WEEK 21 Flashcards
What happens as the temperature of a semiconductor material is raised above room temp?
Its resistivity is reduced and eventually it will go to a point where it turn into a conductor
What are the 3 main diodes?
Silicon diodes, used in rectification;
Zener diodes, used as voltage regulators;
Light-Emitting Diodes (LEDs), used as indicators.
What is the most common diode?
Silicon
What is the main characteristic of a diode?
has a small (ideally zero) resistance to current flow in one direction (the forward direction) and a very high (ideally infinite) resistance in the reverse direction
What is a transfer characteristic?
A transfer characteristic describes how the output of an electronic component or circuit changes in response to its input
What is a Zener diode?
A Zener diode is a special diode that conducts like a normal diode in the forward direction, and also exhibits very little conduction in the reverse direction for low voltages, but when the reverse voltage reaches a critical value, known as the breakdown voltage, it conducts very readily
When a material is doped with 5 electrons what does it turn into?
N-type semiconductor material (negative)
When a material is doped with 3 electrons what does it turn into?
P-type semiconductor material (positive)
What is the structure like in p-type materials?
There are “holes” in the lattice shape as there are 7 electrons. all will form a pair and one will be left, the one that is left therefore has a hole next to it, this makes it positive.
What do holes in the lattice allow?
Conduction of a current because, the lone electron will be looking to pair with another electron.
What is the structure like in n-type lattice?
Addition of 5 electrons produces 9 electrons in the outer shell which is one too many. The “spare” electron is used for conduction.
What are the semiconductor materials that have 4 electrons in its outer shell
Silicon
Germanium
What is a p-n junction?
It is a piece of semiconductor material in which part of the material is p-type and part is n-type.
In this we assume a hole is a positive charge carrier, and electrons and negative
What is forward bias in a p-n junction?
When the p-type is connected to the positive terminal of a battery and the n-type is connected to the negative terminal.
The voltages pushes electrons and holes towards the junction
What is a diode?
It is a two terminal device, having an anode and a cathode terminal
When will a diode have 0 resistance, ideally?
When the current is going forwards
When will a diode have infinite resistance?
When the current is going backwards, on the opposite direction
What voltage does a silicone diode have? in forward bias
0.7, it needs this in order to work.
Current will be at its maximum
What voltage will a silicone diode be for reverse bias?
-0.7 volts
What is a breakdown voltage?
Where a diode reaches a certain voltage at which point it allows current to go in both directions. This is called voltage regulation
What is a capacitors role in a half wave rectifier?
It gets charged when voltage is in its positive cycle, and it then discharged when when voltage supply reverses. This action allows smooth current flow,
When do LEDS work/ turn on?
What are the 2 functions of a transistor switch?
Amplification and switching
What are the three regions of a transistor?
Collector the main current of the circuit
Base, the supply
Emitter sum of base and collector
How much bigger is the collector current to the base current?
x50
What is the emitter current equal to?
The sum of the base and collector currents
The emitter current and base current should nearly be equal as the base current is so small
What does the base current do?
The base current, IB , controls the resistance between the collector and emitter and hence the collector current, IC .
What does a higher base current mean?
The higher the base current, the lower the collector-emitter resistance and so the greater is the collector current, IC .
What does a base resistor do?
Protects the transistor from excessive current
When a transistor is used as a switch why is the linear region avoided?
The load will not have the full supply voltage across it;
VCE is not zero and neither is IC , meaning that power is dissipated in the collector-emitter junction, which can cause the transistor to overheat.
