I'm popping MOSFETS....linear derating factor involved?

[John]

Or simply power the reference from the load.

Hmm...almost too good an idea to even consider.

Trouble is, the load can go down to 0.5V and I haven't seen any 1%, or
better, voltage references that can work with an input voltage that
low. I only need 0.2V out so there is "room" for a reference to work
there though.

Time for another web search!

John
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[Tony Williams]

I was thinking that instead of biasing the op-amp inputs with the
output of the comparator that I could essentially switch Vref (to
the servo loops) on/off by using the output of the comparator as
the source for the voltage reference.

Clamping or switching the Vref (even down to 0v) is
not guaranteed to turn all outputs OFF.

The LM324 has a typical input offset voltage of 3mV.
Even if Vref is an actual 0v there could still be
some opamps whose offset is in the wrong direction
and therefore 'think' they are receiving a 3mV input.

3mV is equivalent to a 300mA output current demand.
Sounds tiny compared to 12.5A, but the MOSFET has no
drain supply, so it has no way of sinking even 300mA
through the current shunt. With no feedback voltage
from the current shunt the opamp will *still* turn
the MOSFET fully ON.

Whatever scheme is used must guarantee that the -ve
input of the opamp is at least 3(5)mV more positive
than the +ve input. This means either driving the
Vref negative, or spending the components to lift
the -ve input.

 

[John]

3mV is equivalent to a 300mA output current demand.
Awwwwww, darn....you're right.
Just when I found some voltage references with a shutdown pin to drive
with the comparator. :-(

I am happy that I actually understood your explanation (which have
always been great, it's me that needs to learn a lot more) though so I
may just find a way out of this yet.

John
-- remove SPAMMENOT for e-mail responses --

 

[John]

Trouble is, the load can go down to 0.5V and I haven't seen any 1%, or
What I thought would be a solution to this was a reference with a
shutdown pin that I could drive with the comparator that's monitoring
the battery voltage (LOAD+ pin). I could then easily bring the servo
loop's Vref to 0V when the battery was disconnected. But Tony
Williams brought up a nasty scenario that requires a negative Vref
(just a bit though) to prevent.

From Tony Williams:
John
-- remove SPAMMENOT for e-mail responses --

 

[John]

Clamping or switching the Vref (even down to 0v) is
How about having the comparator's output drive the supply pin of the
servo loop op-amp? The LT1013's I'm using only draw 0.5mA max so a
comparator that can source 6mA would work (I would eventually have 12
FETs, each driven by a LT1013). Or, I could drive a FET to turn the
power on/off to the op-amps.

The LT1013's data sheet has an absolute max voltage rating of "equal
to the supply voltage" for the inputs though. Since the power is off,
I'm not sure if this means that an input can be fried with the 0.2Vref
going to it when the power would be off.

LTSpice'ing this scenario (using my original schematic, without the
comparator) shows a smooth 1mS ramp up of the gate voltage of the FETs
as the op-amp powers up to 12VDC. Not sure if this has any
relationship to the real-world scenario of powering up an op-amp with
already active inputs though.

May have to wire this one up and scope it out.

John
-- remove SPAMMENOT for e-mail responses --

 

[Terry Given]

That's because there's no such thing as a step, ever.

John

LOL. I asked for that....

OK, you can always create a ramp that a controller cannot follow. which
is a tortured way of saying real controllers have some form of slew-rate
limitation.

Similarly, I had a power supply guy tell me the other day that their
over-voltage circuit was "instantaneous". When pressed, instantaneous
turned into 100us, which is a long time for a junction.

Cheers
Terry

 

[legg]

What I thought would be a solution to this was a reference with a
shutdown pin that I could drive with the comparator that's monitoring
the battery voltage (LOAD+ pin). I could then easily bring the servo
loop's Vref to 0V when the battery was disconnected. But Tony
Williams brought up a nasty scenario that requires a negative Vref
(just a bit though) to prevent.

From Tony Williams:

John
-- remove SPAMMENOT for e-mail responses --

I notice that this thing is manually adjusted. So why not add an
on/off switch?

You'd still want some kind of effective pull-down to prevent connector
surges through load application of dV/dT, through crss. The 1K
resistors currently isolate the gates - perhaps a pnp transistor in
there somewhere would do it.

RL

 

[John]

I notice that this thing is manually adjusted. So why not add an
I do have an on/off switch but any user of this load would have to
remember to turn the unit off before disconnecting the battery and
remember to connect the battery before turning it on. That rule will
last about a week with the guys around here.

