Saturday, February 11, 2012

The BLF177 some better result

Few days later I changed the coils in the lowpass filter.
Almost doubled the inductance from the RFsimm calculated values.
Also thicker wire used 1.2mm .  And the Spraque C's replaced by an Arco 80pF compression type trimmer.
Now the heat developed is much lower and the efficiency increased to about 50%.
Great tool RFsimm99  but still I need to do the old solder work to change real components and test again. 
Now the only wish is  having a bit more gain it needs >10W drive for full output.  I can not let out the 1Ohm parasite stopper at the gate. If so i see  oscillations.
I tried a wire trough 1 ferrite pearl   with 3 ferrite rings no drive power came through!  1 ring i had power but the ring got hot!
Messured 1 wire gives about  70nH (at 500kHz)  Those tiny rings do a lot more then thought!
The BLF177 takes a lot RF gate current at low impedance.
 

A few days  I let it rest it was useless to continue the trial and error method. I went ice-scathing.
Then I did check the  low-pass filter using RFsim99 this is a great tool.  RFsim99 does not work under W7 btw.
It had to be redesigned for a higher cut off frequency. Then the  matching improved a lot.
A good thing to suppress unwanted oscillations was to use a stopper resistor at the gate of the BLF177   10 Ohm  was good  but I had only a small R that  got brown by the drive power. Now I use 2x 0.5W 1 Ohm carbon types.
The capacitors stay cool in the filter. I believe the pass through is okay now.
Possible it was never optimal for 50MHz too and the BLX15 could have been better performing. 
But I did not want to give up on this modern MOS power BLF177.




I have to learn more how to use this great tool.
The L/C   calculated L's  compared to the measured values with the L/C meter gave quite some differences but roughly the L's in use should be about 70nH  now, much smaller values then they where before.

No comments:

Translate