1. Controlling High Power
Modern power transistors can control power levels reaching hundreds of kilowatts. Using power transistors as switches offers numerous advantages, primarily:
(1) Ease of turn-off and a requirement for fewer auxiliary components;
(2) Rapid switching capabilities, allowing for operation at very high frequencies;
(3) A wide range of available voltage ratings, spanning from 100V to 700V.
A few years ago, the switching capacity of transistors was below 10 kW. Today, they can control power levels up to several hundred kilowatts. This progress is largely due to the collaborative efforts of physicists, technicians, and circuit designers to enhance power transistor performance through measures such as:
(1) Increasing the effective chip area of ​​switching transistors;
(2) Simplifying manufacturing technologies;
(3) Employing transistor combinations, such as the Darlington configuration;
(4) Advancing base-drive technologies for high-power switching.

2. Transistor Power Switches Operating Directly on Rectified 380V Mains
Transistor combinations (such as Darlington pairs) and parallel connections are effective methods for increasing transistor switching capacity.
In such high-power circuits, wiring presents a major challenge. High switching speeds can generate significant interference voltages even across very short connecting leads.

3. High Performance Achieved through Simple and Optimized Base-Drive Circuits
Modern base-drive circuits not only drive the power transistor but also provide protection for it—a concept known as "decentralized protection" (as opposed to centralized protection). The functions of the integrated drive circuit include:
(1) turning the power switch on and off;
(2) monitoring the auxiliary power supply voltage;
(3) limiting the maximum and minimum pulse widths;
(4) thermal protection;
(5) monitoring the saturation voltage drop of the switch.