Tim Wescott wrote:> Any good articles in using IGBTs in linear mode? > > With all due respect for the uselessness of SPICE when you can't do the > work on paper -- does anyone know how good a SPICE model designed for an > IGBT in switched service might work in linear mode? Who tends to have > better models for linear service? Whether anyone has models > specifically for IGBTs in linear mode? > > TIA -- IGBTs seem to be enough of a corner case in the semiconductor > world that it's hard to find definitive data about their operation > beyond a cross-section of a generic chip, and some hand-waving arguments > about how it works just like a MOSFET/BJT Darlington-ish pair. >Well,since there is an abundant lack of that information, and you seem to have a have more than a passing interest, then: DIY.
IGBT in Linear Mode
Started by ●May 31, 2011
Reply by ●June 1, 20112011-06-01
Reply by ●June 1, 20112011-06-01
On Tue, 31 May 2011 20:38:48 -0700, Robert Baer <robertbaer@localnet.com> wrote:>Tim Wescott wrote: >> Any good articles in using IGBTs in linear mode? >> >> With all due respect for the uselessness of SPICE when you can't do the >> work on paper -- does anyone know how good a SPICE model designed for an >> IGBT in switched service might work in linear mode? Who tends to have >> better models for linear service? Whether anyone has models >> specifically for IGBTs in linear mode? >> >> TIA -- IGBTs seem to be enough of a corner case in the semiconductor >> world that it's hard to find definitive data about their operation >> beyond a cross-section of a generic chip, and some hand-waving arguments >> about how it works just like a MOSFET/BJT Darlington-ish pair. >> > Well,since there is an abundant lack of that information, and you >seem to have a have more than a passing interest, then: DIY.Testing semiconductors to destruction is tedious and expensive. Especially so for big semiconductors. I was doing that on some Claire mosfet SSRs and discovered that I could tease them to just-before-destruction, by looking at accelerating drain current, probably the thermal precursor to some second breakdown sort of thing. Once I got that sort of calibrated, I could take a lot of data without incinerating a lot of chips. John
Reply by ●June 1, 20112011-06-01
On May 31, 11:44=A0am, Jim Thompson <To-Email-Use-The-Envelope-I...@On- My-Web-Site.com> wrote:> www.irf.com/technical-info/appnotes/an-983.pdf > > Since an IGBT is a 4-layer device one would think that "linear mode" > might be like tip-toeing to the edge of a cliff without a safety rope > ;-)Waaayyyy OT, but yes, I've done that, hung my feet over and climbed down the wall. 5,000 feet vertical. -- Cheers, James Arthur
Reply by ●June 1, 20112011-06-01
On 05/31/2011 09:44 AM, Jim Thompson wrote:> On Tue, 31 May 2011 08:36:46 -0700, Tim Wescott<tim@seemywebsite.com> > wrote: > >> Any good articles in using IGBTs in linear mode? >> >> With all due respect for the uselessness of SPICE when you can't do the >> work on paper -- does anyone know how good a SPICE model designed for an >> IGBT in switched service might work in linear mode? Who tends to have >> better models for linear service? Whether anyone has models >> specifically for IGBTs in linear mode? >> >> TIA -- IGBTs seem to be enough of a corner case in the semiconductor >> world that it's hard to find definitive data about their operation >> beyond a cross-section of a generic chip, and some hand-waving arguments >> about how it works just like a MOSFET/BJT Darlington-ish pair. > > www.irf.com/technical-info/appnotes/an-983.pdf > > Since an IGBT is a 4-layer device one would think that "linear mode" > might be like tip-toeing to the edge of a cliff without a safety rope > ;-)I had a good friend who would dance on the edge of cliffs. I think it was as much to hear the words "Peter, No!" as for the visceral thrill. Somehow, I'm not inclined to do that with my customer's money unless there are clear advantages to success, and the customer's signed up to what I'm doing. -- 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 ●June 1, 20112011-06-01
