Power Transistors

Introduction

 

Power Transistors are electronics components that are use for the control and regulation of voltages and currents with high values. They are the basic components for the implementation of linear and switched mode power supplies, motor control circuits, automotive and aerospace systems, home appliances, and energy management systems

Why are Power Transistors Necessary?

Power Transistors are used to produce, convert, control and regulate high amounts of power output.Typical headphone amplifiers have a low output value (just a fraction of a watt). They are usually implemented with standard low power transistors.On the other hand, amplifiers with hundred-watt output power are used to ensure quality sound in large rooms or concert halls. These amplifiers operate with high-level currents and voltages (more than dozens of amperes and volts). The output stages of such amplifiers can be implemented only with power transistors.

Power Transistors are capable of providing high currents and high blocking voltages and therefore, high power. They can be classified into BJT (Bipolar Junction Transistors), MOSFET (Metal Oxide Semiconductor Field Effect Transistors), and devices such as IGBT (Insulated Gate Bipolar Transistors) that combine bipolar and MOS technologies.
The principle of operation behind high power transistors is conceptually the same as bipolar or MOS transistors. The main difference is that the active area of the power devices is distinctly higher, resulting in a much higher current handling capacity. For this reason, they have large packages.

Three Major Device Technologies

The above figure depicts the typical structure of BJT, MOSFET and IGBT devices.
For a BJT to maintain conduction, a high continuous current through the base region is required. This imposes the necessity of high power drive circuits.
MOSFETs and IGBTs are voltage-controlled devices. The IGBT has one more junction than the MOSFET, which allows for a higher blocking voltage but limits the switching frequency. In IGBTs, during conduction, the holes from the collector p+ region are injected into the n- region. The accumulated charge reduces IGBT's on-resistance and thus the collector-to-emitter voltage drop is also reduced.