STK673-011-E

No.A1137-8/15

(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 13, 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.

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

equation (II):

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

(III)

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.

ITF00811

Positive rotation

current

Reverse rotation

current

T1

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

operation

P1: Pd of IO1

P2: Pd of IO2

P3: Pd of IO3

P4: Pd of IO4

IO1

IO2

IO3

T2

T0

T3

T4

0

IO4