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Need Help with LED power supoply and dimmer

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PatentLawyer

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We are converting legacy lighted display boxes from fluorescent to LED. We have had inconsistent results depending on the power supply/dimmer and LEDs used. Our long time electrical engineer consultant sadly passed away and we are left scratching our heads. I know some LEDs require constant current and some constant voltage. Recently we have had 100% failures of the 3amp power supply used on nour smallest light boxes. We are using a PWM dimmer on the DC side and 3a is plenty for the LEDs used. First question: I can’t determine if the power supply pictured is constant current or constant voltage. I have been assuming constant voltage. What does the solid line above the dashed line between 12v and 3a indicate? Second question: could the PWM device on the DFC side cause the power supply to cook itself trying to maintain constant voltage? The units simply stop working after days to weeks of use. I am also attaching a photo of a ter-down of an LED module for reference. Any input would be greatly appreciated. You can see our art work at Austine [dot] com

46841760-10DC-4759-9412-7EFC0E3D3035.jpeg 9A6DD6C5-41B4-4D40-8889-A60A090B9641.jpeg
 

ronsimpson

Well-Known Member
Most Helpful Member
I think that is a constant voltage power supply.
What is the part numbers on the LEDs?
Tell me more about the dimmer.
Interesting art!
 

PatentLawyer

New Member
Thanks for your input.

It confirms what we believed. However there is no part number on the Samsung LED modules. We are almost certain they are constant voltage because they appear to have current limiting resistors. None of this explains why all 3 amp power supplies fail while 5 amp supplies of the same type do not (with double the load). Any input anyone has would be greatly appreciated..








9w
 

JimB

Super Moderator
Most Helpful Member
None of this explains why all 3 amp power supplies fail while 5 amp supplies of the same type do not (with double the load)
It could be something as simple as:

The 3A PSUs are "marginal" in their design, they are good enough for intermittent duty.

The 5A PSUs are more "conservative" in their design. they may even be a de-rated version of a 7 or 8A PSU.

Without examining a failed 3A PSU and comparing with a healthy 5A PSU, this is all guess work and conjecture.

JimB
 

ronsimpson

Well-Known Member
Most Helpful Member
Have you measured the current or just relied on the LED's ratings for the current?
PWM dimmer on the DC side
It appears that the "dimmer" interrupts the current 100 to 1000 times a second to control the brightness. What happens if the dimmer is removed? Will the 3A supply survive with no dimmer. I design power supplies and some (when built by people with little experience) have a problem with the error amplifier resonating. Going from 0A to 2A and back to 0A at 500hz cause some supplies to go crazy. (sorry non technical term) Here are some pictures that show "over shoot" and "step response".
1549470492563.png
If you power supply has a step response of dark blue (6) and the PWM frequency was near that ring frequency then the power supply is out of control and who know what will happen.
1549470616635.png
 

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philomel

New Member
The 12v, 3A PSU is plenty for the 1.2W load, if that is all it is. The PSU is 12*3=36W. I suspect that the dimmer is sending pack noise into the PSU and killing it. You need a filter between them. Put a 1000 uF 15v cap between the PSU and the switcher, or You could use an inductor in series with the + supply between the switcher and the load.
Try to find the part number for the LED's.
Are you only running one set of LED's?
 
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