Class AB common source mosfet power amplifier

The amplifier? No BS there. Actually there was a Motorola standard part in the mid-60's that used a specially designed OpAmp chip plus

2N2222 and 2N2907 discrete chips to make such a power amplifier. I'm drawing a blank on its part number right now... back to the archive and look ;-)

...Jim Thompson

--
|  James E.Thompson, P.E.                           |    mens     |
|  Analog Innovations, Inc.                         |     et      |
|  Analog/Mixed-Signal ASIC\'s and Discrete Systems  |    manus    |
|  Phoenix, Arizona            Voice:(480)460-2350  |             |
|  E-mail Address at Website     Fax:(480)460-2142  |  Brass Rat  |
|       http://www.analog-innovations.com           |    1962     |
             
         America: Land of the Free, Because of the Brave

So what were they? Left = blue, right = red?

--
Regards, Joerg

http://www.analogconsultants.com/

John Devereux snipped-for-privacy@THISdevereux.me.uk posted to sci.electronics.design:

From what i have read in the thread so far, i think i might suggest a class AC amplifier. Class A around the center +/- 2V or so and class C for larger excursions. Very difficult total design and setup though.

John Devereux snipped-for-privacy@THISdevereux.me.uk posted to sci.electronics.design:

They are called shakers, thank you. And not all that big of one either. I have worked with ones in the 100kW+ rms range. I have seen them big enough to shake a 10,000 lb satellite to 30 G. (random or swept sine)

John Larkin snipped-for-privacy@highNOTlandTHIStechnologyPART.com posted to sci.electronics.design:

For this use it would be a Class D amplifier. Carefully linearized for doing random at various levels.

John Devereux snipped-for-privacy@THISdevereux.me.uk posted to sci.electronics.design:

As a Class D amplifier it may be a much easier design.

Glen Walpert snipped-for-privacy@notaxs.com posted to sci.electronics.design:

The tradeoffs are different at that power level.

Here's a hint: I've seen the inside of an Unholtz-Dickie 10kW shaker amp. For output, this has two water-cooled heatsinks, each mounted with about 50 x stud package BJTs, rated for around 2A, 200V each I would guess. The supply was 70V for each rail, floating so each side (composed of NPNs only!) could drive each half of the output independently. I've never seen this in solid state before, but I do recognize it from exotic tube amplifier designs as the circlotron topology. On the front panel, beside the incredibly over-the-top blur of buttons and setups and conditions and adjustments, are meters showing output voltage up to 100Vrms and collector current up to 200 or 400A (I forget which).

Of course, that's 10kW continuous rated.

A friend of mine enjoys the 1-2kW amps he's built. He's fond of OnSemi parts, of which he's used (I think) TO-3 packaged BJTs for output, and somewhere around +/-80V supply. He says it's stable down to like 1 or 2 ohms load (I forget how much peak current output), and brags that the driver stage can deliver 7A peak to the outputs, providing full power out to 300kHz or so. With that bandwidth, it doesn't matter that it is in fact biased class C. Obviously, he does have a rather hefty toroidial power transformer and lots of heatsinking.

Tim

-- Deep Fryer: A very philosophical monk. Website @

[...]

Sorry for not replying till now - I wanted to simulate it.

It seems to work embarassingly well for resistive and capacitive loads, while inductive loads make it oscillate. Slowing it down, e.g. with capacitors across the opamp current sensing resistors, can make it stable again. I will play with it some more.

Are the diodes for supply sequencing?

--

John Devereux

Yup. Keeps the transistors from frying if the HV supplies aren't up. I like to add a couple of led's in those paths, too, just for fun.

If you want to close an overall loop on output current, inductive loads (the kind I get!) can resonate and wreck loop stability. So loop dynamics, and maybe some load damping, have to be tweaked.

John

I've seen some where they had to regularly pour another layer of concrete onto the foundation and then stop and move to a new spot when the bottom of that concrete "stalactite" was x many feet into the ground (some legal limit for whatever reason).

--
Regards, Joerg

http://www.analogconsultants.com/