Searching for USB Power Supplies that Won’t Explode

USB power supplies are super cheap and omnipresent. They are the Tribble of my household. But they’re not all created equal, and some of them may even be dangerous. I had to source USB power supplies for a product, and it wasn’t easy. But the upside is that I got to tear them all apart and check out their designs.

In order to be legitimate, it’s nice (but not legally required) for a power supply to have UL approval. Some retailers and offices and building managers require it, and some insurance companies may not pay claims if it turns out the damage was caused by a non-UL-approved device.  UL approval is not an easy process, though, and it is time consuming and expensive. The good news is that if you are developing a low voltage DC product, you can pair it with a UL approved power supply and you’re good to go without any further testing necessary.

power_supply_1_overviewIf you are going for FCC approval and are having unintentional emissions testing done (which is more likely than UL as it’s a legal requirement for products that meet certain qualifications), the testing has to be done on the whole solution, so the power supply must be included in the testing, too.

Sourcing cheap electronics in large quantities usually ends up in China, and specifically Alibaba. First, we started with a how-low-can-you-go solution. This wasn’t even a power adapter; it was a power “adapteP”, and the whole batch was mis-printed. Quality control could not be a high priority. After cutting it open, it wasn’t terrible, and it had all the necessary parts. It was surprising how much of it was through-hole, which indicates that the assembly was done mostly by people. That happens when factories are cheaper, hire inexpensive labor, don’t invest in technology, and don’t care as much about quality.

There are certain things you should look for in a power supply to determine the level of risk:

  • Isolation Distance – This is how much space there is between the primary (AC) and secondary (DC 5V) sides. UL requires a few millimeters, and often you’ll see two separate PCBs. On many single-PCB solutions you’ll see a white line meander across the board to distinguish between the two. The smaller this separation, the closer your USB power is to AC line voltage, and if the gap is bridged somehow, you’re in for a world of hurt.
  • Fuse – if there is a short, a lot of current starts flowing, components heat up, and things get dangerous. A thermal cut-off (TCO) fuse (also known as a resettable fuse or a PTC) is a component that breaks the circuit when it gets too hot, like a circuit chaperon. When it cools off, the TCO resets and you can plug the device back in with no harm done. Without the fuse, the supply heats up and current keeps flowing until a component fries, sometimes explosively.
  • Connectors – You don’t want bare leads hanging out in space where they could move and touch something. You don’t want the USB port to be soldered only by its four pins. You don’t want the power pins to be loose.
  • Decent Label – “Adaptep”? Yes, to someone who uses a different alphabet the “P” and R are very similar characters. But still. Also, fake certifications abound. Look for the difference between the CE (China Export) and the CE (Conformité Européenne) labels. And the UL Logo should have a number. So should an FCC label.

So this first adapter? Isolation distance was fine because it was two separate boards, but there was no fuse and no protective tape between components. The connectors were all secure, but the label didn’t make any promises. As for performance, output at 5.34V under my product’s load meant it was a little outside of USB spec (5.25V limit), but not dangerous. On the scope it was ringing with a peak at 5.5 V at 4 kHz.

Of course, sourcing this supply for a second batch proved tricky, and we wanted the USB plug to come out the side instead of the front so it would have a thinner profile against a wall. Additionally, we needed UL approval for a client. Our second attempt was surprisingly successful. This adapter had UL certification, with a number to look up. Note that just having a number isn’t enough; many companies will just put someone else’s number on their product and assume nobody will bother to check. So when you do look it up, and find a different manufacturer, a different enclosure, and it looks more like a refrigerator than a USB power supply, don’t be too surprised. But no, this particular one was great! The label had a company name on it, model number and specs, and certifications that could be verified. Let’s tear it open!

power_supply_2_overviewSweet sweet silicon meat inside an ABS shell! Components wrapped in protective tape, two PCBs for isolation, and even a special injection-molded plastic piece to add additional protection. Components are labeled, and what’s this, an IC to control the oscillation instead of a feedback winding on the transformer? Fancy! It’s pretty clear that this power supply is good, and I’d trust this one.

Comparing this one to the others, there were so many noticeable little details that are important and clearly thought-out. Take, for example, the connection between the prongs and the PCB. On the previous board, it was made with wires soldered by hand. Solid, but time consuming and prone to failure or quality issues. This adapter has metal contacts that snap into the case very solidly so that the prongs cannot get loose. The connection to the PCB is via the springiness of the metal, but notice that the PCB has pads specifically designed to maximize the surface area of that connection. On the next PCB you’ll see no such effort.

Some components were covered in shrink tube, tape, or non-conductive grey adhesive. The assembly was tight with no room for components to shake loose or accidentally touch. And the output was perfect. 4.9 Volts with nary a ripple.

