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LM317 and LM337

Midhun M
Prodigy 230 points
Other Parts Discussed in Thread: LM337, LM317

Hello Sir,

Could you please let me know the following

  1. Thermal resistance for KVU package as it is not available in the datasheet.
  2. Is it mandatory to use 240ohm for R1 resistor or can I use higher resistance is it having any impact on output voltage.
  3. I am using LM337 for -ve output voltages in the datasheet R1 is mentioned as 120ohm could you please let me know if we can use higher resistance and what is the limitation?

Regards,

Midhun

  • 0
    TI__Guru**** 165376 points

    Midhun,

    1) I don't have Tjc available, but it will be low enough that the circuit board / heat sink will ultimately control the thermal response.

    2&3) The low values for feedback have two purposes. First is to consume the minimum current for regulation, but the load could also do that.  Second is to minimize effect of adjust pin current affecting the output voltage.

    There is no maximum resistance, but the load must consume the minimum current and adjust current will reduce the output accuracy.  

  • 0 in reply to Ron Michallick
    Prodigy 230 points

    Hi Ronald,

    Thank you for fast response.

    Since TO-252 is bigger package than SOT-223 i assume thermal resistance will be less for TO-252 thereby junction temperature rise is less compared to SOT-223. 

    Could you let me know what is the minimum current required for regulation for both LM317 and LM337.

    Regards,

    Midhun

  • 0 in reply to Midhun M
    TI__Guru**** 165376 points

    Midhun,

    Look for the "Minimum load current maintain regulation" specification in the data sheet tables.
    The current is lower with less input to output voltage differential. 

  • 0 in reply to Ron Michallick
    Prodigy 230 points

    Thank You Ronald, will go through the datasheet and get back for any additional info is needed.

    Regards,

    Midhun