Help LED Flood lamp power supply reduce flicker and current

S

smilem

Member
Hello, I have bought 20W LED Flood lamp, only to discover it flickers bad, 37%.
I did not test before buying, however I rushed to store to exchange it to anything better.
I discovered that other light flickered 100-150%.

So here is the PCB shot both sides.
The driver chip is BP3319MB
datasheet https://z3d9b7u8.stackpathcdn.com/pdf-down/B/P/3/BP3319MB-BPS.pdf

Original cap is 120V 120uF flicker 37% voltage 86V 30LEDS 188mA current
I added 2x 470uF (total 1060uF) flicker 8.5% voltage 86V 30LEDS 188mA current
I added 1x 390uF (total 1450uF) flicker 5.2% voltage 86V 30LEDS 188mA current

I expected single cap like 470uF would solve the problem, why I need so many caps?
Looking for any help.

Also how to adjust current, the datasheet is not clear about that, see PCB photos any hints?

You can copy image link and open better resolution images.



 
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The charge stored by a capacitor depends on the voltage across the capacitor and the value of the capacitance. The charge can't change unless the voltage changes.

The current in LEDs changes a lot for a very small voltage change, and with the capacitor in parallel with the LEDs, the LEDs effectively keep the capacitor voltage constant, so the charge is approximately constant, and this makes the capacitor fairly ineffective.

To make the capacitor able to store significant charge during the peaks of the mains cycles, and release that charge during the dips in the mains cycle, there has to be a larger voltage change in the capacitor.

One way of achieving that is to add some resistance between the capacitor and the LEDs, which should reduce the flicker. If there is a current regulator between the capacitor and the LEDs, flicker could be virtually eliminated.

As far as I can see, the circuit rectifies the mains and then regulates the current with a switch-mode supply. If you fitted a capacitor after the first rectifier it might be much more effective at reducing ripple. The power factor of the lamp would be worse but that isn't really important with a 20 W light.
 
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Yes, I would see what capacitor there is after the rectification of the mains.
 
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That all depends on what voltage on the secondary there is and the ripple. Your gonna need a DMM or wait until someone more experienced answers.
 
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At 20W, if you have a 240 V, 50 Hz supply, you could use something like a 33 µF capacitor, rated at 400 V dc or more. There would be around 20 V ripple on that, but the light output wouldn't be changing much because of the switch mode power supply between that and the LEDs.

For 120 V, 60 Hz, you need about 120 µF, rated at 200 V dc or more.

1000 µF would be huge and expensive. It would risk overloading things as it charged up. The ripple would be less than 1V which is unnecessarily small for a high voltage supply.
 
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I know this sounds stupid, but...
If you live in North America you might use a "Decora" type on/off switch. Replace it, I had to for our countertop lighting. Most of these switches are not self-cleaning knife type switches and cause grief (especially on gas fire places). E
 
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Most people don't measure the Power-Supply-Noise of an LED Lamp.

Why do You care ?

If You actually need close to zero-Noise, then the Color-Spectrum must also be important.
If either of these is the case,
You will have to build your own Custom-Power-Supply, powering specifically selected COB-LEDs.
 
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