Recommend heat sinks for 2SC1969 BJT

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musclemania05

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Hello I wondering if I could get some recommended heats to use for a rather older BJT which is the 2SC1969 see attached data sheet. My circuit will be dissipating 10 watts of RF power. I guessing I will need about a heat sink of 20 watts. View attachment 2sc1969.pdf
 

Max junction temperature = 150*C, use 120 for safety. Tambient = 40 *C, so you have to dissipate 10 Watts across a temperature of 110*C. The thermal resistance of the junction to case is 6.5*C/W, So the case of the transistor will be at 65*C less then the max, i.e. 120- 65 = 55*C. So the heatsink will have to dissipate 10W with a temperature drop of 55-40 = 15*C. So you need a heat sink with a thermal resistance of 15/10 = 1.5 *C/W.
Note I have based this on an efficiency of 50% (20W in, 10W out), it should be higher, so the heat sink could be a bit smaller.
Frank
 

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