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Induction heater progress

T

Tim Williams

Jan 1, 1970
0
The half bridge was working fine with the MOSFETs, so I wired up the IGBTs
(4 x IRG4PC50UD) with 10 ohm gate resistors and 1/2" wide copper strip,
soldered all neat, film bypass caps no more than an inch from the
transistors, gate drive and power supply both function seperately, let's try
them together... charge PSU caps (flick switch), turn on driver. Ping.
Shit, I don't like that sound. The meter says zero volts on the caps. That
was 60 joules (about 2mF at 250V), and the caps can probably deliver that in
under 100us...way more than those junctions can handle... let's check it
again... flick the switch, BURRZZZ, nope, it's fucking shorted
all-god-damn-right...

MOSFETs worked. What's wrong guys?

Tim
 
W

Winfield Hill

Jan 1, 1970
0
Tim Williams wrote...
The half bridge was working fine with the MOSFETs, so I wired up the IGBTs
(4 x IRG4PC50UD) with 10 ohm gate resistors and 1/2" wide copper strip,
soldered all neat, film bypass caps no more than an inch from the
transistors, gate drive and power supply both function seperately, let's
try them together... charge PSU caps (flick switch), turn on driver. Ping.

What's wrong with starting out your testing at low supply voltages?
Shit, I don't like that sound. The meter says zero volts on the caps.
That was 60 joules (about 2mF at 250V), and the caps can probably deliver
that in under 100us...way more than those junctions can handle... let's
check it again... flick the switch, BURRZZZ, nope, it's fucking shorted
all-god-damn-right...

MOSFETs worked. What's wrong guys?

I was going to remind you that not all IGBTs have reverse diodes, but I
see the IRG4PC50UD does. You aren't actually using IRG4PC50U are you?
 
T

Tim Williams

Jan 1, 1970
0
Winfield Hill said:
What's wrong with starting out your testing at low supply voltages?

I did, for the MOSFETs. For sure I should've started with a resistor load
and +100V, but then, IGBTs ought to be stocky enough, riiiight?...
I was going to remind you that not all IGBTs have reverse diodes, but I
see the IRG4PC50UD does. You aren't actually using IRG4PC50U are you?

Nope, clearly (well as clear as laser printing is x_x) UD type.

Tim
 
R

Rene Tschaggelar

Jan 1, 1970
0
Tim said:
The half bridge was working fine with the MOSFETs, so I wired up the IGBTs
(4 x IRG4PC50UD) with 10 ohm gate resistors and 1/2" wide copper strip,
soldered all neat, film bypass caps no more than an inch from the
transistors, gate drive and power supply both function seperately, let's try
them together... charge PSU caps (flick switch), turn on driver. Ping.
Shit, I don't like that sound. The meter says zero volts on the caps. That
was 60 joules (about 2mF at 250V), and the caps can probably deliver that in
under 100us...way more than those junctions can handle... let's check it
again... flick the switch, BURRZZZ, nope, it's fucking shorted
all-god-damn-right...

MOSFETs worked. What's wrong guys?


A scope to view some waveforms would help...

Rene
 
T

Tim Williams

Jan 1, 1970
0
Rene Tschaggelar said:
A scope to view some waveforms would help...

Well, I've got some stuff like this:
http://webpages.charter.net/dawill/Images/Induction713.jpg
But that's with the MOSFETs. (Output current is probably like 20A.)

I can assure you it was working very nicely: 40-48% duty cycle per output,
<500ns rise/fall time at each MOSFET gate, output voltage waveform under
load shows proper on-resistance slope in forward-bias region (i.e., after
the negative flyback current handled by the body diodes) corresponding to
around 60A output, and output current waveform shows a straight, regular
triangle wave above resonance and a cross between triangle and sine at
resonance. Peak current was around 60A for the MOSFETs, corresponding to a
peak saturation voltage of around 10V.

Considering the IGBTs blew immediately and I don't have a storage scope,
you'll have to build it yourself and view the impulse on yours...

Tim
 
W

Winfield Hill

Jan 1, 1970
0
Tim Williams wrote...
<500ns rise/fall time at each MOSFET gate,

Whoa, I'm pretty sure that's waay tooo slooow.
 
