Recently, various handheld devices like as smart-phone, smart-pad, and notebook computer are developed and demand for these devices is gradually increasing. In order to use electronic devices, an AC/DC adapter designed for each device is needed. Therefore, demand for AC/DC adapter is also continuously increasing as that for electronic equipment increases.
Because of global warming, temperature on Earth continues to rise. As a result, people’s interest in the environment is growing and all countries of the world are strengthening CO2 regulation. Moreover, the market for power supply demands for high efficiency and high power density. To meet this requirement, the AC/DC adapter with high efficiency and high power density is also needed and developed.
The AC/DC adapter is usually connected to the wall outlets with no regard for connection state of the load system. In other words, the AC/DC adapter is often operated without the attached load system. It is generally called no-load condition. Therefore, under no-load condition, the AC/DC adapter just wastes power without any power transfer to the load system. This power consumption is called no-load power or standby power. Standby power has been considered as a waste of electric power and it’s typically 5-10 % of residential electricity use in most developed countries. To reduce standby power, many standby power reduction techniques have been proposed and applied to recent AC/DC adapter. Although the conventional AC/DC adapter with these techniques meets the current standby requirement, some countries are gradually tightening the standby requirement and some computer manufactures are asking for more stringent standby requirement.
The AC/DC adapter can be implemented with two different methods, single-stage approach and two-stage approach. In two-stage approach, the AC/DC adapter is composed with power-factor correction (PFC) stage and DC/DC stage. The PFC stage regulates input harmonic currents for international req...