Transistor Learning Objectives PDF

Transistors (4.1.2.1) Learning Objectives 4.1.2.1.1 Identify transistor symbols (Level 1). 4.1.2.1.2 Identify transistor component description and orientations (Level 1). 4.1.2.1.3 Recall transistor characteristics and properties (Level 1). Summary This lesson continues semicon...

Transistors (4.1.2.1) Learning Objectives 4.1.2.1.1 Identify transistor symbols (Level 1). 4.1.2.1.2 Identify transistor component description and orientations (Level 1). 4.1.2.1.3 Recall transistor characteristics and properties (Level 1). Summary This lesson continues semiconductor theory into transistors. Transistors can be used for amplifying, controlling, and generating electrical signals. Transistors are the active components of microchips and a transistor used as a switch is the fundamental building block of computer circuitry. 2022-11-10 B1-04 Electronic Fundamentals Page 72 of 163 CASA Part 66 - Training Materials Only  Transistors The Transistor Transistors are normally a three terminal semiconductor device used to regulate current, or to amplify an input signal into a greater output signal. Transistors are also used to switch electronic signals. Importantly, however, a transistor on its own does not amplify. The Oxford Dictionary defines amplification as: “The action of increasing the amplitude of an electrical signal or other oscillation”. To amplify something then means that you get more out than you put in which is against the laws of physics. A transistor is simply a control device where a small amount of input current/voltage controls a larger amount of power supply current/Voltage thus giving the impression of amplification. There are two basic categories of transistor: Bipolar Junction Transistor (BJT) Field-Effect Transistor (FET). These two types of devices differ greatly in construction and theory of operation, but their broad applications are similar. Generally, the BJT is categorised as a current-controlled device, whereas the FET is categorised as voltage-controlled. © Aviation Australia Most common transistor types 2022-11-10 B1-04 Electronic Fundamentals Page 73 of 163 CASA Part 66 - Training Materials Only  The History of Transistors The invention of the transistor by American physicists John Bardeen, Walter H. Brattain, and William Shockley, as part of a post-war effort to replace vacuum tubes with solid- state devices, was announced by the Bell Telephone Laboratories in 1948. The first transistor (1947) Although discrete transistors are still used significantly, the vast majority of transistors are built as part of integrated circuits. Transistors are used in virtually all electronic devices, including radio receivers, computers, space vehicles and guided missiles. The BJT was the most common transistor between the 1950's and the 1960's. The BJT was also the first solid-state amplifier element and it began the solid-state electronics revolution. Since the 1970's, the MOSFET (due to its advantages within integrated circuits) has dominated the electronic world making up for 99.9% of all transistors on the market today. It is worth noting that this statistic is heavily influenced by modern computing. The average Central Processing Unit (CPU) of a computer contains upwards of 5 billion MOSFETs and the average Graphics Processing Unit (GPU) contains approximately 30-60 billion MOSFETs. In 1965, Intel's co-founder Gordon Moore predicted that microchip performance and the number of transistors in a microchip would double every two years (Moore's Law). For the most part, this has held true although it is slowing down. As of 2021, manufacturers produce microprocessors with transistors that measure less than 5 nanometers wide (0.0000005 cm). To put that in perspective, a silicon atom is about 0.2 nanometers wide. The basic transistor logic remains the same between those that you will see and implement directly (BJTs and FETs) and those that exist within these complex integrated circuits. 2022-11-10 B1-04 Electronic Fundamentals Page 74 of 163 CASA Part 66 - Training Materials Only  Bipolar Junction Transistors NPN Transistor - BC550 Pinout and Component BJT's are 3 terminal devices with the names of the terminals being Base, Collector, and Emitter. the collector and emitter are normally connected to the power supply though other components and the base is normally in input signal to be amplified. Base the very narrow region in the centre. Collector is a relatively large weakly doped region. the size reduces the resistance and allows greater heat dissipation as this region generates the greatest amount of heat. Emitter is a strongly doped region of the same type as the collector. BJTs are classified as either NPN or PNP according to the arrangement of their N and P materials. Their basic construction and chemical treatment is implied by their names, "NPN" or "PNP." That is, an NPN transistor is formed by introducing a thin region of P-type material between two regions of N-type material. Relating back to diode theory, a transistor is similar to two diodes (two PN junctions) back to back. This diode formation is NOT actually equivalent to a transistor device because the operation of the transistor depends on the interaction of the