Which N Or P Power MOSFETs ?...

[Phil Allison]

Bill Sloman is Besoted with his own bullshit.
==================================

In a particular context.

** The one we were in.

The one you were in. Upside-down-under was being a bit more analytic.

** Yet another stupid, wrong opinion blown straight out Bill\'s arse.

FYI to all,

I actually re-posted the absurd question - with a challenge that Bill try to explain it.

However, just like the narcissistic fake & coward Bill has always been

- he dishonesty avoided it.

Wot a puke.

...... Phil

 

[Jeff Urban]

>The fuckwit OP posted this complete drivel:

\" These days, are they really making full range (20 Hz .. 20 kHz)
speaker elements that can handle 1 kW power levels ?
If not, what is the point of making kW class full range amplifiers ? \"

I posted no such thing, you got your quotes mixed up.

And now I wonder why your posts are not showing up, I can only see them in my email fed. Fucking Google Groups, one of thee day I will get a normal client for tis shit.

Maybe.

If it was going to block anyone why not Slowman ? But I never told it to block anyone.

Well, this is new and improved.

 

[Bill Sloman]

On Sunday, November 22, 2020 at 4:03:10 PM UTC+11, palli...@gmail.com wrote:

Bill Sloman is Besoted with his own bullshit.
==================================

In a particular context.

** The one we were in.

The one you were in. Upside-down-under was being a bit more analytic.

** Yet another stupid, wrong opinion blown straight out Bill\'s arse.

FYI to all,

I actually re-posted the absurd question - with a challenge that Bill try to explain it.

However, just like the narcissistic fake & coward Bill has always been

- he dishonesty avoided it.

When I checked out my response via Goggle groups I found this

\"> \" These days, are they really making full range (20 Hz .. 20 kHz)

speaker elements that can handle 1 kW power levels ?
If not, what is the point of making kW class full range amplifiers ? \"

** Care to translate any of that *gobbledegook* into plain English that makes technical sense ?

There are people who are devoted to the idea of using a single driver to cover the entire audio spectrum - from 20Hz to 20kHz. I\'ve seen a write-up of a huge full range electrostatic speaker that was intended to do just that. Not having to worry about cross-overs is an advantage of this approach, but not a compelling one

Nobody sane seems to bother, and the only bit of the audio range that needs kilowatt power is the low frequency end, so why bother making a high power amplifier that can handle any frequency higher than a couple of hundred Hz? \"

It strikes me as clear and coherent response - but then again it would. Clearly it wasn\'t what Phil wanted or expected, but I don\'t think he can reasonably claim that I avoided it.

Then again, Phil isn\'t known for his reasonableness. My guess is that he stopped reading at the first line in my response and got distracted before he\'d actually read on to get to my response to his challenge.

--
Bill Sloman, Sydney

 

[boB]

On Sat, 21 Nov 2020 18:50:35 -0800 (PST), Bill Sloman
<bill.sloman@ieee.org> wrote:

On Sunday, November 22, 2020 at 3:23:20 AM UTC+11, jla...@highlandsniptechnology.com wrote:
On Sat, 21 Nov 2020 03:00:50 -0500, bitrex <us...@example.net> wrote:

On 11/21/2020 12:44 AM, jla...@highlandsniptechnology.com wrote:
On Fri, 20 Nov 2020 16:27:03 -0800 (PST), Phil Allison
palli...@gmail.com> wrote:

some bit brain fuckhead wrote:
=============================

Yes also because all the graphs and safe operating area curves for
modern switching MOSFETs are of little use when they\'re used in a linear
application.


** FFS post *only* on topics you know something about.

That will narrow the field right down to SFA.

snip

The SOA curve in most switching device datasheets tells you e.g. that
you can push 20 amps at DC with the MOSFET saturated and the case at 25
degrees. Amazing stuff. I try to run all linear power amps pushing 20
amps with the case at 25 degrees personally

We never believed the SOAR curves, so we just pushed them until they
exploded.

That probably means that John Larkin never understood what the Safe Operating Area curves were trying to tell him. They do present a plot of safe drain currents against drain-to-source voltage which does tell you something about operating the parts outside the saturation region, despite Bitrex\'s claim to the contrary,

The data sheet for Phil Allison\'s favourite N-channel part

http://www.irf.com/product-info/datasheets/data/irfp240.pdf

shows just such a curve at figure 8.

http://www.irf.com/product-info/datasheets/data/irfp9240.pdf

shows a very similar datasheet for the P-channel part Phil reccommends. Again, the SOA curve is a figure 8.

