Your phone charger converts power to DC, then back to fake AC
The extra loop lets a tiny transformer step 100 to 240 volt wall power down to what a battery can use.
Real Engineering · $1 vs $50 Phone Charger. What’s the difference?Plug your phone into the wall and you are plugging into the wrong kind of electricity. The outlet delivers 100 to 240 volts, with the exact level set by the local grid, reversing direction 50 or 60 times each second. Your phone battery cannot use that. It needs low voltage power that flows one way, called direct current.
To start, the circuit reshapes that two way flow into a one way flow.
That creates a new problem. To lower the voltage safely, the charger relies on a transformer, a pair of coiled wires that pass energy from one to the other. A transformer requires a shifting magnetic field to pass energy across to the second coil, so it cannot work with steady direct current.
The solution is for the charger to switch its direct current on and off in rapid pulses. Those pulses recreate the back and forth change the transformer needs, even though the power started as direct current.
How far the voltage falls depends on two things, the number of windings on each side of the transformer and the frequency, meaning how many pulses occur per second. The pulse frequency and the coil count together set how far the voltage drops.
The result is that the charger converts the power twice before the transformer finishes the job.
Questions people ask
What is the difference between AC and DC?
Alternating current reverses direction many times a second, while direct current flows one way. Wall outlets supply AC because it travels well over long distances, and batteries supply DC because chemical cells release charge in one steady direction.
What does a transformer actually do?
A transformer is two coils of wire placed close together but not touching. Energy crosses from the first coil to the second through a shifting magnetic field, and the ratio of coils helps set whether voltage steps up or down.
Why can't a phone just use wall power directly?
No. Wall power is much higher voltage than a phone needs, and it is the wrong type of current. A phone battery needs low voltage DC, so the power must be converted first.