Reply by George Herold December 14, 20182018-12-14
On Friday, December 14, 2018 at 11:43:08 AM UTC-5, Lasse Langwadt Christensen wrote:
> fredag den 14. december 2018 kl. 12.42.03 UTC+1 skrev Arie de Muynck: > > On 2018-12-11 15:25, Winfield Hill wrote: > > > I became discouraged of finding a suitable low-capacitance zener to protect the > > > MOSFET gates in my high-voltage amplifier designs. (The protection may be > > > optional, but one sleeps better with it in place.) Even the 50uA-rated > > > low-current zener diodes are in fact larger-die types, with high capacitance. > > > For example, the 7.5-volt MMSZ4693 has about 130pF at zero volts. > > > > > > My solution was to use a Diodes, Inc. D1213A-01WS TVS device, which has a 6 to > > > 10V breakdown and an amazing low 1pF of capacitance. But this can carry limited > > > current in the forward direction, so I added a BAT54WS Schottky diode in > > > parallel. Both devices are in small SOD-323 packages. Total capacitance, 11pF > > > at their zero volt maximum, which doesn't add too awfully much to the 38pF Ciss > > > of the small high-voltage power MOSFETs I'm using. > > > > > > Or maybe one of you has discovered a better solution? > > > > Using the reverse breakdown of an EB-junction, with CB shorted? Often > > that is about 6..7V, low capacitance and very low leakage. Fluke used > > that as DMM input protection. > > > > related, https://youtu.be/BGcKjy_UNQ4
Thanks, If I'm reading the fluke 87 schematic right (at ~5:30) there is 1k (fusible) + 1.5 k ohms of series resistance. Seems like that would be a lot of current at 1000 V_in... there must be some other voltage clamp? George H.
Reply by Lasse Langwadt Christensen December 14, 20182018-12-14
fredag den 14. december 2018 kl. 12.42.03 UTC+1 skrev Arie de Muynck:
> On 2018-12-11 15:25, Winfield Hill wrote: > > I became discouraged of finding a suitable low-capacitance zener to protect the > > MOSFET gates in my high-voltage amplifier designs. (The protection may be > > optional, but one sleeps better with it in place.) Even the 50uA-rated > > low-current zener diodes are in fact larger-die types, with high capacitance. > > For example, the 7.5-volt MMSZ4693 has about 130pF at zero volts. > > > > My solution was to use a Diodes, Inc. D1213A-01WS TVS device, which has a 6 to > > 10V breakdown and an amazing low 1pF of capacitance. But this can carry limited > > current in the forward direction, so I added a BAT54WS Schottky diode in > > parallel. Both devices are in small SOD-323 packages. Total capacitance, 11pF > > at their zero volt maximum, which doesn't add too awfully much to the 38pF Ciss > > of the small high-voltage power MOSFETs I'm using. > > > > Or maybe one of you has discovered a better solution? > > Using the reverse breakdown of an EB-junction, with CB shorted? Often > that is about 6..7V, low capacitance and very low leakage. Fluke used > that as DMM input protection. >
related, https://youtu.be/BGcKjy_UNQ4
Reply by Winfield Hill December 14, 20182018-12-14
Arie de Muynck wrote...
> >> Or maybe one of you has discovered a better solution? > > Using the reverse breakdown of an EB-junction, with > CB shorted? Often that is about 6..7V, low capacitance > and very low leakage. Fluke used that as DMM input > protection.
Yes, that should work well, and was actually my first plan. I didn't have room for an SOT-23, and tilted towards a zener diode, but an SC70 or SOT-23 vs two diodes may be more attractive.
