Heatsinking FRED Diodes

Discussion in 'The Projects Forum' started by Macki, Jul 22, 2010.

  1. Macki

    Thread Starter New Member

    Jun 25, 2010

    I have some ultra fast soft recovery diodes in TO-220 package that I would like to use to reduce the PS noise (hash) threshold in an amplifier currently using two (2) bridge rectifiers for a split B+; i.e., +/- 220V dc. There are some FRED soft recovery bridge rectifiers available however at a cost I would like to avoid.

    The amp at idle draws 200 ma per PS rail through each bridge rectifier for a total of 400 ma.

    I figure 300 ma including power up current surge at 220V rectified output would result in 66 W in each bridge. Would it then be correct to provide 17 Watt of heat-sinking per diode, since I would be using 4 diodes to replace each bridge? Or should I consider the AC input to compute the heat-sinking requirements? Or should the heat-sink size be based on the specified maximum allowable temperature of the diode junction?

    The diodes I will be using are: http://www.fairchildsemi.com/ds/IS/ISL9R1560PF2.pdf

    I realize that the PD of this diode is specified at 30W but I am not sure if that is with or without a heat-sink. The TO-220 package should provide some inherent heat-sinking due to the tab used in its construction.

    Anyhow I thought I would pose the question to the more experienced fellows to be on the safe side and minimize unnecessary work.

    Thanks in advance.
  2. windoze killa

    AAC Fanatic!

    Feb 23, 2006
    Most power ratings in data sheets state weather it is with or without heatsink. It is unlike Fairchild to not include it. The 30W stated is the MAX power disspiation and to acchieve that it should be assumed that it is bolted to a heatsink. Something substantial as well, not one of those little flimsy things.

    Having said all that these diodes are rated at 15A which is the current that would be required to develop the 30W. You have said you will be drawing 400mA so I would guess you would be dissipating 1W therefore I wouldn't expect a heatsink would be needed (but doesn't hurt).

    You have also said this current is at idle.....what is it at full volume????? Thats the figure you need to be looking at.