Den onsdag den 25. november 2015 kl. 21.09.06 UTC+1 skrev John Larkin:> On Wed, 25 Nov 2015 00:57:46 -0800 (PST), habib.bouaziz@gmail.com > wrote: > > >Le mardi 24 novembre 2015 18:00:43 UTC+1, John Larkin a �crit�: > >> On Tue, 24 Nov 2015 00:54:38 -0800 (PST), habib.bouaziz@gmail.com > >> wrote: > >> > >> >Le lundi 23 novembre 2015 21:09:11 UTC+1, John Larkin a �crit�: > >> >> On Mon, 23 Nov 2015 20:15:49 +0100, Habib Bouaziz-Viallet > >> >> <habib@nowhere.com> wrote: > >> >> > >> >> >On 23/11/2015 18:49, John Larkin wrote: > >> >> >> On Mon, 23 Nov 2015 09:19:02 -0800 (PST), habib.bouaziz@gmail.com > >> >> >> wrote: > >> >> >> > >> >> >>> Le lundi 23 novembre 2015 17:57:39 UTC+1, Winfield Hill a �crit : > >> >> >>>> habib.bouaziz@gmail.com wrote... > >> >> >>>>> > >> >> >>>>> --> Vgs becomes smaller when current is increasing through > >> >> >>>>> 100 Ohm resistor > >> >> >>>>> --> then vgs becomes smaller ... There it may have needs > >> >> >>>>> some math or Spice simulation isn't it ? > >> >> >>>> > >> >> >>>> This is likely intentional, because it effectively creates > >> >> >>>> a current limit, which is desirable. Of course the FETs > >> >> >>>> have to be able to handle this. Ultimately the 1.5kV > >> >> >>>> supply will sag and shut down. The current limit would > >> >> >>>> act until the HV byass capacitors are drained. > >> >> >>>> > >> >> >>>> > >> >> >>>> -- > >> >> >>>> Thanks, > >> >> >>>> - Win > >> >> >>> > >> >> >>> Of course as you say "1.5kV supply will sag and shut down". > >> >> >>> E(capacitors) = 1/2 * C * V *V = 0.5J > >> >> >>> P max admissible for th MOSFET = 80W > >> >> >>> > >> >> >>> Let's say the discharge time is about Td = 10ms > >> >> >>> > >> >> >>> E = P.t then P = 50W --> Ok for the MOSFET > >> >> >>> > >> >> >>> But if Td = 1ms the P = 500W --> The MOSFET should blow > >> >> >>> > >> >> >>> May be i missed something ... > >> >> >>> > >> >> >>> Habib. > >> >> >> > >> >> >> The 100 ohm resistors and the opto CTR limit the mosfet currents. > >> >> >> That's not so much to protect the fets as to limit power supply dip. > >> >> >> > >> >> >> One 2SK4177 can dissipate about a kilowatt for one millisecond, and > >> >> >> around 3KW for 100 us. It could easily discharge all the energy that I > >> >> >> have available. > >> >> >Ok i missed the fig. ASO on page p.4/7 > >> >> >http://www.onsemi.com/pub_link/Collateral/ENA0869-D.PDF > >> >> > > >> >> >Since it is a one shot overload, it's ok. Apologies. > >> >> > > >> >> >Habib > >> >> >> > >> >> >> > >> >> > >> >> Oh, don't apologize, we all keep learning stuff. > >> >> > >> >> I just did this, to better understand the mosfet. > >> >> > >> >> https://dl.dropboxusercontent.com/u/53724080/Parts/Fets/2SK4177_Measurements.JPG > >> >> > >> >> They don't guardband that 1500 volt rating much! > >> >> > >> >> > >> >> > >> >> > >> >> > >> >> > >> >> -- > >> >> > >> >> John Larkin Highland Technology, Inc > >> >> picosecond timing precision measurement > >> >> > >> >> jlarkin att highlandtechnology dott com > >> >> http://www.highlandtechnology.com > >> > > >> >John, > >> > > >> >You measure VGss = +-42V ! OnSemi gives absolute VGss = +-20V > >> > > >> >Strange ! Habib. > >> > >> They built a gate protection zener into the chip, and it zeners at 42 > >> volts. They don't want you to apply a low-impedance voltage source to > >> that zener, or you'll fry it. The 20 volt limit is very conservative. > >> > >> Most mosfets have 20 volt abs max gate voltages, even unprotected > >> ones. > >> > >> I've tested a few non-protected mosfets, and the gates typically blow > >> out around 70 volts. The test destroys the fets. > > > >As you say we all learn something new every day ... > > > >Best regards, Habib. > > It's fun to blow up parts and measure things. >check this guy out: https://www.youtube.com/channel/UCl9OJE9OpXui-gRsnWjSrlA I like his iso9000 "approved" health and safety protocol https://youtu.be/EZBhiJq4TL4 -Lasse
ping Win LND150 avalanche
Started by ●November 21, 2015
Reply by ●November 25, 20152015-11-25
