19
The brushless DC fans found in many types of
equipment can be crucial to the performance and
longevity of that equipment. A quick indication of fan
failure, moreover, can be essential in preventing major
damage. Among the many approaches for identifying
and indicating stalled fans, the circuit of Figure 1 is
very simple and reliable.
The fan’s tachometer output connects to the watchdog
input of a µP supervisor (U1). The LED remains off
during normal operation. If the tachometer does not
change state within a watchdog timeout period, U1
lights the LED by asserting its reset output. As a
result, the LED pulses on and off as the supervisor
goes through its watchdog/reset cycle. The LED in
this example has a 200ms on-time and flashes with a
period of 1.6s, which is suitable for most purposes.
A similar article appeared in the November, 2003
issue of EET.
DESIGN SHOWCASE
Supervisor IC indicates
fan failure
Figure 1. The MAX6316 µP supervisor monitors a fan’s tachometer output.
RES
D1
GND
R2
300Ω
R1
20kΩ
TACHMR
V
CC
1
2
3
5
+5V
4
WDI
U1
MAX6316