I did try turning the power to the op-amps on/off with the output of
the comparator and it works very well when the battery is
connected/disconnected cleanly. But, when the battery contacts scrape
(and the power goes on for a few uS, then off, repeating this a bunch
of times), there are big voltage spikes on the FET gates and huge
current surges thru the FETs. I couldn't find any way to slow the
system down that would have it essentially debounce the battery
connecting/disconnecting.


I really didn't understand this but it sounds like what I was just
talking about? That is, connector noise leading to lots of big dV/dT
spikes and as the spikes reach the gates the current spikes like crazy
too?

I would add a transistor in line the gate to be turned off when the
battery was disconnected? The switching would have to be very slow
though to provide a debounce function.

Thanks for your help RL!
John
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[legg]

I do have an on/off switch but any user of this load would have to
remember to turn the unit off before disconnecting the battery and
remember to connect the battery before turning it on. That rule will
last about a week with the guys around here.

I did try turning the power to the op-amps on/off with the output of
the comparator and it works very well when the battery is
connected/disconnected cleanly. But, when the battery contacts scrape
(and the power goes on for a few uS, then off, repeating this a bunch
of times), there are big voltage spikes on the FET gates and huge
current surges thru the FETs. I couldn't find any way to slow the
system down that would have it essentially debounce the battery
connecting/disconnecting.



I really didn't understand this but it sounds like what I was just
talking about? That is, connector noise leading to lots of big dV/dT
spikes and as the spikes reach the gates the current spikes like crazy
too?

I would add a transistor in line the gate to be turned off when the
battery was disconnected? The switching would have to be very slow
though to provide a debounce function.

Vcc
+--------------------------.
1K |
| |
+------+-------3M-----, | ,---------- LOAD+
| | | | LT1013 |
1.25V POT <-+--R2--+--|--|+\ D
Ref | | | | >--+---+1K-+ G
+------+-, | +--|-/ | | <' S
| | | |C1=== +-| |
| | | | | | \ |
'----49K--|--+----|---+---|10K|---+
| | | | |
| | 470 | R7
| | | | |
'--R4---+-------+---+---+--------- LOAD-

I don't think theres much you can do if the part is set to draw
current without the load applied.

If you set the draw to a guaranteed zero (remembering offsets), then
the pull-down can help prevent connector surges.

Amplitude and duration of current surges otherwise are largely
determined by Vcc amplitude, C1 and load inductance.

- Using 5Vcc may have masked problems innitially.

- 10n may be going a little overboard, try 100pF.

The circuit simulates pretty accurately. File attached.

