AN1768 - APPLICATION NOTE

2/2

2. DESIGN EXAMPLE

Let us consider the use of a STPS20H100CT (two

10A, 100V ST Schottky diodes in TO-220 pack-

age) used in a flyback converter (

figure 4).

In a typical worst-case situation, the application

conditions are:

n

Operating junction temperature of the Schottky

diode:

Tj = 100°C

n

Pulse duration of the avalanche current:

tp = 10ns

n

Avalanche energy by pulse through the two

diodes connected in parallel:

•

Table 1 gives:

•

Figure 2 gives:

Ptp

C

Ptp

C

ARM

ARM

(,

)

(,

)

.

100

25

045

°

°

=

•

Fig.3 gives:

Pns T

Ps T

ARM

j

ARM

j

(, )

(, )

10

1

1

µ

=

Finally,

The maximum admissible avalanche energy of the

STPS20H100CT at 10ns and 100°C is:

Consequently,

as

the

guaranteed

value

measured through the two diodes connected in

parallel (48.6µJ > 1.95µJ), the STPS20H100CT

will withstand the avalanche energy generated by

the converter.

Vout

Idiode

Vdiode

Vin

Fig. 4: Topology of a flyback converter.

tp

corresponding energy

in the avalanche area

Fig. 5: Current and voltage waveforms through

the two diodes.

Figure 5 shows the corresponding current and

voltage waveforms through the two diodes.

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