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Diode

Learning diode characteristics

Target    Preparing    Experimentation    Report    Problems

Laboratory target

Making the simple diode circuits and acquainting with diode characteristics.

Lesson preparation

1. Using the datasheet below, find the LED and the diode data: type, maximum forward currents IFmax, maximum reverse voltages URmax, and forward voltage drops ΔUF.

2. Familiarise with the available power source: its voltage Us max and current Is max.
3. Develop the LED circuit indicating whether the breadboard is energised.
4. Develop the circuit and wiring diagrams to explore the forward volt-ampere characteristic of a studied diode. Place a voltage divider between the power supply and the diode to protect the circuit from overloading. Choose the potentiometer of 1 kΩ or 10 kΩ and the buffer resistor to this aim.
5. Provide the circuit link-up with:

   dc voltmeter PV to measure the diode forward voltage UF or reverse voltage UR
   dc ammeter PA to measure the diode forward current IF or reverse current IR

and propose the required meters: their types, measuring limits, and maximum measured values.

6. Sketch an expected volt-ampere characteristic and diode voltage waveform.

Experimentation

1. Familiarise with a LED:

• Wire the red (positive) supply socket of the breadboard with a red bus strip and the black (negative) socket with a black bus strip.
• In the first breadboard row, assemble the circuit for indication whether the breadboard is energised by inserting the current-limiting resistor and the LED to the clips, putting them together, and linking to the bus strips.
• Adjust the power supply voltage to 10 V. Connect it to the breadboard sockets. Self-examine and ask an instructor to examine the assembled circuit.
• Power on the supply and ensure the LED beams. Then, power off the supply and ensure the LED dims. If a fault occurs in any instant, deenergize the breadboard immediately, examine the circuit and eliminate errors.

2. Tune the potentiometer:

• Put together the current-limiting resistor and connect the potentiometer across the bus strips. Wire the potentiometer slider with the blue socket and the negative (black) bus strip with the green socket.
• Choose the meters and assign their ranges and terminals for wiring. Connect the voltmeter across the blue and green sockets. Self-examine and ask an instructor to examine the assembled circuit.
• Power on the supply. Turn the potentiometer knob and find its positions that correspond to the maximum and minimum voltages. Assign the minimum voltage and then power off the supply.

3. Estimate the forward volt-ampere characteristic:

• Assemble the desired circuit, self-examine and ask the instructor to check it.

• Power on the supply. Turn the potentiometer smoothly until the maximum supply voltage or the diode permissible current is achieved. At every step, measure the diode voltage and current, fill the measured values in the protocol, and plot the diagram.

• Restore the minimum voltage and power off the supply.

3. Following the instructor’s permission, switch off the devices, take off the circuit, and introduce proper order in the workplace.

Report contents

1. Wiring diagram of the experimental setup with specification of the components.
2. Circuit diagram of the experimental setup.
3. Calculation of the resistors.
4. Tables of the observed data.
5. Scaled diagrams of the experimental volt-ampere characteristic.
6. Estimation of the knee voltage and the forward voltage drop ΔUF in the upper point of the volt-ampere characteristic.
7. Conclusions regarding estimation, comparison and explanation of the expected and obtained results.
8. Signed protocol.

Optional section

1. Design and assemble the circuit to estimate the reverse volt-ampere characteristic, repeat experimentation, and include the table and the characteristic obtained to your report .
2. Using a signal generator and an oscilloscope, develop and assemble the circuit to trace the diode voltage waveforms U(t) and employ experimentation in the given point of the volt-ampere characteristic.
3. Calculate the diode power dissipation at the maximal anode current and prove your result with simulation.
4. Design the circuit whose supply voltage exceeds the diode breakdown (Us > URmax), calculate the voltage divider, and prove your design with simulation.
5. Design the rectifier circuit which load voltages and currents exceed the diode ratings (ULOAD > URmax, ILOAD > IFmax), and prove your design with simulation.