Have you ever wondered what’s inside your Macbook’s charger? There’s a lot more circuitry crammed into the compact power adapter than you’d expect, including a microprocessor. This charger teardown looks at the numerous components in the charger and explains how they work together to power your laptop. Most consumer electronics, from your cell phone to your television, use a switching power supply to convert AC power from the wall to the low-voltage DC used by electronic circuits. The switching power supply gets its name because it switches power on and off thousands of times a second, which turns out to be a very efficient way to do this conversion.
Switching power supplies are now very cheap, but this wasn’t always the case. In the 1950s, switching power supplies were complex and expensive, used in aerospace and satellite applications that needed small, lightweight power supplies. By the early 1970s, new high-voltage transistors and other technology improvements made switching power supplies much cheaper and they became widely used in computers. The introduction of a single-chip power supply controller in 1976 made switching power supplies simpler, smaller, and cheaper.
Apple’s involvement with switching power supplies goes back to 1977 when Apple’s chief engineer Rod Holt designed a switching power supply for the Apple II. According to Steve Jobs:This is a fantastic quote, but unfortunately it is entirely false. The switching power supply revolution happened before Apple came along, Apple’s design was similar to earlier power supplies and other computers don’t use Rod Holt’s design. Nevertheless, Apple has extensively used switching power supplies and pushes the limits of charger design with their compact, stylish and advanced chargers.
Inside the charger
For the teardown I started with a Macbook 85W power supply, model A1172, which is small enough to hold in your palm. The picture below shows several features that can help distinguish the charger from counterfeits: the Apple logo in the case, the metal (not plastic) ground pin on the right, and the serial number next to the ground pin.
The secondary: smooth, clean power output
The secondary side of the circuit generates the output of the charger. The secondary receives power from the transformer and converts it DC with diodes. The filter capacitors smooth out the power, which leaves the charger through the output cable.
The most important role of the secondary is to keep the dangerous high voltages in the rest of the charger away from the output, to avoid potentially fatal shocks. The isolation boundary marked in red on the earlier diagram indicates the separation between the high-voltage primary and the low-voltage secondary. The two sides are separated by a distance of about 6 mm, and only special components can cross this boundary.
The transformer safely transmits power between the primary and the secondary by using magnetic fields instead of a direct electrical connection. The coils of wire inside the transformer are triple-insulated for safety. Cheap counterfeit chargers usually skimp on the insulation, posing a safety hazard. The optoisolator uses an internal beam of light to transmit a feedback signal between the secondary and primary. The control chip on the primary side uses this feedback signal to adjust the switching frequency to keep the output voltage stable.
For more detail: Macbook charger teardown