depletion regions in the narrow region called the base. 2022-11-10 B1-04 Electronic Fundamentals Page 75 of 163 CASA Part 66 - Training Materials Only  Collector Collector N P Base Base N Emitter Emitter A BJT effectively uses two PN junctions (diodes) back to back When the semiconductor orientation is flipped, a PNP transistor is formed where conversely a thin region of N-type material in introduced between two regions of P-type material. Transistors constructed in this manner have two PN junctions. One PN junction is between the emitter and the base; the other PN junction is between the collector and the base. The two junctions share one section of semiconductor material so that the transistor actually consists of three elements as shown. NPN and PNP Transistors 2022-11-10 B1-04 Electronic Fundamentals Page 76 of 163 CASA Part 66 - Training Materials Only  NPN Transistor A mnemonic for remembering the circuit symbol for a NPN transistor is: Never Points iN (NPN) - Arrow is pointing out between the base and emitter. NPN Transistor - BC550 Pinout and component PNP Transistor A mnemonic for remembering the circuit symbol for a PNP transistor is: Points iN Permanently (PNP) - Arrow is pointing in towards the base from the emitter. © Aviation Australia PNP Transistor - BC327 Pinout and component 2022-11-10 B1-04 Electronic Fundamentals Page 77 of 163 CASA Part 66 - Training Materials Only  Field Effect Transistors © Aviation Australia Junction Field Effect Transistor FETs are available in more varieties than BJTs. FET's are normally 3 terminal devices with the names of the terminals being Drain, Source, Gate. The Drain and Source, are normally connected to the power supply though other components and the Gate is normally in input signal to be amplified. A field effect transistor has only two sections of semiconductor material. The common feature among FETs is that a current flowing through a channel, which is a region of p or n type material, is controlled, by an applied electric field. The part of the transistor that supplies the field must be isolated from the channel, and the method of isolation falls into two basic categories: isolation provided by reverse-biased PN junctions and isolation provided by an electrically insulating material. Devices that use reverse-biased junction isolation are called Junction FETs, Jug FET (Junction Gate FET) or JFETs, and devices that use insulating materials are called Metal-Oxide Semiconductor FETs, MOSFETs, or IG FET(Insulated Gate FET). Most of the transistors contained in today's integrated circuits are MOSFETs. The depletion type MOSFET can be operated in two modes, enhancement mode and depletion mode. JFETs only operate in depletion mode. 2022-11-10 B1-04 Electronic Fundamentals Page 78 of 163 CASA Part 66 - Training Materials Only  © Aviation Australia Field effect transistor symbols All FETs are produced as either N-channel or P-channel. The N-channel for example is a FET with the N-type semiconductor material operating as the channel for current flow. The arrow head points towards the N type material and is drawn on the Gate terminal. Therefor the arrowhead point towards the channel is an N channel and pointing away from the channel is a P channel. MOSFETs can have two operating types; enhancement type and depletion type. Only the depletion type will be covered in detail. The depletion type MOSFET can be operated in two modes, enhancement Mode and depletion Mode. JFETs can only operate in depletion mode. Enhancement Mode Increased voltage applied to the gate increases conductivity of the channel. This allows more current to flow from drain to source or vice versa. Depletion Mode The transistor is "On' by default and allowing current to flow. When a voltage is applied to the gate conductivity is reduced and can even turn the transistor 'Off' like opening a switch. 2022-11-10 B1-04 Electronic Fundamentals Page 79 of 163 CASA Part 66 - Training Materials Only  Junction FET The Junction FET (JFET) has a channel of one semiconductor type the other type positioned around centre channel. Electricity flows through the “channel” from the source to the drain. A voltage connected to the gate, controls the depletion region around the channel. Thus, the voltage connected to the gate controls the current flow through the channel. It works on a similar principle to squeezing a garden hose to restrict the flow of water. © Aviation Australia Junction Field Effect Transistor The JFET works by applying a reverse bias voltage to a gate terminal, at that point the channel is "squeezed" and the electric current is impeded or switched off completely. A JFET is typically ON when there is no voltage between its gate and source terminals (depletion mode). If a potential difference of the correct polarity is applied between its gate and source terminals, the JFET becomes more resistive to current flow, and less current flows in the channel between the source and drain terminals. 