ECE 201L Circuit Analysis Laboratory
Lab 6

This lab provides experience with diodes.

Do the following exercises. Report your results in a Word document. Submit one report per group.

  1. Locate the following diodes: light-emitting diode (LED), 1N4004 rectifier diode, and 1N4148 switching diode.

    Construct the following circuit, shown in Figure 1, using a 100-300 Ω load resistor and a diode. You will need an accurate measurement of the load resistor so use the bench multimeter to make the measurement. Vs is the signal generator. Set the source frequency to 1 kHz and the amplitude to 5 Volts maximum (10 volts peak-to-peak).


    Figure 1. Diode test circuit

    Do the following for each diode:

    1. Examine and capture the resulting input and output signals on the oscilloscope. See example below:

    2. Change the oscilloscope display to XY mode (see instructions at the end of this document) and measure the turn-on voltage of each diode. Capture the resulting oscilloscope images. See example below:

      The XY plot above can be obtained more precisely from a set of DC measurements, as you should do next.

  2. Connect the multimeter to the diode test circuit as shown in Figure 2. Use a DC power source and measure the load voltage with the multimeter. Record both input and output voltages, and measure the value of the load resistance. Take measurements every 0.5 V from 0 to 5 volts. Test each of your three diodes, including the LED.


    Figure 2. Diode test circuit (DC input).

    An example of measured data are shown in Figure 3.


    Figure 3. Example experimental data

    Calculate the turn on voltage Von from the x-intercept and the effective diode series resistance RS from the slope ρ of the linear part of the VL vs Vin curve,where

    In the example above, the linear part of the curve includes input voltages 2 V and above.

    Plot the diode characteristic curve by plotting the diode current ID = VL / RL versus the diode voltage VD = VS − VL, as shown by the example below.


    Figure 4. Example diode characteristic curve, ID vs. VD

  3. Construct the full-wave bridge rectifier shown in Figure 5. Use a 220 Ω resistor for the load. Build one version with 1N4001 diodes and one with light-emitting diodes.


    Figure 5. Full-wave diode-bridge rectifier.

    1. Do the following for each bridge. Measure source voltage on oscilloscope with probes between A and B. Measure load voltage with probes between C and D. Do not attempt to measure both signals on the oscilloscope at the same time, the oscilloscope channels share a common ground and trying to make simultaneous measurements will introduce ground loop problems. Set the frequency of the source to 50 Hz and the amplitude to 10 volts peak-to-peak. Attach oscilloscope images of the source voltage and the load voltage to the report, showing the maximum voltage in each signal.

    2. For the LED bridge: Reduce the input frequency to 1 Hz. Observe the pattern of lights and describe in your report.

To use the XY horizontal mode

The XY horizontal mode converts the oscilloscope from a volts-versus-time display to a volts-versus-volts display using two input channels. Channel 1 is the X-axis input, channel 2 is the Y-axis input. You can use various transducers so the display could show strain versus displacement, flow versus pressure, volts versus current, or voltage versus frequency.

  1. Connect the sine wave signal to phase channel 1, and the output sine wave signal to channel 2. Get a reasonable time scale by pressing the Autoscale key or adjusting the horizontal (time) scale.

  2. Press then Horiz key, then press the Time Mode softkey to change from Normal to XY

  3. Center the signal on the display with the channel 1 and 2 position () knobs. Use the channel 1 and 2 volts/div knobs and the channel 1 and 2 Vernier softkeys to expand the signal for convenient viewing.

Maintained by John Loomis, last updated 5 November 2012