Brochure

ESG
8.528.52
8.528.52
8.52
T
J
- T
A
= P (R
θJC
+ R
θCS
+ R
θSA
)
T
J
- T
A
= 12 (1,3 + 0,1 + 1,0)
T
J
- T
A
= 28,8
hence, T
A
= T
J
- 28,8
T
A
= 100 - 28,8
T
A
= 71,2 °C
1 °C/W
R
θSA
=
T
J
- T
A
P
- (R
θJC
+ R
θCS
)
R
θSA
=
100 - 71,2
12
- (1,3 + 0,1)
R
θSA
=
12 W
P =
T
J
- T
A
R
θJC
+ R
θCS
+ R
θSA
P =
P =
100 - 71,2
1,3 + 0,1 + 1,0
I
Load
=
P
E
Drop
I
Load
=
12
1,2
I
Load
= 10 A
hence,
(a) To determine the maximum allowable ambient
temperature: Heat sink = 1°C/W, Load = 10 A (12 W), TJ-
max. = 100 °C
(b) To determine required heat sink thermal resistance:
Maximum ambient temperature = 71,2 °C, Load = 10 A
(12 W):
(c) To determine maximum load current: Heat sink
= 1 °C/W, ambient temperature = 71,2 °C:
Regardless of whether the SSR is used on a heat sink or
the case is cooled by other means, it is possible to
confirm proper operating conditions by making a direct
base plate temperature measure-ment when certain
parameters are known. The same basic equation is used
except that base plate temperature (TC) is substituted for
ambient temperature (TA) and RθCS and RθSA are deleted.
The temperature gradient now becomes TJ - TC, that is
the thermal resistance (RθJC), multiplied by the junction
power dissipation (P watts). Hence:
Parameter relationships are similar in that solutions can
be found for maximum allowable case temperature,
maximum load current, and required junction to case
(RθJC) thermal resistance. Again, where two parameters
are known, the third can be found as shown in the
following examples (using previous values):
(d) To determine maximum allowable case temperature
for RθJC = 1,3 °C/W and Load = 10 A (12 W):
(e) To determine maximum load current for RθJC =
1,3 °C/W and case temperature = 84,4 °C:
(f) To determine required thermal resistance (RθJC) for
84,4 °C case temperature and 10 amp load (12 watts):
T
J
- T
C
= P (R
θJC
)
T
J
- T
C
= 12
x
1,3
T
J
- T
C
= 15,6
hence, T
C
= T
J
- 15,6
T
C
= 100 - 15,6
T
C
= 84,4 °C
12 W
P =
T
J
- T
C
R
θJC
P =
P =
100 - 84,4
1,3
hence, I
Load
=
P
E
Drop
I
Load
=
12
1,2
I
Load
= 10 A
R
θJC
=
T
J
- T
C
P
R
θJC
=
100 - 84,4
12
R
θJC
= 1,3 °C/W
T
J
- T
C
= P (R
θJC
)