Hi All, well one last swing at my HV reset spad circuit. (circuit scribble or spice file on request.) I need a low input C, P-fet with decent Vds (~40V or greater.)* (It needs to turn off fast (<50ns), some pfets look to have built in gate resistors for safety and these are slower.) Anyway at the moment I've got the BSS84 from infineon https://www.infineon.com/dgdl/Infineon-BSS84PW-DS-v01_05-en.pdf?fileId=db3a3043321e49940132482056d32474 And the Si1021 from Vishay http://www.vishay.com/docs/71410/71410.pdf Do you have another suggestion that I should put on my shopping list? Say, everyone seems to make a BSS84 with slightly different specs... what's up with that? Oh at the moment this is running with a VP0106. (60 pF Cin) This is with dummy load, (3.3 pF cap) Chan. 1 is gate voltage, Chan. 2 is HV on top of cap, about 20V reset (not to scale) https://www.dropbox.com/s/cmfsjbgiyo3b255/pfet-rst.BMP?dl=0 George H. *If there was a much better N-FET, I could flip the whole thing over and run it from a negative HV supply.
Shopping for low C PFET
Started by ●August 17, 2018
Reply by ●August 17, 20182018-08-17
On Friday, August 17, 2018 at 12:10:04 PM UTC-4, George Herold wrote:> Hi All, well one last swing at my HV reset spad circuit. (circuit > scribble or spice file on request.) I need a low input C, P-fet with > decent Vds (~40V or greater.)* (It needs to turn off fast (<50ns), > some pfets look to have built in gate resistors for safety and these > are slower.) > > Anyway at the moment I've got the BSS84 from infineon > https://www.infineon.com/dgdl/Infineon-BSS84PW-DS-v01_05-en.pdf?fileId=db3a3043321e49940132482056d32474 > > And the Si1021 from Vishay > http://www.vishay.com/docs/71410/71410.pdf > > Do you have another suggestion that I should put on my shopping list? > > Say, everyone seems to make a BSS84 with slightly different specs... > what's up with that? > > Oh at the moment this is running with a VP0106. (60 pF Cin) > This is with dummy load, (3.3 pF cap) > Chan. 1 is gate voltage, > Chan. 2 is HV on top of cap, about 20V reset (not to scale) > > https://www.dropbox.com/s/cmfsjbgiyo3b255/pfet-rst.BMP?dl=0Oh my 'scope trace has these ~150 ns wiggles, not sure the cause. Maybe the (~4") ground lead on the x10 probes? GH> > George H. > > > *If there was a much better N-FET, I could flip the whole thing over and run > it from a negative HV supply.
Reply by ●August 17, 20182018-08-17
RF MOSFETs are pretty much goneski, let alone PCHs. These are the smallest PCH for power switching I know of. If you can't make it work, say with a little emitter follower to help gate capacitance, it ain't gonna happen with anything else. :-\ Tim -- Seven Transistor Labs, LLC Electrical Engineering Consultation and Design Website: https://www.seventransistorlabs.com/ "George Herold" <gherold@teachspin.com> wrote in message news:21223089-398f-486f-9028-85edf206922c@googlegroups.com...> Hi All, well one last swing at my HV reset spad circuit. (circuit > scribble or spice file on request.) I need a low input C, P-fet with > decent Vds (~40V or greater.)* (It needs to turn off fast (<50ns), > some pfets look to have built in gate resistors for safety and these > are slower.) > > Anyway at the moment I've got the BSS84 from infineon > https://www.infineon.com/dgdl/Infineon-BSS84PW-DS-v01_05-en.pdf?fileId=db3a3043321e49940132482056d32474 > > And the Si1021 from Vishay > http://www.vishay.com/docs/71410/71410.pdf > > Do you have another suggestion that I should put on my shopping list? > > Say, everyone seems to make a BSS84 with slightly different specs... > what's up with that? > > Oh at the moment this is running with a VP0106. (60 pF Cin) > This is with dummy load, (3.3 pF cap) > Chan. 1 is gate voltage, > Chan. 2 is HV on top of cap, about 20V reset (not to scale) > > https://www.dropbox.com/s/cmfsjbgiyo3b255/pfet-rst.BMP?dl=0 > > George H. > > > *If there was a much better N-FET, I could flip the whole thing over and > run > it from a negative HV supply.
