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