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| university:courses:engineering_discovery:lab_11 [05 Oct 2016 23:09] – [Procedure] Jonathan Pearson | university:courses:engineering_discovery:lab_11 [19 Oct 2016 21:03] – [Objective] Jonathan Pearson |
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| The current gain and low output impedance of the emitter-follower amplifier make it ideal for driving low impedance loads, which may be DC- or AC-coupled. Many amplifiers are designed with emitter-follower output stages placed after voltage gain stages. In this lab we design, build, and evaluate a single Class A emitter-follower amplifier, then place it after the CE amplifier used in the Class A NPN Common-Emitter Amplifier lab in a DC-coupled fashion to illustrate how it can be used to drive an AC-coupled load much heavier than the 1 KΩ load used in that lab, and that it eliminates the gain loss due to the loading of the high output resistance of the CE stage. An example of how an emitter-follower stage can be added to an operational amplifier "inside the loop" to drive a low impedance loudspeaker is shown in the "Audio Amplifier with Electret Microphone" lab. | The current gain and low output impedance of the emitter-follower amplifier make it ideal for driving low impedance loads, which may be DC- or AC-coupled. Many amplifiers are designed with emitter-follower output stages placed after voltage gain stages. In this lab we design, build, and evaluate a single Class A emitter-follower amplifier, then place it after the CE amplifier used in the Class A NPN Common-Emitter Amplifier lab in a DC-coupled fashion to illustrate how it can be used to drive an AC-coupled load much heavier than the 1 KΩ load used in that lab, and that it eliminates the gain loss due to the loading of the high output resistance of the CE stage. An example of how an emitter-follower stage can be added to an operational amplifier "inside the loop" to drive a low impedance loudspeaker is shown in the "Audio Amplifier with Electret Microphone" lab. |
| ==== Objective ==== | ==== Objective ==== |
| To design, build, and test an emitter-follower amplifier using a 2N3904 NPN transistor, with an input resistance of at least 1 KΩ that is capable of driving an AC-coupled 47 Ω load with a 2 V<sub>P-P</sub> sine wave. To increase the load to 10 Ω and observe that this heavier load can still be driven, limited by the available current. To verify that the amplifier has approximately unity gain and that the Q-point is close to its designed value. To observe the buffering effect of the emitter follower and show how output loading is minimal as compared with a CE amplifier. To understand and be able to calculate emitter-follower amplifier voltage gain, power gain, efficiency, and power dissipation. To append the emitter-follower stage to the output of the CE amplifier designed in the "Class A NPN Common-Emitter Amplifier" lab in a DC-coupled fashion to show how buffers are added to voltage gain stages in order to drive low impedance loads. Following completion of this lab you should be able to explain the basic operation of an emitter-follower amplifier, explain how negative feedback stabilizes the gain of a common-emitter amplifier, explain why output loading does not affect an emitter-follower amplifier nearly as much as a CE amplifier, and calculate the amplifier voltage gain, power gain, efficiency, and power dissipation of a Class A emitter-follower amplifier. | To design, build, and test an emitter-follower amplifier using a 2N3904 NPN transistor, with an input resistance of at least 1 KΩ that is capable of driving an AC-coupled 47 Ω load with a 1 V<sub>P-P</sub> sine wave. To increase the load to 10 Ω and observe that this heavier load can still be driven, limited by the available current. To verify that the amplifier has approximately unity gain and that the Q-point is close to its designed value. To observe the buffering effect of the emitter follower and show how output loading is minimal as compared with a CE amplifier. To understand and be able to calculate emitter-follower amplifier voltage gain, power gain, efficiency, and power dissipation. To append the emitter-follower stage to the output of the CE amplifier designed in the "Class A NPN Common-Emitter Amplifier" lab in a DC-coupled fashion to show how buffers are added to voltage gain stages in order to drive low impedance loads. Following completion of this lab you should be able to explain the basic operation of an emitter-follower amplifier, explain how negative feedback stabilizes the gain of a common-emitter amplifier, explain why output loading does not affect an emitter-follower amplifier nearly as much as a CE amplifier, and calculate the amplifier voltage gain, power gain, efficiency, and power dissipation of a Class A emitter-follower amplifier. |
| ==== Materials and Apparatus ==== | ==== Materials and Apparatus ==== |
| * Data sheet handout for the 2N3904 NPN transistor | * Data sheet handout for the 2N3904 NPN transistor |
| - Run PixelPulse and plug in the M1K using the supplied USB cable | - Run PixelPulse and plug in the M1K using the supplied USB cable |
| - Update M1K firmware, if necessary | - Update M1K firmware, if necessary |
| | - Disable “Repeated Sweep” mode; waveforms can be paused for analysis |
| - Set up the M1K to source voltage/measure current on Channel A and measure voltage on Channel B | - Set up the M1K to source voltage/measure current on Channel A and measure voltage on Channel B |
| - Set up Channel A source waveform for a 100 Hz “Sine” output that swings between 2.0 V and of 4.0 V | - Set up Channel A source waveform for a 100 Hz “Sine” output that swings between 2.0 V and of 4.0 V |
