How do they make cellphone adapters, especially "travel adapters", so small?
I once peeked inside an old Nintendo adapter, and it had (among other circuitry) a rather-bulky step-down transformer to bring the voltage down from 220V mains to 12V, and a diode-based rectifier to convert AC to DC. This is my limited knowledge of how power adapters work.
I'm really curious how they manage to fit a transformer inside such the tiny travel adapter – so I tried to google it, and found this disassembly of an Apple adapter. I'm not sure if the thing with the yellow tape around it (towards the end of the vid) was a transformer – is it possible to make transformers so tiny these days?
Or is there some other way to reduce the voltage (apart from using a transformer) that is used in travel adapters?
Best Answer
The smallest travel chargers / adapters available these days do not contain a magnetic transformer.
Instead, isolation and AC coupling is achieved by using piezoelectric transformers: These are really tiny, and flat, in comparison to the conventional magnetic coil based transformer, and work at greater efficiency as well. The frequencies involved are not AC power line frequencies, they are much higher.
See the image below:
The design is the same as described in the answer by Nick Alexeev (switched mode), with power line AC being rectified to DC, then high frequency AC generated, isolated via the Piezoelectric transformer, and rectified again for DC.
The use of high frequencies also reduces the required size of capacitors for smoothing the DC voltage, another key factor contributing to the bulk of older chargers / wall warts.
For additional information about such tiny travel chargers, see this answer.