Subject themes

Though on the whole I try to cowl a range of matters right here within the weblog, common readers might have seen that some quantity of chronological theme-grouping nonetheless goes on. A number of years again, for instance, I wrote a good bit about constructing PCs, each conceptually and in un-teardown (i.e., hands-on meeting) vogue. After that, there was a cluster of posts having to do with numerous nonetheless and video images matters. And final yr (extending into early this yr) I talked loads about lithium-based batteries, each in an absolute sense and relative to sealed lead-acid forebears, in addition to the gear containing them (and recharging them, i.e., photo voltaic cells).

Effectively, honest warning: this submit is the kickoff of one other common-topic cluster, having to do with audio. This isn’t a topic I’ve ignored thus far, thoughts you; think about simply in current instances, for instance, my posts on ambient noise suppression, interconnect schemes, lossy compression algorithms and listening gear (moveable, too), microphones (plus on-PCB ones, tearing them down, and boosting their outputs) and unique headphones, amongst others. However even extra lately, I’ve obtained some “Chi-Fi” (i.e., constructed and typically additionally instantly bought by China-based suppliers) audio gear—class D amplifiers and the like—together with audio gear from a US-based firm that additionally does Stateside meeting, but nonetheless successfully competes within the US and broader worldwide markets.

What’s a wall wart?

Extra on all of that in posts to come back by means of the rest of this yr, possible additionally extending into the following. For now: what does all of this must do with a wall wart? And what is a wall wart, for these of you not already aware of the time period? Right here’s Wikipedia’s take on the subject:

An AC adapter or AC/DC adapter (additionally known as a wall charger, energy adapter, energy brick, or wall wart) is a kind of exterior energy provide, typically enclosed in a case just like an AC plug. AC adapters ship electrical energy to units that lack inside parts to attract voltage and energy from mains energy themselves. The interior circuitry of an exterior energy provide is usually similar to the design that may be used for a built-in or inside provide.

At the moment’s sufferer arrived through a Micca PB42X powered speaker set, bought from an eBay vendor:

The story behind the teardown

They’d beforehand belonged to her son, who in response to her by no means used them (extra on that later), so she was offloading them to make some cash. Drawback was, though she’d despatched me pictures beforehand of the correct speaker (fed by an RCA enter connector set and containing the category D amplifier circuitry for each audio system; a standard strand of speaker wire connects its output to its left-speaker sibling’s enter) powered up, full with a glowing pink again panel LED, no AC adapter was accompanying it when it arrived at my entrance door.

After I messaged her, she despatched me the “wall wart” you’ll see immediately, which not solely was best-case underpowered in comparison with what it ought to have been—12V@500mA versus 18V@2A—however didn’t even work, outputting lower than 200mV, typically measuring optimistic and different instances damaging voltage (on reflection, I want I might have additionally checked for any AC output voltage proof earlier than dissecting it):

She ultimately agreed to offer a partial refund to cowl my replacement-PSU value, leaving me with a “useless” wall wart appropriate just for the landfill. Though…I spotted proper earlier than tossing it that I’d by no means truly taken one aside earlier than. And this’d additionally give me an opportunity to check out the speculation of a hilariously narrated (watch it and pay attention for your self) video I’d beforehand come throughout, proposing a way for getting inside gear with ultrasonic-welded enclosures:

Finest video ever, proper? The subject was of nice curiosity, as I typically got here throughout such-sealed gear and my historic strategies for getting inside (a hacksaw, for instance) additionally threatened to inadvertently mangle no matter was inside.

The teardown

I didn’t have the urged wallpaper knife in my possession; as a substitute, I received a paint scraper with a pointy edge and hammer-compatible different finish:

And within the following overview pictures, with the wall wart as-usual accompanied by a 0.75″ (19.1 mm) diameter U.S. penny for measurement comparability functions, you’ll discover (amongst different issues) the ultrasonic welded joint across the circumference, to which I utilized my pounding consideration:

Full with a closeup of the (in)well-known Prop. 65 sticker…

How’d it work out? Effectively…I received inside, as you’ll see, however the break alongside the joint wasn’t precisely clear. I received’t be placing this wall wart again collectively once more, not that I’d wish to strive on this case:

Perhaps subsequent time I’ll use a extra light-weight hammer, and/or wield it with a lighter contact

Anyhoo, with the injury carried out, the entrance portion of the enclosure lifts off straightaway:

Two issues baffle me concerning the inside of the entrance case piece:

• What’s the purpose of the 2 glue dabs, which aren’t location-relevant to something inside?
• And what if any useful use does that further diagonal plastic piece serve?

