(3) Heat Radiation Design
Heat radiation design for reducing the operation substrate temperature of the hybrid IC is effective in enhancing the
quality of the hybrid IC.
The size of a heat sink varies depending on the average power loss Pd in the hybrid IC. As shown in Figure 6 on
page 14, Pd increases in accordance with the increase of the output current.
Since the starting current and the stationary current coexist in an actual motor operation, Pd cannot be obtained only
from the data shown in Figure 6. Therefore, Pd is obtained assuming that the timing of the actual motor operation is
a repeated operation shown in the following Figure 3.
T1: Starting time of positive rotation
T2: Stationary time of positive rotation
T3: Starting time of reverse rotation
T4: Stationary time of reverse rotation
T0: One cycle time of repeated motor
P1: Pd of IO1
P2: Pd of IO2
P3: Pd of IO3
P4: Pd of IO4
Figure 3. Timing Chart of Motor Operation
The average power loss Pd in the hybrid IC upon an operation shown in Figure 3 can be obtained by the following
Pd = (T1 × P1 + T1 × P2 + T3 × P3 + T4 × P4) ÷ T0 (II)
When the value obtained by the above equation (II) is equal to or less than 3.4W and the ambient temperature Ta is
equal to or lower than 60°C, there is no need of providing a heat sink.
Refer to Figure 7 for data of the operation substrate temperature when no heat sink is used.
The size of the heat sink can be decided depending on θc-a obtained by the following equation (III) and from Figure 8.
θc-a = (Tc max – Ta) ÷ Pd
where Tc max: Maximum operation substrate temperature = 105°C
Ta: Ambient temperature of hybrid IC
Although heat radiation design can be realized by following the above equations (II) and (III), make sure to check that
the substrate temperature Tc is equal to or lower than 105°C after mounting the hybrid IC into a set.