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LF: Re: Re: More smoke...

To: [email protected]
Subject: LF: Re: Re: More smoke...
From: "PA0WFO" <[email protected]>
Date: Sat, 4 Feb 2006 18:53:29 +0100
Delivery-date: Sat, 04 Feb 2006 17:58:39 +0000
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Dear All ,
In my Ropex transmitter I have a class D PA with 2 power fets Fairchild RFP 70N06 with rather generous ratings 70 Amps each and a  max voltage of 60 Volts the supply voltage is 13.8 Volts and a measured output of 154 Watts . When the antenna is mismatched for whatever reason will the Fets break down on voltage  or current peaks ? ( the DC input of 13.8 Volts is properly fused )  and is it possible to prevent voltage breakdown by fitting power zener diodes over the drain and source  of both Fets without spoiling their  efficiency . A fast overcurrentprotection is included in the circuit . The reason for this question is that we had a breakdown in the Ropex Fet final  of PA0VHF while tuning the antenna matching unit out of resonance ( while doing this the input was rather low ) and are wondering what caused it .( The heatsink was not hot at all while tuning up to the rated output )
 
73,William PA0WFO
----- Original Message -----
Sent: Saturday, February 04, 2006 2:03 AM
Subject: LF: Re: More smoke...
 
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