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Which N Or P Power MOSFETs ?

To answer your question: the N-channel MOSFETs are usually operated with their drain more positive than the source, making the gate more positive than the source makes them more conductive drain-source, making the gate negative of the source makes them turn off. A small number are available as Depletion variety whereby they are already conductive when the gate is at zero volts (wrt to source) and so you actually need to drive the gate negative to get them off. The great majority of N-channel mosfets are Enhancement variety which are already fully off at zero gate volts. N-channel mosfets are conceptually a little bit like NPN bipolar transistors (overlooking massive things like gates having no base current, poorly defined turn-on voltage etc etc etc). N-channel mosfets are available in the largest range right up to high voltages.

P-channel mosfets are exactly the opposite, the drain is usually operated negative of the source, driving the gate negative of the source makes them conductive, at zero or positive gate volts (wrt source) they are off. They currently exist only as enhancement devices. They are conceptually a little bit like a PNP bipolar (grossly overlooking all the huge differences hinted at above). P-channel mosfets tend to need larger die area to get same on-resistance as a similar N device, are generally harder to make and so cost more. Really high voltage devices don't exist yet. The variety made is smaller.

All that is explained much better in books like the Art of Electronics or on zillions of web-pages.

piglet

Reply to
piglet
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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.

Reply to
George Herold

Nice, being a single ended class A type, I will pick N or P (fet or bipolar) depending on where I want ground to be. Except in extreme cases the polarity shouldn't matter too much.

George H.

Reply to
George Herold

afaiu schottkys help and unlike usually cross-overs the switching happens at higher output so the relative error is smaller

that's basically class-H, a switching supply that maintains a few volts of headroom on a linear amplifier

Reply to
Lasse Langwadt Christensen

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.

Reply to
John Larkin

And audio amp manufacturers sell them. Sony had a popular unit some thirty years ago.

But for different reasons. Secondary breakdown is a problem in bipolar transistors.

Experience is a hard school ...

There's nothing crazy about the idea - it's a recognised form of audio-amplifier class-G or -H or something. It's also complicated and expensive (though not as expensive as delivery that much power from simpler structure.

--
Bill Sloman, Sydney
Reply to
Bill Sloman

I see y'all f***ed this up with style

Now, this amp is not just a good amp, the topology is brad new and not up f or discussion. the other day I found a fatal error in it and I fixed that. it was ot that it owuld blow up, it is that it owuld not do what I want it to do.

This is for audiophiles. You want to call them audiophools you go right the f*ck ahead but when I see someone with a fifty grand turntable I think "Yo u know, they might just have money".

There are other components that take this amp into the three grand range, t hey will spend that.

The design will not be released for some time. It is new. I have already ta lked to lawyers about this, just because I could. Anyway, there is no discu ssion on topography, or complimentaries. All the output devices will be the same polarity.

My question was simple. I am going to and a bunch of these and I want the b est reliability. Now I remember PNP silicon transistors going before the NP Ns. The opposite was true of germanium to some extent, and fact they made f ew of them probably because of that.

So, this amp only has a single supply. Extremely high current. If I can use P channel I can use a + supply. Well if it is really just as reliable. If N channel is more reliable I have to go wit a negative source which I can d o, but to me it is like thinking upside down.

Maybe I''ll just ask Digikey. And the big chokes, I really want to talk to that company with over $300 each, and who knows on the power transformer. B ut Digikey won't know. They just sell the stuff. (not the transformers thou gh)

Reply to
Jeff Urban

Here is a new (to me) class of linear amp: it's a full analog h-bridge, but with added fets to ground either output phase when less than half swing is needed.

Here's my class-D amp:

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It's specified for 200 watts out, but it might output 20 amps peak now and then. I don't know if I really need the schottky diodes; it depends on the reverse recovery behavior of the fet substrate diodes.

--

John Larkin         Highland Technology, Inc 

Science teaches us to doubt. 

  Claude Bernard
Reply to
jlarkin

We know about audiophiles. Douglas Self isn't one.

We also know about people who think that they have re-invented the wheel. You may have come up with an ingenious new topology, but the over-whelming majority of people who think that they have don't know enough to realise that they haven't.

Some of them will.

Digikey provides links to data sheets. You aren't asking anything difficult, but you didn't ask in a way that would prompt a helpful response from people who use lots of power MOS-FETs.

I haven't used any for years, so I can't say anything useful without doing quite a bit of work.

Getting small volumes of specialised transformers made is still pretty much a cottage industry. There are plenty of people around who do it, but you want somebody close enough to visit in person.

It's not strictly necessary, but it tends to pay off.

--
Bill Sloman,  Sydney
Reply to
Bill Sloman

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

** Fact is, Doug he is one - but clearly not an "audiophool". A term I recall " John Woodgate " laid claim to.

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........ Phil

Reply to
Phil Allison

It is called an EER amplifier (Envelope Erasure and Restoration).

--

-TV
Reply to
Tauno Voipio

It matters a lot if it is going to be a switching amp or a linear amplifier as far as power FETs go so.

Whos says it is a great amplifier ? You or the audiophiles ?

The audiophiles that will spend money won't care or be able to tell if it is better than most any other amplifier of the same power rating pretty much. If it costs a lot of money and you can feed them bullshit, they might just buy it.

Reply to
boB

boB wrote: ======= <

** Really? IRF hexfets are used in both.

But you need complementary pairs for a Class B amp and that limits the choices considerably.

Types IRFP240 & IRFP9240 have been used often in that mode.

.... Phil

Reply to
Phil Allison

ht the f*ck ahead but when

ght just have money".

Douglas Self is on the Peter Baxandall side of that particular divide. He p robably is a "golden-eared boy" but prefers to rely on objective measureme nts rather than subject impressions.

"Audiophile" just means somebody who likes sound, but the term has a lot o f associations.

He's a lot deeper into that particular culture than I ever was, and does se em to have known most of the major players personally. The closest I ever g ot to Peter Baxandall was working for a guy who did his apprenticeship at t he Royal Radar Establishment at Malvern under Peter's supervision.

John did try to pass off a Thomas Love Peacock Welsh song here as authentic ancient Welsh, and I caught him at it. He's basically sound, but not above trying it on.

--
Bill Sloman, Sydney
Reply to
Bill Sloman

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

** Yes - very aware of the "gullible listener" phenomenon. The basis of all audiophoolery. FYI: I did my bit as well - coming up with the *only published* test procedure that demonstrates the fallacy in an instant and is easy for any half technical person to carry out in their own home.

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I shall now dub it " .. the button is not working ? " test.

So simple, long as you can appreciate what the *null result* implies.

..... Phil

Reply to
Phil Allison

Doherty amplifier?

Reply to
John S

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

Perhaps you can get your rich audiophools to avoid the toxic and nuclear contaminated mains power line and go for the pure hum-free silence of battery!

piglet

Reply to
piglet

Hmm OK, do you have to make the fets switch on at the zero crossing?

George H.

Reply to
George Herold

Well, it would need a strategy. A clever one would spread the heat out.

It's probably been done.

--

John Larkin         Highland Technology, Inc 

Science teaches us to doubt. 

  Claude Bernard
Reply to
jlarkin

Gosh, you sound serious. I suspected that your original post was a joke.

--

John Larkin         Highland Technology, Inc 

Science teaches us to doubt. 

  Claude Bernard
Reply to
jlarkin

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