August 2011

Doc ID 3607 Rev 3

1/12

AN604

Application note

Calculation of conduction losses in a power rectifier

Introduction

This application note explains how to calculate conduction losses in a power diode by taking

into account the forward voltage dependence on temperature and the current waveform.

The ideal current and voltage waveforms of an ultrafast diode in a power supply system

during a switching cycle are shown in Figure 1.

Figure 1.

Ideal current and voltage waveforms of a diode in a switch mode power

supply

The conduction losses in a diode appear when the diode is in forward conduction mode due

contributor to the total diode power losses and the junction temperature rising. This is the

reason why it is important to accurately estimate them.

t

t

0

0

T

sw

F

Switching frequency

T

Switching period

Duty cycle

T

Duration of diode conduction

I

Maximum forward current

I

Minimum forward current

V

Forward voltage

V

Reverse voltage

sw

sw

sw

max

min

F

R

δ

δ·

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