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| university:courses:electronics:electronics-lab-11 [07 Dec 2018 13:39] – [Discussion:] add Fritzing files Antoniu Miclaus | university:courses:electronics:electronics-lab-11 [25 Jun 2020 22:07] (current) – external edit 127.0.0.1 |
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| ====== Activity 11. The Emitter follower (BJT) ====== | ====== Activity: The Emitter follower (BJT) ====== |
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| ===== Objective: ===== | ===== Objective: ===== |
| ===== Hardware Setup: ===== | ===== Hardware Setup: ===== |
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| The waveform generator should be configured for a 1 KHz Sine wave with 4 volt amplitude and 0 offset. The Single ended input of scope channel 2 (2+) is used to measure the voltage at the emitter. The Scope configured with channel 1+ connected to display the AWG generator output. When measuring the input to output error, channel 2 of the scope should be connected to display 2+ and 2- differential. | The waveform generator should be configured for a 1 KHz Sine wave with 4 volt amplitude peak-to-peak and 0 offset. The Single ended input of scope channel 2 (2+) is used to measure the voltage at the emitter. The Scope configured with channel 1+ connected to display the AWG generator output. When measuring the input to output error, channel 2 of the scope should be connected to display 2+ and 2- differential. |
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| {{:university:courses:electronics:emit_flw-bb.png|}} | {{:university:courses:electronics:emit_flw-bb.png|}} |
| ===== Hardware Setup: ===== | ===== Hardware Setup: ===== |
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| The waveform generator should be configured for a 1 KHz Sine wave with 2 volt amplitude with the offset set equal to minus the V<sub>BE</sub> of Q<sub>1</sub> ( approximately -0.65V ). This injects a +/- 0.1mA (1V/10KΩ) current into Q<sub>1</sub>‘s emitter. Scope input 2+ measures the change in voltage seen at the emitter. | The waveform generator should be configured for a 1 KHz Sine wave with 2 volt amplitude peak-to-peak with the offset set equal to minus the V<sub>BE</sub> of Q<sub>1</sub> ( approximately -0.65V ). This injects a +/- 0.1mA (1V/10KΩ) current into Q<sub>1</sub>‘s emitter. Scope input 2+ measures the change in voltage seen at the emitter. |
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| {{:university:courses:electronics:out_imp_test-bb.png|}} | {{:university:courses:electronics:out_imp_test-bb.png|}} |
| <WRAP centeralign> Figure 12 Low offset follower Breadboard Circuit </WRAP> | <WRAP centeralign> Figure 12 Low offset follower Breadboard Circuit </WRAP> |
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| The waveform generator should be configured for a 1 KHz Sine wave with 2 volt amplitude with the offset set equal to 0. Scope input channel 2 is set to 500mV / Div. | The waveform generator should be configured for a 1 KHz Sine wave with 2 volt amplitude peak-to-peak with the offset set equal to 0. Scope input channel 2 is set to 500mV / Div. |
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| ===== Procedure: ===== | ===== Procedure: ===== |
| The concept in this circuit is that R<sub>2</sub> acts as current sense resistor. When the load current times R<sub>2</sub>, the sense voltage, reaches about 0.6 (for silicon transistors ) Q<sub>2</sub> begins to conduct and increases current in R<sub>1</sub> which limits the base drive to Q<sub>1</sub>reducing its output current. The maximum current from the circuit is reached when I<sub>L</sub>*R<sub>2</sub> = 0.6. This circuit can be used to protect amplifiers (including push pull amplifiers.), power supplies and other circuits; or it can be used as a constant current circuit. This is not a precision circuit; however it is a simple and effective circuit. | The concept in this circuit is that R<sub>2</sub> acts as current sense resistor. When the load current times R<sub>2</sub>, the sense voltage, reaches about 0.6 (for silicon transistors ) Q<sub>2</sub> begins to conduct and increases current in R<sub>1</sub> which limits the base drive to Q<sub>1</sub>reducing its output current. The maximum current from the circuit is reached when I<sub>L</sub>*R<sub>2</sub> = 0.6. This circuit can be used to protect amplifiers (including push pull amplifiers.), power supplies and other circuits; or it can be used as a constant current circuit. This is not a precision circuit; however it is a simple and effective circuit. |
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| | <WRAP round download> |
| **Resources:** | **Resources:** |
| * Fritzing files: [[ https://minhaskamal.github.io/DownGit/#/home?url=https://github.com/analogdevicesinc/education_tools/tree/master/m2k/fritzing/bjt_emitter_ff | bjt_emitter_ff]] | * Fritzing files: [[downgit>education_tools/tree/master/m2k/fritzing/bjt_emitter_ff_bb | bjt_emitter_ff_bb]] |
| | * LTspice files: [[downgit>education_tools/tree/master/m2k/ltspice/bjt_emitter_ff_ltspice | bjt_emitter_ff_ltspice]] |
| | </WRAP> |
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| **Return to Lab Activity [[university:courses:electronics:labs|Table of Contents]]** | **Return to Lab Activity [[university:courses:electronics:labs|Table of Contents]]** |
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