L14+L15: Diodes Flashcards
What 4 Classifications of Materials are there (in terms of electrical conductivity)
- Insulators (Materials that prevent the flow of I)
- Conductors (Materials that allow the flow of I)
- Semi-Conductors (Materials that behave as conductors in certain cases and behaves as insulators in certain cases)
- Superconductors
What does Bohr’s Atomic model show/describe
What and where are Valence Electrons in the structure of an atom (+what is Coulomb’s Law)
How do electrons become free electrons and start to move in the conduction band
- When an electron gets enough energy, it can leave the valence band and becomes a free electron
- This free electron exists in the Conduction Band
- The region beyond the valence band is called the Conduction Band
- The difference in energy between the valence band and conduction band is called Energy Gap
- It is the amount of energy required for a valence electron to jump to the conduction band
How is Electrical Conductivity defined in terms of valence electrons
The number of valence electrons possessed by any atom determines its electrical conductivity.
What are some Semiconductor materials
Semiconductor materials used in electronics industry are silicon Si, germanium Ge, carbon C. Si is the most widely used one so almost all diodes, transistors, and IC’s manufactured today.
Tetravalent Definition
An atom having four covalent bonds
What do Tetravalent atoms bond together to form
- Tetravalent atoms (Si, Ge, etc) bond together to form a Crystal
- In the Crystalline Stucture valence e of semiconductors are shared between atoms
- 5 tetravalent atoms bond to form a Crystal Lattice
- Si atoms share its 4 valence electrons with each of its neighbours
- So each of them share 4 electrons with others for a total of 8 valence electrons.
What is an Intrinsic Semiconductor
- Intrinsic semiconductors are semiconductors in their purest form.
- At very low T (-273°), the Si crystal structure is locked.
How are Electron-Hole pairs formed
How do Electron-Hole Pairs work
- Holes act as positive charges; they attract free electrons passing through the crystal
- An room T, intrinsic semiconductors have only a few electron-hole pairs (bad conductors)
What is Doping
Doping is the process of adding impurity atoms to the intrinsic semiconductors. Adding a small amount of atoms that have either more or less valence electrons than Si improves greatly the conductivity.
What does the level of conductivity of something depend on
The level of conductivity mainly depends on the number of impurity atoms added during the doping process.
Intrinsic Semiconductor + Impurities = Extrinsic Semiconductor
What are the two major classifications of doping materials
- Trivalent Materials
- Pentavalent Materials
What are Trivalent and Pentavalent Materials
- Trivalent - They have 3 valence electrons (Aluminium, Al, Gallium, Ga, Boron, B)
- Pentavalent - They have 5 valence electrons (Arsenic, As, Antimony, Sb, Phosphorus, P)
What is an Extrinsic Semiconductor
An extrinsic semiconductor isa semiconductor material where the electrical conductivity has been intentionally altered by adding small amounts of impurities through a process called doping, resulting in either n-type (with excess electrons) or p-type (with excess “holes”) semiconductors.
How are N-Type Extrinsic Semiconductors formed (Pentavalent Impurity Doping)
How are P-Type Extrinsic Semiconductors formed
How does Electron Flow Current in a Semiconductor Material work
How does Hole Flow Current in a Semiconductor Material work
How can a diode be formed from semiconductors
Two extrinsic semiconductors, one of which is n-type, and the other one is p-type, a boundary called a “pn” junction is formed and what we get is a basic diode.
Why are pn junctions important
What happens when the pn junction forms
What is the Depletion Region (DR)
- These two layers of positive and negative charges form the “Depletion Region”
- It is called the depletion region because it is depleted from any charge carriers
How far does a depletion region continue for/why does a depletion region stop (how is an electric field generated)
What is Barrier Potential VB
- The pn junction acts like a barrier and blocks any charge flow (current) across the barrier
- The voltage required to overcome is defined according to the potential difference of the electric field across the depletion region
- This potential difference is called the Barrier Potential, VB
What is the Barrier Potential, VB, for silicon based diode and germanium at a charge of 25C
What is Diode Biasing
Applying a DC voltage to establish certain operating conditions for an electronic device.
What does a Forward Diode Bias result in
What happens when V < 0.7VB (Barrier Potential)
When V < 0.7VB, the diode conducts a small amount of current, I, known as leakage current.
What does a graph of current against voltage showing forward bias and reverse bias look like
What does Reverse Bias Result in
- Reverse Bias of a semiconductor diode is the condition in which current I is blocked.
- The voltage applied across the p-n junction is in the opposite polarity to the p and n type materials
How does a Diode act when in reverse bias
What affect does reverse bias have on the depletion zone
Reverse bias widens the depletion zone
What are diodes and what do they do
What does the behaviour of a diode depend on
- It has a non-linear characteristic
- Unlike the resistance, the behaviour of the diode depends on the relative polarity of its terminals
What is the first diode approximation
What is the second diode approximation
What is the third diode approximation
What are Rectifiers
A rectifier is an electrical circuit that converts the AC voltage into DC voltage.
What do diodes actually do in Rectifiers
- The most important components in rectifiers are diodes
- Since diodes are unidirectional (only one direction current flow) devices, they can produce a DC output voltage out of an AC input
What is PIV (Peak Inverse Voltage)
The maximum instantaneous reverse-bias voltage across a diode
What is VBR (Breakdown Voltage)
The reverse breakdown voltage (VBR) is the voltage at which a sharp increase in reverse current occurs
What are the three types of Rectifier Circuits
- Half-Wave Revtifier (Built by one diode)
- Full-Wave Rectifier (Built by two diodes)
- Full-Wave Bridge Rectifier (Built by four diodes)
What happens in a Half-Wave Rectifier when the transformer secondary voltage is positive (>0.7V) and negative (<-0.7V)
How is the input and output of a transformer affected/changed by a Half-Wave Rectifier
What happens in a Full-Wave Rectifier when the transformer secondary voltage is positive (>0.7V) and negative (<-0.7V)
How is the input and output of a transformer affected/changed by a Full-Wave Rectifier
What is an LED
A Light-emitting diode (LED) is a diode that emits a certain colour of light when forward biased.
Electronic Symbol for an LED
How is the colour of an LED determined and what is the voltage drop across the terminals when it is forward biased
- The colour of light emitted by an LED is determined by the type of material used in doping.
- The voltage drop across the terminals of an LED when it is forward biased ranges from 1.5 to 2.5V
What are some applications of LEDs
- Aviation lighting
- Automotive Headlamps
- Advertising
- General Lighting
- Traffic Signals
