University of Pittsburgh

Experiment #5 Lab Report

Diode Applications and PSPICE Introduction

Submission Date:

10/10/2017

Instructors:

Dr. Minhee Yun

John Erickson

Yanhao Du

Submitted By:

Nick Haver & Alex Williams

Station #16

ECE 1201: Electronic Measurements and Circuits Laboratory

Introduction

This lab is an introduction to PSPICE, a tool used for simulating and analyzing circuits. In this lab we analyze some circuits from

Experiment 4 and take a look at some circuits we haven’t seen before. The measurements are taken using a transient analysis over 10

ms and looking at various voltages and currents within the circuits.

Procedure A

I. Purpose

The purpose of Procedure A was to simulate the three diode circuits shown in Fig. 1, Fig. 2, and Fig. 3, analyze these

circuits, and compare our simulation analysis with the real-world measurements obtained in Experiment 4.

II. Procedure

Using the OrCAD PSICE Schematics editor, the circuit shown in Fig. 1 was constructed using D1N4002 diodes for both

D1 and D2. Voltages at points A and B and currents through each of the diodes were measured using a PSPICE simulation.

PSPICE simulation values were compared to those measured in Experiment 4, as shown in Table 1.

The process described above was repeated for the circuit shown in Fig. 2. The circuit was again constructed using D1N4002

diodes. Voltages were measured at points A, B, and C. Currents were measured through diode 1 and diodes 2 and 3.

PSPICE simulation values were again compared to values measured in Experiment 4, as shown in Table 2.

For the circuit shown in Fig. 3, the voltage source V was a 0 to 10 V positive pulse lasting 0.001 seconds. The D1N914

diode was used for this circuit. This was implemented using the VPULSE function in PSPICE. With a pulse duration of

0.001 seconds, rise and fall times were both set to 1 µs. The period of the pulsing cycle was set to 10 ms. Fig. 4 shows the

source voltage and capacitor voltage over one 10ms pulsing cycle. Currents for the diode, capacitor and resistor were

measured and plotted, as shown in Fig. 5. It can be noted that the current-time plot indicates that diode current equals the

sum of resistor current and capacitor current.

Lastly, the PSPICE Schematics editor was used to construct the circuit shown in Fig. 6. The switch was initially closed,

and was opened to time 1 ms. This was simulated using the PSPICE sw_tOpen function. The source voltage, switch off at

time 1ms, and the inductor voltage were plotted over time, as shown in Fig. 7. Inductor voltage was observed to be at its

maximum when the switch was opened, or when the change in current was greatest. This is because inductor voltage is

proportional to the time derivative of current. Only the switch was opened, the circuit continued to function via the diode

in parallel with the voltage source.

III. Summary of Results

Figure 1: First Diode Circuit for Procedure A

Table 1: PSPICE and Measured Value for Circuit in Fig. 1

Parameter PSPICE Simulation Experiment 4 Measured

ID1 0.0 mA 0.007 µA

ID2 2.2 mA 2.203 mA

VA 2.8 V 2.749 V

VB 0.6 V 0.685 V

Figure 2: Second Diode Circuit for Procedure A

Table 2: PSPICE and Measured Value for Circuit in Fig. 2

Parameter PSPICE Simulation Experiment 4 Measured

ID1 4.344 mA 4.358 mA

ID2 = ID3 7.837 µA 4.573 µA

VA 648 mV 0.651 V

VB 648 mV 0.651 V

VC 324 mV 0.319 V

Figure 3: Third Diode Circuit for Procedure A

Figure 4: Voltage Source Pulse and Capacitor Voltage Over Time for the Circuit in Fig. 3

Figure 5: Diode, Resistor and Capacitor Current Over Time for the Circuit in Fig. 3

Figure 6: Fourth Diode Circuit for Procedure A with Switch Opened at t = 1 ms

Figure 7: Voltage Source Pulse and Inductor Voltage Over Time

IV. Conclusion

The first two circuits simulated were also built in lab four, and the results of the simulated version followed as expected.

In the first circuit, diode one is negatively biased, and so no current flows it. The second diode has all of the circuits current

flowing through it instead because it is forward biased. In the second circuit, although diodes two and three were forward

biased, because there were two of them there was a much higher resistance and activation voltage required so almost no

current went through them, but instead through diode one which was also forward biased; this is also what happened in

the measured results from lab 4. The third circuit was an rc circuit, where after the source voltage was cut the voltage

across the capacitor decreased over time which is what is expected. The fourth circuit had an inductor and a source voltage

that was cut by a switch after 1 ms. While the circuit was complete, the inductor was charging, and once the circuit was

cut, the inductor discharged over time.