These have comparatively small die size for a TO-247. Probably better
parts for linear audio out there I am thinking. But that\'s just by
going on the spec sheet. YMMV

If for switching, there is definitely better parts that these at 200V.

Not sure how good Exicon Lateral MOSFETS but supposedly they are
great for class AB or maybe even class A audio amps.

With a good component power sharing technique, (whichever technique
that might be), lots of available FETs should work if you have enough
of them.








><snipped John boasting about something some customer managed to extract from him>

 

[Phil Allison]

boB wrote:

==========

http://www.irf.com/product-info/datasheets/data/irfp9240.pdf


These have comparatively small die size for a TO-247. Probably better
parts for linear audio out there I am thinking. But that\'s just by
going on the spec sheet. YMMV

If for switching, there is definitely better parts that these at 200V.

Not sure how good Exicon Lateral MOSFETS but supposedly they are
great for class AB or maybe even class A audio amps.

** They are normally fine, well most of them are - but they did make a batch of duds once.
Dual chip devices where the chips would lose most of their gm over time.

With a good component power sharing technique, (whichever technique
that might be), lots of available FETs should work if you have enough

** Hexfets (et alia) need careful matching to run in parallel.
Real PITA especially for repairers.

Probably best used as \" current dumpers \" to eliminate the issue altogether.


...... Phil

 

[server]

On Sat, 21 Nov 2020 20:13:43 -0800 (PST), Phil Allison
<pallison49@gmail.com> wrote:

Bill Sloman wrote:
===============

The data sheet for Phil Allison\'s favourite N-channel part
http://www.irf.com/product-info/datasheets/data/irfp240.pdf
shows just such a curve at figure 8.
---------------------------------------------------------------------------

** That curve shows a limit at 100V and 3A for 10ms.
10ms is a long time in audio, when considering reactive load driving ability.

https://www.onsemi.com/pub/Collateral/MJL21193-D.PDF

This common BJT has a limit at 100V of 2A - but for 1 second.
Big difference.

https://www.datasheets360.com/pdf/-60837881188089191

This \" lateral mosfet \" is rated for 4A and 100V for 10ms and 1.25A for 1 second.

Our realtime thermal model for our giant TO247 fets is pretty simple:
a capacitor to ground (thermal mass of the chip), a resistor
(corresponds to theta from junction to heat sink) to a voltage (that
corresponds to measured heat sink temperature). Calculated power
dissipation becomes current dumped into the cap. The resulting cap
voltage scales to junction temp. It\'s just a few lines of code.

We run that circuit simulation maybe 2000 times a second, and shut
down the amp if it hits some effective junction temperature. The RC
tau is about 100 ms, based on dramatic destructive testing of the real
parts. Oops, sorry, elements. No, components.

Our NMR amps are current sources driving specific gradient coils.
Customers program pulses or waveforms, so we can shut down and say
\"don\'t do that\". Audio is not so controllable, so the shutdown would
probably become some sort of limit there.



--

John Larkin Highland Technology, Inc

The best designs are necessarily accidental.

 

[server]

On Sat, 21 Nov 2020 22:49:26 -0800 (PST), Phil Allison
<pallison49@gmail.com> wrote:

boB wrote:

==========

http://www.irf.com/product-info/datasheets/data/irfp9240.pdf


These have comparatively small die size for a TO-247. Probably better
parts for linear audio out there I am thinking. But that\'s just by
going on the spec sheet. YMMV

If for switching, there is definitely better parts that these at 200V.

Not sure how good Exicon Lateral MOSFETS but supposedly they are
great for class AB or maybe even class A audio amps.


** They are normally fine, well most of them are - but they did make a batch of duds once.
Dual chip devices where the chips would lose most of their gm over time.

With a good component power sharing technique, (whichever technique
that might be), lots of available FETs should work if you have enough

** Hexfets (et alia) need careful matching to run in parallel.
Real PITA especially for repairers.

It\'s ususlly easy to assign one opamp per fet, to ensure basically
perfect matching. Opamps are cheaper than giant fets and giant heat
sinks, and the source resistors can drop millivolts, not volts.



--

John Larkin Highland Technology, Inc

The best designs are necessarily accidental.

