How much ripple voltage for an LED is noticable?

[HomeExperiement]

Hi!

Question about LED power supplies. They all have marked ripple voltage. Typically 150mV. How much ripple voltage is human eye capable of noticing when looking at LED strips? And is there difference between 12V and 24V? I have opinion that 150mV ripple on 24V LED strip would give the same amount of flickering as 75mV on 12v LED strip as the voltage ripple percentage is same? Just saw 60 Hz output driver with 150mV ripple on shop and started to wonder if it would be as horrible as 24V AC would be.

 

[berkeman]

Can you measure the ripple current instead? The current is what generates the light in an LED.

 

[HomeExperiement]

Can't measure that, just saw from specs and thought what to make of it. But doesn't voltage drop also cause current drop?

 

[NascentOxygen]

The voltage between the LED terminals would be that across the junction itself plus that due to current through the bulk resistance of the semiconductor material + connections. For a given fluctuation in current, this "ohmic voltage" would differ markedly with size of the LEDs and with the manufacturer.

 

[Rive]

But doesn't voltage drop also cause current drop?

It is, but in case of LEDs this voltage/current thing is not anything linear.
I prefer LED drivers with high switching frequency. At least 50+Hz for stationary usage, but preferably above kHz for everywhere. Pretty much makes ripple invalid.

 

[HomeExperiement]

Who are manufacturing these above kHz power supplies for good price?

 

[anorlunda]

Who are manufacturing these above kHz power supplies for good price?

Switched mode DC power supplies are very common and inexpensive. Wall warts and cell phone chargers use them. The switching frequencies are typically 50 kHz – 1 MHz.

https://en.wikipedia.org/wiki/Switched-mode_power_supply

 

[HomeExperiement]

Switched mode DC power supplies are very common and inexpensive. Wall warts and cell phone chargers use them. The switching frequencies are typically 50 kHz – 1 MHz.

https://en.wikipedia.org/wiki/Switched-mode_power_supply

If I look for example at mean well, they're anything but inexpensive. But besides them I do not know any that has high switching frequency.I was looking from alibaba/aliexpress. And then most of them have ripple 150-240mv and output frequency of 47-63 Hz. I am not sure what to make of it.
And I know that LEDs can be very sensitive to voltage drop. I found this video: and made me wonder if 50Hz frequency at some 200mV ripple is already enough to guarantee what happened in that youtube video?

 

[rbelli1]

If I look for example at mean well, they're anything but inexpensive.

They may not be the cheapest but are very good value for money. The ones I have seen the insides of appear to have been designed to pass all of the safety regulations. Some very cheap ones skimp on that to a great degree.

I was looking from alibaba/aliexpress. And then most of them have ripple 150-240mv and output frequency of 47-63 Hz. I am not sure what to make of it.

Can you list some that you have found that have this?

BoB

 

[HomeExperiement]

Thanks for info. Can you give BoBs website? when I googled them, I came across website that sells tractors...
Btw was I right in guessing that in above post that that the flickering problem that this video showed is due to large ripple (probably 240 mV) + low frequency (probably 50 Hz)? Or is there other reasons for such things?

 

[rbelli1]

Can you give BoBs website? when I googled them, I came across website that sells tractors...

Say what?

BoB

 

[Rive]

And then most of them have ripple 150-240mv and output frequency of 47-63 Hz.

Are you sure that's not the input (line) frequency tolerance? Many switching mode LED drivers are able to handle that input frequency range and 70-240V, so they can be used ~ worldwide.
Actually, I've never seen any switching mode stuff with ripple frequency in that range... It would be really strange.

 

[anorlunda]

I was looking from alibaba/aliexpress. And then most of them have ripple 150-240mv and output frequency of 47-63 Hz. I am not sure what to make of it.
And I know that LEDs can be very sensitive to voltage drop.

Huh? Switching mode power supplies put out DC, not 47-63 Hz. Ripple is a term we use with DC, not AC.

1500 watts! That's what that video talks about. That is enough for thousands of LEDs. And the flicker in the video was on the order of 2 Hz. I'm not at all sure how they did that. Not even half rectified AC gives 2 Hz.Let's start from the basics. How many LEDs of what type will you supply?

This web page, has a little calculator that tells you what LED driver module you need depending on some input parameters.

 

[HomeExperiement]

I thought it was frequency of switching. At least specs made me think of it. For example: this psu.

Here the name says: AC To DC SMPS and then specs said
Output Frequency: 50 / 60 Hz

At least I don't know any other way to interpret it than to take it as switching frequency. And I't like 95% of entire Alibaba.

This calculator makes me a little confused. Why does it have so many fields? For example # of LEDs in each String. I mean if entire strip is 1A/m then does it matter if it's 240/m chips or 300 chips/m? Or min Min LED Voltage ? Should it be 24 as voltage of one cuttable section or 3 as voltage of single SMD chip?

To me it would be much easier to say that it must be able to support 20 meters of 20W/m strip => 400W load. But because when LEDs as I've read consume about 20% more current then actual could rise up to 400*1.2 = 480W, and since I wouldn't want to load psu more than 80% of it's ability then 480*1.2 = 576W. But since 576W is not being sold on market then 600W unit would be ok.

 

[OmCheeto]

And I know that LEDs can be very sensitive to voltage drop. I found this video: and made me wonder if 50Hz frequency at some 200mV ripple is already enough to guarantee what happened in that youtube video?

The title of that video is "VELIKA 1500w Powersource failure"
My guess, given the "AC" clamp on ammeter was reading 7.43 amps, was that the device was not supplying DC. Hence the flicker.
So using it's nameplate ripple data along with the video flicker evidence is rather useless.

 

[Tom.G]

I see a couple problems, one with the supply data sheet, and one with the video.
The advertisement clearly states in both the headline and the in the image that the output is "DC24V", but the specification area shows
" Input Voltage: 110V/220V
Output Frequency: 50/60Hz"
Since Input Voltage rating is frequently followed by the Input Frequency rating, most likely that should read Input Frequency.

The dark and light vertical bands look very much like the beat frequency between the camera frame rate and switching of the LED panel.

This could be due to either:

1. The LED panel being driven by a circuit that sequentially turns succesive columns of the display On and Off to reduce peak current, or
2. caused by the panel configured to exceed the current rating of the power supply and the supply going into current limiting to protect itself.

A well designed system with correctly functioning parts will not show that behaviour.

Without further details of the setup, the true cause can not be determined; only that "Something" is not compatible with the rest of the system.

Cheers,
Tom

 

[HomeExperiement]

A well designed system with correctly functioning parts will not show that behaviour.

Thanks for information. How do you define well designed? As I understand Ripple 0.2V at 50Hz switching frequency won't cause such flicker?

I prefer LED drivers with high switching frequency. At least 50+Hz for stationary usage, but preferably above kHz for everywhere. Pretty much makes ripple invalid.

Finally found 100kHz unit. By making ripple invalid means that even if it falls back to zero it wouldn't be noticed anymore? If for example unit gives 10V out and ripple is also 10V then at 100kHz the load would roughly see it as if it were 5V supply? Not that I found one with 10V ripple but just wanted to check my understanding.

 

[Tom.G]

How do you define well designed?

One that does not exhibit that effect when looked at directly with the naked eye.

As I understand Ripple 0.2V at 50Hz switching frequency won't cause such flicker?

Correct, when looked at with a steady gaze. If looked at while your gaze is rapidly moving past the LEDs, you MAY see SOME visual effects.

If for example unit gives 10V out and ripple is also 10V then at 100kHz the load would roughly see it as if it were 5V supply?

I agree.