| Both sides previous revisionPrevious revisionNext revision | Previous revision |
| university:courses:electronics:electronics-lab-3 [24 Apr 2017 08:09] – rename Antoniu Miclaus | university:courses:electronics:electronics-lab-3 [25 Jun 2020 22:07] (current) – external edit 127.0.0.1 |
|---|
| ====== Activity 3. The BJT connected as a diode ===== | ====== Activity: The BJT connected as a diode ===== |
| |
| ===== Objective: ===== | ===== Objective: ===== |
| ===== Hardware Setup: ===== | ===== 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: ===== | ===== 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. | 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: ===== | ===== Questions: ===== |
| |
| |
| {{ :university:courses:electronics:a3_f2.png?500 |}} | {{ :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: ===== | ===== 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: ===== | ===== 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. | 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. | 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. |
| ===== Directions: ===== | ===== 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 |}} | {{ :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: ===== | ===== 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: ===== | ===== 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. | 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: ===== | ===== Questions: ===== |
| {{ :university:courses:electronics:a3_f4.png?500 |}} | {{ :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: ===== | ===== 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: ===== | ===== Procedure: ===== |
| 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>. | 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: ===== | ===== Questions: ===== |
| |
