Newbie with my first oscilloscope - Is this bad? - Page 1
Forum section: electronics / beginners

author: ElectricPower
author_rank: Frequent Contributor
timestamp: February 24, 2021, 08:37:13 pm
content: I bought an Hantek 5102P scope and i am totally newbie to this, but i tries to meassure noise from an 5V AC/DC adapter when the load is about 2 amps. This is an chinese bought 5V 8A adapter for my 5V LED strip.Here is an capture from the scope:I get an peak to peak voltage around 436mV. Isn't it insanly high?? Or am i doing something wrong here?

author: bob91343
author_rank: Super Contributor
timestamp: February 24, 2021, 09:47:07 pm
content: It could be normal.

author: tunk
author_rank: Super Contributor
timestamp: February 24, 2021, 10:00:26 pm
content: That's reasonably good. Here's a few for comparison:https://lygte-info.dk/review/Power%20AC-DC%205V%202A%20Switching%20Power%20UK.htmlhttps://lygte-info.dk/review/Power%2012V%201.25A%20Power%20supply%20S-15-12%20UK.htmlhttps://lygte-info.dk/review/Power%20AC-DC%2024V%201A%20Aineuu%20TS24-24%20UK.htmlYou could also take a look at his tests of USB chargers:https://lygte-info.dk/info/indexUSB%20UK.html

author: ElectricPower
author_rank: Frequent Contributor
timestamp: February 24, 2021, 10:00:48 pm
content: So around 400mV peak to peak is normal?

author: Refrigerator
author_rank: Super Contributor
timestamp: February 24, 2021, 10:09:50 pm
content: Many good videos by dave:https://www.youtube.com/c/EevblogDave/search?query=measuring%20noise

author: BrokenYugo
author_rank: Super Contributor
timestamp: February 24, 2021, 10:29:52 pm
content: "Normal" isn't really a good term for this situation. What is normal for one power supply and load can be an order of magnitude or two too dirty for another. What you're seeing is likely acceptable to drive LEDs, and probably not indicative of anything wrong. As the videos already mentioned will explain, ripple measurement isn't quite as simple as putting a high bandwidth scope on the rail and reading the peak value.

author: ElectricPower
author_rank: Frequent Contributor
timestamp: February 25, 2021, 05:03:28 am
content: Quote from: BrokenYugo on February 24, 2021, 10:29:52 pmI see. But what if i want to power an Arduino? Will Arduino take that ripple over time?

author: WattsThat
author_rank: Frequent Contributor
timestamp: February 25, 2021, 05:33:54 am
content: An 8 amp supply to power an Arduino that needs perhaps 100 milliamps? In general, why? Just because that’s what you have?Looks questionable to power a micro. But, we know nothing about the measurement conditions so you’re asking people to make assumptions. Lots of assumptions.One thing for sure. If you do power an Arduino with a supply with 400 mv of noise on it, the A/D performance is going to be big time el-stink-o. When using analog, 9vdc from a wall wort into an Uno or similar to utilize the built in linear regulator usually provides a cleaner A/D reference.Disclaimer: I have a strong aversion to those bargain no-name eBay power supplies from China. You get what you pay for. On a good day, they’re only good for about 50% of their current ratings and the other specs, well, you’re looking at the typical performance. Maybe okay for LEDs but I don’t trust them, safety wise. Of course, YMMV.

author: ElectricPower
author_rank: Frequent Contributor
timestamp: February 25, 2021, 05:40:36 am
content: Quote from: WattsThat on February 25, 2021, 05:33:54 amI have made myself an "LED driver" for my WS2811 5V LED strip. I have an soldered PCB with Wemos Di Mini (ESP8266) that gives signal to WS2811. I use WLED app. When i use the 5V adapter i can power my Wemos D1 Mini at the same time as i power my LEDS. One power adapter runs it all. Maybe not he best solution, but the simplest.I have powered it that way and it works just fine, but for how long? I do not know...

author: bob91343
author_rank: Super Contributor
timestamp: February 25, 2021, 06:02:38 am
content: In general, one shouldn't ask for super low ripple from a power supply. Sure the peaks are high but they are so short lived that they don't contain much energy and could be filtered out at the load rather easily. If it were a square wave that high I would agree that it's too much.Add some low ESR capacitors at the load and if you want to get fancy, some series inductance.Speed up the sweep and show us the details of the spikes.

author: ElectricPower
author_rank: Frequent Contributor
timestamp: February 25, 2021, 06:22:14 am
content: Quote from: bob91343 on February 25, 2021, 06:02:38 amHey!..... I'm a beginner.... Really... totally beginner with scopes...