Littelfuse electrical components German Littelfuse models Littelfuse prices

Littelfuse electrical components refer to electronic components that can open a circuit, interrupt current flow, or direct it to another circuit. The most common switches are manually operated electromechanical devices with one or more electrical contacts. "Closed" contacts indicate conduction, allowing current to flow; "open" switches indicate non-conduction, creating an open circuit and preventing current flow. The simplest switch consists of two metal pieces called "contacts"; when they touch, current forms a loop, and when they do not, the circuit is open. When selecting contact metals, their corrosion resistance must be considered, as most metals form insulating oxides after oxidation, preventing normal contact operation. Selection also requires considering electrical conductivity, hardness, mechanical strength, cost, and toxicity. Contacts are sometimes plated with corrosion-resistant metals, typically on the contact surface, to avoid performance degradation due to oxides. Non-metallic conductive materials, such as conductive plastics, are sometimes used for contact surfaces. In addition to contacts, switches have moving parts that make or break the connection. Switches are classified by their moving parts, such as lever switches, push-button switches, and rocker switches, while the moving parts can also be other types of mechanical linkages.

Littelfuse electrical component parameters

Rated voltage: the safe voltage allowed during normal switch operation. Voltage exceeding this value across the switch terminals causes arcing and breakdown between contacts. Rated current: the maximum safe current allowed when the switch is closed; exceeding this value burns out the contacts due to excessive current. Insulation resistance: the resistance between the conductive and insulating parts of the switch. Contact resistance: the resistance between each pair of contacts in the closed state. Dielectric strength: the maximum voltage the switch can withstand between conductors and ground. Service life: the number of operations the switch can perform under normal working conditions.

Littelfuse electrical component advantages

Components do not consume material; even the best vacuum tubes degrade gradually due to cathode atom changes and slow air leakage. Due to technical reasons, early transistors faced similar issues. Transistors consume very little power, only one-tenth to one-hundredth that of vacuum tubes. Unlike vacuum tubes, they do not require filament heating to generate free electrons. A transistor radio can operate for six months to a year on just a few dry cells, which is difficult for vacuum tube radios. No warm-up is required; they work immediately upon startup. For example, transistor radios produce sound instantly, and transistor TVs display images quickly. Vacuum tube equipment cannot achieve this; one must wait a while after startup to hear sound or see images. Clearly, transistors offer significant advantages in military, measurement, and recording applications. They are robust, reliable, shock-resistant, and vibration-resistant, surpassing vacuum tubes. Additionally, transistors are only one-tenth to one-hundredth the size of vacuum tubes and generate little heat, enabling the design of small, complex, and reliable circuits. Although transistor manufacturing processes are precise, the steps are simple, facilitating higher component mounting density.

Littelfuse electrical component performance

(1) Electromotive force: the difference between the equilibrium electrode potentials of two electrodes. (2) Rated capacity: the theoretical capacity of a battery can be precisely calculated based on the amount of active electrode material in the battery reaction equation and the electrochemical equivalent of the active material calculated according to Faraday's law. Due to possible side reactions in the battery and special design requirements, the actual capacity is often lower than the theoretical capacity. (3) Rated voltage: the typical operating voltage of a battery at room temperature, also known as nominal voltage. It serves as a reference when selecting different types of batteries. The actual operating voltage equals the difference between the equilibrium electrode potentials of the positive and negative electrodes under different usage conditions. It depends only on the type of electrode active material, not on the quantity. Battery voltage is essentially DC voltage, but under certain special conditions, phase changes in metal crystals or certain formation films caused by electrode reactions cause minor voltage fluctuations, known as noise. The fluctuation amplitude is small, but the frequency range is wide, distinguishing it from self-excited noise in circuits. (4) Open-circuit voltage: the terminal voltage of a battery in an open-circuit state is called the open-circuit voltage. It equals the difference between the positive and negative electrode potentials when no current flows through the poles. The open-circuit voltage is denoted by V and is generally lower than the electromotive force. This is because the electrode potentials established in the electrolyte are usually stable electrode potentials rather than equilibrium electrode potentials. Generally, the open-circuit voltage can be approximated as the electromotive force. (5) Internal resistance: the resistance encountered by current flowing through the battery interior. It includes ohmic internal resistance and polarization internal resistance, with the latter comprising electrochemical polarization resistance and concentration polarization resistance. Due to internal resistance, the operating voltage is always lower than the electromotive force or open-circuit voltage. Internal resistance is not constant; it changes over time (gradually increasing) during charging and discharging because the composition of active materials, electrolyte concentration, and temperature constantly change. Ohmic resistance follows Ohm's law, while polarization resistance increases with current density, though not linearly. Internal resistance is a key indicator of battery performance, directly affecting operating voltage, current, output energy, and power; lower internal resistance is better. (6) Impedance: Batteries have a large electrode-electrolyte interface area, so they can be modeled as a series circuit of a large capacitor, small resistor, and inductor. However, the actual situation is much more complex, especially since impedance varies with time and DC level; measured impedance is valid only for the specific measurement state. (7) Charge/discharge rate: expressed as either hour rate or C-rate. The hour rate represents the charge/discharge speed by time, numerically equal to the rated capacity (Ah) divided by the specified charge/discharge current (A), resulting in hours. The C-rate is another representation, numerically the reciprocal of the hour rate. The discharge rate of primary batteries is expressed by the time taken to discharge through a fixed resistor to the cutoff voltage. Discharge rate significantly affects battery performance. (8) Service life: Storage life refers to the maximum allowable storage time from manufacture to initial use, measured in years. The total period, including storage and usage, is called the battery's shelf life. Storage life is divided into dry storage life and wet storage life. Cycle life is the maximum number of charge/discharge cycles a rechargeable battery can achieve under specified conditions. Specifying cycle life requires defining the test protocol, including charge/discharge rate, depth of discharge, and ambient temperature range. (9) Self-discharge rate: the rate at which a battery loses capacity during storage. It is expressed as the percentage of capacity lost due to self-discharge per unit storage time relative to the pre-storage capacity.

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