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university:courses:electronics:electronics-lab-8 [28 Oct 2012 19:32] – created Doug Merceruniversity:courses:electronics:electronics-lab-8 [23 Aug 2019 12:53] – Antoniu Miclaus
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-====== Activity 8. Stabilized current source (BJT) ======+====== Activity: Stabilized current source (BJT) ======
  
 ===== Objective: ===== ===== Objective: =====
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 ===== Materials: ===== ===== Materials: =====
  
-Analog Discovery Lab hardware\\+ADALM2000 Active Learning Module\\
 Solder-less breadboard\\ Solder-less breadboard\\
 1 - 2.2KΩ Resistor ( or any similar value )\\ 1 - 2.2KΩ Resistor ( or any similar value )\\
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 ===== Hardware Setup: ===== ===== Hardware Setup: =====
  
-The waveform generator should be configured for a 1 KHz triangle wave with 1.5 volt amplitude and 1.5V offset. The input of scope channel 2 (2+) is used to measure the stabilized output current at the collector of Q2.+{{:university:courses:electronics:bjt_stabilized_cs-bb.png|}} 
 + 
 +<WRAP centeralign> Figure 2 Stabilized current source Breadboard Circuit </WRAP> 
 + 
 +The waveform generator should be configured for a 1 KHz triangle wave with 3 volt amplitude peak-to-peak and 1.5V offset. The input of scope channel 2 (2+) is used to measure the stabilized output current at the collector of Q2.
  
 ===== Procedure: ===== ===== Procedure: =====
  
 The zero gain amplifier can be used to create a stabilized current source. Because the voltage seen at the collector of transistor Q<sub>1</sub> is now more constant with changes in the input supply voltage as represented by AWG1, it can be used as the base voltage of Q<sub>2</sub> to produce a much more constant current in transistor Q<sub>2</sub>. The zero gain amplifier can be used to create a stabilized current source. Because the voltage seen at the collector of transistor Q<sub>1</sub> is now more constant with changes in the input supply voltage as represented by AWG1, it can be used as the base voltage of Q<sub>2</sub> to produce a much more constant current in transistor Q<sub>2</sub>.
 +
 +<WRAP centeralign>{{:university:courses:electronics:bjt_stabilized_cs-wav.png?500|}}</WRAP>
 +
 +<WRAP centeralign> Figure 3 Q<sub>2</sub> collector voltage vs. W1 voltage </WRAP>
 +
 +<WRAP centeralign>{{:university:courses:electronics:bjt_stabilized_cs-wav2.png?500|}}</WRAP>
 +
 +<WRAP centeralign> Figure 4 Q<sub>2</sub> collector current vs. W1 voltage Scopy plot </WRAP>
  
 {{ :university:courses:electronics:a8_f2.png?500 |}} {{ :university:courses:electronics:a8_f2.png?500 |}}
  
-<WRAP centeralign> Figure 2 Q<sub>2</sub> collector current vs. W1 voltage </WRAP>+<WRAP centeralign> Figure 4 Q<sub>2</sub> collector current vs. W1 voltage Excel plot</WRAP> 
 + 
 +**Resources:** 
 +  * LTSpice files: [[ https://minhaskamal.github.io/DownGit/#/home?url=https://github.com/analogdevicesinc/education_tools/tree/master/m2k/ltspice/stabil_csource_ltspice | stabil_csource_ltspice]]
  
 ===== Questions: ===== ===== Questions: =====
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 Based on the delta V<sub>BE</sub> of Q<sub>1</sub> and Q<sub>2</sub>, at what input and output current would the gain be zero for different values of R<sub>2</sub>? Based on the delta V<sub>BE</sub> of Q<sub>1</sub> and Q<sub>2</sub>, at what input and output current would the gain be zero for different values of R<sub>2</sub>?
  
-An exercise for the student is to plot the "stabilized" output current for all the various combinations of Q<sub>1</sub> and Q<sub>2</sub> from the available inventory of transistors. Why does it vary and by how much?+An exercise for the reader is to plot the "stabilized" output current for all the various combinations of Q<sub>1</sub> and Q<sub>2</sub> from the available inventory of transistors. Why does it vary and by how much?
 The output of the simple peaking current source is always less than the input current at the peak by a substantial fraction. What is that fraction and why? The output of the simple peaking current source is always less than the input current at the peak by a substantial fraction. What is that fraction and why?
  
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 The output current has a narrow peak. How could multiple copies of the peaking current source be combined to produce a much wider, flatter peak?  The output current has a narrow peak. How could multiple copies of the peaking current source be combined to produce a much wider, flatter peak? 
  
 +<WRAP round download>
 +**Resources:**
 +  * Fritzing files: [[ https://minhaskamal.github.io/DownGit/#/home?url=https://github.com/analogdevicesinc/education_tools/tree/master/m2k/fritzing/bjt_stab_curr_source_bb | bjt_stab_curr_source_bb]]
 +  * LTspice files: [[ https://minhaskamal.github.io/DownGit/#/home?url=https://github.com/analogdevicesinc/education_tools/tree/master/m2k/ltspice/bjt_stab_curr_source_ltspice | bjt_stab_curr_source_ltspice]]
 +</WRAP>
 +
 +**Return to Lab Activity [[university:courses:electronics:labs|Table of Contents]]**
  
university/courses/electronics/electronics-lab-8.txt · Last modified: 25 Jun 2020 22:07 by 127.0.0.1

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