AoE x-Chapters, using power MOSFETs as linear transistors

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.

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

If I'm lucky maybe some TinyLogic schmitts are in the budget
 
On Thu, 25 Jul 2019 13:10:45 -0400, bitrex <user@example.net> 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.

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

Why does it need a current source?


--

John Larkin Highland Technology, Inc
picosecond timing precision measurement

jlarkin att highlandtechnology dott com
http://www.highlandtechnology.com
 
On 7/25/19 4:24 PM, bitrex wrote:
On 7/25/19 3:17 PM, John Larkin wrote:

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 :(
Click to expand...

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.
 
On 7/25/19 3:17 PM, John Larkin wrote:

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?
Click to expand...

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 :(
 
On Wednesday, July 24, 2019 at 5:54:15 PM UTC-7, Winfield Hill wrote:
> 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
 
John Larkin wrote:

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.
Click to expand...

** 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
 
On 7/25/19 7:55 PM, Phil Allison wrote:
John Larkin wrote:



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.
Click to expand...

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

Cheers

Phil Hobbs
 
bitrex wrote...
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.
Click to expand...

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.


--
Thanks,
- Win
 
bitrex wrote...
Winfield Hill wrote:
bitrex wrote...

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.
Click to expand...

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).


--
Thanks,
- Win
 
On Friday, July 26, 2019 at 11:30:05 AM UTC-4, Winfield Hill wrote:
bitrex wrote...

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
Click to expand...

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

GH
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
Click to expand...
 
On 7/26/19 11:29 AM, Winfield Hill wrote:
bitrex wrote...

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.
Click to expand...

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


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On Thu, 25 Jul 2019 16:55:14 -0700 (PDT), Phil Allison
<pallison49@gmail.com> wrote:

John Larkin wrote:



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.
Click to expand...

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.




--

John Larkin Highland Technology, Inc
picosecond timing precision measurement

jlarkin att highlandtechnology dott com
http://www.highlandtechnology.com
 
In article <lnemjeh2pckf2thlfsjcv419rdnp88mfhn@4ax.com>,
John Larkin <jjlarkin@highland_snip_technology.com> wrote:

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

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.
 
On 7/26/19 3:30 PM, bitrex wrote:
On 7/26/19 2:32 PM, Winfield Hill wrote:
bitrex wrote...
Click to expand...

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

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TEXT -632 296 Left 5 ;Kickstarter (sim only)
 
On 7/26/19 2:32 PM, Winfield Hill wrote:
bitrex wrote...

Winfield Hill wrote:
bitrex wrote...

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).
Click to expand...

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

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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 4Âľ
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)
 
"Winfield Hill" wrote in message news:qhav1702std@drn.newsguy.com...

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
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.
Click to expand...

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
 
On 7/26/19 2:32 PM, Winfield Hill wrote:
bitrex wrote...

Winfield Hill wrote:
bitrex wrote...

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.?
Click to expand...

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

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

Got it
 
On 7/26/19 3:30 PM, bitrex wrote:
On 7/26/19 2:32 PM, Winfield Hill wrote:
bitrex wrote...

Winfield Hill wrote:
bitrex wrote...

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.
Click to expand...

<snip>

No, it's not going to work right. That bias network is wrong.
 
On Fri, 26 Jul 2019 11:40:53 -0700, dplatt@coop.radagast.org (Dave
Platt) wrote:

In article <lnemjeh2pckf2thlfsjcv419rdnp88mfhn@4ax.com>,
John Larkin <jjlarkin@highland_snip_technology.com> wrote:

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.
Click to expand...

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.


--

John Larkin Highland Technology, Inc
picosecond timing precision measurement

jlarkin att highlandtechnology dott com
http://www.highlandtechnology.com
 
On 26/07/2019 7:23 pm, George Herold wrote:
Instead of "With a little prodding" you might substitute,
"For a few haycorns". :^)

GH
Click to expand...

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

piglet
 
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