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TPA3250: Driving a Piezospeaker

Part Number: TPA3250
Other Parts Discussed in Thread: DRV5825P

Hello,

is it possible to utilize TPA3250 to drive a piezo-loudspeaker with 7.8uF capacitance, where a a power resistor is connected between them as well.

Since the piezospeaker owns a operation voltage range of +-24V, a negative output is a "must"?  can we drive them with 0-24V?

Thank you in advance!

Kind regards,

Neo

  • Hi Neo.

    About your questions.

    is it possible to utilize TPA3250 to drive a piezo-loudspeaker with 7.8uF capacitance, where a a power resistor is connected between them as well.

    A: TPA3250 can't be used to drive piezo speaker.  Because piezo is a capacitive load, its impedance will become smaller with frequency increase. And TPA3250 don't have the function of AGL, so TPA3250 can't limit the output voltage at high frequency which will cause OC protection easily.

    Of course, you can also write an algorithm yourself to reduce the amplitude of the high-frequency components in the input measurement to achieve the function of AGL.

    Also, we have a device(DRV5825P) that supports piezo speakers specifically, you can check it out. www.ti.com/.../drv5825p.pdf

    Since the piezospeaker owns a operation voltage range of +-24V, a negative output is a "must"?  can we drive them with 0-24V?

    A: We didn't try this application before. But in theory, this is possible, and the voltage needs to be guaranteed to be within 24V.

    BR.

    Wei Qiu.

  • Hello Qiu,

    thanks for your this information!

    After a 4.7Ohm resistor is added, the resistive impedance will be introduced. It still does not work with a capacitive speaker?

    Could you explain more exactly what is AGL? The gain of this amplifier is fixed by "Inverting voltage Gain 20dB (gain = 10)"  Why do you especially mention the high -frequency component?

    In our application, one of the electrodynamic speaker owns 8 ohm/14V used in BTL configuration, and the amplifier will be supplied with 30Volt. It is shown in Figure 4.of section 7.9 that a 25V supply voltage is enough to drive a 25W load. If the amplitude of the input signal to this amplifier (or the output of DAC) can be limited to 1.4V, is it safe for the speaker?

    Kind regards,

    Nanjun

  • Hi Neo.

    After a 4.7Ohm resistor is added, the resistive impedance will be introduced. It still does not work with a capacitive speaker?

    If you are using a resistor as large as 4.7Ohm, then your application is reasonable. If a smaller resistor is used, since the impedance of the Piezo is very small when outputting high-frequency music, the load impedance at high frequency is the impedance of the resistor. So, if a small resistor is used, it is easy to cause OC protection.

    Could you explain more exactly what is AGL? The gain of this amplifier is fixed by "Inverting voltage Gain 20dB (gain = 10)"  Why do you especially mention the high -frequency component?

    A:AGL is an abbreviation for Automatic Gain Limiter. You can take the file below as a reference. TAS5825M Process Flows (Rev. A) (ti.com)

    In fact, for Piezo speaker applications, it should be noted that Piezo presents a lower impedance at high frequencies and is prone to trigger OC. There are two main solutions to this. One is to use AGL to limit the high-frequency output gain of the power amplifier, and the other is to connect a larger power resistor in series with Piezo, but this will cause a lot of losses.

    As for the application you mentioned, you only need to ensure that the full frequency band of the power amplifier does not trigger OC.

    BR.

    Wei Qiu.

  • Hello Qiu,

    many thanks for this helpful explanation!

    Kind regards,

    Nanjun