Thanks for the advice Alan,
It's looking like a higher voltage device may be the answer.
My existing TX uses the same FET's but only runs at 24 volts.
They may well be running right on their limit and perhaps I've
just been lucky so far !
I must admit that I'm not using a negative voltage clamp :-(
I monitor the gate waveform on a good 'scope and wind up the
drive very slowly.
It never approaches anything like the published maximum.
It will be the work of an instant to place some diodes in
circuit - consider it done.
73 Chris G3XIZ
-----Original Message-----
From: Alan Melia [mailto:[email protected]]
Sent: 28 September 2005 11:41:AM
To: [email protected]
Subject: LF: Re: Advice will be gratefully received
Chris
Ah according to my notes the peak voltage if you verge on Class E can
approach 4 times the supply.....I think that might be your problem. This is
necessary to allow a bit of headroom when tuning as "odd" reactances at the
drain will cause the peak drain voltage to soar. I use 200V devices up to
about 40 -45 volts supply and 500V above that. If you are transformer
driving I assume you have a negative voltage clamp (diode)
Alan G3NYK
----- Original Message -----
From: "OSBORN, Chris" <[email protected]>
To: "LF Group (E-mail)" <[email protected]>
Sent: 28 September 2005 10:43
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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