Dimmable COB "wall switch" lights from HF

PhotonWrangler

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You've seen those stick-up LED COB lights at supermarket checkouts that resemble light switches. Just got a couple from HF that have an on/off/brightness knob instead of the switch, which makes them a little more useful.

I opened one up to see whether the dimmer circuit used a PWM chip or a simple potentiometer, and it's just a series pot. I guess those COB strips have a small enough current draw to not burn up a low wattage pot.
 

Dave_H

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I found similar with small lanterns using a dimming pot. Besides that it's not too efficient (compared to a PWM dimmer even with linear current regulation), some don't have smooth dimming, concentrated in a small range. Looks like some use an audio volume control pot. Perhaps it's no more inefficient than a fixed dropping resistor, but cheap and cheesy design regardless, with cheap PWM dimming ICs such as SGL8022W available.

Going back over a decade I opened up a cheap 4D LED lantern at the time, and found small PCB with PWM dimming circuit, confirmed by my scope. That one is no longer current, but they did it right.

Dave
 

PhotonWrangler

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Yeah, I think this one also uses an audio (log) taper pot rather than a linear one. The brightness suddenly jumps towards the maximum end of the pot's travel.

That's impressive that the lantern used a PWM circuit even though it had some beefy D cells to power it. Yes, they did that right. It seems that earlier LED lighting systems were over-engineered with huge margins as compared to today's race-to-the-bottom mentality. I realize that they have to compete on price in the consumer space but it's still disappointing to see these design shortcuts and cheats.
 
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