Post on 18-Dec-2015
Analogue ElectronicETEC 3824
Diode
Learning Outcomes
At the end of the lesson, students should be able to :
Sketch and explain the characteristics curve of a resistor-diode combination circuit
Sketch and explain the characteristics curves of a zener diode-resistor voltage regulator
Diode
• The semiconductor material with a deficiency of electrons is P-TYPE material.
• The semiconductor material with an excess of electrons is N-TYPE material.
• By fusing P-TYPE and N-TYPE material, a “PN” Junction .is formed (This “PN junction” is a Diode)
Diode
• A diode has the characteristics of:
• an insulator when current tries to flow in one direction.
a conductor when current flows in the other direction.
Diode
DIODE TYPES AND CONNECTIONS
• Power Diodes (rectifier diodes) For ratings up to a few amps the Epoxy Resin
encapsulated diode is commonly used
DIODE TYPES AND CONNECTIONS
or Plastic / Glass encapsulated
IN4004
IN4004
DIODE TYPES AND CONNECTIONS
• Power Diodes (rectifier diodes) for Higher power ratings the Metal Stud mount is
more common
DIODE TYPES AND CONNECTIONS
• Signal diodes Signal diodes are used mainly in low power
applications They have very low capacitance and lower
potential barrier voltage (0.3 v) which gives them a fast recovery rate making them suitable for high speed switching,
AM-FM-TV signal detectors, demodulators, UHF mixers, logic circuits, voltage clamping, surge suppression and other protection circuits
The effects of Forward Bias
• Forward biasing the p-n junction drives holes to the junction from the p-type material and electrons to the junction from the n-type material
• At the junction the electrons and holes combine so that a continuous current can be maintained
a conductor..
The effects of Forward Bias
Diode V-I characteristics
PIV = Peak Inverse Voltage
The effects of Reverse Bias
• The application of a reverse voltage to the p-n junction will cause a transient current to flow as both electrons and holes are pulled away from the junction.
• When the potential formed by the widened depletion layer equals the applied voltage, the current will cease except for the small thermal current.
an insulator
The effects of Reverse Bias
.
The effects of Reverse Bias
• When reverse biased, a p-n diode blocks current flow.
• Current will only flow if the reverse voltage becomes so large as to cause a breakdown of the depletion layer in the device.
• This usually results in device failure
Diode V-I characteristics
PIV = Peak Inverse Voltage
Light-Emitting Diodes (LEDs)
• Emit light in proportion to the forward current through the diode
• Are low voltage devices that have a longer life than incandescent lamps
• Respond quickly to changes in current (10 MHz).
• LEDs have applications in optical-fiber communication and diode lasers
LED
• Symbol
Anode (A)
Cathode (K)
LED
:
LED
LED
LED
Colours of LEDs
Tri-Colour LED
Tri-Colour LED
• The most popular type of tri-colour LED has a red and a green LED combined in one package with three leads.
• They are called tri-colour because mixed red and green light appears to be yellow and this is produced when both the red and green LEDs are on.
Assignment
• Sketch the current (I) vs voltage (V) of a forward bias diode
• Sketch the current (I) vs voltage (V) of a reverse bias diode
Practical Assignment
• Measure and record the current flow in the circuit below, comment on your results and observation
Zener Diodes
• A special silicon diode • When forward biased acts the same as an
ordinary diode • When reversed biased will conduct when the
reverse voltage reaches a particular value • The voltage drop is substantially constant as the
current varies. • The voltage at which reverse conduction takes
place is called the Zener voltage (VZ)
Zener Diodes
• The terminals of a zener diode are identified in the same way as other diodes.
• The body of the diode will have some marking on it to identify its zener voltage (reverse voltage)
• Zener diodes are connected into circuits in reverse bias.
Zener Diodes
• Symbol
Anode Cathode
Zener diode V-I characteristics
0.6V0.1 IZMax
0.8 IZMax
Zener Diodes
• The zener diode is particularly useful in circuits where a relatively constant voltage reference is required
Zener diode V-I characteristics
Voltage Regulator
• The constant reverse voltage of the zener diode makes it a valuable component for the regulation of the output voltage against both variations in the input voltage from an unregulated power supply or variations in the load resistance.
• The current through the zener will change to keep the voltage at within the limits of the threshold of zener action and the maximum power it can dissipate
Voltage Regulator