Electronics 2
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413 Terms
What is a conductor
Materials that conduct electricity
What is an example of a conductor
Copper/Silver/Gold
What is a insulator
Materials that do not conduct electricity
What is an example of an insulator
Plastic/Glass/Rubber
What is a semi conductor
Materials that conduct electricity under certain conditions.
What is an example of a semiconductor
Silicon/Germanium/Gallium Arsenide
What are the two methods of making semiconductors conduct
Heat and doping
What is doping
Adding impurities
What band do electrons normally sit in
Valance band
What band must electronic be in to conduct
Conduction band
What size energy gap do conductors have between the valance band and conduction band
No gap
What size energy gap do insulators have between the valance band and conduction band
A large energy gap
What size energy gap do semi conductors have between the valance band and conduction band
A small energy gap
What was used before semiconductors in electronic devices
Vacuum tubes
What state did vacuum tubes conduct electrons in
Gaseous state
What state do semiconductors conduct electron in
Solid state
What is a hole
A positive charge made by an electron jumping to the conduction band
How does adding impurities increase conductance
It increases the number of available charge carriers
What are the two types of impurities that can be added
N type and p type
How many electronics do N type have in their outer most shell
5
How many electronics do P type have in their outer most shell
3
What happens when a N - type impurity is add to silicon
4 covelent bonds are formed and 1 electron is left available to carry charge
What happens when a P - type impurity is add to silicon
3 covalent bonds are formed and 1 electron hole is created
What group in the peridoic table to N - type impurities come from
5th
What group in the periodic table to p - type impurities come from
3rd
What are the majority charge carriers for N - type semi conductors
Electronics
What are the majority charge carriers for P - type semi conductors
Holes
What are the minority charge carriers for N - type semi conductors
Holes
What are the minority charge carriers for P - type semi conductors
Electrons
What is an example of an N - type semi conductor
Arsenic
What is an example of an P - type semi conductor
Boron
When does a PN juction form
When P type and N type impuritees are joined togther
What is a PN Junction
The boundary between two semiconductors where one is doped with p type and the other n type
What happens at a PN juction
Charges align at the juction line and form a potential barrier
Why do charges align at a PN junction
Due to forces between the charges
What is the potential barrier call at a PN juction
Depletion region
What is the potential difference of the depletion region
The amount of voltage required to move electrons through the electric field
What is the potential barrier for silicon
0.7
what is the potential barrier for germanium
0.3
What external factors can affect the potential barrier
Humidity and temperature
What internal factors can affect the potential barrier
Material and level of doping
If a P type side is connected to the positive terminal, what bias is the diode in
forward bias
If a N type side is connected to the positive terminal, what bias is the diode in
reverse bias
If a P type side is connected to the negative terminal, what bias is the diode in
reverse bias
If a P type side is connected to the negative terminal, what bias is the diode in
reverse bias
What happens when the diode is in forward bias
Current will flow once when the voltage is greater than the potential barrier
What happens when the diode is in reverse bias
The depletion region will increase, increasing resistance and no current will flow
What is the internal structure of a Diode
PN junction
Which direction does electronic current flow
Positive to negative
Which way does conventional current flow
Positve to negative
Why is is easy for electrons to flow from N to P
As they are moving from a high concentration to a low concentration
What happens to the depletion region in a forward biasing diode
It is eliminated
What happens to the depletion region on a reverse biasing diode
It expands as more charges align at the junction
What happens in a forward bias diode when the voltage is less than the barrier potential
The diode does not conduct, there is a small amount of voltage and current across the diode
What happens in a forward bias diode when the voltage is above the barrier potential
There will be a voltage drop across the diode and the remain voltage will go to the rest of the circuit
What does the resistance of a diode respond to
The amount of external voltage applied
What happens to the diodes resistance when the voltage increases in forward bias
Decreseses
What is dynamic resistance
the ratio of a small change in voltage to the corresponding change in current
How do you calculate dynamic resistance
The change in voltage divided by the change in current
How do you calculate dynamic resistance from and IV graph
Calculate the gradient by using a tangent - ohms law
What happens to a diode in reverse diode as you increase the voltage
The resistance increases untill breakdown
What happens at the breakdown point
The diode is damaged and will act as a short circut and the current will exponentially increase
What mathematical equation explains the behaviour of a diode in forward bias
Shockley's
What is reverse saturation current
The current due to minority charge carriers flowing in the oposite direction to the current flowing through the diode
What is the common temperature for components in an enclosed operating system
27
What is static resistance
The resistance calculated at the operating point
Where is the operating point
A specified point on the graph
What is the operating point based on
The circuit, like what components are connected and what this biasing voltage is
What is another names for static resistance
DC
What is another name for dynamic resistance
AC
What are the 3 types of diode approximations
Ideal, practically and actual
What happens in an ideal diode in forwarding bias
It starts conducting as soon as it is connected in forward bias
What will an ideal diode in forward bias behaviour as
A short circuit
What is the voltage drop across an ideal diode in forward bias
0
What happens in an ideal diode in reverse bias
The will be no current flow or breakdown point and all the voltage drops over the diode
What does an ideal diode in reverse bias act like
An open circuit
What are the IV characteristics for an ideal diode in forward bias
No voltage drop and current flowing
What are the IV characteristics for an ideal diode in reverse bias
No current flowing but a voltage drop
What happens in a practical diode in forward bias before the threshold voltage has been reached
It will not conduct
What happens in a practical diode in forward bias when the threshold voltage is reached
It will start conducting with the max amount of current
What is the voltage drop on a practical diode in forward bias
The potential barrier
What happens to a practical diode in reverse bias
There is no current flowing and no breakdown
What are the V characteristics for a practical diode in forward bias
Voltage increases untill biasing voltage and then stops increasing.
What are the V characteristics for a practical diode in reverse bias
The increasing voltage is all dropped over the diode
What are the I characteristics in an practical diode in forward bias
No current flow until biasing voltage is reached and then maximum current flow
What is the I characteristics of an practical diode in reverse bias
No current flow
What does Vf mean
The forward voltage drop across the diode
What does Vbias mean
The biasing voltage (power source)
What does IF mean
The forward bias current
How do you work out the current though the circuit
Ohms law with the voltage being Vbias - Vf
What is the behavior of an actual diode in forward bias before the threshold voltage
There is no current flowing and all the voltage dropping over the diode
What is behavior of an actual diode in forward bias after the threshold voltage
The diode begins to conduct and current will flow, the voltage drop will not remain fixed as it will increase with dynamic resistance
What is the total voltage drop across an ideal diode in forward bias
The threshold voltage + the voltage drop across the dynamic resistance
What does r’d mean
dynamic resistance
How is the forward bias current in an actual diode calculated
Vbias - threshold voltage / Rlimit + r’d
What is an actual forward bias diode modeled as
A closed switch, voltage drop and resistor
What happens in a actual diode in reverse bias
The voltage drop increases and there is a small amount of reverse current until break down
What is an actual reverse bias diode modeled as
An open switch and resistance in parallel
What is a capacitors function
Storing charge
What is the structure of a capacitor
2 plates separated by a dielectric constant