Procedure B

I. Purpose

The purpose of Procedure B was to analysis a half wave and a full wave rectifier to see how they operated in practice. The

source voltage was sinusoidal so that the circuit could be analyzed where half the time the Vs was positive, and the other

half negative, to get a good look at the differences between how the two rectifiers functioned.

II. Procedure

The circuit shown in Fig. 8, described as a half-wave rectifier, was constructed in the PSPICE Schematics editor. A

D1N914 diode was again used for the diode, and a sinusoidal voltage source with 0V offset, 5V amplitude, and 400Hz

frequency was used as the power supply. This was accomplished using the PSPICE VSIN function. For this circuit, the

ground was placed at the negative terminal of the voltage source. Output voltage, or the voltage across RL, was plotted

with time over multiple periods, as shown in Fig. 9.

Next, the circuit shown in Fig. 10, described as a full wave rectifier, was constructed, again using D1N914 diodes and a 1

kΩ resistor. In constructing the full wave rectifier, it was determined that the ground should be placed on either side of the

resistor. This allows the output voltage to be with respect to zero volts, meaning that in applying this rectifier to another

circuit, a common zero voltage (ground) could be easily established. Given that both the circuit and the input sinusoid are

symmetric with respect to voltage, the ground can be placed on either side of the resistor. As with the half wave rectifier,

a sinusoidal voltage source was used with 0V offset, 5V amplitude, and 400 Hz frequency. The output voltage was then

plotted with time over several periods, as shown in Fig. 11.

III. Summary of Results

Figure 8: Half Wave Rectifier Constructed in Procedure B

Figure 9: Sinusoidal Input Voltage (Blue) and Half-Wave Rectifier Output Voltage (Purple)

Figure 10: Full Wave Rectifier Constructed in Procedure B

Figure 11: Full-Wave Rectifier Output Voltage

IV. Conclusion

As its name suggests, the half wave rectifier output results in a positive sinusoid when the voltage source is greater than

zero, and zero voltage when the voltage source is less than zero, as clearly shown in Fig. 9.

Based on the known basic operation of diodes, the results seen in Fig. 11 are not surprising. When the input voltage is

greater than zero, current with flow through diode 1, the load resistor, and diode 3, as label in Fig. 10. When the input

voltage is less than zero, current will flow through diode 4, the load resistor, and diode 2. In either case, the output voltage

will be nearly equal to the input voltage, with some voltage being lost across the diodes.

In both circuits, RMS voltages reflect our predictions. As mentioned earlier, output voltages across the load resistors and

similar to the input voltage sinusoids, the exception being that some voltage is lost over the diodes, as detailed in

Experiment 4. The full-wave rectifier produces a more DC-like output than the half-wave rectifier. While both produce

“positive-only” sinusoids, the full-wave rectifier does so with a frequency identical to that of the input voltage, whereas

the half-wave rectifier achieves this with only half the input frequency.

Procedure C

I. Purpose

The purpose of Procedure C was to take a look at how a Zener diode can effectively regulate a voltage source, preventing

higher voltages from causing problems in a circuit that is only supposed to operate at certain voltage levels. Then, this

voltage regulating circuit was placed into the full wave rectifier across the load to see how it affects the rectifier. Finally,

a capacitor was added into the voltage regulating full wave rectifier to observe how the capacitor can be used to smooth

out the voltage across the load.

II. Procedure

For Procedure C, the circuit shown in Fig. 12 was constructed in the PSPICE Schematics editor. For the Zener diode, diode

D1N750 was selected from the PSPICE libraries. The input voltage was a varied DC voltage, increasing with time from

5V to 10V, in 1 V intervals. This was accomplished with the PSPICE ramp voltage function. This input voltage and the

circuit output voltage were plotted together with time, as shown in Fig. 13. At each input voltage, VO, IZ, and IL were

measured, shown in Table 3.

