AN2025 datasheet(2/11 Pages) STMICROELECTRONICS

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AN2025 - APPLICATION NOTE

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III. Simple method to estimate the maximum avalanche peak power

III.1. Setting the Problem

Most of the time, it is difficult to accurately determinate the avalanche power through the diode in the hard-

ware circuit.

This is mainly due to measuring problems such as delay time between current and voltage probe, the very

low pulse duration and the snubber circuit impact. Generally, in SMPS applications, the maximum

avalanche peak power occurs for a diode having the lowest clamping voltage. Practically, this diode is very

difficult to find.

These are the reasons why STMicroelectronics proposes a simple method to estimate the maximum av-

alanche peak power PPEAK_AV. In most of SMPS applications, this method will be pessimistic (PPEAK_AV

> PAVALANCHE) but sufficient to determine whether or not a given Schottky diode will sustain the applied

avalanche energy. This method only covers Schottky diodes used in rectification function for SMPS (see

figure 4), where the pulse duration of the avalanche current tp is less than 1µs.

Figure 2:

Figure 3:

Figure 4: Typical secondary rectification topologies

PARM tp Tj

()

PARM tp 25

()

--------------------------------------------- versus Tj

PARM tp Tj

()

PARM 1µsTj

()

----------------------------------------- versus Tp

0.2

0.4

0.6

0.8

1.2

100

125

150

175

P(t , T ) /

ARM

(t , 25°C) versus T

ARM

T (°C)

0.001

0.01

0.1

0.01

0.1

100

1000

P(t , T ) /

ARM

(1µs, T , 25°C) versus t

ARM

t (µs)

Transformer

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