Le lundi 23 novembre 2015 15:21:13 UTC+1, Winfield Hill a �crit�:> habib.bouaziz@gmail.com wrote... > > > > Don't understand how it works ... > > The TLP191B acts like a battery. It has > a stack of diodes and runs continuously, > providing about 7V (at 10uA) of gate bias. > https://octopart.com/search?q=TLP191 > http://datasheet.octopart.com/TLP191B%28U%2CC%2CF%29-Toshiba-datasheet-13727684.pdf > > The optocouplers drive the FET source, in > common-gate fashion. > > > -- > Thanks, > - WinI know how the TLP191 works, thanks. My questions was in relation with the current through the MOSFET and power dissipations (hey 1400 V !) ; TLP191 gives 7V --> the MOSFET flows current --> 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 ? Habib.
ping Win LND150 avalanche
Started by ●November 21, 2015
Reply by ●November 23, 20152015-11-23
Reply by ●November 23, 20152015-11-23
On Mon, 23 Nov 2015 07:39:43 +0000, John Devereux <john@devereux.me.uk> wrote:>Winfield Hill <hill@rowland.harvard.edu> writes: > >> John Larkin wrote... >>> >>> >>> I have a low power 1400 volt power supply and I'd like >>> to add a bleeder, and have an LED light up if there's >>> voltage present on the caps. >>> >>> I was thinking about a series stack of three LND150 >>> depletion fets and the LED, with source resistors to >>> set the currents to about 150 uA or so. That would >>> keep the LED brightness constant down to 10 volts >>> maybe, and bleed linearly. >>> >>> At least one of the fets will avalanche, maybe two. >>> I think you said that this is OK. >> >> In general MOSFETs are perfectly happy in avalanche; >> in fact most power parts have avalanche ratings. You >> just have to stay within the power dissipation limit. >> (If you analyze a datasheet "avalanche rating" you'll >> see it's simply derived from junction-temp limit and >> thermal mass from the transient thermal impedance plots, >> using the inductor value, voltage and currents in >> question, so there's nothing special about avalanche.) > >I was testing some opto-fets last week for this - there was nothing in >the datasheet. But an application note says they must not be subjected >to transient voltages outside their rating. > >Customers might connect them to a wire with inductance, or a relay coil >perhaps. > >I started with 100uH but they seemed to be quite happy switching a >couple of Henrys at 0.5A all day. (It was supposed to be a test to >destruction but I felt sorry for them so stopped there!). > >I will be using a TVS anyway now but was curious how much there is to >worry about, really. > >Then there is ESD.The LND150s have gate protection zeners, and body diodes, and can presumably handle some avalanche energy, so they should be pretty tough. But I may as well use a resistor stack into the gates - one more part - so I don't have to argue the situation in the design review. https://dl.dropboxusercontent.com/u/53724080/Circuits/Power/HVPS2.jpg
Reply by ●November 23, 20152015-11-23
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
Reply by ●November 23, 20152015-11-23
John Larkin wrote...> >> Then there is ESD. > > The LND150s have gate protection zeners, and body diodes, > and can presumably handle some avalanche energy, so they > should be pretty tough. > > But I may as well use a resistor stack into the gates - > one more part - so I don't have to argue the situation > in the design review.You could go for a more robust depletion-mode MOSFET, see Table 3.6 in AoE III, page 210, for possibilities. -- Thanks, - Win
Reply by ●November 23, 20152015-11-23
On 23 Nov 2015 06:20:54 -0800, Winfield Hill <hill@rowland.harvard.edu> wrote:>habib.bouaziz@gmail.com wrote... >> >> Don't understand how it works ... > > The TLP191B acts like a battery. It has > a stack of diodes and runs continuously, > providing about 7V (at 10uA) of gate bias. >https://octopart.com/search?q=TLP191 >http://datasheet.octopart.com/TLP191B%28U%2CC%2CF%29-Toshiba-datasheet-13727684.pdf > > The optocouplers drive the FET source, in > common-gate fashion.I Spice-modeled the TLP191B... it's on the Device Models & Subcircuits page of my website. The schematic pin-out doesn't match the datasheet I have. ...Jim Thompson -- | James E.Thompson | mens | | Analog Innovations | et | | Analog/Mixed-Signal ASIC's and Discrete Systems | manus | | San Tan Valley, AZ 85142 Skype: skypeanalog | | | Voice:(480)460-2350 Fax: Available upon request | Brass Rat | | E-mail Icon at http://www.analog-innovations.com | 1962 | I love to cook with wine. Sometimes I even put it in the food.
Reply by ●November 23, 20152015-11-23
On 23 Nov 2015 09:01:58 -0800, Winfield Hill <hill@rowland.harvard.edu> wrote:>John Larkin wrote... >> >>> Then there is ESD. >> >> The LND150s have gate protection zeners, and body diodes, >> and can presumably handle some avalanche energy, so they >> should be pretty tough. >> >> But I may as well use a resistor stack into the gates - >> one more part - so I don't have to argue the situation >> in the design review. > > You could go for a more robust depletion-mode MOSFET, > see Table 3.6 in AoE III, page 210, for possibilities. >We have the LND150s in stock, and they behave very well. We also use DN2530, sweet little SOT89, but it's only 300 volts. I checked out AOE3 as you suggested, and then put the book down on my desk, opened to page 210. Now the book is making very strange crackling noises.
Reply by ●November 23, 20152015-11-23
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, > - WinOf 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.
Reply by ●November 23, 20152015-11-23
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.If there's no photo current in either input loop, the 2SK4177's are OFF... though I'm not sure how well-behaved they are with an essentially floating source. Needs some kind of shut-down means to ensure no photo-current. ...Jim Thompson -- | James E.Thompson | mens | | Analog Innovations | et | | Analog/Mixed-Signal ASIC's and Discrete Systems | manus | | San Tan Valley, AZ 85142 Skype: skypeanalog | | | Voice:(480)460-2350 Fax: Available upon request | Brass Rat | | E-mail Icon at http://www.analog-innovations.com | 1962 | I love to cook with wine. Sometimes I even put it in the food.
Reply by ●November 23, 20152015-11-23
On Mon, 23 Nov 2015 10:12:58 -0700, Jim Thompson <To-Email-Use-The-Envelope-Icon@On-My-Web-Site.com> wrote:>On 23 Nov 2015 06:20:54 -0800, Winfield Hill ><hill@rowland.harvard.edu> wrote: > >>habib.bouaziz@gmail.com wrote... >>> >>> Don't understand how it works ... >> >> The TLP191B acts like a battery. It has >> a stack of diodes and runs continuously, >> providing about 7V (at 10uA) of gate bias. >>https://octopart.com/search?q=TLP191 >>http://datasheet.octopart.com/TLP191B%28U%2CC%2CF%29-Toshiba-datasheet-13727684.pdf >> >> The optocouplers drive the FET source, in >> common-gate fashion. > >I Spice-modeled the TLP191B... it's on the Device Models & Subcircuits >page of my website. > >The schematic pin-out doesn't match the datasheet I have. > > ...Jim ThompsonWe number the four pins 1-2-3-4. Toshiba uses 1-3-4-6.
Reply by ●November 23, 20152015-11-23
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.
