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BME/ISE 3511 Bioelectronics I - Laboratory Exercise #5 Semiconductors (Diodes, LEDs, Zeners) Introduction: Semiconductors are essential elements of all modern analog and digital circuitry. Semiconductors devices derive their properties from the rectification phenomena associated with the PN junction. Electronic semiconductors devices can be divided into many categories/classes. One such class of semiconductors is the diodes. A diode is a simple two terminal non-linear construct which is useful for rectifying and waveform shaping of electrical signals. Diodes can be manufactured to function as simple passive devices (diodes), as light-emitting devices (LEDs), and as lightdetecting devices (photodiodes), and non-linear voltage regulators (Zener diodes). Objective: Become familiar with the basic characteristics of diodes, LEDs, and Zener diodes. Laboratory Equipment and Supplies: DMM, DC Variable Power Supply, Breadboard, Assorted Diodes, LEDs, Zeners, Resistors Background: Refer to Digital Multimeter DMM Model 72-7940 Functions, Ranges, Resolutions, and Accuracy (BME/ISE 3511 Bioelectronics I - Laboratory Exercise #1 Procedures and Guidelines, page 4) for specifications and identification of the various functions and ranges of measurement values. Refer to the DMM itself for examples of the function labels; starting at the top center and moving clockwise: Off, AC Voltage, DC Current, Square Wave Output, Battery Tester, Diode Test, Resistance, and DC Voltage. AC current measurement is not supported. Note: The maximum allowable DC current is 200 mA. Forward and Reverse Biasing: Diode circuits exhibit various behaviors depending on the characteristic and the orientation of the diode in an electronic circuit. Simple diodes conduct heavily when forward biased (cathode connected to the more negative side of the power source). There is a small barrier voltage drop (less than 1 VDC) for forward biased diodes. When reverse biased (cathode connected to the more positive side of the power source), diodes act somewhat as an open circuit up to a point. Reversed biased diodes will begin conducting heavily at the so called breakdown voltage. For simple diodes, if the breakdown voltage is exceeded, then the heavy reverse current generally destroys the diode. A specific class of diodes, Zener diodes, are manufactured such that the Zener breakdown voltage is precisely set at voltages generally in the range of (-1.5 to -120 VDC), rated from ¼ watt to 50 watts, and are designed to operate continuously at the Zener breakdown voltage. Zener diodes are usually oriented in the reverse bias direction and provide crude voltage regulation at the designated Zener breakdown voltage.
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BME/ISE 3511 Bioelectronics I - Laboratory Exercise #5 Semiconductors (Diodes, LEDs, Zeners) Diode Measurement Procedures: Warning : To avoid damage to the digital multimeter or to the device under test, disconnect circuit power and discharge all the high-voltage capacitors before testing diodes. Use the Diode Test Function to check diodes, transistors, and other semiconductor devices. The diode test sends a current through the semiconductor junction, and then measures the voltage drop across the junction. A good silicon junction drops between 0.3 and 0.8 volts. To test a diode out of a circuit, connect the DMM as follows: 1. Set the rotary switch to 2. For forward voltage drop readings on any semiconductor component, connect the red test lead to the component's anode and connect the black test lead to the component's cathode. The measured value shows on the display. 3. When the diode test has been completed, disconnect the connection between the test leads and the circuit under test Notes: • In a circuit, a good diode should still produce a forward voltage drop reading of 0.3V to 0.8V; however, the reverse voltage drop reading can vary depending on the resistance of other pathways between the probe tips. • Connect the test leads to the proper terminals as described above to avoid any display errors. • The LCD will display indicating open-circuit for a reversed connection. • The unit of diode is millivolts (mV), displaying the positive-connection voltage-drop value. Source: MCM DMM Model 72-7940 Operating Manual
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BME/ISE 3511 Bioelectronics I - Laboratory Exercise #5 Semiconductors (Diodes, LEDs, Zeners) Laboratory Procedures, Activities, And Tasks Note: Obtain the diode, LED, and Zener specifications from the Lab GTA. I. Polarity Measurements Diode Use the DMM to determine the polarity (anode and cathode) of a diode. Note any marking on the body of the diode and reference those markings to the anode vs. the cathode. Record your observations in your lab report. LCD Use the DMM to determine the polarity (anode and cathode) of a LED. Note the flat index mark on the side of the LED and reference this index to the anode vs. the cathode. Record your observations in your lab report. Zener Diode Use the DMM to determine the polarity (anode and cathode) of a Zener. Note the flat index mark on the side of the Zener and reference this index to the anode vs. the cathode. Record your observations in your lab report.
