Building opamp circuit first time, using LTspice first time.

[antknee]

I will need 5 Watts maximum, and probably just 2 Watts will be fine.

I mentioned 30 Watts in the context of saying I have adapted a humidifier circuit that supplies 30W. If I wanted I could change that for frequency, piezo capacitance, power and impedance. I could use this circuit but changing many of the components each time I wish to change frequency will be awkward, and I don't need 30W.

I will have another look at the opa452 tomorrow and cross my fingers.

 

[audioguru]

The datasheet for the OPA452 shows on page 6 that it can produce 25V p-p at 100kHz then higher frequencies and higher amplitudes are slew rate limited.

 

[Hero999]

The datasheet for the OPA452 shows on page 6 that it can produce 25V p-p at 100kHz then higher frequencies and higher amplitudes are slew rate limited.

I haven't checked myself but I think that would only be into a resistive load, not a capacitive piezo.

antknee,
What's the impedance of the transducer?

To get 2.5W RMS into a 1kΩ transducer, you need a peak voltage of 70.7V.

This means you'll need to have a +/-73V supply (146V in total) but you won't be able to find an op-amp that will work at this voltage.

I calculated that 5W will require a +/-100V supply which is 200V in total so forget about it.

It would be much easier to use an audio amplifier. If you use an impedance matching transformer, to make your high impedance transducer look like an 8Ω or 4Ω speaker, you'll be able to use a safe low voltage mains powered or battery operated supply, rather than over 100V. You can make your own impedance matching transformer using a ferrite core from an old SMPS or a dead energy saving compact florescent lamp.

 

[antknee]

I will list the electrical spec of the piezo I'm going to copy. I added extra leeway for myself (frequency and power) because its useful for me to do that, however for this discussion it will add confusion. I only definitely know the power consumption and drive voltage. The current and impedance have been implied by calculation, I'll build something very similar but not identical.

Definite : Power = 1Watt
Definite : Drive voltage = 50V peak to peak
Definite : Resonant frequency = 130 KHz
Implied : Current = 20mA peak to peak
Implied : Impedance = 2500 ohms

I have previously tried to get the LM3886 audio amp working but it required a pcb layout and I had too many ground loop problems. I have put that on the back burner because I don't need the 80W or so that it can produce, it does have all the other specs I could need though so I might come back to it later. I have a transformer from an ultrasonic device that uses an audio amp, so that should be ok.

The opa452 is a bit limiting as mentioned. I'm currently looking at the LM7332. It'll probably have something wrong with it for my purpose. They usually do!

Regards.