USB Charger Voltage Problems - Page 1
Forum section: electronics / projects

author: LL0rd
author_rank: Contributor
timestamp: November 01, 2016, 02:32:53 am
content: Hi,I need some help with some specs. On my table I currently have two USB charger. One is a genuine Samsung and the other I bought from the supermarket.First of all, I tested the Samsung charger. Without a load I have bang on 5V and with 1A load, I still have 5V and a flat line on the scope. That's what I have expected from a high quality charger.Then I took the "cheap" charger from the supermarket. Without any load I had 4.9 V. Okay, it's a bit low but okay. But with 1A load, the voltage went up. In mean I had about 5.15V but with spikes to 5.76V. Take a look on the scope image attached.My opinion is, that the charger is not OK. With this spikes it can damage the charging electronic of the mobile phone. Not for nothing we have a lot of failing charging chips like the U2 Chip on iPhones.What's your opinion?

author: singapol
author_rank: Frequent Contributor
timestamp: November 01, 2016, 03:32:26 am
content: I hope you don't take offence by my comments. Is the failure of iphones due to using "unauthorised" cheap chargers? Then educate your clients on this issue. As in life you get what you pay for.From an engineering or technical perspective, samsung charger is designed for only 1 specific task, to charge it's mobile phones. Where as for cheap charger it's manufacturer hopes it will be of "general" use and for the sake of consumers it should come with a warning that if used for charging phones consumer should understand the risks or if it advertises as an alternative replacement charger then it has not sufficiently address to the utility of it's purpose.Look at it this way, Samsung is a big MNC and has a formidable R&D department. The manufacturer is a small outfit hoping to serving a potential market for it's product. The design is probably straight of the datasheet of the controler chip it employs without further testing ,company just want to make a profit as well as trying to offera better mousetrap so to speak or so it thinks.If you think the cheap charger is not ok and if you are worried about the spike issue then try to reverse enginnering and find out why or the difference between these 2 products. I'm sure you will find that the samsunghas more components perhaps better quality or suitability for such a charger. What tricks did samsung employ?My bet is samsung understand the meaning of impedance matching and termination of circuits.

author: CraigHB
author_rank: Regular Contributor
timestamp: November 01, 2016, 04:53:25 pm
content: That's a pretty typical voltage ripple you'd see from a cheap USB wall wart. That's the difference between a name brand unit and an el-cheapo. Most of the time a device can handle ripple like that without issue. It's the big spikes that do damage. They can get through from power surges on the AC side or load dumps on the DC side. Higher end wall warts incorporate some protection from that kind of thing.In general you can find some really poorly made products that come cheaply out of China. You can find good products that originate from there, but there's some really sub-standard stuff that gets through and ends up on the shelves at places like Walmart. These days it's a case of buyer beware more than ever.

author: LL0rd
author_rank: Contributor
timestamp: November 01, 2016, 05:52:21 pm
content: Well, I decided to open this piece of shit and look what's inside.Well, on the first glimpse, I was glad to find a Linear chip inside. On the second glimpse it was not an LT part, but LP with a similar logo. The charger uses the LP3773 chip. And if you compare the design from the data sheet to the design of the charger, you find that some caps are missing or have a lower capacity.

author: wraper
author_rank: Unknown
timestamp: November 01, 2016, 06:04:40 pm
content: QuoteRising voltage is perfectly fine and actually is intentional. That ripple might be because of your electronic load, not necessarily the charger is at fault. PCB don't look that bad, Creepage distance between primary and secondary may be an issue in cheap chargers, but it is not obvious from your picture.