Question for Win Hill

[Jim Thompson]

Win, What N-channel MOSFET do you recommend for:

VDS max = 50V

ID max = 10mA

Typical dissipation ~ 200mW

I know, I know, dumb question, but I don't normally use *any* discrete
devices.

...Jim Thompson

 

[Harry Dellamano]

Win, What N-channel MOSFET do you recommend for:

VDS max = 50V

ID max = 10mA

Typical dissipation ~ 200mW

I know, I know, dumb question, but I don't normally use *any* discrete
devices.

...Jim Thompson
--

Hey Jim,
I can handle any of Win's questions.
Depends how much you derate for HV but the 2N7002 in SMD or 2N7000 in
through hole are the most popular.
Happy Holidays,
Harry

 

[John Larkin]

Win, What N-channel MOSFET do you recommend for:

VDS max = 50V

ID max = 10mA

Typical dissipation ~ 200mW

I know, I know, dumb question, but I don't normally use *any* discrete
devices.

...Jim Thompson

Harry's right... 2N7000/7002. Want a bagful?

I've got a little circuit we just did; it outputs 0-60 volts into 50
ohms through a 1:1 isolation transformer, using 2N7002's. Tr is just
under 2 ns at 60 volts, under 1 ns at 5.

John

 

[Jim Thompson]

Harry's right... 2N7000/7002. Want a bagful?

I've got a little circuit we just did; it outputs 0-60 volts into 50
ohms through a 1:1 isolation transformer, using 2N7002's. Tr is just
under 2 ns at 60 volts, under 1 ns at 5.

John

Not yet. Right now all I needed was a number that was common. I'll
throw it into PSpice and see how it works out, then I might build one
up.

...Jim Thompson

 

[Leon Heller]

Win, What N-channel MOSFET do you recommend for:

VDS max = 50V

ID max = 10mA

Typical dissipation ~ 200mW

I know, I know, dumb question, but I don't normally use *any* discrete
devices.

Will I do, I'm not Win?

I use the Zetex ZVN4210A, when I need an N-channel MOSFET. The ZVN4210G is
similar, but SMT.

Leon

 

[Winfield Hill]

Hey Jim,
I can handle any of Win's questions.
Depends how much you derate for HV but the 2N7002 in SMD or 2N7000
in through hole are the most popular. Happy Holidays, Harry

and John Larkin answered:

Harry's right... 2N7000/7002. Want a bagful?

I've got a little circuit we just did; it outputs 0-60 volts into
50 ohms through a 1:1 isolation transformer, using 2N7002's.
Tr is just under 2 ns at 60 volts, under 1 ns at 5.

Jim Thompson responded...

Not yet. Right now all I needed was a number that was common.
I'll throw it into PSpice and see how it works out, then I might
build one up.

Hah! It appears Harry and John can handle my questions just fine.
Normally I'd respond by building on their fine answers, but my P4
WinXP home computer with its datasheet collection, is dead, despite
considerable efforts to revive it, including an AMD Athlon64 3500+
mobo transplant. <sigh>

The 2n7000 / 2n7002 parts are my jellybeans for low-power use, and
they work well. The 2n7000 became popular after the Supertex VN01,
a small MOSFET we featured in AoE. VP01 is its p-channel mate.

There are some larger alternates that may be preferred in production
because they have higher gate capacitance and are therefore a little
less vulnerable to static damage in handling.

Jim, I should warn you that spice models for these VMOS FETs are
woefully inadequate, failing to correctly model the gate spreading
resistance, the important sub-threshold region, or even the cascode
JFET drain-capacitance scene for that matter. They also lack any
reliable thermal model. Modest analytical calculations can often
better predict a MOSFET's performance under unusual circumstances.

 

[HARRY DELLAMANO]

Hah! It appears Harry and John can handle my questions just fine.
Normally I'd respond by building on their fine answers, but my P4
WinXP home computer with its datasheet collection, is dead, despite
considerable efforts to revive it, including an AMD Athlon64 3500+
mobo transplant. <sigh>

Hey Win, thanks for the kind words.
Tell me about your Athlon64 3500+. I have been plugging along with a Athlon
XP 2700+ (32 BIT) for the last two years and thinking about upgrading to
64. Is it any faster for SPICE sims when operating properly?
Highest regards,
Harry

 

[Jim Thompson]

Hey Win, thanks for the kind words.
Tell me about your Athlon64 3500+. I have been plugging along with a Athlon
XP 2700+ (32 BIT) for the last two years and thinking about upgrading to
64. Is it any faster for SPICE sims when operating properly?
Highest regards,
Harry

I have a 6-month-old Athlon64 3400+ (2.2G clock), 1GB Ram.

