A switching power supply works 

 The switching power supply is the use of high-speed Road on and off through the tube circuit control switch. DC into high frequency alternating current to the transformer, transformer, resulting in one or more sets of voltage need. The reasons for the high-frequency alternating current is high frequency AC transformer transformer circuit efficiency than the 50HZ is much higher. Switching transformer can do small and not very hot work. Low cost. If you do not 50HZ become the high-frequency switching power supply does not make sense. Switching transformer is an ordinary transformer. 
 Simply put, the working principle of the switching power supply is: 
 An AC power input into DC by the rectifier filter; 
 2 high-frequency PWM (Pulse Width Modulation) signal control switch that DC added to the switching transformer primary on; 
 Switching transformer secondary inductance high-frequency voltage rectifier filter supply load; 
 Output part of the control circuit, the feedback circuit to control the PWM duty cycle in order to achieve a stable output. 
 AC power input generally have to go through Eph asthenosphere and the like, the interference of the filter power-down online, but also filter out the interference of power on the grid; the same power, the higher the switching frequency, the smaller the volume of the switching transformer. but the higher the requirements on the switch; switch the transformer secondary can have more than one winding or a winding with multiple taps to get the desired output; generally should also increase the number of protection circuits, such as no-load, short circuit protection, otherwise you may burn the switching power supply. 
 Said above is approximate switching power supply works. In fact, now have a very high integration of a dedicated chip, the external circuit is very simple, and even do free debugging. 
 Regulator (http://www.pandeng.org.cn)