ADD：
Switching power supply include input power filter, input rectifier filter, converter and output rectification filter, control circuit, protection circuit.
Their functions are:
1. Input power filter: remove from the network, such as motor start-up, electrical switches, such as interference from lightning, but also to prevent high frequency switching power supply noise generated by diffusion to the grid.
2. Input rectifier filter: the power input voltage rectifier for providing DC voltage converter.
3. Converter: is a key part of the switching power supply. It transforms the DC voltage into high frequency AC voltage, and play the output part of the role of the input power isolation.
4. Output rectification filter: The output converter high frequency AC voltage rectifier to obtain the required DC voltage, and also to prevent the interference of high frequency noise to the load.
5. Control circuit: detecting the output DC voltage, and compared with the reference voltage, to enlarge. Pulse width modulation oscillator to control the converter to maintain output voltage stability.
6. Protection Circuit: When switching power supply occurred over voltage, over current short circuit protection circuit to switch power to stop working to protect the load and power supply itself.
Some readers will have this question, first 220V AC into DC, then the DC into AC by converter, and finally into a DC output AC again, soliciting a such a large circle, why not to 220V AC DC directly into the required it? In fact, the AC power transformer power transformer initially, be rectified filtered DC voltage is not stable, then adjusted by the required DC voltage, this power supply technology is mature and can reach very high stability, ripple is also small, and there is no interference and switching power supply with noise. But its weakness is the need for large, bulky power frequency converter, the required filter capacitor size and weight is quite large, and the tube is operating in the linear adjustment of status, adjustment of tube voltage drop to a certain extent, the larger the output operating current, the resulting adjustment of tube power too low conversion efficiency, but also a great heatsink installation. In short this power is not suitable for computer use.
Switching power supply has the following characteristics:
1. Small size, light weight: the absence of frequency transformer, so only a linear power supply size and weight of 20 to 30%.
2. Power, high efficiency: power transistors work in the off state, so the power consumption of transistors on a small, high efficiency, typically 60 to 70% and the linear power supply only 30 to 40%.
