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c control electrical components include single heterojunction, double heterojunction, and quantum well laser diodes. Quantum well laser diodes offer the advantages of low threshold current and high output power, making them mainstream products in market applications. Compared to lasers, laser diodes have the advantages of high efficiency, small size, and long service life, but their low output power, poor linearity, and less ideal monochromaticity greatly limit their application in cable television systems, preventing the transmission of multi-channel, high-performance analog signals. In the return path module of a bidirectional optical receiver, upstream transmission generally employs quantum well laser diodes as the light source.

c control electrical component operating principle

The thermistor will remain in a non-tripped state for an extended period; when the ambient temperature and current are in the c region, the heat dissipation power of the thermistor is close to its heat generation power, so it may or may not trip. For a thermistor at the same ambient temperature, the tripping time decreases sharply as the current increases; at relatively higher ambient temperatures, the thermistor has a shorter tripping time and lower holding and tripping currents. The PTC effect refers to a material exhibiting the PTC effect, i.e., the positive temperature coefficient effect, meaning only that the resistance of this material increases with rising temperature. For example, most metal materials exhibit the PTC effect. In these materials, the PTC effect manifests as a linear increase in resistance with temperature, which is commonly referred to as the linear PTC effect. Nonlinear PTC effect: Materials undergoing a phase transition exhibit a phenomenon where resistance increases abruptly by several to more than ten orders of magnitude within a narrow temperature range, known as the nonlinear PTC effect. Many types of conductive polymers exhibit this effect, such as polymer PTC thermistors. These conductive polymers are very useful for manufacturing overcurrent protection devices. Polymer PTC thermistors are used for overcurrent protection and are often referred to as self-resetting fuses (hereinafter referred to as thermistors). Due to their unique positive temperature coefficient resistance characteristics, they are highly suitable as overcurrent protection devices. The usage method of a thermistor is similar to that of a standard fuse, connected in series in the circuit. When the circuit operates normally, the thermistor's temperature is close to room temperature, and its resistance is very low, so connecting it in series does not hinder current flow. However, when an overcurrent occurs due to a fault, the increased heat generation causes the thermistor's temperature to rise. When the temperature exceeds the switching temperature, the resistance increases dramatically instantly, rapidly reducing the current in the circuit to a safe value. After the thermistor trips, the current in the circuit drops significantly, with t representing the tripping time of the thermistor. Due to the good designability of polymer PTC thermistors, their sensitivity to temperature can be adjusted by changing their switching temperature (ts), allowing them to provide both over-temperature and overcurrent protection simultaneously. This makes them suitable for overcurrent and over-temperature protection of lithium-ion and nickel-metal hydride batteries. Influence of ambient temperature on polymer PTC thermistors: A polymer PTC thermistor is a direct-heated, step-type thermistor. Its resistance change process is related to its own heat generation and dissipation conditions; therefore, its holding current, tripping current, and tripping time are influenced by ambient temperature.

c control electrical component structure

A solid-state relay consists of three parts: the input circuit, isolation, and output circuit. Depending on the input voltage category, the input circuit can be divided into DC input circuits, AC input circuits, and AC/DC input circuits. Some input control circuits also feature compatibility with TTL/CMOS, positive/negative logic control, and inversion functions, allowing convenient connection to TTL and MOS logic circuits. For control signals with fixed control voltage, a resistive input circuit is used. The isolation and coupling methods between the input and output circuits of a solid-state relay include optocoupling and transformer coupling. Optocoupling typically uses photodiode-phototransistor pairs, photodiode-bidirectional optically controlled thyristors, or photovoltaic cells to achieve isolated control between the control side and the load side. High-frequency transformer coupling utilizes the self-excited high-frequency signal generated by the input control signal, which is coupled to the secondary side, then demodulated, rectified, and processed by logic circuits to form a drive signal. The power switch of the solid-state relay is directly connected to the power supply and load terminals to realize switching of the load power. Mainly used components include high-power bipolar transistors, unidirectional thyristors, bidirectional thyristors, power MOSFETs, and insulated-gate bipolar transistors (IGBTs). The output circuit of a solid-state relay can also be divided into DC output circuits, AC output circuits, and AC/DC output circuits. Based on the load type, they can be classified into DC solid-state relays and AC solid-state relays. For DC output, bipolar devices or power MOSFETs can be used; for AC output, two thyristors or one bidirectional thyristor are typically used. AC solid-state relays can be further divided into single-phase AC solid-state relays and three-phase AC solid-state relays. Based on the timing of conduction and turn-off, AC solid-state relays can be classified into random-turn-on AC solid-state relays and zero-crossing AC solid-state relays.

c control electrical component operating principle

The main principle of a diode is to utilize the unidirectional conductivity of the PN junction; adding leads and encapsulation to the PN junction forms a diode. A crystal diode is a PN junction formed by P-type semiconductor and N-type semiconductor. A space charge layer forms on both sides of the interface, establishing a built-in electric field. When no external voltage is applied, the diffusion current caused by the carrier concentration difference across the PN junction equals the drift current caused by the built-in electric field, resulting in an electrical equilibrium state. When a forward voltage bias is applied externally, the mutual cancellation of the external electric field and the built-in electric field increases the carrier diffusion current, causing a forward current. When a reverse voltage bias is applied externally, the external electric field and the built-in electric field are further strengthened, forming a reverse saturation current within a certain reverse voltage range that is independent of the reverse bias voltage value. When the applied reverse voltage reaches a certain level, the electric field strength in the space charge layer of the PN junction reaches a critical value, triggering a carrier multiplication process. This generates a large number of electron-hole pairs, resulting in a significant reverse breakdown current, known as the diode breakdown phenomenon. Reverse breakdown of the PN junction is categorized into Zener breakdown and avalanche breakdown.

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