An all-npn Darlington output stage is shown in Fig. 5.42. For all devices V_BE(on)= 0.7 V, V_CE(sat)= 0.2 V, β_F= 100. The magnitude of the collector current in Q₃is 2 mA.

(a) If R_L = 8 Ω, calculate the maximum positive and negative limits of V_o.

(b) Calculate the power dissipated in the circuit for V_o = 0 V.

(c) Calculate the maximum average power that can be delivered to R_L = 8 Ω before clipping occurs and the corresponding efficiency of the complete circuit. Also calculate the maximum instantaneous power dissipated in each output transistor. Assume that feedback is used around the circuit so that V_o is approximately sinusoidal.

Figure 5.42:

Transcribed Image Text:

+12 V Q3 BIAS- 2 mA Q4 Q5 D3 D2 Vo D, RL Q2 Vị