Best MOSFET for output stages

[analog_guy]

Originally Posted by abraxalito

Did you build or did you simulate?

I simulated until I determined the best type of devices.Then I built.

[okkyn]

Originally Posted by onto aban

Don't dismiss EEEngine. they are simple and really work. based on class AB supplied with simple unstable (self oscillating) power regulator. Class-D even class-H may have death too.

http://www.yamahaproaudio.com/downlo...tepaper_en.pdf

Hi onto, salam kenal. Kerja di Polytron Kudus ya? You sound knowledgeable about this EEEngine. Are you doing research on this topic?

[Bob Cordell]

Originally Posted by tiefbassuebertr

Hi Bob,
... in generall or only by certainly topologies? All me known output power stages topologies, where only N-Channel MOSFET's in use, I have listed here:
Only N-Channel MOSFETs (NMOS); better Audio from non complements by Audio Power?

check also my post #43 from this thread.

Regarded the CSPP (circlotron) topology I can not imagine that you really believe this.

I have to say that I am not familiar with all of the possible N-channel-only output stages, but I have never seen a quai-complementary N-channel output stage using source follower on top and CFP structure on bottom that I thought would be able to perform as well as a complementary output stage.

However, here is an example of an N-channel-only output stage that some might like, and would be symmetrical. Use a pair of N-channel devices in push-pull with an output transformer (as if they were tubes).

Cheers,
Bob

[tiefbassuebertr]

Originally Posted by Bob Cordell

I have to say that I am not familiar with all of the possible N-channel-only output stages, but I have never seen a quai-complementary N-channel output stage using source follower on top and CFP structure on bottom that I thought would be able to perform as well as a complementary output stage.

However, here is an example of an N-channel-only output stage that some might like, and would be symmetrical. Use a pair of N-channel devices in push-pull with an output transformer (as if they were tubes).

Cheers,
Bob

The quasi-complementary PP power buffer stage from post 94 (N-channel output stage using source follower on top and CFP structure on bottom) was developed from Mr. Nelson Pass. I have found it in the TAA Book - go to
Crazy Clipping Behavior Quasi Complementary MOSFET Citation 12 TAA Book
At this time no P-Ch MOSFETs available - therefore that design. After release P-Channel MOSFETs from IRF several months later Mr. Pass updated this circuit and remove the CFP on bottom.

The topology you like is that one from follow URL's - so I think:
Zero Feedback Transformer Audio Power Amplifier
index
Push-Pull using only N-Channel MOSFETs

and what about the circlotron like follow URL's (my personal favorite of all push pull variantes)?
http://www.amplimos.it/images/CIRCLOTRON_50W.bmp
Circlotron amp using N-channel mosfets
http://www.davidsaudio.com/Nine.pdf
6moons audio reviews: Thorens TEM 3200

A URL collection from me of the most possible "N-channel-only output stages" you will find there:
URL collection of Totem Pole and CSPP (Single Ended related) Solid State Output Stage
and there:
Only N-Channel MOSFETs (NMOS); better Audio from non complements by Audio Power?

For me the most interested topology for universal use to modify exist amps, if the orig. output power devices too expensive or no longer available seems to be follow:
It's cheap, it's N, it's dirty, it's.... The CIRCLOMOS!!!
unfortunately I haven't time to check out the behaviour until this day.

[ilimzn]

There are 3 topologies that come to mind that make a completely symetrical amp using onlu N-type devices. They all have a phase splitter of some kind in common:
1) totem pole output with bootstrapped concertina type phase splitter (best made with a MOSFET - a BJT would show errors because of Ic not equal to Ie). The top transistor only appears to be working as a follower - the bootstrapping actually makes it common source operation.
2) totem pole output with P-type LTP as phase splitter (usually requires extra positive rail for best rail to rail performance, although bootstrapping can be used with some difficulty). Again, top device only appears as a source follower, since the drive is voltage derived from the LTP output current, terminated to the output, this is a form of bootstrappinf, so the top device again reverts to common source.
3) Circlotron. It requires differential drive with the same DC offset, and is actually possible to do it two ways - source follower based and common source based, but the latter is much more difficult to bias. The source follower version is actually the only topology that comes to mind that utilizes both MOSFETs as anything near source followers and does not require a transformer to merge the phases back together into a single output. The only real disadvantage here are the multiple floating power supplies, bias is actually very simple (don't confuse this with the Bongiorno patent that shows how to cleverly use the Vbe of a BJT output circlotron to compensate itself thermally).

