This article will discuss about the alert function of pc power supply. The main voltage power supply, which supply the computer is +12 volts. Power supply for this circuit should provide a large output current, especially in computers with lots of drive bays. 12 V is applied also to the fans, who tend to work all the time. Usually, the fan motor consumes between 100 and 250 mA, but with newer computers, this value is less than 100 mA. In most computers, fans operate from a +12, but portable models are used for +5 V (or 3.3).
The purpose of Power Good signal is to tell the computer all is well with the power supply and that the computer can continue to operate normally. If the Power-Good signal is not present at startup, the CPU is held in reset state. If a Power-Good signal goes down during operation, the CPU will shut down. The Power-Good signal prevents the computer from attempting to operate on improper voltages and damaging itself.
Power supply not only produces the necessary sites for computer power, but suspends the operation of the system until long as the magnitude of this voltage reaches a value that is sufficient for normal operation. In other words, the power supply does not allow the computer to work with “abnormal” level of supply voltage. Each power supply before getting permission to run the system, the internal inspection and testing of the output voltage. After that, the system board sends a special signal Power_Good. If this signal is not received, the computer will not work. The mains voltage may be too high (or low) for normal operation the power supply, and it may overheat. In any case, the signal Power_Good disappear, leading to either restart or shutdown to complete the system. If your computer shows no signs of life when switched on, but fans and motors drives work, then perhaps there is no signal Power_Good .
Such a radical method of protection was provided by IBM, based on the consideration that in case of overload or overheating of the power supply output voltage to be go beyond the acceptable limits and work on that computer would be impossible.
Power_Good Sometimes signal is used to reset manually. He served on chip clock generator. This chip controls the formation of the clock signal and produces the initial restart. If the signal circuit to ground Power_Good any switch, the clock generation ceases and the processor is stopped. After opening the switch produces a momentary output of the processor and the initial installation allowed the normal signal path Power_Good, a result of running a hardware reboot the computer.
In computers the motherboard form factors (such as ATX, micro-ATX and NLX) provides another special signal. This signal, called PS_ON, the program can be used to turn off the power supply (and, thus, the entire computer). PS_ON signal used by the operating system (eg, Windows 9x), which supports Advanced Power Management (Advanced Power Management – APM). When you select the Shut Down command from the main menu, Windows automatically disables the computer’s power supply. System that does not have this feature, just displays a message stating that you can turn off the computer.