It is more than twice as fast as my last 1.6G P3.

BTW: P4's are _terrible_ for Spice, since Intel did away with
math-specific core... A 1G P3 is faster than a 2G P4 doing Spice.

...Jim Thompson

 

[Winfield Hill]

Jim Thompson wrote...

I have a 6-month-old Athlon64 3400+ (2.2G clock), 1GB Ram.
It is more than twice as fast as my last 1.6G P3.
BTW: P4's are _terrible_ for Spice, since Intel did away with
math-specific core... A 1G P3 is faster than a 2G P4 doing Spice.

Plus the P4's longer pipeline was very damaging. I was running a
3GHz P4, which seemed pretty snappy at Spice. However I do expect
my Athlon64 to do much better. I selected it in part because of the
"no execute" feature implemented in SP2. And was getting tired of
the increasingly power-hungry Intel processors. I have high hopes
for my 939-pin Athlon64, and I look forward to upgrading to one of
the other advanced 939-pin processors once they come down in price.

Jim, what are you working on with your little 50V 0.2W MOSFET?

 

[Jim Thompson]

Jim Thompson wrote...

Plus the P4's longer pipeline was very damaging. I was running a
3GHz P4, which seemed pretty snappy at Spice. However I do expect
my Athlon64 to do much better. I selected it in part because of the
"no execute" feature implemented in SP2. And was getting tired of
the increasingly power-hungry Intel processors. I have high hopes
for my 939-pin Athlon64, and I look forward to upgrading to one of
the other advanced 939-pin processors once they come down in price.

Jim, what are you working on with your little 50V 0.2W MOSFET?

I see so much trash audio here, that, in my "spare time", I decided I
would design an audio amplifier... class AB, but no bias pot
required... and, contrary to my thinking BJTs are better, it will be
power MOSFET output... the little device is for bias... all done just
to prove I can do it better ;-)

...Jim Thompson

 

[Tim Wescott]

I see so much trash audio here, that, in my "spare time", I decided I
would design an audio amplifier... class AB, but no bias pot
required... and, contrary to my thinking BJTs are better, it will be
power MOSFET output... the little device is for bias... all done just
to prove I can do it better ;-)

...Jim Thompson

Will it have the obligatory "audiophile" explanations about how _your_
way of sacrificing a chicken to the audio gods is better than anyone
else's, and that's why it sounds better?

Perhaps you should cryogenicaly treat the PC boards, so the crystalline
structure of the copper on the traces is better aligned? Oh! and use
teflon boards 'cause they're less dissipative of that important high
frequency (1GHz) content?

Don't forget the LN2-dipped wall plugs for the listening room --
http://www.jenatek.com/pages/powercords.html; search on "outlet".

Or are you just going to make some lame claim that it's better 'cause
you actually know what you're doing with the materials at hand?

 

[Jim Thompson]

Jim Thompson wrote:
[snip]

I see so much trash audio here, that, in my "spare time", I decided I
would design an audio amplifier... class AB, but no bias pot
required... and, contrary to my thinking BJTs are better, it will be
power MOSFET output... the little device is for bias... all done just
to prove I can do it better ;-)

...Jim Thompson

[snip]

Or are you just going to make some lame claim that it's better 'cause
you actually know what you're doing with the materials at hand?

"Sounds" good to me ;-)

I may even use lamp cord to connect the speakers.

...Jim Thompson

 

[Winfield Hill]

Jim Thompson wrote...

I see so much trash audio here, that, in my "spare time", I decided
I would design an audio amplifier... class AB, but no bias pot
required... and, contrary to my thinking BJTs are better, it will
be power MOSFET output... the little device is for bias... all done
just to prove I can do it better ;-)

Well, then surely you'll want viable Spice MOSFET models, because
you'll be using the FETs throughout their useful linear range, and
the output-stage crossover region is critical.

Sadly most standard Spice library VMOS models simply don't do the
subthreshold linear region. For example, see the 10-decade plots
on page 123 of our book. A jellybean 2n7000 is rather similar to
the VN01 that we show in figure 3.14, and certainly a proper Spice
model should be able to make that plot. But I'd be surprised if
your standard Spice libraries work properly below say 5 to 20mA,
which is not that far below the FET's maximum current. Keep in
mind that linear power FET circuitry always operates well below
the maximum rated FET switching current, to keep power dissipation
junction heating under control.