[tiefbassuebertr]

Originally Posted by ilimzn

There are 3 topologies that come to mind that make a completely symetrical amp using onlu N-type devices. They all have a phase splitter of some kind in common:
1) totem pole output with bootstrapped concertina type phase splitter (best made with a MOSFET - a BJT would show errors because of Ic not equal to Ie). The top transistor only appears to be working as a follower - the bootstrapping actually makes it common source operation.
2) totem pole output with P-type LTP as phase splitter (usually requires extra positive rail for best rail to rail performance, although bootstrapping can be used with some difficulty). Again, top device only appears as a source follower, since the drive is voltage derived from the LTP output current, terminated to the output, this is a form of bootstrappinf, so the top device again reverts to common source.
3) Circlotron. It requires differential drive with the same DC offset, and is actually possible to do it two ways - source follower based and common source based, but the latter is much more difficult to bias. The source follower version is actually the only topology that comes to mind that utilizes both MOSFETs as anything near source followers and does not require a transformer to merge the phases back together into a single output. The only real disadvantage here are the multiple floating power supplies, bias is actually very simple (don't confuse this with the Bongiorno patent that shows how to cleverly use the Vbe of a BJT output circlotron to compensate itself thermally).

you mean this topologies:
1) totem pole output with bootstrapped concertina type phase splitter (best made with a MOSFET - a BJT would show errors because of Ic not equal to Ie). The top transistor only appears to be working as a follower - the bootstrapping actually makes it common source operation. ... is it really so? - read this:
The Tube CAD Journal: symmetrical solid-state output stages
http://www.amplimos.it/images/N-CH1.JPG

2) totem pole output with P-type LTP as phase splitter
http://peufeu.free.fr/audio/schemas/Kaneda_Mosfet.jpg
http://www.amplimos.it/images/2sk77%...MAHA%20B-1.gif

[ilimzn]

Originally Posted by tiefbassuebertr

you mean this topologies:
1) totem pole output with bootstrapped concertina type phase splitter (best made with a MOSFET - a BJT would show errors because of Ic not equal to Ie). The top transistor only appears to be working as a follower - the bootstrapping actually makes it common source operation. ... is it really so? - read this:
The Tube CAD Journal: symmetrical solid-state output stages
http://www.amplimos.it/images/N-CH1.JPG

2) totem pole output with P-type LTP as phase splitter
http://peufeu.free.fr/audio/schemas/Kaneda_Mosfet.jpg
http://www.amplimos.it/images/2sk77%...MAHA%20B-1.gif

Yes it is so, at least if you want to keep it DC coupled and reasonably uncomplicated.
From your examples, only the bottom amp in the John BRoskie link works it's outputs as source followers but it's AC coupled. The amplimos amp, and the kaneda amp are precisely the arhitecture I mentioned, as is the B-1, but in the case of the B1 it's using depletion mode VFETs (SITs) so the second stage uses N-ch MOSFETs and develops negative bias - which could be confusing you. Here we are talking about MOSFETs so in 99.99% of all cases enhancement mode devices are assumed, which lends itself to a P-ch (or PNP) LTP as the phase splitter in my example (2).
Regarding Broskie's amp, it is possible to do this DC coupled using current conveyors (also LTP's and even simple concertinas could be used to level shift the drive signals for the MOSFETs) but it gets complicated and not easy to manage re stability, as you can't disregard the extra stages.

[Jon Lord]

The problem with all kinds of parallel symmetric (against complementary symmetric) topologies is, that somewhere in the circuit a kind of differential VAS and/or phase splitter means has to be used in such a way, that the two "phases" see different voltage swings and/or completely different output impedances.