J

John - KD5YI

Jan 1, 1970
0
Tim said:
The half bridge was working fine with the MOSFETs, so I wired up the IGBTs
(4 x IRG4PC50UD) with 10 ohm gate resistors and 1/2" wide copper strip,
soldered all neat, film bypass caps no more than an inch from the
transistors, gate drive and power supply both function seperately, let's try
them together... charge PSU caps (flick switch), turn on driver. Ping.
Shit, I don't like that sound. The meter says zero volts on the caps. That
was 60 joules (about 2mF at 250V), and the caps can probably deliver that in
under 100us...way more than those junctions can handle... let's check it
again... flick the switch, BURRZZZ, nope, it's fucking shorted
all-god-damn-right...

MOSFETs worked. What's wrong guys?

Tim


Hi, Tim -

I think the IGBTs have a long storage time relative to FETs. Also a longer
turn off time. Is it possible that your dead time was adequate for the FETs
but not for the IGBTs?

Good luck.

John
 
T

Terry Given

Jan 1, 1970
0
John said:
Hi, Tim -

I think the IGBTs have a long storage time relative to FETs. Also a
longer turn off time. Is it possible that your dead time was adequate
for the FETs but not for the IGBTs?

Good luck.

John

even the so-called super- (or whatever superlative the mfg comes up
with) fast IGBTs are as slow as a wet week cf FETs. its probably that
which is the problem.

I like to configure my desat and current limit/trip circuits to latch
during testing (usually not hard). and *always* bring it up nice and
gentle. big bang testing usually results in exactly that.

if your desat circuit doesnt latch the fault, then you hjust repeatedly
desat the IGBT, Tj ratchets up and *bang*

IGBTs *do not like* being over-voltaged, and *will* shit themselves if
you do. very low inductance is required between the half-bridge and DC
bus. FETs OTOH are far more tolerant (hell, they even have avalanche
ratings). If an IGBT desats, the current is probably around 10x IGBT
rated current (which is probably higher than the current you operate
them at), so for same Toff, Lstray*dI/dt will give voltage drops about
10x bigger than during normal operation. thus it is quite common for
desat circuits to force the IGBTs to blow up whilst attempting to
protect them :) BTFT

some calcs:

Ipk = 20A*sqrt(2) = 30A (too lazy to pick up HP).
IGBT = 50A, 600V
Vdc = 400V
Toff = 500ns (ignore tail current)

Vmargin = 200V = Lstray*dI/dt

Lstray < 200V*500ns/30A < 3.3uH

no worries you say.

alas, the important time is not the fall time, but how long the IGBT
gate cruises thru the threshold region - roughly the width of the flat
spot in Vgs. or you could measure the collector voltage rise time, the
two ought to be fairly similar.

so lets say it fluffs around Vth for say 100ns. Then Lstray < 670nH. not
so easy. Hell, there is 30nH just in the cap, another 30nH in the IGBT
(oops, 2 in series, thats 60nH). so 100nH would be a damn fine trick
(although do-able).

alas, during desat the current might rise as high as 500A, so dV will be
10x - 20x higher, so unless Lstray < 30 - 60nH, kaboom.

this is why real IGBTs come in extremely low inductance packages, drive
manufacturers herniate themselves attempting to reduce L, and good
gatedrives turn off much slower during fault conditions. Semkiron have a
FET in series with the turn-off FET, that shunts a resistor. the desat
circuit turns the lower FET off during a fault, so the extra resistor
gets added to Rgoff, slowing the rise time.

cheers
Terry
 
T

Tim Williams

Jan 1, 1970
0
Winfield Hill said:
Whoa, I'm pretty sure that's waay tooo slooow.

Howso? Slow in general yes, but slow switching time relaxes the dI/dt
requirement. I'm puttering along at 20kHz or so, so there are fewer
transitions per second, not to mention no switching loss at turn-on (zero
voltage/zero current). At any rate that would just cost me what, a
percentage point in efficiency? Out of 98 or 99%? *Shrug*...fine with me.

Tim
 
T

Tim Williams

Jan 1, 1970
0
I don't think so. These are rated for 300ns maximum turn off time (i.e., td
+ tf), which is still under a microsecond even with a very pokey drive
circuit (I'm pretty sure mine does better, though I can't very well test it
with full IGBT miller effect now..).
if your desat circuit doesnt latch the fault, then you hjust repeatedly
desat the IGBT, Tj ratchets up and *bang*

As a matter of fact, the desat light turned on, indicating the optos flipped
the R-S f/f and the SG3524 turned off, turning off the drive, which should
be all within 10us or so.
IGBTs *do not like* being over-voltaged, and *will* shit themselves if
you do. very low inductance is required between the half-bridge and DC
bus.

