EE PRO for TI - 89, 92 Plus
Equations - Class A, B, C Amplifiers
118
Pdc
K
ax VCC
= ⋅ ⋅
⋅
2
Im
π
Eq. 29.4.3
Pdc
K VCC
R
= ⋅ ⋅
⋅
2
2
π
Eq. 29.4.4
The efficiency of power conversion
ζζ
is given by the fifth and sixth equations. The power dissipated by the circuit
Pd is computed in the seventh equation. The eighth equation calculates the voltage V1 across a tuned RLC circuit in
terms of the transconductance gm, load resistance Rl, and output conductance hOE. The final equation calculates
the average collector current IC for a half-sine wave from gm, hOE, Rl and the amplitude of the voltage Vm.
ζ =
Po
Pdc
Eq. 29.4.5
ζ π
= ⋅
K
4
Eq. 29.4.6
Pd
VCC
R
K
K
= ⋅
⋅
⋅
−
⋅
F
HG
I
KJ
2
4
2
2
π
π
Eq. 29.4.7
V
gm Rl Vm
hOE Rl
1
2
2
1
1
2
=
⋅ ⋅
⋅
+
⋅
F
H
G
G
G
I
K
J
J
J
Eq. 29.4.8
IC
gm Vm
hOE Rl
=
⋅
⋅
+
⋅
F
H
G
G
G
I
K
J
J
J
π
1
1
2
Eq. 29.4.9
Example 29.4 -
A Class B amplifier provides 5 W to an effective load of 50
Ω
. The collector voltage is 25 V. If
the peak current is 500 mA, find the average DC current and the efficiency of power conversion.
Input variables
Computed results
Solution -
Use the first, second, fourth and fifth equations to compute the solution for this problem.
Select these by highlighting each equation and pressing the
¸
key. Press
„
to display the input
screen, enter all the known variables and press
„
to solve the equation. The computed results are shown
in the screen displays above.
-PQYP8COCZ
AO#
2Q
A9
4
A
Ω
8%%
A8
%QORWVGFFE
A#
-
ζ
2FE
A9