II. LED Polarity Indicator Construct a simple LED Polarity Indicator according to the following diagram.
Set Power Supply to 6 VDC.
Reverse the polarity of the input voltage and observe and report the results in your lab report.
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Laboratory #5 Tasks/Activities - continued III. Diode Current and Voltage Measurements with respect to Forward and Reverse Biasing The following procedures are to be used in obtaining voltage and current measurements. Reverse Bias Confirm that the DC power supply is turned off. Connect the DC power supply in series with the resistor and the diode such that, the negative side of the power supply is connected to the anode of the diode and the positive side of power supply is connected to the cathode. Turn on the power supply and adjust the output voltage as appropriate (6 VDC). Using the DMM DC Voltage Function, select the appropriate VDC Range: Confirm the VDC power supply voltage and current meter readings. Measure the voltage across the diode and record your result. Measure the voltage across the resistor and record your result. Turn off the power supply and disconnect it from your circuit. Confirm that the DC Power Supply is turned off. Connect the power supply in series with the DMM and the resistor and the diode. Select the DC Current Function and Range = 200 mA. Do Not use any function other than DC Current. Turn on the power supply and adjust the output voltage as appropriate. Record the current reading. Turn off the power supply and disconnect it from your circuit. Forward Bias Confirm that the DC power supply is turned off. Connect the DC power supply in series with the resistor and the diode such that, the negative side of power supply is connected to the cathode and the positive side of the power supply is connected to the anode of the diode. Turn on the power supply and set the output voltage as appropriate (6 VDC). Using the DMM DC Voltage Function, select the appropriate VDC Range: Confirm the VDC power supply voltage by measuring across both the resistor and the diode. Measure the voltage across the diode and record your result. Measure the voltage across the resistor and record your result. Turn off the power supply and disconnect it from your circuit. Confirm that the DC Power Supply is turned off. Connect the power supply in series with the DMM and the resistor and the diode. Select the DC Current Function and Range = 200 mA. Do Not use any function other than DC Current. Turn on the power supply and set the output voltage to 6 VDC. Record the current reading. Turn off the power supply and disconnect power supply and DMM from your circuit.
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Laboratory #5 Tasks/Activities - continued IV. Incremental Diode Voltage and Current Measurements Lab Procedures: Construct a series diode/resistor circuit. There are four separate experiments: diode forward biased, diode reverse biased, Zener diode forward biased, Zener diode reverse biased. Before connecting the power supply: Turn on and set output voltage to 0 Volts. Turn off the power supply. Double check the following: DMM Voltmeter #1 connected in parallel across the diode Function Switch Set to 20 VDC. DMM Voltmeter #2 connected in parallel across the resistor Function Switch Set to 20 VDC. This lab entails constructing four separate diode/resistor series circuits. 1. Simple Diode (Forward Bias) 2. Simple Diode (Reverse Bias) 3. Zener Diode (Forward Bias) 4. Zener Diode (Reverse Bias)
Forward Biased Simple Diode Orient the simple diode in the circuit for forward bias. Turn on DC power supply. Incrementally increase the voltage by 1 volt steps up to a maximum of 12 VDC. Record the Power Supply Voltage and Current Output values at each voltage step. Record the DMM VResistor and VDiode voltage readings. Return the voltage setting to 0 VDC. Turn off the power supply. Calculate and Record - Average Barrier Voltage (VDiode Forward Bias). Reverse Biased Simple Diode Reverse the orientation of the diode. Turn on DC power supply. Incrementally increase the voltage by 1 volt steps up to a maximum of 12 VDC. Record the Power Supply Voltage and Current Output values at each voltage step. Record the DMM VResistor and VDiode voltage readings. Return the voltage setting to 0 VDC. Turn off the power supply. Note any indication that the reverse bias breakdown voltage was breached.
