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Selecting power Fets for 500 KC transmitter

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December 29th 07, 09:58 AM posted to rec.radio.amateur.homebrew

Paul Keinanen Paul Keinanen is offline

Paul Keinanen is offline

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Selecting power Fets for 500 KC transmitter

On Thu, 27 Dec 2007 20:52:20 -0800 (PST), wrote:

Greetings!!!

I plan on building a 500 KC transmitter, 200 watts output. I have
never worked with power FETS before.

What is the selection method used in determining which FET to use??
I see some great FETS
cheap.

Example: IRFP254

250 volt Vdss

RDS on .14

Amps 32 amps

Rise time : 51 NS

Cost; 2.50 each

The data sheet does not spec any freq's ( Ft) like bipolar
transistors?? How do I select the right FET??? freq range

Thanks!!!

The 500 KC transmitter will run at 28 VDC

Those FETs have usually quite large gate capacitances (nanofarads), so
in order to rapidly change the gate voltage (and hence the
drain-source current) rapidly, the driver stage may have to supply a
significant current to charge and discharge this gate capacitance. In
many cases, the driver current limit may limit the operating speed of
the circuit.

Paul OH3LWR

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