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’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 goe...

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