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Original question:

LM337: Max value for output capacitance

LM337: About the LM337 simulation model

Liu Yang
Expert 6715 points
Part Number: LM337

Hi Team,

I am using the simulation model of LM337 in LTSpice. As a circuit, we would like to apply an offset voltage to GND to a standard circuit and raise the output voltage by the offset voltage. However, perhaps the provided model did not give the desired result because the internal reference voltage was fixed.
Is there a model in which the reference voltage of the LM337 is not fixed?

Beat Regards,
Tom Liu

  • 0
    TI__Mastermind 45070 points

    Hi Tom,

    You should be able to do this as the ADJ is not GND. VOUT should always be 1.25 lower than whatever is on the ADJ pin.  

    Does this answer your question?

  • 0 in reply to JCHK
    TI__Expert 6715 points

    Hi John,

    I confirmed by simulation again, but even if the offset voltage was given, the output did not rise higher than 0V in the positive direction. As for usage, we would like to use it as a suction-type +1.3V power supply. Of course, we understand that the data sheet states that the output voltage range is negative voltage only. Does it mean that the simulation model does not support the above behavior because it is out of rating?

    Beat Regards,
    Tom Liu

  • 0 in reply to Liu Yang
    TI__Mastermind 45070 points

    Hi Tom,

    I am able to import this into TINA and with a Zener diode VOUT=VIN-VZ+VADJ:

    Can you share your simulation schematic? 

  • 0 in reply to JCHK
    TI__Expert 6715 points

    Hi John,

    In your result I also saw Vout is lower than 0V. Can Vout be higher than 0V?

    I attached the simulation circuit and the result. Vout is monitored by DC sweeping V4 to the circuit of -5V input and -2.5V output. In the attached figure, Vout is 0V and has reached the ceiling.

    Beat Regards,
    Tom Liu

  • 0 in reply to Liu Yang
    TI__Mastermind 45070 points

    Hi Tom,

    The LM337 can only sink current from the highest potential. I see the issue you are having with the model now and it is likely an issue whether you use TINA or LT Spice, the model internal has a '0' or GND reference. 

    Can you order an EVM to try this on the bench? If not, I can help you to order one if you provide your contact details.