There are vast types of resistors, they can be classified into 3 which are:
• Fixed resistor
• Variable resistor
• Resistor dependent on physical quantity
A Fixed resistor is a resistor that has fixed value of electrical resistance which is not adjustable. Fixed resistor is divided into 7 sub types which include:
i. Carbon composition Resistor (CCR)– It is made out of fine carbon particles (graphite) mixed with ceramic dust (clay) and resin. The mixture is pressed into sticks under high pressure and temperature, thereafter has a solid form. Carbon composition resistors are usually used for the protection of circuits against surge, high voltage power supplies, high energy pulses and welding.
ii. Carbon Film Resistor (CFR)– It is made out of a ceramic carrier with a thin pure carbon film around it, that acts as a resistive material. This process occurs at high temperature and under high pressure. Carbon film resistor is used in high voltage and temperature devices.
iii. Metal Film Resistor (MFR)– It is made of a thin metal film (resistive element) deposited on a ceramic body. They are generally used for high frequency or radio frequency applications due to its low noise and temperature stability characteristics.
iv. Metal Oxide Film Resistor- It is produced with chemical deposition processes which involves the reaction of a pure metal with a gas at low pressure and at a high temperature. Metal Oxide film resistor has better high surge current capability with a much greater temperature rating than metal film resistors.
v.Wirewound Resistor- Wirewound Resistor is made by winding an insulated metallic wire around a core of non-conductive material (ceramic, glass or plastic). The insulated metallic wire usually used has high resistivity. An alloy like Nickel-chromium (Nichrome) or a copper-nickel-manganese alloy called Manganin are used as the residtive element.
Other alloys that can be used as insulated metallic wire include:
• Silver alloys
• Nickel Chromium alloys
• Copper alloys
• Iron Chromium alloys
• Iron Chromium Aluminum alloys
There are three types of wirewound resistor they are:
• Precision wirewound
• Power wirewound
• Potentiometer wirewound
Wirewound resistor can be used as fuse or in circuit breaker.
vi. Metal Foil Resistor- The metal foil resistor is made of an alloy of usually Nichrome with some additives. It is placed on a ceramic carrier which has high heat conductivity. Metal foil resistor is usually used in circuits where noise caused within the circuit (like audio systems) is to be averted. They also used in electronic scales because of its low noise, low temperature coeffient resistance (TCR) and a low thermal electromotive force value.
vii. Surface mount Device (SMD)– SMD resistor is made of a ceramic substrate and onto this is deposited a metal oxide film. SMD resistor is small and rectangular in shape. It is mostly used in electronic devices like cell phones, mp3 and so on due to its size.