PSoC
®
Thermal Management Expansion Board Kit Guide, Doc. No. 001-89649 Rev. **
17
3. Kit Operation
3.1 System Block Diagram and Theory of System Operation
The Appendix contains a
schematic
of the CY8CKIT-036 EBK, along with circuits associated with the four-wire fans and the
different onboard temperature sensors. This section describes the theory of operation for each of those hardware sub-
blocks in the EBK.
3.2 Four-Wire Fan Control
A four-wire fan has two wires for power supply (VDD, ground); the other two wires are used for speed control (PWM signal)
and speed monitoring (tachometer signal), respectively. Fans come in standard sizes
—with 40 mm, 80 mm, and 120 mm
being the most common sizes. One of the important specifications when selecting a fan for a cooling application is how
much air the fan can move. This is specified either as cubic feet per minute (ft
3
/min) or cubic meters per minute (m
3
/min).
The size, shape, and pitch of the fan blades all contribute to the fan’s capability to move air.
With four-wire fans, speed control is made possible through the use of a PWM control signal. Increasing the duty cycle of
the PWM control signal will increase fan speed. Fan manufacturers specify how the PWM duty cycle relates to nominal fan
speed. This is provided either through a table of data points or a graph that shows the relationship.
Figure 3-1
shows an
example of such a chart, with the PWM control duty cycle (as a percentage) displayed on the horizontal axis and the fan
speed (in rpm) displayed on the vertical axis.
Figure 3-1. Example of a Duty-Cycle-to-Speed Chart
0
2000
4000
6000
8000
10000
0
20
40
60
80
100
Duty Cycle to Speed
rp
m
Duty Cycle (%)
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