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Designing High Frequency Signal Piezo Driver.

Category: Hardware

Dear Experts,
I would appreciate your assistance in designing an amplifier that can drive a 2.4MHz piezo to achieve maximum displacement on its resonance frequency. Please let me know if I am mistaken. I have selected a 2.4MHz piezo as it is commonly used in humidifiers.

I have created a Class AB amplifier that is intended to power the piezo. To construct it, I used two transistors with FJL4315 and FJL4215, each with a continuous current capacity of 17A and a 30MHz bandwidth. These transistors were biased using 2N3904 and 2N3906, which have a continuous current of 200mA and a 300MHz bandwidth.

I have tested my circuit on a 10-ohm load and piezo. The waveforms and schematics are attached.

Channel 1 (Yellow):- Voltage across Load
Channel 2 (Purple):- Voltage across 0.1ohm Series Resistor
Channel 3 (Blue):- Input Signal

Please note that the current measurements have been taken with a 0.1-ohm resistor in series with the load.

Input and Output:-
Input Signal:- 2.88Vrms 2.4MHz
Output Signal (10-ohm Load):- 2.69Vrms 2.4MHz
Current (10ohm Load):- 880mArms

Input Signal:- 2.48Vrms 2.4MHz
Output Signal (Piezo Load):- 1.9Vrms 2.4MHz
Current (10ohm Load):- 1.315Arms

To verify if the piezo is achieving maximum displacement, I poured water over it but it did not atomize. The current drawn is very high, and the voltage across it is very low.
Could you clarify if I need impedance matching for piezo circuits, series resonance circuits, or parallel resonance circuits.

Please suggest improvements to my amplifier design and recommend any ICs that meet my requirements.

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  • Hello ,

    The purpose of EngineerZone is to provide forums for the support of select Analog Devices products. Please keep all discussions relevant to Analog Devices products and related topics.

    Best regards,
    Paul

  • I apologize for that, Can you recommend a product that meets my requirements?

  • Hello ,

    To furthermore help you with this, can you provide us the following information:

    1. What is your target supply voltages and current? (single supply or dual supplies?)

    2. What is your target input signal and its parameters? (Max input frequency? Vin magnitude?)

    3. What is your target output signal and its parameters? (Max output frequency? Vout magnitude?)

    4. Your preferred package type of the op amp.

    5. Your preferred gain. (Non-inverting? inverting?)

    6. Will the piezo be located off PCB through a cable externally?
    Piezo elements are electro-mechanical devices that can generate high voltages if mechanically stressed externally.
    Design considerations: may need external Schottky diodes, unipolar TVS diodes on each power supply, additional current limiting resistor between output and load (inside feedback loop) to limit current through output ESD diodes on op amp.

    Best regards,
    Paul

  • Hello Paul,

    I need to actuate a piezo at its resonance frequency of 2.4MHz. Please suggest an IC to operate in either series or parallel resonance for maximum wave transfer.

    Answers:-

    1. Single Supply. (24V 5A max)

    2. 2.4MHz Signal, Amplitude 5V max.

    3. Best according to Series or parallel resonance condition.

    4. Any.

    5. Best fits. 

    6. Piezo will be connected through a cable externally.

    Regards,

    Yash.

  • Hello ,

    Based on the data that you have provided us; since one of your requirements is to have a high supply current, we can conclude that your output current will also be high. Currently, ADI only offers operational amplifiers with output currents of up to 1-2A max. You can check AD8460, LT1210X, and ADA4870 from our product selection table for more details: Selection Table for High Output Current Op Amps ≥ 100mA | Parametric Search | Analog Devices

    The bandwidth of those products should be enough for your application, but in order to furthermore increase their output current drive capabilities, external circuitry and configurations will be required. For more details, you can check the following articles:

    Paralleling Amplifiers Increases Output Drive | Analog Devices
    Increase Amplifier Output Drive Using a Push-Pull Amplifier Stage | Analog Devices

    In addition, since your piezo will also be connected through a cable externally, you will need to consider adding external Schottky diodes, unipolar TVS diodes on each power supply, and an additional current limiting resistor between the output and the load (inside feedback loop) to limit the current through the output ESD diodes of the op amp.

    Best regards,
    Paul

Reply Children
  • I appreciate your help. I will try one of these ICs, and add diodes and current limiting resistors between the output pin and the load.

  • Hello Yashj!

    Be careful to avoid oneport oscillations. Either with your discrete circuit or by driving your piezo with a power opamp, your are driving a mainly capacitive load. I am not familiar with power piezos, but I assumed a behaviour like a crystal or a ceramic resonator, i.e. the equivalent circuit is a series resonant tank circuit and a parallel capacitance. Such a load is capacitve below series and above parallel resonance.

    A emitter follower is prone to oscillations when driving capacitive loads, due to the inductive nature of its output impedance with rising frequencies.

    Best regards

    Robert

  • Hello Edelbastler,

    I have changned piezo, now using 2.4MHz Piezo. And also changed the circuit, now using THS3092 op-amp IC. The input to this circuit is AM signal and in the output signal can't response fast enough to the change in input signal and for period there are oscillations on the output side.

    How can I kill these oscillations and improve the signal integrity ?

  • Hello ,

    The purpose of EngineerZone is to provide forums for the support of select Analog Devices products. Please keep all discussions relevant to Analog Devices products and related topics. Thank you.

    Best regards,
    Paul