The reason is this. Today, a little companion asked me, "I connected a fan to the disposer on my board. I bought a 2-wire fan. I was worried that it would burn out. I wanted to connect it with a resistor current limit. Like LED, I added a pull-up 1K, but the fan did not turn after connecting the resistor". Er ~ ~ ~, this problem, I think it is still due to insufficient understanding of fans. Cooling fans are commonly used in normal work, but it seems that many people do not have a clear understanding of it. What are 2-wire fans, 3-wire fans, 4-wire fans and 6-wire fans?? How can there be so many varieties. It's not clear what you're talking about. Today we will learn the simple knowledge of fans together.
Many people's first contact with the fan is the electric fan at home. This uses 220V AC, so it is called AC fan, which is not within the scope of today's discussion.
Hardware engineers often come into contact with the cooling fans of computers and the cooling fans of various circuit boards. Today we will mainly discuss these fans.
First of all, we need to know whether we can demand fans. At present, we are in a period where the foundation is still electrification transformation. Even if electricity is used as power, electricity is indispensable in the usual living consumption. We encountered a problem in the process of using electric energy. People who have studied physics all know that current has a thermal effect, that is, electric energy will be converted into heat energy in a part of the transmission process. When boiling water, we may not care. When playing mobile phones and computers, we are more disgusted. When running slightly compared with large-scale applications and games, the equipment starts to heat up, so there is a radiator. The radiator is actually a metal block, because the shape of metal is also very stable at high temperature, and the heat conduction is fast, it can quickly take away the heat, so many devices will bring a metal radiator, which will take away the heat of the device and dissipate it in the air. You can understand that the migration of heat can be stopped without additional energy, which is called passive heat dissipation.
However, different devices generate different amounts of heat. The usual CPU computing performance is getting stronger and stronger, consuming more and more electricity, generating more and more heat, and passive heat dissipation is not enough. Therefore, a fan is added to the radiator to increase the activity of the air and take away the heat more quickly. This is called active heat dissipation.
The commonly used cooling fan is a 2-wire DC fan. This is a good understanding. An electrical appliance can start to work when one end is connected to the positive pole of the power supply and one end is connected to the negative pole of the power supply. The essence of the fan is theoretically a motor with fan blades. Everyone has learned the principle of electric motor, let's simply recall it.
The motor explained in Baidu Encyclopedia: A motor is a device that converts electrical energy into mechanical energy. It is the application of energized coils to generate a rotating magnetic field and act on the rotor to form a magneto-electric power rotating torque.
It may sound a bit difficult to understand. Everyone knows that magnets are polar, same-sex repel each other, and opposite-sex attract each other. Put the conductor in a magnetic field and energize it. Because the current has a magnetic effect, the direction of the magnetic field generated by the current and the fixed magnetic field are not different, and the force will be generated by each other. One of the magnetic fields or coils is fixed, and the other will stop moving due to the force, forming rotation.
In order to enhance the heat dissipation performance, the fan with as much power as possible will be selected, but the power of the equipment is not very large at all times, and we will also feel that the fan is too noisy. Therefore, it is necessary to stop the rotation speed control of the fan. The simplest control method is to string a resistor. Let's take this small fan as an example, with a rated power of 5V0.2A, then the equivalent resistance is 5/0.2=25 ohms. When you connect an external resistor, you need to simply calculate the voltage left for the fan according to the partial pressure of the resistor. Assuming that a 1K resistor is connected in series, the voltage of the fan is only 0.12V. In this way, the fan will definitely not work. When the fan does not rotate, it is equivalent to a section of wire, which will only consume electric energy. Assuming that the electric energy is consumed too much, the motor may be burned. In addition, this method is not convenient to change the resistance in real time, so it is only suitable for fixed conditions. It is not good to change the speed after reducing the fan speed.
In order to change the speed of the fan in real time, PWM control method is introduced. Generally, GND or VCC is controlled. The control circuit looks like this:
Of course, the VCC terminal can also be controlled, and the selected device requirement is PMOS.
One problem with this approach is that there is no way to detect whether the fan is really running. Assuming that the fan is broken, it is unknown. It can be used in some ordinary places, but the internal equipment such as computer chassis cannot be seen outside. Continuing to use the fan after being damaged will cause CPU overheating damage.
Therefore, there is a 3-wire fan. The fan has its own FG response inside. The third leg is an FG signal, that is, the speed response. Through it, it can sense whether the fan is really running. Many motherboard system fans are used in this connection.
This three-wire fan connection, the function of controlling the speed depends on the motherboard, the motherboard interface assumes that with speed regulation, the fan can stop speed regulation, assuming that the motherboard does not have this function, then the fan can only run at full speed. The advantage is the ability to identify whether the fan is functioning properly.
Later, the fan was promoted. The fan was equipped with FG response and PWM speed regulation function, and the external control circuit became more simplified, so the speed control function was placed on the fourth foot.
A typical application is the fan of the CPU. The usual CPU fan is 4-pin, and the order is as follows:
There are also some special hosts such as servers that have 6-wire or other line-sequence fans on them. These are special fans. Please refer to the corresponding devices for clarification when using them.
The above is the introduction of several commonly used cooling fan interface, the design of the time demand according to the system demand to suspend the corresponding fan interface selection.