ST STEVAL-IHT001V1, Руководство пользователя

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Functional description UM0277
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2 Functional description
2.1 Performances
This board meets the following requirements:
●
Medium-end appliances: this thermostat board can control the loads traditionally used
in medium-end cold appliances (compressor, light, defrost resistor).
● Electromagnetic Compatibility: the board is able to withstand bursts of more than 2.3kV
during IEC61000-4-4 standard tests without any operational problems (and up to 4.5kV
without any damage). Surge tests have also been performed (IEC61000-4-5 standard):
2 kV bursts can be applied without any damage for the semiconductors.
●
Safety standards have also been taken into account. A 2-mm creepage is ensured
between all high voltage parts and low voltage parts (to achieve the functional
insulation level). The (NTC) thermistor is a class II sensor, and can be put on non-
earthed accessible and conductive parts.
2.2 Ensured functions
2.2.1 Temperature control
The thermal sensor used is an NTC thermal resistor (thermistor) from EPCOS (M2020 5 k
2%). It should be placed on the evaporator of the fridge or the freezer. The controlled
evaporator temperature range should be between -20 and 5 °C. The range can be modified
by changing the value of the resistor placed in series with the NTC (refer to
Appendix A ).
The NTC resistance value decreases, following an exponential variation, when the
temperature increases. Then, to get back the temperature data, the MCU could use a
numerical table. In the STEVAL-IHT001V1 board, a simple resistor has been added in
series with the NTC in order to linearize its thermal response (refer to
Appendix A ). Two
advantages come from this choice:
●
Memory area savings
● Easy way to measure the temperature.
Temperature regulation is achieved by Hysteresis control (see Figure 3 ).
Figure 3. Hysteresis law