Piezo Amplifier

Flyback, either directly or through a step-up transformer.

If you have lots of money and not much time check out Apex amplifiers (they got bought a couple of years ago, I can't remember by whom). That'll give you a basic, ordinary, op-amp that just happens to work at your voltage range. It saves you having to roll your own.

If you want to do it without much effort get a tube amplifier line transformer. Hammond or similar. Or an isolation transformer that presents 230V at the secondary. Then use a voltage doubler and two electrolytic caps, like this:

Depending on the transformer you'll end up with 600-800V. There will be ripple on it so if your amp has a poor power supply rejection ratio (PSRR) you may need a regulator behind it. If you use a 230V iso transformer you'll need larger electrolytics so your voltage doesn't dip below 500V.

If you need some offset just use a 2nd setup like this and add the voltage at the bottom. But (important!): Mind the limited isolation breakdown voltage on the secondaries, there comes a point where it'll go bzzzt ... *PHUT*

Apex (bought by Cirrus) was my first option, but when I saw their crazy prices I have decided to evaluate other cheaper solutions... Thanks to you and Joerg for your advices. Bye

K.

klaus writes

I have not designed any high voltage devices but I have _used_ piezo actuators and would like to make a point here, from a user's perspective. This assumes you are making a product which is going to be sold to other people.

We designed in some piezo actuators which used about 100V. Then we tried to get the equipment certified to the generic industrial safety standard, IEC61010. The biggest problem we had was with these ******* piezo actuators and their drivers, because the voltages were about the magic 42V dc (30V ac) figure. The company who designed them and their drivers seemed totally unaware that there are safety regulations to obey as soon as you exceed these voltages. They used bare enamelled copper wire to the piezos (because they were designed for a vacuum). IEC61010 counts enamel as "no insulation at all". The high voltage wiring needs to be adequately insulated. If it is in a vacuum use PTFE insulation. And make it something easy to solder, and colour coded. Inside your amplifier, make sure there is clear segregation / optoisolation / protection. The IEC61010 tests will assume your 500V can appear across the safety components, so they will need to be adequately rated.

You might also like to look at Linear Tech application note 118:

Me? I'd go the old-fashioned way, step-up line transformer, then rectify.

The I'd use... are you ready for this... vacuum tubes ("valves" on the other side of the pond) for the amplifiers.

Everyone always wants exotic (and failure prone). ...Jim Thompson

Ye olde 6KD6 would be a candidate here:

Or "lampes" where Fred lives :-)

Nah, done it transistorized, many times. What are you afraid of could go wrong?

Under five bucks, meaning even less than a Russian tube:

Short a tube, get a flash... no damage. Now do that to a semiconductor ;-) ...Jim Thompson

Thou shalt not build a contraption this is not protected against the evil forces of a pipe wrench falling onto the output terminals :-)

As long as the wrench falls onto the terminals but not onto the amp itself the tubes are fine I suppose...

robert

Real designers don't use pipe wrenches around exposed electronics.

Designers don't but installers and maintenance folks do :-)

One episode: "Wow, how did that happen?" ... "Well, we have this 5-ton truck and ..."