Parallel Transistors

I have seen several different pictures and schematics of some small signal transmitters that are using parallel NPNs to get 500-900mW of power. I keep running into these examples and they make me wonder.

I decided to try to put it into a simulator to see what it looks like.


This circuit is running in class C. The transistor base needs to be in 1.5-2 voltage
range which is between +10 to +15 dBm range with +20 dBm looking like the upper limit
as it starts getting current hungry in a hurry. I played with some different combinations
of resistors in the voltage divider and adding some DC bias to the base. The DC bias
could make it move into a different class beyond class C but the circuit got extremely
current hungry which makes sense. (Class C is fine for a CW rig with some good low
pass filtering.)


I think that I will draw up this circuit in TinyCad and then move it into FreePCB
to eventually make printed circuit board. Once the board is etched and the parts are
stuffed I will measure and document it. I will then try to remodel this in software
(either in the Java based simulator or LTSpice) to see how the physical model and
software model compare.


In the end this is a gimmick design using small signal parts like a PN2222 (2N2222A)
and/or a 2N3904 to push out some real power. It likely would be more productive and
stable to move this to a push-pull design and evaluate it based upon if it needs to
be in class AB or C depending it's intended use. The other option beyond a push-pull
design is to use a part that is somewhere between the "small signal" parts and the
"high power" parts as a driver or pre-driver, or even a "final" depending on the desired
power level.

With all of that being said... very high fun factor in the design and the software
modeling tonight.

73 de NG0R