RL

Version 4
SHEET 1 1360 1032
WIRE -640 624 -640 80
WIRE -640 832 -640 704
WIRE -464 80 -640 80
WIRE -464 144 -464 80
WIRE -464 272 -464 224
WIRE -464 416 -464 272
WIRE -464 592 -464 480
WIRE -464 832 -640 832
WIRE -464 832 -464 592
WIRE -416 272 -464 272
WIRE -272 272 -336 272
WIRE -272 368 -272 272
WIRE -272 592 -464 592
WIRE -272 592 -272 448
WIRE -224 368 -272 368
WIRE -224 736 -224 368
WIRE -192 640 -192 272
WIRE -192 832 -464 832
WIRE -192 832 -192 640
WIRE -160 80 -464 80
WIRE -160 160 -160 80
WIRE -144 160 -160 160
WIRE -144 448 -144 160
WIRE -144 528 -144 448
WIRE -128 80 -160 80
WIRE -128 160 -144 160
WIRE -112 272 -192 272
WIRE -112 368 -224 368
WIRE -112 448 -144 448
WIRE -112 528 -144 528
WIRE -96 640 -192 640
WIRE -96 736 -224 736
WIRE -16 112 -16 64
WIRE -16 160 -48 160
WIRE -16 160 -16 112
WIRE -16 272 -32 272
WIRE -16 272 -16 160
WIRE 0 480 0 432
WIRE 0 528 -32 528
WIRE 0 528 0 480
WIRE 0 640 -16 640
WIRE 0 640 0 528
WIRE 16 368 -32 368
WIRE 16 368 16 144
WIRE 32 736 -16 736
WIRE 32 736 32 512
WIRE 64 112 -16 112
WIRE 64 144 16 144
WIRE 80 480 0 480
WIRE 80 512 32 512
WIRE 96 320 96 160
WIRE 112 80 -48 80
WIRE 112 96 96 96
WIRE 112 96 112 80
WIRE 112 688 112 528
WIRE 128 64 -16 64
WIRE 128 448 -32 448
WIRE 128 464 112 464
WIRE 128 464 128 448
WIRE 144 96 112 96
WIRE 144 160 144 96
WIRE 144 320 96 320
WIRE 144 320 144 224
WIRE 144 432 0 432
WIRE 160 464 128 464
WIRE 160 528 160 464
WIRE 160 688 112 688
WIRE 160 688 160 592
WIRE 176 272 -16 272
WIRE 176 368 16 368
WIRE 192 640 0 640
WIRE 192 736 32 736
WIRE 208 64 192 64
WIRE 208 128 128 128
WIRE 208 128 208 64
WIRE 224 432 208 432
WIRE 224 496 144 496
WIRE 224 496 224 432
WIRE 304 128 208 128
WIRE 304 176 304 128
WIRE 304 320 144 320
WIRE 304 320 304 256
WIRE 320 496 224 496
WIRE 320 544 320 496
WIRE 320 688 160 688
WIRE 320 688 320 624
WIRE 336 128 304 128
WIRE 336 208 336 128
WIRE 352 128 336 128
WIRE 352 208 336 208
WIRE 352 496 320 496
WIRE 352 576 352 496
WIRE 368 496 352 496
WIRE 368 576 352 576
WIRE 416 320 304 320
WIRE 416 320 416 256
WIRE 416 368 256 368
WIRE 416 368 416 320
WIRE 432 688 320 688
WIRE 432 688 432 624
WIRE 432 736 272 736
WIRE 432 736 432 688
WIRE 448 128 432 128
WIRE 448 160 416 160
WIRE 448 160 448 128
WIRE 464 496 448 496
WIRE 464 528 432 528
WIRE 464 528 464 496
WIRE 480 160 448 160
WIRE 496 528 464 528
WIRE 512 832 -192 832
WIRE 512 864 512 832
WIRE 528 272 256 272
WIRE 528 272 528 176
WIRE 528 288 528 272
WIRE 528 368 416 368
WIRE 544 368 528 368
WIRE 544 448 544 432
WIRE 544 640 272 640
WIRE 544 640 544 544
WIRE 544 656 544 640
WIRE 544 736 432 736
WIRE 640 368 624 368
WIRE 640 512 640 368
WIRE 640 736 544 736
WIRE 640 736 640 512
WIRE 672 80 528 80
WIRE 672 240 672 80
WIRE 672 432 544 432
WIRE 672 432 672 240
WIRE 704 512 640 512
WIRE 704 512 704 448
WIRE 704 608 704 512
WIRE 704 832 512 832
WIRE 704 832 704 688
WIRE 720 240 672 240
WIRE 720 304 720 240
WIRE 752 240 720 240
WIRE 752 512 704 512
WIRE 848 304 720 304
WIRE 864 448 704 448
WIRE 960 304 928 304
WIRE 960 336 960 304
WIRE 960 448 944 448
WIRE 960 448 960 416
FLAG 752 512 -Load
FLAG 752 240 +Load
FLAG 512 864 0
SYMBOL nmos 480 80 R0
SYMATTR InstName M1
SYMATTR Value IRF1405
SYMBOL res -16 256 R90
WINDOW 0 -4 97 VBottom 0
WINDOW 3 -29 34 VTop 0
SYMATTR InstName R1
SYMATTR Value 49K9
SYMBOL res -16 352 R90
WINDOW 0 -2 94 VBottom 0
WINDOW 3 -32 40 VTop 0
SYMATTR InstName R2
SYMATTR Value 49K9
SYMBOL res 448 112 R90
WINDOW 0 0 101 VBottom 0
WINDOW 3 -29 52 VTop 0
SYMATTR InstName R5
SYMATTR Value 1K
SYMBOL res 272 352 R90
WINDOW 0 -2 84 VBottom 0
WINDOW 3 -30 37 VTop 0
SYMATTR InstName R6
SYMATTR Value 10K
SYMBOL res 272 256 R90
WINDOW 0 56 87 VBottom 0
WINDOW 3 29 48 VTop 0
SYMATTR InstName R7
SYMATTR Value 10K
SYMBOL res 512 272 R0
WINDOW 0 -27 29 Left 0
WINDOW 3 -34 68 Left 0
SYMATTR InstName R11
SYMATTR Value .01R
SYMBOL res 320 272 R180
WINDOW 0 23 98 Left 0
WINDOW 3 54 60 Left 0
SYMATTR InstName R13
SYMATTR Value 470
SYMBOL pnp 352 256 M180
WINDOW 0 60 72 Left 0
WINDOW 3 40 40 Left 0
SYMATTR InstName Q1
SYMBOL Opamps\\LT1013 96 64 R0
WINDOW 0 -24 63 Left 0
WINDOW 3 -67 113 Left 0
SYMATTR InstName U3
SYMBOL cap 192 48 R90
WINDOW 0 1 59 VBottom 0
WINDOW 3 -28 13 VTop 0
SYMATTR InstName C2
SYMATTR Value 1E-10
SYMBOL cap 128 160 R0
SYMATTR InstName C3
SYMATTR Value 1E-7
SYMBOL res -32 64 R90
WINDOW 0 0 56 VBottom 0
WINDOW 3 32 56 VTop 0
SYMATTR InstName R15
SYMATTR Value 47R
SYMBOL res 640 352 R90
WINDOW 0 0 56 VBottom 0
WINDOW 3 32 56 VTop 0
SYMATTR InstName R18
SYMATTR Value .005
SYMBOL res 688 592 R0
SYMATTR InstName R19
SYMATTR Value .05
SYMBOL voltage -640 608 R0
WINDOW 0 -60 3 Left 0
WINDOW 3 -76 96 Left 0
WINDOW 123 0 0 Left 0
WINDOW 39 0 0 Left 0
SYMATTR InstName Vcc
SYMATTR Value 12V
SYMBOL voltage 960 320 R0
WINDOW 123 0 0 Left 0
WINDOW 39 0 0 Left 0
SYMATTR InstName V1
SYMATTR Value PWL(0 0 2E-1 0 2.0001E-1 12)
SYMBOL res 944 288 R90
WINDOW 0 0 56 VBottom 0
WINDOW 3 32 56 VTop 0
SYMATTR InstName R20
SYMATTR Value .008
SYMBOL ind 960 432 R90
WINDOW 0 5 56 VBottom 0
WINDOW 3 32 56 VTop 0
SYMATTR InstName L1
SYMATTR Value 5E-7
SYMBOL res -32 144 R90
WINDOW 0 0 56 VBottom 0
WINDOW 3 32 56 VTop 0
SYMATTR InstName R26
SYMATTR Value 3E7
SYMBOL res -480 128 R0
SYMATTR InstName R3
SYMATTR Value 1K
SYMBOL zener -448 480 R180
WINDOW 0 24 72 Left 0
WINDOW 3 24 0 Left 0
SYMATTR InstName D1
SYMATTR Value BZX84C2V7L
SYMBOL res -320 256 R90
WINDOW 0 0 56 VBottom 0
WINDOW 3 32 56 VTop 0
SYMATTR InstName R4
SYMATTR Value 10K
SYMBOL res -256 464 R180
WINDOW 0 36 76 Left 0
WINDOW 3 36 40 Left 0
SYMATTR InstName R8
SYMATTR Value 1000R
SYMBOL nmos 496 448 R0
SYMATTR InstName M2
SYMATTR Value IRF1405
SYMBOL res 0 624 R90
WINDOW 0 -4 97 VBottom 0
WINDOW 3 -29 34 VTop 0
SYMATTR InstName R9
SYMATTR Value 49K9
SYMBOL res 0 720 R90
WINDOW 0 -2 94 VBottom 0
WINDOW 3 -32 40 VTop 0
SYMATTR InstName R10
SYMATTR Value 49K9
SYMBOL res 464 480 R90
WINDOW 0 0 104 VBottom 0
WINDOW 3 -29 52 VTop 0
SYMATTR InstName R12
SYMATTR Value 1K
SYMBOL res 288 720 R90
WINDOW 0 -2 84 VBottom 0
WINDOW 3 -30 37 VTop 0
SYMATTR InstName R14
SYMATTR Value 10K
SYMBOL res 288 624 R90
WINDOW 0 56 87 VBottom 0
WINDOW 3 29 48 VTop 0
SYMATTR InstName R16
SYMATTR Value 10K
SYMBOL res 528 640 R0
WINDOW 0 -27 29 Left 0
WINDOW 3 -34 68 Left 0
SYMATTR InstName R17
SYMATTR Value .01R
SYMBOL res 336 640 R180
WINDOW 0 23 98 Left 0
WINDOW 3 54 60 Left 0
SYMATTR InstName R21
SYMATTR Value 470
SYMBOL pnp 368 624 M180
WINDOW 0 60 72 Left 0
WINDOW 3 40 40 Left 0
SYMATTR InstName Q2
SYMBOL Opamps\\LT1013 112 432 R0
WINDOW 0 -24 63 Left 0
WINDOW 3 -67 113 Left 0
SYMATTR InstName U1
SYMBOL cap 208 416 R90
WINDOW 0 1 59 VBottom 0
WINDOW 3 -28 13 VTop 0
SYMATTR InstName C1
SYMATTR Value 1E-10
SYMBOL cap 144 528 R0
SYMATTR InstName C4
SYMATTR Value 1E-7
SYMBOL res -16 432 R90
WINDOW 0 0 56 VBottom 0
WINDOW 3 32 56 VTop 0
SYMATTR InstName R22
SYMATTR Value 47R
SYMBOL res -16 512 R90
WINDOW 0 0 56 VBottom 0
WINDOW 3 32 56 VTop 0
SYMATTR InstName R23
SYMATTR Value 3E7
TEXT -670 870 Left 0 !.tran 0 3E-1 1E-2 startup

