DESIGN SHOWCASE
Supervisor IC indicates
fan failure
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鈥檚 tachometer output connects to the watchdog
input of a
碌P
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.
+5V
D1
R2
300鈩?/div>
U1
1
2
3
R1
20k鈩?/div>
V
CC
WDI
5
4
MAX6316
RES
GND
MR
TACH
Figure 1. The MAX6316 碌P supervisor monitors a fan鈥檚 tachometer output.
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