Part of the engineer lifestyle is a box, or bag, or drawer full of old but still functional power adapters and battery chargers. The gear they once powered is long gone but these little gems wait patiently for something to do, a load to power.
In the past, I have replaced the batteries in a baby swing with an old modem adapter (remember those?) and presently have a rescued treadmill with a display powered by an old WiFi base station adapter.
My personal collection, carefully gathered over many years, is valued, according to an expert, at over $1.38 (US). You can pretend to not be impressed, but it won’t work.
I recently sat down with a fresh Twinkie and a cheap coffee to review this collection and reflect upon all the devices these relics had powered. While thus engaged, it occurred to me that these little beauties, as a group, can represent significant risk to circuit health. All of them had 120V AC line inputs but the outputs were a mixed bag. AC Out, Positive DC Out, Negative DC Out, 6V, 9V, 12V, 18V, 19.5 V… you get the point. Though none of these voltages is typically regarded as particularly dangerous, these things can destroy a circuit if that circuit was designed for a different voltage.
Here is where the risk lays - there appear to be no standards regarding connectors and voltages and polarities when it comes to adapters and chargers. Read on…
My collection - wild!
Notice something? What do all of these adapters have in common (other than sitting inTex’s barn)?
It definitely is NOT the voltage, current, or center pin polarity…
So, what DO they all have in common?
They all have the same 5.5 mm connector!!!
This means they can all plug into each other’s loads, regardless of Voltage, polarity, or current rating. And, doing so could result in any of the following unpleasant events:
The conditions above have the potential to cause overcurrent/overheating of power feeds and converters, brown out damage, electrical over stress, smoke, fire, and equipment damage. This could happen to devices such as: cable modems, telephones, telephone base stations, printers, wireless access points, GPS, HDD, SSD, desktop remote speakers, security cameras, etc.
Recently, I saw a deal for a refurbished GPS with over a thousand sold and all I thought about was the possible damage caused by transients and wrong supplies. Fortunately, this disaster can be avoided by adding an eFuse at the input to the load. The simplest eFuse solutions will protect against over current, over voltage, and clamp voltage spikes at the input. Protection from reverse current flow and/or reverse supply polarity requires a slightly more sophisticated solution, but only slightly.
TPS24750 + ext circuit
TPS2592ZA, TPS2420, TPS2421-x, TPS2590, TPS25910
TPS2592ZA, TPS2420, TPS2421-x, TPS2590, TPS25910, TPS24750
Add any of these integrated FETs to my wild adapters and my electronic devices are safe!
Let’s start the New Year off right with properly protected devices!
Does anyone else have a collection of adapters at home? If so, please share about them in the comment section below.
And today I nearly plugged a 48V/300 mA, 5.5mm adapter into my laptop while sitting in a guest office at a site to remain nameless.
I love the 5.5 mm photo! It is also the problem I face in dealing with a product design where I want to protect my device from reverse polarity. (Yes, our customers have the same drawers, bins, and boxes of these little critters! I was wondering if you could please suggest a TI LDO regulator (5v, 1 amp to 1.5 amp) that may have reverse polarity protection? ... And are there any special points to pay attention to when selecting a regulator with reverse polarity protection? Thank you. Tom Taylor
For protection against WAPI ( Wrong Adapter Plugged In ) to 23 V I'd recommend the TPS2592BA. It will clamp surges to 6.1 V. A 19 V laptop adapter can be plugged in and this device will Limit the output to 6.1 V nominal. Max current limt and dv/dt can be set also. For reverse hookup protection insert a diode between the TPS2592BA GND pin and the system GND. ( Anode to TPS2592BA, Cathode to system GND ). Any programming component ( RLIM, Cdv/dt ) should be connected to device GND instead of system GND. Of course....this will raise the clamp voltage by a diode drop.
I also having the same collection of cables and adpaters, I personally thinks that by the time most of these accessories wears out, but I have to say that i have purchased the null modem cable from "SF Cable" it has been now 4 years and it is woking perfectly....
It is not helpful that many of these adapters have very small printing making it difficult to identify them. But even more harrowing than the power adapter plug is the RJ-45 jack, which, due to its cost effectiveness and versatility, is being applied to every connection scheme imaginable making monkey-proofing these products almost impossible nowadays.
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