Figure 1
Figure 1

Figure 2
Figure 2   D1 is a silicon pn junction diode. D2 is a Zener diode.

Figure 3
Figure 3

Figure 4
Figure 4   D2 and D4 are Zener diodes.

Lab 2 Diode clipping circuits

In this lab we diode clipping circuits are studied.

The circuit shown in Figure 1 limits the output voltage to voltages less than 9.1V plus Vd. If Vd is 0.7V, the maximum output voltage is approximately 9.8V. For lower output voltages the voltage across the diode is less than 0.7V and the diode does not conduct current. (It is OFF.) The same current flows through the diode and through the resistor. If the diode is OFF, no current flows through the resistor and therefore there is no voltage across the resistor. The output voltage is the same as the input voltage.

  1. Simulate the circuit.
  2. Construct the breadboard and measure the output voltage as a function of the input voltage.
  3. Export the simulated data to excel.
  4. Construct a plot containing both measured and simulated data.
  5. Apply a sinusoidal signal to Vin and observe the output on an oscillosope.

  6. Repeat the steps 1-4 for the circuits shown in Figures 2-4.

Use the part DbreakZ to simulate the Zener diode. This is a generic diode. The model has to be edited to set the breakdown voltage to 9.1V. To edit the diode model. Select the diode. Select model from the EDIT pulldown menu. ( EDIT > MODEL ) In the form that comes up select EDIT INSTANCE (TEXT)

Figure 5   This window comes up in PSPICE with all the spice model parameters. You can change any parameter. Here we added the parameter BV=9.1 to set the breakdown voltage to 9.1.

Figure 5   Simulation circuit

Figure 6   Simulated transfer function showing the output voltage as a function of the input voltage. The output is limited to less than 10.5V

Measured data as well as simulated data can be plotted on the same chart using excel. Select the columns to be plotted (measured as well as simulated). In the tools pulldown menu select;

tools>Options>chart>Plot empty cells as intrepolated.

Now that the measured data is visible, it can be selected. To show data point markers, right click on the measured data trace > Format Data Series > Marker >Custom. Choose a marker to make data points visible.

Figure 7 =IF(C11<9.8,C11,9.8)