Download Practical 19 Characteristics of diodes

Practical 19 Characteristics of diodes
TASK
To investigate the characteristic curve of a practical diode.
EQUIPMENT
•
•
•
•
12V DC power supply
DC multimeter (0–10 V)
EM404 diode or similar
various other diodes and LEDs
as supplied
• connecting wires
• circuit ‘breadboard’
ICT
Most current sensors have a 1 A range and are suitable for this
experiment. They are generally current protected but take care to
check manufacturers’ specifications and use with care. Exceeding
the maximum current rating will permanently damage ammeter or
sensor.
THEORY
Diodes come in many different shapes and sizes. The ability for diodes to effectively allow
current to flow in one direction through a circuit is used in many electronic circuits. Diodes
are often used to prevent damage to a circuit should a reverse voltage be applied to it. They
are also used in ‘rectifying’ AC supplies to the DC required by many electronic systems.
When a diode is placed in a circuit so that it is forward biased conduction does not start until
the voltage reaches the ‘turn on voltage’. For silicon based diodes this voltage is around 0.6 V
and for germanium it is 0.3 V. After this, a very small increase in voltage causes a sudden,
large increase in current.
NOTES ON METHOD
1 Obtain an EM404 diode and try to measure its resistance with a multimeter set to the ‘1’
ohm range. Make sure you measure the resistance ‘both ways’ with the diode both forward
and reverse biased.
Forward biased resistance:
Reversed biased resistance:
Copyright © Pearson Australia 2012 (a division of Pearson Australia Group Pty Ltd) ISBN 978 1 4425 5459 7
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2 Connect up the circuit shown in the following diagram and measure the voltages across the
diode and the resistor. Complete the table.
Approx. DC supply voltage (V)
Voltage (diode)
Voltage (load R)
2
4
6
8
10
12
3 Repeat steps 1 and 2 for at least two other diodes (including LEDs) as supplied.
DATA and ANALYSIS
Construct a suitable graph of your results.
CONCLUSION
1 Is the EM404 diode you have tested silicon or germanium?
2 What are the ‘turn on’ voltages of the other types of diodes tested.
QUESTION
1 Explain your results in terms of the characteristic curve of a diode.
Copyright © Pearson Australia 2012 (a division of Pearson Australia Group Pty Ltd) ISBN 978 1 4425 5459 7
Page 2