That every one mentioned, this is what we’re most keen on, proper?

The insides equally lifted proper out of the remaining piece(s) of the enclosure:

For those who hadn’t already seen, the heftier entrance of the case had survived its encounter with the paint scraper and sledge intact. The smaller again portion…not a lot:

Right here’s an summary of the now-exposed again of the wall wart’s guts. The transformer, which I’m certain you already seen earlier than, dominates the panorama:

Now persevering with (and ending) the rotation in 90° increments:

Let’s take a more in-depth have a look at that PCB hanging off the underside:

I’m, as reader suggestions repeatedly jogs my memory, not an analog or energy electronics skilled by any means, however what I imagine we’re right here is visible proof of a very rudimentary type of AC-to-DC conversion, the four-diode bridge rectifier:

A diode bridge is a bridge rectifier circuit of 4 diodes that’s used within the strategy of changing alternating present (AC) from the enter terminals to direct present (DC, i.e. fastened polarity) on the output terminals. Its operate is to transform the damaging voltage parts of the AC waveform to optimistic voltage, after which a low-pass filter can be utilized to easy the consequence into DC.

 When utilized in its most typical utility, for conversion of an alternating-current (AC) enter right into a direct-current (DC) output, it is named a bridge rectifier. A bridge rectifier gives full-wave rectification from a two-wire AC enter, leading to decrease value and weight as in comparison with a rectifier with a three-wire enter from a transformer with a center-tapped secondary winding.

The low-pass filter talked about within the definition is, after all, the capacitor on the PCB. And re the diodes, the producer (presumably in aspiring to squeeze as a lot revenue as doable out of the design) didn’t even hassle going the (presumably extra expensive) integration route:

Previous to the provision of built-in circuits, a bridge rectifier was constructed from separate diodes. Since about 1950, a single four-terminal part containing the 4 diodes related in a bridge configuration has been obtainable and is now obtainable with numerous voltage and present scores.

Satirically, in trying again at Wikipedia’s “wall wart” web page post-teardown, shortly earlier than I started writing, I occurred to note this very same method showcased in one of many pictures there:

A disassembled AC adapter exhibiting a easy, unregulated linear DC provide circuit: a transformer, 4 diodes in a bridge rectifier, and a single electrolytic capacitor to easy the waveform.

And it’s additionally documented in an attention-grabbing Reddit thread I discovered, which begins out this manner:

Do cheap 12v wall warts normally use a transformer to step mains to about 12vac then bridge rectify and regulate to 12vdc?

Or

Do they use some minimal 1:1 transformer for isolation, rectify to dc then use a buck converter to drop to 12v?

Or another normal intelligent design?

Look once more on the PCB, although, particularly on the markings, and also you may discover one thing curious. Let me transfer a few diodes out of the best way to emphasise what I’m speaking about:

Capacitor C5, the large one for output filtering, is clearly current. However why are there additionally markings for capacitors C1-C4 alongside the diodes…and why are they lacking? The clue, I’ll counsel, seems within the final little bit of Wikipedia’s diode bridge introductory part:

Diodes are additionally utilized in bridge topologies together with capacitors as voltage multipliers.

As soon as once more to save lots of value, I feel the producer of this wall wart developed a PCB that might do double-duty. Populated solely with diodes, it (requoting Reddit) “makes use of a transformer to step mains to about 12vac then bridge rectify and regulate to 12vdc.” And for different wall wart product proliferations with different output DC voltages, you’ll discover a mixture of each diodes and capacitors soldered onto that very same PCB.

Once more, as I mentioned earlier than, I’m not an analog or energy electronics skilled by any means. So, at this level I’ll flip the microphone over to you in your ideas within the feedback. Am I not less than within the ballpark with my principle (are you able to inform that MLB spring coaching simply started as I’m scripting this)? Or have I struck out swinging? And what else about this design did you discover attention-grabbing?

—Brian Dipert is the Editor-in-Chief of the Edge AI and Imaginative and prescient Alliance, and a Senior Analyst at BDTI and Editor-in-Chief of InsideDSP, the corporate’s on-line e-newsletter.

 Associated Content material

• Wall wart + battery = small UPS: Good thought or not?
• When reliability hangs by a “wall wart” thread
• USB bus-powered units put an finish to Wall Warts
• These AC/DC modules: my, how you could have shrunk!
• Finding out USB-C energy provides: Specification deceptions and complicated implementations

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