On Tue, 31 May 2011 15:37:58 -0700, John Larkin <jjlarkin@highNOTlandTHIStechnologyPART.com> wrote:>On Tue, 31 May 2011 11:06:58 -0700, Tim Wescott <tim@seemywebsite.com> >wrote: > >>On 05/31/2011 10:58 AM, John Larkin wrote: >>> On Tue, 31 May 2011 08:36:46 -0700, Tim Wescott<tim@seemywebsite.com> >>> wrote: >>> >>>> Any good articles in using IGBTs in linear mode? >>>> >>>> With all due respect for the uselessness of SPICE when you can't do the >>>> work on paper -- does anyone know how good a SPICE model designed for an >>>> IGBT in switched service might work in linear mode? Who tends to have >>>> better models for linear service? Whether anyone has models >>>> specifically for IGBTs in linear mode? >>>> >>>> TIA -- IGBTs seem to be enough of a corner case in the semiconductor >>>> world that it's hard to find definitive data about their operation >>>> beyond a cross-section of a generic chip, and some hand-waving arguments >>>> about how it works just like a MOSFET/BJT Darlington-ish pair. >>> >>> Don't know about IGBTs, but lots of high-power-rated mosfets will blow >>> up at relatively low power dissipations in linear mode. We had to test >>> a lot of them. >>> >>> ftp://66.117.156.8/ExFets.jpg >> >>The risk is undoubtedly there for IGBTs, as well. They're designed for >>high voltage * low current, or high current * low voltage, not middle^2. >> >>Were they blowing up at the expected power dissipation, or do they tend >>to blow up earlier than their maximum junction temperature & thermal >>conductivity would indicate? > >We tested a bunch of mosfets rated for 300 watts continuous >dissipation. They were bolted to a copper block, and pulsed at various >power dissipations for 0.1 seconds at very low duty cycle. The >application is small-bore MRI gradient drivers. I think we tested them >at 200 volts D-S, can't recall exactly.The specified dissipation figure usually means that you are keeping the die below its maximum temperature by keeping the case at 25 C. When pulsing, then the transient thermal behaviour needs to be taken into account. There's usually a derating curve for that as well. Spice can model the die temperature for that too if the mfr. gives you the thermal circuit. Small die die quicker. boB> >Most of the ones we tried exploded at well below 300 watts. Power >mosfets are apparently optimized for switchmode use, and get something >like a second breakdown effect if made to dissipate lots of power at >high voltages. > >Ixys makes some parts rated for high-power linear use. > >John > >
Reply by ●June 1, 20112011-06-01
boB wrote:> On Tue, 31 May 2011 15:37:58 -0700, John Larkin > <jjlarkin@highNOTlandTHIStechnologyPART.com> wrote: > >> On Tue, 31 May 2011 11:06:58 -0700, Tim Wescott<tim@seemywebsite.com> >> wrote: >> >>> On 05/31/2011 10:58 AM, John Larkin wrote: >>>> On Tue, 31 May 2011 08:36:46 -0700, Tim Wescott<tim@seemywebsite.com> >>>> wrote: >>>> >>>>> Any good articles in using IGBTs in linear mode? >>>>> >>>>> With all due respect for the uselessness of SPICE when you can't do the >>>>> work on paper -- does anyone know how good a SPICE model designed for an >>>>> IGBT in switched service might work in linear mode? Who tends to have >>>>> better models for linear service? Whether anyone has models >>>>> specifically for IGBTs in linear mode? >>>>> >>>>> TIA -- IGBTs seem to be enough of a corner case in the semiconductor >>>>> world that it's hard to find definitive data about their operation >>>>> beyond a cross-section of a generic chip, and some hand-waving arguments >>>>> about how it works just like a MOSFET/BJT Darlington-ish pair. >>>> >>>> Don't know about IGBTs, but lots of high-power-rated mosfets will blow >>>> up at relatively low power dissipations in linear mode. We had to test >>>> a lot of them. >>>> >>>> ftp://66.117.156.8/ExFets.jpg >>> >>> The risk is undoubtedly there for IGBTs, as well. They're designed for >>> high voltage * low current, or high current * low voltage, not middle^2. >>> >>> Were they blowing