The bottom line is you'll have to start your FET-amplifier design
exercise by designing some decent FET models. Let us know what you
come up with.

 

[Mark Jones]

Will it have the obligatory "audiophile" explanations about how _your_
way of sacrificing a chicken to the audio gods is better than anyone
else's, and that's why it sounds better?

Perhaps you should cryogenicaly treat the PC boards, so the crystalline
structure of the copper on the traces is better aligned? Oh! and use
teflon boards 'cause they're less dissipative of that important high
frequency (1GHz) content?

Don't forget the LN2-dipped wall plugs for the listening room --
http://www.jenatek.com/pages/powercords.html; search on "outlet".

Or are you just going to make some lame claim that it's better 'cause
you actually know what you're doing with the materials at hand?

Wow Tim... You really have no idea who Jim is, do you?

A photo of Jim, 35 years ago:
http://www.viaarena.com/htmlimages/macho.jpg

 

[John Woodgate]

I read in sci.electronics.design that Jim Thompson

I may even use lamp cord to connect the speakers.

Provided you design the loudspeakers WITH the lamp cord leads,
everything will be OK.

 

[Jim Thompson]

Jim Thompson wrote...

Well, then surely you'll want viable Spice MOSFET models, because
you'll be using the FETs throughout their useful linear range, and
the output-stage crossover region is critical.

Sadly most standard Spice library VMOS models simply don't do the
subthreshold linear region. For example, see the 10-decade plots
on page 123 of our book. A jellybean 2n7000 is rather similar to
the VN01 that we show in figure 3.14, and certainly a proper Spice
model should be able to make that plot. But I'd be surprised if
your standard Spice libraries work properly below say 5 to 20mA,
which is not that far below the FET's maximum current. Keep in
mind that linear power FET circuitry always operates well below
the maximum rated FET switching current, to keep power dissipation
junction heating under control.

The bottom line is you'll have to start your FET-amplifier design
exercise by designing some decent FET models. Let us know what you
come up with.

Win, Here's a bunch of models. Which would you recommend?

Anasoft-1:

..SUBCKT 2N7000/PLP_XN _ssi_pin0_1 _ssi_pin1_2 _ssi_pin2_3
Cgs 2 3 12.3E-12
V_ssi_pin2 _ssi_pin2_3 3 0
V_ssi_pin1 _ssi_pin1_2 2 0
V_ssi_pin0 _ssi_pin0_1 1 0
Cgd1 2 4 27.4E-12
Cgd2 1 4 6E-12
M1 1 2 3 3 MOST1
M2 4 2 1 3 MOST2
D1 3 1 Dbody
..MODEL MOST1 NMOS(Level=3 Kp=20.78u W=9.7m L=2u Rs=20m Vto=2 Rd=1.186)
..MODEL MOST2 NMOS(VTO=-4.73 Kp=20.78u W=9.7m L=2u Rs=20m)
..MODEL Dbody D(Is=125f N=1.023 Rs=1.281 Ikf=18.01 Cjo=46.3p M=.3423
+ Vj=.4519 Bv=60 Ibv=10u Tt=161.6n)
..ENDS

Anasoft-2:

..SUBCKT 2N7000_XN _ssi_pin0_3 _ssi_pin1_4 _ssi_pin2_5
* Nodes D G S
V_ssi_pin2 _ssi_pin2_5 5 0
V_ssi_pin1 _ssi_pin1_4 4 0
V_ssi_pin0 _ssi_pin0_3 3 0
M1 3 2 5 5 MOD1
RG 4 2 343
RL 3 5 6E6
C1 2 5 23.5P
C2 3 2 4.5P
D1 5 3 DIODE1
*
..MODEL MOD1 NMOS VTO=2.474 RS=1.68 RD=0.0 IS=1E-15 KP=0.296
+CBD=53.5P PB=1 LAMBDA=267E-6
..MODEL DIODE1 D IS=1.254E-13 N=1.0207 RS=0.222
..ENDS 2N7000

Supertex

..MODEL 2N7000 NMOS (LEVEL=3 RS=0.205 NSUB=1.0E15
+DELTA=0.1 KAPPA=0.0506 TPG=1 CGDO=3.1716E-9
+RD=0.239 VTO=1.000 VMAX=1.0E7 ETA=0.0223089
+NFS=6.6E10 TOX=1.0E-7 LD=1.698E-9 UO=862.425
+XJ=6.4666E-7 THETA=1.0E-5 CGSO=9.09E-9 L=2.5E-6
+W=0.8E-2)
..ENDS

