AC adapter
In order to keep the weight of portable devices such as laptops, notebooks, cell phones, etc. as low as possible, the power supply units are usually separated out as external units. The AC adapter is a complete power supply unit for 230 V/115 V mains voltage, which converts this into a low direct voltage( DC) for supplying the mobile terminals and for charging the batteries.
AC adapters, also known as power modules( PM), are small encapsulated units that are connected to the mains voltage via a power cord or the integrated power plug. They use a rectifier to convert the line voltage into a low supply voltage of a few volts. The smoothed and stabilized DC voltage is used to supply the mobile terminals and charge the rechargeable batteries. The mobile devices are connected via an appropriate supply cable.
The problem with these chargers is that there are no standard interfaces for the various mobile devices, for cell phones, digital cameras, PDAs, smartphones, tablet PCs or notebooks. Different voltages, charging currents and plugs are used, so the user needs a separate charger for each portable device and for each battery.
Standardization of chargers
This unsatisfactory state of affairs has been remedied by the activities of a wide variety of organizations and standardization bodies. For example, the USB Implementers Forum( USB-IF) has developed specifications for uniform interfaces with USB Power Delivery ( USB-PD) and USB Battery Charging( USB-BC). USB-PD recognizes different power levels for battery charging. These range from 10 W at 5 V and 2 A to 100 W, but require the use of special cables, since USB and micro USB cables cannot transmit the highest power.
In addition, the EU Commission has defined the Common External Power Supply for mobile devices, specifically for the Micro- USB connector, which is mainly used in smartphones, digital cameras and cell phones. Other organizations that have worked on the standardization of chargers and AC adapters include International Telecommunication Union( ITU) and Open Mobile Terminal Platform( OMTP).