Analog Electronics Problem Solving Series (Part 3): Becoming a Skilled Electronics Engineer

Previously, we brought you a summary of a series of difficult problems that are often encountered in analog electronics learning: Analog Electronics Troubleshooting Series (I): How much do you know about semiconductors and amplifiers?  Analog Electronics Troubleshooting Series (II): Things to know about analog circuit design issues . Today, we bring you Analog Electronics Troubleshooting Series 3 for everyone to learn.

101. What is the most widely used power amplifier circuit at present?

Answer: The most widely used power amplifier circuits at present are OTL and OCL circuits.

102.What is crossover distortion?

Answer: The transistor will only be turned on when |Ui|＞Uon. When the input signal Ui passes through zero before or after, the output signal will be distorted. This distortion is called crossover distortion.

103. How to eliminate crossover distortion?

Answer: In order to eliminate crossover distortion, a suitable static operating point should be set so that both transistors operate in critical conduction or micro-conduction state.

104. For an OCL power amplifier circuit, how do you estimate the maximum output power of the circuit when the power supply voltage and load resistance are known?

Answer: The maximum output power of the OCL power amplifier circuit:

105. For an OCL power amplifier circuit, how do you estimate the power provided by the circuit's power supply when the power supply voltage and load resistance are known?

A: The power provided by the power supply of the OCL power amplifier circuit is:

106. For the OTL power amplifier circuit, how to estimate the maximum output power of the circuit when the power supply voltage and load resistance are known?

Answer: The maximum output power of the OTL power amplifier circuit:

107. For an OTL power amplifier circuit, how do you estimate the power provided by the circuit's power supply when the power supply voltage and load resistance are known?

A: The power provided by the power supply of the OTL power amplifier circuit is:

108. What parameters should you pay special attention to when selecting transistors in power amplifier circuits?

Answer: When selecting transistors in power amplifier circuits, special attention should be paid to the following parameters: the maximum voltage drop that the transistor can withstand, the maximum collector current and the maximum power consumption.

109. What is the maximum undistorted output voltage of the power amplifier circuit?

Answer: The maximum undistorted output voltage amplitude of the power amplifier circuit is equal to the power supply voltage minus the saturation voltage drop of the transistor, that is: Uom = Vcc - UCES.

110. What is the maximum output power of a power amplifier circuit?

Answer: The maximum output power of a power amplifier circuit refers to the maximum AC power that can be obtained on the load when the input voltage is a sine wave and the output is basically undistorted. That is: Pom = Uo × Io.

111. What is the conversion efficiency of a power amplifier circuit?

Answer: The conversion efficiency of a power amplifier circuit refers to the ratio of the maximum output power to the power provided by the power supply, that is, η = Pom/Pv.

112. Please briefly describe the steps for analyzing a power amplifier circuit.

Answer: Since the input signal amplitude of the power amplifier circuit is large, the graphical method should be used for analysis. Generally, the analysis is carried out according to the following steps: ⑴ Calculate the amplitude Uom of the AC voltage that may be obtained on the load of the power amplifier circuit; ⑵ Calculate the maximum output power Pom of the circuit; ⑶ Calculate the average DC power Pv provided by the power supply; ⑷ Calculate the conversion efficiency η.

113. What is the primary breakdown of the power amplifier tube?

Answer: The primary breakdown of the power amplifier tube refers to the phenomenon that when the CE voltage of the transistor increases to a certain value, the collector current suddenly increases.

114. What is the secondary breakdown of the power amplifier tube?

Answer: The secondary breakdown of the power amplifier tube means that after the transistor breaks down once, if the collector current is not limited, the operating point of the transistor will change at a high speed, causing the current to surge and the tube voltage drop to decrease.

115. How to choose transistors in power amplifier circuits?

Answer: When selecting a transistor, the limit parameters should be UCEO＞2Vcc; ICM＞Vcc/RL; PCM＞0.2Pom.

116. When does a transistor dissipate the most power?

Answer: When Uom＝2Vcc/π≈0.6Vcc, PT = PTMAX, that is, the transistor dissipates the maximum power.

117. What is the zero drift phenomenon?

Answer: The phenomenon that the input voltage is zero but the output voltage is not zero and changes slowly is called zero drift.

118.What is temperature drift?

A: When the input voltage is zero, the change in semiconductor device parameters caused by temperature changes causes the output voltage to be non-zero and to change slowly. This phenomenon is called temperature drift. It is the main reason for zero-point drift.

119. What are the methods to suppress zero drift?

Answer: The methods to suppress zero drift are: ⑴ Introducing DC negative feedback into the circuit; ⑵ Using temperature compensation method and using thermistors to offset the changes of the amplifier tube; ⑶ Using "differential amplifier circuit".

120. What are the special problems of direct-coupled amplifier circuits? How to solve them?

A: The special problem of direct-coupled amplifier circuits is the existence of zero-point drift. The solution is to use differential amplifier circuits.

121. What is the function of the differential amplifier circuit?

Answer: The differential amplifier circuit can amplify the differential mode signal and suppress the common mode signal.

122. What is the relationship between common mode signals, zero drift and temperature drift?

A: Temperature drift is the main cause of zero drift, so generally speaking, zero drift refers to temperature drift. Temperature changes are actually equivalent to a common-mode signal for differential amplifier circuits.

123. What are the characteristics of the circuit structure of the differential amplifier circuit?

Answer: The differential amplifier circuit consists of two transistors, and the parameters of all components in the circuit are symmetrical.

124. What is a differential signal?

Answer: The differential signal is the difference between two input signals.