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LM317: Diode selection of lm317

TTG tt
Prodigy 160 points
Part Number: LM317

Dear team. When Cadj is 10uF, how much current D2 may pass. How to choose a small size D2 package.

  • 0
    TI__Genius 12870 points

    Hello,

             Is the concern the peak forward current flowing through the diode in the event of output pin shorting to ground? If so it would depend on the operating output voltage of the LDO. The output voltage would set the voltage of the Adjust Pin and hence determine the amount of forward bias on diode D2 in the event of output pin shorting to GND. Could you let us know what the nominal output voltage is in your application? Regarding the size of D2 package, I apologize, but we are not experts on diodes/rectifiers and hence cant provide suggestions on the matter of their selection. 

    Regards,

    Srikanth  

  • 0 in reply to Srikanth Lolla Venkata
    Prodigy 160 points

    I have two power supplies. One channel is 5V output, and the other one is 21V output. The input voltage is 24V.

  • 0 in reply to TTG tt
    TI__Genius 12870 points

    Hello,

              The discharge current would also depend on the rate of decrease of Vin/Vout, apart from output voltage and capacitor value. Hence, it would not be straightforward to calculate the peak value of the discharge current. I would recommend that you use 1N4002 as your protection diodes (as recommended in the datasheet). The device will be functional for your application with this component. This device (LM317) is more than 30 years old, and as a result ,unfortunately, we can only provide limited support. If you are developing a new design, we would be happy to recommend a new part that could satisfy your requirements. Thanks!

    Regards,

    Srikanth