Resistor Glossary & Terminology

Fusible Resistor (Fuse Resistor, Circuit Protect Resistor):

A resistor designed to protect a circuit against overload; its resistance limits current flow and thereby protects against surges when power is first applied to a circuit; its fuse characteristic opens the circuit when current drain exceeds design limits.

Thermal Cutoff Resistor:

A thermal fuse is a cutoff which uses a one-time fusible link. Unlike the thermostat which automatically resets itself when the temperature drops, the thermal fuse is more like an electrical fuse: a single-use device that cannot be reset and must be replaced when it fails or is triggered. A thermal fuse is most useful when the overheating is a result of a rare occurrence, such as failure requiring repair (which would also replace the fuse) or replacement at the end of service life.

Direct offers "Thermal Cut-off Resistor", a thermal Cut-offs is a fusible alloy and a resistor is a voltage divider, both are surrounded by a ceramic cement with special resin. Under normal operating temperatures the fusible alloy joins the two lead wires within the body of the cutoff and the power resistor acts as a normal function resistor. When the preset temperature of the cutoff is reached, the fusible alloy melts and with the aid of the special resin, complete cutoff is ensured.

Thermal fuse resistors are usually found in heat-producing electrical appliances such as coffeemakers and hair dryers. They function as safety devices to disconnect the current to the heating element in case of a malfunction (such as a defective thermostat) that would otherwise allow the temperature to rise to dangerous levels, possibly starting a fire.

Anti-Surge Resistor (RCR):

Surges in electronic circuits are caused by internal conditions — switching operations from other electronic components or due to external conditions on the AC power mains — switching operations in the power grid or from nearby lightning strikes, either directly to the power distribution system or to nearby ground. Electronic products have to be surge immune to ensure their continued reliable operation if subjected to realistic levels of surge voltages, and they are required to comply with safety requirements. Direct's RCR series is a perfect fit when an anti-surge resistor is required.

Light Dependent Resistor (LDR):

A photoresistor or light dependent resistor or cadmium sulfide (CdS) cell is a resistor whose resistance decreases with increasing incident light intensity. It can also be referenced as a photoconductor.

A photoresistor is made of a high resistance semiconductor. If light falling on the device is of high enough frequency, photons absorbed by the semiconductor give bound electrons enough energy to jump into the conduction band. The resulting free electron (and its hole partner) conduct electricity, thereby lowering resistance.

Carbon Composition Resistor (CCR):

CCR is made up of a solid rod of conductive composite material, the chemical composition of which is altered to produce different resistance values. The general composition consists of the carbon conductor and ceramic filler materials. By altering the ratio of filler to conductor it is possible to change the resistance value. Interference-fit end caps are attached to the rods, leads are welded onto these caps, and the resistor body is then protected with a specially formulated epoxy coating. The resistors are then colour code marked.

Ayrton-Perry Winding:

Winding of two wires in parallel but opposite directions to give better cancellation of magnetic fields than is obtained with a single winding.

Wirewound technology has long been known as a leading technology for power resistor needs. The most critical drawback with this technology is that it is inherently inductive. This is logical given that a wirewound inductor and a wirewound resistor are made with essentially the same materials and processes. This fact limits the use of wirewounds for applications with high switching speeds, which require low inductance.

Now the same standard wirewounds can be used for these applications by using a non-inductively wound version. This manufacturing method greatly reduces the inductance of any given resistor size and value combination, however it does not completely eliminate the inductance. A non-inductively wound wirewound has one winding in one direction and one in the other direction; known as Ayrton Perry winding. This non-inductive winding is available in all Direct standard wire-wound resistor series.

Select Resistors With Optimum Technology to Best Match The Performance

Comparision of Axial Lead Resistor Characteristics Table
Characteristics Thin Film Thick Film Wire Wound Alloy Strip
Carbon Film Metal Film Metal Oxide Film Metal Glaze Film Standard Non-Inductive
Tolerance (%) ±0.01              
Temperature Coefficient (PPM/°C) 5              
Operating Temperature Range (°C) 200              
Wattage (W) 1/16              
Resistance Range (Ω) 0.1              
Volume Size Standard Standard Standard Standard Standard Bigger Compact
High Frequency Available Available Available Available None Available Available
Cost Cheap Fair Fair Fair High High Fair
Noise Fair Good Fair Fair Fair Good Good
Stability Fair Excellent Good Good Excellent Good Excellent

Comparision of Axial Lead Resistor Functions Table
Class Advantage Disadvantage
Carbon Resistors Cheap, General Purposes High TCR,
Metal Film Resistors Low TCR, Tight Tolerance, High Stabililty Fair Withstanding Voltage
Metal Oxide Resistors Replace high resistance wire wound resistor, Good withstanding voltage Resistance Range Limitation,Fair Tolerance
Wirewound Resistors High Pulse Load, Anti-Surge,High Stabililty High Inductance, Resistance Range Limitation
Non-Inductive Resistors High Pulse Load, Anti-Surge, High Stabililty Resistance Range Limitation, High Cost
Ceramic Housed Cement Resistors Rugged, excellent heat dissipation, withstanding high temperature Heavy Weight, Big Volume
Metal Glaze Resistors High Pulse Load, Anti-Surge, High Stabililty High TCR, Fair Tolerance
Alloy Strip Low TCR, Low Ohmic Fair Tolerance

General Commercial Resistor Information

General Purpose Resistors With Customized Service:

Direct Electronics is expanding business to include a broad range of General Purpose Resistor products designed for high volume applications. This expanded range of commercial resistor presents a more comprehensive product offering for Customer Experience Management (CEM) and other high volume customers that require quality products at competitive pricing.

Backed by the same customer service, technical support and quality assurance that Direct has always provided, these new commercial products enable you the opportunity to source a wider range of resistors from a trusted supplier.

General Use:

When an ambient temperature exceeds a rated ambient temperature, resistor shall be applied on the derating curve by derating the load power. General purpose resistor under overloads is not combustion resistant and is likely to emit, flame, gas, smoke, red heat, etc. Flame retardant resistor generally emit smoke and red heat in a certain power and over but do not emit fire or flame.

When resistors are shielded or coated with resin etc., stress from the storage heat and the resin are applied. So, performance and reliability should be checked well before use.

When a voltage higher than rated is applied in a short time (single pulse, repeated pulses, surge, etc.), it does not necessarily ensure safety that an effective wattage is not higher than a rated wattage. Then consult with us with your specified pulse wave shape. Resistors shall be used in a condition causing no dew condensation.

Keep temperature from rising by choosing resistor with a higher rated capacity; do not use a component having the exact load value required. For considerations of safety in extended period applications, the rating should be more than four times higher than the actual wattage involved, but never use resistors at less than 25% of its rated power.

In applications where resistors are subject to intermittent current surges and spikes, be sure in advance that the components selected are capable of withstanding brief durations of increased load.

Do not exceed the recommended rated load. Resistor must used within the rated voltage range to prevent the shortening of service life and/or failure of the wound resistance elements.

Minimum load: Resistor must be utilized at 1/10 or more of the rated voltage to prevent poor conductance due to oxidation build-up. For basic particulars for cautions, refer to EIAJ Technical Report RCR-2121 "Guidance for care note on fixed-resistors".

Commercial Resistor Catalogue and Design Notes Download: