Solid state high voltage audio frequency amplifier

[TimFox]

Note that the four 1 kV supplies needed for two stereo channels are ungrounded, while the 12 V supplies for the op amps are grounded.

[magic]

It seems H-bridge configuration on single 2kV supply would be simpler

[cdev]

Thank you!  Frankly, I had never seen solid state devices that handle such high voltages.

Ive been curious about the kinds of optics that could be used in high contrast video projection .. MEMS, lasers, etc.

Also I have a friend who is interested in lasers for astronomy.


Basically they burn a hole in the haze.. to see clearly.. Always wondered how they do it. His wife is also an old friend, they are both into this very energetic stuff.. Literally.

I am not volunteering my devices, but for years I have had two IC's they are PA-08 by Apex, I think. They appear to be broadband op-amps that operate at high voltages. Ive been holding on to them for use with servos or mechanical devices that require high voltage and rapid response.
They work from DC to over 1 MHz, and support quite a bit of power if adequately heat sinked.

They look interesting. I got them at an estate sale, with sockets. They were owned by a retired engineer for RCA, who appears to have designed solid state devices and knew a lot about transistors, ICs etc.

Maybe that device, PA-08 might suit your bill. I am curious about what I could do with mine.

Last year we evaluated the Apex PA443 HV Dual amp when we needed outputs to +-150V (they are rated to +-175V). Quickly designed a built a test PCB (see below) to interface with an AWG, hosed up the PA443 footprint tho

The idea was to evaluate the amps performance with special type waveforms for a new Phased Array Controller which required 128 independent programmable channels capable of suppling +-150V precision waveforms. Additional research into the phase array voltage controlled elements reveled the voltage requirement could be relaxed to +-100V, so we ended up selecting the OPA462 for various reasons including footprint (we used 128 individual amps, later possibly expanding to 256 or even more).

Anyway, recall the PA443 performed well and had no serious issues. If one can live with the 350V (+-175V) max supply level, these might be a consideration if you can get them!! Edit: The data sheet shows (Fig 16) an application capable of supplying 660Vpp using a Push-Pull arrangement.

https://www.apexanalog.com/resources/products/pa441u-pa443u.pdf

Best,
(Attachment Link)

[TimFox]

Back in the late 1970s, when still a grad student, before high-voltage MOSFETs, I built an interesting high-voltage amplifier for electrostatic deflection in a 100 kV ion-beam system.
Delco had just come out with some high voltage (800 to 1000 V Vceo, if I remember correctly) NPN transistors in TO-3.
I connected some cascodes with 2N2219 NPN (TO-5) transistors into an interesting totem-pole (looking like an over-developed TTL output stage), powered by +/- 400V.
An op-amp drove the base of the lower cascode through two 2N5416 PNPs in cascode to hold the negative voltage.
Since the current through the high-voltage transistors was not very high, each was mounted on a 2 sq in black heatsink on a perfboard.

[Conrad Hoffman]

Yes, the past! Years ago I worked for Burleigh Instruments Inc., who made piezoelectric devices for the scientific and optical world. We made several high voltage amplifier products, all using those Delco high voltage electronic ignition transistors. DTS-723 and some others. Later we used (I think) BU-209 or something similar, probably TV horizontal deflection transistors. Interestingly, you'll find a HV amplifier circuit in Art of Electronics that's near identical to the one we made for decades at Burleigh. They made some minor changes and improvements, but it was obvious at first glance that it was the same circuit. It's actually a totem pole based on low voltage TTL logic, where you have the top transistor charging the load, and the bottom transistor dumping to ground through a diode, pulling the base of the upper transistor down with it. Not so great at high audio frequencies, but surprisingly linear for what it was. Not sure if it could reach 20 kHz or not. Did work great with capacitive loads.

[NiHaoMike]

I have seen a design for a refrigeration piezoelectric expansion valve driver that was just a small flyback converter along with a divider circuit to sense the output voltage and a high voltage MOSFET switching in a resistor for faster discharge. The bandwidth is on the order of a few Hz, however, and it only had to go up to 800V with no polarity reversal.

[David Hess]

IMO, it's hard to do if you look at the slew rate needed based on voltage and bandwidth. Then you have the capacitance to drive at high frequencies. Makes me want to use a lower voltage amp and a transformer!

The high output voltage is going to require high gain so the amplifier can be decompensated to raise slew rate and gain-bandwidth product.  For fixed compensation amplifiers where this is not possible, a fixed gain stage can be added within the feedback loop to multiply the slew rate and gain-bandwidth product.  Dedicated low voltage audio power amplifiers are almost always decompensated for exactly this reason.

[Marco]

Check out this page from tubecad, if you havent already.

Voltage sharing and bandwidth seem to me to be constrained with the magnitude gate resistor dividers in that design.

In simulation it's okay to say 10 kHz with a 3xPMOS stack consisting of FQP3P50s and 333k resistors, but at 100 kHz it's screwed ... and for the closed loop control you want a little bandwidth to spare. With 33k resistors it works okay at 100 kHz, but now you're burning around 10 W peak in the top resistor at low frequencies and DC.

Resistors dividers in high voltage stacks get toasty if you want to go fast.