ATX Power Supply Detailed Explanation

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ATX Power Supply Detailed Explanation [Copy link]

 

1. ATX power supplies have 20-pin and 24-pin types, black ground wire, orange 3.3V, red 5V, and yellow 12V.

2. The traditional power switch determines the working state of the machine, but the ATX power supply is not like this. It mainly relies on the +5VSB output and PS-ON output to determine the power switch. Through the control of the PS-ON signal, the power supply can be controlled by the voltage. After the ATX power supply is turned off, the weak current retained promotes the Stand-B* function, so that the ATX power supply can be directly controlled by the operating system to achieve remote startup.

3. ATX power supplies are all potential-controlled switches rather than mechanical switches, so you need to find the pin that can activate the power supply from the row of wire holes on the power supply.

4.20 pins

The standard definition of ATX power pins is:

Pin 14 PS-ON is used to control the power on and off. How can a single pin control the switch without a loop? In fact, all ground wires (GND) can form a loop with any other pin. The so-called "low potential" turns on and "high potential" turns off means that when Pin 14 is short-circuited with the GND pin, the potential of Pin 14 itself is low, and the power is turned on, and vice versa. Now it is very clear - if you want to turn on the ATX power supply without a motherboard, you only need to short-circuit Pin 14 (green wire, also marked green in the picture) with any GND pin (black wire, marked gray in the picture).

5.24 pin

Power pin definition:

1. +3.3V; 2. +3.3V; 3. Ground; 4. +5V; 5. Ground; 6. +5V; 7. Ground; 8. PWRGD (good power supply); 9. +5V (standby); 10. +12V; 11. +12V; 12. 2*12 connector reconnaissance; 13. +3.3V; 14. -12V; 15. Ground; 16. PS-ON# (power supply remote switch); 17. Ground; 18. Ground; 19. Ground; 20. No connection; 21. +5V; 22. +5V; 23. +5V; 24. Ground

6.What do the various voltages power?

　　6.1＋12V

　　+12V generally provides power for the spindle motor and seek motor of the hard disk, optical drive, and floppy drive, as well as the operating voltage for the ISA slot and the logic signal level of the serial port and other circuits. If the +12V voltage output is abnormal, it often causes unstable disk reading performance of the hard disk, optical drive, and floppy drive. When the voltage is low, the optical drive will have serious disk picking, the hard disk will have more logical bad sectors, bad sectors will often appear, the system will easily freeze, and it will not be able to be used normally. When it is high, the speed of the optical drive is too high, it is easy to lose control, and it is more likely to explode the disk. The hard disk will show stalling and flying.

　　6.2-12V

　　The -12V voltage provides the logic judgment level for the serial port, which requires a small current, generally less than 1 ampere. Even if the voltage deviation is large, it will not cause failure, because the 0 level of the logic level is -3 to -15V, which has a wide range.

　　6.3＋5V

　　+5V power is the working voltage provided to CPU and integrated circuits such as PCI, AGP, ISA, etc. It is the main working power supply of the computer. The quality of its power supply is directly related to the system stability of the computer. The +5V output current of most AMD CPUs is greater than 18A, and the current provided by the latest P4CPU is at least 20A. In addition, the +5VSB power supply current required by AMD and P4 machines is at least 720MA or more, and the power supply power required by P4 system computers is at least 230W.

　　If there is not a large enough +5V voltage provided, the CPU will slow down, blue screens will appear frequently, the screen image will freeze, etc., and the computer's operation will become very unstable or unreliable.

　　6.4-5V

　　-5V also provides judgment level for logic circuits. The current required is very small, which generally does not affect the normal operation of the system and the probability of failure is very small.

　　6.5+3.3V

　　This is a special setting for the ATX power supply to provide power for the memory. The voltage requirements are strict, the output is stable, the ripple factor must be small, and the output current must be large, which must be more than 20 amps. When using SDRAM memory, most motherboards directly output this power to the memory slot in order to reduce costs. Some mid-to-high-end motherboards use high-power field tubes to control the power supply of the memory for safety, but this tube may be burned out if the memory is inserted incorrectly. If the motherboard uses +2.5V DDR memory, a voltage conversion circuit is installed on the motherboard. If the voltage of this line is too low, it will be easy to freeze or often report memory errors, or the WIN98 system will prompt a registry error, or the operating system cannot be installed normally.

