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Assuming that the power dissipation is shared equally among the four power transistors (2 channels × 2), thermal resis-
tance ¸ j-c is 2.6° C/W and
Pd × (¸ c-a + 2.6/4) + Ta d" 150° C........................................ (3)
Thermal resistance ¸ c-a of a heat sink must satisfy ine-
qualities (1) and (3).
Figure 3 shows the relation between Pd and ¸ c-a given
from (1) and (3) with Ta as a parameter.
[Example] The thermal resistance of a heat sink is
obtained when the ambient temperature speci-
fied for a stereo amplifier is 50° C.
Assuming VCC = ± 26V, RL = 8&! ,
VCC = ± 22V, RL = 4&! ,
RL = 8&! : Pd1 = 23.6W at 1/10 Po max.
RL = 4&! : Pd2 = 28.2W at 1/10 Po max.
The thermal resistance of a heat sink is
obtained from Figure 3.
RL = 8&! : ¸ c-a1 = 3.18° C/W
IC Power dissipation, Pd - W
RL = 4&! : ¸ c-a2 = 2.66° C/W
Figure 3. STK4142II ¸ c-a Pd
Tj when a heat sink is used is obtained from
(3).
RL = 8&! : Tj = 140.4° C
RL = 4&! : Tj = 143.4° C
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This catalog provides information as of July, 1997. Specifications and information herein are subject to change without notice.
No. 2665 8/8
Thermal resistance of heat sink,
¸
c-a -
°
C/W
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