Reply by ●August 17, 20182018-08-17
On Friday, August 17, 2018 at 1:45:38 PM UTC-4, Tim Williams wrote:> RF MOSFETs are pretty much goneski, let alone PCHs. These are the smallest > PCH for power switching I know of.Thanks Tim. I did search under the RF mosfet tag at DK. There was one. PN5033 https://media.digikey.com/pdf/Data%20Sheets/Central%20Semiconductor/PN5033.pdf listed as a p-chan J-fet! I thought they didn't make those. (?) George H.> > If you can't make it work, say with a little emitter follower to help gate > capacitance, it ain't gonna happen with anything else. :-\ > > Tim > > -- > Seven Transistor Labs, LLC > Electrical Engineering Consultation and Design > Website: https://www.seventransistorlabs.com/ > > "George Herold" <gherold@teachspin.com> wrote in message > news:21223089-398f-486f-9028-85edf206922c@googlegroups.com... > > Hi All, well one last swing at my HV reset spad circuit. (circuit > > scribble or spice file on request.) I need a low input C, P-fet with > > decent Vds (~40V or greater.)* (It needs to turn off fast (<50ns), > > some pfets look to have built in gate resistors for safety and these > > are slower.) > > > > Anyway at the moment I've got the BSS84 from infineon > > https://www.infineon.com/dgdl/Infineon-BSS84PW-DS-v01_05-en.pdf?fileId=db3a3043321e49940132482056d32474 > > > > And the Si1021 from Vishay > > http://www.vishay.com/docs/71410/71410.pdf > > > > Do you have another suggestion that I should put on my shopping list? > > > > Say, everyone seems to make a BSS84 with slightly different specs... > > what's up with that? > > > > Oh at the moment this is running with a VP0106. (60 pF Cin) > > This is with dummy load, (3.3 pF cap) > > Chan. 1 is gate voltage, > > Chan. 2 is HV on top of cap, about 20V reset (not to scale) > > > > https://www.dropbox.com/s/cmfsjbgiyo3b255/pfet-rst.BMP?dl=0 > > > > George H. > > > > > > *If there was a much better N-FET, I could flip the whole thing over and > > run > > it from a negative HV supply.
Reply by ●August 17, 20182018-08-17
"George Herold" <gherold@teachspin.com> wrote in message news:e890f96e-b16b-4020-a851-8733a9fd5f8d@googlegroups.com...> listed as a p-chan J-fet! I thought they didn't make those. (?) >P-JFETs, there's still a very few of those around, yeah. No idea what people use them for... Tim -- Seven Transistor Labs, LLC Electrical Engineering Consultation and Design Website: https://www.seventransistorlabs.com/
Reply by ●August 17, 20182018-08-17
Tim Williams wrote>RF MOSFETs are pretty much goneski, let alone PCHs. These are the smallest >PCH for power switching I know of.I used a lot of BF245 A / B / C. It now is still available in a smaller package as BF545 A only 700 MHz 6.5 mA/V Only 30V. can be reverse used (drain source). The BF245 has a noise of 1.5 dB at 15V 100 MHz, I see no noise figure for BF545. https://www.digikey.com/number/en/nxp-usa-inc/568/BF545/35911
Reply by ●August 18, 20182018-08-18
On 08/17/2018 12:09 PM, George Herold wrote:> Hi All, well one last swing at my HV reset spad circuit. (circuit > scribble or spice file on request.) I need a low input C, P-fet with > decent Vds (~40V or greater.)* (It needs to turn off fast (<50ns), > some pfets look to have built in gate resistors for safety and these > are slower.) > > Anyway at the moment I've got the BSS84 from infineon > https://www.infineon.com/dgdl/Infineon-BSS84PW-DS-v01_05-en.pdf?fileId=db3a3043321e49940132482056d32474 > > And the Si1021 from Vishay > http://www.vishay.com/docs/71410/71410.pdf > > Do you have another suggestion that I should put on my shopping list? > > Say, everyone seems to make a BSS84 with slightly different specs... > what's up with that? > > Oh at the moment this is running with a VP0106. (60 pF Cin) > This is with dummy load, (3.3 pF cap) > Chan. 1 is gate voltage, > Chan. 2 is HV on top of cap, about 20V reset (not to scale) > > https://www.dropbox.com/s/cmfsjbgiyo3b255/pfet-rst.BMP?dl=0 > > George H. > > > *If there was a much better N-FET, I could flip the whole thing over and run > it from a negative HV supply. >https://www.digikey.com/product-detail/en/epc/EPC2038/917-1138-1-ND/5774048 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 https://hobbs-eo.com
Reply by ●August 18, 20182018-08-18
