Input Impedance for IRF540N

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Input Impedance for IRF540N

Postby WA2WVL » Thu Jan 26, 2006 2:19 pm

One of the fastest power supply FETs available is the IRF540N. It is suitable for Class E amplifiers in the high HF and low VHF frequencies running off 13.6V. ( $.98 from Allied)

The input impedance was measured to be:





The R was measured with a high Q "L" network while the J was calculated from the data sheet.

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Postby steve_qix » Sun Jan 29, 2006 12:35 pm

Yes, a lot of the low power MOSFETs are very good for high frequencies.

I've been working on a 10 meter class E design using low price parts and this one is on the possible list.

If we want to maintain the same safety factor as the most of the current 40/80/160 meter class E rigs in use today (100% voltage/current at
200% peak, under stress, positive modulation), each device will handle 5
volts at 2 amperes at carrier. If one wanted to push the safety factor,
the device could handle a lot more power.

IXYS also some RF rated MOSFETs that will handle about 5 times the voltage, and that are not too expensive. I'm currently experimenting with these. If I could run 25 volts at about an ampere per MOSFET, and use 4 MOSFETs in two modules, that would be about 100 watts of power. This is (my) design goal for 10 meters - 100 watts.

Be nice to have 10 meters in order for the next sunspot high!


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