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
Two Modes of a Photo-Conductive Diode?
Photovoltaic Mode = Measures Voltage
Photoconductive Mode = Measures Current
Is a Photo-Conductive Diode used in FWD or REV bias?
Reverse Bias
What are Photoconductive Diodes constructed of?
Selenium, Germanium & Silicon
Positives of a Schottky Barrier Diode?
Very fast operating at low voltages
Better High Frequency Performance
Very small Reverse Bias to make it stop
Extremely Low reverse current
Negatives of a Schottky Barrier Diode?
Low Reverse breakdown voltage
The diode cannot withstand large current surges
Heat causes the barrier to form slowing response times
What is a Thyristor?
A 4 layer 3 terminal semiconductor device
Thyristors are trigged by?
The application of high voltage
A temp increase
Application of an appropriate gate signal
An increase in light
How many Thyristors turn off?
Removal of the power supply
Power supply reversal
Application of pulse to the gate
What is an SCR & Its use?
An SCR is a four layer P-N-P-N Semiconductor
Used in Rectification, Switching & Power Control
What is the process / action of turning off a SCR called?
Commutation
How is an SCR turned off
The anode current must be reduced to near zero ( Minimum Value of the holding current has the symbol I*H
How is anode current reduced below holding current?
Reduce or Disconnect the power supply voltage
Disconnecting the SCR from the supply by means of a switch
Making the anode negative with respect to the cathode
Temporarily short circuiting the anode to the cathode
Application of a DIAC?
a DIAC is used to drive the TRIAC ensuring both half cycles of the sinewave are used
“VCC” stands for?
Collector DC supply voltage
Is the BASE - EMITTER junction of a transistor FWD or REV bias?
Always FWD bias
Is the BASE - COLLECTOR junction of a transistor FWD or REV bias?
Always REV bias
Does a Darlington Transistor create high or low gain>
High Gain
What makes the Common Emitter transistor configuration unique?
Is make the Input 180 degrees out of phase
How do you identify the common element in a transistor
Identify the input
Identify the output
The Remaining element is the common one
Voltage Gain In a Common Emitter?
Medium
Current Gain in a Common Emitter?
Medium
Power Gain in a common Emitter?
High
Input & Output resistance in a common Emitter?
Medium
Whats the current Gain in a common emitter circuit called?
BETA
Applications of a common Emitter?
Low Noise Amp’s
Phase Shift Amp’s
General Audio Amp’s
Most common use for Common Collector?
Impedance matching
What causes instability in a Transistor?
Operation from a different Q point or the Q point drifts up or down the Load line
Does a forward bias base-emitter have a neg or pos temp co-efficient?
Negative
What causes a Bias shfit?
As the junction temperature increases, resistance and VBE drops resulting in the shift
How do you improve stability in a Base-Emitter Junction?
DC Negative ( - ) feedback
Characteristics of a UJT?
It cannot be used to amplify a signal
It is used as a ON - OFF switch
Are UJT’s unidirectional?
Yes
What are PUT’s?
They are Programmable UJT’s
How is a PUT’s parameter set?
Via external resistors
How is a photo transistor activated
Via light, current increases as light increases
What is a Opto-isolator?
Both an infrared LED and a photodetector
How can the influence of Beta be reduced?
via the addition of emitter resistance
What does the symbol ƞ mean in terms of a UJT
The intrinsic standoff ratio
Most common use for UJT’s
Trigging SCR’s
Relaxation Oscillators
Is an enhancement mode MOSFET OFF or ON at 0 voltage?
OFF
Is a Depletion Mode MOSFET, Off or On at 0 voltage
ON
Do VFETS suffer from thermal runaway?
No
Why must MOSFETs be handled with care
The dielectric acts as a capacitor making it vulnerable to static discharge.
What’s makes VFET different to MOSFET
Faster switching and ability to handle larger current
Difference in bais in JFET and MOSFET
JFET is always reverse biased
MOSFET:
Reverse bias - depletion mode
Fwd bias - enhancement mode
What region does the JFET operate in as an amplifier
Pinch off region
How is resistance controlled in a FET
Electric field at right angles to current
What is the resistance of a FET dependant on
Reverse voltage bias
What is the resistance of a FET dependant on
Reverse voltage bias
Advantage of an Opto-Isolator
Very small response times: in the megahertz range
What is tailored to be identical to permit highest measurement if coupling
Wavelength responce
