ENGR325 Electronics II
Lab #2 – Diode Applications
· To see a number of circuit applications for diodes
· To get experience with using diodes to change waveforms
1. Design, build, and test a dc power supply that uses a 120V:12.6VCT transformer and a Zener diode (1N5231B) to regulate the output to 5.1V. The load is to vary from an open circuit (no load) to a value of 100Ω. The ac line voltage can vary from 110V to 120V. I would suggest allowing only 0.5Vpp of ripple before the regulator.
Follow these steps:
a. Calculate the peak value out of the transformer on each side of the center tap before the diodes (convert from rms to the peak value Vp).
b. Calculate the maximum value of the voltage Vm after the diodes have rectified it (subtract Vγ).
c. Calculate the maximum current to the load ILmax (when the load is 100Ω).
d. Calculate the maximum Zener current IZmax for the ˝ W diode.
e. Calculate the minimum Zener current IZmin as 10% of the maximum IZmax (to keep away from the knee).
f. Get the value of filter capacitor C using the specified ripple voltage and the maximum total current of IZmin + ILmax.
g. Find the value of R using the minimum voltage drop across it and the maximum current through it ((Vm-Vr)-VZ)/(IZmin + ILmax). Determine the power this resistor must dissipate. Select a suitable standard resistor for R.
h. Build the circuit.
i. Set the input for 120Vrms. Measure the output voltage at no load and with the 100Ω attached. Check to be sure that the ripple voltage is less than 0.5Vpp as specified. Calculate the “load regulation” according to 100%*(VNL-VFL)/VNL.
j. Connect the 100Ω load. Measure the output voltage for an input of 110Vrms and for 120Vrms. Calculate the “source regulation” according to 100%*(Vout120-Vout110)/Vout120.
For your report give the design requirements, show your circuit and the calculations you did to determine its values, and report your test results.
2. Design a diode (1N4148) circuit that will accept a +10Vpp triangle wave as the input and produce these outputs:
a. A triangle waveform with the positive part removed.
b. A triangle waveform with the portion of the waveform above +4V removed.
c. A triangle waveform with the negative portion of the waveform just half the original amplitude.
d. A triangle waveform like the original but varying from 0 to 20Vp. Also, try a square wave.
For your report state the design requirement in each case, show the circuit you used to meet that requirement, and present a record or sketch of the output waveform you observed. Comment on your success at meeting the requirement.