Application examples

AN302

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1.3

Example 3: motor control (2)

The small high-impedance motor (Figure 4) seems to operate without problems. However,

the motor is intended for mounting on out-door equipment. It is installed in summer and

works well. But in winter, the fault described above occurs.

What has happened?

The designer studied the operation of his circuit at an ambient temperature of 25 °C. But the

holding current varies inversely with the temperature. Thus, as the temperature decreases,

the holding current increases and the phenomenon described in example 2 occurs.

Again, it is essential to take into account the temperature effects on the device parameters

for circuits which have to operate at extremes of temperature. It is not sufficient to use the

values given for an ambient temperature of 25 °C.