> >Regards, >Arie de Muijnck
-- Thanks, - Win
Reply by Arie de Muynck December 14, 20182018-12-14
On 2018-12-11 15:25, Winfield Hill wrote:
> I became discouraged of finding a suitable low-capacitance zener to protect the > MOSFET gates in my high-voltage amplifier designs. (The protection may be > optional, but one sleeps better with it in place.) Even the 50uA-rated > low-current zener diodes are in fact larger-die types, with high capacitance. > For example, the 7.5-volt MMSZ4693 has about 130pF at zero volts. > > My solution was to use a Diodes, Inc. D1213A-01WS TVS device, which has a 6 to > 10V breakdown and an amazing low 1pF of capacitance. But this can carry limited > current in the forward direction, so I added a BAT54WS Schottky diode in > parallel. Both devices are in small SOD-323 packages. Total capacitance, 11pF > at their zero volt maximum, which doesn't add too awfully much to the 38pF Ciss > of the small high-voltage power MOSFETs I'm using. > > Or maybe one of you has discovered a better solution?
Using the reverse breakdown of an EB-junction, with CB shorted? Often that is about 6..7V, low capacitance and very low leakage. Fluke used that as DMM input protection. Regards, Arie de Muijnck
Reply by Clifford Heath December 13, 20182018-12-13
On 14/12/18 5:04 am, Phil Hobbs wrote:
> On 12/12/18 10:22 PM, Clifford Heath wrote: >> On 12/12/18 10:02 am, Clifford Heath wrote: >>> On 12/12/18 3:05 am, Winfield Hill wrote: >>>> Phil Hobbs wrote... >>>>> >>>>> On 12/11/18 9:25 AM, Winfield Hill wrote: >>>>>> I became discouraged of finding a suitable low-capacitance zener >>>>>> to protect >>>>>> MOSFET gates in my high-voltage amplifier designs.  (The >>>>>> protection may be >>>>>> optional, but one sleeps better with it in place.)  Even the >>>>>> 50uA-rated >>>>>> low-current zener diodes are in fact larger-die types, with high >>>>>> capacitance. >>>>>> For example, the 7.5-volt MMSZ4693 has about 130pF at zero volts. >>>>>> >>>>>> My solution was to use a Diodes, Inc. D1213A-01WS TVS device, >>>>>> which has a >>>>>> 6 to 10V breakdown and an amazing low 1pF of capacitance.  But it can >>>>>> only carry limited current in the forward direction, so I added a >>>>>> BAT54WS >>>>>> Schottky diode in parallel.  Both devices are in small SOD-323 >>>>>> packages. >>>>>> Total capacitance, 11pF at their zero volt maximum, which doesn't >>>>>> add too >>>>>> awfully much to the 38pF Ciss of my small high-voltage power MOSFETs. >>>>>> >>>>>> Or maybe one of you has discovered a better solution? >>>>> >>>>> The Central Semi CSL05 looks decent at 1.2 pF, but it has a series >>>>> diode >>>>> to prevent forward current.  How about the ESD0P2RF-02LS at 0.25 pF? >>>> >>>>   Missed the CSL05, SL05, a typo?  Anyway, yes, dozens of amazing low- >>>>   capacitance TVS protection devices available, handling high peak >>>>   currents for a few microseconds.  But my designs (similar to AoE III >>>>   Fig 3.111, page 209) must handle 150mA continuous forward current, >>>>   ordinary zeners can do it just fine.  That's what the added Schottky >>>>   diode is for.  It contributes most of the capacitance, but increasing >>>>   the node capacitance from 38pF to 50pF is an acceptable penalty. >>> >>> Can you tune out the Schottky diode's capacitance with a small series L? >>> >>> Is there anything like a string of PIN diodes in a single package? >>> >>> I've just used Skyworks SMP1330 to protect an RF LNA. The combination >>> of low capacitance (0.7pF) and ability to sink power (almost 1 watt) >>> is remarkable. If I understand it, as the device approaches >>> conduction the I layer thins, increasing capacitance rapidly, so it >>> becomes "conductive" even before the diode turns on. >> >> I'm still hoping someone will try to answer these questions.
> PIN diodes generally have gross forward recovery waveforms.
