How Many Special Types of Resistors and its working.

Besides carbon and wire wound resistors, some special types of Resistors are also made for a specific uses.

Total five types Of Resistor- 

1). Ballast Resistor- it is made by a substance which has a positive temperature coefficient such as nickel iron alloy. it has a property of variation in its resistance value for a change in its temperature. Hence, an increase in the magnitude of current flowing through its causes a corresponding increase in its temperature and which in turn results in an increase in its resistance value.
 the increase in its resistance value decreases the magnitude of current flowing through it. in this way a ballast reistor stabilizes the circuit current within a definite range. These resistors are used for current stabilization in various types of electronic equipments.
2). PTC ( Positive Temperature Coefficient) Resistor- a register made of a substance which has a positive temperature coefficient is called PTC. The resistance value of PTC is directly proportional to its temperature. hence, an increase in the magnitude of voltage applied for the external temperature causes an increase in its resistance wich in turn reduces the magnitude of current flowing through it. A PTC is used for bias stabilisation in transistorized circuits. there, it is connected in the emitter circuit. if due to any reason the magnitude of emitter current rises above a definite value, it causes an increase in its resistance value. in turn, it results in a decrease in the emitter current. therefore, the effect of increase in the magnitude of current is controlled by it. It is made by a mixture of nickel oxide, manganese oxides and Cobalt oxide. it is known as thermistor also. it is also known as sensistor.

3). NTC (Negative Temperature Coefficient) Resistor- A resistelor made of a substance which has a negative temperature Coefficient is called a NTC. In the beginning (after switching on the circuit), it has a very high resistance and thus the circuit current is quite small. slowly and slowly its temperature start to rise which results in an increase in the magnitude of current flowing through it. an increase in the magnitude of current results in an increase in its temperature which again result in an increase in the circuit current. in this way, after a few seconds its temperature rises to a sufficiently high value and the magnitude of current reaches at its maximum value. under such conditions the resistance value of NTC is minimum. the device is used in timer circuits, valve filament circuit eti. if a valve filament is allowed to be heated up at a slow rate or in other words the magnitude of its heating current is control in such a manner that it rises slowly then the working file of a valve filament can be increased up to a great extent. It is made by graphite. this is also known as thermistor. the PTC and NTC resistor can perform switching operation at a specific temperature. they are also used for measurement and temperature compensators.
4). Varistor- also a special type of reistor and it has following two types: Varistors are also known as voltage dependent resistors (VDR).
I). Symmetrical Varistors-  It is made of carbide granules and a ceramic binder material. it has a property that its resistance value is controlled by the magnitude of current flowing through it. at High magnitude of current, the resistance is low and vice-versa. since the magnitude of current in a circuit is proportional to supply voltage, therefor, a Varistors can be used for controlling voltage fluctuation within a limit of few volts. it is also known as VDR (voltage dependent resistor) and it is used for controlling voltage fluctuations.
II). Unsymmetrical Varistors- it is made of a semiconductor material. It has a property of controlling the magnitude of current of a circuit by the direction of flow of current. It is also called a Varistors diode. it is used as a rectifier also in certain type of circuits.
5). LDR ( Light Dependent Resistor)- it is made of selenium. it has a property that its resistance value decreases on the incidence of light rays on it and thus the magnitude of current flowing through it is increased. In other words, it is a photobsensitive resistor. it is used in light operated control circuits. you can make a counter for counting the persons passing through a narrow path, a garage door opener which can open the door automatically on the incidence of light from a torch or car headlight, and automatic street light control which can switch 'on' street lights in the night and switch off them in the day light automatically.
Figure

Post a Comment

0 Comments