1、 Definition of power supply
A converter that converts alternating current into direct current needed by a PC (personal computer) computer to work.
2、 The importance of power supply
For computers, the two most important hardware are CPU and power supply. CPU is equivalent to human brain and power supply is equivalent to human heart. According to statistics, 40% - 60% of computer failures are caused by power supply, while a power supply only accounts for 2% - 3% of the whole machine. Improper selection of power supply may not only burn CPU, motherboard and hard disk, but also cause other losses.
3、 Working principle and flow of switching power supply
The working principle of switching power supply is to convert the high input AC voltage into the low DC voltage needed by PC by using high frequency switching technology
Work flow: when the power supply enters the power supply, the high-frequency clutter and interference signals are removed through the yoke coil and capacitor filter, and then the high-voltage DC power is obtained through rectification and filtering, and then it enters the core part of the power supply switch circuit. The switching circuit converts DC into high-frequency pulsating DC, and then sends high-frequency switching transformer to step down, and then filters out the high-frequency AC part, so as to finally output relatively pure low-voltage DC for computer use.
The commercial power filters the clutter and interference signal through choke coil and capacitor. After inductor coil and capacitor, full bridge circuit rectification and large capacity filter capacitor filtering, the current changes from high-voltage AC to high-voltage DC, and then through the turn-on cut-off of two switch tubes, the DC is converted to high-frequency pulsating DC, and then sent to high-frequency switch transformer for step-down. The pulse voltage after step-down also needs to be rectified and filtered by diode and filter capacitor. In addition, it will hinder the filter capacitor of 1-2 inductance coils from filtering high frequency AC components together.
4、 Interface of power supply
There are many groups of interfaces in the power supply, including 20 core motherboard plug, 4-core driver plug and 4-core small floppy drive plug. There is only one 20 core motherboard plug with directionality, which can effectively prevent misinsertion. There is also a fixed device on the plug, which can hook the socket on the motherboard to avoid reverse connection. ATX power interface can be divided into + 5V, + 12V, + 3.3V, - 5V, - 12V and + 5V sb according to the different output voltage, and these wiring colors are also different.
① + 5V (red line). It is mainly used for power supply of the main board, including the main board, memory, CPU and some other devices on the main board. The signal appliances of optical drive and hard disk are also powered by + 5V power supply.
② + 12V (yellow line). It mainly supplies power for the drive circuit of standard equipment, such as cooling system such as fan, and is generally connected to adapter card.
③ + 3.3V (Orange Line). At present, the voltage of CPU and AGP is getting lower and lower, so the new ATX specification adds 3.3V voltage, so it doesn't need to change from + 5V to + 3.3V
④ - 5V (white line), - 12V (blue line). These two voltages separately support ISA bus, channeling port and other old equipment, which are rarely used now.
⑤ + 5V sb (purple line). It is exactly the same as + 5V voltage, but it has its own circuit, which has nothing to do with other power supply circuits. Moreover, whether the computer is turned on or not, as long as the power supply is powered on, it can always remain on. This power supply supports some devices that activate the system, such as network cards that support network wake-up.
⑥ PS-on line (green line). The switch of complex operating system management power supply is a kind of motherboard signal, which becomes soft power supply together with + 5V sb to realize software, network wake-up and other functions.
⑦ PG (power good) signal (gray line). The PG signal cable is connected to the main board and is controlled by the monitoring software of the main board. Before the system starts, the internal voltage check and test is completed through this line. If there is no PG signal, the system cannot be started.
5、 Filter circuit
EMI filter circuit
The main function of EMI filter circuit is to filter out the interference of high-frequency pulse of external power grid to the power supply, and also to reduce the electromagnetic interference of switching power supply itself to the outside world. In the high quality power supply, there are two EMI filter circuits: one is in the power socket, the other is on the PCB board of the power supply. These two EMI circuits can well filter out the high frequency clutter and in-phase interference current in the power grid, at the same time, reduce the electromagnetic radiation generated in the power supply to the minimum, so that the electromagnetic radiation discharged to the power supply will not cause adverse effects on the human body or other equipment.
