Page 179 - Electrical Equipment Handbook _ Troubleshooting and Maintenance
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POWER ELECTRONICS, RECTIFIERS, AND PULSE-WIDTH MODULATION INVERTERS
9.6 CHAPTER NINE
FIGURE 9.8 (a) The symbol of a power transistor. (b) The voltage-current characteristic of a power transistor.
FIGURE 9.9 (a) A transistor with a resistive load. (b) The voltage-current characteristic of this transistor
and the load.
If the base current is equal to i , the transistor will not be on or off. This is highly unde-
B 3
sirable because a large collector current will flow, dissipating a lot of power in the transistor.
If the base current is high enough, the transistor becomes completely saturated. It con-
ducts without wasting a lot of power. A major drawback of large power transistors is their
relatively slow switching from on to off, because a large base current is needed or removed
to turn them on or off.
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