AoE x-Chapters, using power MOSFETs as linear transistors

[Winfield Hill]

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

[John Larkin]

Post by Winfield Hill
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.

Loading Image...

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.

[boB]

On Wed, 24 Jul 2019 08:43:15 -0700, John Larkin

Post by John Larkin

Post by Winfield Hill
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]

boB wrote...

Post by boB
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.

Post by boB
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.

Post by boB
Anything about paralleling mosfets in linear mode ?

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

[Winfield Hill]

Winfield Hill wrote...

Post by Winfield Hill
boB wrote...

Post by boB
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.

[boB]

Post by Winfield Hill
boB wrote...

Post by boB
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.

Post by boB
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.

Post by boB
Anything about paralleling mosfets in linear mode ?

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

Just like bipolar transistor paralleling.

Thanks

[John Miles, KE5FX]

Post by Winfield Hill
No, that's not an easy subject. Source resistors...

Hey, if you guys don't cover it, who will? If it were easy, nobody
would look to you for hints. :)

Bob Cordell brings up a few points in his book on audio power
amps that you could repeat, or perhaps reference in the bibliography.
E.g., source resistors alone may not be enough to make up for poorly-
matched FETs, but FETs from the same manufacturing lot are usually
easy to match. Lateral MOS behaves (very) differently than VMOS
due to its tempco, but lateral parts are expensive and hard to come by.
Gate resistors are more important than usual when paralleling FETs due
to their tendency to oscillate, but there goes your phase response.

He suggests Zobel networks between the gate and drain terminals as an
alternative. He also references a note on stability of paralleled
FETs by Ed Oxner that I can't find.

-- john, KE5FX

[Phil Allison]

Post by John Larkin
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.

** However, Larkin failed to do the *bleeding obvious thing* and use MOSFETs characterised for liner operation - ie Lateral types as made by Hitachi and others.

Another example of his massive and insane prejudice against any and all things that even smack of "audio".

Wot a cretin.



.... Phil

[Phil Hobbs]

Post by Phil Allison

Post by John Larkin
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.

** However, Larkin failed to do the *bleeding obvious thing* and use MOSFETs characterised for liner operation - ie Lateral types as made by Hitachi and others.
Another example of his massive and insane prejudice against any and all things that even smack of "audio".
Wot a cretin.

Imagine anybody wanting to go faster than 20 kHz. The very _idea_!

Cheers

Phil Hobbs

[Phil Allison]

Post by Phil Hobbs
Imagine anybody wanting to go faster than 20 kHz. The very _idea_!

** Stick to posting about stuff you understand.

Cos you are making a total ass of yourself posting smartarse crap like this.

You are a pathetic wanker - Hobbs.


..... Phil

[Phil Hobbs]

Post by Phil Allison

Post by Phil Hobbs
Imagine anybody wanting to go faster than 20 kHz. The very _idea_!

** Stick to posting about stuff you understand.
Cos you are making a total ass of yourself posting smartarse crap like this.
You are a pathetic wanker - Hobbs.
..... Phil

I'm so relieved to have you protecting my reputation so zealously. ;)

Cheers

Phil Hobbs

[John Larkin]

On Fri, 26 Jul 2019 08:19:52 -0400, Phil Hobbs

Post by Phil Hobbs

Post by Phil Allison

Post by John Larkin
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.

** However, Larkin failed to do the *bleeding obvious thing* and use MOSFETs characterised for liner operation - ie Lateral types as made by Hitachi and others.
Another example of his massive and insane prejudice against any and all things that even smack of "audio".
Wot a cretin.

Imagine anybody wanting to go faster than 20 kHz. The very _idea_!
Cheers
Phil Hobbs

What's strange is that many mosfets will switch a lot faster -
sometimes 20x faster - than the numbers on the data sheet.

[Phil Hobbs]

Post by John Larkin
On Fri, 26 Jul 2019 08:19:52 -0400, Phil Hobbs

Post by Phil Hobbs

Post by Phil Allison

Post by John Larkin
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.

** However, Larkin failed to do the *bleeding obvious thing* and use MOSFETs characterised for liner operation - ie Lateral types as made by Hitachi and others.
Another example of his massive and insane prejudice against any and all things that even smack of "audio".
Wot a cretin.

Imagine anybody wanting to go faster than 20 kHz. The very _idea_!

What's strange is that many mosfets will switch a lot faster -
sometimes 20x faster - than the numbers on the data sheet.

That's been so since 1982ish that I know about, and probably as long as
they've existed. Probably to help the apps engineers escape the wrath
of customers who couldn't reproduce the datasheet numbers. ;)

Cheers

Phil Hobbs

[John Larkin]

On Thu, 25 Jul 2019 16:55:14 -0700 (PDT), Phil Allison

Post by Phil Allison

Post by John Larkin
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.

** However, Larkin failed to do the *bleeding obvious thing* and use MOSFETs characterised for liner operation - ie Lateral types as made by Hitachi and others.
Another example of his massive and insane prejudice against any and all things that even smack of "audio".
Wot a cretin.

This cretin designs and sells a lot of electronics, and has fun doing
it. I guess I'm dumb and happy.

Can you suggest some part numbers for high power n and p channel
lateral fets? Something in the 200 volt, 400 watt ballpark?

I'm not fundamentally prejudiced against audio, but most audio design
is really bad and mostly subjective. And boring.

We're using a very nice TI class D "audio" amp in a couple of designs
now.

[Dave Platt]

Post by John Larkin
Can you suggest some part numbers for high power n and p channel
lateral fets? Something in the 200 volt, 400 watt ballpark?

Exicon has the ECW20N20/ECW20P20, which are 200-volt 250-watt parts in
TO-264. ECF20N20/ECF20P20 seem to be the same dice, in TO-3. These
types look as if they're two 125-watt dice in a single package.

Their ProFusion arm sells 'em directly.

As far as I can tell, Exicon is the only company making the
lateral-MOSFET dice these days; there may be multiple companies
packaging them.

[John Larkin]

Post by Dave Platt

Post by John Larkin
Can you suggest some part numbers for high power n and p channel
lateral fets? Something in the 200 volt, 400 watt ballpark?

Exicon has the ECW20N20/ECW20P20, which are 200-volt 250-watt parts in
TO-264. ECF20N20/ECF20P20 seem to be the same dice, in TO-3. These
types look as if they're two 125-watt dice in a single package.
Their ProFusion arm sells 'em directly.
As far as I can tell, Exicon is the only company making the
lateral-MOSFET dice these days; there may be multiple companies
packaging them.

https://www.profusionplc.com/parts/ecw20n20

"They offer superb sonic characteristics"

What can that mean?

Does Hitachi still make laterals? I couldn't find them.

