How phone chargers are made
About 30 workers can build 8,000 phone chargers in an eight-hour day, and each one takes more than 20 steps.
- stations
- 8
- things upstream
- 89
- raw sources
- 26
- steps from the ground
- 9
The short version
A phone charger contains a small circuit board that turns mains alternating current into low-voltage direct current. Parts are plugged into the board and soldered, and the flux is brushed off. The board is tested, fitted into a plastic case, run under load in an aging test, then sealed by ultrasonic welding and tested again before packing.
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Wind the transformer
Fine copper wire is wound around a small core in two separate coils. The transformer steps the wall voltage down and keeps the high-voltage side electrically separate from the phone cable.
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Place the components
Capacitors, resistors, diodes, the transformer and a controller chip are placed on the printed board, some by machine and some plugged in by hand.
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Solder and brush the board
Solder joins every part to the board. Workers then brush away the flux residue and check the joints.
Goes in -
Test the bare board
The assembled board is powered on and checked for output and load, so bad units are caught before they go into a case.
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Mold the case
Flame-retardant polycarbonate or ABS plastic is injected into steel molds to make the two halves of the casing. Flame resistance is a safety requirement for anything plugged into the wall.
Goes in -
Fit the prongs and port
Brass prongs are pressed into the back half and a USB port is mounted on the front. The board is soldered to them and set into the case.
Goes in -
Run the aging test
Assembled chargers run under load for a period on an aging rack. Weak parts tend to fail here, before the case is sealed.
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Weld the case shut
An ultrasonic welder melts the plastic where the two halves meet, with no glue or screws. Each unit gets a last check before packing.
Worth repeating
- A charger's transformer can be tiny because it switches at several hundred kilohertz or more, where a linear supply's transformer works at 50 or 60 Hz.
- Lithium-ion batteries cannot handle indefinite trickle charging, so the charging has to stop on its own.
Back to the ground
Follow every input upstream and phone charger starts as these 26 raw sources.
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Sources
Cite this page: "How phone chargers are made." Assembly Line, 2026-11-03. https://assemblyline.org/make/phone-charger