Transistors Flashcards
What is a transistor?
It is a semiconductor device that can be used in the amplification of signals or it can be also used as a switch.
What is a transistor made out of?
Semiconductor material that has been doped.
What is the basic operation of a transistor?
Voltage is applied through one of the terminals and this will control the voltage that is flowing through another pair of terminals. The controlled output can be higher than the input.
What is a triode?
It is an evacuated vacuum tube, much like the earlier diodes but it has a grid in between the anode and the cathode. The voltage that is applied to the grid will control the current that flows through the tube.
How does the grid of a triode act as a gate for electrons?
If we apply a negative voltage to the grid, then more electrons will be repelled so fewer will get through which creates a smaller current. If we apply a positive voltage, then more will get through which will increase the current.
What is doping?
It is the process that adding impurities to semiconductor material to alter its electrical properties. If we dope with boron(P type), then we add in holes as boron only has 3 valence electrons. If we dope with phosphorus (N type) then we add electrons because it has 5 valence electrons.
How does a transistor act like a diode?
We can have an NPN transistor or a PNP transistor. This has to do with what type of doping each section has. But we can think of a transistor as two diodes that are back to back. This means that one diode will always be connected in the reverse bias and stop the flow of electricity.
What happens to a transistor when we add another power source?
If we have two power sources, then we will have two forward based diodes.
What are the advantages of a transistor over a Vacuum tube?
No cathode heater
Very small size
Lots of them can be manufactured into an IC
Low operating voltages
Low sensitivity to mechanical shock
Not prone to breakage of the glass envelope
Does not require maintenance
What are the advantages of Vacuum Tubes over Transistors
silicon transistors can age and fail,.
Vacuum tubes achieve better electron mobility so high power high frequency oscillation is achieved easier.
Transistors are prone to electrical discharge and other thermal events.
Vacuum tubes are not sensitive to cosmic rays.
Vacuum tubes have better audio applications, create a lower harmonic distortion.
What are the two main types of transistors?
BJT’s (Bipolar Junction transistors)
FET’s (Field effect transistors.)
How can we categorize transistors?
Semiconductor material Structure polarity max power rating max operating frequency application physical packaging amplification factor
What are the three symbols for an FET and what do they mean?
S = Source. This is where the current enters the gate D = Drain. This is where current leaves the channel. G = Gate. This is the terminal that controls the conductivity. Applying voltage here allows the control of the drain current.
What are the three symbols for a BJT and what do they mean?
B = Base. C = collector. E = Emitter.
What are the differences between BJT’s and FETs?
BJT’s are current controlled while FET’s are voltage controlled.
BJTs have a smaller input impedance.
BJTs have a greater gain
FET’s are smaller in size, they are more expensive to manufacture.
FET’s are more popular.