Class AB common source mosfet power amplifier

Ok...try now..

D from BC

Ltspice..

Class B

:) The "use a switcher" solution is not new to me - I *did* look into it, and it looked quite hard at these power levels, (compared to a simple "common drain"/complementary pair follower linear). Also the manufacturer of the actuator recommends against usage with class D amplifiers, for reasons which are not totally clear to me. There is a concern about magnetic field noise. Etc.

You *can* buy amplifiers for this application, and they are class AB, linear. I know I should just buy one, but they are not cheap and I got interested and wanted to see if I could make one. It doesn't look too difficult, a conventional audio amplifier "scaled up". Then I got curious about a whether common-source version was practical. That option is looking like a bit too much effort at present, for a one-off, but still interesting to think about.

A switching amplifier will dissipate far less heat.

Efficiency is usually less about saving energy and more about not dissipating it in inconvenient places.

Have you looked at big-ass audio amps for PA (stage) systems? Not consumer stuff. They're powerful, nearly indestructible, and comparatively cheap because even pro audio gear is mass-produced.

Here's something that will produce quite a bit of vibration. The PL340 will put 4000 continuous watts into a 4 ohm bridge. The class-D PL380 puts 5000 watts into 8 ohms.

robert

Thanks, I think these could be an option too.

TI has a line of CMOS OAs with zero crossover distortion using just this type of complementary AB output stage biased with matched current mirrors and driven by injecting the drive into a high impedance node in such a way to disrupt its equilibrium. I'm sure you an duplicate that with discretes and additional OAs to substitute for the various matching requirements.

He who placeth positive supply in lower half of schematic and vice versa shall have perpetual insomnia ;-)

...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 | |

The shaker mfgr recommendation against class D amplifiers may be quite old, say from the time of the 16 kHz switching frequency servo amplifier (a short lived early design which was a big pain in the ear). Modern class D amplifiers leak a lot less of the switching frequency, which is now high enough to easily filter to very low levels. There is probably no longer any valid reason for not using a good class D amp, at least if you decide to buy one. (Your linear approach is certainly easier to design and make work for a one off.)

Everybody knows that electricity is heavy, so likes to fall from the top of the sheet down.

John

Yes, I am sure I could easily do that. Ahem.

I did look at lots of rail-to-rail output stages - with my level of expertise, they were difficult to interpret. It looked likely they would be relying on characteristics that are well defined with on-chip parts, but difficult with discretes. E.g. ratios of emitter areas, thermal and gain matching.

Yep. My recent consultation in Rancho Bernardo had "port order" requirements for left and right edges of the schematics.

...Jim Thompson

And I wish nothing less for whoever came up with the LM324 pinout.

Best regards, Spehro Pefhany

Here's the basic idea of a "perfect" class AB signal splitter, similar to what Win posted, and sort of like what I use in my ultralinear NMR gradient drivers. It really has zero crossover distortion, and quiescent bias is independently adjustable from splitter gain.

The idea of taking signals from an opamp's power supply pins has been around for decades.

John

Isn't the LM324 the device that can be plugged into a socket, rotated off by 180°, and NOT fry?

...Jim Thompson

Yep. I was doing it in 1971 in regulators for the Hughes TOW Missile.

...Jim Thompson

Jim Thompson a écrit :

Supplies?

Can't say as I've actually tried it (that I can remember anyway, I'm sure it could have happened) but it's a 14-pin DIP with power pins in the middle on both sides, plus on the "bottom", GND on the "top". I don't think it would survive unless the supply current was limited.

Best regards, Spehro Pefhany

Maybe it was the "guaranteed fry" that I was trying to suppress from memory ?:-)

...Jim Thompson