# How to drive a piezo at 1MHz

#### Tonny Davila

Joined May 25, 2018
2
Hi guys.

I have been working on a project but I got stuck designing a driver for a ultrasound transducer (piezo).

Im using a piezo like this.

The thing is that I have been designing this by parts. My intial idea was to make something like this circuit.

This simulation actually works. The relay is just to change the frequency of the input. In real world this should not work because MJEs bandwidth is about 1MHz and also they only can handle 150VCE. The pot RV1 should increase or decrease Vin of the load (Piezo). Also here I was considering a piezo as a Resistive load but I was making some research and I realized that they behave as a capacitive load. And its resonance frequency is about 1-18KHz so for obvious reasons this should not work for a piezo transducer.

I tried to start over and understand first how transistors behave at this frequencies. And I made this really simple circuit:

The input is a square wave 12 Vpp (minimum is 0V).
And my result is that I get at the output only 0V. But if I add a capacitor I get this:

Question 1:
Why I have to add a capacitor in series to make this circuit work? This is something related to impedance of the transistor on that range of frequencies?

Question 2:
For my first design maybe changing MJEs for other high voltage/high frequency transistors (or even MOSFETs) maybe the circuit could work?

Question 3:
If I change transistors (question 2), and also I change my load adding an inductor to change resonance frequency to make it resonate to a higher frequency? I mean counter the capacitive load of the piezo with an inductor. If this does not help, should I buy a piezo that resonates at 1MHz? Or there is a way to make this piezos to resonate at 1MHz?

Question 4:
Any other idea to drive an square wave that the amplitude can be handled by a pot and also that it has a frequency of 1MHz and 3MHz to a piezo transducer?

Thanks guys for reading my post.

#### Janis59

Joined Aug 21, 2017
1,178
Typical driver for piezo actuator is something like iR2153 or NE555 (or faster another IC circuit like hip6301) overclocked up to 1...1.5 MHz and halfbridge MOSFET-based output booster. The main problem of actuators is they have a rather large impedance thus the voltage must be rather high, say 300V or 1200V etc.
Never seen it may be fed by low voltage low current low power and low speed bjt-brewed amplifier. Reccomendation - mind the overall architecture before to solder anything.

P.S. RE: ""Or there is a way to make this piezos to resonate at 1MHz?"" Sure, decrease the physical sizes, area, cross section, thickness, and it will come together with lost Power.

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