On Wed, 06 Jul 2011 17:55:21 -0700, Tim Wescott <tim@seemywebsite.com> wrote:>On 07/06/2011 05:49 PM, Jim Thompson wrote: >> On Wed, 06 Jul 2011 17:40:31 -0700, Tim Wescott<tim@seemywebsite.com> >> wrote: >> >>> On 07/06/2011 05:28 PM, Jim Thompson wrote: >>>> On Wed, 06 Jul 2011 16:08:31 -0700, Tim Wescott<tim@seemywebsite.com> >>>> wrote: >>>> >>>>> On 07/06/2011 03:32 PM, Jim Thompson wrote: >>>> [snip] >>>>>> >>>>>> What are you trying to model? >>>>>> >>>>>> ...Jim Thompson >>>>> >>>>> IGBT, in linear mode to boot. >>>>> >>>> [snip] >>>> >>>> Suddenly struck me, WHY do want an IGBT in linear mode? >>> >>> Because that's what the customer is insisting on. >>> >>>> What characteristics are you trying to emulate? >>> >>> A single honking-big device (we weren't able to find Really Big MOSFETs, >>> and would have to use _lots_ in parallel). >>> >>>> You might be better off with an MOS/Bipolar combination. >>> >>> Strange, that's what I told my customer! >>> >>> They _do_ have a record of success with an IGBT in the circuit -- I'm >>> just helping them drive it better -- so it's hard to argue against it. >>> >>> If I could find a bipolar transistor in a single honking-big module that >>> may fly with them. >> >> Voltage rating? > >'bout 100V > >> Current rating? > >'bout 400A > >> Required saturation voltage? > >Not very important -- several volts would do OK. Keep in mind that it's >used as a linear pass element for the most part. > >> Is load inductive? > >Resistive > >> IGBT's are inherently snap action devices. How do >> you propose keeping them from "snapping" ?? > >Well, it's that last that is exactly what worries me, it is why I tried >to talk the customer into MOSFETs, and it is why I'd be interested in >some other alternative. My original proposal to keep them from >"snapping" was to keep them out of the circuit entirely -- that didn't work. > >I do know, however, that they've had these devices in-circuit in a >previous product and are happy with it, so it's hard to budge them.Got any 100V/400A NPN's lined up, or are you planning paralleling? ...Jim Thompson -- | James E.Thompson, CTO | mens | | Analog Innovations, Inc. | et | | Analog/Mixed-Signal ASIC's and Discrete Systems | manus | | Phoenix, Arizona 85048 Skype: Contacts Only | | | 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.
Spicemod??
Started by ●July 6, 2011
Reply by ●July 6, 20112011-07-06
Reply by ●July 6, 20112011-07-06
On 07/06/2011 06:05 PM, Jim Thompson wrote:> On Wed, 06 Jul 2011 17:55:21 -0700, Tim Wescott<tim@seemywebsite.com> > wrote: > >> On 07/06/2011 05:49 PM, Jim Thompson wrote: >>> On Wed, 06 Jul 2011 17:40:31 -0700, Tim Wescott<tim@seemywebsite.com> >>> wrote: >>> >>>> On 07/06/2011 05:28 PM, Jim Thompson wrote: >>>>> On Wed, 06 Jul 2011 16:08:31 -0700, Tim Wescott<tim@seemywebsite.com> >>>>> wrote: >>>>> >>>>>> On 07/06/2011 03:32 PM, Jim Thompson wrote: >>>>> [snip] >>>>>>> >>>>>>> What are you trying to model? >>>>>>> >>>>>>> ...Jim Thompson >>>>>> >>>>>> IGBT, in linear mode to boot. >>>>>> >>>>> [snip] >>>>> >>>>> Suddenly struck me, WHY do want an IGBT in linear mode? >>>> >>>> Because that's what the customer is insisting on. >>>> >>>>> What characteristics are you trying to emulate? >>>> >>>> A single honking-big device (we weren't able to find Really Big MOSFETs, >>>> and would have to use _lots_ in parallel). >>>> >>>>> You might be better off with an MOS/Bipolar combination. >>>> >>>> Strange, that's what I told my customer! >>>> >>>> They _do_ have a record of success with an IGBT in the circuit -- I'm >>>> just helping them drive it better -- so it's hard to argue against it. >>>> >>>> If I could find a bipolar transistor in a single honking-big module that >>>> may fly with them. >>> >>> Voltage rating? >> >> 'bout 100V >> >>> Current rating? >> >> 'bout 400A >> >>> Required saturation voltage? >> >> Not very important -- several volts would do OK. Keep in mind that it's >> used as a linear pass element for the most part. >> >>> Is load inductive? >> >> Resistive >> >>> IGBT's are inherently snap action devices. How do >>> you propose keeping them from "snapping" ?? >> >> Well, it's that last that is exactly what worries me, it is why I tried >> to talk the customer into MOSFETs, and it is why I'd be interested in >> some other alternative. My original proposal to keep them from >> "snapping" was to keep them out of the circuit entirely -- that didn't work. >> >> I do know, however, that they've had these devices in-circuit in a >> previous product and are happy with it, so it's hard to budge them. > > Got any 100V/400A NPN's lined up, or are you planning paralleling?I wish I did! I don't think I'm going to budge them off of their IGBT decision unless things start going "BANG!" in the lab. I'm hoping to convince them to do tests on prototypes, though. -- Tim Wescott Wescott Design Services http://www.wescottdesign.com Do you need to implement control loops in software? "Applied Control Theory for Embedded Systems" was written for you. See details at http://www.wescottdesign.com/actfes/actfes.html
