Hi Chris,
With the 2.2 V, drive an optocoupler! Like 4N28, CNY17/4 or similar.
This can be done with 2.2 V (use a resistor of a few 10 Ohm, calculate
it). It shifts the level to a 12V logic. The slightly distorted signal
will look perfect after the divide by 2 stage and will have a perfect
50% duty cycle. Then drive a MOF-FET driver with this signal.
BTW for a class-D PA with opposite phase gate voltages i would generally
receommend to use a gate transformer! It makes sure that there can never
be a positive voltage on both gates to the same time, since vgs1 is
always -vgs2, what ever transients are doing. Then you don't need to
care about propagation delay, rise time and such stuff.
73, Stefan
Am 01.01.2018 11:38, schrieb Chris Wilson:
Hello LF'ers, and a happy and healthy New Year to you all.
I use my U3S QRP Labs exciter to drive a PA on 137kHz, and it works
fine. Hans, the designer, made changes allowing a 180 degree out of
phase pair of signals to come from the Si5351A synthesizer chip with
the intention of this being able to drive a push pull Class D FET
driver chip directly without a X2 signal being divided and split by a
preceding IC, please see original and simplified circuits below. I
tried this but it appears the circa 2.2V outputs of the Si5351A chip
are not sufficient to drive the inputs of the IR2110 FET driver.
Any ideas please? Thanks.
Original PA circuit (works fine with "normal" U3S driving the 74F74
direct with CLK0 output):
http://www.gatesgarth.com/amp.jpg
Modded amp circuit (simplified in the hope of building with one less
IC):
http://www.gatesgarth.com/amp-modded.jpg
IR2110FET driver specs:
http://www.gatesgarth.com/IR2110.pdf
74F74 IC specs:
http://www.gatesgarth.com/74F74.pdf
U3S schematic:
http://www.gatesgarth.com/u3s-schematic.jpg
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