When charger is connected with the AC supply, the LED starts glowing to indicate the proper operation of the charger.
Latest mobile chargers are kind of power supply units that use the Switched Mode Power Supply (SMPS) technology. To understand the working phenomenon of a mobile charger, we need to understand the concept of Power Supply Unit (PSU). PSU is a device that transfers electrical energy from one end to another by changing its fundamental characteristics according to the requirements. Example of a PSU is an application that converts AC mains voltage to regulated DC voltage. PSUs can be of two types depending on the mode of operation – Linier and Switching.
In these switching mode chargers, energy transfer is done by continuously switching electrical components (inductor, capacitor, etc) on and off. We can control the output voltage/current by varying the duty cycle, frequency or the corresponding phase. Using the SMPS technology makes the chargers smaller and lighter by elimination of low frequency transformers. It also presents a greater efficiency than the conventional methods which uses bulky transformers.
The AC supply first enters through the line filters in the charger. Line filters are the kind of electronic filters that are placed between an electronic device and an external line to alter/attenuate the electromagnetic interference effect. Now filtered signal are made to pass through the full wave bridge rectifier circuit. Rectifier converts the AC voltage to DC.
Output DC voltage from rectifier circuit passes through the PFC (Power Factor Correction) circuit which operates power circuits at their maximum efficiency. Further the voltage signal is transferred to the pulse transformer that is a special type of transformer optimized to produce rectangular electrical pulses.
Pulse transformers are categorized into two categories – power and signal transformers. The one used here is a power transformer. It reduces the voltage level of the input power and gives a low voltage power that is exactly required to charge the battery.