An application example

AN4021

6/10

Doc ID 022588 Rev 1

3

An application example

Let us consider the example of a 45 W notebook adapter, using a flyback converter

Figure 5 shows the ideal waveforms of the diode. The duty-cycle of the transistor is:

δ = 0.2

and the transformer ratio is: m = 0.148.

Let us calculate the maximum reverse losses in the diode for this application.

Figure 4.

Flyback converter

Figure 5.

Ideal current and voltage waveforms of the diode in the flyback converter

STPS20M100S

Control

m

t

t

0

Spike

I (t)

D

V

F

I

R

I (t)

D

V (t)

D

V (t)

D

-V

R

- (m · V + V )

in

out

δ·T

SW

T

SW

0