Piezo-electric signal tweak

Thread Starter


Joined Jan 17, 2007
Hello all,

I'm trying to interrupt a signal being delivered to a piezo-electric actuator, this signal is a "floating" one and has no reference to ground, from what I've deduced so far. The signal starts with a series of quick pulses peaking at 120V, lasting about 0.6 ms in total, and then quickly comes down to around 12V, and that stage can last up to 16 ms. This actuator is for the quick opening and closing of a very special valve in a machine whose behavior I'm trying to tweak a little.
So what I'm trying to do is to cut short the 12V signal a few moments AFTER the 120V signal ends.
I have tried using lots of different components for this purpose, but since the signal is floating, there's virtually no reference ground. And I have not being able to use a transistor nor a darlington, beause they both need a little current to work and the piezo driver is delivering only the current that the piezo component needs. I haven't been able to make it work with MOSFETs either.

The only thing that's worked so far is when I used an opto-isolated SCR. But once an SCR is triggered, it won't switch off until the signal being delivered to the piezo actuator ends... I've tried using the SCR forced commutation technique, but I can't make it work either due to limits in the capacitive load that the piezo driver will accept.

And that pretty much sums up what my dilemma is...

See attached waveform image (ignore the yellow trace). The circuit shown is only an approximate representation of what I think the piezo driver might look like, that is because the driver is encapsulated in resin, and I can't peek inside.

Any suggestions?