AoE x-Chapters, using power MOSFETs as linear transistors

W

Winfield Hill

Guest
DRAFT copy of a useful section in the upcoming
AoE x-Chapters, about using power MOSFETs as
linear transistors. Subthreshold region, etc.
Comments, errors found, etc. Thanks!

https://www.dropbox.com/s/0ph15moamo0mlt4/3x.5_MOSFETs_Linear-Transistors_DRAFT.pdf?dl=1


--
Thanks,
- Win
 
On 24 Jul 2019 07:59:31 -0700, Winfield Hill <winfieldhill@yahoo.com>
wrote:

DRAFT copy of a useful section in the upcoming
AoE x-Chapters, about using power MOSFETs as
linear transistors. Subthreshold region, etc.
Comments, errors found, etc. Thanks!

https://www.dropbox.com/s/0ph15moamo0mlt4/3x.5_MOSFETs_Linear-Transistors_DRAFT.pdf?dl=1

These x-chapters look like they will be great, classic stuff for
decades. A bit different audience than AoE probably.

Back when we were in the NMR gradient driver business, we ran
switcher-type mosfets as constant-current linear amps, with PPM levels
of settling and noise; one box had 20 KW peak output. We just wrapped
an opamp around each fet to hide all the sub-threshold complexities.

What we couldn't hide was blowing up the fets in the far corners of
the SOAR graph. That involved a lot of testing behind protective
plexiglas sheets to absorb the shrapnel.

https://www.dropbox.com/s/4nxm7m2q3j3buvc/ExFets.jpg?raw=1

Some presumably switching fets were just a lot better as linear amps
than most.

MRI gradient amps are usually switchers, but they are too slow and
noisy for NMR.



--

John Larkin Highland Technology, Inc

lunatic fringe electronics
 
On 24/07/2019 3:59 pm, Winfield Hill wrote:
DRAFT copy of a useful section in the upcoming
AoE x-Chapters, about using power MOSFETs as
linear transistors. Subthreshold region, etc.
Comments, errors found, etc. Thanks!

https://www.dropbox.com/s/0ph15moamo0mlt4/3x.5_MOSFETs_Linear-Transistors_DRAFT.pdf?dl=1

Thanks. The M1 mosfet symbol used in fig 3x.44 looks wrong.

piglet
 
On Wed, 24 Jul 2019 08:43:15 -0700, John Larkin
<jjlarkin@highlandtechnology.com> wrote:

On 24 Jul 2019 07:59:31 -0700, Winfield Hill <winfieldhill@yahoo.com
wrote:

DRAFT copy of a useful section in the upcoming
AoE x-Chapters, about using power MOSFETs as
linear transistors. Subthreshold region, etc.
Comments, errors found, etc. Thanks!

https://www.dropbox.com/s/0ph15moamo0mlt4/3x.5_MOSFETs_Linear-Transistors_DRAFT.pdf?dl=1

These x-chapters look like they will be great, classic stuff for
decades. A bit different audience than AoE probably.

Back when we were in the NMR gradient driver business, we ran
switcher-type mosfets as constant-current linear amps, with PPM levels
of settling and noise; one box had 20 KW peak output. We just wrapped
an opamp around each fet to hide all the sub-threshold complexities.

What we couldn't hide was blowing up the fets in the far corners of
the SOAR graph. That involved a lot of testing behind protective
plexiglas sheets to absorb the shrapnel.

https://www.dropbox.com/s/4nxm7m2q3j3buvc/ExFets.jpg?raw=1

Some presumably switching fets were just a lot better as linear amps
than most.

MRI gradient amps are usually switchers, but they are too slow and
noisy for NMR.

Couldn't find the Ixis 4000V IXTx03N400 part on their site but they
also don't seem to allow searching by Vds parameter.

In the list, footnote a says first sorted by Vds and then die size.
Die size meaning power dissipation I presume which are relatable to
each other...

I also notice the applications are strictly small signal and not power
like for audio power amplifiers ?

Anything about paralleling mosfets in linear mode ? (I may just not
have looked closely enough)
 
"Winfield Hill" wrote in message news:qh9roj0fdi@drn.newsguy.com...

