Which N Or P Power MOSFETs ?

I thought we'd done with Trump, but it seems he's decided to post here :-(

--
Cheers 
Clive

nd it can't work. The drawing was on the bench and I saw the problem immedi ately, at a glance. Damn.

tty much non-negotiable.

r 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 ?

One way of making a decent class-AB audio output stage used complementary p airs of power FET - a P-channel device with it's source tied to the positiv e rail, and and N-channel device with it's source tied to the negative rail .

You use bipolar transistors to monitor the current being fed into the speak ers and generated the gate drives for the power MOSFETs. The tricky bit is keeping both MOS-FETs just on when the output is half-way between the rails . People like Douglas Self have written reams on the subject.

Buy one of his books, or one of his amplifiers. The amplifier will work bet ter than anything you can build for yourself, and by the time you've blown up a few big power MOSFET's it will also turn out to be the cheaper option.

If you are very lucky, Phil Allison will chip in here. He won't be polite b ut his well-informed.

--
Bill Sloman, Sydney

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.

--

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.

Why? Because our president-elected is bipolar?

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

piglet

Instead of going straight for 140V/18A try your ideas first as a headphone amp then you can use little TO-92 fets in white proto-board and each burnout only wastes cents?

piglet

140 * 18 = 2520. Think big heat sinks.

--

John Larkin         Highland Technology, Inc 

Science teaches us to doubt. 

  Claude Bernard

I thought nobody would volunteer to turn a technical thread into politics.

Thanks for stepping up.

--

John Larkin         Highland Technology, Inc 

Science teaches us to doubt. 

  Claude Bernard

Thanks piglet, you can tell I'm an audio expert. :^) Not much when searching for class G/H but this seems good.

GH

Vertical MOSFETs when used as linear amps have basically all the same problems BJTs can have, thermal runaway and second breakdown.

Lateral MOSFETs are more well-behaved but there are few of them on the market and they tend to be filthy expensive.

The drive requirements for vertical MOSFETs as linear amps at high powers isn't much improved with respect to BJTs, either.

Or just a 50 watt amp. That requires what, about +/- 35 volt rails to deliver 20 VRMS into an 8 ohm load.

Differential input stage feeding a bootstrap VAS followed by a 2N3055 Darlington and a 2N3055 Sziklai to make a PNP is a classic. 8 transistors if you use a current source for the input pair.

bitrex is completely wrong as usual :

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

** Yeah right - problems that were solved 40 years ago.

** Neither claim is true.

Both TO3 and flat pak laterals are available at tolerable prices.

Their advantages easily outweigh the extra cost.

..... Phil

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

** Straight out of the Beatles era.

" Love, love me do.... "

..... Phil

Phil's behind the times as usual, modern devices like HEXFETs are not immune (PDF):

Well which do you like?

The power stage in my Onkyo TX 2500 Mk II is very much like that, except it adds a voltage source bias to give about 35 watts class AB from +/-

40 volt rails. From about 1978 I think. They didn't bother with a current source in the pair tail.

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