UM1036
Board description
Doc ID 18293 Rev 1
23/48
sensed through an NTC resistor RT1. The measured signal is amplified with an operational
amplifier and then fed through the J2 motor connector to the MCU control unit to be read
with an A-D converter. The signal is also fed to the U9A comparator where it is compared
with a 2.5 V reference voltage. The precision reference U10 TS3431 provides this 2.5 V
reference voltage. The output signal of the comparator is fed into the IPM to stop the
commutation of the connected motor as well as into the MCU control unit through the J2
connector. With the value of the used resistor networks and applied NTC resistor, the
shutdown temperature of the heatsink is somewhere between 85 °C and 90 °C.
3.3.9
Active heatsink cooling
For better thermal transfer of heat from the heatsink, active fan cooling is implemented on
the board. The aluminum profile used is type 8424 from PADA Engineering. The
temperature is sensed with the NTC resistor and compared with a reference voltage in
comparator U9B. The fan is switched on automatically when temperature of the heatsink
reaches approximately 40 °C and is switched off when temperature of the heatsink falls to
35 °C. The thermal resistance of the heatsink, when the fan is not activated, is visible in
Figure 13
, the thermal resistance with active fan cooling is visible in
Figure 14
.
Figure 13.
Thermal resistance of the heatsink
2TH
#7
2THFORRELATEDDISSIPATEDPOWER7
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