DRAFT copy of a useful section in the upcoming
AoE x-Chapters, about using power MOSFETs as
linear transistors. Subthreshold region, etc.
Comments, errors found, etc. Thanks!

https://www.dropbox.com/s/0ph15moamo0mlt4/3x.5_MOSFETs_Linear-Transistors_DRAFT.pdf?dl=1

Well, Win.... I would be interested in how well your mosfet data could be
fitted to the DMOS extension that models subthreshold shown here

http://www.anasoft.co.uk/MOS1Model.htm

Also, the fit to the capacitances of the above model would be useful as
well...and indeed the Quasi sat region as well. I don't really do any real
physical work anymore, its all on that expensive Cadence suite...


-- Kevin Aylward
http://www.anasoft.co.uk - SuperSpice
http://www.kevinaylward.co.uk/ee/index.html
 
On 7/24/19 10:59 AM, Winfield Hill wrote:
DRAFT copy of a useful section in the upcoming
AoE x-Chapters, about using power MOSFETs as
linear transistors. Subthreshold region, etc.
Comments, errors found, etc. Thanks!

https://www.dropbox.com/s/0ph15moamo0mlt4/3x.5_MOSFETs_Linear-Transistors_DRAFT.pdf?dl=1

Do you have anything in the X or AoE III (sorry, don't have a copy yet,
just my well-worn AoE II) on low-voltage current sources? JFETs in
linear region, depletion MOSFETs, etc?

This old chestnut works okay in some situations down to ~2 volts it kind
of sucks the lemon wrt tempco and output impedance, though:

<https://tinyurl.com/yxn7mej4>
 
On Wed, 24 Jul 2019 18:01:51 -0400, bitrex <user@example.net> wrote:

On 7/24/19 10:59 AM, Winfield Hill wrote:
DRAFT copy of a useful section in the upcoming
AoE x-Chapters, about using power MOSFETs as
linear transistors. Subthreshold region, etc.
Comments, errors found, etc. Thanks!

https://www.dropbox.com/s/0ph15moamo0mlt4/3x.5_MOSFETs_Linear-Transistors_DRAFT.pdf?dl=1



Do you have anything in the X or AoE III (sorry, don't have a copy yet,
just my well-worn AoE II) on low-voltage current sources? JFETs in
linear region, depletion MOSFETs, etc?

This old chestnut works okay in some situations down to ~2 volts it kind
of sucks the lemon wrt tempco and output impedance, though:

https://tinyurl.com/yxn7mej4

For low currents, this works pretty well:

https://www.dropbox.com/s/d4ntmq7fdzah69a/LED_Isrc_data.JPG?raw=1

The tempcos track nicely, as long as the transistor doesn't self-heat
much.

There are a bunch of IC current limiters around now.




--

John Larkin Highland Technology, Inc
picosecond timing precision measurement

jlarkin att highlandtechnology dott com
http://www.highlandtechnology.com
 
Am 25.07.19 um 00:20 schrieb John Larkin:
On Wed, 24 Jul 2019 18:01:51 -0400, bitrex <user@example.net> wrote:

On 7/24/19 10:59 AM, Winfield Hill wrote:
DRAFT copy of a useful section in the upcoming
AoE x-Chapters, about using power MOSFETs as
linear transistors. Subthreshold region, etc.
Comments, errors found, etc. Thanks!

https://www.dropbox.com/s/0ph15moamo0mlt4/3x.5_MOSFETs_Linear-Transistors_DRAFT.pdf?dl=1



Do you have anything in the X or AoE III (sorry, don't have a copy yet,
just my well-worn AoE II) on low-voltage current sources? JFETs in
linear region, depletion MOSFETs, etc?

This old chestnut works okay in some situations down to ~2 volts it kind
of sucks the lemon wrt tempco and output impedance, though:

https://tinyurl.com/yxn7mej4


For low currents, this works pretty well:

https://www.dropbox.com/s/d4ntmq7fdzah69a/LED_Isrc_data.JPG?raw=1

The tempcos track nicely, as long as the transistor doesn't self-heat
much.

There are a bunch of IC current limiters around now.

If noise plays a role, don't use Osram, use Avago HLMP-6000.
(as long as Broadcom does not kill it.)

