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Author Topic: LED flicker  (Read 458 times)
N3DT
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Posts: 1647




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« on: July 07, 2019, 08:13:41 PM »

I got these G8 LED bulbs to replace the current sink incandescent for the under counter lights. It's got 4 lamps each unit, a 32" strip. The LED's draw 1/100 the current (.02 instead of 2A each) of the regular G8 bulbs, that's cool and the lights are lots cooler (not hot), but in one area it's too bright and so I switch the things to low and that puts a diode in line with the AC and the LED's flicker. Wife doesn't mind it, but I do and I was wondering if I put a capacitor on the output side of the diode if it would help. But I was reading it's really more about the internal drivers for the LED's since they are a DC device and the drivers don't like low voltage. Anyone try this? The bulbs were touted as dimmable and no flicker.
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K5LXP
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« Reply #1 on: July 08, 2019, 04:04:15 AM »

 
If they're getting pulsed DC via half wave rectified AC then my guess is they would absolutely benefit from some filtering.  You could easily experiment with adding some electrolytic caps to see what value gives you the result you like.

Mark K5LXP
Albuquerque, NM
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N3DT
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« Reply #2 on: July 08, 2019, 07:33:05 AM »

I guess the question is, is the flicker a result of pulsed DC driving the LED's or is it the lower voltage to the driver that's making them flicker. I kind of think it's a result of lower voltage in general. But I could certainly try a cap to see if it does anything.

I remember the first time I messed with these new LED lights, I was trying to time shutters off some old cameras by shining one of the new LED flashlights through the shutter and measuring the resultant time with a photo diode receiver. To my complete surprise, the diode was capturing the pulsed wave form of the LED flashlight. They increase the brightness on these flashlights by changing the pulse width of the driver to the LED. It was a very nicely formed square wave on the old O-scope. I ended up having to use a different source to time the shutters.
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WA3SKN
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« Reply #3 on: July 10, 2019, 02:47:35 PM »

Measure voltage to the light.
Apply that voltage DC to the light and see how it responds.
Apply that voltage AC and see how it responds.
73s.

-Mike.
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W6EM
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Posts: 1940




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« Reply #4 on: July 10, 2019, 04:32:46 PM »

I guess the question is, is the flicker a result of pulsed DC driving the LED's or is it the lower voltage to the driver that's making them flicker. I kind of think it's a result of lower voltage in general. But I could certainly try a cap to see if it does anything.

I remember the first time I messed with these new LED lights, I was trying to time shutters off some old cameras by shining one of the new LED flashlights through the shutter and measuring the resultant time with a photo diode receiver. To my complete surprise, the diode was capturing the pulsed wave form of the LED flashlight. They increase the brightness on these flashlights by changing the pulse width of the driver to the LED. It was a very nicely formed square wave on the old O-scope. I ended up having to use a different source to time the shutters.
From my own tinkering experience, I think you'll find that the LEDs won't dim enough to suit you.  After all, if you do feed them with a sine wave, being diodes, they only use half a cycle anyway.  Adding a diode just introduces another 0.6V drop.  You might want to try building a small PWM controller using a 555 timer and a power mosfet.  Adjusting the width of the pulse is the most common approach.  Just Google "555 PWM" and some simple circuits should pop up.....
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KL7CW
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« Reply #5 on: July 10, 2019, 10:28:36 PM »

A quick search on the internet shows that G8 LED lamps come in various color temperatures and various wattages which probably indicates different intensity.  If you cannot find a bulb of the correct brightness, my next suggestion would be just to add a piece of semi opaque material between the bulb and the lens...to filter out part but not too much light.  Please check carefully that the bulb or material does not get too hot, but the bulbs I saw were only something like 2 to 4 watts so this may not be a problem. Try for something which will not easily burn.  Possibly even a thin coating of black ink even from a marker pin on the bulb may be enough darkening.  Years ago I tried to reduce the brightness of a small incandescent lamp with a diode in the USA.  Worked fine as far as we could tell.  Tried the same scheme at my daughters house in the UK with a 220 volt bulb and a diode.  There was a very noticeable flickering which bothered some of us.  I think we just got by with it in the USA since the bulb would flicker at 60 Hz with the diode.  In the UK with 50 Hz AC the flicker rate was low enough for eyes to detect.  Not sure this helps, but just some things to think about.           Rick  KL7CW
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