A class B complementary push-pull output stage is supplied from rails and drives a…

PHYSICS · Multi-part · Fermi University Physics · Electronics, Instrumentation & Communication · Semiconductor devices and analogue circuits · Semiconductor devices and analogue circuits

Inside the Instrument, Ch Multistage amplifiers, the Miller effect and output stages

Problem

A class B complementary push-pull output stage is supplied from rails ±VCC\pm V_{CC} and drives a resistive load RLR_L. Its output power is Pout(Vp)=Vp2/2RLP_{\rm out}(V_p) = V_p^2/2R_L and the power drawn from the supplies is PS(Vp)=2VCCVp/πRLP_S(V_p) = 2V_{CC}V_p/\pi R_L, where VpV_p is the peak output voltage. ((a)) Write PD(Vp)=PS(Vp)−Pout(Vp)P_D(V_p) = P_S(V_p) - P_{\rm out}(V_p) and find the value of VpV_p that maximises it. ((b)) Show that the maximum dissipation is PD,max⁡=2VCC2/π2RLP_{D,\max} = 2V_{CC}^2/\pi^2R_L. ((c)) For rails of ±20 V\pm20\,\mathrm{V} into RL=4 ΩR_L = 4\,\Omega, evaluate VpV_p at this maximum, its value as a percentage of the rail, PD,max⁡P_{D,\max}, and this operating point's output power as a percentage of the full-swing output power (Vp=VCCV_p = V_{CC}).

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