 

[bitrex]

On 11/21/2020 9:50 PM, Bill Sloman wrote:

On Sunday, November 22, 2020 at 3:23:20 AM UTC+11, jla...@highlandsniptechnology.com wrote:
On Sat, 21 Nov 2020 03:00:50 -0500, bitrex <us...@example.net> wrote:

On 11/21/2020 12:44 AM, jla...@highlandsniptechnology.com wrote:
On Fri, 20 Nov 2020 16:27:03 -0800 (PST), Phil Allison
palli...@gmail.com> wrote:

some bit brain fuckhead wrote:
=============================

Yes also because all the graphs and safe operating area curves for
modern switching MOSFETs are of little use when they\'re used in a linear
application.


** FFS post *only* on topics you know something about.

That will narrow the field right down to SFA.

snip

The SOA curve in most switching device datasheets tells you e.g. that
you can push 20 amps at DC with the MOSFET saturated and the case at 25
degrees. Amazing stuff. I try to run all linear power amps pushing 20
amps with the case at 25 degrees personally

We never believed the SOAR curves, so we just pushed them until they
exploded.

That probably means that John Larkin never understood what the Safe Operating Area curves were trying to tell him. They do present a plot of safe drain currents against drain-to-source voltage which does tell you something about operating the parts outside the saturation region, despite Bitrex\'s claim to the contrary,

The data sheet for Phil Allison\'s favourite N-channel part

http://www.irf.com/product-info/datasheets/data/irfp240.pdf

shows just such a curve at figure 8.

http://www.irf.com/product-info/datasheets/data/irfp9240.pdf

shows a very similar datasheet for the P-channel part Phil reccommends. Again, the SOA curve is a figure 8.

snipped John boasting about something some customer managed to extract from him

The claim I\'m making is that those constant power curves at the right
assume the temperature is uniform across the MOSFET die, as it\'s likely
to be in a switching application where it\'s either fully off or each
pulse is putting it solidly into the ohmic region.

 

[server]

On Sun, 22 Nov 2020 13:09:47 -0500, bitrex <user@example.net> wrote:

On 11/21/2020 9:50 PM, Bill Sloman wrote:
On Sunday, November 22, 2020 at 3:23:20 AM UTC+11, jla...@highlandsniptechnology.com wrote:
On Sat, 21 Nov 2020 03:00:50 -0500, bitrex <us...@example.net> wrote:

On 11/21/2020 12:44 AM, jla...@highlandsniptechnology.com wrote:
On Fri, 20 Nov 2020 16:27:03 -0800 (PST), Phil Allison
palli...@gmail.com> wrote:

some bit brain fuckhead wrote:
=============================

Yes also because all the graphs and safe operating area curves for
modern switching MOSFETs are of little use when they\'re used in a linear
application.


** FFS post *only* on topics you know something about.

That will narrow the field right down to SFA.

snip

The SOA curve in most switching device datasheets tells you e.g. that
you can push 20 amps at DC with the MOSFET saturated and the case at 25
degrees. Amazing stuff. I try to run all linear power amps pushing 20
amps with the case at 25 degrees personally

We never believed the SOAR curves, so we just pushed them until they
exploded.

That probably means that John Larkin never understood what the Safe Operating Area curves were trying to tell him. They do present a plot of safe drain currents against drain-to-source voltage which does tell you something about operating the parts outside the saturation region, despite Bitrex\'s claim to the contrary,

The data sheet for Phil Allison\'s favourite N-channel part

http://www.irf.com/product-info/datasheets/data/irfp240.pdf

shows just such a curve at figure 8.

http://www.irf.com/product-info/datasheets/data/irfp9240.pdf

shows a very similar datasheet for the P-channel part Phil reccommends. Again, the SOA curve is a figure 8.

snipped John boasting about something some customer managed to extract from him


The claim I\'m making is that those constant power curves at the right
assume the temperature is uniform across the MOSFET die, as it\'s likely
to be in a switching application where it\'s either fully off or each
pulse is putting it solidly into the ohmic region.

Makes no sense. Fig 8 clearly has data at 200 volts and 5 amps.

I don\'t see any assumptions about temperature uniformity. The SOAR
curve just specs what is safe.

(Not that I unreservedly believe them. Processes change more often
than data sheets.)




--

John Larkin Highland Technology, Inc

The best designs are necessarily accidental.

 

[bitrex]

On 11/22/2020 1:41 PM, jlarkin@highlandsniptechnology.com wrote:

On Sun, 22 Nov 2020 13:09:47 -0500, bitrex <user@example.net> wrote:

On 11/21/2020 9:50 PM, Bill Sloman wrote:
On Sunday, November 22, 2020 at 3:23:20 AM UTC+11, jla...@highlandsniptechnology.com wrote:
On Sat, 21 Nov 2020 03:00:50 -0500, bitrex <us...@example.net> wrote:

On 11/21/2020 12:44 AM, jla...@highlandsniptechnology.com wrote:
On Fri, 20 Nov 2020 16:27:03 -0800 (PST), Phil Allison
palli...@gmail.com> wrote:

some bit brain fuckhead wrote:
=============================

Yes also because all the graphs and safe operating area curves for
modern switching MOSFETs are of little use when they\'re used in a linear
application.


