Exam 1 - 1.1 to 2.8 Flashcards
How many valance electrons in a semiconductor
4
Whats the energy level of an atom’s shell measured in?
Electron Volts (eV)
What is a hole?
Absence of an electron where one could exist
Whats an Instrinsic semiconductor
When it has no impurities
What is Doping?
Addition of impurities to the lattice structure
If the added impurity has only 3 electrons what is it called?
A Trivalent Impurity
Common Trivalent elements
- Aluminum
- Boron
- Gallium
- Indium
If the added impurity has 5 electrons, whats it called?
A pentavalent impurity
Common Pentavalent impurity
Antimony
Arsenic
Bismuth
Phosphorus
Whats the Depletion Region?
When enough voltage is applied the electrons will fill the holes on the Positive side to create a negative charge and leave a positive on the negative - this moment is when the depletion region develops
What happens to the depletion region when Forward Bias?
The Width of the depletion region is reduced and the barrier potential decreases
What happens to the depletion region when Reverse Bias
The Width of the depletion region is increased and the barrier potential is increased
What is Reverse Breakdown voltage & effect if current is not limited?
Reverse breakdown voltage is the voltage across a reverse bias diode at which avalanche breakdown occurs and the diode conducts heavily
- If current is not limited the diode will destory itself
What is Reverse/Leakage current
As temp increases, the additional thermal energy causes more electrons to break away from the atoms, this creates more electron-hole pairs and more MINORITY CARRIERS
What is forward voltage drop?
This is the voltage across the diode when current flows through the diode in forward direction
What is Diode clamping?
A Circuit which can set the positive or negative peak of the input AC signal at a required level
Disadvantage of a Half-Wave Rectifier
High Ripple voltage
Effects of a Full wave rectifier
The output voltage frequency is double that of the input frequency, also has a stable output voltage
Disadvantage of a full wave rectifier?
Dependent on the use of a centre tap output transformer
Main use for a half-wave voltage doubler?
To provide a second voltage without the use of a transformer
Disadvantage of a Voltage doubler?
Hard to regulate
Ripple is hard to filter
The output cap must be able to withstand x2 the input voltage
The PIV is twice the input voltage
What i used to balance current of diodes mounted in parallel
Balancing Resistors or inductors are wired in series to equal out the current
Zener Diodes can act?
In both reverse or negative bias, plus avalanche breakdown happens at a higher point
What is Avalanche Breakdown?
As the reverse bias becomes more and more negative, a point is reached where the few minority carriers have developed enough velocity to liberate additional carriers through ionization
What are the two main categories of how Varactor Diodes are used
Tuning and Hormonic Diodes
What is a Varistor?
A non linear resistor which has its resistance controlled via applied voltage
If the voltage applied is doubled in a varistor what happens to current? ( Thryrite )
The Current is increased 11 times
What is a tunnel diode?
A small two terminal semi-conductor containing a single junction formed by heavily doped materials
In a tunnel diode oscillator, where should the operating point be?
Closest to the centre of the negative-resistance curve
What happens to the Junction Capacitance in a reverse bias in a Varactor
The Junction capacitance decreases due to the depletion region widening
What happens to the Junction Capacitance in a forward bias in a Varactor
The Junction capacitance increases due the depletion region shortening
Common use for a varactor?
The most common use for a varactor is to allow remote adjustment of the resonant frequency of a tuned circuit
Two Rules of a LED?
They Must be connected in the correct polarity
Must not be connected directly across a battery
