Message 27518 in TECH.WW
From: G8MNY
Date: Sat, 08 Aug 26 08:02:00 Z
Newsgroups: TECH.WW
Subject: Regulating a Plug Top PS
Message-ID: <1435_GB7CIP>
Path: N2NOV|VA2RIZ|VK3AT|VK7AX|GB7CIP
R:260808/0804z @:N2NOV.#RICH.NY.USA.NOAM $:1435_GB7CIP
R:260808/0804Z 4211@VA2RIZ.#LAN.QC.CAN.NOAM LinBPQ6.0.25
R:260808/0804Z 30696@VK3AT.#MEL.VIC.AUS.OC LinBPQ6.0.24
R:260808/0803Z 15399@VK7AX.#ULV.TAS.AUS.AUNZ LinBPQ6.0.24
R:260808/0802Z @:GB7CIP.#32.GBR.EURO #:1435 [Caterham Surrey GBR] $:1435_GB7CIP
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!
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!
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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