What is the Box on Laptop Chargers?

If you've ever looked at your laptop charger, you might have noticed a massive, rectangular box along the cable (unless you're using a Mac).

There are various functions going on within this box, such as voltage conversion, AC to DC conversion. I'm going to discuss each one of these functions and how they are achieved.

Voltage Conversion

The box contains a transformer to achieve the voltage conversion. However, in reality there are various types of transformers such as a step-up or step-down transformers where the former increases voltage and the latter decreases voltage.

Why is this needed? This is due to the voltage needed for a device (like a laptop) is much lower than what the mains provides. So we need to reduce the voltage before it reaches the device.

Typically, a laptop charger will use a step-down transformer as the voltage supplied from the wall outlet (typically 120V or 230V +10%/-6% depending on your location) is much higher than what the laptop requires (usually between 19V to 20V).

Now, how does a transformer actually achieve this voltage conversion? Because at the moment it just seems a bit like magic. At a basic level there is a iron core shaped like a hollow square (□) with windings on 2 opposite sides (typically made of copper or aluminium).