Device Electrical Characteristics

The resistor is a linear device and is characterized by a “straight-line equation”. It dissipates power as heat, its value in ohms can vary as to the tolerance rating (ohms ± % of rated value). The resistor cannot store energy.

An inductor or capacitor is an energy storage device; a capacitor’s current or an inductor’s voltage does not change instantaneously. Initial conditions can apply to both of these devices.

The ideal capacitor has zero conductance or infinite resistance and the ideal inductor has zero resistance or infinite conductance. Ideally, neither device dissipates heat (power). The total power consumed or delivered in an RLC is presented as a complex variable (phasor) with a real (dissipated power by resistors) and imaginary (reactive power ) component.

It should be mentioned that, a capacitor’s conductance (or an inductor’s resistance) only approaches zero and the rated component value (Farads for capacitors or Henries for inductors) may also vary. These variants in addition to EMI and environmental effects would require you to alter your design or analysis somewhat, depending on how critical they are to your design or model.

The Ideal voltage vs. current characteristics for the resistor, inductor and capacitor are shown below in Table 1.

source : PDHengineer.com
Course No E-6002
First Order RLC Circuits: Time Domain
Analysis

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Resistor Combination

Resistors can be connected such parallel or series.

Resistors are in series if they are connected in tandem and carry exactly the same current. Resistors are arranged in a chain, so the current has only one path to take. The current is the same through each resistor. The total resistance of the circuit is found by simply adding up the resistance values of the individual resistors.

Resistors are in parallel if they are connected in the same nodes and have exactly the same voltage across their terminals. Resistors are arranged with their heads connected together, and their tails connected together. The current in a parallel circuit breaks up, with some flowing along each parallel branch and re-combining when the branches meet again. The voltage across each resistor in parallel is the same. The total resistance of a set of resistors in parallel is found by adding up the reciprocals of the resistance values, and then taking the reciprocal of the total.

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TYPES OF RESISTORS

Resistors are made in many forms, but all belong in either of two groups: fixed or variable. The relative sizes of all fixed and variable resistors change with the wattage (power) rating, increasing in size for increased wattage ratings in order to withstand the higher currents and dissipation losses.

• Fixed Resistors

Resistors of this type are readily available in values ranging from 2.7 ⍀ to 22 M⍀. For use with printed circuit boards, fixed resistor networks in a variety of configurations are available in miniature packages.

• Variable Resistors

Variable resistors, as the name implies, have a terminal resistance that can be varied by turning a dial, knob, screw, or whatever seems appropriate for the application. They can have two or three terminals, but most have three terminals. If the two- or three-terminal device is used as a variable resistor, it is usually referred to as a rheostat. If the three- terminal device is used for controlling potential levels, it is then commonly called a potentiometer. Even though a three-terminal device can be used as a rheostat or potentiometer (depending on how it is connected), it is typically called a potentiometer when listed in trade magazines or requested for a particular application .

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Resistor - Color Coding and Standard Value

The flow of charge through any material encounters an opposing force similar in many respects to mechanical friction. This opposition, due to the collisions between electrons and between electrons and other atoms in the material, which converts electrical energy into another form of energy such as heat, is called the resistance of the material. Resistance is measured in Ohms (Ω), the capital Greek letter omega. The circuit symbol for resistance appears in figure below with the graphic abbreviation for resistance (R).

 Most resistors have four coloured band. The first three bands determine the resistance, the fourth band indicates its tolerance. Tolerance is how much the resistance varies drom its specified value, given as percentage : e.g 5% tolerance is indicated by a gold fourth band. It means that a 100 Ohm resistor could actually be between 95-105 Ohm.

E.g., the grey-red-brown-gold resistor is 820 Ohm Resistor.

There are also 5 band resistors. The first four bands determine resistance and the fifth indicates the tolerance generally these are a 1% tolerance resistor, much more accurate than 5% resistor. To determine the resistance, the first three rings are the significant value, the fourth ring is the number of zeros following or multiplier. Eg. 1kOhm is brown-black-black-brown-brown

 

Resource : My lecture note

                  Introductuory Circuit Analysis by Boylestad

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