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TPA3255: DC offset and transformer coupling

Ulf Seifert
Prodigy 50 points
Part Number: TPA3255


I use the device in PBTL mode to drive a transformer with only 30mOhms DC resistance of the primary. To prevent core saturation / asymmetrical magnetization I want to compensate the output offset voltage.

I found significant changes of the offset voltage if I hold a 1MOhm voltage probe of my oscilloscope at one of the inputs. Does it function to put a trim resistor (1MOhm) at both inputs tied with its tap to GND?

Another measure could be a xx kOhm resistor between the two inputs to minimize the input offset voltage. Would this improve the offset of the outputs?

Thanks in advance

Ulf

  • 0
    TI__Genius 11080 points

    Serfert,

    Add resistor is not correct way to decrease the DC offset voltage, because the source of DC offset is from mismatch of +/- channel, which are low impedance voltage source. DC offset can be changed as long as the external pull up/down resistor has similar impedance as +/- channel output (<100mohm), which is almost impossible for real application.

    The correct way to remove the DC offset is add a AC coupling capacitor, that will block all DC offset voltage.

    Dylan