16 Replies Latest reply on Jun 7, 2019 6:48 AM by andrewj

    Question regarding thermal resistance of a UA7805 regulator

    andrewj

      From the datasheet, the TO-220 package has the following thermal characteristics:

       

      Rja = 19C/W

      Rjc(top) = 17C/W

      Rjp(top) = 3C/W  (jp in this case means Junction-to-exposed pad)

       

      Am I right in thinking that for a TO-220, the Rjp value is a reference to the tab when used with a heatsink?  Typically, Rjc would be used, but if this was the case, then adding a heatsink of any thermal resistance > 2C/W would make it worse!  An older version of this datasheet just referred to:

      Rja = 19C/W

      Rjc = 3C/W

       

      This would tie in with my interpretation.

       

      Thanks,

       

      Andrew