The regulator circuit in Fig. 12 was then placed across the output of the full wave rectifier in Fig. 10 that was examined I

Procedure B, shown in Fig. 14. The sinusoidal voltage source (noted as V4 in Fig. 14) was set to have a 0V offset, 9V

peak, and 400 Hz frequency. Like in Procedure B, D1N914 diodes were used for the full-wave rectifier. A 200Ω resistor

(noted as R2 in Fig. 14) was used as the load resistor, with the ground placed at the bottom side of the resistor. This was

done to again operate the Zener diode in the reverse bias region, as was done in the first part of Procedure C. Measuring

output voltage from the other side of the load resistor enabled the output to be plotted with respect to ground. This output

was plotted with time, as shown in Fig. 15.

Next, a capacitor was placed in series with the 51Ω resistor of the full-wave-rectifier/regulator circuit shown in Fig. 14.

The basic premise behind adding a capacitor is that a capacitor can retain and discharge over time. A true DC power supply

provides a constant DC voltage. The rectified and regulated output seen in Fig. 15, while a consistently positive voltage,

is far from a constant DC voltage. A capacitor can be charged when the input is at higher voltages, and then discharged

when the input is at lower voltages. Under ideal conditions, capacitance and input frequency could be adjusted to provide

a near-constant DC output voltage.

First, a 2µF capacitor was added to the full-wave rectifier/regulator circuit. The sinusoidal voltage source was again set to

have a 0V offset, 9V peak, and 400 Hz frequency. Output voltage was plotted with time, as shown in Fig. 16. The 2µF was

then replaced with a 20µF capacitor and the output voltage was again plotted with time, as shown in Fig. 17.

III. Summary of Results

Figure 12: Zener Diode Voltage Regulator Circuit

Figure 13: Input DC Step Voltage (Blue) and Regulator Output Voltage (Purple)

Table 3: Current and Voltage Measurements for Voltage Regulator Circuit in Fig. 12

Vs (V) Vo (V) Iz (mA) IL (mA)

5.0 3.972 .2985 19.86

6.0 4.611 4.174 23.06

7.0 4.704 21.50 23.52

8.0 4.738 40.27 23.69

9.0 4.760 59.33 23.80

10.0 4.778 78.51 23.89

Figure 14: Schematic of Zener Diode Regulator Circuit on the Output of Full-Wave Rectifier

Figure 15: Output Voltage of Rectifier/Regulator Circuit

Figure 16: Output Voltage of Rectifier/Regulator Circuit with 2µF Capacitor Added

Figure 17: Output Voltage of Rectifier/Regulator Circuit with 20µF Capacitor Added

IV. Conclusion

As shown in Fig. 13, the Zener diode in reverse bias operation regulates the output voltage by limiting the voltage to

approximately 4.8V. With an input voltage of 10 VDC, the output voltage without the Zener diode would be calculated as

a voltage divider follows:

𝑉𝑜 =200Ω

200Ω + 51Ω(10 𝑉) = 7.97 𝑉 (1)

With the reversely biased Zener diode in parallel with the load, however, the output voltage is limited to approximately

4.8V.

Fig. 15 shows the output voltage when the regulator circuit in Fig. 12 was added to the output of the full-wave rectifier, as

shown in Fig. 14. This output voltage is not surprising, as it is merely a combination of the characteristics observed when

these circuits were evaluated separately. First, the full-wave rectifier mirrors the negative portion of the input sinusoid,

and the voltage of the entire wave is slightly decreased due the voltage lost across the diodes. This voltage is then further

reduced due to the voltage regulation of the Zener diode operating in the reverse bias region.

While the output voltage shown in Fig.16 may appear identical to the output without the capacitor, it should be noted that,

unlike in Fig. 15, the output voltage is constantly above zero. This is further noticeable in Fig. 17, the output when a 20µF

capacitor was used. As mentioned earlier, capacitance and frequency (which dictates the time between peak voltages)

could be adjusted to provide a near-constant DC output voltage.

Experiment Conclusion

The experiments with PSPICE proved to be a quick and effective way of testing circuits. The Circuits that were done in lab 4 and then

compared with the PSPICE simulations both showed the diodes acting in the same manner. The experiments from Procedures B and C

also followed as expected, with the circuits acting as they would be expected to in real life. Overall, it has been demonstrated that

PSPICE can be an effective tool for analyzing circuits quickly and accurately.

References

ECE 1201 Website: http://engrclasses.pitt.edu/electrical/faculty-staff/gli/1201/