Heat sink for power amplifiers

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Mabrok

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Hi,
I am doing Doherty power amplifier design with 25 Watt power capability using CGH40010F transistors provided by cree. My question is: Do I need to insert heat sink under the substrate to avoid overheating and transistor damaging? thanks
 

insufficient information

what class of power amplifier?
what frequency range?
what is the power supply voltage?

you want 25W output while the spec sheet says 12.5W typical and 65% efficiency, both at Psat
(guaranteed minimum 10W and 55% at 3.7 GHz)

so 25W out, at 55% efficiency means 45W in, for losses in transistor (mostly) of 20W
which is greater than the rating of your part

I suggest you get an amplifier transistor with at least a 30W rating
then look at heat sink or not
 
(S)he did say transistors - so maybe has a cunning plan to parallel several to get the 25W, in either case h-sinking is often by way of the tabs

the data sheet shows some serious heatsinking - picture at end - this should give the OP a clue ...
 

Doherty topology (combination of class AB & class C connected in parallel)
frequency range 3.4-3.6 GHz
For class AB, VDS= 28 v, VGS = -3.2 v
Class C, VDS = 28 V, VGS = -5 v
Already simulated and got the required 25 Watt Psat
 

according to the simulation, how much power is dissipated in the transistor?
 
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