Cooling SOT233

Discussion in 'General Electronics Chat' started by snav, Mar 10, 2015.

  1. snav

    Thread Starter Active Member

    Aug 1, 2011
    I'm using ams1117 adjustable regulators in experimenting with LED drivers but although they are rated for 1a I am finding them hard to maintain even a 280ma load(3.6v*.28=1w) without getting hot. Currently using single 1w LED as load. I have preregulated the input voltage down to just above the dropout threshold for the device but the self heating still makes it problematic for durability. I currently have one soldered to a pad 3.5cm-sq over a full groundplane and according to the mfg that should see a 55degC/w rise. The only thermal connections are a very small tab and three small feet. Has anyone here worked with these and can make suggestions?

    The plan is to configure these in CC mode so variable supply voltages won't damage the LED array. Originally it was planned to use at 1a for 3x3 arrays but no possibility it seems. 1x9 strings @ 280ma are alternative.
  2. MikeML

    AAC Fanatic!

    Oct 2, 2009
    The problem is that the minimum voltage drop across the regulator plus the 1.25 reference voltage plus a bit of headroom adds up to almost 4V. It is this 4V total times the LED current that makes for the large dissipation.

    It is possible to build a CC circuit that has a much lower minimum drop...