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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.
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
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
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
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
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
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