Diode Characteristics and Properties Flashcards
What are diodes?
Semiconductors that allow the flow of electricity one way
To check forward resistance of a diode, the positive terminal lead of a multimeter should be connected to…
The anode
What gives the colour of an LED?
The active element
An atom with 5 electrons in its outer shell is part of P or N type material?
N type material
What is an SCR?
Silicon controlled rectifier (thyristor)
What are the properties of a thyristor?
- 3 terminal device used for switching
- turned on by a positive voltage at the gate
- silicon based
What component is used to turn AC to DV?
- Diode
- Thyristor
- Transistor
Diode
What type of diode gives off light photons when forward biased?
LED
To function, how much voltage does a germanium diode require?
0.3V forward biased
To function, how much voltage does a silicon diode require?
0.7V forward biased
What is a zener diode used for?
Voltage control.
It stabilises voltage at a predetermined level
When a diode is forward biased, what is the current flow due to?
The majority carriers (electrons and holes)
An atom with 5 electrons in its outer shell is part of what?
An N-type material.
It is pentavalent and will provide an extra free electron making the material N type.
Phosphor and Arsenic are examples
In a PN junction, what is the depletion region?
A depletion/lack of free electrons and holes in a vicinity of the junction.
It is reduced when the junction is forward biased
How is an SCR turned on?
A positive voltage at the gate
In a semiconductor junction diode, where are the electrons minority carriers?
Within the P region
If a rectifier circuit is designed to convert positive and negative cycles into DC output, what is the process called?
Full-wave rectification
Which type of diode (silicon or germanium) has the lower forward bias voltage?
Germanium diode
What are indium and aluminium used for in diodes?
They are a neutral semiconductor
How can the conductivity of an intrinsic semiconductor be improved?
By doping the materials
What are the electrodes of an SCR?
- gate
- anode
- cathode
How is an SCR switched off?
- Removing the source potential/reducing it below minimum holding current
- Reversing the current
A zener diode is reverse biased. When forward biased, what happens to a zener diode?
It will conduct like an ordinary rectifier diode.
When light falls onto a photo sensitive diode, it causes the resistance to…
Decrease
What is an intrinsic material?
A pure material
What is the typical voltage drop across an LED?
1.6V to 2.4V
Around 2V
A thyristor has high resistance when…
Switched off
A zener diode has what characteristics of voltage and current?
- Constant voltage
- variable current
What is the purpose of using two diodes in parallel?
Prevents damage by excessive current
Voltage remains the same, current is split.
What is antimony?
A donor material
When will a photodiode increase its resistance?
When less light falls on it
Do photodiodes work in forward or reverse bias?
Reverse
In a forward bias diode, current is carried by…
Both majority and minority carriers, but mainly majority. (Electrons and holes)
Reverse bias is minority only.
What would a serviceable diode read when a multimetrer is connected to it?
0.7V when forward biased
What is the maximum reverse voltage for any LED?
5V
What is a silicon diode used for?
Rectification
What is a germanium diode used for?
Demodulation
What is a diode connected across a relay coil used for?
Dissipate coil spikes on switch off
How many diodes are used in a full wave 3-phase rectifier circuit?
6 diodes
How does a photodiode operate?
Reverse bias conditions.
- leaking current increasing with light increasing
- resistance
Reverse bias systems will _______ the potential barrier.
Increase
