3/5

AN444 APPLICATION NOTE

Repetitive pulses operation

In repetitive pulse operation the power dissipation can be calculated by the following formula:

When r tends to zero we find:

Where F is the commutation frequency.

EXAMPLE OF APPLICATION

Commutation of a coil supplied by a battery. The different parameters of the application are:

Single pulse

We find:

Pp = 34.2 x 4 = 136.8W

tp = 1.08ms

The data sheet gives Pp 1500W for tp = 1.08ms then this 1.5KE36P can be used in this application.

Repetitive pulse operation

The commutation frequency is equal to 10Hz so:

P = 980mW.

Rth = 75°C/W and Tj max = 175°C.

Tj = 0.98 x 75 + 50 = 123.5°C < Tj max

So we can also use this Transil in repetitive pulse operation.

PF

V

L

⋅

r

-----------------------------

×

I

p

[

V

V

CC

–

r

---------------------------------------





+

V

V

CC

–

V

V

CC

–

rI

p

+

----------------------------------------------------





ln

=

P

1

2

---LFI

p

2

V

V

V

CC

–

---------------------------------------





=

tp

1.4

–

10 10

3

–

⋅⋅

23

×

---------------------------------------





–

34.2

14

–

34.2

14

–

34

×

+

-------------------------------------------





ln

=

P

10

34.2 10 10

3

–

⋅⋅

3

---------------------------------------

×

4

[

34.2 14

–

3

---------------------





+

34.2 14

–

34.2

14

–

34

×

+

-------------------------------------------





ln

=