Ahh, interesting, and unsurprising. The I layer has to re-establish, of course. I suppose the same thing happens with rectifier diodes. In the case of diodes turning on to protect a MOSFET gate, perhaps the turn-off delay wouldn't be a problem however. Clifford Heath.
Reply by Clifford Heath December 13, 20182018-12-13
On 14/12/18 7:59 am, tabbypurr@gmail.com wrote:
> On Thursday, 13 December 2018 18:07:38 UTC, Phil Hobbs wrote: >> On 12/13/18 5:21 AM, Clifford Heath wrote: >>> On 13/12/18 7:34 pm, Tim Williams wrote: >>>> "Clifford Heath" <no.spam@please.net> wrote in message >>>> news:1gkQD.5$rw6.0@fx27.iad... > >>>>>> Can you tune out the Schottky diode's capacitance with a small >>>>>> series L? >>>>>> >>>>>> Is there anything like a string of PIN diodes in a single package? >>>>>> >>>>>> I've just used Skyworks SMP1330 to protect an RF LNA. The >>>>>> combination of low capacitance (0.7pF) and ability to sink power >>>>>> (almost 1 watt) is remarkable. If I understand it, as the device >>>>>> approaches conduction the >>>>>> I layer thins, increasing capacitance rapidly, so it becomes >>>>>> "conductive" even before the diode turns on. >>>>> >>>>> I'm still hoping someone will try to answer these questions. >>>>> >>>>> Winfield perhaps? >>>> >>>> You can only tune out by about 50%, corresponding to the famous >>>> doubling of bandwidth for peaked amplifiers.&nbsp; The ideal is closer to >>>> 3x for an infinite order network, but those are hard to build and >>>> tune, ;-) so we settle for 2nd order (CL), sometimes 3rd order (CLC). >>> >>> Hmmm, fair enough. >>> >>>> String of diodes, no idea. >>> >>> A stack of low-C PIN diodes, to be specific, with the sudden C change >>> around threshold. >>> >>>> High voltage rectifiers (over 2kV or so). >>> >>> Those actually are PIN, but just too big (too much C, even in series). >>> >>>> Low voltage zeners work about as well as a stack of diodes, so *shrug*. >>> >>> As a stack of PIN diodes? These don't turn on like ordinary diodes, is >>> my point. I bet there's a package that has four pairs that could be >>> strung together. >>> >>> Clifford Heath. >> >> Series inductive peaking will get you about sqrt(2) bandwidth >> improvement with a flat response. A constant-resistance T coil will get >> you a factor of 2.8, at the price of an extra lead. >> >> Cheers >> >> Phil Hobbs > > L may improve f response, but you now have L in series with your D: how does that bear on its protective functionality?
There's L in the source of the MOSFET too, at much lower R. As long as the gate TC isn't too much faster than the source, it works fine. Win did this a few years back when testing Tom McEwen's patent on it, after a discussion here. Clifford Heath.
Reply by December 13, 20182018-12-13
On Thursday, 13 December 2018 18:07:38 UTC, Phil Hobbs  wrote:
> On 12/13/18 5:21 AM, Clifford Heath wrote: > > On 13/12/18 7:34 pm, Tim Williams wrote: > >> "Clifford Heath" <no.spam@please.net> wrote in message > >> news:1gkQD.5$rw6.0@fx27.iad...
