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G8MNY > TECH 24.03.24 10:13l 56 Lines 2174 Bytes #999 (0) @ WW
BID : 3990_GB7CIP
Read: GUEST
Subj: Regulating a Plug Top PS
Path: IZ3LSV<I0OJJ<LU4ECL<VK2RZ<GB7CIP
Sent: 240324/0911Z @:GB7CIP.#32.GBR.EURO #:3990 [Caterham Surrey GBR] $:3990_GB
From: G8MNY@GB7CIP.#32.GBR.EURO
To : TECH@WW
By G8MNY (Corrections Nov 19)
(8 Bit ASCII graphics use code page 437 or 850, Terminal Font)
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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