Electronic – How does a cell phone charger work?

power supply

I have studied that there is a transformer which steps down the ac voltage after then bridge rectifier to convert into ac to dc and then given to filter, this is what I have learnt in books, but when I open a mobile charger I couldn't figure it out how it actually works?

Best Answer

Phone chargers are incorrectly named. Most are 5 V power supplies. The charge control is done inside the phone. The power supply will continue to give out 5 V when the phone is completely charged.

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Figure 1. Switched-mode power-supply block diagram.

How it works:

  • The mains voltage is rectified to provide a high voltage DC supply.
  • A transistor "chopper" switches this on and off at high frequency.
  • A small transformer steps this down to a low-voltage high-frequency AC.
  • A rectifier converts this to low-voltage DC.
  • The chopper controller feeds back to the chopper and adjusts the chopping cycle to maintain the required voltage on the output - usually 5 V.

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Figure 2. Anatomy of an SMPS 'charger'. Image source: Analogic Tips.

  1. Plug pins.
  2. Four diodes for the bridge rectifier.
  3. Smoothing capacitor for high-voltage DC.
  4. Switching transistor.
  5. Switching transformer.
  6. 5 V supply indication LED.
  7. Output rectifier and filter.
  8. Opto-isolator for feedback from the output to the chopper controller.