I should take a pic. (It would suck though, since I already removed the
three shorted IGBTs.) I've got 10 film caps totally packed in where the
copper strips are closest.
FETs OTOH are far more tolerant (hell, they even have avalanche
ratings).

Which reminds me, wtf is an IGBT's Vce(max) anyways? Sure, it says it can
handle 600V...what's it do at 601? Nothing? Depends? I also find it
suspicious that there's no avalance rating...
some calcs:
...
so lets say it fluffs around Vth for say 100ns. Then Lstray < 670nH. not
so easy. Hell, there is 30nH just in the cap, another 30nH in the IGBT
(oops, 2 in series, thats 60nH). so 100nH would be a damn fine trick
(although do-able).

Well what say ye of 4.5" of copper strip? (That's from end to end, the
nearest IGBT's internal diode is of course closer, so as to anchor the
flyback pulse.)
this is why real IGBTs come in extremely low inductance packages,

So International Rectifier didn't sell me "Real IGBTs"? For shame!
S'posted all over the data sheet! ;o)
drive
manufacturers herniate themselves attempting to reduce L, and good
gatedrives turn off much slower during fault conditions.

Ah, good idea.

Tim
 
T

Terry Given

Jan 1, 1970
0
Tim said:
I don't think so. These are rated for 300ns maximum turn off time (i.e., td
+ tf), which is still under a microsecond even with a very pokey drive
circuit (I'm pretty sure mine does better, though I can't very well test it
with full IGBT miller effect now..).

perhaps. I once got some "hyper fast" IR igbts, rated for 150kHz, and
they sucked major league canal water. IMO totally unusable above 20kHz
or so. lies, damn lies, and shit mfgs put in datasheets. IR for example
always spec Rdson at Tj = 25C, and their so-called power ratings are
even bigger bollocks - its not uncommon to see a "maximum power" figure
that is greater than Tjmax/Rtheta

As a matter of fact, the desat light turned on, indicating the optos flipped
the R-S f/f and the SG3524 turned off, turning off the drive, which should
be all within 10us or so.

I forget if your circuit latches the fault. if not, a diode should make
it do so. as a general rule of thumb, the desat ought to turn the damn
IGBT off by itself, then indicate thru an opto that all isnt well in the
state of denmark. Note that Hamlets approach (piss around for ages)
inevitably results in a high mortality rate :)

all my gatedrives do exactly that, and stay latched off until the main
drive opto turns off (IOW the controller turns the igbt off), then reset
themselves. the controller is then responsible for making sure it wont
re-start the IGBT - it latches the fault, in a far more permanent sense.

even then, via the front panel, its possible to reset the fault, and try
again. customers even did this often enough to ratchet up the die
temperature until kaboom. for a 600A drive, 5-10 resets in quick
succession would kill it ;) Later generations of product got real smart,
running thermal models and having ever-increasing timeouts between
allowing resets, spcifically to prevent this.

I should take a pic. (It would suck though, since I already removed the
three shorted IGBTs.) I've got 10 film caps totally packed in where the
copper strips are closest.




Which reminds me, wtf is an IGBT's Vce(max) anyways? Sure, it says it can
handle 600V...what's it do at 601? Nothing? Depends? I also find it
suspicious that there's no avalance rating...

thats because they dont avalanche, they erupt :)

I cant really tell you what the max voltage is, but if you feel like
sacrificing an IGBT, you can measure it - crank up Vce slowly, until the
IGBT shits itself. normally its not much higher than the rated voltage.
which is the voltage at the die, and therefore = bus voltage + LdI/dt.
Well what say ye of 4.5" of copper strip? (That's from end to end, the
nearest IGBT's internal diode is of course closer, so as to anchor the
flyback pulse.)

its the total loop, dude. I cant see abse, but if you take a pic of the
setup, with a ruler for scale, and post it (and email it to me) I'll
tell you what Lbus is (roughly), and others will do likewise (or point
out my crap calculations).

the general rule of thumb is: without a parallel-plate transmission
line, forget it. double-sided copper-clad board is great for this job
though, a sharp knife and a soldering iron allow you to make a suitable
"pcb" that contains bus caps and IGBTs.

So International Rectifier didn't sell me "Real IGBTs"? For shame!
S'posted all over the data sheet! ;o)

http://www.eupec.com/gb/2_PRODUCTS/2_1_ProductRange/pdf/db_fz600r65kf1.pdf

thats a "real" IGBT - 6,500V 600A :)
Ah, good idea.

