Chris, Alan, LF,
Am 24.11.2010 11:26, schrieb Alan Melia:
Chris I dont think slowing the drive edges will be the answer. This is a
switching PA and needs to switch quickly otherwise the dissipation will rise
rapidly.
Exactly :-)
Any slowing edge will have to be on the drain side in the form of
a low pass filter. Unstable loads will lead to excessive voltages at the
drain which cause breakdown even if the voltage rating is 4 times the supply
(the usual spec.) Why a transformer the tranformer arced is the question,
there should not be that high a voltage there
Exactly!
I rather assume that the transformer has had to less primary turns and
went into saturation on that frequency. Then it became hot and some
turns' insulations are molten. When the temperature increases to very
high values, the relative permittivity decreases, so the L, so the
currents can become excessive and so it was probably an "over-power
death" of the FETs.
When applying a primary coupling winding directly on the loading coil,
the PA impedance can be transformed there, without anything that can go
into saturation. Just the wires should be kept short between PA and coil.
Just like Tesla-transformeers are fed with a primary winding of some
turns, something between 5 and 20 probably. The galvanic decoupling may
be an additional advantage in some cases.
73, Stefan
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