[Dave Platt]

Post by John Larkin
https://www.profusionplc.com/parts/ecw20n20
"They offer superb sonic characteristics"
What can that mean?

Whatever the Marketing people want it to. :-)

Post by John Larkin
Does Hitachi still make laterals? I couldn't find them.

As far as I can tell, Hitachi/Renesas is no longer making laterals.
These seem to have gone entirely out of the market supply-chain years
ago.

I read one person's comment that suggested that laterals were a victim
of one of the big Japanese earthquakes, some years ago (possibly the
Miyagi quake of 2008 although I'm not certain). Several of the
Japanese earthquakes in the last decade-and-change had a serious
impact on semiconductor-manufacturing facilities, with production of
many items being shut down.

Lateral MOSFETs may have been one type which wasn't in-demand enough
to merit restarting (or rebuilding) the production lines after the
rubble stopped bouncing around.

[Lasse Langwadt Christensen]

Post by Dave Platt

Post by John Larkin
https://www.profusionplc.com/parts/ecw20n20
"They offer superb sonic characteristics"
What can that mean?

Whatever the Marketing people want it to. :-)

Post by John Larkin
Does Hitachi still make laterals? I couldn't find them.

As far as I can tell, Hitachi/Renesas is no longer making laterals.
These seem to have gone entirely out of the market supply-chain years
ago.
I read one person's comment that suggested that laterals were a victim
of one of the big Japanese earthquakes, some years ago (possibly the
Miyagi quake of 2008 although I'm not certain). Several of the
Japanese earthquakes in the last decade-and-change had a serious
impact on semiconductor-manufacturing facilities, with production of
many items being shut down.
Lateral MOSFETs may have been one type which wasn't in-demand enough
to merit restarting (or rebuilding) the production lines after the
rubble stopped bouncing around.

isn't many of the RF power fets lateral? like the MRF101BN , MRF300AN mentioned a few days ago

[Phil Allison]

Post by Dave Platt

Post by John Larkin
Does Hitachi still make laterals? I couldn't find them.

As far as I can tell, Hitachi/Renesas is no longer making laterals.
These seem to have gone entirely out of the market supply-chain years
ago.

** I have about 100 N and P channel Hitachi TO3 mosfets.

Types 2SJ56 and 2SK176, 250V, 8A 125W.

Amplifiers that use them no longer come to me for service so they are up for sale.


.... Phil

[Winfield Hill]

Phil Allison wrote...

Post by Phil Allison
** I have about 100 N and P channel Hitachi TO3 mosfets.
Types 2SJ56 and 2SK176, 250V, 8A 125W.
Amplifiers that use them no longer come to me for
service so they are up for sale.

eBay.

[Phil Allison]

Post by Winfield Hill
Phil Allison wrote...

Post by Phil Allison
** I have about 100 N and P channel Hitachi TO3 mosfets.
Types 2SJ56 and 2SK176, 250V, 8A 125W.
Amplifiers that use them no longer come to me for
service so they are up for sale.

eBay.

** Try taking a look.



... Phil

[t***@gmail.com]

Post by John Larkin

Post by Dave Platt

Post by John Larkin
Can you suggest some part numbers for high power n and p channel
lateral fets? Something in the 200 volt, 400 watt ballpark?

Exicon has the ECW20N20/ECW20P20, which are 200-volt 250-watt parts in
TO-264. ECF20N20/ECF20P20 seem to be the same dice, in TO-3. These
types look as if they're two 125-watt dice in a single package.
Their ProFusion arm sells 'em directly.
As far as I can tell, Exicon is the only company making the
lateral-MOSFET dice these days; there may be multiple companies
packaging them.

https://www.profusionplc.com/parts/ecw20n20
"They offer superb sonic characteristics"
What can that mean?

sound good if you smack em with a hammer


NT

[Phil Allison]

Post by John Larkin

Post by Phil Allison
** However, Larkin failed to do the *bleeding obvious thing* and use MOSFETs characterised for liner operation - ie Lateral types as made by Hitachi and others.
Another example of his massive and insane prejudice against any and all things that even smack of "audio".
Wot a cretin.

This cretin designs and sells a lot of electronics,

** So fucking what?

You are a king size cretin anyway.

Post by John Larkin
Can you suggest some part numbers for high power n and p channel
lateral fets? Something in the 200 volt, 400 watt ballpark?

**Plenty of 250V laterals available, some even higher, in both P and N.

One uses as many as needed with huge advantage over switching types.

Cos you are stubborn, autistic shithead - you have never tried them.

Post by John Larkin
I'm not fundamentally prejudiced against audio,

** Ridiculous lie.

Post by John Larkin
but most audio design
is really bad and mostly subjective. And boring.

** Absolute bollocks.

Post by John Larkin
We're using a very nice TI class D "audio" amp in a couple of designs
now.

** Yawnnnnnnn....



... Phil

Post by John Larkin
--
John Larkin Highland Technology, Inc
picosecond timing precision measurement
jlarkin att highlandtechnology dott com
http://www.highlandtechnology.com

[John Larkin]

On Fri, 26 Jul 2019 20:00:57 -0700 (PDT), Phil Allison

Post by Phil Allison

Post by John Larkin

Post by Phil Allison
** However, Larkin failed to do the *bleeding obvious thing* and use MOSFETs characterised for liner operation - ie Lateral types as made by Hitachi and others.
Another example of his massive and insane prejudice against any and all things that even smack of "audio".
Wot a cretin.

This cretin designs and sells a lot of electronics,

** So fucking what?
You are a king size cretin anyway.

Post by John Larkin
Can you suggest some part numbers for high power n and p channel
lateral fets? Something in the 200 volt, 400 watt ballpark?

**Plenty of 250V laterals available, some even higher, in both P and N.

Got links?

[piglet]

Post by Winfield Hill
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

[Winfield Hill]

piglet wrote...

Post by piglet

Post by Winfield Hill
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!

[Kevin Aylward]

Post by Winfield Hill
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

[Winfield Hill]

Kevin Aylward wrote...

Post by Kevin Aylward

Post by Winfield Hill
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.

Post by Kevin Aylward
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.

[Kevin Aylward]

Post by Winfield Hill
Kevin Aylward wrote...

Post by Winfield Hill

Post by Winfield Hill
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!

Post by Winfield Hill
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.

Post by Winfield Hill
Also, the fit to the capacitances of the above model ...

Although we show one company's attempt at SPICE
modelling 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.

So... I would say though, that I am not particular enamoured of the Sandler
technique of adding subthreshold modelling. In principle, its a little bit
precarious. It has potential for convergence issues. Its correcting for a
zero current discontinuity by adding a feedback loop.

