 -0500, legg <le...@nospam.magma.ca> wrote: > > >On Thu, 30 Dec 2021 19:04:22 +1100, Sylvia Else <syl...@email.invalid> > >wrote: > > > >>On 30-Dec-21 4:11 pm, jla...@highlandsniptechnology.com wrote: > >>> Version 4 > >> > >><snip> > >> > >>What is the use-case for this that a conventional digital isolator > >>wouldn't be suitable for? > > > >Sometimes used in lower frequency isolated gate drive, when minimal > >magnetics cost is the aim. > > It's faster than most isolators, and is DC-coupled, after a power-up > priming shot.Not a claim that's worth making for a purely theoretical transformer driving an LT Spice generic Schmitt trigger. No parallel capacitance across either inductor, and no current induced in the transformer core - it's a little too theoretical too swank about. It worked fine when I did it in 1979, but I wasn't around to see it go into production (if it did). -- Bill Sloman, Sydney
Reply by ●December 30, 20212021-12-30
On Friday, December 31, 2021 at 1:54:28 PM UTC+11, jla...@highlandsniptechnology.com wrote:> On Thu, 30 Dec 2021 13:54:42 -0500, Phil Hobbs <pcdhSpamM...@electrooptical.net> wrote: jla...@highlandsniptechnology.com wrote: > >> On Thu, 30 Dec 2021 10:22:06 -0500, Phil Hobbs <pcdhSpamM...@electrooptical.net> wrote: > >>> legg wrote: > >>>> On Thu, 30 Dec 2021 19:04:22 +1100, Sylvia Else <syl...@email.invalid> wrote: > >>>>> On 30-Dec-21 4:11 pm, jla...@highlandsniptechnology.com wrote: > >>>>>> Version 4 > >>>>> > >>>>> <snip> > >>>>> > >>>>> What is the use-case for this that a conventional digital isolator wouldn't be suitable for? > >>>> > >>>> Sometimes used in lower frequency isolated gate drive, when minimal magnetics cost is the aim. > >>> > >>> Or very fast edges are needed, as in the examples JL and I posted in the "CML-CML level shifter" thread. Logic isolators don't go much faster than 40 ns AFAICT. > >> > >> That circuit was just a doodle. It would need tweaking in real life. It's most elegant when the transformer time constant matches the Schmitt feedback time constant, and when the final RC also damps any leakage inductance ringing. That actually gets complex. > >> > >> It really doesn't need a Schmitt gate, but it's nice. > > > >That's one place where the common-gate GaN FET trick is good--it pretty > >well ignores reasonable amounts of ringing. I need to try it out to see > >if the body diode of the EPC parts is quick enough. > > > ><https://www.ti.com/lit/an/snoaa36/snoaa36.pdf> has an interesting > >discussion of how third-quadrant conduction works in GaN FETs, but > >doesn't give any numbers. > > > >It does make the point that the reverse conduction mechanism isn't a > >diode as in vertical MOSFETs, but is just the channel turning on in the > >reverse direction (drain and source exchanged). > > > >That's all majority-carrier conduction, so there's no reverse recovery > >issue, and since the channel turns on due to the gate voltage and not > >diffusion, there should be no forward recovery delay either. > >> Our lamented ATF-50189 made a fabulous diode in a couple of modes. D+G > against source, S+G against drain. 400 mV drop, 1 amp, 1 pF. > > https://www.dropbox.com/s/4ql98sfpm6oarnd/Ephemt_Diode.JPG?raw=1 > > The SAV parts could be useful as diodes. Sims look promising, but I > haven't tried it for real. > > (fix the wrap!)Snipped the .asc file. I could fix the wrap, but whatever symbol John inserted for his SAV parts didn't make it. The models were there - as strings of text - but not as any kind of manipulable component, even after I'd let LT Spice update itself. I suppose I could try to generate symbols to latch on to the SAV541 and SAV541 data, but it doesn't strike me as a sensible use for my time. -- Bill Sloman, Sydney
