----- Original Message -----
From: Hans-Albrecht Haffa <[email protected]>
To: <[email protected]>
Sent: Sunday, April 24, 2005 10:28 AM
Subject: LF: Divider by 10 or 100 for 136k out
HEF4017 to divide by 5 and
4013 to divide by 2 ?
Waiting for Your suggtestions,
Hans-Albrecht
DK 8 ND
__________________________________________________________
Dear Hans-Albrecht, LF Group
This is one possibility for divide-by-10. The easiest way to get an exact
50% duty cycle is to make the final stage of the divider a "toggle"
connected flip-flop to divide by 2. A circuit which does this is shown as
part of the G3YXM portable TX (page 61 of "LF today"). The 4000-series ICs
are convenient if you are running everything from a 12V supply, but if you
want divide-by-100 from 13.6MHz they are marginal - the guaranteed clock
frequency for a 4017 is only 5.5MHz with 15V supply, and the 4013 is 12MHz.
A better choice for divide-by-100 is the 74HC390, which contains 2
divide-by-5, and 2 divide-by-2 circuits, so will do the job with a single IC
( http://www.semiconductors.philips.com/pip/74HC390N.html ). Note this
requires a supply around 5V, and a 0V/+5V logic level input, but it will
work up to 60MHz or so. Make sure that, as before, you make the last divider
stage one of the divide-by-2 counters; the divide-by-5 does not give a
symmetrical output. If you require complementary phase outputs, it would be
best to use an external flip-flop as the final divide by 2 stage.
Cheers, Jim Moritz
73 de M0BMU
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