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VISHAY IGBT驱动光耦应用指导.pdf


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VISHAY IGBT驱动光耦应用指导.pdf
文档介绍:
VISHAY SEMICONDUCTORS

Optocouplers and Solid-State Relays Application Note 91
IGBT/MOSFET Gate Drive Optocoupler
INTRODUCTION TO IGBT voltage drive, which means that it is possible to have a less
The Insulated Gate Bipolar transistor (IGBT) is a plex circuit with lower power pared to
between a MOSFET (metal oxide semiconductor field effect a BJT. IGBTs are used for high current, high voltage
transistor) and a BJT (bipolar junction transistor) since it applications when switching speed is important (table 1).
combines the positive aspects of MOSFETs and BJTs.
The IGBT has the fast switching capability of the MOSFET TABLE 1- IGBTS VS. MOSFETS
and is capable of handling the high current values typical of
IGBTS POWER MOSFETS
a BJT. In addition, IGBTs have a lower on-state voltage drop
TYPE VOLTAGE DRIVEN VOLTAGE DRIVEN
and are capable of blocking higher voltages.
Very high, small
Current density per High at low voltage
The IGBT, as a first approximation, can be modeled as a trade-off with
voltage drop low at high voltage
PNP transistor driven by a power MOSFET, as shown in switching speed
figure 1. Switchung losses Low to medium Very low
C
IGBT SWITCHING BEHAVIOR
One of the important performance features of any switching
device is the switching (turn-on and turn-off) characteristic,
since significant power losses are incurred during these
switching states.
When driving inductive loads, the device under goes higher
G
stress. Hence, it makes sense to study the turn-on and
turn-of time of the IGBT/MOSFET when driving inductive
loads.
The IGBT’s internal input capacitance (CGE) and Miller
capacitance (C ) impacts the IGBT turn-on behavior. But
E GC
the CGC effect is very small and negligible. Figure 3
Fig. 1 - Simplified IGBT Equivalent Circuit illustrates the parasitic IGBT capacitances.
Figure 2 shows the mon symbols used for IGBT. C
C C
CGC
APPLICATION NOTE APPLICATION
CGC = feedback or Miller
G G capacitance
G
CGE = input capacitance
CE
E = output capacitance
C
E E GE
Fig. 2 - IGBT Symbols
E
The equivalent circuit for the input of IGBT is the same as a
MOSFET and is purely capacitive. This allows the use of a Fig. 3 - IGBT Parasitic Capacitances

Rev. 1.3, 24-Oct-11 1 Document Number: 81227
For technical questions, contact: optocoupleranswers@
THIS DOCUMENT IS SUBJECT TO CHANGE WITHOUT NOTICE. THE PRODUCTS DESCRIBED HEREIN AND THIS DOCUMENT
ARE SUBJECT TO SPECIFIC DISCLAIMERS, SET FORTH AT ?91000
Application Note 91
hay Semiconductors
IGBT/MOSFET Gate Drive Optocoupler
Most datasheets specify the voltage-dependent low-signal
capacitance of IGBT/MOSFETs in the off-state (table 2). C
I
TABLE 2 - IGBT AND MOSFET CAPACITANCE C
CCG
CAPACITANCE IGBTS POWER MOSFETS
R
Input Ciss = CGE + CGC Ciss = CGS + CGD gate
dV/dt
Reverse transfer Crss = CGC Crss = CGD
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