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

Fan Speed Control
16
Figure 5 Type B Operation, Stay On at Minimum RPM, Off at 0% 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
% of ful l spe e d
Example Min.
RPM
Example Min.
PWM
The fan stays on at
minimum speed for
PWM duty cycle
values below the
minimum PWM
duty cycle, and
shuts off at 0%
PWM duty cycle
In Type C implementation the fan will stop running when the current provided to the motor
windings is insufficient to support commutation. The fan should not be damaged from this. The
fan would also turn off the motor at 0% PWM duty cycle input. See Figure 6.