1st part drop in turned-on position across the IGBT cannot be lower than the voltage drop across the diode between the emitter and base of the transistor VT1. The typical volt-ampere characteristics of IGBT are presented in Fig.1.27. It can be seen that at turned-on position the forward voltage drop across the transistor is low (here about 1 V), that in complex with easy control and fast transient speeds provides a wide application of the transistors in power electronics. It can be noted that an admissible temperature of structure of IGBT is +150 °C. As it can be seen a current through the transistor depends on the value of a control voltage. To provide a full turn-on state with small voltage drop (under 2 V) rather large control voltage close to the maximum admissible 20 V has to be applied. For obtaining a turned-off position a reverse control voltage up to minus 20 V can be applied.
C VT3
VT1
IC
VT4
VT2 G
C
G
R E
E
Fig.1.26. The principal substitution circuit of the IGBT
When an internal p-n-p transistor of the IGBT is turned-on it is not in the deep saturated situation since it is restricted by a circuit of a base current generating method in the transistor VT1. Therefore IGBT turn-off process is sufficiently fast — from 100 ns to 3000 ns. If turn-off process is fast then switching power losses are relatively low and it allows operating with high switching frequency. IGBTs can be divided into 3 groups: • S — with standard switching speed when full turn-on interval lasts for about 25 ns but turn-off process till 1600 ns; the common switching energy losses are about 7.0 mJ (for transistor of the rated current 10 A) and transistor can operate with switching frequency till 1 kHz; • F — fast IGBT with full turn-on time about 13 ns, turn-off time about 600 ns, ener gy losses in switching processes about 1,8 mJ (for transistor of rated current 10 A) and such transistor can operate with switching frequency up to 10 kHz; • U — ultra-fast IGBT with turn-off time 190 ns and energy losses in switching processes about 1 mJ which can work with tenth kilohertz switching frequency.
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EnergoelektronikaEN BOOK.indb 50
07.05.2018 18:16:49