AN604 Datasheet, PDF (1/12 Pages) STMicroelectronics – Calculation of conduction losses in a power rectifier

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
I_D(t)
I_Max
I_Min
0
V_D(t)
V_F
0
V_R
δ·T_sw
T_sw
I_D(t)
V_D(t)
t
t
F_sw
T_sw
δ
δ·T_sw
I_max
I_min
V_F
V_R
Switching frequency
Switching period
Duty cycle
Duration of diode conduction
Maximum forward current
Minimum forward current
Forward voltage
Reverse voltage
The conduction losses in a diode appear when the diode is in forward conduction mode due
to the on-state voltage drop (V_F). Most of the time the conduction losses are the main
contributor to the total diode power losses and the junction temperature rising. This is the
reason why it is important to accurately estimate them.
August 2011
Doc ID 3607 Rev 3
1/12
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