But this is China, and component sourcing problems are a thing, so I guess I shouldn’t have been surprised when these supplies were no longer available. In retrospect, maybe these were unsold overstock, or possibly QC rejects. That would explain why they were only slightly more expensive than the others. And so we moved on to another supplier; one that could pad-print our logo on top.

power_supply_differencesAt first glance these power supplies appeared identical. But close inspection reveals slight differences in the style around the USB and the raised ridges on the underside. The label was completely different, and gone was the number next to the UL logo. There was no company name on the supply either, and the company we purchased from turned out to be a reseller and not the OEM. Also, why was the output 4.7-5V, and why did my scope say 5.5V (but surprisingly stable)?

Inside was a completely different beast. Using a single PCB, the creep distance was about a millimeter. You can see the white line meandering through the bottom of the PCB that shows the high and low sides. The USB port wasn’t soldered to the PCB except by the four signal/power pins (see the bottom side lower left and the hanging USB connection pins), and there was a capacitor with really long uncovered leads and the positive side dangerously close to the USB shell. There was almost no protective tape, no shrink tube on the leads, and no protection in case of a short.


In the end, I wouldn’t trust the two non-UL supplies with anything worth more than a few bucks, and certainly not my cell phone. I’d have really big reservations about reselling them to customers who don’t know the difference. The UL-approved one was great, but the other two are only good for powering low-current-draw devices that are not sensitive to voltage. Also, finding a reliable supplier in China is HARD.

Check out a much more thorough analysis of this and pretty much every USB power supply cube by [Ken Shirriff]. It’s surprising how little has changed in four years with these supplies, and his analysis goes into how the circuits behind these supplies work, identifying each component and its purpose.

We also covered a Sparkfun teardown of some power supplies with similar conclusions, and a Fail of the Week in which a faulty USB power adapter was the likely cause of a fire.

How To Know When An Accelerator Is Not Right For Your Startup

A few weeks ago we ran an article on the benefits of accelerator programs. While I agreed with almost everything in it, the article still bothered me, and I wanted to start a discussion about when an accelerator is not appropriate. So many startups are regularly asked “have you thought about Kickstarter? Shark Tank? Are you raising money? YCombinator?” These questions are constantly ingrained into people’s brains and they come to think those are the only options.

The reality is that there are lots of ways to build a company, and Kickstarter, Shark Tank, angel investors, and accelerators are all new within the last few years, and they aren’t right for many people. So let’s look at when an accelerator is right for you.

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Waiting for China to Re-Open, From Huaqiangbei

The Chinese New Year is something we keep in mind at least half of the year, and probably still don’t plan for properly. In case you’re new to the situation: The Chinese New Year celebration empties out Shenzhen of its more than 12 million residents for the better part of a month. It’s the one time of year that manufacturing sector workers (and everyone that supports that ecosystem) travels home to visit family.

For those involved in manufacturing goods in Shenzhen, this part of the year leaves us cut off from one of our vices and we count the days until our tracking numbers and order confirmations start to show signs of life. It’s an inconvenience of an entirely different nature if you are one of the lonely few that stays in the city during the holiday. [Ian] over at Dangerous Prototypes wrote a blog post from his office in Huaqiangbei which is a sub-district of Shenzhen, China to share the experience with us.

Shenzhen is uniquely a migrant-worker city, and when emptied of the factory employees there are not enough people to patronize local services like markets and restaurants so they also shut down. But an empty city offers its own interesting entertainment like wicked fireworks sessions. As always, [Ian] does a great job of sharing this peculiar part of Shenzhen culture. He also kindly points out some of the offensive offers that come through the inter-webs from desperate customers who have poorly planned around the holiday.

A Hackers Guide to Arts, Crafts, Food, and Music in Shenzhen

When you mention Shenzhen, many people think about electronic gadgets, cheap components, manufacturing, and technology. I’m there quite often and find that all of the technology and manufacturing related stress can be overwhelming at times. Sometimes I feel the need to escape it all so I go to markets and places that aren’t traditionally associated with technology so I can clear my head as well as expose myself to something different. It provides me with a constant source of new design ideas and also allows me to escape the persistent tech treadmill that Shenzhen runs on. There are a lot of places in Shenzhen that I consider hidden gems that don’t get a lot of press since mainstream media associates Shenzhen with either factories or technology. Here are my favorite places to window shop and de-stress in Shenzhen.