It would be preferable to simply add a controlled current using a B source
in parallel to the mosfet. One would then use an exp() function directly
rather than using a diode. One could then wrap that with a tanh() to
terminate its effect at larger currents.

A case in point, is... at my day job... we had an updated kit from X-Fab for
the process that were using just this last couple of weeks. All my existing
spice tests failed due to convergence issues. I traced it down to some
modelling problems in the natural mosfets. They had newly introduced B
Sources into the subckts, for reasons unknown. They were flagging up
convergence issues all over the place. A bare mosfet worked ok, but once one
put them into a real circuit, it fell apart.

So, if a mainstream fab can release a model kit that fails...

It might be worth mentioning in that section that LTSpice does model the
non-linear gd capacitance and has a subthreshold extension as well. Being
that millions of people use LTSpice, its getting to be a tad moot that
Spice3 don't support certain features. Additionally, there are other spices
that also do, with even other enhancements possible worth a mention... :-)


-- Kevin Aylward
http://www.anasoft.co.uk - SuperSpice
http://www.kevinaylward.co.uk/ee/index.html

[bitrex]

Post by Winfield Hill
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>

[John Larkin]

Post by bitrex

Post by Winfield Hill
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
<https://tinyurl.com/yxn7mej4>

For low currents, this works pretty well:

Loading Image...

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

There are a bunch of IC current limiters around now.

[Gerhard Hoffmann]

Post by John Larkin

Post by bitrex

Post by Winfield Hill
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
<https://tinyurl.com/yxn7mej4>

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/***@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

[John Larkin]

Post by Gerhard Hoffmann

Post by John Larkin

Post by bitrex

Post by Winfield Hill
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
<https://tinyurl.com/yxn7mej4>

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.)
<
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.

[bitrex]

Post by John Larkin

Post by bitrex

Post by Winfield Hill
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
<https://tinyurl.com/yxn7mej4>

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.

[bitrex]

Post by bitrex

Post by John Larkin

Post by bitrex

Post by Winfield Hill
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
<https://tinyurl.com/yxn7mej4>

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

[bitrex]

Post by bitrex

Post by John Larkin

Post by bitrex

Post by Winfield Hill
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
<https://tinyurl.com/yxn7mej4>

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.

If I'm lucky maybe some TinyLogic schmitts are in the budget

[John Larkin]

Post by bitrex

Post by John Larkin

Post by bitrex

Post by Winfield Hill
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
<https://tinyurl.com/yxn7mej4>

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.

Why does it need a current source?

[bitrex]

Post by John Larkin

Post by bitrex
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.

Why does it need a current source?

They don't wanna pay for fast, low voltage op amps or logic and such.
The circuit is gonna be in a semi-disposable product so cost is not
no-object :(

[bitrex]

Post by bitrex

Post by John Larkin

Post by bitrex
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.

Why does it need a current source?

They don't wanna pay for fast, low voltage op amps or logic and such.
The circuit is gonna be in a semi-disposable product so cost is not
no-object :(

The idea i'm messing with is bring the frequency down to something more
sensible from the self-resonant of a couple hundred MHz with some
low-loss inductance in series. Then use some negative resistance to
compensate for the bad Q down there. Can all be done with FETs and BJTs,
at low voltages.

I'm not under any kind of NDA so I'll post my result if I don't fail and
am sent to work camp in forest.

[Winfield Hill]

bitrex wrote...

Post by bitrex
The idea i'm messing with is bring the frequency down to something
more sensible from the self-resonant of a couple hundred MHz with
some low-loss inductance in series. Then use some negative resistance
to compensate for the bad Q down there. Can all be done with FETs
and BJTs, at low voltages.

You might want to experiment with piglet (Eric Wagner)'s idea
of adapting a foldback current-limit circuit into a negative-
resistance current source. We wrote it up for section 2x.12,
in the AoE x-Chapters book, see draft copy on DropBox.

https://www.dropbox.com/s/2urywtwwlpt6sjb/2x.12_negative-resistance_WH.pdf?dl=1

I played with SPICE and added a 100uA 1.5-volt low-voltage
version. It might be fast enough, if you scale the resistors
to run it at 2mA or even 10mA. You might do a pnp version.

[bitrex]

Post by Winfield Hill
bitrex wrote...

Post by bitrex
The idea i'm messing with is bring the frequency down to something
more sensible from the self-resonant of a couple hundred MHz with
some low-loss inductance in series. Then use some negative resistance
to compensate for the bad Q down there. Can all be done with FETs
and BJTs, at low voltages.

You might want to experiment with piglet (Eric Wagner)'s idea
of adapting a foldback current-limit circuit into a negative-
resistance current source. We wrote it up for section 2x.12,
in the AoE x-Chapters book, see draft copy on DropBox.
https://www.dropbox.com/s/2urywtwwlpt6sjb/2x.12_negative-resistance_WH.pdf?dl=1
I played with SPICE and added a 100uA 1.5-volt low-voltage
version. It might be fast enough, if you scale the resistors
to run it at 2mA or even 10mA. You might do a pnp version.

Hi Win, thank you, very nice!

If I'm allowed a more luxurious ~2.5 volts I came up with this modified
Lambda diode circuit. It uses a JFET and pnp for the negative
resistance, plus current mirror for biasing up the diode (it won't start
into a lossy inductor on its own) and some Colpitts-like feedback.

The 10u has 35 ohms of series resistance to represent a somewhat crappy L.

I am concerned about Vgs spread on real JFETs, though, and whether a
circuit of this topology will actually oscillate in the real world
consistently. It can be fiddly to start in LTSpice. An AC 1 current
source into the node shows a current gain of about 20dB into the inductor