 

[John]

Vcc
<Spice file snipped>

Thanks RL!
I wasn't able to find the Spice model for the BZX84C2V7L zener but did
find a model for a BZX84C3V0LT1. Looked close enough (hopefully).

Running the sim gave me a huge voltage spike from the "battery" at
about 189.4mS. The voltage source indicates a linear rise from 0V to
12V starting at 200mS so I'm a bit confused about the timing. I'm
probably missing something somewhere though as I'm a SPICE newbie.

Using IRF1405's I get a single 128A spike (with a tiny bit of ringing)
thru the FETs when the battery goes high.

Using IRFP2907's I get a single 145A (or so) spike but then the
circuit oscillates at 0-14A thru each FET for the rest of the sim.

The transconductance of the 2907's is a lot higher than the 1405's so
that might explain the current oscillations. The gate voltages do
oscillate a bit for the sim using the 1405's but I guess they're not
sensitive enough for that to be a problem?

Gotta stomp that initial spike too but I can play with the model to
see how that might be done.

John
-- remove SPAMMENOT for e-mail responses --

 

[Winfield Hill]

John wrote...

I wasn't able to find the Spice model for the BZX84C2V7L zener but did
find a model for a BZX84C3V0LT1. Looked close enough (hopefully).

Running the sim gave me a huge voltage spike from the "battery" at
about 189.4mS. The voltage source indicates a linear rise from 0V to
12V starting at 200mS so I'm a bit confused about the timing. I'm
probably missing something somewhere though as I'm a SPICE newbie.

Using IRF1405's I get a single 128A spike (with a tiny bit of ringing)
thru the FETs when the battery goes high.

Using IRFP2907's I get a single 145A (or so) spike but then the
circuit oscillates at 0-14A thru each FET for the rest of the sim.

The transconductance of the 2907's is a lot higher than the 1405's so
that might explain the current oscillations. The gate voltages do
oscillate a bit for the sim using the 1405's but I guess they're not
sensitive enough for that to be a problem?

Gotta stomp that initial spike too but I can play with the model to
see how that might be done.

I've repeatedly said it here before on s.e.d., but I'll say it
again, spice power MOSFET models fail to account for operation
as linear circuit elements, where you're near or completely in
the "subthreshold" region, and they can therefore completely
goof up circuit modeling containing them. Measure your MOSFET's
transconductance curves (or measure Id vs Vgs) and compare this
to the spice model. Use Vds = 2V. At low currents you can use
continuous measurements - but use pulsed measurements at higher
currents, where the power dissipation exceeds say one watt.

After you see just how horrible the models are, you can use
Google to learn my solution, and that of others.

 

[Jim Thompson]

John wrote...

I've repeatedly said it here before on s.e.d., but I'll say it
again, spice power MOSFET models fail to account for operation
as linear circuit elements, where you're near or completely in
the "subthreshold" region, and they can therefore completely
goof up circuit modeling containing them. Measure your MOSFET's
transconductance curves (or measure Id vs Vgs) and compare this
to the spice model. Use Vds = 2V. At low currents you can use
continuous measurements - but use pulsed measurements at higher
currents, where the power dissipation exceeds say one watt.

