Transistors Flashcards

1
Q

What is a transistor?

A

It is a semiconductor device that can be used in the amplification of signals or it can be also used as a switch.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

What is a transistor made out of?

A

Semiconductor material that has been doped.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

What is the basic operation of a transistor?

A

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.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

What is a triode?

A

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 well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

How does the grid of a triode act as a gate for electrons?

A

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.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

What is doping?

A

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 well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

How does a transistor act like a diode?

A

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.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

What happens to a transistor when we add another power source?

A

If we have two power sources, then we will have two forward based diodes.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

What are the advantages of a transistor over a Vacuum tube?

A

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

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

What are the advantages of Vacuum Tubes over Transistors

A

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.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

What are the two main types of transistors?

A

BJT’s (Bipolar Junction transistors)

FET’s (Field effect transistors.)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

How can we categorize transistors?

A
Semiconductor material
Structure
polarity
max power rating
max operating frequency
application
physical packaging
amplification factor
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

What are the three symbols for an FET and what do they mean?

A
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.
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

What are the three symbols for a BJT and what do they mean?

A
B = Base. 
C = collector.
E = Emitter.
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

What are the differences between BJT’s and FETs?

A

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.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

When would we use a BJT over an FET?

A

If we need a circuit for a difficult environment like a vehicle. or in high demanding applications like high frequency amplification and signal switching.

17
Q

How do we control the conductivity of an FET?

A

By controlling the voltage across the drain and the source. This creates a magnetic field which controls the conductivity.

18
Q

What type of charge carriers do both types of transistors use?

A

BJT’s will use both electrons and holes

FET’s will only use electrons.

19
Q

In a BJT diagram, what does the emitter arrow point to and what is the equation for the emitter current?

A

The arrow will point in the direction of conventional current flow, or towards the N region. The emitter current is the sum of the base and collector currents:
Ie = Ic + Ib

20
Q

What is the saturation mode of operation?

A

The transistor acts like a short circuit and current can flow freely from the collector to the emitter.

21
Q

What is the cut off mode of operation?

A

The transistor will act like an open circuit. No current can flow from the collector to the emitter.

22
Q

What is the active mode of operation?

A

The current from the collector to the emitter is proportional to the current flowing into the base.

23
Q

What is the Reverse-Active mode of operation?

A

It is the same as the active mode but instead the current will flow in the reverse direction so from the emitter to the collector.

24
Q

What are the BJT regions of operation?

A

If the voltage between the base and the emitter (Vbe) is:
below 0.7V then transistor is in the cutoff region and Ic=Ib=Ie=0
When Vbe = 0.7V and Vce = 0.2V then the transistor is in the saturated region.
When Vbe = 0.7V and Vce > 0.2V then it is in the active region.
In active mode, the currents are exponentially dependant on Vbe

25
Q

What are the equations for the emitter and collector current for a BJT in the active region?

A

Ic = BIb
Ie = (B + 1)Ib
B is the gain of the transistor, it is constant for a transistor ( between 50 and 200).
The fact that the collector current is a large multiple of the base current is what allows it to be used as an amplifier.

26
Q

How do we use a transistor as a switch?

A

Making use of the cutoff and saturation states of the transistor.

27
Q

What is a relay?

A

An electromechanical switch. It uses an electromagnet to close or open a switch. Applications are for when a circuit needs to be controlled by a low power signal, or where several circuits need to control one signal.

28
Q

What are the advantages of transistors vs Relays?

A

They are much faster.
Less power consumption
Less current needed to initiate the switching.
Smaller size than the relays.

29
Q

What are the advantages of the Relay over the Transistor?

A

Can switch AC or DC while a transistor can only switch DC.
Can switch high voltages.
More suitable for large currents
Can switch many contacts at once.
Electrical isolation between the controlling circuit and the circuit to be controlled.