# VLC LED desk lamp, mode change



## Dave_H (Oct 14, 2020)

VLC stands for Very Low Cost 

I have been using small cheap touch LED table lamps for a few years. They are convenient 
and work remarkably well for the price ($4 typically) as sources of low-level light 
for short intervals. These run from 3xAA, some also from 5v through USB jack. Some versions
have rechargeable battery, at higher cost.

There are different styles including a bendable "gooseneck" or with head which folds 
up or down. One brand name is Voltax (for reference, not an endorsement).

One lamp initially did not work, and its low cost and return inconvenience made me want 
to fix it myself if possible.

Removing four screws from the bottom revealed a small PCB, having control IC SGL8022W. 
A small copper touch pad connected to this chip by a wire had detached from top of plastic 
case. By sticking it back on, normal operation was restored.

(besides, for cheap returned device hardly worth cost of repair, it would likely be junked; 
so it was saved from landfill).

The lamp has low-medium-high settings with each touch, but no memory of desired setting 
so you have to cycle through to the level you want, and to turn it off, which is mildly 
annoying (though you get used to it).

From what I can tell, circuit uses linear (not switching) current regulation with PWM dimming. 

Datasheet for the SGL8022W is available and although language is a bit difficult to follow, 
chip has different control modes, including on/off and continuous (versus 3-step) dimming. 
This is set by two IC pins connected either to positive supply or ground.

http://www.mikrocontroller.net/attachment/214214/20130601111832.pdf

On PCB was found two IC mode pins OPT1 (pin 6) and OPT2 (pin 8) connected to ground 
which gives 3-stage control as detailed in datasheet. By carefully desoldering pin 6 and bending 
it up from its PCB pad, then connecting to a short wire to V+ (battery + wire), I was able to 
change mode to on/off (short touch) with continuous up/down dimming (long touch). Brightness
level is maintained over off/on cycles.


I also have a small LED under-counter strip light about a foot long, 24 SMT LEDs, 3W,
3-stage touch brightness, runs from 12vdc, looks and works great. It uses QT168X control 
chip which is visible through the clear top. It operates in similar fashion: low-medium-
high-off. Have not found datasheet for it yet, considering a similar mod.

Dave


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## Dave_H (Oct 18, 2020)

I've opened up a few different but similar lamps, and found they all use SGL8022W chip so appears
it is fairly common. Not too much in the way of other neat hidden chip features apart from the
on/off and dimming modes.

Dave


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## Dave_H (Nov 16, 2020)

Touch-on/touch-off mode from this modification seems to work fine. So far I have not found any products
using this chip which can take advantage of different modes. For the cost of one or two cheap slide
switches (10c maybe?) they could sell the product for a few bucks more and offer users added flexibility.


Dave


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