** FFS post *only* on topics you know something about.

That will narrow the field right down to SFA.

snip

The SOA curve in most switching device datasheets tells you e.g. that
you can push 20 amps at DC with the MOSFET saturated and the case at 25
degrees. Amazing stuff. I try to run all linear power amps pushing 20
amps with the case at 25 degrees personally

We never believed the SOAR curves, so we just pushed them until they
exploded.

That probably means that John Larkin never understood what the Safe Operating Area curves were trying to tell him. They do present a plot of safe drain currents against drain-to-source voltage which does tell you something about operating the parts outside the saturation region, despite Bitrex\'s claim to the contrary,

The data sheet for Phil Allison\'s favourite N-channel part

http://www.irf.com/product-info/datasheets/data/irfp240.pdf

shows just such a curve at figure 8.

http://www.irf.com/product-info/datasheets/data/irfp9240.pdf

shows a very similar datasheet for the P-channel part Phil reccommends. Again, the SOA curve is a figure 8.

snipped John boasting about something some customer managed to extract from him


The claim I\'m making is that those constant power curves at the right
assume the temperature is uniform across the MOSFET die, as it\'s likely
to be in a switching application where it\'s either fully off or each
pulse is putting it solidly into the ohmic region.


Makes no sense. Fig 8 clearly has data at 200 volts and 5 amps.

I don\'t see any assumptions about temperature uniformity. The SOAR
curve just specs what is safe.

(Not that I unreservedly believe them. Processes change more often
than data sheets.)

There are several articles about the topic:

<https://sound-au.com/articles/hexfet.htm>

<https://www.eeweb.com/practical-considerations-of-trench-mosfet-stability/>

\"Figure 1 shows the typical SOA curve included in most power MOSFET
datasheets. The constant power curves, shown to the right of constant
current line within the SOA boundary, are extracted from the thermal
data with the assumption that the junction temperature is essentially
uniform across the power MOSFET die. The dissipated power does not cause
a catastrophic failure to the device, but brings its junction
temperature up to the maximum guaranteed temperature when the applied
power pulse is evenly distributed on the die surface.\"

Thermal gradients, blowin \'em up:

<https://river.cat/2012/07/How-to-Kill-a-MOSFET>

 

[John S]

On 11/22/2020 12:41 PM, jlarkin@highlandsniptechnology.com wrote:

On Sun, 22 Nov 2020 13:09:47 -0500, bitrex <user@example.net> wrote:

On 11/21/2020 9:50 PM, Bill Sloman wrote:
On Sunday, November 22, 2020 at 3:23:20 AM UTC+11, jla...@highlandsniptechnology.com wrote:
On Sat, 21 Nov 2020 03:00:50 -0500, bitrex <us...@example.net> wrote:

On 11/21/2020 12:44 AM, jla...@highlandsniptechnology.com wrote:
On Fri, 20 Nov 2020 16:27:03 -0800 (PST), Phil Allison
palli...@gmail.com> wrote:

some bit brain fuckhead wrote:
=============================

Yes also because all the graphs and safe operating area curves for
modern switching MOSFETs are of little use when they\'re used in a linear
application.


** FFS post *only* on topics you know something about.

That will narrow the field right down to SFA.

snip

The SOA curve in most switching device datasheets tells you e.g. that
you can push 20 amps at DC with the MOSFET saturated and the case at 25
degrees. Amazing stuff. I try to run all linear power amps pushing 20
amps with the case at 25 degrees personally

We never believed the SOAR curves, so we just pushed them until they
exploded.

That probably means that John Larkin never understood what the Safe Operating Area curves were trying to tell him. They do present a plot of safe drain currents against drain-to-source voltage which does tell you something about operating the parts outside the saturation region, despite Bitrex\'s claim to the contrary,

The data sheet for Phil Allison\'s favourite N-channel part

http://www.irf.com/product-info/datasheets/data/irfp240.pdf

shows just such a curve at figure 8.

http://www.irf.com/product-info/datasheets/data/irfp9240.pdf

shows a very similar datasheet for the P-channel part Phil reccommends. Again, the SOA curve is a figure 8.

snipped John boasting about something some customer managed to extract from him


The claim I\'m making is that those constant power curves at the right
assume the temperature is uniform across the MOSFET die, as it\'s likely
to be in a switching application where it\'s either fully off or each
pulse is putting it solidly into the ohmic region.


