Doc ID 15772 Rev 2

7/14

AN2991

Stalled rotor management

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2

Stalled rotor management

2.1

Protection by thermal cut-off

In the case of a stalled rotor operation, the over current protection is commonly ensured by

a thermal cut-off. This component, also called “klixon”, is mandatory to prevent the

compressor from over-heating. Klixons are well adapted for motor protection, but not for

semiconductors. Indeed, the turn-off time is in the range of 15 s. The silicon switch will

withstand a high current that will only decrease thanks to the motor winding heating. In

practice, the rms current can fall from 9 A rms to around 4.5 A rms, for a 150 W compressor.

The maximum junction temperature reached by the ACST610-8T can then equal 162 °C as

shown by the simulation results in Figure 7.

As this temperature exceeds the maximum allowed steady state temperature (125 °C),

reliability tests have been performed to check the robustness of the silicon switches after

such stress. ACST610 devices can withstand such currents up to more than 10 thousand

times. This easily covers the number of stalled rotor operations that can happen during the

life cycle of a refrigerator or freezer.

Figure 7. ACST610 junction temperature during stalled rotor operation

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Current in the device (A)

Junction temperature (°C)

Time (s)

Time (s)