Zener Diode & LED

Question 1

What is a Zener diode?

Answer 1

A Zerner diode is a special device designed for operation beyond its breakdown voltage rating in the reverse direction.

Question 2

When a diode is broken down in the reverse direction, it enters what is known as _________.

Answer 2

Zener Region

Question 3

What is the difference between junction diode and Zener diode?

Answer 3

Junction diode- allows current to flow in one direction (forward bias) and blocks it in the reverse direction.

Zener Diode- allows current to flow in the forward direction like a junction diode, but also permits current to flow in the reverse direction when the voltage exceeds a specific value called the ZENER BREAKDOWN VOLTAGE.

Question 4

If the Zener diode connected in forward bias, it conduct with a very small voltage drop of approximately _____ across it

Answer 4

0.7V

Question 5

If the Zener diode connected in reverse bias, it maintains a _____________ across itself over a wide range of current.

Answer 5

constant voltage

Question 6

The reverse characteristic makes the Zener diode unique, and allows it to be used as a______________.

Answer 6

voltage regulator

Question 7

The two typical Zener Diode ratings are:

Answer 7

1. Zener Voltage rating (2V to 200V)
2. Wattage rating (250mW to 50W)

Question 8

Any device connected to parallel to Zener will have a ___________ even if current through load i changing

Answer 8

constant voltage drop

Question 9

What is LED?

Answer 9

LED is a type of diode that emits light when an electric current passes through it.

Question 10

What does LED stand for?

Answer 10

Light-Emitting-Diodes

Question 11

The forward current rating of the LED is in the rang of only ____ to ____, so the proper rating of current -limiting resistor must be connected in series with it.

Answer 11

10 to 50mA

Question 12

What is a Photodiodes?

Answer 12

The photdiode is a special PN junction diode in which light striking the junction increases the conductivity of the diode.

Question 13

How does photodiode operated?

Answer 13

Reverse bias

Question 14

the maximum reverse voltage for photodiodes is ________.

Answer 14

20V

Question 15

For photo diode, when illuminance increases, the photo diode current _________ and is amplified by the transistor to operate the control relay

Answer 15

Incresease

Question 16

how is a zener diode tested?

Question 17

How does the colour of the LED light determined

Answer 17

the energy level of the photons.

Question 18

The basic LED is formed by joining

Answer 18

Gallium Arsenide or Gallium Phosphide

Question 19

The two primary ways of producing white LED lights are:

Answer 19

1. one employs the use of three individual LEDs that emit the primary colors of red, green and blue. (RGB)
2. employs a blue and ultraviolet LED with a yellow phosphor coating.

Question 20

why white LED light is commonly use?

Answer 20

they have low power consumption.

Question 21

Junctions have a PIV rating of _____________

Answer 21

100V or greater.

Question 22

LED typical PIV rating of _________.

Answer 22

5 volts

Question 23

How can LED be tested?

Answer 23

It can be tested in a manner similar to that of testing a junction diode.

Question 24

How do you identify LED lead?

Answer 24

shorter lead is cathode and larger lead is anode.

Question 25

How many LED light does Seven-Segment Display contains?

Answer 25

8

Question 26

The seven-segment display can be used to display any number form _______ to ______.

Answer 26

0 to 9

Question 27

LED generally operates with a current about ______ or less

Answer 27

20mA

Question 28

LED must have ___________ connected in series

Answer 28

current-limit resistor

Question 29

LED light will have a voltage drop of approximately______. Pg. 497

Answer 29

1.7V

Question 30

If an LED is connected into an AC circuit, will the output be AC or DC?

Answer 30

DC, because LED are diodes, and diodes only allow current to flow in one direction.

Question 31

What does the arrow pointing away fron a diode symbol mean?

Answer 31

lights being emitted, or given off, by the diode. Conventional current flow direction

Question 32

An LED is connected into a 24V DC circuit. The current should be limited to a maximum of 20 mA. What is the minimum size resistor that should be connected in series with the LED?

Answer 32

1200 ohms or 12Kilo-ohms

using ohms law!!!! R=V/I

Question 33

When used as a photovoltaic device, how much voltage is generally produced by a photodiode?

Answer 33

the output voltage is 0.45 volt

Question 34

With the supply of 12 Volt Dc circuit, If the resistor is connected in series with the LED, it will have a voltage drop of ___________.

Answer 34

10.3 volts.

12V (supply voltage) -1.7V (Voltage drop) =10.3 v

Question 35

LED should be reverse bias. True or False?

Answer 35

False, it should not reverse bias LEDs, as they have a low PIV rating of about 6 V. If this reverse voltage is exceeded, they may be destroyed

Question 36

When using a Sanwa VOM to test a diode the polarity of the leads are…..

Answer 36

red is positive and black is negative

Question 37

to identify the rating of a certain transistor, it is necessary to look in ___________.

Answer 37

data book or specification

Question 38

the term beta defines the transistors current gain and is determined by

Answer 38

the ratio of the collector current to the base current.

Question 39

Sometime “Beta” symbol is listed as _____.

Answer 39

hFE

Question 40

If the PIV of a diode is exceeded , the current ________

Answer 40

Avalanche!!!!

Question 41

When used as a voltage regulator, zener diodes are connected in _______ bias

Answer 41

Reverse