 # Surface Mount Components- Resistors & Capacitors

###### Resistor is an electrical component that reduces the electric current. One or more resistor can be used to provide the correct amount of current to specific components within an electronic device.

These are often soldered onto a printed circuit board to limit the amount of current that flows to different electrical paths. If too little current reaches a components it may not operate. If too much current is allowed through, it can damage the components. Therefore, resistor play an important role in an electronic circuit. The current flows in one end and the remaining current flows out the other. The resulting current is inversely proportional to the resistance. This is in Ohm’s law, which states that the current(I) is to the voltage(V) divided by the resistance (R).

What Resistor actually do

The resistor is a passive device and doesn’t do anything actively to your to your circuit.

It’s actually a pretty boring device. if you add some voltage to it, nothing really happens.

By using resistor, you can design your circuit your circuit to have the current and voltages that you want to have in your circuit. So the resistor gives the designer control over his circuit.

###### Resistors in parallel:- The total equivalent resistance of resistors in parallel R is given by:

When user add resistors in parallel the total resistance is decreased.

###### Resistors in series:- The total equivalent resistance of resistor in series R(total) is the sum of the resistance values. So when you add resistors in series the total resistance is increased

###### Resistor Color codes:- The resistance & tolerance are measured on the resistor with color code bands that denotes the values of the resistance.

Types of color codes:

. 4 bands digit , digit, multiplier , tolerance.

. 5bands digit, digit, multiplier, tolerance.

. 6bands digit, digit, multiplier, tolerance, temperature coefficient

###### Different Type of resistor:

potentiometer: Potentiometer has an adjustable resistance

Photo-resistor: Reduces resistance when exposed to light.

Variable resistor: Variable resistor has an adjustable resistance

Power resistor: Power resistor is used for high power circuit and has largedimensions.

Surface mount:(SMT/SMD)Resistor: SMT resistor have small dimensions. The resistors are surface mounted on the printd circuit board(PCB) this method is fast and requires small board area.

Resistor network: Resistor network is a chip that contains several resistor with similar or different values

Surface mount:

SMT/SMD resistors have small dimensions. The resistor are surface mounted on the printed circuit board(PCB). this method is fast and require small boards area.

Resistor Network

Resistor network is a chip that contains several resistor with similar or different values

###### Capacitor

Is a passive electronic component that stores energy in the form of an electrostatic field. It consists of two conducting plates separated by an insulating material called the dielectric.

The capacitance is directly proporational to the surface areas of the plates, and is inversely proportional to the separation between the plates. Capacitance  also depends on the dielectric constant of the substances separting the plates. It consists of two or more parallel conductive (metal) plates which are not connected or touching each other, but are electrically separated either by air or by some form of a good insulating material such as waxed paper, mica, ceramic, plastic or some form of a liquid gel as used in electrolytic capacitors. The insulating layer between a capacitors plates is commonly called the Dielectric.

Capacitors have may Applications:

. Electric power Surge protectors

. Computers RAM memory and Keyboards

. radios and electronic circuit

. Electronic flashes for cameras

###### CAPACITOR Symbols: There are two types of electrical charges:

Positive charges in the form of protons and negative charges in the form of Electrons. When a DC voltage is placed across a capacitor, The positive (+ve) charge quickly accumulates on one plate while a corresponding and opposite negative(-ve) charges accumulates on the other plate. For every particle of +ve charges that arrives at one plate a charges of the same sign will depart form the -ve plate.

Capacitor types

Capacitance Example:-

A capacitor is constructed from two conductive metal plates 30cm 50cm which are spaced 6mm apart from each other and uses dry air as its only dielectric material. Calculate the capacitance of the capacitor then the value of the capacitor consisting of two plates separated by air is calculated as 221pf or 0.221nF.