Power supply 20pin ต อก บเมนบอร ด24pinได ม ย

What is the difference between 20-pins ATX power cables and 24-pins ATX power cables for motherboard? I see that Cooler Master Silent Pro PSU has an extensible plug, showing 20 pins + 4 pluggable pins.

Since I'm having troubles with my motherboard, which has 24 pins, I tried to connect only the first 20 and the system booted up fine.

I'm curious: can any ATX motherboard run with 20-pins power? Will I simply experience lower performance?

asked Sep 6, 2012 at 20:14

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You can plug a 20 pin ATX power cable into a motherboard with a 24 pin ATX connector [...] The 24 pin motherboard connector is actually just the 20 pin connector with 4 extra pins added on the end. The original 20 pins were unchanged. The extra 4 pins are not separate rails. They're just extra lines to provide more current to the same rails. [...] I've never heard of exceptions and it doesn't make sense for motherboard makers to create any.

and...

A 20 pin power cable only fits into one end of a 24 pin motherboard connector so you can't insert it incorrectly.

however, it appears that there is no current limiting on a 20 pin ATX PSU, as I assumed there would be...

They added those extra 4 pins for a reason. When you plug a 20 pin cable into a 24 pin connector you're not providing the extra current carrying capacity which may be needed by the motherboard. If your motherboard's current requirements are low enough then it will work properly with only a 20 pin power cabled plugged in. But if the motherboard draws enough current, then you can overheat the 20 pins you're using on the 24 pin connector. I've seen enough pictures of burned ATX main connectors to assure you that this happens. [...] Connectors really do get hot if you overload them so the safest thing to do is use a real 24 pin power supply on a motherboard with a 24 pin connector. Note that your 24 pin machine may work fine with a 20 pin power supply until you add a PCI Express card later on down the road. PCI Express cards can draw up to 75 watts through the motherboard connector so adding an expansion card can substantially increase power draw through the main power cable.

Lastly, as an aside:

If you have an ATX power supply with a 24 pin main cable, it's okay to plug it into a motherboard with a 20 pin connector.

If you use high-end graphics card with an additional 6-pin or 8-pin power header, you may try to use an adapter that converts two 4-pin peripheral cables into a 6-pin PCI Express cable. For such an application, the PSU typically has to be >400W, or otherwise you may not have enough current rating on 12 volt output. Finally, an old PSU may cause a start up problem. Today's motherboards are using PWR_OK signal for proper timing. Upon initial power up it is first kept low. Then it should be asserted TTL logic high by the power supply within 100 to 500 ms after +12 VDC, +5 VDC, and +3.3 VDC outputs reach their regulation bands. Conversely, it has to switch to TTL low state when any of positive DC voltages falls below its under voltage threshold, or at least 16 ms after input power has been removed. An old cheap PSU may not have "Power OK" circuitry and might just connect pin 8 to +5V. Modern systems may have booting problems and may not work without properly functioning PWR_OK signal.

USING a 24 PIN PSU with 20 PIN BOARD.

Many new ATX12V v2 compliant PC power supplies come with a dual 24/20 (sometimes called 20+4) connector for backward compatibility. It has the last four pins on a detachable section that slips out, so you can plug it into an older motherboard (see the diagram above). Just don't plug the remaining 4-pin piece anywhere- it is not compatible with any other circuits! If your PSU happens to have a solid 24-pin connector, you can still try to insert it into 20-pin slot with the last four pins hanging over the edge of the board's connector. Alternatively, you can buy a 24 to 20 pin adapter. To check compatibility of a specific model see Intel's database and selector of tested PSU. Another potential problem with using a new PSU with a very old computer is today's PSUs usually do not provide minus 5V output (they either don't have the white wire going to pin 20 at all, or they leave it not connected inside). Even some of ATX-I PSUs may not have "-5V", which was made optional in ATX12V spec version 1.2 as of 2002. The minus 5V rail was used by ISA cards. It was phased out when ISA were replaced by PCI. If you have an old computer with ISA slots, it will still need this bus. In this case, if you can't find a power supply with such a rail, you can derive it from -12V by adding a negative linear regulator, such as MC79M05. Since minus 5V bus can draw up to 0.3A current according to ATX spec v.1, this regulator will dissipate up to (12-5)×0.3=2.1W. This may be too much for a stand alone device, so may you need to attach it to a little heatsink. Also see our tutorial on laptop batteries.

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