Almost every modern person has at least heard that transistors are widely used in various electronic and electrical devices. Experts in electronics know that transistors are divided into bipolar and field. The main difference between the two is that bipolar transistors are driven by a current that is supplied to their base, while the field ones are supplied by voltage, the potential of which is applied to the gate of these elements.
There is also another type of transistor that was developed in the late 70's. last century and is called IGBT. This semiconductor device combines the basic characteristics of a bipolar transistor and a field effect transistor: it is similar in structure to a bipolar device, but is voltage controlled. This interesting property is achieved due to the fact that the gate as a control electrode is made insulated.
IGBT structure
From the point of view of its internal structure, the IGBT is made as a composite structure and is a combination of a field effect transistor and a bipolar transistor. The bipolar part of the structure takes over the power functions, while the field element implements the control functions. The names of two electrodes are borrowed from the bipolar element: the collector and the emitter, and on the field - the control electrode is called the gate.
Both main blocks of the structure form a single whole and are interconnected as shown in Figure 1. It follows from it that the IGBT transistor can be considered a development of the well-known Darlington circuit, implemented from two bipolar transistors.
Benefits
The scheme of interaction of its main blocks used in IGBT elements allows eliminating one of the the main disadvantages of a powerful bipolar transistor: a relatively small gain in current. Thus, when constructing key elements, the required power of the control circuits is significantly reduced.
The use of a bipolar structure in an IGBT transistor as a force eliminates the saturation effect, which noticeably increases its response speed. At the same time, the maximum operating voltage increases and the on-state power loss decreases. The most advanced elements of this type switch currents of hundreds of amperes, and the operating voltage reaches several thousand volts at operating frequencies up to several tens of kHz.
Design and scope of IGBT transistor
In its design, as follows from Figure 2, the IGBT transistor has a traditional design, supports direct mounting on a radiator, and also does not require changes in the design and installation technology of power circuits electronics.
It goes without saying that IGBTs can be incorporated into modules. An example of one of them is shown in Figure 3.
The focus areas of IGBT applications are:
- sources of pulse type of power supply with direct current;
- electric drive control systems;
- sources of welding current.
Along with conventional and uninterruptible power supplies of various equipment, IGBT transistors are attractive for electric transport, because allow for high precision control of tractive effort and eliminate jerks typical of mechanically controlled systems when movement.