Log in to myMicrochip to access tools and benefits. Sign up in just one minute.
Maximize Your Experience: Reap the Personalized Advantages by Completing Your Profile to Its Fullest. Update Here
Stay in the loop with the latest from Microchip. Update your profile while you are at it. Update Here
Complete your profile to access more resources. Update Here
true
AN772
| Title |
Title
Speed Error in PWM Fan Control Systems (TC646, TC647, TC649)
|
|---|---|
| Name |
Name
AN772
|
| Date |
Date
06/24/2015
|
| Application Categories |
Application Categories
Power Supply & Conversion /
Thermal Management
|
| Product Categories |
Product Categories
Power Management ICs /
PWM Controllers
Thermal Management /
Fan Controllers
|
| Description |
Description
Brushless DC fan speed can be varied using pulse-width modulation (PWM). The typical PWM control scheme inserts a power switch in series with the fan as shown in Figure 1. In such applications, an increase in the active duty cycle causes a corresponding increase in fan speed (i.e., fan speed is proportional to tON/(tON + tOFF). Conventional wisdom states that PWM duty cycle alone determines operating speed (for example, the fan speed runs at 50% of maximum when the PWM duty cycle is 50%). In reality, the fan operates at a higher percentage of full speed for any given duty cycle. The resulting difference between actual fan speed and the corresponding PWM duty cycle (herein referred to as Speed Error) can be problematic in open loop fan control systems.
|