Version 4
SHEET 1 2432 1620
WIRE 432 -320 432 -432
WIRE 432 -320 224 -320
WIRE 640 -320 432 -320
WIRE 224 -256 224 -320
WIRE 176 -192 -144 -192
WIRE 640 -160 640 -320
WIRE 224 32 224 -160
WIRE 848 32 224 32
WIRE 1280 32 912 32
WIRE 224 144 224 32
WIRE 640 192 640 -80
WIRE 640 192 288 192
WIRE 640 288 640 192
WIRE -144 416 -144 -192
WIRE 224 416 224 240
WIRE 224 416 -144 416
WIRE 640 416 640 368
WIRE 640 416 224 416
WIRE 848 416 640 416
WIRE 1024 416 848 416
WIRE 1024 464 1024 416
WIRE 640 480 640 416
WIRE -352 528 -352 448
WIRE -144 544 -144 416
WIRE 848 560 848 416
WIRE 1024 592 1024 528
WIRE 1280 592 1280 32
WIRE 1280 592 1024 592
WIRE 640 640 640 560
WIRE 640 640 432 640
WIRE 1024 656 1024 592
WIRE -352 704 -352 608
WIRE -144 704 -144 624
WIRE 224 736 224 416
WIRE 640 736 640 640
WIRE 432 784 432 640
WIRE 432 784 288 784
WIRE 576 784 432 784
WIRE 848 800 848 640
WIRE 1024 800 1024 720
WIRE 640 896 640 832
WIRE 224 912 224 832
WIRE 224 1056 224 992
WIRE 640 1056 640 976
FLAG -352 704 0
FLAG -352 448 Vcc
FLAG 432 -432 Vcc
FLAG 224 1056 0
FLAG 640 1056 0
FLAG 1024 800 0
FLAG 848 800 0
FLAG -144 704 0
SYMBOL pnp 288 240 R180
SYMATTR InstName Q1
SYMATTR Value BC557B
SYMBOL res 624 -176 R0
SYMATTR InstName R1
SYMATTR Value 10k
SYMBOL res 624 272 R0
SYMATTR InstName R2
SYMATTR Value 2.2k
SYMBOL voltage -352 512 R0
WINDOW 3 24 44 Left 2
WINDOW 123 0 0 Left 0
WINDOW 39 0 0 Left 0
SYMATTR Value 2.5
SYMATTR InstName V1
SYMBOL njf 176 -256 R0
SYMATTR InstName J1
SYMATTR Value J113
SYMBOL npn 288 736 M0
SYMATTR InstName Q3
SYMATTR Value BC546B
SYMBOL res 208 896 R0
SYMATTR InstName R7
SYMATTR Value 50
SYMBOL npn 576 736 R0
WINDOW 3 66 66 Left 2
SYMATTR InstName Q4
SYMATTR Value BC546B
SYMBOL res 624 464 R0
SYMATTR InstName R8
SYMATTR Value 10k
SYMBOL ind 832 544 R0
SYMATTR InstName L2
SYMATTR Value 10µ
SYMATTR SpiceLine Rser=35
SYMBOL cap 1008 464 R0
SYMATTR InstName C1
SYMATTR Value 470p
SYMBOL cap 1008 656 R0
SYMATTR InstName C2
SYMATTR Value 470p
SYMBOL cap 912 16 R90
WINDOW 0 0 32 VBottom 2
WINDOW 3 32 32 VTop 2
SYMATTR InstName C3
SYMATTR Value 47p
SYMBOL res 624 880 R0
SYMATTR InstName R6
SYMATTR Value 10k
SYMBOL current -144 544 R0
WINDOW 123 24 108 Left 2
WINDOW 39 0 0 Left 0
SYMATTR InstName I1
SYMATTR Value ""
SYMATTR Value2 AC 1
TEXT -472 768 Left 2 !.ac oct 10 100k 10Meg

[Winfield Hill]

bitrex wrote...

Post by bitrex

Post by Winfield Hill
bitrex wrote...

Post by bitrex
The idea i'm messing with is bring the frequency down to something
more sensible from the self-resonant of a couple hundred MHz with
some low-loss inductance in series. Then use some negative
resistance to compensate for the bad Q down there. Can all be
done with FETs and BJTs, at low voltages.

You might want to experiment with piglet's idea ...

Hi Win, thank you, very nice!
If I'm allowed a more luxurious ~2.5 volts I came up with this
modified Lambda diode circuit.

What oscillation frequency do you envision? From 200 MHz down
to low MHz? Will your circuit work up that high?, I see 10k
resistors, etc.?

BTW, your added inductor esr doesn't show on the schematic
(it's better to add parts to show these things explicitly).

[bitrex]

Post by Winfield Hill
bitrex wrote...

Post by bitrex

Post by Winfield Hill
bitrex wrote...

Post by bitrex
The idea i'm messing with is bring the frequency down to something
more sensible from the self-resonant of a couple hundred MHz with
some low-loss inductance in series. Then use some negative
resistance to compensate for the bad Q down there. Can all be
done with FETs and BJTs, at low voltages.

You might want to experiment with piglet's idea ...

Hi Win, thank you, very nice!
If I'm allowed a more luxurious ~2.5 volts I came up with this
modified Lambda diode circuit.

What oscillation frequency do you envision? From 200 MHz down
to low MHz? Will your circuit work up that high?, I see 10k
resistors, etc.?

1-2MHz is fine. The actual lossy inductor will be about 0.5uH to 4 uH, I
intend to "swamp" it with a somewhat larger low-loss inductor so it
starts reliably despite the variation. And then the idea is that the
oscillation frequency will deviate a bit in response to the smaller one
being stretched/compressed. a few 10s of khz deviation is fine

Post by Winfield Hill
BTW, your added inductor esr doesn't show on the schematic
(it's better to add parts to show these things explicitly).

Got it

[bitrex]

Post by Winfield Hill
bitrex wrote...

Post by bitrex

Post by Winfield Hill
bitrex wrote...

Post by bitrex
The idea i'm messing with is bring the frequency down to something
more sensible from the self-resonant of a couple hundred MHz with
some low-loss inductance in series. Then use some negative
resistance to compensate for the bad Q down there. Can all be
done with FETs and BJTs, at low voltages.

You might want to experiment with piglet's idea ...

Hi Win, thank you, very nice!
If I'm allowed a more luxurious ~2.5 volts I came up with this
modified Lambda diode circuit.

What oscillation frequency do you envision? From 200 MHz down
to low MHz? Will your circuit work up that high?, I see 10k
resistors, etc.?
BTW, your added inductor esr doesn't show on the schematic
(it's better to add parts to show these things explicitly).

Here is a time domain of the fleshed-out idea oscillating OK in the sim.
A few hundred cycles of the resonant frequency injected into the tank
gets it moving, in the simulation.

There's a gyrator in series with the lossy-L to bring the "self-resonant
frequency" down.

The desired result is that when the inductance of the lossy-L is changed
(by compressing or stretching the physical coil) the frequency deviates
a bit.

That's about it.