Reply by ●July 7, 20112011-07-07
On Wed, 06 Jul 2011 18:11:20 -0700, Tim Wescott <tim@seemywebsite.com> wrote:>On 07/06/2011 06:05 PM, Jim Thompson wrote:[snip]>> >> Got any 100V/400A NPN's lined up, or are you planning paralleling? > >I wish I did! I don't think I'm going to budge them off of their IGBT >decision unless things start going "BANG!" in the lab. I'm hoping to >convince them to do tests on prototypes, though.It's probably possible to make a linear IGBT with judicious tub and isolation placement. Can you curve trace one of these dudes? ...Jim Thompson -- | James E.Thompson, CTO | mens | | Analog Innovations, Inc. | et | | Analog/Mixed-Signal ASIC's and Discrete Systems | manus | | Phoenix, Arizona 85048 Skype: Contacts Only | | | 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 ●July 7, 20112011-07-07
On 07/06/2011 07:40 PM, Tim Wescott wrote:> On 07/06/2011 05:28 PM, Jim Thompson wrote: >> On Wed, 06 Jul 2011 16:08:31 -0700, Tim Wescott<tim@seemywebsite.com> >> wrote: >> >>> On 07/06/2011 03:32 PM, Jim Thompson wrote: >> [snip] >>>> >>>> What are you trying to model? >>>> >>>> ...Jim Thompson >>> >>> IGBT, in linear mode to boot. >>> >> [snip] >> >> Suddenly struck me, WHY do want an IGBT in linear mode? > > Because that's what the customer is insisting on. >You probably know this, but just in case you don't, i ought to warn you. IGBTs are thermally unstable in linear mode, I had a guy from IR explain this to me years ago. When driven hard into saturation, they are just barely thermally stable, ie. the current roughly shares over the device area, at least enough to allow rated currents. When allowed into linear mode, even for microseconds, they don't share well at all, and the current hogs to the hottest spot of the die. This allows thermal runaway, even if it only persists for us every on-cycle. So, even if significantly derated and run on cold heat sinks, they will have a HUGE tendency to self-destruct when run in the linear region. When part of the die gets hot, the SOA is reduced, and the (partial) transistor has difficulty turning off. Jon
Reply by ●July 7, 20112011-07-07
On Thu, 07 Jul 2011 16:54:28 -0500, Jon Elson <jmelson@wustl.edu> wrote:>On 07/06/2011 07:40 PM, Tim Wescott wrote: >> On 07/06/2011 05:28 PM, Jim Thompson wrote: >>> On Wed, 06 Jul 2011 16:08:31 -0700, Tim Wescott<tim@seemywebsite.com> >>> wrote: >>> >>>> On 07/06/2011 03:32 PM, Jim Thompson wrote: >>> [snip] >>>>> >>>>> What are you trying to model? >>>>> >>>>> ...Jim Thompson >>>> >>>> IGBT, in linear mode to boot. >>>> >>> [snip] >>> >>> Suddenly struck me, WHY do want an IGBT in linear mode? >> >> Because that's what the customer is insisting on. >> >You probably know this, but just in case you don't, i ought to warn you. >IGBTs are thermally unstable in linear mode, I had a guy from IR explain >this to me years ago. When driven hard into saturation, they are just >barely thermally stable, ie. the current roughly shares over the device >area, at least enough to allow rated currents. When allowed into linear >mode, even for microseconds, they don't share well at all, and the >current hogs to the hottest spot of the die. This allows thermal >runaway, even if it only persists for us every on-cycle. So, even if >significantly derated and run on cold heat sinks, they will have a HUGE >tendency to self-destruct when run in the linear region. When part of >the die gets hot, the SOA is reduced, and the (partial) transistor has >difficulty turning off. > >JonI'd use an N-channel MOS plus an NPN: Drain connected to Collector Source connected to Base Gate as the Input Emitter to a Ballast Resistor (*) Collector/Drain to Load (*) Probably going to need emitter ballast resistors to split the load up amongst multiple NPN's. ...Jim Thompson -- | James E.Thompson, CTO | mens | | Analog Innovations, Inc. | et | | Analog/Mixed-Signal ASIC's and Discrete Systems | manus | | Phoenix, Arizona 85048 Skype: Contacts Only | | | 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 ●July 7, 20112011-07-07
