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G8MNY  > TECH     19.08.18 08:30l 57 Lines 2695 Bytes #8 (0) @ WW
BID : 34334_GB7CIP
Subj: Fluorescent 12V Dimmers
Sent: 180819/0626Z @:GB7CIP.#32.GBR.EURO #:34334 [Caterham Surrey GBR]

By G8MNY                                            (New Aug 06)
(8 Bit ASCII graphics use code page 437 or 850, Terminal Font)

For /P operation a 12V fluorescent lamp is often too bright once your eyes get
acclimatised to the dark. This not only annoyingly attracts all flying moths in
the area, but also drains your battery more than needed. Here is a simple
modification that should work on most simple lamp designs.

     Fuse   On                                       _______
         ³      ³  SOT  ³            ³    ³      )||(   : \/ :
        _³_     ³   R  R pot      25V³+  === u1  )||(   :    : 
        /_\      \³ ³  100k     220u===   ³______)||(   :    : Fluorescent
   Idiot ³      T2ÃÄÁÄÄÄ´            ³    ³       ||(   :    : Lamp
   Diode ³      e/³      \³<- Light  ³     \³     ||(   :    :
         ³      ³       T3Ã<- Feed-  ³   T1 ÃÄÄÄ¿ ||(   :    :
         ³      ³       e/³<- back   ³    e/³    )||(___:_/\ :
         ³      ³       ³            ³    ³     ³ ||(_______³
 -ve     ³ 10u ===         Bias R    ³    ³ 10n===

T1 is the usual self oscillating power switching NPN (TAB or 2N3055). Instead
of say a 220ê bias R to +12V, a lower value 150ê is used in series with a
variable voltage/current supply. This consists of a switched volume control pot
(e.g. small edge wheel type) that also turns the lamp on, the pot is wired as a
variable R to be at minimum resistance on turn on, to ensure the lamp lights.

The current though this variable R controls the base drive of T2 (BC107), but
this drive can be shorted out by an optical NPN T3 (e.g. metal case TO92 NPN
with the top cut off). The optical feedback regulates on low brilliances only,
tending to reduce any flicker. T3 needs an aperture so see the lamp or to be
placed next to the tube to see its light.

Adjust the maximum value of the variable R with fixed 'Select On Test' R in
parallel to get a good no off dimming action. Try 47k - 2M SOT as needed.

If the inverter does not have a 220uF across the 12V, do add one, as it does
reduced the pulse current on the wiring (aerial). Do not put the fluorescent
lamps near aerials as it can make a good RF mixer as well as noise sources!

Using a dimmed lamp may also extend lamp life, that is surprisingly sort on
these single ended pulse DC lit lamps. Remember to turn the lamp around to wear
out the other electrode to extend the lamp life!

Y don't U send an interesting bul?

73 de John G8MNY @ GB7CIP

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