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--- university:courses:electronics:electronics-lab-3 [26 Oct 2012 21:12] – created Doug Mercer
+++ university:courses:electronics:electronics-lab-3 [25 Jun 2020 22:07] (current) – external edit 127.0.0.1
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-====== Activity 3. The BJT connected as a diode =====
+====== Activity: The BJT connected as a diode =====
 ===== Objective: =====
@@ Line 6: / Line 6: @@
 ===== Materials: =====
-Analog Discovery Lab Hardware\\
+ADALM2000 Active Learning Module\\
 Solder-less Breadboard\\
 - 1KΩ Resistor (or any similar value)\\
@@ Line 13: / Line 13: @@
 ===== Directions: =====
-The current vs. voltage characteristics of the base-emitter junction of an NPN transistor can be measured using the Discovery Lab hardware and the following connections. Set up the breadboard with waveform generator, W1, attached to one end of resistor R<sub>1</sub>. Also connect scope input 2+ here. Connect the base and collector of Q<sub>1</sub> to the opposite end of R<sub>1</sub> as shown in the diagram. The emitter of Q<sub>1</sub> is connected to ground. Connect scope input 2- and scope input 1+ to the base - collector node of Q<sub>1</sub>. (Scope input 1- can be optionally grounded as well).
+The current vs. voltage characteristics of the base-emitter junction of an NPN transistor can be measured using the ADALM2000 Lab hardware and the following connections. Set up the breadboard with waveform generator, W1, attached to one end of resistor R<sub>1</sub>. Also connect scope input 2+ here. Connect the base and collector of Q<sub>1</sub> to the opposite end of R<sub>1</sub> as shown in the diagram. The emitter of Q<sub>1</sub> is connected to ground. Connect scope input 2- and scope input 1+ to the base - collector node of Q<sub>1</sub>. (Scope input 1- can be optionally grounded as well).
 {{ :university:courses:electronics:a3_f1.png?500 |}}
@@ Line 21: / Line 21: @@
 ===== Hardware Setup: =====
-The waveform generator should be configured for a 100 Hz triangle wave with 3 volt amplitude and 0 offset. The differential scope channel 2 (2+, 2-) measures the current in the resistor (and in the transistor). Scope channel 1 (1+) is connected to measure the voltage across the transistor. The current flowing through the transistor, is the voltage difference 1+ and 1- divided by the resistor value (1KΩ).
+The waveform generator should be configured for a 100 Hz triangle wave with 6 volt amplitude peak-to-peak and 0 offset. The differential scope channel 2 (2+, 2-) measures the current in the resistor (and in the transistor). Scope channel 1 (1+) is connected to measure the voltage across the diode connected transistor. The current flowing through the transistor, is the voltage difference 2+ and 2- (which is the channel 2 voltage) divided by the resistor value (1KΩ).
+{{ :university:courses:electronics:npn_diode-bb.png |}}
+<WRAP centeralign> Figure 2 NPN diode breadboard circuit </WRAP>
 ===== Procedure: =====
 Load the captured data in to a spreadsheet program like Excel and calculate the current. Plot the current vs. the voltage across the transistor (V<sub>BE</sub>). No current flows in the reverse direction. In the forward conduction region, the voltage, current relationship is logarithmic. If the current is plotted on a log scale the line should be straight.
+{{:university:courses:electronics:npn_diode_c_vs_v-wav.png|}}
+<WRAP centeralign> Figure 3 NPN diode XY plot</WRAP>
+{{ :university:courses:electronics:npn_diode-wav.png |}}
+<WRAP centeralign> Figure 4 NPN diode waveform </WRAP>
 ===== Questions: =====
@@ Line 41: / Line 51: @@
 ===== Directions: =====
-Set up the breadboard with the waveform generator output attached to one end of the series connected resistor 100? R<sub>1</sub> and base and collector of Q<sub>1</sub> as shown in figure 2. The emitter is connected to the negative 5 Volt fixed power supply. Scope channel 1 (1+) is connected to the base - collector node while 1- is connected to the emitter node. Scope channel 2 measures the voltage across R<sub>1</sub> and thus the current through Q<sub>1</sub>. The PNP 2N3906 is chosen over the NPN 2N3904 because the PNP emitter base breakdown voltage is less than the +10 V max that  can be generated using Discovery while the NPN's is likely to be higher than 10 V.
+Set up the breadboard with the waveform generator output attached to one end of the series connected resistor 100Ω R<sub>1</sub> and base and collector of Q<sub>1</sub> as shown in figure 2. The emitter is connected to the negative 5 Volt fixed power supply. Scope channel 1 (1+) is connected to the base - collector node while 1- is connected to the emitter node. Scope channel 2 measures the voltage across R<sub>1</sub> and thus the current through Q<sub>1</sub>. The PNP 2N3906 is chosen over the NPN 2N3904 because the PNP emitter base breakdown voltage is less than the +10 V max that  can be generated using ADALM2000 while the NPN's is likely to be higher than 10 V.