On 17/08/2018 17:09, George Herold wrote:> Hi All, well one last swing at my HV reset spad circuit. (circuit > scribble or spice file on request.) I need a low input C, P-fet with > decent Vds (~40V or greater.)* (It needs to turn off fast (<50ns), > some pfets look to have built in gate resistors for safety and these > are slower.) > > Anyway at the moment I've got the BSS84 from infineon > https://www.infineon.com/dgdl/Infineon-BSS84PW-DS-v01_05-en.pdf?fileId=db3a3043321e49940132482056d32474 > > And the Si1021 from Vishay > http://www.vishay.com/docs/71410/71410.pdf > > Do you have another suggestion that I should put on my shopping list? > > Say, everyone seems to make a BSS84 with slightly different specs... > what's up with that? > > Oh at the moment this is running with a VP0106. (60 pF Cin) > This is with dummy load, (3.3 pF cap) > Chan. 1 is gate voltage, > Chan. 2 is HV on top of cap, about 20V reset (not to scale) > > https://www.dropbox.com/s/cmfsjbgiyo3b255/pfet-rst.BMP?dl=0 > > George H. > > > *If there was a much better N-FET, I could flip the whole thing over and run > it from a negative HV supply. >If I read the scope right looks like the gate drive slews to -4V in 20ns, which if your 60pF Cin is used then grossly simplified I make the gate drive current a mere 12mA. Also looks like the drain doesnt do much till gate hits 3.5V so if you can increase the gate drive voltage, sharpen it and make it stiffer then you'd get closer to your target? piglet
Reply by ●August 18, 20182018-08-18
On Saturday, August 18, 2018 at 2:40:03 PM UTC-4, piglet wrote:> On 17/08/2018 17:09, George Herold wrote: > > Hi All, well one last swing at my HV reset spad circuit. (circuit > > scribble or spice file on request.) I need a low input C, P-fet with > > decent Vds (~40V or greater.)* (It needs to turn off fast (<50ns), > > some pfets look to have built in gate resistors for safety and these > > are slower.) > > > > Anyway at the moment I've got the BSS84 from infineon > > https://www.infineon.com/dgdl/Infineon-BSS84PW-DS-v01_05-en.pdf?fileId=db3a3043321e49940132482056d32474 > > > > And the Si1021 from Vishay > > http://www.vishay.com/docs/71410/71410.pdf > > > > Do you have another suggestion that I should put on my shopping list? > > > > Say, everyone seems to make a BSS84 with slightly different specs... > > what's up with that? > > > > Oh at the moment this is running with a VP0106. (60 pF Cin) > > This is with dummy load, (3.3 pF cap) > > Chan. 1 is gate voltage, > > Chan. 2 is HV on top of cap, about 20V reset (not to scale) > > > > https://www.dropbox.com/s/cmfsjbgiyo3b255/pfet-rst.BMP?dl=0 > > > > George H. > > > > > > *If there was a much better N-FET, I could flip the whole thing over and run > > it from a negative HV supply. > > > > If I read the scope right looks like the gate drive slews to -4V in > 20ns, which if your 60pF Cin is used then grossly simplified I make the > gate drive current a mere 12mA.I think less (Dang I should have put my spice sim in drop box.) I'm a brute force type. (subtle takes experience) The p-fet's source is.. (there are some 1nF and 10nF not shown) HV---+---1mA limit---+--------+ | | | 0.1mA lim. | R4 500 | | S | +-----------------+| +---+ | | | | | R1 400k 1M? R2 | | | | | +| | +--+--|<--|<--|<---+ + D | | | | | R5 C 3.3pF 2M? R3 \ | 4M | | \| +--+-Gnd Gnd |--4V /| sig gen.-74hc14 x6 ---R6 100--< | The diodes are 1n5711 Schottky. (I don't need three anymore.) The C is my spad and R5 leaks off some voltage. I get about 25 mA through R6, which give me ~10 Vgs if I pulse it for a long time. (1-200ns) My big time suck is R4 and Cin.. Say if I stuck the right amount of L in series with R4, would that get the gate on sooner and off faster? George H.> > Also looks like the drain doesnt do much till gate hits 3.5V so if you > can increase the gate drive voltage, sharpen it and make it stiffer then > you'd get closer to your target? > > piglet
Reply by ●August 18, 20182018-08-18
On Saturday, August 18, 2018 at 1:00:48 PM UTC-4, Phil Hobbs wrote:> On 08/17/2018 12:09 PM, George Herold wrote: > > Hi All, well one last swing at my HV reset spad circuit. (circuit > > scribble or spice file on request.) I need a low input C, P-fet with > > decent Vds (~40V or greater.)* (It needs to turn off fast (<50ns), > > some pfets look to have built in gate resistors for safety and these > > are slower.) > > > > Anyway at the moment I've got the BSS84 from infineon > > https://www.infineon.com/dgdl/Infineon-BSS84PW-DS-v01_05-en.pdf?fileId=db3a3043321e49940132482056d32474 > > > > And the Si1021 from Vishay > > http://www.vishay.com/docs/71410/71410.pdf > > > > Do you have another suggestion that I should put on my shopping list? > > > > Say, everyone seems to make a BSS84 with slightly different specs... > > what's up with that? > > > > Oh at the moment this is running with a VP0106. (60 pF Cin) > > This is with dummy load, (3.3 pF cap) > > Chan. 1 is gate voltage, > > Chan. 2 is HV on top of cap, about 20V reset (not to scale) > > > > https://www.dropbox.com/s/cmfsjbgiyo3b255/pfet-rst.BMP?dl=0 > > > > George H. > > > > > > *If there was a much better N-FET, I could flip the whole thing over and run > > it from a negative HV supply. > > > > https://www.digikey.com/product-detail/en/epc/EPC2038/917-1138-1-ND/5774048 >Oh boy those look like fun... 450 bump spacing.. I assume that's um. Is it possible to dead bug hand solder such a tid bit? George H.> 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 > https://hobbs-eo.com
