The C1815 transistor is a general-purpose transistor and can also used as an audio frequency amplifier. The majority of transistors are coded for easy identification although these designations can vary by manufacturer. One or two letters are usually followed by a series of numbers, and then possibly more numbers. Therefore, a C1815 transistor may also be identified as a 2SC1815 transistor. The letter C in this series identifies the transistor for general-purpose use.
Made from semiconductor materials, a transistor has three leads, or terminals, and sometimes more. These are used to switch electronic signals, or pulses, or to amplify the signals. Further information can also be obtained just from the part number. The '2S' portion of the number indicates that the C1815 transistor is good for high-frequency applications and is in Negative-Positive-Negative (NPN) configuration. The other three-lead transistor configuration is Positive-Negative-Positive (PNP).
The first negative end of the transistor is connected to the negative side of a circuit, and controls the flow of electrons to the positive region in the middle. The other negative end of the transistor controls the electrons leaving the positive, middle portion. The semiconductor material that is used to manufacture the transistor determines the NPN or PNP configuration.
Leads on a transistor are identified as the emitter, base, and collector. The emitter is the output for the supply. The base acts a control gate for a larger electrical input at the collector, which — as its name implies — collects energy. For example, when a C1815 transistor is used in a video application, the emitter sends out the video output signal. This is processed through the base, which could be a low video signal, and powered by the collector, which may be a 5-volt energy supply.
By varying the electrical current at the base of a transistor, the amount of power flowing from the collector to the emitter can be controlled. For instance, in digital circuits, a transistor is on when it receives 5-volts, and off when it receives less than that amount. General ratings for a C1815 transistor include a power dissipation of 0.4 watts at an ambient temperature of 77° Fahrenheit (25° Celsius). The transistor is capable of a collector current of 0.15 amps. The collector-to-base voltage can be up to 60-volts.
The term 'transistor' came from the combination of the words, transfer and resistor. A field-effect transistor (FET) was originally designed as a replacement for a triode — part of older vacuum tube technology. The use of transistors helped the electronics industry change rapidly, and improvements in technology are allowing smaller components to be used to manufacture smaller devices.