TO: Bucknell Electrical Engineering Class of 1997
FROM: Christopher Roome & Brent Spangler
DATE LAB #4 PERFORMED: Wednesday October 25, 1995
DATE LAB SUBMITTED: Monday November 6, 1995
Procedure: Circuit #4 is to be constructed using either a 1N4007 or a 1N4148/914 Si diode. A 4V peak sine wave is to be used to drive the circuit, this signal is produced using the Hewlett Pac kard 3314A Function Generator. A 6205B Dual DC Power Supply can be used to generate the 1V and -2V signals of the internal voltage sources in the circuit. A Hewlett Packard 54601A Oscilloscope should next be used to monitor the inpu t voltage and output voltage on channel 1 and channel 2 respectively. From the observed relationship between the input and output voltages, the function of the circuit should be deduced.
Analysis: The 4007 Si diode was selected to be used in the construction of circuit #4. With a 4V sine wave being supplied as the circuit input voltage, a 1k resistor is used as a current limiter i n order to avoid the destruction of the circuit due to too high of current through the diodes. This four volt driving potential can be considered as a varying range of dc voltages,from negative four volts to positive four volts. Next, using the Hewlett Packard 54601A oscilloscope, the output voltage is observed to plateau as the input voltage approaches its peaks. This demonstrates the clamping effect of the circuit on the input voltage. This result is due to the presence of t he two diodes in parrallel with opposite polarities, each in series with a cooresponding voltage source. Provided the input voltage is greater than 1.7 volts, the diode with the one volt source in series acts as a short and allows the excess current to f low to ground, thus limiting the positive peak voltage to 1.7 volts. Conversely for input voltages less than -2.7 volts the diode in series with the -2 volt source acts as a short and also allows excess current to flow to ground, thus limiting the negati ve peak voltage to -2.7 volts. In this way the output is clamped between -2.7 volts and 1.7 volts. The xy mode of the oscilloscope was used to view the output voltage dependence on the input voltage in the form of a Vout-Vin Plot. Then a PSpice simulatioin was performed to validate the experimental results obtained for the circuit. PSpice determined the negative output voltage to be -2.66 volts and the positive output voltage to be 1.67 volts. This deviation in output voltage values can be attributed to the use of the default diode in the P Spice simulation. A triangular wave was also used as the input to circuit #4. It can be observed that the output voltages remain clamped between 1.7V and -2.7V.
Conclusion: In conclusion, circuit #4 acts as a voltage clamp. Since the 4007 Si diode has a turn on voltage of .7V, the peak clamping voltages can be set by adding a voltage source in series with a diode. In the case of this lab, when the diode was placed in series with a 1V voltage source, the voltage was clamped at the combined voltge of 1.7V. Then when the diode was placed in series with the -2V voltage source, the voltge was clamped at -2.7V.
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