Makes no sense. Fig 8 clearly has data at 200 volts and 5 amps.

I don\'t see any assumptions about temperature uniformity. The SOAR
curve just specs what is safe.

For a single pulse, yes? So, one pulse and you\'re done forever?

(Not that I unreservedly believe them. Processes change more often
than data sheets.)

 

[bitrex]

On 11/22/2020 2:08 PM, John S wrote:

On 11/22/2020 12:41 PM, jlarkin@highlandsniptechnology.com wrote:
On Sun, 22 Nov 2020 13:09:47 -0500, bitrex <user@example.net> wrote:

On 11/21/2020 9:50 PM, Bill Sloman wrote:
On Sunday, November 22, 2020 at 3:23:20 AM UTC+11,
jla...@highlandsniptechnology.com wrote:
On Sat, 21 Nov 2020 03:00:50 -0500, bitrex <us...@example.net> wrote:

On 11/21/2020 12:44 AM, jla...@highlandsniptechnology.com wrote:
On Fri, 20 Nov 2020 16:27:03 -0800 (PST), Phil Allison
palli...@gmail.com> wrote:

some bit brain fuckhead wrote:
=============================

Yes also because all the graphs and safe operating area curves for
modern switching MOSFETs are of little use when they\'re used in
a linear
application.


** FFS post *only* on topics you know something about.

That will narrow the field right down to SFA.

snip

The SOA curve in most switching device datasheets tells you e.g. that
you can push 20 amps at DC with the MOSFET saturated and the case
at 25
degrees. Amazing stuff. I try to run all linear power amps pushing 20
amps with the case at 25 degrees personally

We never believed the SOAR curves, so we just pushed them until they
exploded.

That probably means that John Larkin never understood what the Safe
Operating Area curves were trying to tell him.  They do present a
plot of safe drain currents against drain-to-source voltage which
does tell you something about operating the parts outside the
saturation region, despite Bitrex\'s claim to the contrary,

The data sheet for Phil Allison\'s favourite N-channel part

http://www.irf.com/product-info/datasheets/data/irfp240.pdf

shows just such a curve at figure 8.

http://www.irf.com/product-info/datasheets/data/irfp9240.pdf

shows a very similar datasheet for the P-channel part Phil
reccommends. Again, the SOA curve is a figure 8.

snipped John boasting about something some customer managed to
extract from him


The claim I\'m making is that those constant power curves at the right
assume the temperature is uniform across the MOSFET die, as it\'s likely
to be in a switching application where it\'s either fully off or each
pulse is putting it solidly into the ohmic region.


Makes no sense. Fig 8 clearly has data at 200 volts and 5 amps.

I don\'t see any assumptions about temperature uniformity. The SOAR
curve just specs what is safe.


For a single pulse, yes? So, one pulse and you\'re done forever?

For switching applications the SOA curves are very useful tools for part
_rejection_ they tell you unambiguously what a part can\'t do.

They\'re less useful for part-selection/optimization. And for linear
operation the curves often look worse particularly for lower
voltage/high transconductance devices, but why are they gonna show you
the part look bad for an application 99% of people looking at the part
aren\'t gonna use it for.

 

[Klaus Kragelund]

On 22-11-2020 07:49, Phil Allison wrote:

boB wrote:

==========

http://www.irf.com/product-info/datasheets/data/irfp9240.pdf


These have comparatively small die size for a TO-247. Probably better
parts for linear audio out there I am thinking. But that\'s just by
going on the spec sheet. YMMV

If for switching, there is definitely better parts that these at 200V.

Not sure how good Exicon Lateral MOSFETS but supposedly they are
great for class AB or maybe even class A audio amps.


** They are normally fine, well most of them are - but they did make a batch of duds once.
Dual chip devices where the chips would lose most of their gm over time.

With a good component power sharing technique, (whichever technique
that might be), lots of available FETs should work if you have enough

** Hexfets (et alia) need careful matching to run in parallel.
Real PITA especially for repairers.

Probably best used as \" current dumpers \" to eliminate the issue altogether.

