Drivers
Transistors
Very small electronic circuits packaged inside a chip. only use small currents when they operate, but many A device that turns an electronic signal back into a 'real-world' signal, such as light or sound. use much higher currents. An The metal leg that gives an output from an integrated circuit. from an A small circuit that is packaged inside a chip case. can be connected to the ‘base’ leg of a Components which do not conduct electricity unless they are turned on by a (different) electrical current. This means they can be used as switches, amplifiers and in other ways. so that an output device that requires higher current can work.
Transistors act like A mechanically operated device that allows current to flow through it when its contacts are closed., and the most common types are called A negative-positive-negative transistor - a transistor is a type of electrical switch.. They have three legs:
- The input leg of an NPN transistor.
- The output leg of an NPN transistor.
- The leg of an NPN transistor that connects to 0 volts (V).
The base leg acts as the control and needs around 0.6 volts (V) to switch ‘on’. Once an input of 0.6 volts has triggered the base leg, a much larger current can flow through the collector or emitter leg.
The output pin from an integrated circuit (IC) will normally have a protective An electrical component that restricts the flow of electrical charge. Fixed-value resistors do not change their resistance, but with variable resistors it is possible to vary the resistance. connected in Connected to a circuit in such a way that the same current flows through each component in turn. Opposite of in parallel. between the output and the base leg of a transistor. This is to protect the base leg by controlling current flow.
The emitter leg connects to 0 volts (V), often called A term used to describe 0 volts (V)., and the collector connects to + volts (V) through the output device, which will ‘turn on’ when 0.6 volts (V) flows into the base leg of the transistor.
Transistors are easily damaged so it is important not to mix up the three legs. To help identify the legs, some transistors have a dot near the collector, and/or a tab near the emitter. Each type of transistor is identified by a code printed on the side.
A single A semiconductor used for amplification - either NPN (negative-positive-negative) or PNP (positive-negative-positive). cannot have both High amplification of current, measured at the collector leg. and The output leg of a transistor is on or ‘high’. current. A Two transistors connected together to produce higher gain than just one. is a special arrangement of bipolar transistors that combines a high gain transistor with a high-current transistor. The combined transistors allow both a higher gain and a larger amount of current to flow than would be possible with a single transistor.
Thyristors
A A latching electrical switch. is a component that can be used in A circuit that remains ‘on’ once activated., such as simple alarms. Whereas a transistor will ‘turn on or off’ depending if 0.6 volts (V) flows into the base leg, a thyristor will turn on when around 2 volts (V) flows into the The input leg of a thyristor.. It will then remain ‘latched’ on until the thyristor is reset by The connection of + volts (V) and 0 volts (V). across the Negatively charged, the electrode where electricity flows out of. and Positively charged, the electrode where electricity flows into., as shown by SW1 in the diagram below:
