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. > > 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
fast, small low-capacitance zener to protect MOSFET gates
Started by ●December 11, 2018
Reply by ●December 13, 20182018-12-13
Reply by ●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.� 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 ●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. 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 HobbsL 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 ●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. 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 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 ●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 ●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 ●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 ●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_UNQ4Thanks, 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.
