N_BJT_N11

N_BJT_N11 - Analog Electronics

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1 Bipolar Junction Transistors (BJTs) (11)

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2 BIPOLAR JUNCTION TRANSISTORS (BJT’s) Page (397) 5.2.2 Graphical Representation of Transistor Characteristics it is sometimes useful to describe the transistor i-v characteristics graphically. Figure 5.16 shows the ic-v BE characteristic, which is the exponential relationship Figure 5.16 The i C v BE characteristic for an npn transistor.
3 BIPOLAR JUNCTION TRANSISTORS (BJT’s) 5.2.2 Graphical Representation of Transistor Characteristics . . Which is identical (except for the value of constant n) to the diode i-v relationship. The i C -v BE and i B -v BE characteristics are also exponential but with different scale currents: I S / α for i E , and I s / β for i B . Since the constant of the exponential characteristic, 1/ V T is quite high (≈ 40), the curve rises very sharply. For V BE smaller than about 0.5 V, the current is negligibly small. Also, over most of the normal current range v BE lies in the range of 0.6 to 0.8 V. Figure 5.16 The i C v BE characteristic for an npn transistor.

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4 BIPOLAR JUNCTION TRANSISTORS (BJT’s) 5.2.2 Graphical Representation of Transistor Characteristics . . In performing rapid first-order dc calculations we normally will assume that V BE = 0.7 V, which is similar to the approach used in the analysis of diode circuits (Chapter 3). For a pnp transistor, the i c -v EB characteristic will look identical to that of Fig. 5.16 with v BE replaced with v EB . Figure 5.16 The i C v BE characteristic for an npn transistor.
BIPOLAR JUNCTION TRANSISTORS (BJT’s) 5.2.2 Graphical Representation of Transistor Characteristics . . As in silicon diodes, the voltage across the emitter-base junction decreases by about 2 mV for each rise of 1°C in temperature, provided that the junction is operating at a constant current. Figure 5.17 illustrates this temperature dependence by depicting i C -v BE curves at three different temperatures for an npn transistor. Figure 5.17

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N_BJT_N11 - Analog Electronics

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