A better Chinese 12V adapter

Article By : Michael Dunn

Rather than admitting defeat after uncovering somehorrid Chinese-made 12 V adapters, I only found my curiosity piqued. I decided to keep looking.

Giving up on China-direct sources like AliExpress, I turned to Amazon. After browsing the reviews for many an AC adapter, it seemed pretty clear that the Amazon name wouldn’tguaranteea quality unit, but I still felt my chances were greater than with Ali.

Some PSUs on the site are shipped from a third party, others by Amazon. I chose one of the latter, a couple of 12 V 6 A adapters, ostensibly made by a company called Selectec (Amazon.ca link;Amazon.com link).

My initial Impressions were positive. The unit felt solid, and would supply up to 6.9 A before shutting down. At the rated 6 A, cable drop amounted to 0.75 V. Not great, but I’ve seen much worse.

让它热稳定3负载resulted in what I’d call acceptable temperature rise. I’d estimate a case hot-spot of maybe 50 °C, with most of the case being cooler. At a bit over 5 A however, I found the case became unacceptably hot (sorry…I must learn to be more diligent with actual temperature measurements).

Not having tested any name brand adapters from North American or European manufacturers, I can’t tell you what the norm is for adapter ratings. How hot dotheyget at full load? All I can say at the moment is not to run Chinese adapters at more than half or maybe two-thirds rated load if you expect a reasonable lifetime from them. Though I do have a2 A adapterthat handles continuous full load with some aplomb. It’s in a bigger housing than most of that power rating, so that may offer a hint on derating. The 6 A unit is admittedly in a small case for its rating (30×50×109 mm).

But you came for a teardown. Let’s have a look.

Figure 1Hacksaw meets case. The PCB-heatsink assembly is pleasingly solid. (As always, images are zoomable.)

Figure 2The heatsink is held in place by the twoTO-220devices, as well as silicone(?) around the bridge rectifier (PCB top-left), fuse (bottom-left), and transformer T1 (right of centre).

Figure 3The SMD contingent. U1, six pins, a bit right of centre, is the controller IC. Its code appears to be “ANrG1”.

Notice the EMI filter? No, neither do I. Do you believe the FCC and CE certifications? No, neither do I.

The AC connector is not IEC, but two-terminal “shaver” style. Yet there’s a ground connection on the PCB, which is connected to a couple of those blue ceramic HV caps, and…the negative DC output.

The output rectifier is Schottky inTO-220, presumably a dual – paralleled.

StudyFigure 3. Notice a few thick lines in the silkscreen? I wonder if these are meant to be milled isolation slots. If so, someone forgot to cut them.

There you have it. A 12 V adapter that, while not a total horror, isn’t anything to get too excited about either. It has its qualities, but is clearly also suspect.Caveat emptor.

Related articles:

• Teardown: 12V AC adapters – The Horror
• Whipping a cheap LED PSU into usable shape
• Teardown: LED touch controllers & PSU
• My kingdom for a 12V adapter

—Michael Dunnis Editor in Chief at EDN with several decades of electronic design experience in various areas.