A5219

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 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 300Ω U1 1 2 3 R1 20kΩ VCC WDI 5 4 MAX6316 RES GND MR TACH Figure 1. The MAX6316 µP supervisor monitors a fan’s tachometer output. 19 ...