AN4021 Datasheet, PDF (1/10 Pages) STMicroelectronics – Calculation of reverse losses in a power diode

AN4021
Application note
Calculation of reverse losses in a power diode
Introduction
This application note explains how to calculate reverse losses in a power diode by taking
into account the impact of the junction temperature (T_j) as well as the reverse voltage V_R on
the leakage current.
The ideal current and voltage waveforms of an ultrafast diode in a power supply system
during a switching cycle are illustrated 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
I_D(t)
V_D(t)
0
V_D(t)
V_F
I_R
0
V_R
δ·T_SW
T_SW
Fsw Switching frequency
t
Tsw Switching period
δ
Duty cycle
δ·Tsw Duration of diode conduction
t
I_Max Maximum forward current
I_Min
Minimum forward current
V_F
Forward voltage
V_R Reverse voltage
The reverse losses in a diode are the result of a reverse bias applied on the diode. They are
due to the leakage current (I_R). This parameter (I_R) increases exponentially with the junction
temperature. Most of time, the reverse losses are negligible for bipolar and silicon carbide
diodes. For silicon Schottky structured diodes, these losses should be accurately estimated
as they are the main origin of the thermal runaway risk phenomenon (See AN1542).
April 2012
Doc ID 022588 Rev 1
1/10
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