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Re: 20V power supply



I currently use a surplus 12V to 20V step up switcher with my Transystem
3733. I use a homebrew 145 to 28 Mhz. converter to feed my 10M receiver. I
have used this with the 2 to 10 converter, without a case of any sort,
sitting right on top of the switcher with no noticeable noise. I have no
information about the switcher other than it's of commercial "computer
grade" quality. (now THAT's an oxymoron).

Howie AB2S

----- Original Message -----
From: "Estes Wayne-W10191" <W10191@motorola.com>
To: <amsat-bb@amsat.org>
Sent: Wednesday, January 30, 2002 12:15 PM
Subject: [amsat-bb] 20V power supply


> Dave Guimont wrote:
>
> I can use 12v battery power, but require two batteries to supply the 20v
needed
> by the CalAmp converter
>
> Wayne replies:
>
> I also need 20 Volts to power my TranSystem downconverter and 28V coaxial
relay.  Last night I discovered the National Semiconductor LM2577T-ADJ
"Simple Switcher step-up voltage regulator".  I'm going to order one ($5.72
from the Radio Shack commercial catalog) to build a boost regulator with 13V
input, 18-20V output.
>
> The regulator only needs 10 external components.  The most critical
components are the inductor, high-current Schottky diode, and low-ESR filter
capacitor.  In my junkbox I have a ferrite cores to wind an inductor, 1N5822
diodes, and filter capacitors from a salvaged switching power supply.  The
inductor design would be very critical if I needed 1.5A output current.  But
it shouldn't be extremely critical to supply 350 mA to my coaxial relay, DEM
preamp, TranSystem downconverter and PTC thermistor (initial surge current
is about 700 mA when the PTC thermistor is cold).
>
> The switching frequency is 52 kHz.  I will put the regulator circuit in an
aluminum box, but that won't do much to attenuate the magnetic field from
the inductor.  I will put .01 uF RF bypasses on the input and output cables
to minimize conducted RFI.  I suspect that the 52 kHz harmonics won't go all
the way up to 2401 MHz.  If harmonics go up to 123 MHz (downconverter IF
frequency), hopefully 55 dB gain of the preamp and downconverter will make
the AO40 signal much stronger than any RFI.  Are these reasonable
assumptions?  Does anybody have construction tips for minimizing RFI from
homebrew switching power supplies?
>
> Go here for more information about the LM2577T-ADJ switching regulator.
> http://www.national.com/pf/LM/LM2577.html
<http://www.national.com/pf/LM/LM2577.html>
>
> Wayne Estes W9AE
> Mundelein, IL, USA
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