Chapter 4

Q. 4.7

In the triode amplifier of Fig. 4-14, V_{GG} = 4  \text{V},  V_{PP} = 300  \text{V},  R_L = 10  kΩ, and R_G = 2  kΩ. The plate characteristics for the triode are given by Fig. 4-13(b).    (a) Draw the dc load line; then determine the quiescent values (b) I_{GQ},   (c) V_{GQ},   (d) I_{PQ}, and (e) V_{PQ}.



Verified Solution

(a)   For the given values, the dc load line (4.11) has the i_P intercept
i_P = \frac{V_{PP}}{R_L}  –  \frac{v_P}{R_L}          (4.11)
\frac{V_{PP}}{R_L} = \frac{300}{10  ×  10^3} = 30  \text{mA}

and the v_P intercept V_{PP} = 300  \text{V}. These intercepts have been utilized to draw the dc load line on the plate characteristics of Fig. 4-13(b).

(b) Since the polarity of V_{GG} is such that v_G is negative, negligible grid current will flow (I_{GQ} ≈ 0).

(c) For negligible grid current, (4.10) evaluated at the Q point yields V_{GQ} = -V_{GG} = -4  \text{V}.
I_{G} = -\frac{V_{GG}}{R_G}  –  \frac{v_G}{R_G}          (4.10)

(d) The quiescent plate current is read as the projection of Q_n onto the i_P axis of Fig. 4-13(b) and is I_{PQ} = 8  \text{mA}.

(e) Projection of Q_n onto the v_P axis of Fig. 4-13(b) gives V_{PQ} = 220  \text{V}.