Anartik.com’s Blog

PWM

PWM is a process for controlling analog circuits via digital processor outputs. PWM is widely used in robotics, embedded systems, communications etc. and has made its way into mainstream computing via Intel. The focus of this tech note is PWM applications in computing.

PWM provides the most effective means of managing your system fans which can result in noise reduction, extended fan life and energy savings. PWM sends a digital signal to a IC in your PWM fan or device without the need for digital to analog conversion which can result in signal noise.

1) PWM is backwards compatible with any standard 3 pin Molex header. Of course if you use a 3 pin header you lose PWM control but keep power and RPM sensing. A properly wired fan will use a standard PWM connector that has a polarization rib to keep the fan from being plugged in incorrectly. Please note that if you are using wiring extensions or Y’s that a 4 pin PWM plug will not fit into a 3 pin hooded adapter. They will however work with adapters that use a open 3 pin male header connection w/o a hood. Many 3 pin fan controllers use hooded connections so beware.

2) PWM is the present and the future of computing. LGA1366 motherboards generally include at least one PWM header for the CPU cooler and some will include 2 or more. Even if you don’t have a controlling device the purchase of PWM enabled fans helps protect your investment.

3) Depending on the fans used and the rating of the motherboard header up to 5 fans can be daisy chained using Y adapters. Once you start chaining you maintain PWM control but lose RPM reporting for all but the first fan. There are some wiring products on the market that are incorrectly constructed so beware. As with a 3 pin Y cable only one side of the Y should be reporting RPM. There are also some products that claim to be PWM splitters but half the Y is just a standard 3 pin connection.

4) There are a few controllers/hubs starting to appear on the market. These are for systems without any motherboard PWM control or to augment PWM ready systems. They tend to vary greatly in function and quality.

Anartik.com currently carries several PWM fans and will continue to expand this line. We also carry Molex PWM female connectors and will soon carry other electrical accessories like Y’s and extensions. While I expect to carry a selection of standard 3 and 4 pin fans for some time to come 4 pin PWM fans will eventually become the norm.

On the CPU cooler side the Scythe Mugen 2, Shuriken, Kama Angle, AC Freezer 7 Pro and the Reeven core contact cooler come standard with PWM fans. Expect to see more coolers follow this standard in the near future.

It is my opinion that PWM is here to stay and will rapidly become as standard as the 3 pin RPM connection. The fans for the most part are here although there is more to PWM than just slapping an IC into existing fan models. Fans really need to be designed for PWM to eliminate any fan noise that may be induced by PWM control. So not all PWM fans are created equal and will vary in quality of the PWM function. On the control side PWM has a ways to go. Motherboards need to start including more PWM connections with better controls in the BIOS and/or software. On the fan controller side more work is also needed. Some fan controllers may only include one PWM connection and product selection is still rather limited.

Jim Phillips
Anartik.com