Power amplifier circuit

fighting

Power amplifier circuit [Copy link]

Test Questions

1. Choose the appropriate answer and fill in the blank. Just fill in A, B or C.

( 1) The maximum output power of a power amplifier circuit is the maximum power that can be obtained on the load when the input voltage is a sine wave and the output is basically undistorted .

A. AC power B. DC power C. Average power

( 2) The conversion efficiency of a power amplifier circuit refers to .

A. The ratio of output power to the power consumed by the transistor

B. Ratio of maximum output power to average power provided by the power supply

C. The ratio of the power consumed by the transistor to the average power provided by the power supply

( 3) In the OCL Class B power amplifier circuit, if the maximum output power is 1W, the maximum power consumption of the collector of the power amplifier tube in the circuit is approximately .

A．1W B．0.5WC．0.2W

( 4) When selecting transistors in power amplifier circuits, special attention should be paid to the following parameters .

A．β B．I_CM C．I_CBO

D．BU_CEO E．P_CM F．f_T

( 5) If the value of the transistor saturation voltage drop in the circuit shown in Figure T9.1 _is │UCES│ , then _the maximum output power POM = .

A． B． C．

Figure T9.1

Answer: ( 1) A (2) B (3) C (4) BDE (5) C　

2. The circuit is shown in Figure T9.2. It is known that the saturated tube voltage drop of _T1 and T2 _{is │UCES│} = 2V, and the DC power consumption can be ignored.

Figure T9.2

Answer the following questions:

( ₁ ) What are the functions of R3 , R4 _, and T3 _?

( 2) What are the maximum output power P _om that can be obtained on the load and the conversion efficiency η of the circuit?

( 3) Assume that the effective value of the maximum input voltage is 1V. In order to make the peak value of the maximum undistorted output voltage of the circuit reach 16V, how many kilo- ohms should _{the resistor} R6 be at least ?

exercise

9.1 Analyze whether the following statements are correct. Put a “√” in the brackets if they are correct and an “×” in the brackets if they are wrong .

( 1) In a power amplifier circuit, the greater the output power, the greater the power consumption of the power amplifier tube. ( )

( 2 ) The maximum output power of a power amplifier circuit refers to the maximum AC power that can be obtained on the load without distortion .

( 3) When the maximum output power of the OCL circuit is 1W, the maximum collector dissipation power of the power amplifier tube should be greater than 1W. ( )

( 4) The common point between power amplifier circuit, voltage amplifier circuit and current amplifier circuit is

1 ) Make the output voltage greater than the input voltage; ( )

2 ) Make the output current greater than the input current; ( )

3 ) Make the output power greater than the input power provided by the signal source . ( )

( 5) The difference between power amplifier circuit and voltage amplifier circuit is

1 ) The former has a higher power supply voltage than the latter; ( )

2 ) The former has a larger voltage amplification factor than the latter; ( )

3 ) The former is more efficient than the latter; ( )

4 ) Under the same power supply voltage, the maximum undistorted output voltage of the former is larger than that of the latter; ( )

( 6) The difference between a power amplifier circuit and a current amplifier circuit is

1 ) The former has a larger current amplification factor than the latter; ( )

2 ) The former is more efficient than the latter; ( )

3 ) Under the same power supply voltage, the output power of the former is greater than that of the latter. ( )

Solution: ( 1) × (2) √ (3) × (4) × × √

（5）× × √ √ （6）× √ √　

9.2 Given the circuit shown in Figure P9.2, the saturated tube voltage drop of tubes T1 _and T2 is _│UCES│＝_{3V ,} VCC＝15V , RL _＝ 8Ω. Choose the correct answer to fill in the blank.

1 ) The function of D1 and D2 tubes _in the _circuit is to eliminate .

A. Saturation distortion B. Cutoff distortion C. Crossover distortion

( 2) In static state, the transistor emitter potential is U _EQ .

A．＞0V B．＝0V C．＜0V

( 3) Maximum output power P _OM .

A．≈28W B．＝18W C．＝9W

( 4) When the input is a sine wave, if _R1 is poorly soldered, that is, open circuit, the output voltage will be.

A. Sine wave B. Only positive half wave C. Only negative half wave

( 5) If D1 is _poorly soldered, then T1 _tube .

A. May burn out due to excessive power consumptionB. Always saturatedC. Always cut off

Answer: ( 1) C (2) B (3) C (4) C (5) A

9.3 In the circuit shown in Figure P9.2, it is known that V _CC = 16V, R _L = 4Ω, the saturation tube voltage drop of T1 and T2 tubes │ _U CES _│ = _2V , and the input voltage is large enough. Question:

( 1) What are the maximum output power P _om and efficiency η ?

( 2) What is the maximum power consumption of the transistor _, PTmax ?

( 3) In order for the output power to reach P _om , what is the approximate effective value of the input voltage?

9.4 In the circuit shown in Figure P9.4, it is known that the forward voltage of the diode _{is UD} = 0.7V, _the │UBE│ when the transistor is turned on is 0.7V, and the static potential of the emitters of tubes _T2 and T4 _{is UEQ} = 0V.

Question:

( 1) What are the static potentials of the bases of tubes _T1 , T3 _, and T5 _?

( 2) Assume R2 = _10kΩ , R3 = 100Ω. If the quiescent current of the base of tubes T1 _and T3 _can be ignored, what is the quiescent current of the collector of tube T5? In quiescent _{state ,} uI = _?