up at the expected power dissipation, or do they tend >>> to blow up earlier than their maximum junction temperature& thermal >>> conductivity would indicate? >> >> We tested a bunch of mosfets rated for 300 watts continuous >> dissipation. They were bolted to a copper block, and pulsed at various >> power dissipations for 0.1 seconds at very low duty cycle. The >> application is small-bore MRI gradient drivers. I think we tested them >> at 200 volts D-S, can't recall exactly. > > > The specified dissipation figure usually means that you are keeping > the die below its maximum temperature by keeping the case at 25 C. > > When pulsing, then the transient thermal behaviour needs to be taken > into account. There's usually a derating curve for that as well. > Spice can model the die temperature for that too if the mfr. gives > you the thermal circuit. > > Small die die quicker. > > boB >Yabbut, the transient cooling is _better_ than the steady state cooling, because the heat is flowing into surroundings that are cooler than they would be in steady-state. Cheers Phil Hobbs -- Dr Philip C D Hobbs Principal ElectroOptical Innovations 55 Orchard Rd Briarcliff Manor NY 10510 845-480-2058 email: hobbs (atsign) electrooptical (period) net http://electrooptical.net
Reply by ●June 1, 20112011-06-01
On 1 Jun 2011 02:40:01 -0500, boB wrote:>On Tue, 31 May 2011 15:37:58 -0700, John Larkin ><jjlarkin@highNOTlandTHIStechnologyPART.com> wrote: > >>On Tue, 31 May 2011 11:06:58 -0700, Tim Wescott <tim@seemywebsite.com> >>wrote: >> >>>On 05/31/2011 10:58 AM, John Larkin wrote: >>>> On Tue, 31 May 2011 08:36:46 -0700, Tim Wescott<tim@seemywebsite.com> >>>> wrote: >>>> >>>>> Any good articles in using IGBTs in linear mode? >>>>> >>>>> With all due respect for the uselessness of SPICE when you can't do the >>>>> work on paper -- does anyone know how good a SPICE model designed for an >>>>> IGBT in switched service might work in linear mode? Who tends to have >>>>> better models for linear service? Whether anyone has models >>>>> specifically for IGBTs in linear mode? >>>>> >>>>> TIA -- IGBTs seem to be enough of a corner case in the semiconductor >>>>> world that it's hard to find definitive data about their operation >>>>> beyond a cross-section of a generic chip, and some hand-waving arguments >>>>> about how it works just like a MOSFET/BJT Darlington-ish pair. >>>> >>>> Don't know about IGBTs, but lots of high-power-rated mosfets will blow >>>> up at relatively low power dissipations in linear mode. We had to test >>>> a lot of them. >>>> >>>> ftp://66.117.156.8/ExFets.jpg >>> >>>The risk is undoubtedly there for IGBTs, as well. They're designed for >>>high voltage * low current, or high current * low voltage, not middle^2. >>> >>>Were they blowing up at the expected power dissipation, or do they tend >>>to blow up earlier than their maximum junction temperature & thermal >>>conductivity would indicate? >> >>We tested a bunch of mosfets rated for 300 watts continuous >>dissipation. They were bolted to a copper block, and pulsed at various >>power dissipations for 0.1 seconds at very low duty cycle. The >>application is small-bore MRI gradient drivers. I think we tested them >>at 200 volts D-S, can't recall exactly. > > >The specified dissipation figure usually means that you are keeping >the die below its maximum temperature by keeping the case at 25 C.Sure. A copper block does that pretty well, for a tenth of a second. But the point I was making is that most power mosfets are designed to work in switchmode, and can blow up at way under rated power dissipation when used in linear applications, namely dissipating power with higher Vds. We were blowing up "300 watt" mosfets at 150 watts, in 50 milliseconds, bolted to a copper block. John
Reply by ●June 1, 20112011-06-01
