Grades 6–8 · Machines
How does a phone charger turn wall electricity into a steady supply?
A phone needs a controlled electrical supply, but a wall outlet provides alternating voltage. The adapter between them performs several jobs. It converts the form of the supply, reduces its voltage and separates the accessible output from the mains side with an insulating barrier.
In the diagramA charger changes and regulates the supplyOne isolated switching-adapter designAC → DCrectifierRapidswitchingMagneticcouplingOutputregulationInsulating barrier12.5 Winput energy rate10 W5 V × 2 A2.5 Wheat lossOutput power + heat loss = input powerInvented efficiency: 80% • not a circuit guide
In one common switching design, a rectifier first makes a one-direction supply. An electronic switch then produces rapid pulses in a magnetic component. A changing magnetic field transfers energy to a separate winding across the insulating barrier. Output electronics rectify and smooth the result, while feedback adjusts the switching to regulate the output.
The drawing uses a 5 V output. At 2 A, output power is 5 × 2 = 10 W. If the illustrative efficiency is 80%, input power is 12.5 W and 2.5 W becomes heat. The adapter supplies the phone; charging electronics also manage energy entering the battery. Real adapters vary their supported output settings, so these figures describe only the example.
About this explanation
Starting knowledge: Recognize electric current, voltage and power as different quantities.
Sources
- Texas Instruments — USB AC/DC adapter
- Texas Instruments — TIDA-01623 isolated AC/DC adapter reference design