Most FETs are not good for using in linear mode, e.g Class AB due to the
Spirito effect:

https://www.google.com/search?q=spirito+effect&oq=spirito+effect&aqs=chrome..69i57j0.3591j0j4&sourceid=chrome&ie=UTF-8

 

[bitrex]

On 11/22/2020 3:29 PM, Klaus Kragelund wrote:

On 22-11-2020 07:49, Phil Allison wrote:
  boB wrote:

==========

http://www.irf.com/product-info/datasheets/data/irfp9240.pdf


These have comparatively small die size for a TO-247. Probably better
parts for linear audio out there I am thinking. But that\'s just by
going on the spec sheet. YMMV

If for switching, there is definitely better parts that these at 200V.

Not sure how good Exicon Lateral MOSFETS but supposedly they are
great for class AB or maybe even class A audio amps.


  ** They are normally fine, well most of them are - but they did make
a batch of duds once.
   Dual chip devices where the chips would lose most of their gm over
time.

With a good component power sharing technique, (whichever technique
that might be), lots of available FETs should work if you have enough

** Hexfets  (et alia)  need careful matching to run in parallel.
    Real PITA especially for repairers.

   Probably best used as \" current dumpers \"  to eliminate the issue
altogether.


Most FETs are not good for using in linear mode, e.g Class AB due to the
Spirito effect:

https://www.google.com/search?q=spirito+effect&oq=spirito+effect&aqs=chrome..69i57j0.3591j0j4&sourceid=chrome&ie=UTF-8

Nah many will work fine if you de-rate everything conservatively but you
don\'t need a SOA curve to tell you this.

 

[Phil Hobbs]

On 11/19/20 7:42 PM, John Larkin wrote:

On Thu, 19 Nov 2020 15:25:29 -0800 (PST), George Herold
ggherold@gmail.com> wrote:

On Thursday, November 19, 2020 at 4:51:32 PM UTC-5, John Larkin wrote:
On Thu, 19 Nov 2020 09:12:04 -0800 (PST), George Herold
gghe...@gmail.com> wrote:

On Thursday, November 19, 2020 at 11:51:58 AM UTC-5, piglet wrote:
On 19/11/2020 15:52, George Herold wrote:
On Thursday, November 19, 2020 at 10:37:06 AM UTC-5, jla...@highlandsniptechnology.com wrote:
On Thu, 19 Nov 2020 05:31:20 -0800 (PST), George Herold
gghe...@gmail.com> wrote:

On Thursday, November 19, 2020 at 7:25:48 AM UTC-5, Jeff Urban wrote:
Many know I set out to build a really good amp. Well after all that I found it can\'t work. The drawing was on the bench and I saw the problem immediately, at a glance. Damn.

But I did find it. Now it needs power MOSFETs for outputs. This looks pretty much non-negotiable.

I forget which is which but they are all the same. Al either ?N channel or P channel. The difference it the power supply. Which is easier to design, but what if the better choice need negative, ? Then I draw it upside down, so what ?

So which is better or more linear or whatever ?

We are in the 140V/18A range.
Is this a linear amp? If so that\'s a lot of heat.
Do you have \"Art of Electronics\". (The 2nd ed. is probably fairly cheap now.)

George H.
The problem is not well specified. \"Good amp\" is not very clear.

Class-D amps are simple and efficient. I\'m designing one right now.

Most mosfets are designed for switching and don\'t take kindly to
linear operation, way out there on their SOAR curve. They tend to blow
up at some fraction of their rated power dissipation; bipolars do that
too.

We learned about that.

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



--

John Larkin Highland Technology, Inc

Science teaches us to doubt.

Claude Bernard
Here\'s a crazy idea... ( idea stolen from a linear power supply with stepped taps
on the transformer.) How about a linear amp (inner loop) with some switched
power supply rails... ? It would probably be ugly.
George H.

Yep, it\'s been done already. Goes by weird names like class \"H\" or \"G\"
or whatever marketing thinks sounds cool.

piglet
Thanks piglet, you can tell I\'m an audio expert. :^)
Not much when searching for class G/H but this seems good.
https://sound-au.com/articles/class-g.htm

GH
We don\'t know if the OP wants to drive motors or speakers or rail
guns.

Yeah. The load is important. R\'s are easy.
Walking around thinking, I don\'t really like the multi-tapped
G-amp anymore than the two tap A/B amp. (+/-)
When driving weird loads cross-over distortion.. hic-ups is a concern.
I\'m thinking the 3 tap class G thing has three times as many
cross-overs... depending on the amplitude.

So how about a class D amp doing a (relatively) slow power rail.
(say 1 ms)
and a class A amp inside doing the fast stuff. (1 us?)
I\'m thinking single sided.
That wouldn\'t work for a short pulse.