2022-11-10 B1-04 Electronic Fundamentals Page 80 of 163 CASA Part 66 - Training Materials Only  Aviation Australia N Channel JFET In the diagram shown on the left the depletion region is shrunk enough to let current pass through the N-channel. In the diagram on the right the depletion region is blocking current flow between the drain and source. Metal Oxide Semiconductor FET A MOSFET is also a field effect transistor. Most MOS FET's normally have 3 connections The effect of the voltage applied on the gate increases and reduces the channel conductivity which affects the current flow from the source to the drain. The gate is insulated from the channel by a thin film of silicon dioxide. The channel material connects the drain and source. Depletion type MOSFETs can be operated in either depletion or in enhancement mode. Aviation Australia Metal Oxide Semiconductor FET 2022-11-10 B1-04 Electronic Fundamentals Page 81 of 163 CASA Part 66 - Training Materials Only  MOSFETs can be either P-channel or N-channel. The gate voltage controls current flow through channel. For example, in an N-channel MOSFET run in enhancement mode, a positive gate voltage enhances channel size therefore increasing current flow and in depletion mode a higher negative voltage on the gate reduce the source to drain current. Aviation Australia N Channel MOSFET Transistor Symbols BJT and FET (JFET and MOSFET) transistors have the following schematic symbols. Each transistor (generally) has three terminals. The BJTs terminals are referred to as the following elements; the Collector (C), the Base (B) and the Emitter (E). FET terminals are referred to as the Drain (D), the Gate (G) and the Source (S). MOSFET BJT JFET N-Channel P-Channel NPN PNP N-Channel P-Channel D D G G C E D D B G G S S E C Depletion Type S S © Aviation Australia Field effect transistor symbols 2022-11-10 B1-04 Electronic Fundamentals Page 82 of 163 CASA Part 66 - Training Materials Only  The circle around each transistor symbol is optional and often schematics will not use it. The letters (B, C and E or D, G and S) are also not always a requirement in the schematic and often not included. The diagram below shows two variations of the same circuit, the circuit on the left has the transistor symbols circled and the circuit on the right does not. Both circuits operate the same way. The transistors below are not labelled, however based on the diagram their type and orientation can be inferred. For instance, the transistors are BJTs (based on the circuit symbol) and the arrow is pointing outward from the base. The arrow will always point from base to emitter or emitter to base. In this case the arrow pointing from the base to the emitter which indicates that this is an NPN transistor. Both transistors in this circuit are identical. © Aviation Australia Example of circuit schematic with and without 2022-11-10 B1-04 Electronic Fundamentals Page 83 of 163 CASA Part 66 - Training Materials Only  Transistor Properties A transistor can use a small signal applied between one pair of its terminals to control a much larger signal at another pair of terminals. This property is called gain. It can produce a stronger output signal, a voltage or current, which is proportional to a weaker input signal and thus, it can act as an amplifier. Alternatively, a transistor can be used to turn current on or off in a circuit as an electrically controlled switch, where the amount of current is determined by other circuit elements. As previously explained, a BJTs terminals are referred to as the Collector (C), the Base (B) and the Emitter (E). A BJT can be used as an amplifier, or a switch. The FET has different terminals but perform the same function. As shown in the basic transistor operation diagram, when a small current (small signal) is applied to the base terminal (B), a larger current can flow from the collector (C) to the emitter (E). This is the basis of transistor operation, however the device has several other important uses. © Aviation Australia Basic transistor operation A helpful analogy is that a transistor blocks the main flow when turned off, and allows the main flow when turned on (a Voltage is applied). The flow the turns the transistor on can be much smaller than the flow that runs through the main pipe, which gives it the amplification properties. 2022-11-10 B1-04 Electronic Fundamentals Page 84 of 163 CASA Part 66 - Training Materials Only  © Aviation Australia Transistor water flow analogy There is however, a relationship between the base current and the collector current. A base current increase is proportional increase the collector current. For example, if amplification is 200, and the applied base current is 2 mA then the current that will flow into the collector is 0.2 A. This relationship works up until the maximum rated values of the transistor, pushing the collector too high past the 'breakdown' will cause an avalanche, and the current to rapidly increase, likely damaging component. Controlling Transistors Previously it was mentioned that a BJT is considered current-controlled and a FET is considered voltage-controlled. To turn a BJT on, a voltage is applied to the base. This implies a voltage AND a current are applied to the base. The BJT being current-controlled means that it doesn't care about the amount of voltage, it will turn "on" with any voltage sufficient to forward bias the Base Emitter junction and cause current to be provided to the base. 2022-11-10 B1-04 Electronic Fundamentals Page 