 {{ :university:courses:electronics:a3_f2.png?500 |}}
+<WRAP centeralign> Figure 5 PNP Emitter Base Reverse breakdown configuration </WRAP>
-<WRAP centeralign> Figure 2 PNP Emitter Base Reverse breakdown configuration </WRAP>
 ===== Hardware Setup: =====
-The waveform generator should be configured for a 100 Hz triangle wave with 5 volt amplitude and 0 volt offset. Scope channel 1 (1+) is used to measure the voltage across the transistor. The setup should be configured with channel 2 connected across resistor R<sub>1</sub> (2+, 2-). Both channels should be set to 1 V per division. The current flowing through the transistor is the voltage difference between 2+ and 2- divided by the resistor value (100Ω).
+The waveform generator should be configured for a 100 Hz triangle wave with 10 volt amplitude peak-to-peak  and 0 volt offset. Scope channel 1 (1+) is used to measure the voltage across the transistor. The setup should be configured with channel 2 connected across resistor R<sub>1</sub> (2+, 2-). Both channels should be set to 1 V per division. The current flowing through the transistor is the voltage difference between 2+ and 2- divided by the resistor value (100Ω).
+{{ :university:courses:electronics:pnp_emitter-bb.png |}}
+<WRAP centeralign> Figure 6 PNP Emitter breadboard circuit </WRAP>
 ===== Procedure: =====
 The Lab hardware power supplies limits the maximum voltage available to less than 10 volts. The emitter base reverse breakdown voltage of many transistors is larger than this. In the configuration shown voltages between 0 volts and 10 volts ( W1 peak to peak swing ) can be measured.
+{{ :university:courses:electronics:pnp_emitter-wav.png |}}
+<WRAP centeralign> Figure 7 PNP Emitter waveform </WRAP>
 Capture the scope waveforms and export them into a spreadsheet program such as Excel. For the 2N3906 PNP used in the example, the breakdown voltage of the emitter base junction is around 8.5 volts.
@@ Line 62: / Line 77: @@
 Now connect the collector to the emitter. How does this change the breakdown voltage?
-Try measuring the NPN 2N3904 emitter base reverse breakdown voltage. You can also check the emitter base breakdown voltage for the two power transistors, TIP31 and TIP32, which are included in the Analog Parts Kit. Are they higher or lower than the PNP 2N3906 and is it lower than the +10 volts you can measure with this setup? If it is higher what could you add to the setup to allow you to measure higher breakdown voltages?
+Try measuring the NPN 2N3904 emitter base reverse breakdown voltage. You can also check the emitter base breakdown voltage for the two power transistors, TIP31 and TIP32, which are included in the ADALP2000 Analog Parts Kit. Are they higher or lower than the PNP 2N3906 and is it lower than the +10 volts you can measure with this setup? If it is higher what could you add to the setup to allow you to measure higher breakdown voltages?
 ====== Lowering the effective forward voltage of the diode ======
@@ Line 78: / Line 93: @@
 ===== Directions: =====
-Set up the breadboard with waveform generator W1 attached to one end of the series connected resistor R<sub>1</sub> and collector of NPN Q<sub>1</sub> and the base of PNP Q<sub>2</sub> as shown in the diagram. The emitter of Q<sub>1</sub> is connected to ground. The collector of Q<sub>2</sub>is connected to Vn (5V). The first end of Resistor R<sub>2</sub> is connected to Vp (5V). The second end of R<sub>2</sub> is connected to the base of Q<sub>1</sub> and the emitter of Q<sub>2</sub>. Single ended input of scope channel 2 (2+) is connected to the collector of Q<sub>1</sub>.
+Set up the breadboard with waveform generator W1 attached to one end of the series connected resistor R<sub>1</sub> and collector of NPN Q<sub>1</sub> and the base of PNP Q<sub>2</sub> as shown in the diagram. The emitter of Q<sub>1</sub> is connected to ground. The collector of Q<sub>2</sub>is connected to Vn (-5V). The first end of Resistor R<sub>2</sub> is connected to Vp (+5V). The second end of R<sub>2</sub> is connected to the base of Q<sub>1</sub> and the emitter of Q<sub>2</sub>. Single ended input of scope channel 2 (2+) is connected to the collector of Q<sub>1</sub>.
