Analogue Electronic ETEC 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

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 materialp-n junctionp-typen-type At the junction the electrons and holes combine so that a continuous current can be maintained combine  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. p-n junctionelectrons and holes When the potential formed by the widened depletion layer equals the applied voltage, the current will cease except for the small thermal current. depletion layer 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 :

Colours of LEDs

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 0.6V 0.1 I Z Max 0.8 I Z Max

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.zener diode 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 dissipatezener action

Voltage Regulator