Calculation example

AN316

12/17

DocID3567 Rev 4

Equation 5

This power corresponds to an operating temperature of 75 °C. The data sheets indicate the

power at 25 °C, so we have to correct the power according to the curves of admissible

power versus initial temperature (see Figure 4).

Equation 6:Thus we obtain

5.1.3

Selection of the Transil

We can now establish an initial specification of the Transil to use.

Equation 7:

The ST product type corresponding to these characteristics is the SMCJ30A.

Equation 8:

5.1.4

SMCJ30A datasheet.

A

V

V

I

Z

where

I

V

P

P

CL

P

5

.

11

13

50

200

=

Ω

-

+

=

-

=

=

I

P

V

P

VV

CL

V

P

W

A

V

575

5

.

11

50

=

·

=

P

P

P

P

P

P

×

W

W

C

C

PP

C

P

P

719

8

.

0

575

)

25

(

8

.

0

)

75

(

)

25

(

=

=

°

°

=

°

P

P

P

P

V

RM

29 V

V

RM

50 V for I

P

= 11.5 A

P

P

(25°C) = 719 W /1ms

≥

≤

C

ms

W

P

A

I

V

V

V

V

V

V

T

P

PP

CL

BR

RM

°

=

=

=

=

=

=

-

/

10

9

.

9

1

/

1500

32

;

4

.

48

max

3

.

33

min

30

4

α

V

CL max

×