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Has anyone looked closely
at Jim's Class D/E EER tx ?
Sent: Sunday, July 31, 2011 2:47 PM
Subject: Re: LF: frequency doubler and divider
Oh dear, sorry for 1000s mails today.
I got another idea:
If you want a 50% duty cycle at 2x f input, you may just add another XOR gate
and do the same again. Then having 4x f input at an unaccurate duty cycle and
feed that to the 4013. Here we are at 50% at 2x f input :-) Will that work? With
to cheep ICs and 2x R and 2x C? :-) I'll try!
73, Stefan
Am
31.07.2011 15:31, schrieb Stefan Schäfer:
Ah,
regarding the overlap times: I successfully tried a SG3525 SMPS driver to
obtain a defined dead-time. So i won't need the inverted signal but a 50% duty
cycle anyway. Power losses of the FETs (4x IRFP460) have been excellent
low!
73s
Am 31.07.2011 15:16, schrieb Andy Talbot:
No, that doesn't work to give a true square wave. If the RC
delay is not exactly 50% you get a repeated double pulse waveform and not a
series of equally spaced 2.F pulses. On dividing this by
2, you end up with exactly what you had before.
Been there - done that.. :-)
The only practical way is to double the frequency, filter it to remove
all odd order terms and the half fundamental then square it up and
divide.
Andy
2011/7/31 Stefan Schäfer <[email protected]>
LF, VLF,
I just re-invented the wheel ;-) Just by
thinking i found one possible way how to double and divide a rectangular
signal, to achieve an accurate 50 % duty cycle :-)
One could take a
simple XOR gatter like a CD4070 and a RC circuit. The time constant has to
be about the half of the period of the wanted frequency, e.g. 3.6 us for
137 kHz. The output of the RC circuit (voltage across C) and the original
signal is fed to one single input of the gatter. Then the output frequency
will be 2x f input.
All this can be found in the internet as well,
of course. But if you don't know about that possibility you don't know
what to seach in the web too. At least i haven't found that method by
searching and it also wasn't discussed here in the recent time.
Furthermore i never saw it on a PA design by amateurs i found in the
web.
The output signal of the 4070 is then fed to the well known
frequency divider consisting out of e.g. a CD4013. Then output frequency
will be the same as on the input but the duty cycle will be accurate
50%!
This is one method to (re-) obtain a suitable drive signal for
a H bridge PA or class D PA after passing the driver signal through an
optocoupler or so. I'm sure i will use that method now in several
circuits, like in the new LF PA that still causes some problems, excactly
on that matter!
Later i found on the German wiki site: http://de.wikipedia.org/wiki/XOR-Gatter#Frequenzverdopplung
73,
Stefan/DK7FC
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