<
https://www.flickr.com/photos/137684711@N07/24354944411/in/album-72157662535945536/
>

I'm preparing an article "The Silence Of The Lamps" :)
The HLMP6000 is quite dark. I have the gut feeling: the brighter, the
more noise.

cheers, Gerhard
 
On Thu, 25 Jul 2019 00:49:17 +0200, Gerhard Hoffmann <dk4xp@arcor.de>
wrote:

Am 25.07.19 um 00:20 schrieb John Larkin:
On Wed, 24 Jul 2019 18:01:51 -0400, bitrex <user@example.net> wrote:

On 7/24/19 10:59 AM, Winfield Hill wrote:
DRAFT copy of a useful section in the upcoming
AoE x-Chapters, about using power MOSFETs as
linear transistors. Subthreshold region, etc.
Comments, errors found, etc. Thanks!

https://www.dropbox.com/s/0ph15moamo0mlt4/3x.5_MOSFETs_Linear-Transistors_DRAFT.pdf?dl=1



Do you have anything in the X or AoE III (sorry, don't have a copy yet,
just my well-worn AoE II) on low-voltage current sources? JFETs in
linear region, depletion MOSFETs, etc?

This old chestnut works okay in some situations down to ~2 volts it kind
of sucks the lemon wrt tempco and output impedance, though:

https://tinyurl.com/yxn7mej4


For low currents, this works pretty well:

https://www.dropbox.com/s/d4ntmq7fdzah69a/LED_Isrc_data.JPG?raw=1

The tempcos track nicely, as long as the transistor doesn't self-heat
much.

There are a bunch of IC current limiters around now.

If noise plays a role, don't use Osram, use Avago HLMP-6000.
(as long as Broadcom does not kill it.)


https://www.flickr.com/photos/137684711@N07/24354944411/in/album-72157662535945536/


I'm preparing an article "The Silence Of The Lamps" :)
The HLMP6000 is quite dark. I have the gut feeling: the brighter, the
more noise.

cheers, Gerhard

But the Osram orange is so pretty.


--

John Larkin Highland Technology, Inc
picosecond timing precision measurement

jlarkin att highlandtechnology dott com
http://www.highlandtechnology.com
 
In article <qh9roj0fdi@drn.newsguy.com>,
Winfield Hill <winfieldhill@yahoo.com> wrote:
DRAFT copy of a useful section in the upcoming
AoE x-Chapters, about using power MOSFETs as
linear transistors. Subthreshold region, etc.
Comments, errors found, etc. Thanks!

https://www.dropbox.com/s/0ph15moamo0mlt4/3x.5_MOSFETs_Linear-Transistors_DRAFT.pdf?dl=1

Nice - thanks!

It might be well worthwhile to have a discussion of the thermal/SOA
issues involved in using power V-MOSFETs in linear applications where
they may be called upon to dissipate a significant amount of power (I
can't recall if this is discussed in detail in the MOSFET section of
the new AoE)... if so, recapping or expanding on it might be helpful.
 
Dave Platt wrote...
In article <qh9roj0fdi@drn.newsguy.com>,
Winfield Hill <winfieldhill@yahoo.com> wrote:
DRAFT copy of a useful section in the upcoming
AoE x-Chapters, about using power MOSFETs as
linear transistors. Subthreshold region, etc.
Comments, errors found, etc. Thanks!

https://www.dropbox.com/s/0ph15moamo0mlt4/3x.5_MOSFETs_Linear-Transistors_DRAFT.pdf?dl=1

Nice - thanks!

It might be well worthwhile to have a discussion of the thermal/SOA
issues involved in using power V-MOSFETs in linear applications where
they may be called upon to dissipate a significant amount of power (I
can't recall if this is discussed in detail in the MOSFET section of
the new AoE)... if so, recapping or expanding on it might be helpful.

Yes, you are correct. That has been requested,
in a rather coherent manner, and it's on my short
list. I have three more weeks to add more stuff.


--
Thanks,
- Win
 
bitrex wrote...
On 7/24/19 10:59 AM, Winfield Hill wrote:
DRAFT copy of a useful section in the upcoming
AoE x-Chapters, about using power MOSFETs as
linear transistors. Subthreshold region, etc.
Comments, errors found, etc. Thanks!

https://www.dropbox.com/s/0ph15moamo0mlt4/3x.5_MOSFETs_Linear-Transistors_DRAFT.pdf?dl=1

Do you have anything in the X or AoE III (sorry, don't have a copy yet,
just my well-worn AoE II) on low-voltage current sources? JFETs in
linear region, depletion MOSFETs, etc?

This old chestnut works okay in some situations down to ~2 volts it kind
of sucks the lemon wrt tempco and output impedance, though:

https://tinyurl.com/yxn7mej4

We don't go much into the region below a few volts.
But note that a BJT works well down to Vce = 200mV.

