I've gone ALL GaN now.
Well, for you and your business of pre-made boxes, sure. But the average Joe, wanting to build something simple, isn't going to go that far.
And people are doing this. I continue to receive requests to update the links, hence, bumping this post with them.
Latest devices from GaN Systems in leadless packages, cheap and very easy to drive.
With a Qg of 2nC a single driver can drive 3 devices.
I've decided to use CMCD as it seems to be the simplest and most efficient for a single band design, >90% on a good day. Push pull with 6 devices gives 100W wi 30V@3A7.
Yes, and they aren't really something the average Joe are going to try to build because the absolute need for surface-mount techniques, a pre-heater, magnification, and on and on.
The industry is moving toward more and more surface-mount cooling packages such as this, as opposed to a through-hole package which allows for off-PCB cooling. Off-PCB cooling typically takes place on a heatsink, which inherently will have a lower thermal resistance and cool more efficiently than a PCB, at the cost of a chunk of aluminum, or at least metal, and maybe a fan. On-PCB cooling, such as required by these sorts of SMD packages, require a 4 or more layer PCB and extra space on the PCB to obtain best (and probably sufficient) cooling. If you find that your PCB is insufficient, you can add extra cooling to the SMD-cooling PCB, but it requires ...wait for it... a heatsink and you will have to attach it either by thermal adhesive or push pins, if you have put in arrangements for that. Off-PCB heatsink cooling allows for ad-hoc cooling adjustments, post-PCB fab, and I find to be more flexible overall.
Cooling is not something to be ignored. If the efficiency is 90% and Pout is 100 Watts as you claim, then you are dissipating 10 Watts in the small area of the devices and the immediate area of the devices on the PCB. That is not a trivial consideration, especially in the context of a 30, 60 or 120-minute transmission.
These parts have low breakdown voltages which probably forces you into using a CMCD architecture, as opposed to a Class E architecture, in order to get the RF output power you are claiming, because of the peak drain voltage excursion in Class E. Nothing wrong with CMCD (I'm actually doing some myself) but it does bring a slightly higher complexity, with the need for a non-overlapping clock generator/due diligence to make sure you aren't cross conducting and some sort of output balun, be it a traditional wound one or an LC balun, because at these power levels the typical output impedance is significantly less than 50 Ohms. On the other hand, if you are intent on using a low BV transistor in Class E, a cascode architecture should work.
The datasheet says an NVG (negative-voltage generator) is not mandatory with these GaN Systems devices but they also say that negative voltages are recommended to suppress gate voltage spikes. I would say the you may have some turn on/turn off issues (due to spiking and other things) if you are not able to source a negative gate drive voltage. This gets to the complexity issue; Qg is low with these, which helps in some ways, but then there are other things that make it complex.
All of this navel gazing is a long way of saying that there is no such thing as a free lunch and tradeoffs are everywhere.
I have other designs in the works for things that someone without a lab full of equipment and a Ph. D. could build. I am at the point where 90% of the things that I put some time into I decide to not pursue further after making the PCB layout or evaluating prototypes. This is about right in light of my professional experience. That percentage will come down in the future.
By the way, you can do similar things to your GaN Systems stuff with plain-old inexpensive MOS, especially when you consider that you are using one MOS transistor to multiple GaN Systems transistors, with the necessary extra parasitic capacitance that comes from a multi-transistor PCB layout. Also, no need for an NVG.
Watch this space! (Actually it will be another thread!!)
Nice try at getting around the ban on you advertising your wares here. If you are only publishing pictures with textual descriptions and
not the schematics, gerbers and measured results, then you are just advertising.
