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Thermal Design

            To obtain maximum reliability in switch mode power supplies, thermal management becomes essential, as high component temperature are undoubtedly one of the major causes of premature failure in switch mode systems.

 

            In practice the dissipation in switch mode Application is difficult to establish with any real degree of confidence. Under these conditions, a known thermal resistance in the heat conduction path is used to establish the heat flow and hence the junction dissipation. Table 3.5 shows the junction temperature for various components used in converter modules.

           

Table 3.5 Junction Temperature

(The room temperature is 30C)

 

S.No.

Name of the device

Thermal resistance C/W

Power Loss

Meas. Temp. C

Junction Temp. C

Allowable Junction Temp.

1.

MOSFET IRFP150N

41.19

0.41

33

49.88

-55 to 175

2.

Diode IR50SQ100

44

0.45

40

59.8

-55 to 175

3.

{WM Ic SG1524B

80

0.2

32.6

48.6

150

4.

NAND gate CD4093BE

80

0.24

32

51.2

110

5.

Comparator LM358

238

0.11

32

58.2

110

6.

Comparator LM311

134

0.18

32

56.1

110

7.

Comparator LM324

103

0.25

33

58.8

125

8.

Opto-coupler IL300

470

0.1

31

35.7

100



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