Aug
12
2009

Why was micro-USB chosen as the standard mobile phone charger?

Micro-USB charging on the left. mini-USB on the right (photo by In Veritas Lux - CC-BY)

Micro-USB charging on the left. mini-USB on the right (photo by In Veritas Lux - CC-BY)

In June 2009, most of the big mobile phone makers decided to adopt the micro-USB connector as the standard for their chargers. Nokia, Sony Ericsson, Motorola, LG, Samsung, NEC and others have agreed to use this connector. Apple is going to keep their proprietary connector for the iPhone, but will produce a micro-USB adapter so that iPhones can be charged using the new standard charger.

With these big names on board, the standard is sure to be a success. We can look forward to using just one kind of charger to charge any kind of phone. The phone makers like the idea, because it’s an excuse to remove the charger from the box. Why supply a charger if everyone has a standard charger already? Environmentally, this makes sense, as currently millions of proprietary chargers are thrown away each year when their devices are discarded.

With a single standard in place for charging mobile phones, we should see the same charger adopted for other rechargeable devices: cameras, GPS units, music players, walkie-talkies, electronic games, etc. Over the next few years we can expect to see USB charging sockets appearing just about everywhere: in wall sockets, on the back of appliances, and on the car dashboard. This in turn will hasten the arrival of a plethora of small USB-powered devices.

So the adoption of this new standard will trigger quite a revolution! But why was micro-USB chosen for the connector?

The makers of cellphones like its tiny size. It is very thin, and phone manufacturers are always looking for ways to make their devices as slim as possible.

Micro-USB is also a data connector, so the device only needs one socket for simultaneous charging and data transfer (it will charge whenever it is connected to a computer).

But why was mini-USB not chosen? The “mini” connector is only a little larger than the “micro”, and has one advantage: it’s easier to plug it in the right way round. The “micro” USB connector has a slightly asymmetrical shape so that it can only be inserted one way, but it’s not visually obvious (at a glance) which way to plug it in, nor can you reliably line it up “by feel” in the dark. That is really the only downside of micro-USB for this purpose.

Well, mini-USB was ruled out because it’s not robust enough. The mini-USB socket includes tiny springs which press the contacts together, and these can break or lose their springiness after around five thousand connections and disconnections. The micro-USB connector moves the springs from the socket to the cable, resulting in a much more durable socket (rated for 10,000 connection-disconnection cycles). Additionally, if a spring fails, it’s simple and cheap to replace the micro-USB cable, whereas with mini-USB a spring failure would entail an expensive repair or replacement of the device itself.

In a few years we’ll look back and wonder how we managed with every device requiring a seemingly-different charger.

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1 Comment

  • eiffel says:

    It’s almost a year after this article was written, and many devices now come with micro-USB charging. However some of those devices (such as the Nokia N900) use surface-mounting for the micro-USB socket, and there have been problems with these sockets coming loose due to the solder pads breaking. The right way to do it is to use a micro-USB socket with pins that go through the circuit board, or else to attach the micro-USB socket to the case of the device.

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