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"Standard", "Special", and "Specific". The Specific quality grade applies only to devices developed based on a
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equipment and industrial robots
Special: Transportation equipment (automobiles, trains, ships, etc.), traffic control systems, anti-disaster
systems, anti-crime systems, safety equipment and medical equipment (not specifically designed
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Specific: Aircraft, aerospace equipment, submersible repeaters, nuclear reactor control systems, life
support systems or medical equipment for life support, etc.
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M7 98. 8
Application Note D13686EJ1V0AN00
3
INTRODUCTION
Power MOSFETs are now used in a wide variety of electronic devices. Particularly for implementing switching power
supplies, which are emerging as the main power supply circuit of electronic devices, power MOSFETs have become
indispensable because their increasingly compact, high-efficiency circuit designs easily enable faster operation.
In general, when switching speed increases, flyback voltage may damage the device as a result of wiring inductance,
for example. This must be taken into consideration when designing electronic circuits. It is possible to prevent devices
from being damaged by flyback voltage by using products with guaranteed avalanche capability.
This document introduces the characteristics of a series of NEC-developed MOSFETs with a high avalanche-energy
capability (high sustain capability) and a high breakdown voltage of 250 V or greater.
1. Avalanche-Energy Capability
Sustain damage is the most important consideration in switching power supplies, a typical MOSFET application.
Damage from such causes as over-current and over-voltage during transient periods or unstable operation (i.e. when
starting or load short-circuiting) are examples of actual faults that may occur. Sustain tolerance is the qualitative
measure of this sustain damage. Of sustain tolerance, the avalanche-energy capability discussed here is subject to the
most rigorous test conditions (non-clamp conditions).
Figure 1-1 shows an avalanche-energy capability test circuit. Initially, 1/2
×
LI
(peak)
of energy is accumulated in the
2
inductance from the drain current flowing when the FET is on. This energy generates a flyback voltage that exceeds the
drain-source breakdown voltage when the power is turned off and causes avalanche breakdown in the FET. Stress, as
shown below, is applied due to this avalanche breakdown, and the circuit may be damaged as a result.
Figure 1-1. Avalanche-Energy Capability Test Circuit
Avalanche state
I
(peak)
I
D
Inductance
L
V
DD
50
Ω
PG
Power supply
V
DD
=150 V
When ON
0
Starting T
ch
L is in the order of several hundred
µ
H.
The time that the FET is on, T
on
, is short,
in the order of several dozen
µ
s.
Therefore, the inductance current rises with
a gradient of nearly V
DD
/ L.
V
GS
0
Energy is accumulated when ON.
I
D
I
AS
BV
DSS
V
DSS
(Rating exceeded)
V
DS
V
DD
When turned OFF
T
on
20 V
0V
V
GS
=20 0 V
Single pulse
DUT
Gate resistance
R
G
=25
Ω
Absorbed by FET as avalanche energy when
turned OFF.
Application Note D13686EJ1V0AN00
5
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