PC/CP300 Electronics Laboratory II

Zener Diodes and Photodiodes Lab Requirements

Objective

A photodiode is used in a manner which is very similar to that of a Zener diode, so it makes sense to study them together.

• to wire up a Zener diode as a voltage reference
• to use a photodiode in a circuit
  

Equipment

• bench supply, digital meter
• breadboard, resistors
• other components as required by the design
• one of:
  • Zener diode [datasheet]
    Use the same Zener diode that you used with the motor and relay.
  • photodiode [datasheet]

Procedure

1. In the datasheet for the Zener diode, look up the zener voltage and rated current for the device you have.
   
   Calculate the resistor required for a voltage divider using the 12V bench supply.
   
   Wire up the circuit according to your calculations and measure the output voltage.
   
   Demonstrate your results to the lab supervisor.
   
   
2. Connect the photodiode to a voltmeter. You should see a voltage which changes with the light falling on it. This is photovoltaic mode of the photodiode. Consider the direction of the voltage to represent forward bias for the photodiode.
   
   You might not know that an LED can operate like a photodiode. Try the same thing you just did with an LED.
   
   
3. Now wire up the photodiode in series with a decade resistor, again using the 12V supply. Apply power and ground so that the photodiode is in reverse bias. This is the photocurrent mode of the photodiode. (Note that in this case, you may actually see a negative voltage across the pohotodiode at times due to the photovoltaic mode.)
   
   Measure the reverse voltage as you adjust the resistance keeping the light constant. What resistance value gives the greatest change in reverse voltage between light and dark?
   
   Measure the reverse voltage as you adjust the light keeping the resistance constant. What is the range of reverse voltages you observe going from light to dark?
   
   Demonstrate your results to the lab supervisor.