ECET 329 – Analog and Digital Electronics

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Lab 3 - Diodes Introduction The laboratory exercise is designed to familiarize you with diodes and typical diode circuits.

Equipment • DC Power Supply • Function Generator • Digital Multimeter • Oscilloscope • Assorted Resistors • Assorted Capacitors • 4 Diodes - 1N914 • 4 LED – (2 Red, 2 Green) • Bread Board • BNC T • BNC to Alligator Cable • BNC to BNC Cable • 2 Scope Probes

Procedure 1. Build the circuit shown below. The function generator (V1) should be set for a

triangular wave going from −10 to +10 volts. The frequency should be relatively slow (1 kHz). The resistor should be approximately 1000Ω. Perform a circuit simulation.

a. Take oscilloscope screen shots that show both the voltage from the function generator and the voltage over the diode.

2. Using the same circuit as above, fix the source voltage at 3 volts and measure the voltage across all the components in the circuit.

a. Calculate the current flow using the measured data. b. What is the forward voltage of the diode?

ECET 329 – Analog and Digital Electronics

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3. Using the same circuit, replace the diode with an LED and replace the resistor with a value near 400 ohms. Observe what happens. Vary the input voltage until the LED turns on.

a. What is the forward voltage of the LED? b. Derive an expression for the current through the LED as a function of the

source voltage.

4. Build the circuit shown below using the 1N914 diodes. Consider R1 as the load resistor.

a. Take oscilloscope screen shots that show both the voltage from the function generator and the voltage over the resistor.

b. Is there ever a point in time when only one diode is on?

5. Replace the diodes in the circuit above with LEDs. Calculate a value for R1 so that the LEDs will have 20mA flowing through them when they are on. Change R1 to this value and run the circuit. If you do not have the resistor value you calculated, you may change the source voltage until you get the correct current.

What to Turn In • One formal lab report per group, including:

o A cover page including: ! Lab title ! Course ! Group Members

o An Equipment & Parts Section including ! Listing of all equipment and parts used

o An Experimental Procedure & Results Section including: ! Answers to the questions ! Oscilloscope screen shots