BTW, you should really get AoE III, you'll enjoy it.


--
Thanks,
- Win
 
Kevin Aylward wrote...
"Winfield Hill" wrote in message news:qh9roj0fdi@drn.newsguy.com...

DRAFT copy of a useful section in the upcoming
AoE x-Chapters, about using power MOSFETs as
linear transistors. Subthreshold region, etc.
Comments, errors found, etc. Thanks!

https://www.dropbox.com/s/0ph15moamo0mlt4/3x.5_MOSFETs_Linear-Transistors_DRAFT.pdf?dl=1

Well, Win.... I would be interested in how well your mosfet
data could be fitted to the DMOS extension that models
subthreshold shown here

http://www.anasoft.co.uk/MOS1Model.htm

Thanks, Kevin, I'll have to study your material.

> Also, the fit to the capacitances of the above model ...

Although we show one company's attempt at SPICE
modeling capacitance, it's an area I've stayed away
from. I've been happy to model HV amplifiers in the
region well away from the supply rails, where I can
simply use a fixed value appropriate to the region.


--
Thanks,
- Win
 
piglet wrote...
On 24/07/2019 3:59 pm, Winfield Hill wrote:
DRAFT copy of a useful section in the upcoming
AoE x-Chapters, about using power MOSFETs as
linear transistors. Subthreshold region, etc.
Comments, errors found, etc. Thanks!

https://www.dropbox.com/s/0ph15moamo0mlt4/3x.5_MOSFETs_Linear-Transistors_DRAFT.pdf?dl=1

Thanks. The M1 mosfet symbol used in fig 3x.44
looks wrong.

Thanks, you are correct!


--
Thanks,
- Win
 
boB wrote...
Couldn't find the Ixis 4000V IXTx03N400 part on their site
but they also don't seem to allow searching by Vds parameter.

The column "Part Number" had a footnote marker, "x".

(x) replace the symbol “x” with the corresponding
upper-case package letter in the “Packages” columns.

The package columns had characters: P A Y U H, etc.
Substitute the character in the IXTx03N400 and get,
e.g., IXTH03N400 for the TO-247 package. That's a
4kV part, nice! Oops, Littelfuse has now taken over
IXYS, and it appears that part has gone! But Google
will still show you its datasheet.

I also notice the applications are strictly small
signal and not power like for audio power amplifiers?

Well, we do deal with high power, but as stated,
these are HV amp, rather than audio amp oriented.

> Anything about paralleling mosfets in linear mode ?

No, that's not an easy subject. Source resistors...


--
Thanks,
- Win
 
Winfield Hill wrote...
boB wrote...

Couldn't find the Ixis 4000V IXTx03N400 part on their site
but they also don't seem to allow searching by Vds parameter.

The column "Part Number" had a footnote marker, "x".

(x) replace the symbol “x” with the corresponding
upper-case package letter in the “Packages” columns.

The package columns has characters: P A Y U H, etc.
Substitute the character in the IXTx03N400 and get,
e.g., IXTH03N400 for the TO-247 package. That's a
4kV part, nice! Oops, Littelfuse has now taken over
IXYS, and it appears that part has gone! But Google
will still show you its datasheet.

The Littelfuse website is a mess. But you can find
the IXYS HV MOSFET parts here (2500 to 4700 volts):
https://www.littelfuse.com/products/power-semiconductors/discrete-mosfets/n-channel-standard/very-high-voltage.aspx

They may have replaced 4kV parts with 4.5kV parts.


--
Thanks,
- Win
 
On 24 Jul 2019 17:54:01 -0700, Winfield Hill <winfieldhill@yahoo.com>
wrote:

boB wrote...

Couldn't find the Ixis 4000V IXTx03N400 part on their site
but they also don't seem to allow searching by Vds parameter.

The column "Part Number" had a footnote marker, "x".

(x) replace the symbol “x” with the corresponding
upper-case package letter in the “Packages” columns.

The package columns had characters: P A Y U H, etc.
Substitute the character in the IXTx03N400 and get,
e.g., IXTH03N400 for the TO-247 package. That's a
4kV part, nice! Oops, Littelfuse has now taken over
IXYS, and it appears that part has gone! But Google
will still show you its datasheet.

