D6 Flashcards
How many valence electrons do insulators have?
five or more
How many valence electrons do conductors have?
3 or less
How many valence electrons do semi conductors have?
exactly 4
What are the two most commonly used semiconductor elements?
silicon and germanium
Silicon is the most common semiconductor element because?
it can with stand higher temperatures
Purified semiconductor materials arrange themselves into a
crystal-lattice structure
Semi-conductor atoms tend to share their valence electrons in an
covalent bond
To make a semiconductor a better conductor, a small amount of impurity is introduced this is called
doping.
Creating a N-type semiconductor a ________ atom is used
pentavalent
A N-type semiconductor has an excess of
electrons and is negatively charged
To create a P-type semiconductor a ___________ element is used.
trivalent
List three trivalent atoms
aluminum
boron
gallium
List three pentavalent atoms
arsenic
antimony
phosphorous
A P-type semiconductor has an unfilled
hole and is considered positively charged or less negative
Semiconductors have a negative temperature coefficient of resistance. explain
this means that as the temperature increases the resistance decreases.
When a joining a P-type material to a N-type material it creates a ____________ potential
barrier
The barrier potential for silicon diodes is
.7 Volts
The barrier potential for germanium diodes is
.3 Volts
When the cathode is more positive than the anode (reverse bias) how is the barrier potential at the PN junction is strengthened.
free electrons in the N-type material attracted to the positive side
the holes in the P-type material are attracted toward the negative
depletes the junction region of any available charge carriers thus blocking current flow.
When an external voltage is applied that makes the cathode more negative than the anode the barrier junction will weaken and
current will flow this is called forward bias
As the current in a diode increases the resistance tends to decrease due to the negative temperature coefficient of semiconductors this
decrease in forward resistance combines with the increase in current so that the small voltage drop remains the same.
What is PIV
Peak inverse voltage is the point at which a diode can no longer block current flow. Beyond this point the diode breaks down and current avalanches
For a diode to conduct it must be
forward-biased
To remember anode and cathode (only for conventional current flow
Current flows alphabetically, anode to cathode
When a diode is connected across an inductive DC load so as to prevent arcing during switching operations, it is called
freewheeling diode
Describe a Zener diode
designed to operate beyond its breakdown voltage rating in the reverse direction (reverse bias)
If a silicon Zener diode is dropping .7 volts across it what is wrong?
It is hooked up back to front.
Define Zener voltage
is the regulated voltage that is maintained across the Zener diode when it operates with reverse bias.
What are Zener diodes good for?
voltage regulator
How does a Zener diode regulate voltage?
When the breakdown voltage is reached the drop-off is sharp keeping the voltage constant.
What must we do when installing a Zener diode as a voltage regulator?
DC input voltage must exceed the Zener voltage
Hook Zener diode in reverse-bias
instal series current-limiting resistor
Connect load in parallel with Zener diode
Photodiode is a special PN junction diode in which
light striking the junction increases the conductivity of the diode
If two blocks of N-type semiconductor material are separated with a very thin layer of P-type semiconductor material then
a NPN transistor is created
If the two outer blocks are made of P-type semiconductor, and if the separating layer is N-type semiconductor then
a PNP transistor is formed
Signal transistors
are used in the milliwatt range
Power transistors
are used in the watt range
What does BJT stand for?
bipolar-junction transistor
Transistor terms: Q
transistor
Transistor terms:Ib
Base current
Transistor terms:Ic
Collector current
Transistor terms:Ie
Emitter current
Transistor terms:Rb
Base circuit resistance (control)
Transistor terms:Rc
Collector circuit resistance (load)
Transistor terms:V Rb
Voltage drop across base circuit resistance
Transistor terms: V Rc
Voltage drop across collector circuit resistance
What is the advantages of using a transistor as a relay instead of a coil/contact relay?
the transistor has no contacts to pit no coil to burn out no moving parts to wear out it is completely solid-state
the magnitude of the base current actually controls
the amount of collector current that can flow
usually by the beta factor or the transistor
Transistor terms: Beta
expresses the magnitude of collector current controlled by a specific value of base current
Transistor terms: Alpha = Ic/Ie
since the emitter current is always greater than the collector current alpha is always less then 1
Transistor terms: Cut off
if the base current is reduced to a value close to zero then no collector current is allowed to flow.
Transistor terms:Saturation
If increasing the base current any further cannot allow any more collector current to flow the transistor is said to be saturated.
Which way does the arrow on a transistor diagram point?
from P to N
Transistor terms: biasing
setting the value of Vce for a transistor
