Page 47 - Power Electronics Handbook

40 Power semiconductor devices

n- epitaxy n- epitaxy

Polysilicon gale Sillcon dioxlde

_I

Gate

Figure 1.22 The Insulated Gate Bipolar Transistor: (a) construction; (b) simplified equivalent
circuit; (c) symbol

base and by adding an n+ buffer layer, which reduce the gain of the p-n-p,
and by reducing the value of rb which reduces the gain of the parasitic n-p-n
device.

1.8 Power Darlington

One of the disadvantages of using power transistors is their low gain at high
current levels, which requires a large base current, placing stringent
requirements on the base drive circuitry. This is one of the reasons why
thyristors, which need a fraction of the gate power for turn-on, are so
popular. The power Darlington, named after its inventor, also overcomes
this disadvantage by using a combination of two transistors, one to provide