In order to use the transistor as a switch, it must be driven into the saturation region with enough base current. When we apply a high enough current at the base of the transistor, it makes a path for the collector current to go through the base towards the emitter. The region responsible for a transistor to work as a switch are Saturation Region and the Cut-off Region. So the collector current increases in proportional to the base current. In the active region, the collector current is β times the base current, i.e., In the active region, the transistor emitter junction is forward biased and the collector junction is reverse biased. The active region lies between the cut-off and saturation regions. Here I C= collector current and I E = emitter current. In other words, the transistor operates as a short circuit or closed switch carrying maximum current which implies: In the saturation region, both the collector and emitter junctions are forward biased. The collector and Emitter currents are maximum in this region. In the saturation region, transistor works like a short circuit or closed switch. Here I C= collector current, I E = emitter current, and I B = base current. Hence in the cut-off region, the base, emitter, and collector current are zero. The transistor then allows current to flow from the +9 volts to the 0vs, and the lamp comes on. When the switch is pressed a current passes through the resistor into the base of the transistor.

Diagam 'A' Diagram 'B' The circuit shown in diagram B is based on an NPN transistor. A small current or voltage at the base allows a larger voltage to flow through the other two leads (from the collector to the emitter). When a transistor is to be connected in a circuit, it is necessary to know which. Diagram 'A' shows an NPN transistor which is often used as a type of switch. In the cut-off region, both the collector and emitter junctions are reverse biased. There are three leads in a transistor viz. The base, collector and emitter currents are all zero in this region. The following mainly discuss the bipolar transistors, field-effect transistors, and some other typical types of transistors. In the cut-off region, transistor works as an open circuit or open switch. The three terminals of a bipolar transistor are an emitter, a base, and a collector composed of N-type and P-type semiconductors The three terminals of the field-effect transistor are the source, the gate, and the drain. Like every other transistor BC548 transistor works in three regions: The NPN transistorbehaves like two PN junctions diodesconnected back to back. When a transistor is to be connected in a circuit, it is necessary to know which terminal is which. An NPN transistor has three terminals a collector, emitter and base. There are three leads in a transistor viz. Working States OR Modes of Operation of BC548: An NPN transistor is the most commonly used bipolar junction transistor, and is constructed by sandwiching a P-type semiconductorbetween two N-type semiconductors. Max Storage & Operating temperature Should Be: -55 to +150 oCĬircuit Applications of BC548 transistor:.Collector Dissipation (Pc): 625 milliwatt

Generally the transistor configurations are three types they are common base (CB). DC Current Gain range (h FE): 110 – 800 Different Configurations of Transistors - Common Base, Collector & Emitter.Max Collector-Emitter Voltage (V CE): 30V.Specifications and characteristics like Absolute maximum ratings, Block diagram, biasing methods, and package dimensions can be found in the datasheet. You can find detailed information on BC548 in the datasheet given above. ( iii) When the leads of a transistor are spaced around the circumference of a circle, the three leads are generally in E-B-C order clockwise from a gap.Click this link to view the entire DATASHEET of BC548 ( ii) When the leads of a transistor are in the same plane but evenly spaced, the central lead is the base, the lead identified by dot is the collector and the remaining lead is the emitter. The collector lead is identified by the larger spacing existing between it and the base lead. ( i) When the leads of a transistor are in the same plane and unevenly spaced, they are identified by the positions and spacings of leads. However, there are three systems in general use as shown in Fig. The identification of the leads of transistor varies with manufacturer. If a proportion,, (having a value of up to 0.995 in modern transistors), of the holes passing into the base from the emitter, pass through the base-collector. In the Common Emitter or grounded emitter configuration, the input signal is applied between the base, while the output is taken from between the collector and. There are three leads in a transistor viz.

Transistor base collector emitter