Tim

Cheers
Terry
 
T

Tim Williams

Jan 1, 1970
0
Terry Given said:
perhaps. I once got some "hyper fast" IR igbts, rated for 150kHz, and
they sucked major league canal water. IMO totally unusable above 20kHz
or so. lies, damn lies, and shit mfgs put in datasheets. IR for example
always spec Rdson at Tj = 25C, and their so-called power ratings are
even bigger bollocks - its not uncommon to see a "maximum power" figure
that is greater than Tjmax/Rtheta

Yipe. Then, why hasn't someone sued them for falsified information?
I forget if your circuit latches the fault.

Well, it kicks an R-S flip-flop, which can only be reset by a pushbutton
wired to supply a couple-microsecond pulse to the reset pin.
if not, a diode should make
it do so. as a general rule of thumb, the desat ought to turn the damn
IGBT off by itself, then indicate thru an opto that all isnt well in the
state of denmark. Note that Hamlets approach (piss around for ages)
inevitably results in a high mortality rate :)

Fair enough. Nonetheless, I tested the desat detection circuits and there's
under 10us between a desat pulse and everything inbetween the gate itself
(F/F, '3524, transformer (high side), driver).
even then, via the front panel, its possible to reset the fault, and try >
again. customers even did this often enough to ratchet up the die
temperature until kaboom. for a 600A drive, 5-10 resets in quick
succession would kill it ;)

Heh heh. It would be nice if I had a 10Gohm resistor on hand, so that 2.7nF
reset pulse generating capacitor can't charge too fast, but alas...
thats because they dont avalanche, they erupt :)

Sooo, it's more like an SCR? Once-per-IGBT-SCR? So what happens if I push
1mA CCSource into the collector, will voltage rise to ~600V then kill to 0
or 2V? Will it stabilize like a zener? How about 10mA? 100?
I cant really tell you what the max voltage is, but if you feel like
sacrificing an IGBT, you can measure it - crank up Vce slowly, until the
IGBT shits itself. normally its not much higher than the rated voltage.
which is the voltage at the die, and therefore = bus voltage + LdI/dt.

What if I make L go to shit, and make a shorting-commutating bridge? Izzat
much safer for this stuff?
its the total loop, dude.

Well...yeah...fine... 4.5" each way (end to end), plus film caps in the
middle, plus about 1/2" max. seperation between the strips.
I cant see abse, but if you take a pic of the
setup, with a ruler for scale, and post it (and email it to me) I'll
tell you what Lbus is (roughly), and others will do likewise (or point
out my crap calculations).
Alright...

the general rule of thumb is: without a parallel-plate transmission
line, forget it.

What significance is a TL at these edge rates? I'm not doing anything
nanosecondey here.
double-sided copper-clad board is great for this job
though, a sharp knife and a soldering iron allow you to make a suitable
"pcb" that contains bus caps and IGBTs.

If the goal is to add distributed capacitance to slow e.g. flyback pulses,
wouldn't a small (say 0.047uF) cap at each IGBT be more effective? How
about 10-20 spaced evenly along the strip?

Meh... there's a toob bigger ;o)
http://www.cpii.com/eimac/catalog/169218.htm

Tim
 
T

Terry Given

Jan 1, 1970
0
Tim said:
Yipe. Then, why hasn't someone sued them for falsified information?

lies, damned lies, and shit marketing people make up. read the data
sheet very carefully.

over the last 2 years I've picked a lot of SO-8 substitute FETs. I do
this by calculating Rdson at Tj = 125C. many mfgs dont give you this
figure, they give you the 25C figure and have a scalar curve of
Rdson-vs-Tj. these curves are different, too - so 2 FETs with the same
Rdson at 25C may be quite different at 125C. I've seen scalars ranging
from 1.4 - 1.7. I presume its a function of mfg process, perhaps some of
the semiconductor theorists can explain why. I just know to look carefully.

Well, it kicks an R-S flip-flop, which can only be reset by a pushbutton
wired to supply a couple-microsecond pulse to the reset pin.

jolly good.
Fair enough. Nonetheless, I tested the desat detection circuits and there's
under 10us between a desat pulse and everything inbetween the gate itself
(F/F, '3524, transformer (high side), driver).

OK, next question: how big is the IGBT die? can you dissolve the epoxy
off one of the corpses, and measure it? then we can do a simple
adiabatic heating calc to work out how much time you really have.

volume*density = mass,

mass*specific heat = J/K

pick some suitable dT (eg Tj = 200C is BAD, I use dT = 100C)

now you know how many joules it takes.

divide joules by desat power (bus volts*desat current)

voila, max. desat time.

again. customers even did this often enough to ratchet up the die



Heh heh. It would be nice if I had a 10Gohm resistor on hand, so that 2.7nF
reset pulse generating capacitor can't charge too fast, but alas...




