LF: RE: 472 kHz PA running at 12 VDC

["Ken" <ken.h.wright@btinternet.com>]

Would be much appreciated.

Ken

M0KHW

-----Original Message-----
From: owner-rsgb_lf_group@blacksheep.org
[mailto:owner-rsgb_lf_group@blacksheep.org] On Behalf Of Stefan Schäfer
Sent: 27 June 2012 23:33
To: rsgb_lf_group@blacksheep.org
Subject: LF: 472 kHz PA running at 12 VDC

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