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Electronic Circuits - Part 2

The reader may wonder why the amplifier stages studied in previous chapters are not suited to high-power applications. Suppose we wish to deliver 1 W to an 8- speaker. Approximating the signal with a sinusoid of peak amplitude VP, we express the power absorbed by the speaker as: | Electronic Circuits Part 2 Teacher: Dr. LUU THE VINH Output Stages Chapter 13 & & Power Amplifiers The chapter outline is shown below. Basic Stages Emitter Follower Push−Pull Stage and Improved Variants Large-Signal Considerations Omission of PNP Transistor High-Fidelity Design Heat Dissipation Power Ratings Thermal Runaway Efficiency and PA Classes Efficiency of PAs Classes of PAs PA - Power Amplifier 13.1 General Considerations The reader may wonder why the amplifier stages studied in previous chapters are not suited to high-power applications. Suppose we wish to deliver 1 W to an 8 - speaker. Approximating the signal with a sinusoid of peak amplitude VP, we express the power absorbed by the speaker as: Where VP = p2 denotes the root mean square (rms) value of the sinusoid and RL represents the speaker impedance. For RL = 8 and Pout = 1 W, Also, the peak current flowing through the speaker is given by VP = 4V (13.1) Important observations The resistance that must be driven by the . | Electronic Circuits Part 2 Teacher: Dr. LUU THE VINH Output Stages Chapter 13 & & Power Amplifiers The chapter outline is shown below. Basic Stages Emitter Follower Push−Pull Stage and Improved Variants Large-Signal Considerations Omission of PNP Transistor High-Fidelity Design Heat Dissipation Power Ratings Thermal Runaway Efficiency and PA Classes Efficiency of PAs Classes of PAs PA - Power Amplifier 13.1 General Considerations The reader may wonder why the amplifier stages studied in previous chapters are not suited to high-power applications. Suppose we wish to deliver 1 W to an 8 - speaker. Approximating the signal with a sinusoid of peak amplitude VP, we express the power absorbed by the speaker as: Where VP = p2 denotes the root mean square (rms) value of the sinusoid and RL represents the speaker impedance. For RL = 8 and Pout = 1 W, Also, the peak current flowing through the speaker is given by VP = 4V (13.1) Important observations The resistance that must be driven by the amplifier is much lower than the typical values (hundreds to thousands of ohms) seen in previous chapters. The current levels involved in this example are much greater than the typical currents (milliamperes) encountered in previous circuits. The voltage swings delivered by the amplifier can hardly be viewed as “small” signals, requiring a good understanding of the large-signal behavior of the circuit. The power drawn from the supply voltage, at least 1W, is much higher than our typical values. A transistor carrying such high currents and sustaining several volts (e.g., between collector and emitter) dissipates a high power and, as a result, heats up. High-power transistors must therefore handle high currents and high temperature. 12.1 General Considerations Based on the above observations, we can predict the parameters of interest in the design of power stages: (1) “Distortion,” i.e., the nonlinearity resulting from large-signal operation. A high-quality audio amplifier must achieve a very