85 of 163 CASA Part 66 - Training Materials Only  Transistor Basic Circuits A transistor is used to amplify or switch electronic signals and electrical power. Two basic examples of this can be seen in the following circuit diagrams. Transistor as an Amplifier © Aviation Australia BJT as an amplifier 2022-11-10 B1-04 Electronic Fundamentals Page 86 of 163 CASA Part 66 - Training Materials Only  Transistor as a Switch © Aviation Australia NPN BJT as a switch 2022-11-10 B1-04 Electronic Fundamentals Page 87 of 163 CASA Part 66 - Training Materials Only  Transistor Operation In the graph IB0 to IB6 show Increasing levels of Base current, IB0 has no base current and although there may be a very small leakage current this is considered to be the transistor switched OFF. The yellow region is not used as the increasing voltage between the collector and emitter acts like a resistor and current increases with voltage. In the green region difference in current from the CE voltage is insignificant giving approximately a constant current source. The green region between 0.7 V and VCE is used for amplification. The red region is where the collector emitter voltage goes too high (above VCE) and will destroy the transistor. BJT operating regions graphed The JFET, MOSFET and their variations all have slightly different operating modes and regions. Similar to the NPN and PNP transistors however, each region of operation is utilised for a different use case. Remembering the three pins are drain, gate and source, so the terminology is slightly different to the diagram above. 2022-11-10 B1-04 Electronic Fundamentals Page 88 of 163 CASA Part 66 - Training Materials Only  Transistor Biasing In order for the transistor to operate effectively as an amplifier, the two PN junctions must be correctly biased with external voltages. Only the NPN transistor will be used to explain the theory of operation. PNP operation is the same, but the bias voltages and current directions will be the opposite polarities. Base/Emitter junction is forward biased, it has a positive voltage applied to the Base with respect to the Emitter. The Emitter collector voltage should be of polarity to reverse bias the Collector Base junction. In this case it will be positive at the Collector with respect to the Emitter. As stated the BJT transistor is current controlled so the Base voltage is adjusted until the the base current is halfway between minimum and maximum. In this condition the voltage to be amplified will then affect the Base current flow which controls the Collector Emitter current, as Base/Emitter increases the Collector Emitter current increases and as Base/Emitter decreases the Collector Emitter current decreases. © Aviation Australia NPN transistor in a circuit 2022-11-10 B1-04 Electronic Fundamentals Page 89 of 163 CASA Part 66 - Training Materials Only  Transistor Orientation Transistor Circuit Example Base/Emitter Voltage = 2 volts. Collector/Emitter Voltage = 20 volts. The following circuit shows a transistor biased with a base voltage VBB and a collector emitter voltage VCC. The amplification functions by applying a small voltage to the base and having a larger voltage available between the collector and emitter VCC. If VBB is only 2 volts most of the voltage will be dropped across the resistor RB limiting the current in the base, if the base current can change from 0 to 20 mA and the collector/emitter current changes from 0 to 2A. Using 0.02 A to control a 2 A output, amplifying the input signal from 0.02 A to an output of 2 A is called a gain of 100. Aviation Australia NPN BJT circuit with 2 V base voltage and 20 V collector/emitter voltage Using the same example as above, with the current amplification can be converted into a voltage amplification by comparing the base/emitter voltage change with the voltage change across the collector/emitter. A base/emitter voltage change of 0.3 V to 0.7 V would control a voltage of 0 V to 20 V giving a voltage gain of 20/0.4 or 50. 2022-11-10 B1-04 Electronic Fundamentals Page 90 of 163 CASA Part 66 - Training Materials Only  Aviation Australia NPN BJT circuit In the transistor amplifier circuit diagram the the base bias voltage is produced from the Common Collector voltage (VCC) using a voltage divider network. The input voltage (Vin) or signal is applied to the centre of the voltage divider and base of the transistor. Notice that as the base current increases the output voltage reduces. This is the result of the increased collector/emitter current creating a voltage drop across the collector resistor reducing the output voltage (Vout)towards zero. Aviation Australia Transistor amplifier circuit 2022-11-10 B1-04 Electronic Fundamentals Page 91 of 163 CASA Part 66 - Training Materials Only  The following diagram shows the transistor used as a switch. On the right, there is no voltage applied to the base, the transistor is open circuit (high resistance) so no current flows. On the left, there is a positive voltage applied (NPN Transistor) the transistor is switched on permitting current to flow between collector and emitter. Aviation Australia Transistor as a switch 2022-11-10 B1-04 Electronic Fundamentals Page 92 of 163 CASA Part 66 - Training Materials Only