George H.


A real class-D amp is better than any human can tell, assuming we are
talking audio here. That\'s certainly a reasonable way to get
kilowatts.

I think there is a class of RF power amps that modulate the power
supplies of the final, to track the RF envelope. Delay lines are
involved I recall.

Sure. It\'s called a \"plate modulator\".

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC / Hobbs ElectroOptics
Optics, Electro-optics, Photonics, Analog Electronics
Briarcliff Manor NY 10510

http://electrooptical.net
http://hobbs-eo.com

 

[Don]

piglet <erichpwagner@hotmail.com> wrote:

<snip>

Your mention of chokes reminds me of this interesting and unusual amplifier:

https://www.dropbox.com/s/df5kxw3wsjw73pz/ChokeLoadedAmplifierElectronics-World-1999-11.pdf?dl=0

<snip>

The base of Tr6 connects to one end of R12. Is the other end of R12
supposed to connect to Tr10\'s drain?

What\'s the deal with the dashed line around Tr10, Tr11, L2, Sw1, etc?
Is the dashed line supposed to denote a module?

Danke,

--
Don, KB7RPU, https://www.qsl.net/kb7rpu
There was a young lady named Bright Whose speed was far faster than light;
She set out one day In a relative way And returned on the previous night.

 

[Phil Allison]

Klaus Kragelund fabricated :

============================

Most FETs are not good for using in linear mode, e.g Class AB due to the
Spirito effect:

** Horse\'s manure.

I bet you have zero experience dealing with commercial mosfet amplifiers.


...... Phil

 

[John S]

On 11/22/2020 3:34 PM, Phil Hobbs wrote:

On 11/19/20 7:42 PM, John Larkin wrote:
On Thu, 19 Nov 2020 15:25:29 -0800 (PST), George Herold
ggherold@gmail.com> wrote:

On Thursday, November 19, 2020 at 4:51:32 PM UTC-5, John Larkin wrote:
On Thu, 19 Nov 2020 09:12:04 -0800 (PST), George Herold
gghe...@gmail.com> wrote:

On Thursday, November 19, 2020 at 11:51:58 AM UTC-5, piglet wrote:
On 19/11/2020 15:52, George Herold wrote:
On Thursday, November 19, 2020 at 10:37:06 AM UTC-5,
jla...@highlandsniptechnology.com wrote:
On Thu, 19 Nov 2020 05:31:20 -0800 (PST), George Herold
gghe...@gmail.com> wrote:

On Thursday, November 19, 2020 at 7:25:48 AM UTC-5, Jeff Urban
wrote:
Many know I set out to build a really good amp. Well after all
that I found it can\'t work. The drawing was on the bench and I
saw the problem immediately, at a glance. Damn.

But I did find it. Now it needs power MOSFETs for outputs.
This looks pretty much non-negotiable.

I forget which is which but they are all the same. Al either
?N channel or P channel. The difference it the power supply.
Which is easier to design, but what if the better choice need
negative, ? Then I draw it upside down, so what ?

So which is better or more linear or whatever ?

We are in the 140V/18A range.
Is this a linear amp? If so that\'s a lot of heat.
Do you have \"Art of Electronics\". (The 2nd ed. is probably
fairly cheap now.)

George H.
The problem is not well specified. \"Good amp\" is not very clear.

Class-D amps are simple and efficient. I\'m designing one right now.

Most mosfets are designed for switching and don\'t take kindly to
linear operation, way out there on their SOAR curve. They tend
to blow
up at some fraction of their rated power dissipation; bipolars
do that
too.

We learned about that.

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



--

John Larkin Highland Technology, Inc

Science teaches us to doubt.

Claude Bernard
Here\'s a crazy idea... ( idea stolen from a linear power supply
with stepped taps
on the transformer.) How about a linear amp (inner loop) with
some switched
power supply rails... ? It would probably be ugly.
George H.

Yep, it\'s been done already. Goes by weird names like class \"H\" or
\"G\"
or whatever marketing thinks sounds cool.

piglet
Thanks piglet, you can tell I\'m an audio expert. :^)
Not much when searching for class G/H but this seems good.
https://sound-au.com/articles/class-g.htm

GH
We don\'t know if the OP wants to drive motors or speakers or rail
guns.

Yeah.  The load is important.  R\'s are easy.
Walking around thinking, I don\'t really like the  multi-tapped
G-amp anymore than the two tap A/B amp. (+/-)
When driving weird loads cross-over distortion.. hic-ups is a concern.
I\'m thinking the 3 tap class G thing has three times as many
cross-overs... depending on the amplitude.

