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LM741: Offset adjustment

Gregory Morris
Prodigy 20 points
Part Number: LM741
Other Parts Discussed in Thread: LM2904B, TLV9351, TLV171

All schematics I have seen for the LM741 offset adjustment show a 10k potentiometer. Can other values be used? I am replacing an LM11C (too sensitive) in a DC ammeter circuit with an LM741, and the current design uses a 5k multi-turn  potentiometer. The LM741 is ideal here as it is low cost and the circuit does not require high gain, speed, or sensitivity.

  • Former Member
    0 Former Member

    Hi Gregory,

    The internal schematic shows 1k resistors below the transistors of the current mirror on the input stage.  So, I would think you're not limited to a 10k potentiometer.  It's probably just a typical value used to balance sensitivity and the ability to drive the offset null well in one direction.

    If you have the luxury of selecting a new amp, I would be happy to make some suggestions.  The 741 has been around for a while and I'm confident we could find something that gives you better performance for a similar price.  Let me know if this would be of interest to you.

    Regards,
    Daniel

  • 0
    Guru 140200 points

    Hi Gregory,

    also keep in mind that the LM11 has the trim pot is connected to VCC (positive supply voltage) while the LM741 has it connected to VEE (negative supply voltage) !

    Kai

  • Former Member
    0 Former Member in reply to kai klaas69

    Thanks Kai!

    Gregory, although it does not directly answer your question, you may also find section 3 of this application note to be useful.

    Regards,
    Daniel

  • 0 in reply to Former Member
    Prodigy 20 points

    Thanks Kai & Daniel!

    The application note is very helpful. I think I can use a a 5k pot here without affecting performance, and will test that very soon.

    I am open to replacement suggestions for the LM741.

    Regards,

    Greg

  • Former Member
    0 Former Member in reply to Gregory Morris

    Hi Greg,

    The TLV9351 and TLV171 are both higher performance options for comparable cost.  The LM2904B may also do the trick as it has better performance, with the exception of a little more noise, but at a much lower price.

    ► Part Number LM741 TLV9351 TLV171 LM2904B
    Manufacturer TI TI TI TI
    Channel Count 1 1 1 2
    Vs Range 10V to 44V 4.5V to 40V 2.7V to 36V 3V to 36V
    GBW (MHz) 1 3.5 3 1.2
    Slew Rate (V/µs) 0.5 20 1.5 0.5
    Vos max @ 25oC (mV) 3 1.8 2.7 3
    Vos Drift, typ (µV/oC) 15 1.5 1 3.5
    Rail-to-Rail --- In to V-, Out In to V-, Out In to V-
    IQ typ (mA) 1.7 0.65 0.525 0.3
    VN (nV/√Hz) 30 15 16 40
    ISC typ (mA) 25 60 30 30
    IBIAS (typ) (pA) 80000 10 10 10000
    Operating Temperature (°C) 0 to 70 | -40 to 85 -40 to 125 -40 to 125 -40 to 125
    Available Packages PDIP-8 SOT23-5 | SC70-5 | SOT23-6 SOIC-8, SOT-23-5

    SOIC-8, TSSOP-8

    Regards,
    Daniel

  • Former Member
    0 Former Member in reply to Gregory Morris

    Hi Greg,

    I know it's been a while since we've heard from you.  Hopefully that means your questions has been fully answered.

    I'm going to mark the thread as closed for now.  But, please do come back and let us know if you have any follow up questions.

    Regards,
    Daniel