Do you want to reduce noise?

Back in the 90’s fan controllers used a very basic voltage control by choosing VDC input that varies within the voltage range of the fan(6-13.8V) from standard voltage on the PCBA. Then came the use of ordinary resistors to slow the fans down, fans equipped with thermal resistors, and various potentiometers for a manual speed control option by the user.

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Now in the digital age, if you want to control the speed of your fans and motors, PWM control is the preferred means. In the PC world, all motherboards today are outfitted with at least one 4-pin PWM header. High-end boards have several inputs that support a PWM system that is a very effective and smart way to control the fans. However, since the introduction of PWM in 2003, there are many companies that are still not familiar with its advantages. And to complicate things, there are many applications that will use the low-end method of PWM that can add complications to the design efforts based on the circuit design of the fan brand you are working with.

Therefore, we will explain what PWM is, how it works, how you should design for it in the beginning and use in your systems.  The number one issue is that there are IC manufacturers out there that make fan controllers that PWM the voltage instead of having a direct PWM input, I like to call the throttle wire😊 With that said you have to watch how you are being directed to set up your speed control system.

Fans normally come with bare lead wires approximately 300mm long, please note that it is NOT industry standard to sell fans with a “standard” connector on it. That might be applicable to a certain industry, but not across the board. When you see that a fan has more than 2 wires you know you have added features for the model. A base model fan will come with 2 wire, positive (red) and negative (black). Next step up is a three-wire model; positive and negative to power up plus a tachometer(yellow). The tach is just like what you have in your car, it tells you how fast your motor is spinning, the RPMS.  This is done via a square wave output that produces 2 pulses per revolution (in a 4-pole motor). The signal is open collector so that you can define its voltage level in your system.  The next version is the 4-wire version. You have the 3 wires as listed about and the 4th wire added for the PWM input (or throttle😊).

Pulse Width Modulation

PWM(Pulse Width Modulation) or modulation with the width of an impulse, is a widespread term in the world of electrical engineering. PWM is very common in many industries from telecom, audio, motors, machines and anything else that has a DC motor. Most of you sales engineers and electrical engineers probably have experience in one way or another with this technology, but if not, that is the reason for the write up.

In simple terms the PWM is operating like a switch that is constantly doing on and off cycles which regulates the amount of power the fan circuit is seeing. The fan motor will get a constant 12V input with a 4-wire design and then the throttling up and down will happen by adjusting the duty cycle of the PWM input. TECH NOTE, if you are using a fan circuit that is going to chop the VDC to the fan with only 2 or 3 wires, you have to make sure you have a “analog” circuit in the and make sure to use a really low frequency, less than 100hz. This the less than desirable way, but if you must. It is a good idea to check with your fan supplier and make sure compatibility is good. Nothing worse that some quality issues right after launch!

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The motor is being fed pulses of power. Here is what the input cycle looks like, The duty cycle is what you are will want to correlate to the Thermal Profile in your system. This is normally done with a series of thermistors in your application that will report the local temperatures in your designated spots.   The fans can then be throttled up and down to accomplish your needed cooling when it is demanded. If for some reason no PWM signal is present (or lost), almost all fans will respond by going to 100% full speed.

Why is PWM so important? Well, it helps you manage many of the hurtles in developing a complete system; Why run the fan at full speed of the systems does not need it? Why run the fan at full speed and consume the added energy to do so? Why listen to the fan at full speed if the system is idol? AND it gives you the flexibility to tune the thermal performance of your system. Many new high end fans will have Microcontrollers in them to make changing our program in the fan even easier too, then you can have your cake and eat it too! If you are new to PWM and would like to know more, we are here to help.