Class AB amplifier

There's a circuit in the Art of Electronics, page 169. If you don't have a copy, that's one of the pages that Google has scanned, just type "low-power piezo driver" into the search box. Pages 168-171 are available. As you can see, two high-voltage power MOSFETs are used, one to pull up and the other to pull down, via a diode. That kind of output stage is called a totem pole, and was used in TTL logic gates designed in the late 60s.

We used BUZ-50B power MOSFETs in our original design, but you can substitute an IRFBG20 or another HV part. Infineon's SPA02N80C3 is a low-cost 800V part in stock at DigiKey, with a low gate capacitance, Ciss = 290pF. Its Coss is much higher than the IRFBG20, 130 vs 52pF.

Many thanks, just what I was looking for. I will see if I can get a copy from Amazon, looks like a very useful book.

Simon

Why 500 volts?

I posted my optocoupler-based hv amp to a.b.s.e. a while back. It takes about 6 or so parts. But the highest-voltage optos I know of are

Cascoding low-voltage optocouplers with depletion-mode mosfets should work fine.

John

At 1mA load who needs push-pull.

Personally, I'd use a TUBE, driven from the cathode with solid state whatever. UNKILLABLE ;-)

...Jim Thompson

What, single-ended class A with a resistive pullup? Do the math.

Well, at 5 KV maybe.

John

Duh, invoke a +1000V supply. At 1mA, it's *practically* static electricity, no one will notice. ;-)

Tim

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

Slow scan crt focus with a +6kV dc offset There's a schematic at

So what's a few watts amongst friends ?:-)

I've actually done it at 30KV... almost 50 years ago, when there were damn few semiconductors ;-)

...Jim Thompson

You'll see that it's an expensive book, however, the old saying "you get what you pay for" absolutely applies here.

If you do get it, perhaps you can coerce Mr. Hill into autographing it for you.

Bob

"Jim Thompson" wrote in message news: snipped-for-privacy@4ax.com...

Yep. I agree.

Back in 1980, I built a fully complimentary bridged AB 400V amplifier (using two NPNs in series and two PNP's in series [the inside guys were slaves]) to directly drive electret headphones.

It worked extrememly well, but when I needed to build another one I didn't want all that complexity. The second one was a pair of NPNs with resistor pullups. The resistor value was selected low enough to give me adequate high frequency response (into the capacitive load of the headphones). It did get hotter than the first one, but WTF? It still works after about 20 years of use.

Bob

I've used a 1B3 HV diode as an active regulator element, with the control being the filament voltage.

John

How's this?

The real nuisance will be the hv insulated filament transformers.

At lower voltage, do this with depletion fets.

John

Ooooooh :-(

...Jim Thompson

You don't need the negative supply (or opto-coupler) unless you need to get really close to ground.

...Jim Thompson

Jim Thompson a écrit :

On a friend's toobs amplifier which had some pb with push-pull quiescent current balancing and really huge primary inductance, I had him doing that within a FB loop. (he was crazy about having an opamp 'in the signal path' despite it wouldn't really have been with a more classical solution. You know that kind of guy).

A 1B3 also make a great hv cap for an ac voltage divider.

John

I was thinking of an opamp with +-2000 volt supply rails.

There's a tube, still in use by Kepco or somebody, that's a nice 8KV pentode. And the old color teevees had a shunt regulator tube that was good to 25 kv or something absurd.

John

Either: The 6BK4C (and similar types), a beam triode -- so constructed to prevent ions from destroying the rare earth oxide cathode, it was used as a shunt regulator to control the high voltage directly; Or, a pulse shunt regulator like the 6HS5, also a beam triode with very low perveance but very high current and voltage capacity and gain. These were used to control the height of the flyback pulse as it took place (at the sweep tube's anode, so big peaky voltages!), thereby regulating HV.

Tim

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