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Hacking Chinese State Media

A while ago, a few journalists from China visited the Metalab hackerspace in Vienna. They wanted to do a story on ‘fablabs’ and ‘makerspaces’, despite the objections to the residents of the Metalab hackerspace. Apparently, mentioning ‘hacking’ on China Central Television (yes, it’s called CCTV) is a big no-no.

hacking-chinese-state-mediaWanting to send a message to at least a few people in China, the members of the hackerspace had to think laterally. Metalab member [amir] came up with a way to encode data that could be printed on t-shirts. These bright, colorful squares featured in all of the interviews with Metalab members carried messages like, “free tibet!”, “remember tian’anmen 1989” and “question the government. dont trust the propaganda”

All the videos are available in this playlist, and [amir]’s code to generate the colorful rectangles of political activism can be found here.

In a related note, we’d like to say ‘hi’ to our one reader in North Korea. Yes, according to the stats and analytics, we have one reader in North Korea.

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Two New FPGA Families, Designed in China

The two largest manufacturers of FPGAs are, by far, Altera and Xilinx. They control over 80% of the market share, with Lattice and others picking up the tail end. The impact of this can be seen in EE labs and alibaba; nearly every FPGA dev board, every instructional, and every bit of coursework is based on Altera or Xilinx chips.

There’s a new contender from the east. Gowin Semiconductor has released two lines of FPGAs (Google translate) in just under two years. That’s incredibly fast for a company that appears to be gearing up to take on the Altera and Xilinx monolith.

The FPGA line released last week, the GW1N family, is comprised of two devices with 1,152 and 8,640 LUTs. These FPGAs are built on a 55nm process, and are meant to compete with the low end of Altera’s and Xilinx’ offerings. This adds to Gowin’s portfolio introduced last May with the GW2A (Google translate) family, featuring devices ranging from 18,000 to 55,000 LUTs and DSP blocks. Packages will range from easily solderable QFN32 and LQFP100, to BGA packages with more pins than an eighteenth century seamstress at the royal ball.

For comparison, Xilinx’ Spartan-6 LX family begins with devices featuring 3,840 LUTs and 216kb of block RAM, with larger devices featuring 147,443 LUTs and up to 268kb of block RAM. Altera’s Cyclone IV E devices are similarly equipped, with devices ranging from 6,272 to 114,480 LUTs. Between the two device families introduced by Gowin recently, nearly the entire market of low-end FPGAs is covered, and they’re improving on the current offerings: the GW1N chips feature random access on-chip Flash memory. Neither the low-end devices from Altera nor devices from Lattice provide random-access Flash.

The toolchain for Gowin’s new FPGAs is based nearly entirely on Synopsys’ Synplify Pro, with dedicated tools from Gowin for transforming HDL into a bitstream for the chip. This deal was inked last year. As for when these devices will make it to market, Gowin is hoping to send out kits to well-qualified devs soon, and the devices may soon show up in the warehouses of distributors.

Gowin’s FPGAs, in contrast to the vast, vast majority of FPGAs, are designed and fabbed in China. This gives Gowin a unique home-field advantage in the land where everything is made. With LVDS, DSP, and other peripherals these FPGAs can handle, Gowin’s offerings open up a wide variety of options to developers and product engineers a few miles away from the Gowin plant.

The GW1N and GW2A families of FPGAs are fairly small when it comes to the world of FPGAs. This limitation is by capability though, and not number of units shipped. It’s nearly tautological that the largest market for FPGAs would be consumer goods, and Gowin is focusing on what will sell well before digging in to higher end designs. We will be seeing these chips show up in devices shortly, and with that comes a new platform to tinker around with.

If you’re looking to make your mark on the world of open source hardware and software, you could do worse than to start digging into the synthesis and bitstream of these Gowin chips. Just months ago, Lattice’s iCE40 bitstream was reverse engineered, and already there are a few boards capitalizing on a fully open source toolchain for programmable logic. With more capable FPGAs coming out of China that could be stuffed into every imaginable product, it’s a golden opportunity for hardware hackers and developers alike.

[Thanks for the tip Antti]

The Factory of the World – Hackaday Documentary on the Shenzhen Ecosystem

When it comes to manufacturing, no place in the world has the same kind of allure as the Pearl River Delta region of China. Within just an hour-long train ride, two vastly different cultures co-exist, each with its unique appeal that keeps attracting engineers, entrepreneurs, and hustlers alike. On the mainland side, cities like Shenzhen and Guangzhou bring the promise of cheap components, low-cost contract work, and the street cred of “having done the Shenzhen thing.” And on the island, the capitalist utopia called Hong Kong glows with all of its high finance and stories of lavish expat lifestyles.

As the “new” China evolves, it seems like it’s exactly the convergence of these two cultures that will bring the biggest change—and not just to the area but to the whole world. Still, understanding what exactly is going on and what the place is really all about remains a mystery to many. So, this June, we jumped on the bandwagon and headed east, trying to get our own feel for the whole thing.

Here’s what we came back with…

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