Heat sink for power amplifiers

[Mabrok]

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

 

[wwfeldman]

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

 

[Easy peasy]

(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 ...

 

[Mabrok]

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

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

 

[wwfeldman]

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