On 05/31/2011 10:36 AM, Tim Wescott wrote:> Any good articles in using IGBTs in linear mode? > > With all due respect for the uselessness of SPICE when you can't do the > work on paper -- does anyone know how good a SPICE model designed for an > IGBT in switched service might work in linear mode? Who tends to have > better models for linear service? Whether anyone has models specifically > for IGBTs in linear mode? > > TIA -- IGBTs seem to be enough of a corner case in the semiconductor > world that it's hard to find definitive data about their operation > beyond a cross-section of a generic chip, and some hand-waving arguments > about how it works just like a MOSFET/BJT Darlington-ish pair. >At least when I worked with them, it was STRONGLY discouraged. The problem was that while FETs have negative thermal coefficient, so the current tends to share over the area of the transistor, the IGBT has a positive coefficient, so current tends to "hog" to the hottest area of the transistor, leading to rapid damage. The only way to fight this is to saturate the transistor quickly and hard. Jon
Reply by ●June 1, 20112011-06-01
John Larkin wrote:> On Tue, 31 May 2011 17:29:35 -0700, Joerg <invalid@invalid.invalid> > wrote: > >> John Larkin wrote: >>> On Tue, 31 May 2011 11:06:58 -0700, Tim Wescott <tim@seemywebsite.com> >>> wrote: >>> >>>> On 05/31/2011 10:58 AM, John Larkin wrote: >> [...] >> >>>>> ftp://66.117.156.8/ExFets.jpg >>>> The risk is undoubtedly there for IGBTs, as well. They're designed for >>>> high voltage * low current, or high current * low voltage, not middle^2. >>>> >>>> Were they blowing up at the expected power dissipation, or do they tend >>>> to blow up earlier than their maximum junction temperature & thermal >>>> conductivity would indicate? >>> We tested a bunch of mosfets rated for 300 watts continuous >>> dissipation. They were bolted to a copper block, and pulsed at various >>> power dissipations for 0.1 seconds at very low duty cycle. The >>> application is small-bore MRI gradient drivers. I think we tested them >>> at 200 volts D-S, can't recall exactly. >>> >>> Most of the ones we tried exploded at well below 300 watts. Power >>> mosfets are apparently optimized for switchmode use, and get something >>> like a second breakdown effect if made to dissipate lots of power at >>> high voltages. >>> >>> Ixys makes some parts rated for high-power linear use. >>> >> FETs should always be ok when not exceeding the SOA. Did you go outside >> of the SOA? 100msec is usually the lowest run or already considered DC. > > Since they were rated for 300 watts continuous, we clearly weren't out > of the SOA at less than 300 watts. >300W is most likely a marketing spec. But no matter what, a power rating has nothing to do with SOA. A FET can be perfectly ok at 3V/100A (300W) but explode with gusto at 50V/20A (100W). The SOA diagram will tell you. Like this one in the link Lasse brought: http://ixdev.ixys.com/DataSheet/DS100239%28IXTK-TX200N10L2%29.pdf> I have seen some mosfet SOA curves that included voltage effects. I > recall seeing a fet whose SOA was reduced by about 4:1 at higher > voltages. >They all drop off in the SOA at higher voltage.> For the fets we selected, we wound up estimating a thermal model. In > the amplifier, > > ftp://jjlarkin.lmi.net/Amp.jpg >Nice blue theme color there :-)> we have a uP that digitizes rail voltages (up to +-200), amp output > voltage, fet currents, and heatsink temperature. It runs a realtime > simulation of junction temperatures and shuts things down at an > estimated 140C Tj. That lets us push the fets pretty hard. > > But seriously, switchmode fets get fragile at higher voltages. The > SOAs probably assume they are running close to saturation. [1] > > John > > [1] I use "saturation" in the bipolar sense, low Vds, ohmic region. > Some people use the word to mean operating fets in the higher voltage, > constant-current region. >It's all spelled out in the SOA curves. Don't push you luck there or it'll go ... tssk ... *PHOOMP* Thing is, if you are just a wee bit into forbidden SOA turf it may all work fine for many months until one of the FETs really gets sick of it. -- Regards, Joerg http://www.analogconsultants.com/ "gmail" domain blocked because of excessive spam. Use another domain or send PM.
