Running LEDs in series with a constant Current power supply. How did get rid of 7.2 khz noise/ripple

Thread Starter

wrightpt

Joined May 21, 2017
15
Hello,

I found the need to learn about electronics when improving the lighting in my office.

I currently have two strings of leds, all leds are run in series. Each string has 23 leds with 6v forward voltage and I am running them at 175 milliamps. The power supply is the following: HLG-120H-350A. These leds came out of the back-light panel of an LED tv, a local tv tech said it was alright to run them at these specifications, or at or below 200 milliamps.

Here is the issue, I am getting a bit of eye strain with these. I took them by the tech's office and he said the ripple or noise in the line is at 7.2 khz. If I add a capacitor and/or an inductor can it take care of noise at that level?

I guess my basic question is will an inductor or capacitor smooth out the current at the 7.2 khz level to the point that it raises the ripple to something like 45khz?

I want less interference. To me that means raising the khz noise in the line to the point it can't be noticed. Any input on this would be awesome.

Thank you,

Patrick
 

R!f@@

Joined Apr 2, 2009
9,734
Welcome to AAC

Aside from you running 23 leds with a Vf 6V, how did the tech figure out the 7.2KHz ripple.
For argument sake say that is PWM frq since the PSU has dimming capability. Even that is undetectable by the eye even though that is way high for LED dimming.

So again where did the 7.2KHz came from ?

Is it that you are getting fatigue due to the color temperature of the LED's ?
 

R!f@@

Joined Apr 2, 2009
9,734
That thing will be outputting around 70VDC at channel 1. That is assuming 3V Vf for each LED with 23 of them in series.
The tech is right about running the leds below 200mA. I suggest that you go lower and experiment which level tht is best for your eyes.

The spec is wrong. It should be 1V - 100 VDC. With CC voltage can vary between tht
 

Thread Starter

wrightpt

Joined May 21, 2017
15
Welcome to AAC

Aside from you running 23 leds with a Vf 6V, how did the tech figure out the 7.2KHz ripple.
For argument sake say that is PWM frq since the PSU has dimming capability. Even that is undetectable by the eye even though that is way high for LED dimming.

So again where did the 7.2KHz came from ?

Is it that you are getting fatigue due to the color temperature of the LED's ?
The power supply does not having dimming capability. I have the "A" version at the end and the "B" version has the dimming capability. He hooked it up to an oscilloscope i thnk. He did it right in front of me.

The temperature is not giving me fatigue. what my screen puts out and what my leds put out are at different frequencies it feels like. I know this because I used to have led tubes and the frequency was much slower bc they hoooked in to the direct line at operated at 60 hz.

Will an inductor or capacitor help with a 7.2khz noise in a DC circuit?

Welcome to AAC

Aside from you running 23 leds with a Vf 6V, how did the tech figure out the 7.2KHz ripple.
For argument sake say that is PWM frq since the PSU has dimming capability. Even that is undetectable by the eye even though that is way high for LED dimming.

So again where did the 7.2KHz came from ?

Is it that you are getting fatigue due to the color temperature of the LED's ?
 

Thread Starter

wrightpt

Joined May 21, 2017
15
That thing will be outputting around 70VDC at channel 1. That is assuming 3V Vf for each LED with 23 of them in series.
The tech is right about running the leds below 200mA. I suggest that you go lower and experiment which level tht is best for your eyes.

The spec is wrong. It should be 1V - 100 VDC. With CC voltage can vary between tht
They have 6v forward voltage. He measured two ways. the constant current range is from 230 to 470 on the power supply. I honestly dont think the specs are wrong.
 

R!f@@

Joined Apr 2, 2009
9,734
What happens when you reduce the drive current ?
I service Led TV's for living. Replaced all kind of LEDs.
I never came across a LED that has 6V Vf.
Can you show a picture of the LED strip ?
Do you have a DMM ?
 

Thread Starter

wrightpt

Joined May 21, 2017
15
What happens when you reduce the drive current ?
nothing. brightness stays the same and voltmeter shows change in current but no real difference. no light blue change in color that comes from over driving the led.

Are you aware if an inductor or capacitor will help? how to choose a capacitor? How to make the proper size conductor?

I may be forced to go back to fluorescent lights.
 

R!f@@

Joined Apr 2, 2009
9,734
A cap across the LED strip won't change much but an LC or RC might.
I doubt you would find much difference.

Can you try using a different power source ?
 

R!f@@

Joined Apr 2, 2009
9,734
Aah ! Cannot see the LEDs.
But still, those look like the most common used ones.
My DMM can light the LED dimly so I do no think they are 6V Vf.
I cannot say what you have for sure.
 

Thread Starter

wrightpt

Joined May 21, 2017
15
The HLG power supply is the only power source I have unfortunately. I do not have the original driver that came in the tv
 

Thread Starter

wrightpt

Joined May 21, 2017
15
Aah ! Cannot see the LEDs.
But still, those look like the most common used ones.
My DMM can light the LED dimly so I do no think they are 6V Vf.
I cannot say what you have for sure.
We put a voltmeter across the leds after they were lit. DC current measured 6 per led.
 

R!f@@

Joined Apr 2, 2009
9,734
I never got eye fatigue from the LEDs I scavenge. May be because I run them off from my linear PSU or off the original PSU of the TV.
Never encountered this issue so I cannot say for sure what to do.
May be u need to experiment on different approaches
 

R!f@@

Joined Apr 2, 2009
9,734
We put a voltmeter across the leds after they were lit. DC current measured 6 per led.
You cannot measure current across a LED.
You can measure voltage drop.
Current needs to be measured in series with the LEDs.
Could be that you are driving the LED too much.

Is there a way to limit the LED current to 100mA
 

Thread Starter

wrightpt

Joined May 21, 2017
15
constant current linuear power supply. May need to look in to that. not sure what kind HLG Mean Well but shall find out very shortly.
 

Thread Starter

wrightpt

Joined May 21, 2017
15
You cannot measure current across a LED.
You can measure voltage drop.
Current needs to be measured in series with the LEDs.
Could be that you are driving the LED too much.

Is there a way to limit the LED current to 100mA
Lowest the power supply goes is 168 i think is what the techs meter showed.. its rated for 175 technically.
 
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