the boards.
SchematicI've put together an approximate schematic showing the charger circuit. Click for a larger version.
These circuits are very smallLooking 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. Most of the components are surface-mount devices which are soldered directly to the printed circuit board. The smallest components, such as the resistor pointed out in the picture, are known as "0402" size since they are .04 inches by .02 inches. The larger resistors to the left of the mustard seed handle more power and are known as "0805" size since they are .08 x .05 inches.
Transformer teardownThe flyback transformer is the key component of the charger, the largest component, and probably the most expensive. But what's inside? I took apart the transformer to find out.
The transformer measures roughly 1/2" by 1/2" by 1/3". Inside, the transformer has three windings: a high voltage primary input winding, a low voltage auxiliary winding to provide power to the control circuits, and a high-current low voltage output winding. The output winding is connected to the black and white wires coming out of the transformer, while the other windings are connected to the pins attached to the bottom of the transformer.
The outside of the transformer has a couple layers of insulating tape. The second line appears to start with "FLEX", for Flextronics. Two grounded strands of wire are wrapped around the outside of the transformer to provide shielding.
After removing the shielding and the tape, the two halves of the ferrite core can be removed from the windings. Ferrite is a rather brittle ceramic material, so the core broke during removal. The core surrounds the windings and contains the magnetic fields. Each core piece is roughly 6mm x 11mm x 4mm; this style of core is known as EQ. The circular center section is very slightly shorter than the ends, creating a small air gap when the core pieces are put together. This 0.28mm air gap stores the magnetic energy for the flyback transformer.
Underneath the next two layers of tape is a 17-turn winding of thin varnished wire, which I think is another shield winding to return stray interference to ground.
Underneath the shield and another two layers of tape is the 6-turn secondary output winding that is connected to the black and white wires. Note that this winding is heavy-gauge wire, since it is feeding the 1A output. Also note that the winding is triple-insulated, which is a UL safety requirement to ensure that the high voltage primary remains isolated from the output. This is one place where cheap chargers cheat - they just use regular wire instead of triple-insulated, and also skimp on the tape. The result is there's not much protecting you from high voltage if there's an insulation flaw or power surge.
Under the next double layer of tape is the 11-turn heavy gauge primary power winding, that powers the controller IC. Since this winding is on the primary side, it doesn't need to be triple insulated. It's just insulated with a thin layer of varnish.
Under the final double layer of tape is the primary input winding, which is 4 layers of approximately 23 turns each. This winding receives the high voltage input. Since the current is very low, the wire can be very thin. Because the primary has about 15 times as many turns as the secondary winding, the secondary voltage will be 1/15 the primary voltage, but 15 times the current. Thus, the transformer converts the high voltage input to low voltage, high current output.
The final picture shows all the components of the transformer; left to right shows the layers from the outside tape to the innermost winding and bobbin.
Apple's huge profit marginsI was surprised to realize how enormous Apple's profit margins must be on these chargers. These chargers sell for about $30 (if not counterfeit), but that must be almost all profit. Samsun