Reading a low Resistance Rheostat

#12

Joined Nov 30, 2010
18,224
LM2940 datasheet, page 6, note 3: theta J-A = 53 C/W
Highest allowable temperature inside the chip is 150 C.

1.15 watts times 53 centigrade = 61 degrees above room temperature (in centigrade).
"Room temperature" is usually estimated as 25 C so the temperature of the hottest spot inside the chip would be 88 C. You can call that too hot if you want to. In that case, add a heat sink.
 

Thread Starter

denpo

Joined Aug 17, 2010
11
LM2940 datasheet, page 6, note 3: theta J-A = 53 C/W
Highest allowable temperature inside the chip is 150 C.

1.15 watts times 53 centigrade = 61 degrees above room temperature (in centigrade).
"Room temperature" is usually estimated as 25 C so the temperature of the hottest spot inside the chip would be 88 C. You can call that too hot if you want to. In that case, add a heat sink.
Thanks you so much.
I was scratching my head over the figure 36 on page 15... lol, wrong place.
I will need a heatsink otherwise is quickly start shutting itself on and off.
The LM2940 will be screwed to the alum casing and connected to be board with wires.
 
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