ATX is the working power supply of the computer, the role is to convert the AC 220V power supply for internal computer use DC 5V, 12V, 24V power supply.
ATX power supply circuit structure
Each part of the circuit not only the function of mutual cooperation, mutual penetration and the circuit parameters are very strict, slightly improper circuit can not work normally. The circuit can be divided into two parts: part from the power input to the switch transformer T1 before the circuit (including auxiliary power supply of the original circuit), directly linked to the part of the circuit and AC 220V voltage, touch will received an electric shock, known for high voltage circuit; another part of the circuit switch transformer T1, discord AC 220V directly connected, said for the low pressure side of the circuit. Two through C03, C04, C05 high voltage ceramic capacitor circuit, to eliminateelectrostatic interference.
The characteristics of ATX power supply
Compared with the AT power supply, ATX power supply increased by “+3.3V, +5VSB, PS-ON” three output. The “+3.3V” output is mainly used for CPU, and “+5VSB”, “PS-ON” output reflects the characteristics of power ATX. ATX power supply the main features is that it does not use the traditional electric switch to control the power supply is working, but the combination of “the + 5VSB, PS-on” to realize the power of opening and closing, as long as the PS-on signal level change control, can control the power of the opening and closing. “PS-ON” is less than 1V when the voltage of switch, turn off the power greater than 4.5 volts.
The core circuit of ATX power supply
ATX power conversion main circuit and at power supply, but also the “double half bridge it flyback circuit, PWM (pulse width modulation) controller also uses TL494 chip control, but canceled the electric power switch. Due to the cancellation of the electric power switch, so as long as the pick of the power line, in the transform circuit will have +300V DC voltage, and auxiliary power supply TL494 to provide working voltage, to start power ready prepared. Characteristics of ATX power supply is the use of TL494 chip pin 4 of the “death drive control function, when the pin voltage is 5V, TL494 8, 11 feet no output pulse, two switch tube deadline, the power supply is in standby state, the output voltage. When the fourth foot 0V TL494, a trigger pulse supplied to the switchtube, the power supply in normal working condition. One way of the output of the auxiliary power to send TL494, another output by the divider circuit “+ 5VSB” and “PS-on” two signal voltage, all of them is + 5V. Among them, “+ 5VSB output connected to the ATX motherboard” power monitoring unit “, as its working voltage, + 5VSB output can provide the working current of 10mA. “Power monitoring unit of output and the PS-on is connected, in the trigger button switch (non locking switch is not pressed, the PS-on is + 5V. It connects to the voltage comparator U1 the positive input end and U1 negative input voltage is about 4.5V. As the voltage comparator U1 output is + 5V, TL494 sent to the” death drive control foot “, ATX power supply in the standby state. When you press the motherboard power monitor button trigger switch (installed on the panel of the mainframe box), the PS-on variable to a low level, the output of the voltage comparator U1 to 0V, the host ATX power supply is opened. Then press the trigger button switch once on the panel, the “PS-ON” into+5V, then turn off the power. At the same time can also be used to control the program “outputpower monitoring components”, make “PS-ON” into +5V, auto power off. As in the WIN9X platform,issued a shutdown instruction, ATX power off automatically.
Fault analysis of the motherboard does not power
Due to the ATX power supply opening subject to the motherboard power monitoring unit, so when the ATX hosts appear to be not the fault, could not immediately identify fault is the power supply itself or the motherboard “power monitoring unit”, to the maintenance to bring a certain degree of difficulty. Based on the above analysis, we can between the PS-on output and then about a 100 ohm resistor and the PS-on “change to a low level, will be able to start the ATX power supply, which can distinguish the fault position. Also reminds us, if ATX motherboard power monitoring part failure, because of its maintenance is difficult, we can skip the power monitoring unit “, direct control of PS-on voltage, will be able to open or close the host. Of course, the automatic closing functionwithout the host.
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