Sooo, it's more like an SCR? Once-per-IGBT-SCR? So what happens if I push
1mA CCSource into the collector, will voltage rise to ~600V then kill to 0
or 2V? Will it stabilize like a zener? How about 10mA? 100?

hopefully Win or someone will step in and answer this - I cant. I have
read some papers on this, but all I can remember is DONT DO IT.

the only igbts I have lying around are 600A 1200V parts, and I'm not
willing to sacrifice them....
What if I make L go to shit, and make a shorting-commutating bridge? Izzat
much safer for this stuff?

its just different. then you have the converse problem - turn all igbts
off and kaboom.

philosophically, it is usually a bad idea to throw out an entire design
when one runs into problems - the learning (lifetime) curve resets, and
now you get to discover all the problems with the new design. far better
to measure the amount of funny. As long as the basic topology isnt too
unsuited to the task, the problems can usually be fixed.

that being said, sometimes the answer is to throw it out and start
again, but IME thats not usually the case.

Although I have worked with a number of people who routinely do this
(abandon entire designs) and their hardware is *always* in a state of
"dodgy prototype". Never hire such people. If you do, fire them. the
technical term is "idiot"


Well...yeah...fine... 4.5" each way (end to end), plus film caps in the
middle, plus about 1/2" max. seperation between the strips.

what you want to do is get, say, 1mm lexan, and place your strips on
either side of that, with the lexan somewhat wider than the strips
(clearance, 3-6mm ought to do). just like a 2-sided PCB.

I'll guess its 1mm thick, and 1" wide strip.

according to Terman, Radio Engineers Handbook, p.52:

l = 4.5"
b = 1"
c = (1/25.4)"
D = 0.5" + 1"/2 + 1"/2 = 1.5"

L = 0.1016*l*[ln(D/(b+c)) + 1.5 - D/l + 0.2235*(b+c)/l) uH

{ 2.303*log() = ln() }

L = 0.1016*4.5*[0.36685 + 1.5 - 0.333 + 0.0516] uH
L = 724nH

its pretty clear that strip thickness c does bugger all.

for 0.5" wide strip, b = 0.5" and D = 1" so L = 879nH

thats a lot.

the inductance of the film caps is also not negligible. it would be
reasonable to slice the bus inductance into n identical sections, each
feeding a cap then the next section. you could then quickly hack up a
spice simulation, and measure the effective inductance seen looking into
the end of the strip.

its fairly easy to measure the cap ESL, hell the mfg may even tell you
the SRF. betcha its 10nH or more though, but probably < 30nH.

Alright...

anytime in the next 8-12 seconds would be fine ;)

the next important thing is the half-bridge interconnects. the upper
IGBT collector could (should) bolt directly to the +Vdc strip, but then
you need to connect its emitter (luckily, this is a long skinny leg, so
as to maximise its inductance) to the collector of the lower IGBT, whose
emitter ought to connect directly to the -Vdc strip.

crazy thought:

bend upper E leg over top of case, solder wide strip to it (the folding
will help cancel out the inductance). then sit lower IGBT on top of
this, solder it up, and do a similar trick for its E, running the wide
strip down to the -Vdc bus. best not to think about the heatsinking
(until you realise that making the strip very thick does bugger all to
L, in which case it morphs into a heat spreader/sink).

you can now see why I use multilayer structures (2mm Cu plates & lexan
for big stuff, 10Oz pcb for little stuff, 1-4Oz pcb for toys).

with single powerex U-series IGBTs arranged as a half-bridge, there is
another great trick. after you kill one, gut it. then you will see how
the module internal bus-bars run - up one side of the module. Re-do your
half-bridge layout such that the internal bus-bars of each IGBT are as
close together as possible - IOW spin one IGBT 180 degrees. this
minimises the total inductance. If not, you just placed the two internal
bus bars 160mm apart (c.f. 5mm), thereby maximising the total
inductance, and ensuring that in the event of a desat (and perhaps even
during normal operation) kaboom :)

What significance is a TL at these edge rates? I'm not doing anything
nanosecondey here.

bloody low L. for a parallel plate transmission line, width b,
separation a, L = Uo*b/a, Uo = 1.2566*uH/m (R,W,vD p.250 table 5.11b)

25.4mm wide, 1mm spacing, L = 50nH/m.

