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  • Q 1. What is a Resistor?

    The resistor is a passive electrical component that creates resistance in the flow of electric current. In almost all electrical networks and electronic circuits they can be found. The resistance is measured in ohms (Ω). An ohm is the resistance that occurs when a current of one ampere (A) passes through a resistor with a one volt (V) drop across its terminals. The current is proportional to the voltage across the terminal ends. This ratio is represented by Ohm’s law:
    R=V / I
    Resistors are used for many purposes. A few examples include limiting electric current, voltage division, heat generation, matching and loading circuits, gain control, and setting time constants. They are commercially available with resistance values over a range of more than nine orders of magnitude. They can be used as electric brakes to dissipate kinetic energy from trains, or be smaller 
    than a square millimeter for electronics.
  • Q 2. What is Resistor Characteristics?

    A Dependent on the application, the electrical engineer specifies different properties of the resistor. The primary purpose is to limit the flow of electrical current; therefore the key parameter is the resistance value. The manufacturing accuracy of this value is indicated with the resistor tolerance and is expressed as a percentage of the resistance value (for example ±5%). Many other parameters that affect the resistance value can be specified, such as long term stability or the temperature coefficient. The temperature coefficient, usually specified in high precision applications, is determined by the resistive material as well as the mechanical design. 

    In high frequency circuits, such as in radio electronics, the parasitic capacitance and inductance can lead to undesired effects. Foil resistors generally have a low parasitic reactance, while wirewound resistors are among the worst. For accurate applications such as audio amplifiers, the electric noise of the resistor must be as low as possible. This is often specified as microvolts noise per volt of applied voltage, for a 1 MHz bandwidth. For high power applications the power rating is important. This specifies the maximum operating power the component can handle without altering the properties or damage. The power rating is usually specified in free air at room temperature. Higher power ratings require a larger size and may even require heat sinks. Many other characteristics can play a role in the design specification. Examples are the maximum voltage or the pulse stability. In situations where high voltage surges could occur, this is an important characteristic. 

    Sometimes not only the electrical properties are important, but the designer also has to consider the mechanical robustness in harsh environments. Military standards sometimes offer guidance to define the mechanical strength or the failure rate.
  • Q 3. What is TCR?

    A Resistance of resistor changes with temperature; and TCR stands for temperature coefficient of resistance, which indicates that when temperature changes by 1℃, the relative change of resistance in ppm/℃. Resistance will return to initial value with temperature returns to normal temperature. Calculation formula:

    图片 1

    R1: Resistance (Ω) measured under room temperature 
    R2: Resistance (Ω) measured at -55℃ or +125℃ 
    T1: Room temperature. 
    T2: -55℃ or +125℃
  • Q 4. What is the function of jumper? Why precision is not required by 0Ω?

    A Jumper resistor is also known as 0Ω resistor. ① In circuit design, the power supply can be separated as multiple channels with 0Ω resistor for commissioning or compatible design. ② It can be used as jumper. If certain section of the line is not used, just simply attached a 0Ω resistor (appearance will not be affected). ③ When the parameter of the matching circuit is uncertain, it can be replaced by 0Ω first and replace it with component with specific value during commissioning. ④ When wiring is impossible, you can also add a 0Ω resistor. ⑤ Under high-frequency signal, it can act as inductor or capacitor (related to the characteristics of external circuit) for dealing with EMC problems. ⑥ Used for cross-over connection of current circuit to provide shorter returning path and reduce interference. ⑦ Sometimes, user will change settings during circuit configuration. In order to reduce maintenance cost, 0Ω resistor can be used as alternative of jumper and welded on board. The actual resistance of a 0Ω resistor is not zero, the definition of which is ≦50mΩ (or ≦20mΩ). Therefore, parts with ±1% or ±5% share the same specifications. For functional perspective, jumper resistance dose not require precision. What user needed is the maximum rated current (i.e. current allowed to pass) instead of cannot be purchased or produced.
  • Q 5. What is Resistor Applications?

    There is a huge variation in fields of applications for resistors; from precision components in digital electronics to measurement devices for physical quantities. A few popular uses are described below:
    Resistors in series and parallel
    In electronic circuits, resistors are very often connected in series or in parallel. A circuit designer might, for example, combine several resistors with standard values (E-series) to reach a specific resistance value. For series connections, the current through each resistor is the same and the equivalent resistance is equal to the sum of the individual resistors. For parallel connections, the voltage across each resistor is the same. The inverse of the equivalent resistance is equal to the sum of the inverse values for all the parallel resistors. The articles resistors in parallel and resistors in series provide detailed introduction to these concepts and calculation examples. To solve even more complex networks, Kirchhoff’s circuit laws may be used.
    Measure electrical current (shunt resistor)
    Electrical current can be calculated by measuring the voltage drop over a precision resistor with a known resistance, which is connected in series with the circuit. The current is calculated by using Ohm’s law. This is a called an ammeter or shunt resistor. Usually this is a high precision manganin resistor with a low resistance value.
    Resistors for LEDs
    LED lights need a specific current to operate. A too low current will not light up the LED, while a too high current might burn out the device. Therefore, they are often connected in series with resistors to set the current. These are called ballast resistors and passively regulate the current in the circuit.
  • Q 6. How to Choose the Appropriate Resistor?

    Resistor selection requires three steps:
    1. Determine the resistance and the watts to be dissipated by the resistor
    2. Determine the proper "Watt Size" (physical size) as controlled by watts, volts, permissible temperatures, mounting conditions and circuit conditions
    3. Choose the most suitable kind of unit, including type, terminals and mounting.

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