91Ó°ÊÓ

A class A transformer-coupled amplifier uses a \(25: 1\) transformer to drive a \(4-\Omega\) load. Calculate the effective ac load (seen by the transistor connected to the larger turns side of the transformer).

What turns ratio transformer is needed to couple to an \(8-\Omega\) load so that it appears as an \(8-\mathrm{k} \Omega\) effective load?

Calculate the transformer turns ratio required to connect four parallel \(16-\Omega\) speakers so that they appear as an \(8-\mathrm{k} \Omega\) effective load.

A transformer-coupled class A amplifier drives a \(16-\Omega\) speaker through a \(3.87: 1\) transformer. Using a power supply of \(V_{C C}=36 \mathrm{~V}\), the circuit delivers \(2 \mathrm{~W}\) to the load. Calculate: a. \(P(\) ac \()\) across transformer primary. b. \(V_{L}(\mathrm{ac})\). c. \(V(\mathrm{ac})\) at transformer primary. d. The rms values of load and primary current.

Draw the circuit diagram of a class A transformer-coupled amplifier using an \(n p n\) transistor.

Draw the circuit diagram of a class B npn push-pull power amplifier using transformercoupled input.

Calculate the efficiency of a class \(\mathrm{B}\) amplifier for a supply voltage of \(V_{C C}=22 \mathrm{~V}\) driving a 4- \(\Omega\) load with peak output voltages of: a. \(V_{L}(\mathrm{p})=20 \mathrm{~V}\). b. \(V_{L}(\mathrm{p})=4 \mathrm{~V}\)

Sketch the circuit diagram of a quasi-complementary amplifier, showing voltage waveforms in the circuit.

Calculate the harmonic distortion components for an output signal having fundamental amplitude of \(2.1 \mathrm{~V}\), second harmonic amplitude of \(0.3 \mathrm{~V}\), third harmonic component of \(0.1 \mathrm{~V}\), and fourth harmonic component of \(0.05 \mathrm{~V}\).

Determine the maximum dissipation allowed for a \(100-\mathrm{W}\) silicon transistor (rated at \(25^{\circ} \mathrm{C}\) ) for a derating factor of \(0.6 \mathrm{~W} /{ }^{\circ} \mathrm{C}\) at a case temperature of \(150^{\circ} \mathrm{C}\).