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Transformer with integrated current sense?

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KaneTW:
Long story short, I'm planning to use a fullbridge topology to drive ultrasonic transducers at various frequencies (around 40-100kHz, with a switching frequency of ~500kHz).

Due to the metal-bodied transducers being in contact with the case, I need to run them through a transformer so that the side that touches the case can be grounded.

My original plan for a driver PCB involved a current sense transformer and direct drive, but since I'm now isolating the entire output: is there an off-the-shelf way to combine the isolation and current sense transformer?

A shunt instead of the current transformer could work, but that'd replace it with an opamp.

Ideas?

NiHaoMike:
Put a current sense resistor in series with the low side of the secondary. Or swap to a half bridge design with twice the supply voltage to eliminate the need for an output transformer.

T3sl4co1l:
Nah, you need two magnetic paths to do that.

But current transformers are readily available, have more bandwidth than Hall effect sensors or shunt amps, and better CMRR than amps.

Huh, is that 40-100kHz fundamental with a PWM at 500k?  What's that for?

Tim

KaneTW:
I need to keep track of phase for resonance tracking, and that becomes pretty difficult with a square-wave drive according to simulations. 

So I use a modulated PWM signal that, after an output filter, appears to give a pretty decent sinewave into a (series resonant) piezo load.

T3sl4co1l:
Weird...

I'm literally playing with a (same frequency) resonant controller at the very moment; it seems to track phase just fine (it's using a type 2 phase detector, between driven voltage and load current, of a series resonant LC tank).

You would probably want to do the inverse, since a piezo is a majority capacitive load.  That is, current-sourcing inverter, sense voltage for feedback.

Heh, I have a few control boards to spare, if you're interested.

Tim

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