[AMPS] SPS elaboration

[Radio WC6W]

Happy Monday everyone!
  I suppose I should clarify just a bit what I meant by the .1 uF output
capacitor...

  WARNING... most of the items in the following discussion are NOT
isolated from the AC line!

 The .1 cap is the "final" capacitor in a two stage 3KW switching power
supply (SPS) design consisting of a Power Factor Correcting (PFC) boost
input stage (375 volts nominal) and a Zero Voltage Switching (ZVS) DC to
DC converter output stage incorporating a step-up transformer whose turns
ratio determines the output voltage.    Note: the screen voltage may be
sourced from a separate winding on this transformer so as to track the
plate voltage.

  In this implementation, energy storage, to filter the AC line, is
provided by a 4000 uF / 450 V capacitor at the output of the PFC.   This
provides the "power" and all that the small output cap is required to do
is pacify the edges of the output converter which is already very close
to being a "DC" signal. 

  An overcurrent sense circuit on the output of this contraption can shut
down the output stage in a couple of microseconds in the event of a
glitch or other fault which in any event only has about 1/100 of the
energy available as in a typical amplifier power supply of this
capability.

  As far as filtering and shielding are concerned, it is much less
trouble to tame this critter than the thing that it is attached too!

  I don't think that a 3 KW UPS is any more challenging in our modern
world than a 4CX5000 based amplifier though, a supply of this sort IS a
lot more work than hooking up 4 diodes, a capacitor and a 100 pound
transformer!  :-)

  Of course, if one was really trying to replace a 400 lb transformer
that implies 10+ KW capability.   Some of the SPS components scale up
well and some don't...  Transformer cores become hard to find above the
3KW level... but with a judicious design topology... the first thing that
comes to mind would be to use 4 transformers, connecting the primaries in
parallel and the secondaries in series... it should be doable.

  Speaking of transformers... that is the most "work" of this entire
approach since nothing "standard" is available, one actually has to wind
the parts.  The choke for the PFC circuit isn't much work as it is wound
with solid wire but, the converter transformer(s) require Litz wire
techniques.

  There are plenty of robust power FET's available from IXYS, APT, IR and
others plus there are some very advanced driver IC's (with helpful
Ap-notes) made by MicroLinear, LinearTech and Unitrode.   And with just a
bit of careful design, the parts aren't as prone to going BANG as they
once were!

  Incidently, I have an acquaintance who put together an 8KW (40KW peak!)
SPS, to drive a Tesla coil (a truly unruly load) of all things, about 5
years ago when the current (affordable) FET state of the art dictated a
number of devices in parallel.

 So, not impossible, but a bit of a challenge...

73,
  Marv WC6W







*

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