TRANSISTORS

• A transistor is one of the most important devices ever to be invented.
• Transistors come in many shapes and sizes, with two main types being the bipolar and the field effect.
• Transistors can act as a switch to control circuits and can also amplify signals.
• Small low power transistors are enclosed in a racing case to help protect the internal parts, while higher power transistors will have a partly metal case to help remove the heat which is generated.
• Transistors are usually found attached to a heat sink, which helps remove the unwanted heat.
• Inside a DC Bench power supply, there are some mosfet transistors which are attached to very large heat sinks.
• For electronic circuits with small currents, we can use resin body transistors which do not require a heat sink.
• On the body of the transistor, there is text which tells us the part number, which can be used to find the manufacturers datasheet.
• Each transistor is rated to handle a certain voltage and current, so it is important to check these sheets.
• The transistor has three pins labelled E, B and C, which stand for the emitter, the base and the collector.
• Typically, with these resin body type transistors, the left pane is the emitter, the middle is the base, and the right side is the collector.
• To distinguish between NPN and PNP transistors, check the part number.
• The current gain can be found in the manufacturers datasheet.
• NPN and PNP transistors are the two main types of bipolar transistors, which look nearly identical but have different circuit connections.
• With an NPN transistor, the main circuit and the control circuit are connected to the positive of the battery and the main circuit is off until the switch on the control circuit is pressed.
• Transistors are shown on electrical drawings with symbols like these, where the arrow is placed on the emitter and points in the direction of conventional current.
• A light bulb can be illuminated by connecting it to a battery, and a switch can be installed into the circuit to control the light by interrupting the power supply.
• A transistor can automate this process by blocking the flow of current, causing the light to turn on when a small voltage is applied to the base pin.
• The transistor acts as an amplifier, allowing a small voltage and current to control a larger voltage and current.
• A microphone can vary the voltage signal on the base pin, amplifying a speaker in the main circuit to form a very basic amplifier.
• Electrons can flow easily through the copper, but they can't flow through the rubber insulator.
• Electricity is the flow of electrons through a wire.
• P type doping adds in a material such as aluminium, which has only three electrons in its valence shell.
• The base wire in a PNP transistor is connected to the P type layer.
• Each silicon atom is surrounded by four other silicon atoms, each wanting eight electrons in its valence shell but the silicon atoms only have four electrons in their valence shell, so they sneakily share an electron with their neighbouring atom to get the 8 desired.
• Silicon is an example of a semiconductor with one too many electrons in the valence shell for it to be a conductor, it acts as an insulator.
• The PN junction can be sandwiched together to form an NPN or PNP transistor.
• The entire transistor is enclosed in a resin to protect the internal materials.
• Inside the transistor, the collector pin and the emitter pin are located in an NPN transistor, with two layers of N type material and one layer of P type.
• Silicon can act as both an insulator and a conductor if doped with a small amount of another material, known as P type and N type doping.
• At this junction, a depletion region is formed where some of the excess electrons from the N side move over to occupy the holes in the P side.