So how about a class D amp doing a (relatively) slow power rail.
(say 1 ms)
and a class A amp inside doing the fast stuff.  (1 us?)
I\'m thinking single sided.
That wouldn\'t work for a short pulse.

George H.


A real class-D amp is better than any human can tell, assuming we are
talking audio here. That\'s certainly a reasonable way to get
kilowatts.

I think there is a class of RF power amps that modulate the power
supplies of the final, to track the RF envelope. Delay lines are
involved I recall.

Sure.  It\'s called a \"plate modulator\".

Cheers

Phil Hobbs

Where would be the delay line in a plate modulator?

 

[ke...@kjwdesigns.com]

On Sunday, 22 November 2020 at 15:15:25 UTC-8, Don wrote:
....

The base of Tr6 connects to one end of R12. Is the other end of R12
supposed to connect to Tr10\'s drain?

Yes, I checked my copy of the original and the line is missing, but pretty certain that\'s where it goes.

What\'s the deal with the dashed line around Tr10, Tr11, L2, Sw1, etc?
Is the dashed line supposed to denote a module?

If you follow the line around it is enclosing the low level circuitry that is constructed on strip-board (as described in the text after \"Construction and Performance\".

The power components are mounted on the chassis and heat sink.

kw

Danke,

--
Don, KB7RPU, https://www.qsl.net/kb7rpu
There was a young lady named Bright Whose speed was far faster than light;
She set out one day In a relative way And returned on the previous night.

 

[boB]

On Sun, 22 Nov 2020 10:41:03 -0800, jlarkin@highlandsniptechnology.com
wrote:

On Sun, 22 Nov 2020 13:09:47 -0500, bitrex <user@example.net> wrote:

On 11/21/2020 9:50 PM, Bill Sloman wrote:
On Sunday, November 22, 2020 at 3:23:20 AM UTC+11, jla...@highlandsniptechnology.com wrote:
On Sat, 21 Nov 2020 03:00:50 -0500, bitrex <us...@example.net> wrote:

On 11/21/2020 12:44 AM, jla...@highlandsniptechnology.com wrote:
On Fri, 20 Nov 2020 16:27:03 -0800 (PST), Phil Allison
palli...@gmail.com> wrote:

some bit brain fuckhead wrote:
=============================

Yes also because all the graphs and safe operating area curves for
modern switching MOSFETs are of little use when they\'re used in a linear
application.


** FFS post *only* on topics you know something about.

That will narrow the field right down to SFA.

snip

The SOA curve in most switching device datasheets tells you e.g. that
you can push 20 amps at DC with the MOSFET saturated and the case at 25
degrees. Amazing stuff. I try to run all linear power amps pushing 20
amps with the case at 25 degrees personally

We never believed the SOAR curves, so we just pushed them until they
exploded.

That probably means that John Larkin never understood what the Safe Operating Area curves were trying to tell him. They do present a plot of safe drain currents against drain-to-source voltage which does tell you something about operating the parts outside the saturation region, despite Bitrex\'s claim to the contrary,

The data sheet for Phil Allison\'s favourite N-channel part

http://www.irf.com/product-info/datasheets/data/irfp240.pdf

shows just such a curve at figure 8.

http://www.irf.com/product-info/datasheets/data/irfp9240.pdf

shows a very similar datasheet for the P-channel part Phil reccommends. Again, the SOA curve is a figure 8.

snipped John boasting about something some customer managed to extract from him


The claim I\'m making is that those constant power curves at the right
assume the temperature is uniform across the MOSFET die, as it\'s likely
to be in a switching application where it\'s either fully off or each
pulse is putting it solidly into the ohmic region.


Makes no sense. Fig 8 clearly has data at 200 volts and 5 amps.

I don\'t see any assumptions about temperature uniformity. The SOAR
curve just specs what is safe.

(Not that I unreservedly believe them. Processes change more often
than data sheets.)

Oh My ! Process changes are changes that I have to worry about. Or
used to have to at least. Back in the 1990s, in one of our power
inverters, we used a certain Motorola (On Semi) FET in the circuit.

They worked fine untill they did a die shrink on that part.

Inverters have to surge and we rely on the large die area for
transient thermal transfer. They said \"but the RdsOn is the same !\"

Well... They did not understand evidently how that can hurt the
thermal impedance in the application.

As I remember, we changed to Harris Semicondutor (then Fairchild and
On Semi again I think) and all was well.

Never had a problem like that again luckily.