A better Chinese 12V adapter

Article By : Michael Dunn

I’ve investigated some execrable & dangerous adapters in the past. Is this one really any better?

Rather than admitting defeat after uncovering some horrid 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’t guarantee a 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.

Letting it thermally stabilize with a 3 A load 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 do they get 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 a 2 A adapter that 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 1 Hacksaw meets case. The PCB-heatsink assembly is pleasingly solid. (As always, images are zoomable.)

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

Figure 3 The 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 in TO-220, presumably a dual – paralleled.

Study Figure 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.

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

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