AN609 View Datasheet(PDF) - Vishay Semiconductors
Part Name
Description
Manufacturer
AN609 Datasheet PDF : 9 Pages
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AN609
Vishay Siliconix
Table 4
R-C VALUES FOR FILTER
Thermal Resistance (°C/W)
Junction to
RF1
Ambient
6.2277
Case
164.8787 n
RF2
7.9322
888.8177 m
RF3
7.6428
1.2671
RF4
47.9015
1.0331
Thermal Capacitance (Joules/°C)
Junction to
Ambient
Case
CF1
16.9231 m
166.0609 u
CF2
156.4465 m 357.5156 u
CF3
2.8690 m
4.6473 m
CF4
1.2888
304.1798 u
Foot
N/A
N/A
N/A
N/A
Foot
N/A
N/A
N/A
N/A
Step 9
Repeat steps 3 through 7 described above and compare
the simulation results obtained by using the j-a filter con-
figuration shown in Figure 8 with the simulation results
obtained by using the j-a tank configuration in Figure 5.
120W
(A) j-a Filter.dat (active)
Temperature: 27.0
150c
100W
80W
100c
60W
40W
50c
20W
0W
0s
1
100ms 200ms 300ms 400ms
I(I1)
2 V(R1:1)
Time
>>
0c
500ms 600ms
Figure 8: j-a Filter Simulations
Red: Junction temperature
Purple: Power profile
The transient power profile for high-power, short-dura-
tion or even single incidence may exhibit a high temper-
ature rise at the junction before the heat is conducted
away from the package. In such cases, j-c or j-f thermal
models are useful.
Table 5 describes the single pulse profile to be analy-
zed.
Table 5:
Time (sec)
0
10 µs
90 µs
100 µs
1s
Power (Watts)
0
900
900
0
0
Duration = 1 second
Ambient temperature = 25 °C
Follow the same steps as those described in Example 1,
except that the R-C values are obtained from the j-c part
of the Table 3 and Table 4. The schematic diagram for
the j-c tank configuration is shown in Figure 9.
Junction Temperature
R1
R2
R3
R4
18.1348u 713.7923m 1.3126
1.1896
C1
C2
C3
C4
81.2397u
I2
673.3554u
C:\Si7390DP_RC\900w100uS.txt
Power Profile
I
15.6345m
6.7185m
V1
25Vdc
Ambient
0
Figure 9: j-c Tank Configuration
We can observe that the junction temperature value
obtained by either configuration is within couple of
degrees Centigrade. These results are acceptable for all
practical purposes.
(b) Example 2
Aim: Demonstrate the use of the junction-to-ambient (j-
c) model and verify that the junction temperatures
obtained by each model configuration are comparable.
Document Number 73554
07-Oct-05
www.vishay.com
5
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