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LM258: large output deviation

Yang Wu
Intellectual 2820 points
Part Number: LM258

Hi team,

I have a issue about LM258 from my customer, the output deviation becomes very large when in mass production (for prototype, fine), do you have some comments?

* it's a differential amp to detect the working state of  compressor on AC line as below, and you can also find the attached Tina file.

LM258.TSC

  • 0
    TI__Guru*** 139906 points
    Hello Yang,

    The Tina file shows a 0.1 ohm resistor on the input, the LM258 amplifies the sense resistor voltage which represents the current in the AC neutral line. The signal gain is 14.6 and the noise and input offset voltage gain is one higher, 15.6. Vio range for LM258 is 5mV for 25C and 7mV full range. Out 1 has up to 15.6 * 5mV = +/-78mV variance due to Vio (room temperature).

    The input is AC voltage. For negative input voltage the output will rise as expected at the programmed gain. For positive input voltage the LM258 will try to go low. The output won't be zero because the feedback current through R33 and R31 will flow into the LM258 output and the output will be higher than 0V.

    How much variance is seen in production and how was it measured?