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Low frequency amplifier

Tom Curran
Prodigy 60 points
Other Parts Discussed in Thread: TPA3116D2, TPA3118D2, OPA569, TPA3123D2EVM

Hi, 

I am looking for an audio amplifier capable powering a variety of voice coil motors, down to a low frequency (ideally less than 5Hz). The main requirements are to be able to:

Drive two 4 ohm impedances simultaneously, with a power of up to 20 [W] per voice coil.

Drive a single 8.5 ohm impedance, at up to approx 20 [W].

Drive a single 2 ohm impedance, at 5-15 [W].

Ideally, the amplifier will be available as an EVM to reduce design and manufacturing time for the small quantities we need.

The TPA3118D2 and TPA3116D2 were recommended as suggestions, but datasheets cut off at 20Hz for frequency response.

Would it be possible to use these amplifiers down to a lower frequency, or would it be better to switch to simply using power amplifiers (we've used OPA569 for a custom application in the past)? It looks like THD+N increases significantly for the TPA3116D2 at low frequencies, so perhaps it would be better to use something like the TPA3251D2? Again, low frequency response is not visible on the chart.

I also worry that the EVM could filter out low frequency amplification, but possibly this could be changed by replacing components.low

Thanks,

Tom.

  • 0
    TI__Mastermind 45085 points
    Hi Tom,
    The amplifiers are characterized in the audio band of 20Hz to 20kHz. But you could possibly use them below 20Hz. You will need to test these to see if they will work for you. The TPA3116D2 would be a good choice because the thermal design can be tailored to your needs. You can extend the low frequency response by increasing the value of the coupling capacitors. See section 7.3.2 in the datasheet to determine the input coupling capacitor value.
  • 0 in reply to Gregg Scott
    Prodigy 60 points

    Thanks for this suggestion. I will look at this.

  • 0 in reply to Gregg Scott
    Prodigy 60 points

    I just ordered a TPA3123D2EVM through digikey to test at low frequency, but now I realize that the application diagram in its spwc sheet, and its EVM, have 470 uf DC blocking capacitors on the output, which has a large impact on the low freq response. The 3116 and 3118 saythat they contain DC protection to prevent damage, and the application circuit and evm do not include DC blocking capacitors.

    Is there improved technology in the 3116 and 3118 that would make them better for low freqdue to not having to use a DC blocking cap to protect the voice coil?

  • 0 in reply to Tom Curran
    TI__Mastermind 45085 points

    The TPA3116 and TPA3118 are full bridge output or BTL.  They do not have the output blocking capacitors. They will work better for you application.