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Offset null for LF356

Tony Piazza
Prodigy 140 points

I am using an LF 356 in the non inverting mode. I have connected the offset null ckt as suggested in the TI data sheet with the wiper of the null pot connected to the +12V supply. I am using -12V, Vee on pin 4. The input voltage is 0 - 5 VDC. The gain is nearly 1. The amplifier is working but turning the 25k offset null pot has no effect on the output.

Does the offset null circuit (pins 1 and 5) not work for the non inverting ckt? For non inverting should I connect the wiper to Vee, -12V? My input voltage will never go negative. Should I use ground instead of -12V, Vee on pin 4?

  • 0
    TI__Guru 52536 points

    Hi Tony,

    The offset adjust pins should only change the offset by a few millivolts, maybe +/- 10mV at the most.

    The offset adjust pins are designed to correct for the amplifiers internal offset voltage, so that you can "tweak" the offset voltage to zero.

    You will need a meter that can resolve millivolts to see the change.

    Regards,

  • 0 in reply to Paul Grohe
    Prodigy 140 points
    Thank you Paul. Do you have advice on how to adjust the output DC level by about 0.75 V? The input is from a sensor that spans from 0.5V to 4.5V. With gain I can get the output to span from about 0.75V to 5.75. Now I need to shift this down from 0V to 5V.