Figure 1: 2 pin, 3 pin, and 4 pin connectors.
If a computer does not have a radiator, its internal temperature will be infinitely high, and eventually the
hardware will be burned directly. Whether it is for the CPU, graphics card, chassis, or power supply, heat
dissipation is required. As the most mainstream heat dissipation method, air cooling is to use cooling fans to assist the radiator or other electronic components
to dissipate heat.
There are many classification methods for cooling fans, including DC and AC, brushed and brushless, ball bearing and
oil bearing fans. We mainly talk about the connectors of cooling fans here. In cooling fans, the connector types can
be divided into 2-pin, 3-pin, and 4-pin. According to the design of the hardware, cooling fans of different hardware
such as CPU and graphics card will use cooling fans with different numbers of pins.
Then what is the difference between the 2-pin, 3-pin, and 4-pin fans? Continue to read down and we will explain them
to you one by one.
1. 2 Pin Fan
Figure 2: 2 pin fan.
The 2-pin fan has two connecting wires, which are red and black. The structure is very simple. One wire is used for
power supply, and the other is used for grounding.
As long as this kind of fan is connected to electricity, the fan can turn, but at a fixed and full speed. Besides,
the computer cannot measure and adjust the speed of the fan.
2. 3 Pin Fan
Figure 3: 3 pin fan.
The 3-pin fan has 3 connecting wires, which have one more wire compared to the 2-pin. The extra yellow wire (or the
color of the three wires is black, yellow and green) is used for speed measurement. Thanks to this cable, we can see
the real-time speed of the fan with some software.
And the speed of this kind of fan can also be adjusted, that is, to make it turn fast or slow, but there is a
disadvantage that the speed can only be adjusted through the input voltage. The higher the voltage, the higher the
current, the faster the fan will turn, and vice versa.
This speed adjustment method is more troublesome. It depends on whether the motherboard can support it, and also
needs to enter the BIOS to set. The 3-pin fan can also be connected to an external speed controller to realize the
fan speed regulation function.
3. 4 Pin Fan
Figure 4: 4 pin fan connector vs 3 pin fan connector diagram.
The 4-pin fan has an extra wire on the base of the 3-pin. This wire does a lot, and is called the PWM line. What is
PWM? The technical name is Pulse Width Modulation. Is it very professional? Give you an example and you will
understand.
If you want to adjust the brightness of a small lamp, you can use a sliding rheostat to change the resistance value
of the circuit, and then you can adjust the brightness of the lamp. Now there is a more advanced technology to
adjust the brightness of this lamp, and that is PWM. How to adjust?
First of all, a switch must be connected, and this is not an ordinary switch. The professional name is a transistor,
and its function is that it can be used as a switch. Then if the switch is on for 5 seconds, the lamp will light on
for 5 seconds, and if the switch is off for 5 seconds, the lamp will stop lighting on for 5 seconds. The transistor
switch will not give the lamp such a long time to be on and off, and the on-time and off-time are calculated in
microseconds and other small units.
For example, a 0.1 millisecond cycle of on and off can not be seen by us, because our human eyes cannot see the
flicker of such a short time, what you see is that the brightness of the light is reduced. If the lamp is replaced
by a fan, what is displayed is the change of the fan speed. This is PWM regulation, which is used to control the
speed of the fan, and does not need to rely on the BIOS of the motherboard.
Figure 5: 4 pin PWM fan duty cycle under different workloads.
4. Interconnection of 3-Pin and 4-Pin Fan Connectors, and Precautions
Sometimes even if the fan is controlled by 4-pin PWM, it still cannot intelligently control the speed when it is connected to the motherboard. This problem may be related to the motherboard, because the 4-pin headers on the motherboard are not necessarily PWM-controlled or maybe it is voltage-controlled.
Figure 6: The 4 pin fan header of PWM based speed control vs that of voltage based speed control from, NOCTUA website.
NOCTUA mentioned this problem in the official FAQ. When you meet this problem, you need to check the description of
the motherboard manufacturer's manual. If words such as NC and VCC are mentioned, it means that it does not support
PWM speed regulation, but by adjusting the voltage.
Another problem is the mixed insertion of 3-pin and 4-pin fans. Since they have the same two pins, they can be
mixed-inserted. Of course, the 4-pin fan will lose the PWM speed control function when inserted into the 3-pin
header. The 3-pin fan will not automatically get the PWM speed control function even if it is inserted into the
4-pin header.
Figure 7: Radiator cooling fan.
5. Conclusion
At present, 2-pin fans are rare in daily use, and 3-pin and 4-pin are more common. From the perspective of user experience, choosing a 4-pin fan and motherboard with PWM function is the first choice. Fortunately, this matter is not a problem now. The fans on most motherboards and CPU coolers are 4-pin PWM. 4-pin PWM fan is relatively better, and can automatically adjust the speed of the fan according to the temperature of hardware such as the CPU.
