Instructional Objectives on Diode Clipping Circuits - Experiment 3 | EE 462G, Lab Reports of Electrical and Electronics Engineering

Download Instructional Objectives on Diode Clipping Circuits - Experiment 3 | EE 462G and more Lab Reports Electrical and Electronics Engineering in PDF only on Docsity! EE 462G Laboratory # 3 Diode Clipping Circuits by Drs. A.V. Radun and K.D. Donohue (2/07/07) Department of Electrical and Computer Engineering University of Kentucky Lexington, KY 40506 Updated 10/5/07 by Stephen Maloney (Lab 2 – Report due at beginning of lab period) (Pre-lab 3 and Lab-3 Datasheet due at the end of the lab period). I. Instructional Objectives • Design and implement clipping circuits based on the attributes of semiconductor diodes. (See Horenstein 4.1 and 4.2) II. Transfer Characteristics This lab introduces diode circuits that alter input waveform shapes (wave shaping) and the graphical modeling of their transfer characteristics. Clipping circuits are used to restrict an output voltage to a particular range of values. The output voltage will be proportional to the input voltage as long as the input voltage lies within the desired range. Outside this range the output is clipped (held) to a constant value until the input falls within the “linear” range, where the output follows the input. The nonlinear switch-like properties of the diode can be used to implement this function. Clipping circuits are used in signal processing applications, radio modulation systems, and power supplies. III. Pre-Laboratory Exercises Transfer Characteristic of Diode 1) Use data from the previous lab (Lab 2), and plot the following on the same graph (use different line styles to distinguish the plots): • The measured I-V curve obtained with the curve tracer • The result of the Shockley diode equation with the best-fit parameters. (Note the diode current can get very large from this equation and cause the vertical axis to get so large that it obscures the curve tracer data plot. Do not let this happen. Limit the range of the values evaluated on the Shockley equation to those of the curve tracer data so differences between the model and measured data in the critical regions can be seen clearly). • A vertical line at the forward bias voltage value that was estimated in the last lab. This line should appear somewhat tangential to the exponentially increasing diode current. • Make sure the axes of the plot are properly labeled. This plot will be used for discussing observed results between the predicted and measured results of the clipping circuit. Clipped Sine Wave Generation 2) For the circuits shown in figures 1a, b, and c, where battery voltages V1 and V2 are to be treated symbolically, but have values of 1.2V, assuming ideal diodes (negligible internal resistance and a forward bias voltage of Vf, treated symbolically, but with a value of .7V): • Sketch the input and output waveforms (Vs, Vout versus time) for a 250Hz input sine wave of amplitude 2.8 Vrms. DO NOT USE SPICE (see question 3), DERIVE the equations for the output by hand. • Label the input and output waveforms with their functional representation (in the case of Vout this will be a piecewise function with inequalities, where the output is a specific value or function over a range of input voltage values) • Sketch the transfer characteristic (Vout versus Vs) for Vs ranging between -5V and +5V. Be sure to label any slopes and mark on the axis the values where the transfer characteristic 3) For the same source as described in the previous problem, use SPICE to graph the output of the circuit in Fig.1c for several periods where V1=V2= 1.2 V. Use SPICE to obtain the transfer characteristic of the circuit in Fig. 1c for Vs between -5V and +5V. 4) The circuit in Fig. 1b is modified to result in the circuit in Fig. 1d. Describe how the measured output may change as a result of this modification IN A REAL WORLD CIRCUIT. (Hint - read the lecture slides again) Power Distribution 5) For the circuit in Fig. 1a, assuming VS is a 250Hz sine wave at 2.8 Vrms, write a MATLAB script to: • Determine the average power delivered by the source, and absorbed by the resistor and diode. • Modify the circuit in Fig. 1a by adding a 5.1kΩ load resistor. Determine the power absorbed by all elements and delivered by the source. This can be done two ways in MATLAB: symbolically, or with some form of numerical integration. Both require deriving the equations for the voltage and current through each element or provided by the source, and the finding the average power using the formula found in the lecture slides. Those interested in numerical integration could start by looking up the trapezoid rule.