Re: 6cm rf?
160 C junction temperature is pretty standard for this
technology, the data that is missing is the thermal resistance,
junction to case measured in C/W, and power added efficiency.
Without it you cannot calculate the permitted dissipation of the
device and the expected output power WRT the junction temperature.
Yes it can manage a P1dB of 2W but maybe only with a 20% duty
cycle for thermal considerations.
If the value of thermal resistance is say 15C/W, then if you
dissipate 5W in the junction, the junction rises to 75 degrees
above the case, that would be manageable as the heatsink would
have to keep the case at a max of 85C
if the value is 30 then the same 5W dissipation would put the
junction at 170C even if you kept the case anchored at 20C with a
fantastic heat sink.
we can guess from the figures.. at 400mW the data sheets states that the max case temperature is 85C and that this is at 5V and 600mA That is 3W in, 400mW out 2.6W dissipation ie about 14% efficiency
If you assume that at these values the case temperature is allowed to approach the max of 85C the the junction will also be OK below 160 C, some 75C above case. 75/2.6 is 28.8 C/W thermal resistance.
Lets say the efficiency reaches 30% at the P1dB point of 2w out, that would require a junction dissipation of 4.4W
With that thermal resistance which is a constant, the junction would be 127C above the case. Thus the case must not rise above 33C
Thats quite low, requiring a very good heatsink and likely a low duty cycle
These calculations make a few assumptions and may be quite a bit
off, I may even have made a slip on the calculator but they look
about right to me and support the supposition that 1W or maybe a
bit more output, with good design and typical amateur duty cycles,
is probably feasible.
There are a lot of devices out there that look good for really
high output power at the P1dB point but being designed (thermally)
for a lower mean power means they just cant realise that P1dB for
a useful time. Not all data sheets tell you the whole story :(
On 20/05/2021 21:26, militaryoperator via groups.io wrote: