PowerWise® Design University

Operational Amplifier Applications

Research Assignement Answers

   
Q:

The LM107 amplifier is the National Semiconductor part used in all the applications found in AN-20. If you wanted to buy 60 parts of the TO-5 (H08C) package, how much would each part be? Are there any samples available? If so, what kind of package do the samples come in?

A:

$3.20 each, there are samples available in the unpackaged die. See LM107 product folder.

   
Q:

The LM107 is an old operational amplifier. When it was introduced, it was one of the best operational amplifiers in the world. The LF411 is a newer op amp with lower offset current. On top of the LM411 product folder there is an upgraded part with improved input bias current and input voltage, which part is this? What is the most inexpensive, 1K unit cost for each part?

A:

The improved amplifier is LMC6081
$0.52 for the LF411 and $1.10 for the LMC6081

   
Q:

The LF411 can be used in many LM107 applications. However, the LMC6081 can be used in some LM107 applications, but not others. Why not? 

A:

Its common-mode range does not go to the POSITIVE rail, whereas the LM107 and LF411 have their CM range to the POSITIVE rail. The LMC6081 can also run on 15 volts (max) total supply, but not as high as the 30 volts of the LM107 or LF411.

See datasheets LM107, LF411, and LMC6081

   
Q:

The LF411 and LM107 can be used for some LMC6081 applications, but not others. Why not?

A:
  • The LM107's input current is too big. The LM107 and LF411 common-mode range goes to the positive rail, whereas the LMC6081 has its CM range to the negative rail. The LMC6081 can run as low as 4.5 volts total supply, and the LF411 needs at least +/- 5 volts (10 volts total supply voltage).

    See datasheets LM107, LF411, and LMC6081

    •    
    Q:

    The compensation trade off is discussed in the Inverting Amplifier and non-inverting amplifier application for the LM107, which normally uses an external compensation capacitor. What is the advantage of having a higher value of a compensation capacitor? What is the advantage of having a SMALLER value of a compensation capacitor?

    A:

    A higher value of the compensation capacitor creates lower output noise, less slew rate, and better tolerance of capacitive loads. A smaller value of a compensation capacitor creates a larger bandwidth, more slew rate and less of a phase shift. See AN-20.