Anyway it looks good here but I'm concerned if it will be annoying to
get operating reliably on a breadboard in particular the part-to-part
tolerance on the JFET, any suggestions would be appreciated on that front

Version 4
SHEET 1 2432 1748
WIRE 432 -320 432 -432
WIRE 432 -320 224 -320
WIRE 640 -320 432 -320
WIRE 224 -256 224 -320
WIRE -304 -208 -304 -288
WIRE 176 -192 16 -192
WIRE 640 -160 640 -320
WIRE -304 -32 -304 -128
WIRE 224 0 224 -160
WIRE 1184 0 224 0
WIRE 1664 0 1248 0
WIRE 224 112 224 0
WIRE 640 160 640 -80
WIRE 640 160 288 160
WIRE 640 288 640 160
WIRE -176 416 -288 416
WIRE 16 416 16 -192
WIRE 16 416 -96 416
WIRE 224 416 224 208
WIRE 224 416 16 416
WIRE 640 416 640 368
WIRE 640 416 224 416
WIRE 960 416 640 416
WIRE 1200 416 960 416
WIRE 1408 416 1200 416
WIRE 1472 416 1408 416
WIRE 1408 464 1408 416
WIRE -288 528 -288 416
WIRE 640 560 640 416
WIRE 960 560 960 416
WIRE 1408 592 1408 528
WIRE 1664 592 1664 0
WIRE 1664 592 1408 592
WIRE 1408 656 1408 592
WIRE 1200 672 1200 416
WIRE -288 704 -288 608
WIRE 960 720 960 640
WIRE 960 720 880 720
WIRE 1136 720 960 720
WIRE 224 752 224 416
WIRE 640 752 640 640
WIRE 576 800 288 800
WIRE 1408 800 1408 720
WIRE 880 832 880 720
WIRE 960 960 960 720
WIRE 1024 960 960 960
WIRE 1200 960 1200 768
WIRE 1200 960 1104 960
WIRE 640 992 640 848
WIRE 224 1008 224 848
WIRE 1200 1024 1200 960
WIRE 224 1152 224 1088
WIRE 640 1152 640 1072
WIRE 880 1200 880 896
WIRE 1200 1200 1200 1104
WIRE 1200 1200 880 1200
WIRE 1200 1328 1200 1200
WIRE 1344 1328 1200 1328
WIRE 1488 1328 1344 1328
WIRE 1200 1392 1200 1328
WIRE 1344 1456 1344 1328
WIRE 1488 1456 1488 1328
WIRE 1200 1536 1200 1472
WIRE 1200 1648 1200 1616
WIRE 1344 1648 1344 1536
WIRE 1344 1648 1200 1648
WIRE 1488 1648 1488 1520
WIRE 1488 1648 1344 1648
WIRE 1200 1728 1200 1648
FLAG -304 -32 0
FLAG -304 -288 Vcc
FLAG 432 -432 Vcc
FLAG 224 1152 0
FLAG 640 1152 0
FLAG 1408 800 0
FLAG 1200 1728 0
FLAG -288 704 0
FLAG 1472 416 Out
IOPIN 1472 416 Out
SYMBOL pnp 288 208 R180
SYMATTR InstName Q1
SYMATTR Value BC557B
SYMBOL res 624 -176 R0
SYMATTR InstName R1
SYMATTR Value 10k
SYMBOL res 624 272 R0
SYMATTR InstName R2
SYMATTR Value 2.2k
SYMBOL voltage -304 -224 R0
WINDOW 3 24 44 Left 2
WINDOW 123 0 0 Left 0
WINDOW 39 0 0 Left 0
SYMATTR Value 2.5
SYMATTR InstName V1
SYMBOL njf 176 -256 R0
SYMATTR InstName J1
SYMATTR Value J113
SYMBOL npn 288 752 M0
SYMATTR InstName Q3
SYMATTR Value BC546B
SYMBOL res 208 992 R0
SYMATTR InstName R7
SYMATTR Value 50
SYMBOL npn 576 752 R0
WINDOW 3 66 66 Left 2
SYMATTR InstName Q4
SYMATTR Value BC546B
SYMBOL cap 1392 464 R0
SYMATTR InstName C1
SYMATTR Value 470p
SYMBOL cap 1392 656 R0
SYMATTR InstName C2
SYMATTR Value 470p
SYMBOL cap 1248 -16 R90
WINDOW 0 0 32 VBottom 2
WINDOW 3 58 36 VTop 2
SYMATTR InstName C3
SYMATTR Value 47p
SYMBOL res 624 976 R0
SYMATTR InstName R6
SYMATTR Value 10k
SYMBOL npn 1136 672 R0
WINDOW 3 66 66 Left 2
SYMATTR InstName Q2
SYMATTR Value BC546B
SYMBOL res 1184 1008 R0
SYMATTR InstName R3
SYMATTR Value 47
SYMBOL res 944 544 R0
SYMATTR InstName R4
SYMATTR Value 2.2k
SYMBOL res 1120 944 R90
WINDOW 0 0 56 VBottom 2
WINDOW 3 32 56 VTop 2
SYMATTR InstName R5
SYMATTR Value 68k
SYMBOL cap 864 832 R0
SYMATTR InstName C4
SYMATTR Value 470p
SYMBOL ind 1184 1376 R0
SYMATTR InstName L1
SYMATTR Value 4µ
SYMATTR SpiceLine Rser=0 Cpar=0
SYMBOL res 624 544 R0
SYMATTR InstName R8
SYMATTR Value 10k
SYMBOL voltage -288 512 R0
WINDOW 123 0 0 Left 0
WINDOW 39 0 0 Left 0
SYMATTR InstName V2
SYMATTR Value SINE(0 1 1Meg 0 0 0 1000)
SYMBOL res -80 400 R90
WINDOW 0 0 56 VBottom 2
WINDOW 3 32 56 VTop 2
SYMATTR InstName R9
SYMATTR Value 10k
SYMBOL res 1184 1520 R0
SYMATTR InstName R10
SYMATTR Value 50
SYMBOL res 1328 1440 R0
SYMATTR InstName R11
SYMATTR Value 100k
SYMBOL cap 1472 1456 R0
SYMATTR InstName C5
SYMATTR Value 10p
TEXT -352 48 Left 2 !.tran 100m
TEXT 1592 1488 Left 5 ;Lossy L
TEXT -632 296 Left 5 ;Kickstarter (sim only)

[bitrex]

Post by Winfield Hill
bitrex wrote...

There was an error with that .asc here is the corrected version:

Version 4
SHEET 1 2432 1748
WIRE 432 -320 432 -432
WIRE 432 -320 224 -320
WIRE 640 -320 432 -320
WIRE 224 -256 224 -320
WIRE -288 -192 -288 -272
WIRE 176 -192 16 -192
WIRE 640 -160 640 -320
WIRE -288 -16 -288 -112
WIRE 224 0 224 -160
WIRE 1184 0 224 0
WIRE 1664 0 1248 0
WIRE 224 112 224 0
WIRE 640 160 640 -80
WIRE 640 160 288 160
WIRE 640 288 640 160
WIRE -176 416 -288 416
WIRE 16 416 16 -192
WIRE 16 416 -96 416
WIRE 224 416 224 208
WIRE 224 416 16 416
WIRE 640 416 640 368
WIRE 640 416 224 416
WIRE 960 416 640 416
WIRE 1200 416 960 416
WIRE 1408 416 1200 416
WIRE 1472 416 1408 416
WIRE 1408 464 1408 416
WIRE -288 528 -288 416
WIRE 640 560 640 416
WIRE 960 560 960 416
WIRE 1408 592 1408 528
WIRE 1664 592 1664 0
WIRE 1664 592 1408 592
WIRE 1408 656 1408 592
WIRE 1200 672 1200 416
WIRE 640 688 640 640
WIRE 640 688 432 688
WIRE -288 704 -288 608
WIRE 960 720 960 640
WIRE 960 720 816 720
WIRE 1136 720 960 720
WIRE 224 752 224 416
WIRE 640 752 640 688
WIRE 432 800 432 688
WIRE 432 800 288 800
WIRE 576 800 432 800
WIRE 1408 800 1408 720
WIRE 816 832 816 720
WIRE 960 960 960 720
WIRE 1024 960 960 960
WIRE 1200 960 1200 768
WIRE 1200 960 1104 960
WIRE 640 992 640 848
WIRE 224 1008 224 848
WIRE 1200 1024 1200 960
WIRE 224 1152 224 1088
WIRE 640 1152 640 1072
WIRE 816 1200 816 896
WIRE 1200 1200 1200 1104
WIRE 1200 1200 816 1200
WIRE 1200 1328 1200 1200
WIRE 1344 1328 1200 1328
WIRE 1488 1328 1344 1328
WIRE 1200 1392 1200 1328
WIRE 1344 1456 1344 1328
WIRE 1488 1456 1488 1328
WIRE 1200 1536 1200 1472
WIRE 1200 1648 1200 1616
WIRE 1344 1648 1344 1536
WIRE 1344 1648 1200 1648
WIRE 1488 1648 1488 1520
WIRE 1488 1648 1344 1648
WIRE 1200 1728 1200 1648
FLAG -288 -16 0
FLAG -288 -272 Vcc
FLAG 432 -432 Vcc
FLAG 224 1152 0
FLAG 640 1152 0
FLAG 1408 800 0
FLAG 1200 1728 0
FLAG -288 704 0
FLAG 1472 416 Out
IOPIN 1472 416 Out
SYMBOL pnp 288 208 R180
SYMATTR InstName Q1
SYMATTR Value BC557B
SYMBOL res 624 -176 R0
SYMATTR InstName R1
SYMATTR Value 10k
SYMBOL res 624 272 R0
SYMATTR InstName R2
SYMATTR Value 2.2k
SYMBOL voltage -288 -208 R0
WINDOW 3 24 44 Left 2
WINDOW 123 0 0 Left 0
WINDOW 39 0 0 Left 0
SYMATTR Value 2.5
SYMATTR InstName V1
SYMBOL njf 176 -256 R0
SYMATTR InstName J1
SYMATTR Value J113
SYMBOL npn 288 752 M0
SYMATTR InstName Q3
SYMATTR Value BC546B
SYMBOL res 208 992 R0
SYMATTR InstName R7
SYMATTR Value 50
SYMBOL npn 576 752 R0
WINDOW 3 66 66 Left 2
SYMATTR Value BC546B
SYMATTR InstName Q4
SYMBOL cap 1392 464 R0
SYMATTR InstName C1
SYMATTR Value 470p
SYMBOL cap 1392 656 R0
SYMATTR InstName C2
SYMATTR Value 470p
SYMBOL cap 1248 -16 R90
WINDOW 0 0 32 VBottom 2
WINDOW 3 58 36 VTop 2
SYMATTR InstName C3
SYMATTR Value 47p
SYMBOL res 624 976 R0
SYMATTR InstName R6
SYMATTR Value 10k
SYMBOL npn 1136 672 R0
WINDOW 3 66 66 Left 2
SYMATTR Value BC546B
SYMATTR InstName Q2
SYMBOL res 1184 1008 R0
SYMATTR InstName R3
SYMATTR Value 47
SYMBOL res 944 544 R0
SYMATTR InstName R4
SYMATTR Value 2.2k
SYMBOL res 1120 944 R90
WINDOW 0 0 56 VBottom 2
WINDOW 3 32 56 VTop 2
SYMATTR InstName R5
SYMATTR Value 68k
SYMBOL cap 800 832 R0
SYMATTR InstName C4
SYMATTR Value 470p
SYMBOL ind 1184 1376 R0
SYMATTR InstName L1
SYMATTR Value 4µ
SYMATTR SpiceLine Rser=0 Cpar=0
SYMBOL res 624 544 R0
SYMATTR InstName R8
SYMATTR Value 10k
SYMBOL voltage -288 512 R0
WINDOW 123 0 0 Left 0
WINDOW 39 0 0 Left 0
SYMATTR InstName V2
SYMATTR Value SINE(0 1 1Meg 0 0 0 1000)
SYMBOL res -80 400 R90
WINDOW 0 0 56 VBottom 2
WINDOW 3 32 56 VTop 2
SYMATTR InstName R9
SYMATTR Value 10k
SYMBOL res 1184 1520 R0
SYMATTR InstName R10
SYMATTR Value 50
SYMBOL res 1328 1440 R0
SYMATTR InstName R11
SYMATTR Value 100k
SYMBOL cap 1472 1456 R0
SYMATTR InstName C5
SYMATTR Value 10p
TEXT -352 48 Left 2 !.tran 100m
TEXT 1592 1488 Left 5 ;Lossy L
TEXT -632 296 Left 5 ;Kickstarter (sim only)

[bitrex]

Post by bitrex

Post by Winfield Hill
bitrex wrote...

Post by bitrex

Post by Winfield Hill
bitrex wrote...

Post by bitrex
The idea i'm messing with is bring the frequency down to something
more sensible from the self-resonant of a couple hundred MHz with
some low-loss inductance in series.  Then use some negative
resistance to compensate for the bad Q down there.  Can all be
done with FETs and BJTs, at low voltages.

You might want to experiment with piglet's idea ...

Hi Win, thank you, very nice!
If I'm allowed a more luxurious ~2.5 volts I came up with this
modified Lambda diode circuit.

  What oscillation frequency do you envision?  From 200 MHz down
  to low MHz?   Will your circuit work up that high?, I see 10k
  resistors, etc.?
  BTW, your added inductor esr doesn't show on the schematic
  (it's better to add parts to show these things explicitly).

Here is a time domain of the fleshed-out idea oscillating OK in the sim.
A few hundred cycles of the resonant frequency injected into the tank
gets it moving, in the simulation.

<snip>

No, it's not going to work right. That bias network is wrong.

[George Herold]

Post by Winfield Hill
bitrex wrote...

Post by bitrex
The idea i'm messing with is bring the frequency down to something
more sensible from the self-resonant of a couple hundred MHz with
some low-loss inductance in series. Then use some negative resistance
to compensate for the bad Q down there. Can all be done with FETs
and BJTs, at low voltages.

