STK672-732AN-E
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5. Thermal design
[Operating range in which a heat sink is not used]
Use of a heat sink to lower the operating substrate temperature of the IPM (Intelligent Power Module) is effective in
increasing the quality of the IPM.
The size of heat sink for the IPM varies depending on the magnitude of the average power loss, PdAV, within the IPM.
The value of PdAV increases as the output current increases. To calculate PdAV, refer to “Calculating Internal IPM
Loss” in the specification document.
Calculate the internal IPM loss, PdAV, assuming repeat operation such as shown in Figure 1 below, since
conduction during motor rotation and off time both exist during actual motor operations,
Figure 1. Motor Current Timing
T1 : Motor rotation operation time
T2 : Motor hold operation time
T3 : Motor current off time
T2 may be reduced, depending on the application.
T0 : Single repeated motor operating cycle
I
O
1 and I
O
2 : Motor current peak values
Due to the structure of motor windings, the phase current is a positive and negative current with a pulse form.
Note that figure 1 presents the concepts here, and that the on/off duty of the actual signals will differ.
The IPM internal average power dissipation PdAV can be calculated from the following formula.
PdAV = (T1P1+T2P2+T30) TO ---------------------------- (I)
(Here, P1 is the PdAV for I
O
1 and P2 is the PdAV for I
O
2)
If the value calculated using Equation (I) is 1.5W or less, and the ambient temperature, Ta, is 60C or less, there is no
need to attach a heat sink. Refer to Figure 2 for operating substrate temperature data when no heat sink is used.
[Operating range in which a heat sink is used]
Although a heat sink is attached to lower Tc if PdAV increases, the resulting size can be found using the value of
c-a in Equation (II) below and the graph depicted in Figure 3.
c-a = (Tc max-Ta) PdAV ---------------------------- (II)
Tc max : Maximum operating substrate temperature = 105C
Ta: IPM ambient temperature
Although a heat sink can be designed based on equations (I) and (II) above, be sure to mount the IPM in a set and
confirm that the substrate temperature, Tc, is 105C or less.
The average IPM power loss, PdAV, described above represents the power loss when there is no avalanche operation.
To add the loss during avalanche operations, be sure to add Equation (3-2), “Allowable STK672-7** Avalanche
Energy Value”, to PdAV.
IO1
IO2
-IO1
0 A
T1
T2
T3
T0
Motor phase current
(sink side)