4.5" of this TL is 1.26nH, which pisses all over your 0.5" spaced
strips, by almost 3 orders of magnitude :)

remember, a transmission line is a lumped circuit element for l <
lambda/20 (ish), as in your case, and as you can see, its a damned good one!

If the goal is to add distributed capacitance to slow e.g. flyback pulses,
wouldn't a small (say 0.047uF) cap at each IGBT be more effective?

yes. but the cap L must be low. if you use a 1" long film cap, it'll
have quite high L. special "IGBT snubber" caps exist (often designed to
bolt directly to the IGBT terminals) with inductances on the order of 1-2nH.

If you use a pcb, then you can plop down HV smt caps (dont hand-solder
them lest they EXPLODE) which are dirt cheap, and have about 1nH ESL
(it'll be at least a 1206 package, perhaps bigger).

beware smt film caps though - some (WIMA IIRC) are actually leaded caps,
legs bent alongside body, and metal plates welded on. so the inductance
is really no better than the leaded cap itself.

How
about 10-20 spaced evenly along the strip?

see above wrt inductance of each piece of strip.

I've got a paper somewhere (buried under huge pile of shit no doubt)
where it is "proven" that valves always beat silicon at high enough
power levels, cos they can get a lot hotter. roll on SiC.

Cheers
Terry
 
W

Winfield Hill

Jan 1, 1970
0
Tim Williams wrote...
... I tested the desat detection circuits and there's under
10us between a desat pulse and everything inbetween ...

The thing about fast switching is this. If you're starting a load
with no current, and use soft switching, fine. But if you have
enough inductance and are running "continuous" current, as opposed
to "dis-continuous" current, then soft switching can be a disaster.
That's because the switch may be on enough to carry most of the load
current, as enforced by the inductor, but not on enough to have low
voltages across its terminals. The instantaneous power dissipation
can be damaging, to say the least.

With respect to desat detection, there's a time delay for that to
work, typically 5 to 10us, and this can be big trouble - it's just
a matter of how high the dissipation is during this time. If the
the IGBT is switching into a full short, or is carrying full load
current, with high terminal voltages, this time can be too long.

Not to say these issues are necessarily related to your failure,
but I do suggest a little more respect for their implications.
 
T

Tim Williams

Jan 1, 1970
0
Winfield Hill said:
The thing about fast switching is this. If you're starting a load
with no current, and use soft switching, fine. But if you have
enough inductance and are running "continuous" current, as opposed
to "dis-continuous" current, then soft switching can be a disaster.
That's because the switch may be on enough to carry most of the load
current, as enforced by the inductor, but not on enough to have low
voltages across its terminals. The instantaneous power dissipation
can be damaging, to say the least.

Well, transistors just look like a CCS, so terminal voltage would certainly
skyrocket with dissipation if Ic exceeds say, 100-200A.

I've got gate at 10V on-state, so that shouldn't be a problem. According to
the 'data'sheet, that should be enough for 200A, and temperature makes no
difference in this characteristic at that current. It neglects to mention
Gm or threshold variation though. I don't like the idea of running it up to
say, 15V, since it pops at a mere 20V (what dumb silicon burner makes
Vg(max) ONLY +/-20V? sheesh), and if anything should pulse it a mere 5V,
it's done for.

Tim
 
F

Fritz Schlunder

Jan 1, 1970
0
I've got gate at 10V on-state, so that shouldn't be a problem. According to
the 'data'sheet, that should be enough for 200A, and temperature makes no
difference in this characteristic at that current. It neglects to mention
Gm or threshold variation though. I don't like the idea of running it up to
say, 15V, since it pops at a mere 20V (what dumb silicon burner makes
Vg(max) ONLY +/-20V? sheesh), and if anything should pulse it a mere 5V,
it's done for.

Tim


Greetings Tim.

Chances are the IGBT's gate dielectric is not nearly as vulnerable as you
think. According to this app note by International Rectifier:

http://www.irf.com/technical-info/appnotes/an-983.pdf

Read section 8.2 (absolute maximum ratings) under the italicized title
"Maximum Gate-to-Emitter Voltage (Vge)"

It claims typical gate dielectric rupture occurs around 80V (!!), but is
limited to 20V for other reasons.

By running your gates at 10V you are probably risking more harm than good.
They don't show part to part variation min/max graphs, so I'm not sure you
can fully trust that all of your IGBT parts can handle 200A@10V Vge without
dropping into the linear region.
 
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