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VA3HRA > WP       01.06.17 20:24l 67 Lines 2602 Bytes #999 (0) @ EU
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Subj: SB TECH @ WW < G8MNY $45060_GB7CIP
Sent: 170601/1854Z 20642@KA3BVJ.PA.USA.NA BPQ1.4.65

Regulating a Plug Top PS
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By G8MNY                                  (New Oct 08)
(8 Bit ASCII graphics use code page 437 or 850, Terminal Font)

Small odd PS are availble at rallies etc. these are either lighwieght Switch
Mode regulated types, unsuitable if you want low QRM, or the heavier
transformer type with unregulated output (e.g. says 12V but 19V off load). If
there is room, here is what is needed to regulate one of these, & if of course
you can open box!
                        +19V        ³     ³
L<ÄÄÂÄÄÄthÄÄ¿ || __/+\_     ³   1k    \ /e     ³     ³
   m22  fuse )||( ~\-/~³   +³   ³    ÄÄÂÄÄ     ³1m  _³_
   neon      )||(   ³  ³   ===  ÀÄÄÄÄÄÄ´      ===   /_\D2
N<ÄÄÁÄÄÄÄÄÄÄÙ || ÀÄÄ)ÄÄÙ Cap³4m7      _³_    C2³16v  ³
                    ³       ³25v      /_\'14V  ³     ³

If there is room & it safe to do so, I often add a mains neon & series high
value mains resistor (e.g. 2x 100k) to warn the unit is on. This MUST be done
safely on the mains side of the box with the neon light visable through a small
hole, not with the neon poking out!

³  ___±±±___~~~~~~~~|³
³N³   ±±±   ³    C2 |³
³E³   ±±±   ³      N|³
³O³   ±±±   ³Br    P|====DC
³N³   ±±±   ³      N|³
³ ³___±±±___³  Cap  |³
³     ±±±  _________|³

To keep the regulator circuit simple I used a high gain darlington TAB
transistor mounted on a folded ally plate on the secondary side of the box. The
NPN emitter followers the zener 14V voltage to give about 13V regulated.

I could just as easily used a 12V low drop out regulator (uplifted to 13.8V)
instead & gained current limiting!

The 2 diodes (1N4001) are protection features, D1 ensures the output can't be
more than +0,7V higher than the input, & D2 stops reverse polarity harm
(external fuse?).
As with all small PS heat can be a problem, derate the PSU if needed, or
improve ventalation with bigger holes etc.

Why Don't U send an interesting bul?

73 De John, G8MNY @ GB7CIP

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