Philips:

..SUBCKT 2N7000/PLP 1 2 3
Cgs 2 3 12.3E-12
Cgd1 2 4 27.4E-12
Cgd2 1 4 6E-12
M1 1 2 3 3 MOST1
M2 4 2 1 3 MOST2
D1 3 1 Dbody
..MODEL MOST1 NMOS(Level=3 Kp=20.78u W=9.7m L=2u Rs=20m Vto=2 Rd=1.186)
..MODEL MOST2 NMOS(VTO=-4.73 Kp=20.78u W=9.7m L=2u Rs=20m)
..MODEL Dbody D(Is=125f N=1.023 Rs=1.281 Ikf=18.01 Cjo=46.3p M=.3423
+ Vj=.4519 Bv=60 Ibv=10u Tt=161.6n)
..ENDS

Ancient MicroSim:

..model M2n7000 NMOS(Level=3 Gamma=0 Delta=0 Eta=0 Theta=0 Kappa=0.2
+ Vmax=0 Xj=0 Tox=2u Uo=600 Phi=.6 Kp=1.073u W=.12 L=2u Rs=20m
+ Vto=1.73 Rd=.5489 Rds=48MEG Cgso=73.61p Cgdo=6.487p Cbd=74.46p Mj=.5
+ Pb=.8 Fc=.5 Rg=546.2 Is=10f N=1 Rb=1m)

Zetex:

..SUBCKT M2N7000/ZTX 3 4 5
* Nodes D G S
M1 3 2 5 5 MOD1
RG 4 2 343
RL 3 5 6E6
D1 5 3 DIODE1
..MODEL MOD1 NMOS VTO=2.474 RS=1.68 RD=0.0 IS=1E-15 KP=0.296
+CGSO=23.5P CGDO=4.5P CBD=53.5P PB=1 LAMBDA=267E-6
..MODEL DIODE1 D IS=1.254E-13 N=1.0207 RS=0.222
..ENDS

...Jim Thompson

 

[Winfield Hill]

Jim Thompson wrote...

Win, Here's a bunch of models. Which would you recommend?

Anasoft-1:
Anasoft-2:
Supertex
Philips:
Ancient MicroSim:
Zetex:

Oops, I asked for that one! OK, good question, I'll retire and
consider it. But *First* I have to get my Athlon64 running, so
I can play with your selection of models, plus a few I have.
It's a good and fair question you asked. Thanks, I think!

 

[John Larkin]

Jim Thompson wrote...

Well, then surely you'll want viable Spice MOSFET models, because
you'll be using the FETs throughout their useful linear range, and
the output-stage crossover region is critical.

Sadly most standard Spice library VMOS models simply don't do the
subthreshold linear region. For example, see the 10-decade plots
on page 123 of our book. A jellybean 2n7000 is rather similar to
the VN01 that we show in figure 3.14, and certainly a proper Spice
model should be able to make that plot. But I'd be surprised if
your standard Spice libraries work properly below say 5 to 20mA,
which is not that far below the FET's maximum current. Keep in
mind that linear power FET circuitry always operates well below
the maximum rated FET switching current, to keep power dissipation
junction heating under control.

The bottom line is you'll have to start your FET-amplifier design
exercise by designing some decent FET models. Let us know what you
come up with.

Weird. Last few power amps I designed, I didn't simulate anything.

John

 

[Jim Thompson]

On 31 Dec 2004 10:58:23 -0800, Winfield Hill


Weird. Last few power amps I designed, I didn't simulate anything.

John

Actually the last audio amplifier I designed was doodled on paper,
built on a hand-painted PCB, and worked first time powered-up.

That would have been 1977 when I bought my first 280Z.

I bought a good Pioneer tuner and added my own design bridge amps to
give a little "boost" to the audio ;-)

...Jim Thompson

 

[Winfield Hill]

John Larkin wrote...

Weird. Last few power amps I designed, I didn't simulate anything.

Right, it's more fun to do the various calculations than to run a
boring simulation. But next comes the point where one has to either
get out the drill and soldering iron, or procrastinate by firing up
Spice to test the design. I assume that's Jim's position, because
he wrote, "I'll throw it into PSpice and see how it works out, then
I might build one up." Well, that's when Spice becomes interesting.
If it can be believed, that is. Hmm, does the tool test the design,
or does the design test the tool?