> >>>> Can you tune out the Schottky diode's capacitance with a small > >>>> series L? > >>>> > >>>> Is there anything like a string of PIN diodes in a single package? > >>>> > >>>> I've just used Skyworks SMP1330 to protect an RF LNA. The > >>>> combination of low capacitance (0.7pF) and ability to sink power > >>>> (almost 1 watt) is remarkable. If I understand it, as the device > >>>> approaches conduction the > >>>> I layer thins, increasing capacitance rapidly, so it becomes > >>>> "conductive" even before the diode turns on. > >>> > >>> I'm still hoping someone will try to answer these questions. > >>> > >>> Winfield perhaps? > >> > >> You can only tune out by about 50%, corresponding to the famous > >> doubling of bandwidth for peaked amplifiers.&nbsp; The ideal is closer to > >> 3x for an infinite order network, but those are hard to build and > >> tune, ;-) so we settle for 2nd order (CL), sometimes 3rd order (CLC). > > > > Hmmm, fair enough. > > > >> String of diodes, no idea. > > > > A stack of low-C PIN diodes, to be specific, with the sudden C change > > around threshold. > > > >> High voltage rectifiers (over 2kV or so). > > > > Those actually are PIN, but just too big (too much C, even in series). > > > >> Low voltage zeners work about as well as a stack of diodes, so *shrug*. > > > > As a stack of PIN diodes? These don't turn on like ordinary diodes, is > > my point. I bet there's a package that has four pairs that could be > > strung together. > > > > Clifford Heath. > > Series inductive peaking will get you about sqrt(2) bandwidth > improvement with a flat response. A constant-resistance T coil will get > you a factor of 2.8, at the price of an extra lead. > > Cheers > > Phil Hobbs
L may improve f response, but you now have L in series with your D: how does that bear on its protective functionality? NT
Reply by Phil Hobbs December 13, 20182018-12-13
On 12/13/18 5:21 AM, Clifford Heath wrote:
> On 13/12/18 7:34 pm, Tim Williams wrote: >> "Clifford Heath" <no.spam@please.net> wrote in message >> news:1gkQD.5$rw6.0@fx27.iad... >>>> Can you tune out the Schottky diode's capacitance with a small >>>> series L? >>>> >>>> Is there anything like a string of PIN diodes in a single package? >>>> >>>> I've just used Skyworks SMP1330 to protect an RF LNA. The >>>> combination of low capacitance (0.7pF) and ability to sink power >>>> (almost 1 watt) is remarkable. If I understand it, as the device >>>> approaches conduction the >>>> I layer thins, increasing capacitance rapidly, so it becomes >>>> "conductive" even before the diode turns on. >>> >>> I'm still hoping someone will try to answer these questions. >>> >>> Winfield perhaps? >> >> You can only tune out by about 50%, corresponding to the famous >> doubling of bandwidth for peaked amplifiers.&#2013266080; The ideal is closer to >> 3x for an infinite order network, but those are hard to build and >> tune, ;-) so we settle for 2nd order (CL), sometimes 3rd order (CLC). > > Hmmm, fair enough. > >> String of diodes, no idea. > > A stack of low-C PIN diodes, to be specific, with the sudden C change > around threshold. > >> High voltage rectifiers (over 2kV or so). > > Those actually are PIN, but just too big (too much C, even in series). > >> Low voltage zeners work about as well as a stack of diodes, so *shrug*. > > As a stack of PIN diodes? These don't turn on like ordinary diodes, is > my point. I bet there's a package that has four pairs that could be > strung together. > > Clifford Heath.
