Asklemmy

43513 readers

1515 users here now

A loosely moderated place to ask open-ended questions

Search asklemmy 🔍

If your post meets the following criteria, it's welcome here!

Open-ended question
Not offensive: at this point, we do not have the bandwidth to moderate overtly political discussions. Assume best intent and be excellent to each other.
Not regarding using or support for Lemmy: context, see the list of support communities and tools for finding communities below
Not ad nauseam inducing: please make sure it is a question that would be new to most members
An actual topic of discussion

Looking for support?

Looking for a community?

Lemmyverse: community search
sub.rehab: maps old subreddits to fediverse options, marks official as such
[email protected]: a community for finding communities

~Icon~ ~by~ ~@Double_[email protected]~

founded 5 years ago

MODERATORS

[email protected]

409

Do you often hear the ringing of switching power supplies and devices when you are in a quiet space? (self.asklemmy)

submitted 7 months ago* (last edited 7 months ago) by j4k3 to c/[email protected]

154 comments fedilink hide all child comments

I'm curious, how many people are aware of these sounds. I have designed, etched, and built my own switching power supplies along with winding my own transformers. I am aware of the source of the noise. So, does anyone else hear these high frequency sounds regularly?

you are viewing a single comment's thread
view the rest of the comments

[–] RunawayFixer 1 points 7 months ago* (last edited 7 months ago) (2 children)

Is this all leds or just some? Led lights / led screens?

I'm genuinely curious. I think I'm more sensitive to flickering lights than most (I see a flickering light/screen where others see none), but my experience with flickering lights has vastly improved since led lights became standard and high fps ips screens became basically the standard in office settings.

What led lights I still see flicker: some laptop screens, I suspect a faulty psu. And I've seen led halogen bulb replacements have issues.

What I used to see flicker: every freaking tube pc screen. It was maddening, computer rooms especially.

Edit: led lights in halogen fixtures is apparently a known problem: https://www.ledkia.com/blog/uk/how-to-fix-a-flickering-led-bulb/

[–] [email protected] 2 points 7 months ago

I think it has to do with the frequency they operate at (when dimmed?) . 50/60 Hz is obvious, but some with a higher frequency are still recognizable.

Any time there is motion I get a strobe light effect. Either when looking at something that's moving or moving my eyes to look at something. It's like when you wave your hand in front of you when looking at an old CRT TV.

[–] Ross_audio 2 points 7 months ago (1 children)

It depends on the AC-DC converter used.

The cheapest one is a "half wave rectifier"

That uses a diode to block the half of the AC wave headed in the wrong direction. Then a capacitor to charge and release the wave headed in the right direction in something nearing a flat output.

It does vary it's output and flicker at mains frequency.

The smaller the capacitor or larger the load, the bigger the dropouts. The more pronounced the flicker.

Full wave rectifiers are better, they flip the direction of the other half of the wave, so will have a shorter dropout to smooth over. If they've cheated out on the capacitor or they're overloaded they'll also have flicker though.

[–] Aceticon 2 points 7 months ago* (last edited 7 months ago)

I don't think there are any half-wave rectifiers used for those things since the 4 diodes needed for a bridge rectifier are cheap and you can even get the whole bridge as just one package.

The difference is mainly on how much that abs(sin()) wave remains untouched or not.

There are really good AC-DC conversion methods that will output a very steady DC voltage with very low voltage ripple, but from what I've seen cheap LED lights just have a bridge rectifier, a big capacitor, enough led filaments/chips in series to have a large combined voltage drop and a resistor to limit the current, so the LEDs still see a ton of voltage oscillation (transformed into a current oscillation by the resistor that's mean the limit the current, which is what affects LED brightness) hence the flickering.