Passive and Active Electronic Components - Resistor

 

Passive and Active Electronic Components

 

•        An electronic circuit is comprised of different individual components, grouped as passive components and active components.

 

•        The components which do not in themselves provide gain are called passive components. Eg. resistors, capacitors and inductors.

 

•        Components which provide amplification or switching are called active components. Eg. diodes, transistors and Ics.

 

RESISTORS

 

•        A resistor is a two terminal electrical or electronic component that opposes an electric current by producing a voltage drop between its terminals in proportion to the current, that is

Ohm’s law: V = IR.

•        The electrical resistance is equal to the voltage drop V across the resistor divided by the current I through the resistor.

•        Resistors are the parts of electrical networks and electronic circuits. Resistors are used in almost every electronic circuit for controlling the current and/or voltage in the circuit.

•        Without resistance, every circuit would be a short circuit.

•        All resistors commonly used in electronic circuits are divided into two general categories:

1.    Fixed

2.    Variable

•        Types of Resistors are further classified depending on: types of resistance material used, method of their manufacturing and its internal constructions.

 

Resistor Identification

The resistors are either colour coded or provided with identification stamp.


Variable Resistors

 

•        In electronic circuit it is required to adjust the values of current and voltages so as to get desired results; such as to adjust the volume of band or brightness of TV picture.

•        For such and similar applications variable resistors are used.

a) Pots

•        Smaller variable resistors commonly used in the electronic circuits are called potentiometers or “pots”.

•        It basically consists of track of some kind of resistive material to which a movable wiper makes contact.

•        The moving contact will determine whether the resistance in the circuit is minimum or maximum.

 

 

As per the applications, the variable resistors are of two types:

                                                                          i.     Preset Potentiometer

•        These are the potentiometer of simple construction either open or enclosed, and designed for limited wiper movements (such as for trimming, adjusting or readjusting the electronic circuits).

•        Generally an adjusting tool is required.

•        Important characteristics are:

a)   precise adjustability

b)   good stability of the set value.

 

                                                                           ii.     Control Potentiometer

 

•        The potentiometer is required to continuously vary over the whole of its track.

•        Hence its mechanical and electrical design should permit a large wiper movements.

•        As per the type of material used for it, the variable resistors are classified as follows:

a)   Carbon potentiometer

b)   Ceremet potentiometer

c)    Wire wound potentiometer

 

                                                                      iii.        Colour Code of Resistors and Examples

 

Example 1. What would be the colour code for 12 fi resistor?

Solution: The colour code: Brown, Red, Black refers to 12 fi.

The multiplier colour black represents the number 0 and tells us that no noughts should be added to the first two digits, thus representing 1 and 2 only.

Example 2. What would be the colour code for 47 fi?

Solution: The colour code: Yellow, Violet, Black refers to 47 fi.

Using this method for indicating values between 10 fi and 100 fi means that all resistor values require the same number of bands.

Example 3. What would be the value of the resistor with the following colours: brown, black, gold?

Solution: Above colours indicate a 1 fi resistor.

Example 4. What would be the colour code for 2.2 fi with ±5% tolerance?

Solution: The colour code: Red, Red, Gold refer to a 2.2 fi resistor.

Metal film resistors, manufactured to 1 or 2% tolerance, often use a code consisting of four coloured bands instead of three. The code works in the same way, with the first three bands interpreted as digits and the fourth band as the multiplier.

Example 5. For 1 kfi metal film resistor what would be the colour bands?

Solution: The colour code: Brown, Black, Brown (+brown or red for tolerance) refer to a 1 kfi resistor.

Example 6. For 56 kfi metal film resistor what would be the colour bands?

Solution: The colour code: Green, Blue, Black, Red (+brown or red for tolerance) refer to a 56 kfi resistor. It is worth pointing out that the multiplier for metal film resistors with values from 1 kfi upwards is brown (rather than red, as in the three colour system), while the multiplier for 10 kfi upwards is red (instead of orange). You are likely to use low value resistors and metal film resistors on some occasions and it is useful to   know how to read their codes. However, most of the resistors you use in building electronic circuits will be carbon film types with values indicated using the three band colour code.


Team RRA 

 

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