resistor电阻.docVIP

Resistor From Wikipedia, the free encyclopedia Jump to: navigation, search A typical axial-lead resistor Partially exposed Tesla TR-212 1 kΩ carbon film resistor Axial-lead resistors on tape. The tape is removed during assembly before the leads are formed and the part is inserted into the board. Three carbon composition resistors in a 1960s valve (vacuum tube) radio A resistor is a two-terminal electronic component having a resistance (R) that produces a voltage (V) across its terminals that is proportional to the electric current (I) through it in accordance with Ohms law: V = IR Resistors are elements of electrical networks and electronic circuits and are ubiquitous in most electronic equipment. Practical resistors can be made of various compounds and films, as well as resistance wire (wire made of a high-resistivity alloy, such as nickel-chrome). The primary characteristics of a resistor are the resistance, the tolerance, the maximum working voltage and the power rating. Other characteristics include temperature coefficient, noise, and inductance. Less well-known is critical resistance, the value below which power dissipation limits the maximum permitted current, and above which the limit is applied voltage. Critical resistance is determined by the design, materials and dimensions of the resistor. Resistors can be integrated into hybrid and printed circuits, as well as integrated circuits. Size, and position of leads (or terminals), are relevant to equipment designers; resistors must be physically large enough not to overheat when dissipating their power. Contents [hide] 1 Units 2 Theory of operation 2.1 Ohms law 2.2 Series and parallel resistors 2.3 Power dissipation 3 Construction 3.1 Lead arrangements 3.2 Carbon composition 3.3 Carbon film 3.4 Thick and thin film 3.5 Metal film 3.6 Metal Oxide film 3.7 Wirewound 3.8 Foil resistor 3.9 Ammeter shunts 3.10 Grid resistor 3.11 Special varieties 4 Variable resistors 4.1 Adjustable resistors 4.2 Potentiometers 4.