( 3) If i _B1 > i _B3 in static state , which parameter should be adjusted to make i _B1 = i _B2 ? How to adjust it?

( 4) Can the number of diodes in the circuit be 1, 2, 3, or 4? Which one do you think is the most appropriate? Why?

9.5 In the circuit shown in Figure P9.4, it is known that the saturation tube voltage drop of tubes T2 and T4 is │ _U CES _│ = _2V , and the power supply current can be ignored in static state. What are the maximum output power P _om and efficiency η that can be obtained on the load?

9.6 In order to stabilize the output voltage and reduce nonlinear distortion, please introduce appropriate negative feedback in the circuit shown in Figure P9.4 through resistor _Rf ; _{and estimate the value of} Rf when the voltage gain is about 10 .

9.7 Estimate the maximum collector current, maximum tube voltage drop and maximum collector power consumption of tubes _T2 and T4 _in the circuit shown in Figure P9.4 .

9.8 In the circuit shown in Figure P9.8, it is known that V _CC = 15V, the saturation tube voltage drop of T1 and T2 tubes │ _U CES _│ = _2V , and the input voltage is large enough. Solution:

( 1) The effective value of the maximum undistorted output voltage;

( 2) The maximum value of the current on the load _resistor RL ;

( 3) Maximum output power P _om and efficiency η .

9.9 In the circuit shown in Figure P9.8, R4 and R5 can act as short-circuit protection. Question: When the output is short-circuited due to a fault, what are the maximum collector current and power consumption of the _{transistor ?}

9.10 In the circuit shown in Figure P9.10, it is known that V _CC = 15V, the saturation tube voltage drop of _T1 and T2 _tubes │ U _CES │ = 1V, the maximum output voltage amplitude of the integrated operational amplifier is ±13V, and the conduction voltage of the diode is 0.7V.

Figure P9.10

( 1) If the input voltage amplitude is large enough, what is the maximum output power of the circuit?

( 2) In order to increase the input resistance, stabilize the output voltage, and reduce nonlinear distortion, what kind of AC negative feedback should be introduced? Draw a diagram.

( 3) If U _i = 0.1 V, U _o = 5 V, then the value of the resistor in the feedback network is approximately

9.11 The OTL circuit is shown in Figure P9.11.

Figure P9.11

( 1) In order to maximize the maximum undistorted output voltage amplitude, what should be the emitter potential of T2 and T4 in static state? If it is not appropriate, which component parameter should generally _be adjusted _?

( 2) If the saturation tube voltage drop of tubes T2 _and T4 _│UCES│ = _3V , and the input voltage is large enough, what are the maximum output power Pom and efficiency _{η of the circuit?}

( 3) How should I _CM , U _{(BR) CEO} and PCM _be selected for _T2 and T4 _{tubes ?}

9.12 It is known that the saturated tube voltage drop of T1 and T2 tubes _in the _circuit shown in Figure P9.12 _{is │UCES│} ＝ 2V, and _the │UBE│ when turned on is │＝0.7V, and the input voltage is large enough.

Figure P9.12

( 1) What are the static potentials at points A, B, C, and D?

( 2) In order to ensure that tubes T2 _and T4 _work in the amplification state and the tube voltage drop │ U _CE │ ≥ 3V, what are the maximum output power P _om and efficiency η of the circuit?

9.13 Figure P9.13 shows two power amplifier circuits with bootstrapping. Explain the paths of the output loop current of the power amplifier tube during the positive and negative half cycles of the input signal, and indicate which components play a bootstrapping role .

Figure P9.13

9.14 LM1877N-9 is a 2-channel low-frequency power amplifier circuit, powered by a single power supply, with a peak- to-peak value of the maximum undistorted output voltage U _OPP = ( V _CC -6) V, and an open-loop voltage gain of 70 dB. Figure P9.14 shows a practical circuit composed of one channel in LM1877N-9, with a power supply voltage of 24 V. C ₁ ~ C ₃ can be regarded as a short circuit for AC signals; R ₃ and C ₄ play a phase compensation role, and the load can be regarded as 8Ω.

Figure P9.14

( 1) Static state u _P , u _N , , u _O respectively?

( 2) Assuming the input voltage is large enough, what are the maximum output power P _om and efficiency η of the circuit?

9.15 The circuit is shown in Figure 9.4.6. Answer the following questions:

（1） ≈？

( 2) If the peak-to-peak value of the maximum undistorted output voltage is 27V when VCC = 15V, what are the maximum output power _Pom and efficiency η of the _{circuit ?}

( 3) In order for the load to obtain maximum output power, what is the approximate effective value of the input voltage?

9.16 TDA1556 is a 2-channel BTL circuit. Figure P9.16 shows a practical circuit composed of one channel in TDA1556. It is known that V _CC = 15V and the maximum output voltage amplitude of the amplifier is 13V.

Figure P9.16

( 1) In order to maximize the maximum undistorted output voltage amplitude obtained on the load, what volts should the reference voltage U _{REF be? What volts are} u _O1 and u _O2 respectively in static state ?

( 2) If U _i is large enough, what are the maximum output power P _om and efficiency η of the circuit?

( 3) If the voltage gain of the circuit is 20, what is the approximate effective value of the input voltage in order for the load to obtain the maximum output power?

9.17 TDA1556 is a 2-channel BTL circuit. Figure P9.17 shows a practical circuit composed of one channel of TDA1556. It is known that V _CC = 15, and the maximum output voltage amplitude of the amplifier is 13V.