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. 

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

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

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

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.

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.

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

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.&#4294967295; 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

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

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.&#4294967295; 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.