updated 12:05 am EDT, Thu May 24, 2012
Well-designed adapter protects phone from damage, malfunction
Electronics technician Ken Shirriff has completed a teardown in minute detail of the Apple iPhone charger, revealing higher-quality manufacturing techniques and parts along with more attention to detail than is normally seen in smartphone chargers. The $29 charger and cable combo costs more to make than a typical AC USB charger, but remains a highly-profitable unit despite the extra care taken. Shirriff also did a teardown on a cheaper "clone" iPhone charger, and strongly recommends that under no circumstances should they be used, calling them "tiny, cheap, and dangerous."
Apple's charger uses a flyback switching power supply, like most USB chargers. Simply put, it takes AC input and produces five watts of smooth 5-volt power with a "surprisingly complex and innovative" circuit designed to produce carefully-filtered and smooth power, to prevent any dirty power interference with the touch screen when plugged in.
The unit is a switching power supply, where input (AC) power is switched on and off about 70,000 times per second by internal circuitry to get the exact voltage needed by the device. Generally speaking, switching power supplies are small and generate little waste heat when compared to normal power adapters. Many companies use switching power adapters for electronic devices -- Samsung, for example, uses the same base technology for their adapter.
As with most other Apple products, the difference between this USB charger and others is attention to detail. Shirriff found an uncommon level of thought put into the charger, including two large capacitors and an inductor filter for the output of the adapter, rather than the standard one capacitor. The extra filtering is likely used to prevent a 60Hz hum in audio playback. A grounded metal shield covers the high-frequency components. This metal shield and a shield winding around the transformer provides an extra level of electromagnetic interference absorption.
Additionally, the post-2008 recall version of the charger firmly anchors the AC prongs into the case with large metal flanges, instead of just a dot of glue and friction. A complex over-temperature shutdown circuit goes a long way in protecting expensive Apple devices from abnormal operating conditions or failures. Isolation distances between high and low voltage areas within the charger are placed well beyond the demands of physics or electronics regulations.
Shirriff also did an assembly cost breakdown, and given certain volume assumptions, he guesses that the extra components in the charger account for perhaps an additional dollar over any given third-party adapter's components. Apple's charger is of exceptionally high quality, says Shirriff, and given the cost of the components, there's no reason why more chargers shouldn't be built this way. That said, Apple does charge a premium for the adapter compared to its competitors, and Shirriff notes that the adapter is "nearly all profit" for Apple. [photos via Ken Shirriff]