How does a power semiconductor operate under real world conditions?
In the real world, actual power semiconductors do not meet these ideal characteristics. For example, Fig. 1-2(a) shows a control signal applied to an ideal power semiconductor switch whose output exhibits zero transition time when turning on and off (Fig. 1-2(b)). When the transistor is off (not conducting current) power dissipation is very low because current is very low. When the transistor is on (conducting maximum current) power dissipation is low because the conducting resistance is low. In contrast, an actual power switch exhibits some delay when turning on and off, as shown in Fig. 1-2(c). Therefore, some power dissipation occurs when the switch goes through the linear region between on and off. This means that the most power dissipation depends on the time spent going from the off to on and vice versa, that is, going through the linear region. Thus, the faster the device goes through the linear region, the lower the power dissipation and losses.
