[aprssig] DC Switching supplies for backup comms (APRS)

Robert Bruninga bruninga at usna.edu
Tue Jan 3 15:01:21 CST 2017


I have talked much about using common Switching Power supplies driven
directly from the 100 to 330 VDC from solar arrays or EV car batteries or
other sources for backup/emergency power.  But Tom, notes that as the
technology of switching power supplies continues to improve, more and more
of them will no longer work on DC input...  This, due to new PFC
circuitry..... ARGH!

So, collect your "supply" junk now...  (trying to bypass the PFC circuitry
and go directly to the DC/DC switcher will always be a unique challenge for
each supply found...)

-----Original Message-----From: Tom Tengdin

Yes,  original full wave bridge - input cap design switching power supplies
work just fine on DC input....  BUT now they add a forward converter between
bridge and main input cap for PowerFactorCorrection (PFC).

>From Wikipedia:

In the case of a switched-mode power supply, a boost converter is inserted
between the bridge rectifier and the main input capacitors.

The boost converter attempts to maintain a constant DC bus voltage on its
output while drawing a current that is always in phase with and at the same
frequency as the line voltage. Another switched-mode converter inside the
power supply produces the desired output voltage from the DC bus. This
approach requires additional semiconductor switches and control electronics,
but permits cheaper and smaller passive components. It is frequently used in
practice.

=============

Boost or forward converter is driven so that current extracted from the line
is proportional to instantaneous line voltage.  Which is a definition of
resistance.  So the power supply "looks" like a resistive load to the
incoming main.

When trying to run the supply from HV DC, the timing from the 60 Hz sinewave
is gone and the forward converter doesn't know what to do, and so the power
supply doesn't produce any output.


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