On 07/09/2011 05:26 PM, Jim Lux wrote:
On 7/9/11 7:49 AM, Marco IK1ODO wrote:
Hello Paul,
thanks for info. Another list member gave me two good links: KO4BB has
the schematic of PS board (!) in
http://www.ko4bb.com/cgi-bin/manuals.pl?dir=05)_GPS_Timing/Z3801/Z3801A_Power_Supply
and there are some more info in
http://www.realhamradio.com/GPS_Frequency_Standard.htm
All this confirms my analysis, and since it works well without the first
converter I will leave it alone, as you say :-) - if you look at the
first converter schematic, it is really quite complex; and if you power
the Z3801 from 48V it has nothing to do.
In the telecom world, the 48V is -48V, with the positive being ground.
Maybe that's why?
Maybe, our trusty good old -48 VDC. :)
But if they have the isolation in them, which they usually have, it
should not be that which is the reason.
The other thing is that this gives them a way to make multiple versions
with different supply voltages by only changing one converter. As others
have pointed out, too, it might let you use a wide input range converter
as the first step.
It is available in multiple voltages, so this is much more likely.
There's also a matter of using "off the shelf" converters. I've built
more than one piece of lab gear this kind of strategy.. you have a box
full of 28V to whatever you need (+5, +/-15V, etc.) so then you need a
AC to 28V
What we do is that we either do AC to -48 VDC switcher or a filter/fuse
module to the internal 48 VDC. Using 48 VDC as internal high-voltage
supply is very handy. At first they wanted to use a common centrallized
switcher, but starting to do pin-count analysis for currents etc. they
realized that high voltage means less current. It is hardly a unique
realization so therefore there is a lot of 48 VDC to whatever switchers
around.
So, 48 VDC is a handy internal voltage, regardless of what is on the
outside.
Cheers,
Magnus
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