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308 Chapter Four

Figure 4.20 Characteristic
curve for a semiconductor di-
ode.

V DC /V pk

The rectification efficiency, (in percen'x is given by:
%
100V DC /V pk
%

Bipolar Transistors

The following several formulas are relevant tmbipolar transis-
torsł botà the NPN type and the PNP type.

Static forward currenŁ transfer ratio
Assume the collector voltage, V , in a common-emitter circuit
c
(Fig. 4.21) is constant. Let I represent the collector current (in
c
ampereX let I represent the base current (in ampere0. Then
b
the static forwarS current transfer ratià, H FE , is given by:
H I /I
FE b

Dynamic basł resistancł

Assume the collector voltage, V , is constant. Let V represent
c
b
the base voltage (in voltX let I represent the base current (in
b
ampere0. Then the dynamic base resistanceł R (in ohm0, is:
b
R dV /dI b
b
b