transformer (electrical component). An electrical component used to change the voltage and current in an alternating current circuit. The core of a transformer is made of a stack of soft iron laminations, and the windings, which consist of several coils of insulated wire, are wound around the core. The winding connected to the power source is called the primary winding, and the windings connected to the electrical loads are called secondary windings.
The voltage difference between that across the primary winding and that across any one of the secondary windings is directly proportional to the ratio of the number of turns in the secondary winding to the number of turns in the primary winding. The higher the ratio, the higher the secondary voltage.
The current difference between that in the primary winding and that in the secondary winding is inversely proportional to the ratio of the number of turns in the secondary winding to the number of turns in the primary winding. The higher the ratio, the lower the secondary current.

transformer/rectifier. See T/R.
transistor (electronic component). An active semiconductor device with three electrodes: an emitter, a collector, and a base. A large flow of electrons between the emitter and the collector is controlled by a much smaller flow of electrons between the emitter and the base. Transistors are physically small, require almost no power for their operation, are extremely rugged, and are low in cost. See NPN transistor and PNP transistor.
transistor voltage regulator (aircraft electrical system component). A type of voltage regulator used in an aircraft electrical system to control the output voltage of an alternator. A zener diode senses the alternator output voltage, and power transistors control the amount of current flowing through the alternator field coil.