MF,
For the homebrewers, here is my prototype of a MF class D PA that
operates at 12 V DC. Input frequency is divided by 4, so a normal HF TRX
can be used (set to 160m / 1.9 MHz) to drive the PA. The input power
must not exceed the range of 1...4 watts. The output power can be
switched in 2 steps between ~15W and up to 100W, depending on the output
impedance and input voltage (10...15V). The output impedance is not so
critical, Z=R may be in the range of 30 Ohm to infinity. The FETs are
IRFZ48N types, the driver is a ICL7667CPA. The transformer uses RF litz
wire, 30x0.1mm diameter. I didn't spend to much effort for optimising
the efficiency, not at this power level. During a CW QSO or longer calls
at 50 W RF power the heat sink (which is just a 3mm thick Al plate)
becomes hand warm.
The measured efficiency is 88 % at 18W RF power and 80% at 50W RF power.
The needed power for the driver circuitry is included in this measurement.
If someone is interested i may convert the circuit from my mind into a
schematic as a png file.
73, Stefan/DK7FC
https://dl.dropbox.com/u/19882028/MF/DK7FC%20472%20kHz%20PA%2015W%2B100W.JPG
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