On 07/06/2011 07:55 PM, Tim Wescott wrote:>> Voltage rating? > > 'bout 100V > >> Current rating? > > 'bout 400A >At 100 V, IGBTs have no advantage. Their ONLY advantage, in fact, is low IR drop in saturation. MOSFETs are inherently self-balancing, and most designs share current well on their dies too, eliminating many of the thermal runaway difficulties with IGBTs. Paralleling 8 big TO-247 devices should work fine to get to 400 A, although depending on available cooling, more might be better. Of course, if you are dropping a LOT of voltage across them, you may hit the power limit and need more devices. There are big FETs made, but the takeover of the inverter world by IGBTs has reduced the choice. But, don't be fooled, just because IGBTs have taken over in 400+V saturated switching, doesn't mean they are good for all things, as certainly they are NOT good at linear operation. The only reason your customer has had some success with IGBTs is because inverter manufacturers have to face the short circuit problem. With early IGBTs, the transistors would always fail in secondary breakdown during a short circuit event, ie. the command to turn them off would be ignored. The transistor manufacturers are working hard to improve this, and so they have made secondary breakdown harder to enter, but it still is a real problem with IGBTs. My guess is the long-term survivability of IGBTs in this mode will not be good, the thermal instability will greatly shorten the life of the devices. This is a real hidden problem, no measurement from the outside will reveal how much of the die is conducting. The transistors will appear to be handling the load fine until they fail shorted suddenly. Jon
Reply by ●July 11, 20112011-07-11
On Wed, 06 Jul 2011 14:48:53 -0700, Tim Wescott <tim@seemywebsite.com> wrote:>IntuitSoft has a program called Spicemod >(http://www.intusoft.com/spicemod.htm#Requirements) > >It's a "SPICE model builder" that takes data sheet parameters and makes >SPICE models -- including using subcircuits, if just a .MODEL statement >isn't going to be enough. > >I'm skeptical. > >Has anyone used it? Have you had good success? Do you think that >models (particularly IGBT models) that come from it can be trusted?Tim, What approach did you decide on? ...Jim Thompson -- | James E.Thompson, CTO | mens | | Analog Innovations, Inc. | et | | Analog/Mixed-Signal ASIC's and Discrete Systems | manus | | Phoenix, Arizona 85048 Skype: Contacts Only | | | 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 ●July 11, 20112011-07-11
On 07/11/2011 08:34 AM, Jim Thompson wrote:> On Wed, 06 Jul 2011 14:48:53 -0700, Tim Wescott<tim@seemywebsite.com> > wrote: > >> IntuitSoft has a program called Spicemod >> (http://www.intusoft.com/spicemod.htm#Requirements) >> >> It's a "SPICE model builder" that takes data sheet parameters and makes >> SPICE models -- including using subcircuits, if just a .MODEL statement >> isn't going to be enough. >> >> I'm skeptical. >> >> Has anyone used it? Have you had good success? Do you think that >> models (particularly IGBT models) that come from it can be trusted? > > Tim, What approach did you decide on?I think we're going to hand fit, and I'm going to be conservative about my design so that it'll still work even if the IGBT's are slower than expected (and I'm _not_ going to be responsible of they latch up!!). -- Tim Wescott Wescott Design Services http://www.wescottdesign.com Do you need to implement control loops in software? "Applied Control Theory for Embedded Systems" was written for you. See details at http://www.wescottdesign.com/actfes/actfes.html
Reply by ●July 11, 20112011-07-11
On Mon, 11 Jul 2011 09:24:25 -0700, Tim Wescott <tim@seemywebsite.com> wrote:>On 07/11/2011 08:34 AM, Jim Thompson wrote: >> On Wed, 06 Jul 2011 14:48:53 -0700, Tim Wescott<tim@seemywebsite.com> >> wrote: >> >>> IntuitSoft has a program called Spicemod >>> (http://www.intusoft.com/spicemod.htm#Requirements) >>> >>> It's a "SPICE model builder" that takes data sheet parameters and makes >>> SPICE models -- including using subcircuits, if just a .MODEL statement >>> isn't going to be enough. >>> >>> I'm skeptical. >>> >>> Has anyone used it? Have you had good success? Do you think that >>> models (particularly IGBT models) that come from it can be trusted? >> >> Tim, What approach did you decide on? > >I think we're going to hand fit, and I'm going to be conservative about >my design so that it'll still work even if the IGBT's are slower than >expected (and I'm _not_ going to be responsible of they latch up!!).I'm fond of telling clients, "I disagree with your decision, please sign this release acknowledging that I so advised you." 99-44/100% back down... no one out there wants to be responsible ;-) ...Jim Thompson -- | James E.Thompson, CTO | mens | | Analog Innovations, Inc. | et | | Analog/Mixed-Signal ASIC's and Discrete Systems | manus | | Phoenix, Arizona 85048 Skype: Contacts Only | | | 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 ●July 11, 20112011-07-11
