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LM358: Series resistance

Brian Haught
Prodigy 80 points
Part Number: LM358

We are using a LM358 as a voltage-follower with an RC low-pass filter on the input to a 0-5V light sensor signal. The signal has significant 100kHz noise from the electronic ballast. Currently, R = 100k ohm, C = 0.1uF. What is the max value we can safely use for R without causing issues?

  • 0
    TI__Guru*** 140136 points
    Brian,

    Input bias current does create a DC voltage drop on the resistor. Resistors do create their own noise. Up to 1M should be OK.

    Keep in mind that LM358 input common mode is 0V to VCC - 1.5V (VCC - 2V) for wider temperature.
    Output range is same as input range when sourcing current or sinking a small current, 0V to VCC -1.5V.

    If VCC is 5V and input is 0 to 5V, you can expect 0V to 3.6V output.