AC enters the charger
AC power enters the charger through a removable AC plug.
A big advantage of switching power supplies is they can be designed to run on a wide range of input voltages.
By simply swapping the plug, the charger can be used in any region of the world,
from European 240 volts at 50 Hertz to North American 120 volts at 60 Hz.
The filter capacitors and inductors in the input stage prevent interference from exiting the charger through the power lines. The bridge rectifier contains four diodes, which convert the AC power into DC.
(See above video for a great demonstration of how a full bridge rectifier works.)
The input components in a Macbook charger. The diode bridge rectifier is attached to the metal heat sink with a clip.
PFC: smoothing the power usage
The next step in the charger’s operation is the Power Factor Correction circuit (PFC), labeled in purple.
One problem with simple chargers is they only draw power during a small part of the AC cycle.[5]
If too many devices do this, it causes problems for the power company.
Regulations require larger chargers to use a technique called power factor correction so they use power more evenly.
The PFC circuit uses a power transistor to precisely chop up the input AC tens of thousands of times a second; contrary to what you might expect, this makes the load on the AC line smoother. Two of the largest components in the charger are the inductor and PFC capacitor that help boost the voltage to about 380 volts DC.[6]