I also notice the applications are strictly small
signal and not power like for audio power amplifiers?

Well, we do deal with high power, but as stated,
these are HV amp, rather than audio amp oriented.

Anything about paralleling mosfets in linear mode ?

No, that's not an easy subject. Source resistors...

Just like bipolar transistor paralleling.

Thanks
 
On 25/07/2019 00:59, Winfield Hill wrote:
DRAFT copy of a useful section in the upcoming
AoE x-Chapters, about using power MOSFETs as
linear transistors. Subthreshold region, etc.
Comments, errors found, etc. Thanks!

https://www.dropbox.com/s/0ph15moamo0mlt4/3x.5_MOSFETs_Linear-Transistors_DRAFT.pdf?dl=1

p187 "drain current of 10 Âľ V at a drain voltage of 0.1V"
uV should be uA


You did mention in the main AOE3 book some stuff about the DC SOA of
power MOSFETs at high VDS. I mean the region where part of the die can
hog current and melt, (due to negative temperature coefficient of Vth
and consequent positive tempco of ID and power density, for each region
of the die). In the main book I think you also mentioned the related
issue of current hogging between MOSFETs in separate packages, due to
the same tempco problems. Perhaps you'd consider expanding on that topic
or at least referring to it in this X-chapter.
 
On 7/25/19 1:10 PM, bitrex wrote:
On 7/24/19 6:20 PM, John Larkin wrote:
On Wed, 24 Jul 2019 18:01:51 -0400, bitrex <user@example.net> wrote:

On 7/24/19 10:59 AM, Winfield Hill wrote:
DRAFT copy of a useful section in the upcoming
AoE x-Chapters, about using power MOSFETs as
linear transistors.  Subthreshold region, etc.
Comments, errors found, etc.  Thanks!

https://www.dropbox.com/s/0ph15moamo0mlt4/3x.5_MOSFETs_Linear-Transistors_DRAFT.pdf?dl=1




Do you have anything in the X or AoE III (sorry, don't have a copy yet,
just my well-worn AoE II) on low-voltage current sources? JFETs in
linear region, depletion MOSFETs, etc?

This old chestnut works okay in some situations down to ~2 volts it kind
of sucks the lemon wrt tempco and output impedance, though:

https://tinyurl.com/yxn7mej4


For low currents, this works pretty well:

https://www.dropbox.com/s/d4ntmq7fdzah69a/LED_Isrc_data.JPG?raw=1

The tempcos track nicely, as long as the transistor doesn't self-heat
much.

There are a bunch of IC current limiters around now.





I have a client who wants low-voltage oscillator (~2 volts) with very
low Q "meander" inductors, printed on a piece of flexible plastic film
or something. The inductance varies as the film is compressed or
deformed and hence the oscillator frequency.

The self-resonant frequency of these is around 100MHz, at 10MHz probably
like 4uH with 100 ohm ESR and 10p parallel capacitance
 
On 7/24/19 6:20 PM, John Larkin wrote:
On Wed, 24 Jul 2019 18:01:51 -0400, bitrex <user@example.net> wrote:

On 7/24/19 10:59 AM, Winfield Hill wrote:
DRAFT copy of a useful section in the upcoming
AoE x-Chapters, about using power MOSFETs as
linear transistors. Subthreshold region, etc.
Comments, errors found, etc. Thanks!

https://www.dropbox.com/s/0ph15moamo0mlt4/3x.5_MOSFETs_Linear-Transistors_DRAFT.pdf?dl=1



Do you have anything in the X or AoE III (sorry, don't have a copy yet,
just my well-worn AoE II) on low-voltage current sources? JFETs in
linear region, depletion MOSFETs, etc?

This old chestnut works okay in some situations down to ~2 volts it kind
of sucks the lemon wrt tempco and output impedance, though:

https://tinyurl.com/yxn7mej4


For low currents, this works pretty well:

https://www.dropbox.com/s/d4ntmq7fdzah69a/LED_Isrc_data.JPG?raw=1

The tempcos track nicely, as long as the transistor doesn't self-heat
much.

There are a bunch of IC current limiters around now.

I have a client who wants low-voltage oscillator (~2 volts) with very
low Q "meander" inductors, printed on a piece of flexible plastic film
or something. The inductance varies as the film is compressed or
deformed and hence the oscillator frequency.

Not an insurmountable problem but I'm a bit stumped for a temperature
stable current source down there.
 

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