After you see just how horrible the models are, you can use
Google to learn my solution, and that of others.

Or learn how to fit data to Level=7 models ;-)

...Jim Thompson

 

[Terry Given]

Or learn how to fit data to Level=7 models ;-)

...Jim Thompson

Or, better yet, convince the suppliers of discretes to part with such
models. Oh how we envy you your fab-level models

Cheers
Terry

 

[Jim Thompson]

Or, better yet, convince the suppliers of discretes to part with such
models. Oh how we envy you your fab-level models

Cheers
Terry

Awhile back I made a half-hearted attempt and scaled a Level=7
(monolithic) device up into the ampere range to show it could be done,
but Win didn't like it... complained about the ~0.8V threshold ;-)

...Jim Thompson

 

[Winfield Hill]

legg wrote...

I don't think the mosfet model is very relevent in getting first-order
performance of current surges which are dominated by either the op
amp slew rate or the gate circuit's ability to keep the gate pulled
below a threshold and the stray impedances of the voltage source,
depending upon the initial settings that set up bias on the gate.

Point taken, I didn't look, but there's the time-honored
case of servo-loop integrator windup to consider.

 

[Winfield Hill]

Jim Thompson wrote...

Awhile back I made a half-hearted attempt and scaled a Level=7
(monolithic) device up into the ampere range to show it could
be done, but Win didn't like it... complained about the ~0.8V
threshold ;-)

And an incorrectly-high transconductance. But those issues,
I imagine, could be easily fixed if one understood level 7
models. Perhaps you could give us a little tutorial?

 

[legg]

I wasn't able to find the Spice model for the BZX84C2V7L zener but did
find a model for a BZX84C3V0LT1. Looked close enough (hopefully).

Running the sim gave me a huge voltage spike from the "battery" at
about 189.4mS. The voltage source indicates a linear rise from 0V to
12V starting at 200mS so I'm a bit confused about the timing. I'm
probably missing something somewhere though as I'm a SPICE newbie.

Using IRF1405's I get a single 128A spike (with a tiny bit of ringing)
thru the FETs when the battery goes high.

Using IRFP2907's I get a single 145A (or so) spike but then the
circuit oscillates at 0-14A thru each FET for the rest of the sim.

The transconductance of the 2907's is a lot higher than the 1405's so
that might explain the current oscillations. The gate voltages do
oscillate a bit for the sim using the 1405's but I guess they're not
sensitive enough for that to be a problem?

Gotta stomp that initial spike too but I can play with the model to
see how that might be done.

Remember that battery terminal glitching is better modelled by a
switch, rather than by a changing voltage at the terminals.The voltage
source is low-z, regardless of its voltage, the contact intermittence
would be high z, outside of an arc.

I don't think the mosfet model is very relevent in getting first-order
performance of current surges which are dominated by either the op
amp slew rate or the gate circuit's ability to keep the gate pulled
below a threshold and the stray impedances of the voltage source,
depending upon the initial settings that set up bias on the gate.

RL.

 

[John]

I've repeatedly said it here before on s.e.d., but I'll say it

Never saw your earlier statements about MOSFET models so I'm glad you
were willing to say it again.

I'll be adding RL's circuit modofications to my prototype in a day or
two (crazy busy now) and will compare it to the sim. I will also do
the transconductance curve plotting then. It'll be good learnin' for
me.

I've also found your programmable slew rate controller (using
a programmable transconductance opamp) and everyone pretty well
everyone seems to have the LM13700 in stock. I also found Steven M.
Sandler and Charles E. Hymowitz's article in the May 2005 issue of
Power Electronics Technology with their updated SPICE model for a
MOSFET.

LOTS and lots to learn.
Thanks Win,
John
-- remove SPAMMENOT for e-mail responses --

 

[John]

Point taken, I didn't look, but there's the time-honored
I've also started taking a look at op-amp integrators and slew-rate
limiters.

John

-- remove SPAMMENOT for e-mail responses --

 

[Jim Thompson]

Jim Thompson wrote...

And an incorrectly-high transconductance. But those issues,
I imagine, could be easily fixed if one understood level 7
models. Perhaps you could give us a little tutorial?

I would except I'm not sure the extraction can be done by hand. There
are companies, for example, Silvaco, that just push the data into a
computer and their software "UTMOST" spits out the model.

It might be possible to do it with Excel. I'll give it some thought.

...Jim Thompson