Some incarnations of this parallel symmetric paradigm try to solve this by using differential VAS stages running at extreme bias voltage levels and heavy cascoding. The B-I e.g. uses a -200V (the -C voltage) supply to achieve this (and the negative bias of the V-FETs), but nevertheless there is still a bunch of problems:

- The VAS for the upper (push) transistor still sees (AC wise) the full voltage swing, while the corresponding path of the lower (pull) transistor sees only the gate voltage variation.
- Another drawback of these common parallel schemes is the very ill-informed use of non-inverting feedback, which btw. kills any symmetry from the input stage onwards (by means of unavoidable common mode distortions) ...
- Just another con is the inherent asymmetrical slew rate bahaviour (especially of the totem pole flavours of this paradigm) ...

The asymmetries introduced by these mechanisms can't be reduced very well, so why even think about such topologies at power levels of 200W (or even 22kW ;-), especially since these tend to love Class A operation ?

And finally, believe me, the Yamaha B-I produces lots of even order distortions, which it shouldn't do if the parallel symmetry idea could really work here (and even anywhere else) and it even doesn't sound better than (partially) complementary amplifiers of half the complexity and driver supply voltage and ten times better reliability ...

But then there is still the rather dogmatic question, if topological symmetry is an ultimate goal at all, especially since a bridge mode of any topology (and some matching) always leads into a naturally symmetrical behaviour ...

[Bob Cordell]

Originally Posted by Jon Lord

The problem with all kinds of parallel symmetric (against complementary symmetric) topologies is, that somewhere in the circuit a kind of differential VAS and/or phase splitter means has to be used in such a way, that the two "phases" see different voltage swings and/or completely different output impedances.

Some incarnations of this parallel symmetric paradigm try to solve this by using differential VAS stages running at extreme bias voltage levels and heavy cascoding. The B-I e.g. uses a -200V (the -C voltage) supply to achieve this (and the negative bias of the V-FETs), but nevertheless there is still a bunch of problems:

- The VAS for the upper (push) transistor still sees (AC wise) the full voltage swing, while the corresponding path of the lower (pull) transistor sees only the gate voltage variation.
- Another drawback of these common parallel schemes is the very ill-informed use of non-inverting feedback, which btw. kills any symmetry from the input stage onwards (by means of unavoidable common mode distortions) ...
- Just another con is the inherent asymmetrical slew rate bahaviour (especially of the totem pole flavours of this paradigm) ...

The asymmetries introduced by these mechanisms can't be reduced very well, so why even think about such topologies at power levels of 200W (or even 22kW ;-), especially since these tend to love Class A operation ?

And finally, believe me, the Yamaha B-I produces lots of even order distortions, which it shouldn't do if the parallel symmetry idea could really work here (and even anywhere else) and it even doesn't sound better than (partially) complementary amplifiers of half the complexity and driver supply voltage and ten times better reliability ...

But then there is still the rather dogmatic question, if topological symmetry is an ultimate goal at all, especially since a bridge mode of any topology (and some matching) always leads into a naturally symmetrical behaviour ...

Alas, different people have different views of what constitutes symmetry. The blind pusuit of any particular symmetry at the expense of common sense should be avoided. Just because both the push and pull output transistors are the same type in a quasi-complementary output stage does not make its operation the least bit symmetrical.

Similarly, those who pursue symmetry just because it looks cool on a schematic are just as likely to end up with a poor-sounding amplifier as anyone else.

No amplifier design that I know of is perfectly symmetrical in every sense. Pick your poison, but do so wisely.

Cheers,
Bob

[KSTR]

Originally Posted by analog_guy

I simulated until I determined the best type of devices.Then I built.

Do you happen to have (LT)spice models of the BUZ90x's which actually work? I'm in great favor of those Magnatec/Exicon laterals (have used them several times with zero issues) but I have not found yet spice models that are realistic in any true sense of the word...