2-85. Figure 2-19 is not just the basic transistor amplifier as shown in Figure 2-14, but a
class A amplifier configured as a CE using fixed bias. From Figure 2-19 you should be
able to conclude the following about the amplifier:
It is thermally unstable because of its fixed bias.
It has low efficiency but good fidelity because of its class A operation.
It has good voltage, current, and power gain because it is configured as a CE.
The type of bias, class of operation, and circuit configuration are all clues to the function
and possible application of the amplifier.
2-86. Transistors, like electron tubes, are available in a large variety of shapes and sizes
and each with its own unique characteristics. The characteristics for each of these
transistors are usually presented on SPECIFICATION SHEETS or they may be included in
transistor manuals. Although many properties of a transistor could be specified on these
sheets, manufacturers list only some of them. The specifications listed vary with different
manufacturers, the type of transistor, and the application of the transistor. The
specifications usually cover the following items.
A general description of the transistor, includes the following:
The kind of transistor. This covers the material used (such as germanium or
silicon, the type of transistor [NPN or PNP], and the construction of the
transistor [whether alloy junction, grown, diffused junction, and so forth]).
Some of the common applications for the transistor (such as audio amplifier,
General sales features (such as size and packaging [mechanical data]).
TRANSISTOR ABSOLUTE MAXIMUM RATINGS
2-88. The "Absolute Maximum Ratings" of the transistor are the direct voltage and
current values that if exceeded in operation may result in transistor failure. Maximum
ratings usually include collector-to-base voltage, emitter-to-base voltage, collector current,
TRANSISTOR TYPICAL OPERATING VALUES
2-89. These values are presented only as a guide. The values vary widely and are
dependent upon operating voltages and also upon which element is common in the circuit.
The values listed may include collector-emitter voltage, collector current, input resistance,
load resistance, current-transfer ratio (another name for alpha or beta), and collector cutoff
current, which is leakage current from collector to base when no emitter current is applied.
Transistor characteristic curves may also be included. A transistor characteristic curve is a
graph plotting the relationship between currents and voltages in a circuit. More than one
curve on a graph is called a "family of curves."
23 June 2005