- 1 Power for Internal Peripheral Devices
- 1.1 Four Pin Molex Power Connector
- 1.2 Serial ATA Power Connector
- 1.3 Berg Floppy Power Connector
- 1.4 Six Pin PCI Express Power Connector
- 1.5 Three Pin Molex KK Type Connector
- 2 Motherboard Power Connector Types
- 2.1 Standard ATX Connectors
- 2.1.1 20 Pin ATX Power
- 2.1.2 20+4 Pin ATX Power
- 2.1.3 24 Pin ATX Power
- 2.1.4 Technical Notes
- 2.2 Legacy AT Motherboard Power Connector
- 2.1 Standard ATX Connectors
- 3 Additional Motherboard Power and CPU Power
- 3.1 Six Pin Inline Auxiliary Power Connector
- 3.2 Eight Pin CPU Power Connector
- 3.3 AMP ATX 12v Power Connector
- 4 Additional Charts and Data
- 4.1 Power Connector List With Introduction Chronology
- 4.2 Connector Picture Chart
- 4.3 Inside the ATX Power Supply
- 5 Front Panel Header Connectors
Power for Internal Peripheral Devices
Four Pin Molex Power Connector
Molex Drive Connector
Typically used for 5¼ drives such as CD Rom and DVD Drives. Used for legacy IDE, EIDE, and ATA Hard Drives.
Serial ATA Power Connector
Berg Floppy Power Connector
Typically used for 3½ floppy disk drives.
Six Pin PCI Express Power Connector
PCI Express GFX Connector
Three Pin Molex KK Type Connector
Typically used for internal cooling fans.
Motherboard Power Connector Types
The eight power supply form factors are:
- PC / XT
- Baby AT
Standard ATX Connectors
Three common ATX power to motherboard connector configurations, a 20 pin connector, a 20 +4 pin connector, and a 24 pin connector. The 20 +4 may be used for either 20 pin connector motherboards or 24 pin connector motherboards. The first 20 pins are a consistent standard on all three configurations.
20 Pin ATX Power
The 20-pin Main power connector is standard for all power supplies conforming to the ATX and ATX12V 1.x form factors, and consists of a Molex Mini-Fit, Jr. connector housing with female terminals. For reference, the connector is Molex part number 39-01-2200 and the terminals are part number 5556.
The total power handling capacity of this connector is only 251 watts, which is lower than many systems need today.
20+4 Pin ATX Power
24 Pin ATX Power
As a general rule of thumb +/-5% is considered OK for voltage variation.
- Using a 24 pin power connector on a 20 pin motherboard
The 24 pin male power connector can also be used on a 20 pin motherboard by allowing the four extra to hang off the side, given there is room (one one motherboard example a capacitor is in the way.)
- Using a 20 pin power connector on a 24 pin motherboard
Technically this is also possible to do, however, you risk overloading the 20 pin connector. It is possible to do this because the additional 4 connectors on a 24 pin power connector supply additional voltage to the motherboard into common circuits. Without the additional 4 connectors, you will be drawing more power than the maximum rating through the 20 pin connector which will cause it to overheat.
- A Closer Look at the Extra 4 Power Supply Pins
The 4-pin +12V power connector is specified for all power supplies conforming to the ATX12V form factor, and consists of a Molex Mini-Fit, Jr. connector housing with female terminals. For reference, the connector is Molex part number 39-01-2040 and the terminals are part number 5556. This is the same style of connector as the ATX Main power connector, except with fewer pins.
- Hot-Starting and ATX Power Supply Not Connected to a Motherboard
The old AT style power supplies could easily be turned on when not connected to a motherboard because the switch was mechanical. ATX power supplies are electronically switched via the motherboard. It is possible to turn on an ATX power supply when not connected to a motherboard.
To turn on an ATX power supply not connected to a motherboard short between the green and black wires on the 20 or 24-pin connector, with a paper clip or piece of wire.
You can use any of the black "ground" wires. There is a single green wire you must use for the jumper. While the jumper is connected the power supply should turn on and it will remain on as long as the jumper is connected. Once the jumper is removed then the power supply will turn off.
Legacy AT Motherboard Power Connector
The original PC starting in 1981 used two cables (Molex 90331) to connect the power supply to the motherboard. They connected side by side into the motherboard, and they could easily be reversed accidentally, or inverted which will result in damage to the motherboard. When connecting them to the motherboard it was important to observe the "black to black" rule.
|Pin number||Wire color||Description|
|2||red||+5 volts or connector key|
On an AT system the power supply delivered a majority of power at 5 volts since most of the motherboard ran at that voltage. One rail was 5v and the other 12v.
Additional Motherboard Power and CPU Power
Six Pin Inline Auxiliary Power Connector
ATX 2.02/2.03 and ATX12V 1.x Auxiliary Power Connector
When more amperage is required by the motherboard before the 24 pin connector was devised, this six pin inline connector was equipped with power supplies to provide supplemental power to the motherboard.
The total power handling capacity of this connector is 58 watts. When combined with the 20 Pin ATX motherboard power connector the total power delivery capability to the motherboard is 309 watts maximum.
Eight Pin CPU Power Connector
Required connector for modern dual CPU motherboards
AMP ATX 12v Power Connector
4 pin connector for the Intel Pentium 4 CPU
Additional Charts and Data
Power Connector List With Introduction Chronology
|Version||Introduction date||Included connectors|
|PCI Express 2.0||2007|
Connector Picture Chart
Inside the ATX Power Supply
The power supply can be fully discharged by connecting the black and red wires together.
Front Panel Header Connectors
The most common question might be, which is positive, the white or the colored wire? For the LED connectors, the colored wire is usually indicative of a positive polarity.
+ colored wire- white
For the power LED indicator, insert the connector with the colored wire into the header with the '+' mark. If you've connected it the other way around, you won't see the LED light up when the system is powered. Also observe the proper polarity when connecting the hard drive LED connector.
For the power switch connector, polarity isn't really important. The same holds true for the reset connector.
When you connect the speaker, you should observe proper polarity. Some motherboards have built-in buzzers and as such, the speaker connection is not needed.
+ red- black