　　6.6＋5VSB (+5V standby power supply)

　　The ATX power supply provides +5V 720MA power to the motherboard through PIN9, which provides power for WOL (Wake-up On Lan), boot circuit, USB interface and other circuits. If you do not use network wake-up and other functions, please turn off such functions and remove the jumper to prevent these devices from drawing current from the +5VSB power supply terminal.

　　6.7P-ON (power switch terminal)

　　The P-ON terminal (PIN14) is the power switch control terminal. This port controls the working state of the main power supply of the switching power supply by judging the level signal of this port. When the signal level of this port is greater than 1.8V, the main power supply is off; if the signal level is lower than 1.8V, the main power supply is on. Therefore, when the switching power supply is powered on separately, a multimeter can be used to test the output signal level of this pin, which is generally around 4V. Because the voltage output by this pin is a signal level, the switching power supply has a current limiting resistor inside, and the output current is also within a few milliamperes, so we can directly use a short wire or an open paper clip to directly short-circuit PIN14 and PIN15 (that is, ground, and pins 3, 5, 7, 13, 15, 16, and 17) to start the switching power supply. At this time, we can use a multimeter to test whether the output voltage of the switching power supply is normal when it is offline.

　　Remember: Sometimes, even though the output voltage of the power supply we tested with a multimeter is correct, it still does not work when connected to the system. This is mainly because the power supply cannot provide enough current. The typical manifestation is that the system restarts or shuts down irregularly. So in this case, we have to replace the power supply with a higher power.

　　6.8P－OK (power good signal)

　　Generally speaking, if the output of the gray line P-OK is above 2V, then the power supply can be used normally; if the output of P-OK is below 1V, the power supply will not guarantee the normal operation of the system and must be replaced.

　　6.9220VAC (mains input)

　　Generally, we don't care about the mains power supply used by computers, but it is necessary for computers to work and is often overlooked. When installing a computer, we must use a 220V mains power socket with a good grounding device, and the variation range should be within 10%. If the mains power variation range is too large, we'd better use a wide range switching power supply between 100-260V, or use an online UPS power supply.

　　- Reserve power supply

　　4-pin (1*4) interface, providing power for PCI Express x16 graphics card, 1, +12V; 2, ground; 3, ground; 4, +5V

　　8-pin (2*4) interface. Not all 915/925 motherboards have this reserve power interface. It can only be seen on some high-end motherboards.

　　For i915/925 motherboards, there are two common power supply combinations: one is 24-pin main power supply + ATX 12V, which can provide 144W of power for the motherboard. The other is 20-pin main power supply + ATX 12V + standby power supply, the main power supply and standby power supply each provide 72W, a total of 144W.

　　According to Intel's specifications, it provides 2A of +5V current for each card. If using 6 expansion slots + PCI Express x16 full load form, they cannot exceed 14A, otherwise even the strongest power supply will not be able to provide enough power, and excessive current may cause the motherboard to burn out.

sizhaoyang

What you are talking about is a bit complicated. I am a novice. I thought it was simple before, but it seems not so simple.

azcazc

Yes, for a novice like me, it has been explained in detail.

okhxyyo

sizhaoyang posted on 2022-11-18 11:04 What you are talking about is a bit deep. I am a novice. I thought it was simple before, but it seems not so simple

It is difficult when you don't understand it, but it is easy after you understand it. If you encounter a problem, you can understand it by breaking it down bit by bit. If you have any questions, you are welcome to ask questions in the forum at any time, and the experts in the forum will help you answer your questions.

yinlijun2017

I have understood almost all the things I don't understand. I can solve the problems slowly when I encounter them. Thank you for sharing.

yinlijun2017

I have almost understood the parts I didn't understand. When I encounter problems, I can slowly figure them out. Thank you for sharing. Thank you.