high frequency driver for ultrasonic cleaning transducer

we are currently building a driver for our ultrasonic cleaning transducer. The operating voltage of the ultrasonic cleaning transducer is 500volts to 1.2kilo volts and the maximum power output is 50watts. here is the circuit that we made:

The circuit is not working when we tested it with 24volts as the source for the h-bridge.

I would also like to ask for other alternatives other than an h-bridge to be use for this circuit.

Hiya Keith!

Don't give up on your H-bridge yet... [while I haven't checked your driver circuit in detail for appropriate 'dead-time' (guard bands between drive applied to the separate phases) generation], there were a couple of dubious aspects about the design of the MOSFET gate drive circuits that might warrant a closer look.

Have a peek at the TI app note: **broken link removed**, as it describes some of the design considerations when driving MOSFETs in applications like yours.

For starters, I'd be wary of the series 1N914 diodes D5-D8 in your schematic. While I can see you're trying to avoid significant reverse bias of the gate, they also prevent the removal of the gate charge and will extend the FET switch-off times considerably. This will lead to rail-to-rail shorts (and possibly dead FETs) when the opposite phase is energised.
On the same note, why have you included C7-C10 (100 pF)? As far as I can tell, these will only serve to worsen the FET switching characteristics. Likewise the 22K resistors (R2,3,10,11) are much too high, forming a discharge time constant far exceeding (1/ultrasonic switching frequency) given the ~1 nF of MOSFET gate capacitance.

While I suspect with some attention to redesigning the H-bridge drive circuitry it will fit your needs nicely, another method commonly used is a step-up transformer with series inductance (to resonate away the transducer capacitance). Although much lower powered than your application, you can see the concept applied in the schematic here: http://kitsrus.com/projects/k126.pdf

Some extra food for thought: There are dedicated bridge driver ICs available (such as G5 HVIC: Next Generation HVIC Platform) which *greatly* simplify HV bridge design. Maybe one of these might help out...?

Good luck!

I agree about the switch-off delay and dead time problem. Supplementing active pull-down circuits at the gates could help. If you're not worried about slow switch-off and respective losses, you should at least increase the time constants of the dead time generators to avoid H bridge shoot through.

For simplicity I would use the transducer and its resonating inductance as part of a tuned circuit which you drive with a single transistor in class C from a 50V supply line.
Frank

Send the asm file ill check it out

---------- Post added at 20:27 ---------- Previous post was at 20:26 ----------

Send the asm file
i believe u using LTSPICE
make sure l1 primary for l2 l3
make sure l4 primary for l5 l6
u will need isolated scope for that ....meaning the probe tip or shield is NOT grounded.
remove the 4k resistor i believe the ultra sonic is a capacitor tweeter try 0.1u 100vac