You might want to experiment with piglet (Eric Wagner)'s idea
of adapting a foldback current-limit circuit into a negative-
resistance current source. We wrote it up for section 2x.12,
in the AoE x-Chapters book, see draft copy on DropBox.
https://www.dropbox.com/s/2urywtwwlpt6sjb/2x.12_negative-resistance_WH.pdf?dl=1

Instead of "With a little prodding" you might substitute,
"For a few haycorns". :^)

GH

Post by Winfield Hill
I played with SPICE and added a 100uA 1.5-volt low-voltage
version. It might be fast enough, if you scale the resistors
to run it at 2mA or even 10mA. You might do a pnp version.
--
Thanks,
- Win

[piglet]

Post by George Herold
Instead of "With a little prodding" you might substitute,
"For a few haycorns". :^)
GH

:) I get a mention in the great book - Yay!

piglet

[Winfield Hill]

piglet wrote...

Post by piglet

Post by George Herold
Instead of "With a little prodding" you might substitute,
"For a few haycorns". :^)
GH

:) I get a mention in the great book - Yay!
piglet

We used your real name, rather than piglet,
would you prefer that moniker was included?

[piglet]

Post by Winfield Hill
piglet wrote...

Post by piglet

Post by George Herold
Instead of "With a little prodding" you might substitute,
"For a few haycorns". :^)
GH

:) I get a mention in the great book - Yay!
piglet

We used your real name, rather than piglet,
would you prefer that moniker was included?

Thanks Win, real name is fine.

piglet / Erich Wagner

[George Herold]

Post by piglet

Post by George Herold
Instead of "With a little prodding" you might substitute,
"For a few haycorns". :^)
GH

:) I get a mention in the great book - Yay!
piglet

Sweet!
I don't really understand how it works.. :^)

Hey, mentioning 'great books' did you see this,
(some computer conjecture proven)
https://www.scottaaronson.com/blog/?p=4229
Mind you, I'm mostly clueless...
so I don't understand parts,
which is part of being a pooh bear. :^)

Hey would you send me an email to;
gherold.. at sign.... teachspin,com
that comma should be a period.

George H.

[piglet]

Post by George Herold
Hey, mentioning 'great books' did you see this,
(some computer conjecture proven)
https://www.scottaaronson.com/blog/?p=4229
Mind you, I'm mostly clueless...
so I don't understand parts,
which is part of being a pooh bear. :^)

Looks too mathesy for me, I will have to reread very slowly several
times. Pooh has brain and wisdom, piglet is just always anxious.

piglet

[Phil Hobbs]

Post by piglet

Post by George Herold
Hey, mentioning 'great books' did you see this,
(some computer conjecture proven)
https://www.scottaaronson.com/blog/?p=4229
Mind you, I'm mostly clueless...
so I don't understand parts,
which is part of being a pooh bear. :^)

Looks too mathesy for me, I will have to reread very slowly several
times. Pooh has brain and wisdom, piglet is just always anxious.
piglet

"That's the bravest kind of not blinching there is." --Pooh

Cheers

Phil Hobbs

[t***@gmail.com]

Post by George Herold

Post by Winfield Hill
bitrex wrote...
You might want to experiment with piglet (Eric Wagner)'s idea
of adapting a foldback current-limit circuit into a negative-
resistance current source. We wrote it up for section 2x.12,
in the AoE x-Chapters book, see draft copy on DropBox.
https://www.dropbox.com/s/2urywtwwlpt6sjb/2x.12_negative-resistance_WH.pdf?dl=1

Instead of "With a little prodding" you might substitute,
"For a few haycorns". :^)
GH

I expect the vast majority of readers will have zero interest in the interpersonal stuff of people they don't know, I'd skip it other than to mention it as Eric's circuit.


NT

[bitrex]

Post by t***@gmail.com

Post by George Herold

Post by Winfield Hill
bitrex wrote...
You might want to experiment with piglet (Eric Wagner)'s idea
of adapting a foldback current-limit circuit into a negative-
resistance current source. We wrote it up for section 2x.12,
in the AoE x-Chapters book, see draft copy on DropBox.
https://www.dropbox.com/s/2urywtwwlpt6sjb/2x.12_negative-resistance_WH.pdf?dl=1

Instead of "With a little prodding" you might substitute,
"For a few haycorns". :^)
GH

I expect the vast majority of readers will have zero interest in the interpersonal stuff of people they don't know, I'd skip it other than to mention it as Eric's circuit.
NT

Yeah it's a good edit

[bitrex]

Post by Winfield Hill
bitrex wrote...

Post by bitrex
The idea i'm messing with is bring the frequency down to something
more sensible from the self-resonant of a couple hundred MHz with
some low-loss inductance in series. Then use some negative resistance
to compensate for the bad Q down there. Can all be done with FETs
and BJTs, at low voltages.

You might want to experiment with piglet (Eric Wagner)'s idea
of adapting a foldback current-limit circuit into a negative-
resistance current source. We wrote it up for section 2x.12,
in the AoE x-Chapters book, see draft copy on DropBox.
https://www.dropbox.com/s/2urywtwwlpt6sjb/2x.12_negative-resistance_WH.pdf?dl=1
I played with SPICE and added a 100uA 1.5-volt low-voltage
version. It might be fast enough, if you scale the resistors
to run it at 2mA or even 10mA. You might do a pnp version.

Apologies for the message/.asc spam earlier, but here is a working revision:

