where I

The current shown in Figure 6 is a simple overtemperature

detector for power devices. In this example, an audio power

amplifier IC is bolted to a heat sink and an LM56 Celsius

temperature sensor is mounted on a PC board that is bolted

to the heat sink near the power amplifier. To ensure that the

sensing element is at the same temperature as the heat sink,

the sensor’s leads are mounted to pads that have feed

throughs to the back side of the PC board. Since the LM56 is

sensing the temperature of the actual PC board the back

side of the PC board also has large ground plane to help

conduct the heat to the device. The comparator’s output

goes low if the heat sink temperature rises above a threshold

set by R1, R2, and the voltage reference. This fault detection

output from the comparator now can be used to turn on a

cooling fan. The circuit as shown in design to turn the fan on

when heat sink temperature exceeds about 80˚C, and to turn

the fan off when the heat sink temperature falls below ap-

proximately 75˚C.

01289321

FIGURE 6. Audio Power Amplifier Overtemperature Detector

01289322

FIGURE 7. Simple Thermostat

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