4.1.1 Semi Conductors Flashcards
What is a diode?
Two terminal electronic components
What does the diode do?
Conducts current in a single direction by applying low resistance in one direction and high in the other.
In a schematic symbol for a diode what is the arrow end?
Anode
In a schematic symbol for a diode what is the bar end?
Cathode
What does a generic diode symbol look like?
Line with an arrow and bar.
What does a schottky diode symbol look like?
Line with an arrow and ‘s’ bar (tips of s curl round)
What does a shockley diode symbol look like?
Line with two bars and a diagonal connecting the two.
What does a constant current diode symbol look like?
Line with an arrow and an ‘I’ bar
What does a zener diode symbol look like?
Not to be confused with a schottky, it is a line with an arrow and ‘s’ bar but the ends don’t curl.
What does a light emitting diode symbol look like?
Line with arrow and bar, surrounded by circle and arrows pointing away.
What does a photo diode symbol look like?
Line with arrow and bar, surrounded by circle and arrows pointing towards.
What does a step recovery diode symbol look like?
Line with an arrow and ‘L’ shaped bar.
What does a tunnel diode symbol look like?
Line with an arrow and backwards ‘c’ bar
What does a varactor diode symbol look like?
Line with an arrow and double bar
What does a Pin diode symbol look like?
Line with an arrow and bar, between them is a little square.
What does a vacuum tube diode symbol look like?
Completely different to the rest, big circle with a load of squiggles.
What are diodes susceptible too?
Electro static discharge
What are diodes made of?
Semi conductors
What can semiconductors be manufactured as?
Single discrete devices- diodes and transistors
Multiple- fully integrated circuits
What is a fundamental semiconductor device?
Positive negative junction diode
How are positive negative diodes fabricated?
Doping together two sides of a single crystal semiconductor with opposite impurities.
In a positive negative junction diode with side of the junction has an excess of electrons?
Negative
Diodes can be thought of as check valves, how do they decide whether to ‘block’ the current or let it through?
Depletion layer
What is a depletion layer?
When P and N materials are bonded together, electrons migrate to fill holes on the p side, leaving a depletion zone.
What is the depletion zone sometimes referred too as?
Barrier region
What is a diode being forward bias doing?
Conducting
What is a diode being reverse bias doing?
Insulating
If the p type is connected to the plus of the battery what does it do the depletion layer?
Narrow, making it function as a conductor
What is a the barrier potential or trigger of a diode?
High resistance to current flow at the point of switching.
What happens when diodes are connected in series?
The forward current flowing through each diode is the same. Therefore the current must not exceed a individual diode rating.
In series diodes what is the voltage drop?
Germanium- 0.3V
Silicon- 0.7V
What happens to the current when diodes are in parallel?
The current is divided across them.
What is the benefit of parallel diodes but the risk too it?
They current they can carry can be increased as it shared, but if one were too fail, then the others may be above their rating.
Parallel diodes don’t conduct current equally, therefore what kind of diode is required if the same output is required?
Identical diodes.
What is a thyristors other name?
Silicon controlled rectifier
How many layers does a thyristor have?
4
What is a thyristor?
Fast electronic switches (up to 400Hz)
Due to the way thyristors are constructed how many p-n junctions are formed?
3
What are the three operating states of thyristors?
Reverse blocking
Forward blocking
Forward conducting
What is reverse blocking?
voltage is applied that would reverse bias an equivalent diode.
What is forward blocking?
voltage is applied that would forward bias an equivalent diode but the thyristor has not been triggered into conduction.
What is the breakdown voltage?
The point at which enough voltage is applied to allow the thyristor to conduct
What is the benefit of thyristors?
Very large currents and high power levels can be switched
Why are thyristors used in light dimming systems?
used to reduce the average voltage supplied to the lights, by controlling the gate trigger signal position.
What does LED stand for?
Light emitting diode
How do LED’s work?
When the electron re-aligns with a hole it emits energy in the form of photons.
What is the voltage range of an LED?
1.4 to 4.5V (Purple to white)
What is the switching time for a red emitting diode?
50 nanoseconds
What is the switching time for green emitting diodes?
400 nanoseconds
LEDs in the visible range are manufactured with what?
Gallium Arsenide Phosphide (GaAsP)
What is used to emit infrared light from LEDs?
Gallium Arsenide with zinc and sillicon.
What does the junction of a photo conductive diode respond to?
Light, and more specifically to longer wavelengths, such as red and infra-red
Which way is a photo diode junction biased?
Reverse
What is the proper name for a varistor?
Voltage Dependant Resistors
What does the effective semiconductor layer of a VDR consist of?
Many small, highly conductive crystal particles, each of which is covered with an extremely thin barrier layer and sintered together.
What does the symbol for a varistor look like?
Line with a rectangle and a tick through it.
What does the U mean on a varistor symbol?
EU standard for voltage
What is the resistance level of varistors?
Inversely proportional to the voltage applied
What are varistors used for?
Protect against excess voltage, and regulating voltage.
Where is a rectifier diode used?
used in applications that require high current, such as power supplies
What does a rectifier diode do?
Convert AC-DC
What range of amps can rectifier diodes handle?
1-100
What make rectifier diodes recognisable?
They are cased in metal, acting as a heat sink.
How can you tell if a diode is faulty in the open circuit condition?
The reading is high resistance in both directions
When a multimeter is set to diode test, what voltage does it supply?
2.5-3.5V
When tested in the forward bias condition what voltage would the diode show?
0.6-0.7V
When tested in the reverse bias condition what would the multimeter display?
OL- Overload, high internal resistance
If a diode has failed open circuit, it shows what on the multimeter?
Indicates OL in both forward and reverse or internal voltage of the meter.
If a diode has failed in the short circuit condition, what does the meter show?
Shows 0 in both directions, and makes an audible beep depending on meter type.
