• State Resolved
  • Locked Locked
  • Replies 4 replies
  • Subscribers 64 subscribers
  • Views 1011 views
  • Users 0 members are here
Support feedback
Options
Options
Related

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

lm338: datasheet figure 44 10-a regulator

joe ceri
Prodigy 20 points

Part Number: LM338

Schematic shows a lm107(307) as a comparator, but shows no feedback. Is this amp to be run open loop?

  • 0
    Guru 140200 points
    Hi Joe,

    this schematic is very very old. Many of these dinosaurs schemes do not work in real life, because they need undocumented specifications to work, or assume typical specifications. As example: See the specified input voltage range of LM107. The positive input voltage range typically includes the positive rail, but this is not guaranteed. Guaranteed for the LM307 is a voltage which is 3V under the positive rail! If you have a look at your scheme, then you will notice, that when actually 5A is flowing through the lower 0.1R shunt, a voltage of 0.5V will drop. So, the LM107 sees an input voltage which is only 0.5V away from the rail. So, there's a good chance, that the circuit isn't working at all.

    Kai
  • 0 in reply to kai klaas69
    TI__Expert 4435 points
    Hi Joe,

    LM107(307) had an internal compensation capacitor. Many amplifiers have internal compensation, so in the absence of external compensation they are still operating with feedback.

    The System Examples are offered as ideas to the system (application) designer. The application designer is left with the task of working out the details, starting from the idea. We're here to help with any other questions you have.
  • 0 in reply to kai klaas69
    Prodigy 20 points
    Thank you for your response.
    It would seem that the LM307 must be operated with input and feedback resistors to control the input junction voltage and have a gain other than the 160(max) open loop gain.
    The reason I look to old circuits is because I have lots of old parts laying around.
    Joe.
  • 0 in reply to joe ceri
    TI__Expert 4435 points
    Hi Joe,

    If you want to use LM307 as a difference amplifier, then yes you would need input and feedback resistors. In this example, the LM307 is used as a comparator and running open loop (internally compensated only).

    training.ti.com/ti-precision-labs-op-amps-comparator-applications-4