Power switches bipolar transistors

The development of this hybrid combination in a bipolar transistor has greatly enhanced the application of power transistors in the field of power conversion and variable-speed drives. It possesses the qualities of both the power bipolar transistor (BJT) and the power MOSFET. Like a power MOSFET, it is a voltagc-eontrollcd switching device... 

There are two major types of power switches used today the bipolar power transistor (BJT) and the power MOSFET. The IGBT (integrated gate bipolar transistor) is used in the higher power industrial applications, such as 1 kW power supplies and electronic motor drives. The IBGT has a slower turn-off than does the MOSFET, so it is typically used for switching frequencies of less than 20 kHz. 

The power MOSFET is the most common choice as a power switch. Its cost and saturation loss are comparable to the bipolar transistor in most applications and it switches five to ten times faster. It is also easier to use in a design. 

Semiconductor switches in power electronic inverters are commonly made up of a transistor together with a diode in anti-paraUel connection as depicted in Fig. 2.13a for a bipolar transistor to provide a path for an inductive load current when conducting switches are turned off and thus to avoid damage of the transistors in an inverter. MOSFET transistors have a built-in diode. Figure2.13b shows a bond graph model of such a transistor-diode pair. 

Zero-current-transition PWM converters (Hua, Leu, and Lee, 1992) Figure 10.91 shows an example of zero-current transition boost converter. This approach is useful in high power converters when insulated gate bipolar transistors (IGBTs) or bipolar transistors are used as the switching devices. 

Figure 3-32 Waveforms for a bipolar power transistor within a PWM switching power supply.

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