Introduction of Battery
A battery is a group of cells that generate energy from the internal chemical reaction. The cell itself consists of two different conducting materials as the electrodes that are immersed in an electrolyte. In batteries the chemical reaction between the electrodes and the electrolyte results in a separation of electric charges, in the form of ions and free electrons. Then the two electrodes have a difference of potential that provides voltage output from the cell.
History of Battery
From the old days of radio, dry batteries are still called A, B, and C batteries, according to their original functions in vacuum tube operation. The A battery was used to supply enough current to heat the filament for thermionic emission of electrons from a heated cathode. A typical rating is 4.5 V or 6 V with a load current of 150 mA or more. The C battery was used for a small negative dc bias voltage at the control grid, typically 1.5 V, with practically no current drain.
The A battery is seldom used any more , although a 6 V lantern battery has ratings like an A battery. However, the function of a B battery with medium voltage and current ratings is the same now as it always was. Transistors need a steady dc voltage for the collector electrode, which receives charges from the emitter through the base electrode. For an NPN transistor, positive voltage is needed at the collector or negative voltage at the emitter, with a PNP transistor, the polarities are reversed. The positive dc supply voltage is called B+ or + Vcc. In a small transistor radio with a 9 V battery, as an example the battery is the + Vcc supply. The same requirements for dc supply voltage apply to integrated circuits, as the IC chip contains transistor amplifiers.
Importance of Battery
In more easy way we can define the battery in this way that a battery is a combination of cells. The chemical battery has always been important as a dc voltage source for the operation of radios and other electronic equipment. The reason is that a transistor amplifier needs dc operating voltages in order to conduct current. With current in the amplifier, the circuit can be used to amplify an ac signal. Originally, all radio receivers used batteries. Then rectifier power supplies were developed to convert the ac power line voltage to dc output, eliminating the need for batteries. However, now batteries are used more than ever for all types of electronics portable equipment.
The function of a battery is to provide a source of steady dc voltage of fixed polarity. Furthermore, the battery is a good voltage for a circuit s the load to produce the desired load current. An important factor is the internal resistance ri makes the output voltage drop, but a constant value of load current can be maintained.