Message-ID: <5A4A5600.4030607@posteo.de>
Date: Mon, 01 Jan 2018 16:38:40 +0100
From: DK7FC <selberdenken@posteo.de>
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References: <1245872871.20180101103858@gmail.com>
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Subject: Re: LF: Si5351A syntehsiser able to fire a FET driver chip directly??
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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
>
>
>
>
>