ENGR325 Electronics II

**Lab #2 – Diode Applications**

**Objectives:**

· To see a number of circuit applications for diodes

· To get experience with using diodes to change waveforms

**Procedures:**

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 0.5V_{pp}
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 V_{p}).

b. Calculate the maximum value of the voltage V_{m}
after the diodes have rectified it (subtract Vγ).

c. Calculate the maximum current to the load I_{Lmax}
(when the load is 100Ω).

d. Calculate the maximum Zener current I_{Zmax} for the ˝ W diode.

e. Calculate the minimum Zener current I_{Zmin} as
10% of the maximum I_{Zmax} (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 I_{Zmin}
+ I_{Lmax}.

g. Find the value of R using the minimum voltage drop across
it and the maximum current through it ((V_{m}-V_{r})-V_{Z})/(I_{Zmin} + I_{Lmax}). Determine the power this resistor must
dissipate. Select a suitable standard
resistor for R.

h. Build the circuit.

i. Set the input for 120V_{rms}. Measure the output voltage at no load and
with the 100Ω attached. Check to be
sure that the ripple voltage is less than 0.5V_{pp} as specified. Calculate the “load regulation” according to 100%*(V_{NL}-V_{FL})/V_{NL}.

j. Connect the 100Ω load. Measure the output voltage for an input of
110Vrms and for 120Vrms. Calculate the
“source regulation” according to 100%*(V_{out120}-V_{out110})/V_{out120}.

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 __+__10V_{pp}
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 20V_{p}. 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.