SANYO DENKI DC cooling fan Open Loop vs Closed Loop control

Closed loop fan control has often been associated with external controllers to modify a DC fan’s performance. However, many SANYO DENKI fans utilize an internal closed loop speed control to enhance performance.

This brief article will explain the differences between open and closed loop control and how to tell what type of loop control the fan model has.

Open Loop Control

Open loop control is basically just a free running motor and is the simplest design. It has no internal feedback circuitry and so the speed (RPM) can be affected by changes in pressure or temperature. Most of our older fan models are open loop controlled.

In order to tell if a DC fan is open loop controlled, look at the Speed vs PWM duty cycle graph provided in the data sheet. As you can see below, the nominal speed (black line) is not linear over the PWM duty cycle range.

Graph of OpenLoop. Speed vs PWM duty of a cooling fan

Advantage: Lowest cost because there is no feedback circuitry.

Disadvantage: Will not self-correct the RPMs when conditions change.

Closed Loop Control

Over the last decade, many of our new fan models have closed loop control which keeps the speed (RPMs) constant regardless of temperature or back pressure variations. This is accomplished by adding a feedback circuit to the motor control via an internal tachometer signal so that the feedback circuit automatically makes corrections to bring the speed back to nominal. 

For example, below is a Speed vs PWM duty cycle graph showing a fan with closed loop control. As you can see, the RPMs are linear  over the PWM duty cycle range and will autocorrect the speed up to +/- 5% of the nominal value over the duty cycle range. This percentage can vary based on the fan model.

a graph of closed loop DC cooling fan speed vs PWM duty

Advantage: Will autocorrect the RPMs based on external changes to maintain a constant airflow and thus  provides the desired temperature in a system.

Disadvantage: Adds a small cost increase since additional internal feedback circuitry is needed.

In closing, DC fans with closed loop control feature are a great way to maintain constant fan performance over the PWM duty cycle even when changes in system pressure or temperature occur.

If in doubt if a fan model has open or closed loop control, please feel free to contact your local SANYO DENKI AMERICA sales office or sales rep, and we will be glad to help you.

Written by Gary Masessa


SANYO DENKI has been a trusted provider of cooling solutions for various industries, with fans being a crucial component in many advanced devices. Contact us for a quote, or to discuss your device's customization requirements.

Our experienced application engineers and field engineers will provide support on the customization or any other technical support for your equipment. Contact our representatives or distributors to start discussing your next project.

Contact Us

Leave a Reply

Your email address will not be published. Required fields are marked *