Regulating a Plug Top PS
From
G8MNY@4:902/6 to
WW on Fri Jan 10 06:00:47 2025
By G8MNY (Corrections Nov 19)
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Small odd PS are availble at rallies etc. these are either lighweight 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!
ÚÄ´<ÃÄ¿D1
+19V ³ ³
Br ÚÄÄÄÄÄÄÄÂÄÄÄÂÄÄÄÁ¿NPNÚÁÄÄÄÄÂÄÄÄÄÄÂÄÄ>+13V
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
ÀÄÄÄÄÄÄÄÁÄÄÄÄÄÄÄÄÄÄÁÄÄÄÄÄÄÄÁÄÄÄÄÄÁÄÄÄ>-ve
Also 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!
ÚÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ¿
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
ÀÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÙ
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?).
HEATING
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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