Series inductive peaking will get you about sqrt(2) bandwidth improvement with a flat response. A constant-resistance T coil will get you a factor of 2.8, at the price of an extra lead. 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 Phil Hobbs December 13, 20182018-12-13
On 12/12/18 10:22 PM, Clifford Heath wrote:
> On 12/12/18 10:02 am, Clifford Heath wrote: >> On 12/12/18 3:05 am, Winfield Hill wrote: >>> Phil Hobbs wrote... >>>> >>>> On 12/11/18 9:25 AM, Winfield Hill wrote: >>>>> I became discouraged of finding a suitable low-capacitance zener to >>>>> protect >>>>> MOSFET gates in my high-voltage amplifier designs.&nbsp; (The protection >>>>> may be >>>>> optional, but one sleeps better with it in place.)&nbsp; Even the >>>>> 50uA-rated >>>>> low-current zener diodes are in fact larger-die types, with high >>>>> capacitance. >>>>> For example, the 7.5-volt MMSZ4693 has about 130pF at zero volts. >>>>> >>>>> My solution was to use a Diodes, Inc. D1213A-01WS TVS device, which >>>>> has a >>>>> 6 to 10V breakdown and an amazing low 1pF of capacitance.&nbsp; But it can >>>>> only carry limited current in the forward direction, so I added a >>>>> BAT54WS >>>>> Schottky diode in parallel.&nbsp; Both devices are in small SOD-323 >>>>> packages. >>>>> Total capacitance, 11pF at their zero volt maximum, which doesn't >>>>> add too >>>>> awfully much to the 38pF Ciss of my small high-voltage power MOSFETs. >>>>> >>>>> Or maybe one of you has discovered a better solution? >>>> >>>> The Central Semi CSL05 looks decent at 1.2 pF, but it has a series >>>> diode >>>> to prevent forward current.&nbsp; How about the ESD0P2RF-02LS at 0.25 pF? >>> >>> &nbsp; Missed the CSL05, SL05, a typo?&nbsp; Anyway, yes, dozens of amazing low- >>> &nbsp; capacitance TVS protection devices available, handling high peak >>> &nbsp; currents for a few microseconds.&nbsp; But my designs (similar to AoE III >>> &nbsp; Fig 3.111, page 209) must handle 150mA continuous forward current, >>> &nbsp; ordinary zeners can do it just fine.&nbsp; That's what the added Schottky >>> &nbsp; diode is for.&nbsp; It contributes most of the capacitance, but increasing >>> &nbsp; the node capacitance from 38pF to 50pF is an acceptable penalty. >> >> Can you tune out the Schottky diode's capacitance with a small series L? >> >> Is there anything like a string of PIN diodes in a single package? >> >> I've just used Skyworks SMP1330 to protect an RF LNA. The combination >> of low capacitance (0.7pF) and ability to sink power (almost 1 watt) >> is remarkable. If I understand it, as the device approaches conduction >> the I layer thins, increasing capacitance rapidly, so it becomes >> "conductive" even before the diode turns on. > > I'm still hoping someone will try to answer these questions. > > Winfield perhaps? > > Clifford Heath. >
PIN diodes generally have gross forward recovery waveforms. 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 Clifford Heath December 13, 20182018-12-13
On 13/12/18 7:34 pm, Tim Williams wrote:
> "Clifford Heath" <no.spam@please.net> wrote in message > news:1gkQD.5$rw6.0@fx27.iad... >>> Can you tune out the Schottky diode's capacitance with a small series L? >>> >>> Is there anything like a string of PIN diodes in a single package? >>> >>> I've just used Skyworks SMP1330 to protect an RF LNA. The combination >>> of low capacitance (0.7pF) and ability to sink power (almost 1 watt) >>> is remarkable. If I understand it, as the device approaches >>> conduction the >>> I layer thins, increasing capacitance rapidly, so it becomes >>> "conductive" even before the diode turns on. >> >> I'm still hoping someone will try to answer these questions. >> >> Winfield perhaps? > > You can only tune out by about 50%, corresponding to the famous doubling > of bandwidth for peaked amplifiers.&#2013266080; The ideal is closer to 3x for an > infinite order network, but those are hard to build and tune, ;-) so we > settle for 2nd order (CL), sometimes 3rd order (CLC).
Hmmm, fair enough.
> String of diodes, no idea.
A stack of low-C PIN diodes, to be specific, with the sudden C change around threshold.
> High voltage rectifiers (over 2kV or so).
Those actually are PIN, but just too big (too much C, even in series).
> Low voltage zeners work about as well as a stack of diodes, so *shrug*.
As a stack of PIN diodes? These don't turn on like ordinary diodes, is my point. I bet there's a package that has four pairs that could be strung together. Clifford Heath.