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LM4950: Buzzing sound audio amplifier

Muhammad Faisal
Prodigy 120 points
Part Number: LM4950

Hi

I am using LM4950 Audio Amplifier whcih is connected to 1:10 transformer which then is connected to the ultrasonic transducer.

When I play an audio file (65kHz-70kHz signal but not raised cosine),  the cirucit generates some buzzing.  The audio amplifier and transformer are placed close to each other so I am not sure whether it is from the trasnformer or the audio amplifier. Please note that nothing is connected at the output of the transformer. 

I have checked the signal at the output of the transformer and the waveform is not distorted but not sure why the amplifier makes this sound. The sound goes away when I disconnect the output of the audio amplifier from the trasnformer.

WIth the raised cosine chirp (65kHz - 70kHz), there is no buzzing or sound.

Any idea?

Thanks

Regards

  • 0
    TI__Mastermind 20085 points

    Hi Muhammad,

    This kind of application has potential issues like transformer saturation and DC offset.
    1)Transformer saturation can permit very high primary currents that put an audio power amplifier into the shutdown if the device has short-circuit protection. You can refer the Audio Power Amplifier Operation with Transformer Load application report to find further information about this.
    2)Primary resistances are generally low, so DC offset can generate some current in them. It's just necessary to make sure offset current is insignificant compared to the saturation point of the transformer.

    Best Regards
    José Luis Figueroa
    Audio Applications Engineer