Reply by ●June 1, 20112011-06-01
On Wed, 01 Jun 2011 15:24:17 -0700, Joerg <invalid@invalid.invalid> wrote:>John Larkin wrote: >> On Tue, 31 May 2011 17:29:35 -0700, Joerg <invalid@invalid.invalid> >> wrote: >> >>> John Larkin wrote: >>>> On Tue, 31 May 2011 11:06:58 -0700, Tim Wescott <tim@seemywebsite.com> >>>> wrote: >>>> >>>>> On 05/31/2011 10:58 AM, John Larkin wrote: >>> [...] >>> >>>>>> ftp://66.117.156.8/ExFets.jpg >>>>> The risk is undoubtedly there for IGBTs, as well. They're designed for >>>>> high voltage * low current, or high current * low voltage, not middle^2. >>>>> >>>>> Were they blowing up at the expected power dissipation, or do they tend >>>>> to blow up earlier than their maximum junction temperature & thermal >>>>> conductivity would indicate? >>>> We tested a bunch of mosfets rated for 300 watts continuous >>>> dissipation. They were bolted to a copper block, and pulsed at various >>>> power dissipations for 0.1 seconds at very low duty cycle. The >>>> application is small-bore MRI gradient drivers. I think we tested them >>>> at 200 volts D-S, can't recall exactly. >>>> >>>> Most of the ones we tried exploded at well below 300 watts. Power >>>> mosfets are apparently optimized for switchmode use, and get something >>>> like a second breakdown effect if made to dissipate lots of power at >>>> high voltages. >>>> >>>> Ixys makes some parts rated for high-power linear use. >>>> >>> FETs should always be ok when not exceeding the SOA. Did you go outside >>> of the SOA? 100msec is usually the lowest run or already considered DC. >> >> Since they were rated for 300 watts continuous, we clearly weren't out >> of the SOA at less than 300 watts. >> > >300W is most likely a marketing spec. But no matter what, a power rating >has nothing to do with SOA. > >A FET can be perfectly ok at 3V/100A (300W) but explode with gusto at >50V/20A (100W). The SOA diagram will tell you. Like this one in the link >Lasse brought: > >http://ixdev.ixys.com/DataSheet/DS100239%28IXTK-TX200N10L2%29.pdf > > > >> I have seen some mosfet SOA curves that included voltage effects. I >> recall seeing a fet whose SOA was reduced by about 4:1 at higher >> voltages. >> > >They all drop off in the SOA at higher voltage. > > >> For the fets we selected, we wound up estimating a thermal model. In >> the amplifier, >> >> ftp://jjlarkin.lmi.net/Amp.jpg >> > >Nice blue theme color there :-) > > >> we have a uP that digitizes rail voltages (up to +-200), amp output >> voltage, fet currents, and heatsink temperature. It runs a realtime >> simulation of junction temperatures and shuts things down at an >> estimated 140C Tj. That lets us push the fets pretty hard. >> >> But seriously, switchmode fets get fragile at higher voltages. The >> SOAs probably assume they are running close to saturation. [1] >> >> John >> >> [1] I use "saturation" in the bipolar sense, low Vds, ohmic region. >> Some people use the word to mean operating fets in the higher voltage, >> constant-current region. >> > >It's all spelled out in the SOA curves. Don't push you luck there or >it'll go ... tssk ... *PHOOMP* > >Thing is, if you are just a wee bit into forbidden SOA turf it may all >work fine for many months until one of the FETs really gets sick of it.I haven't needed to do it in quite a while, but you CAN hook a behavioral device into your simulation to automatically plot SOA curves. I've even been known to have it also plot the spec as well ;-) ...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.
