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LF: RE: Re: Advice will be gratefully received

To: "'[email protected]'" <[email protected]>
Subject: LF: RE: Re: Advice will be gratefully received
From: "OSBORN, Chris" <[email protected]>
Date: Wed, 28 Sep 2005 11:40:20 +0100
Delivery-date: Wed, 28 Sep 2005 11:41:05 +0100
Envelope-to: [email protected]
Reply-to: [email protected]
Sender: [email protected]

Thanks for the advice Jeff,
All points noted.

I must confess that all of the published designs seem to use a logic driver
IC.
I must be being awkward using an inductor :-(
Maybe I'd better stick to a proven design..

I'll take a photo soon and risk ridicule - HI!

73 Chris G3XIZ



-----Original Message-----
From: F6CWN [mailto:[email protected]]
Sent: 28 September 2005 10:21:AM
To: [email protected]
Subject: LF: Re: Advice will be gratefully received


Hello Chris,

At first,"RIP poor MOS"!

I prefer use MOS with higher VDS.
The driver must absorb energy, because the Ciss capacitance, i use TSC426 or
TC4429 driver.
It sis better to separate the cooling radiators to minimize the reaction
between the two parts
of the bridge (capacity Drain / Ground, the ground is "hot").
A problem with reactive loading, the coils of the LPF are reversible.
A little photography of your PA can help...

73: Jeff / F6CWN/p




----- Original Message ----- From: "OSBORN, Chris" <[email protected]>
To: "LF Group (E-mail)" <[email protected]>
Sent: Wednesday, September 28, 2005 10:43 AM
Subject: LF: Advice will be gratefully received





The PA FET's in my new home brew transmitter keep exploding !

I'm using push-pull  IRF520's rated at 100 V Vds and my supply is 30
volts.
I am careful not to exceed the V gs.

The gates are driven with a toroidal transformer and the whole
circuit is just a scaled up version of my original TX, which works fine.
It generates healthy power into a 50 ohm dummy load but on
connection to the aerial circuit - bang !
The aerial system is identical to that used with the old TX !

Has anyone any ideas on what's causing the problem and how to cure
it ?

I'm running out of FET's and my nerves are somewhat frayed (shell
shock!)

73 Chris G3XIZ


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