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Laboratory #5 Tasks/Activities - continued IV. Incremental Diode Voltage and Current Measurements - continued Forward Biased Zener Diode Orient the Zener diode in the circuit for forward bias. Turn on DC power supply. Incrementally increase the voltage by 1 volt steps up to a maximum of 12 VDC. Record the Power Supply Voltage and Current Output values at each voltage step. Record the DMM VResistor and VDiode voltage readings. Return the voltage setting to 0 VDC. Turn off the power supply. Calculate and Record - Average Barrier Voltage (VDiode Forward Bias). Reverse Biased Zener Diode Reverse the orientation of the Zener diode. Turn on DC power supply. Incrementally increase the voltage by 1 volt steps up to a maximum of 12 VDC. Record the Power Supply Voltage and Current Output values at each voltage step. Record the DMM VResistor and VDiode voltage readings. Return the voltage setting to 0 VDC. Turn off the power supply. Determine the Zener diode breakdown voltage. Conclusions: You must annotate any references you consulted in answering the following questions. You may wish to use a word processor to complete your answers and attach the printout to your Laboratory Exercise #5 Report Form. Draw conclusions regarding Diode Voltage Forward Bias Diode Voltage Reverse Bias Zener Diode Voltage Forward Bias Zener Diode Voltage Reverse Bias
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BME/ISE 3511 Bioelectronics I - Laboratory Exercise #5 Report Form Semiconductors (Diodes, LEDs, Zeners) I affirm that I personally participated in the collection and analysis of the data for this laboratory exercise and that I personally contributed to the completion of this laboratory report. Student Name: ___________________________________________ Signature: ___________________________________________ Date: __________________
I affirm that I personally participated in the collection and analysis of the data for this laboratory exercise and that I personally contributed to the completion of this laboratory report. Student Name: ___________________________________________ Signature: ___________________________________________ Date: __________________
Grade: ___________________
Grader Comments:
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BME/ISE 3511 Bioelectronics I - Laboratory Exercise #5 Report Form I. Polarity Measurements 1. Draw a sketch of any markings or references on the body of the diode that identify either the anode or the cathode lead.
2. Which lead (cathode or anode) is indicated by the flat index mark on the side of the LED
II. LED Polarity Indicator Circuit Specifications: LED #1
LED #2
VLED ILED Vin Rs
III. Diode Circuit Voltage and Current Measures (Forward and Reverse Biasing) LED Reverse Bias (6 VDC) DC Power Supply
Voltage Setting
Current Setting
Circuit Measurements
Voltage Across Diode
Voltage Across Resistor
Circuit Current
LED Forward Bias (6 VDC) DC Power Supply
Voltage Setting
Current Setting
Circuit Measurements
Voltage Across Diode
Voltage Across Resistor
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Circuit Current
BME/ISE 3511 Bioelectronics I Laboratory Exercise #5 Report Form IV. Incremental Diode Voltage and Current Measurements Calculated Current
Diode
R = 220 Ω
Vin 1 2 3 4 5 6 7 8 9 10 11 12
Vs
Forward Is VR
VD
Zener Diode Reverse Is VR
Vs
VD
Forward Barrier Voltage
Vs
Forward Is VR
VD
Vs
Reverse Is VR
VD
Forward Barrier Voltage Breakdown Voltage ?
Average =
Zener Breakdown Voltage Average =
Table 1 Diode and Zener Diode Current and Voltages
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