Version 4
SHEET 1 2432 1748
WIRE 432 -320 432 -432
WIRE 432 -320 112 -320
WIRE 640 -320 432 -320
WIRE 112 -256 112 -320
WIRE -416 -208 -416 -288
WIRE 64 -192 -96 -192
WIRE 640 -160 640 -320
WIRE -416 -32 -416 -128
WIRE 112 0 112 -160
WIRE 1184 0 112 0
WIRE 1664 0 1248 0
WIRE 112 112 112 0
WIRE 640 160 640 -80
WIRE 640 160 176 160
WIRE 640 256 640 160
WIRE -288 416 -400 416
WIRE -96 416 -96 -192
WIRE -96 416 -208 416
WIRE 112 416 112 208
WIRE 112 416 -96 416
WIRE 368 416 112 416
WIRE 640 416 640 336
WIRE 640 416 368 416
WIRE 960 416 640 416
WIRE 1200 416 960 416
WIRE 1408 416 1200 416
WIRE 1888 416 1408 416
WIRE 1408 464 1408 416
WIRE -400 528 -400 416
WIRE 640 528 640 416
WIRE 960 528 960 416
WIRE 1408 592 1408 528
WIRE 1664 592 1664 0
WIRE 1664 592 1408 592
WIRE 1408 656 1408 592
WIRE 368 672 368 416
WIRE 1200 672 1200 416
WIRE -400 704 -400 608
WIRE 640 720 640 608
WIRE 640 720 432 720
WIRE 960 720 960 608
WIRE 960 720 816 720
WIRE 1136 720 960 720
WIRE 1408 800 1408 720
WIRE 112 896 112 416
WIRE 640 896 640 720
WIRE 816 928 816 720
WIRE 368 944 368 768
WIRE 368 944 176 944
WIRE 576 944 368 944
WIRE 960 960 960 720
WIRE 1024 960 960 960
WIRE 1200 960 1200 768
WIRE 1200 960 1104 960
WIRE 1200 1056 1200 960
WIRE 112 1136 112 992
WIRE 640 1136 640 992
WIRE 816 1200 816 992
WIRE 1200 1200 1200 1136
WIRE 1200 1200 816 1200
WIRE 112 1296 112 1216
WIRE 640 1296 640 1216
WIRE 1200 1328 1200 1200
WIRE 1344 1328 1200 1328
WIRE 1488 1328 1344 1328
WIRE 1200 1392 1200 1328
WIRE 1344 1456 1344 1328
WIRE 1488 1456 1488 1328
WIRE 1200 1536 1200 1472
WIRE 1200 1648 1200 1616
WIRE 1344 1648 1344 1536
WIRE 1344 1648 1200 1648
WIRE 1488 1648 1488 1520
WIRE 1488 1648 1344 1648
WIRE 1200 1728 1200 1648
FLAG -416 -32 0
FLAG -416 -288 Vcc
FLAG 432 -432 Vcc
FLAG 112 1296 0
FLAG 640 1296 0
FLAG 1408 800 0
FLAG 1200 1728 0
FLAG -400 704 0
FLAG 1888 416 Out
IOPIN 1888 416 Out
SYMBOL pnp 176 208 R180
SYMATTR InstName Q1
SYMATTR Value BC557B
SYMBOL res 624 -176 R0
SYMATTR InstName R1
SYMATTR Value 10k
SYMBOL res 624 240 R0
SYMATTR InstName R2
SYMATTR Value 4.7k
SYMBOL voltage -416 -224 R0
WINDOW 3 24 44 Left 2
WINDOW 123 0 0 Left 0
WINDOW 39 0 0 Left 0
SYMATTR Value 2.5
SYMATTR InstName V1
SYMBOL njf 64 -256 R0
SYMATTR InstName J1
SYMATTR Value J113
SYMBOL npn 176 896 M0
SYMATTR InstName Q3
SYMATTR Value BC546B
SYMBOL res 96 1120 R0
SYMATTR InstName R7
SYMATTR Value 50
SYMBOL npn 576 896 R0
WINDOW 3 66 66 Left 2
SYMATTR Value BC546B
SYMATTR InstName Q4
SYMBOL cap 1392 464 R0
SYMATTR InstName C1
SYMATTR Value 180p
SYMBOL cap 1392 656 R0
SYMATTR InstName C2
SYMATTR Value 180p
SYMBOL cap 1248 -16 R90
WINDOW 0 0 32 VBottom 2
WINDOW 3 58 36 VTop 2
SYMATTR InstName C3
SYMATTR Value 47p
SYMBOL res 624 1120 R0
SYMATTR InstName R6
SYMATTR Value 10k
SYMBOL npn 1136 672 R0
WINDOW 3 66 66 Left 2
SYMATTR Value BC546B
SYMATTR InstName Q2
SYMBOL res 1184 1040 R0
SYMATTR InstName R3
SYMATTR Value 22
SYMBOL res 944 512 R0
SYMATTR InstName R4
SYMATTR Value 4.7k
SYMBOL res 1120 944 R90
WINDOW 0 0 56 VBottom 2
WINDOW 3 32 56 VTop 2
SYMATTR InstName R5
SYMATTR Value 47k
SYMBOL cap 800 928 R0
SYMATTR InstName C4
SYMATTR Value 1.5n
SYMBOL ind 1184 1376 R0
SYMATTR InstName L1
SYMATTR Value 4µ
SYMATTR SpiceLine Rser=0 Cpar=0
SYMBOL res 624 512 R0
SYMATTR InstName R8
SYMATTR Value 10k
SYMBOL voltage -400 512 R0
WINDOW 123 0 0 Left 0
WINDOW 39 0 0 Left 0
SYMATTR InstName V2
SYMATTR Value SINE(0 1 1Meg 0 0 0 1000)
SYMBOL res -192 400 R90
WINDOW 0 0 56 VBottom 2
WINDOW 3 32 56 VTop 2
SYMATTR InstName R9
SYMATTR Value 10k
SYMBOL res 1184 1520 R0
SYMATTR InstName R10
SYMATTR Value 50
SYMBOL res 1328 1440 R0
SYMATTR InstName R11
SYMATTR Value 100k
SYMBOL cap 1472 1456 R0
SYMATTR InstName C5
SYMATTR Value 10p
SYMBOL npn 432 672 M0
SYMATTR InstName Q5
SYMATTR Value BC546B
TEXT -464 48 Left 2 !.tran 10m
TEXT 1592 1488 Left 5 ;Lossy L
TEXT -744 296 Left 5 ;Kickstarter (sim only)

[Winfield Hill]

bitrex wrote...

Post by bitrex

Post by Winfield Hill
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
<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.

[Dave Platt]

Post by Winfield Hill
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.

[Winfield Hill]

Dave Platt wrote...

Post by Dave Platt

Post by Winfield Hill
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.

[Chris Jones]

Post by Winfield Hill
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 µ 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.

[George Herold]

Post by Winfield Hill
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

I'm using some big mosfet as part of a 77k to 400K heater.
The Fet's 'down the probe' with three to-220 pack R's.
(The R's and supply voltage limit the power to a few watts.)
An opamp up top closes the loop... I've added various C's
to the loop to slow things down...
At some point my design becomes, bang on various 'ports'
and try to damp out the ringing.

(If no ringing, then maybe something can be faster?)

George H.

Post by Winfield Hill
--
Thanks,
- Win

[Winfield Hill]

George Herold wrote...

Post by George Herold
An opamp up top closes the loop... I've added
various C's to the loop to slow things down...

Depending on where you add the C's, they may
simply add poles, or lower pole frequencies,
to destabilize the feedback loop.

[George Herold]

Post by Winfield Hill
George Herold wrote...

Post by George Herold
An opamp up top closes the loop... I've added
various C's to the loop to slow things down...

Depending on where you add the C's, they may
simply add poles, or lower pole frequencies,
to destabilize the feedback loop.

Right, 1/2 the time I need more R in the loop.

George H.

Post by Winfield Hill
--
Thanks,
- Win