Apple is renowned for obsessing over tiny details and making its products as beautiful on the inside as they are on the outside, and the company maintains that design policy for everything it creates, whether it’s a $1,200 MacBook Pro, or a $30 iPhone charger.
In fact, Apple has gone to great lengths to ensure those tiny iPhone chargers are safe and efficient, and it uses state of the art technology to do that — which is why its chargers are more expensive than most.
Ken Shirriff has torn down one of Apple’s iPhone chargers on his blog, and he’s made a number of interesting discoveries. First, they are very different to similar products from the likes of Samsung, and it’s clear the Cupertino company has a heavy focus on quality and safety — though that’s hardly surprising when we’re talking about Apple.
The iPhone charger is a switching power supply that turns the input power on and off around 70,000 times a second to get the right output voltage. As you can see from the image above, the charger consists of two circuit boards, both slightly under one inch square in size. The one at the top is the primary board, which handles the high voltage input circuitry, while the one at the bottom handles the low voltage output circuitry.
Shirriff stresses just how small Apple’s components really are:
Looking at these pictures, it’s easy to lose track of how very small these components are, and how the charger crams all this complexity into one inch. The following slightly magnified picture shows a quarter, a grain of rice, and a mustard seed to give a size comparison.
So, other than its tiny size, what makes Apple’s charger so special? Well, Sherriff says it’s “clearly a high-quality power supply designed to produce carefully filtered power.” Apple has put a lot of effort into reducing EMI interference — likely to prevent any interference with the iPhone’s touchscreen — and it has introduced a number of components that aren’t found in similar chargers.
The input AC is filtered thorugh a tiny ferrite ring on the plastic case (see photo below). The diode bridge output is filtered by two large capacitors and an inductor. Two other R-C snubbers filter the diode bridge, which I’ve only seen elsewhere in audio power supplies to prevent 60Hz hum;perhaps this enhances the iTunes listening experience. Other chargers I disassembled don’t use a ferrite ring and usually only a single filter capacitor. The primary circuit board has a grounded metal shield over the high-frequency components (see photo), which I haven’t seen elsewhere. The transformer includes a shield winding to absorb EMI. The output circuit uses three capacitors including two relatively expensive tantalum ones and an inductor for filtering, when many supplies just use one capacitor. The Y capacitor is usually omitted from other designs. The resonant clamp circuit is highly innovative.
In addition to these things, Apple uses “super-strong” AC prongs and a “complex over-temperature/over-voltage shutdown circuit” which all help make this charger extra safe.
Shirriff concludes that Apple crams a lot of high-tech components into an incredibly small space to create a high quality, super safe charger that makes rival chargers look like a high school electronics project. The only downside is, we have to pay a little extra for it.