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Re: 20V power supply

Another very good approach to boost 12V to 17+ volts is to use
commercial packaged DC-DC converters.  As an example, I use a
CDI (Conversion Devices, Inc.) model 1505S12-A1 unit to power
the bias tee for my TSI 3733 converters.  The little 2" X 2"
X 3/8" thick unit converts 12V to 5V 1A in an isolated output.
Since the output is isolated from the input, you are free to
put the 5V output in series with the 12V input and get 17V
total, plenty to run the 3733 or any other device using a
7812 regulator.  These things cost way too much to buy new,
so I watch closely for them at hamfests, and can usually find
them for $1 to$5.   There are also models which accept 12V
in and produce +12 and -12V out.  Those are particularly useful
for operating surplus SMA 24V microwave coaxial relays for your
portable stations.    Just be sure that there is input-output
isolation if you are going to series boost the input voltage 
with them, and the load current capability is not exceeded.
  John  W5EME

Jari Koivurinne wrote:
> > 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.
> >
> Hello!
> I currently use a LM2587T-step-up voltage regulator in my 144 to 10386MHz
> 1W transverter as a 28V coaxial relay power supply. Only normal bypasses
> are used.
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