Zener Diode & LED Flashcards
What is a Zener diode?
A Zerner diode is a special device designed for operation beyond its breakdown voltage rating in the reverse direction.
When a diode is broken down in the reverse direction, it enters what is known as _________.
Zener Region
What is the difference between junction diode and Zener diode?
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.
If the Zener diode connected in forward bias, it conduct with a very small voltage drop of approximately _____ across it
0.7V
If the Zener diode connected in reverse bias, it maintains a _____________ across itself over a wide range of current.
constant voltage
The reverse characteristic makes the Zener diode unique, and allows it to be used as a______________.
voltage regulator
The two typical Zener Diode ratings are:
- Zener Voltage rating (2V to 200V)
- Wattage rating (250mW to 50W)
Any device connected to parallel to Zener will have a ___________ even if current through load i changing
constant voltage drop
What is LED?
LED is a type of diode that emits light when an electric current passes through it.
What does LED stand for?
Light-Emitting-Diodes
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.
10 to 50mA
What is a Photodiodes?
The photdiode is a special PN junction diode in which light striking the junction increases the conductivity of the diode.
How does photodiode operated?
Reverse bias
the maximum reverse voltage for photodiodes is ________.
20V
For photo diode, when illuminance increases, the photo diode current _________ and is amplified by the transistor to operate the control relay
Incresease
how is a zener diode tested?
How does the colour of the LED light determined
the energy level of the photons.
The basic LED is formed by joining
Gallium Arsenide or Gallium Phosphide
The two primary ways of producing white LED lights are:
- one employs the use of three individual LEDs that emit the primary colors of red, green and blue. (RGB)
- employs a blue and ultraviolet LED with a yellow phosphor coating.
why white LED light is commonly use?
they have low power consumption.
Junctions have a PIV rating of _____________
100V or greater.
LED typical PIV rating of _________.
5 volts
How can LED be tested?
It can be tested in a manner similar to that of testing a junction diode.
How do you identify LED lead?
shorter lead is cathode and larger lead is anode.
How many LED light does Seven-Segment Display contains?
8
The seven-segment display can be used to display any number form _______ to ______.
0 to 9
LED generally operates with a current about ______ or less
20mA
LED must have ___________ connected in series
current-limit resistor
LED light will have a voltage drop of approximately______. Pg. 497
1.7V
If an LED is connected into an AC circuit, will the output be AC or DC?
DC, because LED are diodes, and diodes only allow current to flow in one direction.
What does the arrow pointing away fron a diode symbol mean?
lights being emitted, or given off, by the diode. Conventional current flow direction
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?
1200 ohms or 12Kilo-ohms
using ohms law!!!! R=V/I
When used as a photovoltaic device, how much voltage is generally produced by a photodiode?
the output voltage is 0.45 volt
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 ___________.
10.3 volts.
12V (supply voltage) -1.7V (Voltage drop) =10.3 v
LED should be reverse bias. True or False?
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
When using a Sanwa VOM to test a diode the polarity of the leads are…..
red is positive and black is negative
to identify the rating of a certain transistor, it is necessary to look in ___________.
data book or specification
the term beta defines the transistors current gain and is determined by
the ratio of the collector current to the base current.
Sometime “Beta” symbol is listed as _____.
hFE
If the PIV of a diode is exceeded , the current ________
Avalanche!!!!
When used as a voltage regulator, zener diodes are connected in _______ bias
Reverse
