Hi Paul,
In one of my early PA designa i also used an IR2110 to drive FETs having
4 nF gate capacity. At 137 kHz the driver became quite hot and the total
life time was just about 20 hours. In my opinion this driver is not a
good choice for 137 kHz when using large FETs.
The ringing should be reduced by first reducing stay inductances and
then maybe adding 1 to 5 Ohm in series to the gate. I spread the winding
of the gates in my H bridge equally over the core and then twisted the
two wires. Also i soldered them as close as possible to the FET, to
reduce galvanic coupling.
73, GL, Stefan
Am 30.11.2018 21:50, schrieb N1BUG:
All I know is this amp had very little drain ringing and worked well
with FQA34N20 FETs but it is not happy with FQA32N20.
I slowly increased drain voltage but at 200W out (of a kilowatt
deck), there were obvious issues related to the ringing.
I've gone back to my old faithful 200W output Class E amp for now. I
am running WSPR-2 33% 137.437.
Paul
On 11/30/18 3:25 PM, Andy Talbot wrote:
Cross conduction spikes can also be dealt with by inserting a bit of
inductance between top and bottom FETs of a totem pole, or in each leg of a
push-pull pair. As done in the old Decca transmitters, and I cribbed for
my 700 Watt 137 design.
The inductor absorbs the short spike and returns the energy via clamp
diodes to the supply
See http://www.g4jnt.com/137tx.pdf
A lot simpler than worrying about generating a special drive waveform with
gaps
Andy
www.g4jnt.com
On Fri, 30 Nov 2018 at 20:19, Hans-Albrecht Haffa<[email protected]> wrote:
Dear OMs, dear Paul,
To prevend current spikes by cross conduction of both fets it is necesary
to use a gate drive circuit with dead time, as used in power supplies. But
in this case there is a no current flow time in both transistors, what may
cause spikes in the drain circuit. Damping of oscillations in the drain
circuit may also reached by quiescent current, not used for class D PAs. To
load the spikes to the load is not possible in an LW-PA, like in an
flyback-transformer of an switch mode power supply, as the load is an
LP-Filter that filters by reflections of the applied voltage.
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