 {{ :university:courses:electronics:a3_f3.png?500 |}}
-<WRAP centeralign> Figure 3 Configuration to lower effective forward voltage drop of diode </WRAP>
+<WRAP centeralign> Figure 8 Configuration to lower effective forward voltage drop of diode </WRAP>
 ===== Hardware Setup: =====
-The waveform generator should be configured for a 100 Hz triangle wave with 4 volt amplitude and 2 volt offset. Scope channel 2 (2+) is used to measure the voltage across the transistor. The current flowing through the transistor, is the voltage difference between scope input 1+ and 1- divided by the resistor value (1K?).
+The waveform generator should be configured for a 100 Hz triangle wave with 8 volt amplitude peak-to-peak and 2 volt offset. Scope channel 2 (2+) is used to measure the voltage across the transistor. The current flowing through the transistor, is the voltage difference between scope input 1+ and 1- divided by the resistor value (1K?).
+{{ :university:courses:electronics:loweff_vdrop-bb.png |}}
+<WRAP centeralign> Figure 9 Lower effective forward voltage drop of diode - breadboard circuit </WRAP>
 ===== Procedure: =====
 The turn on voltage of the "diode" is now about 100mV compared to 650mV for the simple diode connection in the first example. Plot the V<sub>CE</sub> of Q<sub>1</sub> as W1 is swept.
+{{ :university:courses:electronics:loweff_vdrop-wav.png |}}
+<WRAP centeralign> Figure 10 Lower effective forward voltage drop of diode - waveform </WRAP>
 ===== Questions: =====
@@ Line 116: / Line 137: @@
 {{ :university:courses:electronics:a3_f4.png?500 |}}
-<WRAP centeralign> Figure 4 V<sub>BE</sub> Multiplier configuration </WRAP>
+<WRAP centeralign> Figure 11 V<sub>BE</sub> Multiplier configuration </WRAP>
 ===== Hardware Setup: =====
-The waveform generator should be configured for a 100 Hz triangle wave with 2 volt amplitude and 2V offset. The Single ended input of scope channel 2+ is used to measure the voltage across the transistor. The setup should be configured with channel 1+ connected to display the output of generator W1 and channel 2+ connected to display the collector voltage of Q<sub>1</sub>. The current flowing through the transistor, is the voltage difference between the W1 measured by scope input 1+ and scope input 2+ divided by the resistor value (1KΩ).
+The waveform generator should be configured for a 100 Hz triangle wave with 4 volt amplitude peak-to-peak and 2V offset. The Single ended input of scope channel 2+ is used to measure the voltage across the transistor. The setup should be configured with channel 1+ connected to display the output of generator W1 and channel 2+ connected to display the collector voltage of Q<sub>1</sub>. The current flowing through the transistor, is the voltage difference between the W1 measured by scope input 1+ and scope input 2+ divided by the resistor value (1KΩ).
+{{ :university:courses:electronics:vbe_multiplier-bb.png |}}
+<WRAP centeralign> Figure 12 V<sub>BE</sub> Multiplier breadboard circuit </WRAP>
 ===== Procedure: =====
@@ Line 126: / Line 150: @@
 Starting with the potentiometer R<sub>3</sub> set at the middle of its range the voltage at the collector of Q<sub>2</sub> should be about 2 times V<sub>BE</sub>. With R<sub>3</sub> set to its minimum the voltage at the collector should be 9/2 (or 4.5) times V<sub>BE</sub>. With R<sub>3</sub> set to its maximum the voltage at the collector should be 9/7 times V<sub>BE</sub>.
+{{ :university:courses:electronics:vbe_multiplier-wav.png |}}
+<WRAP centeralign> Figure 13 V<sub>BE</sub> Multiplier breadboard waveform </WRAP>
+<WRAP round download>
+**Resources:**
+  * Fritzing files: [[downgit>education_tools/tree/master/m2k/fritzing/bjt_diode_bb | bjt_diode_bb]]
+  * LTSpice files: [[downgit>education_tools/tree/master/m2k/ltspice/bjt_diode_ltspice | bjt_diode_ltspice]]
+</WRAP>
 ===== Questions: =====
 How does the voltage vs current characteristics of this V<sub>BE</sub> multiplier compare to those of a simple diode connected transistor?
-Aside from the position of the pot wiper, do the values of R<sub>2</sub>, R<sub>3</sub> and R<sub>4</sub> effect the shape of the I vs V curve? To arrive an answer try using values much larger and much smaller than those listed above.
+Aside from the position of the pot wiper, do the values of R<sub>2</sub>, R<sub>3</sub> and R<sub>4</sub> effect the shape of the I vs V curve? To arrive at an answer try using values much larger and much smaller than those listed above.
+**Return to Lab Activity [[university:courses:electronics:labs|Table of Contents]]**

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