4-Wire Pulse Width Modulation (PWM) Controlled Fans Specification

Fan Speed Control
15
Figure 4 Type A Operation, Minimum RPM, Stay on at Minimum RPM
Speed vs. PWM Duty cycle
0
5
10
15
20
25
30
35
0 5 10 15 20 25 30 35
PWM Duty Cycle
ExampleMin.
RPM
Example Min.
PWM
% of full speed
The fan stays on at
minimum speed for
all PWM duty cycle
values below the
minimum PWM
duty cycle
In a Type B implementation the fan will run at minimum RPM for all non-zero PWM duty cycle
values less than minimum duty cycle and turn off the motor at 0% PWM duty cycle. See Figure 5.