Main characteristic parameters of resistor
The main parameters of a resistor include its resistance value, tolerance, rated power, and temperature coefficient.
1. Nominal resistance: The resistance value marked on the resistor.
2. Tolerance: The percentage of the difference between the nominal resistance and the actual resistance to the nominal resistance is called the resistance deviation, which indicates the accuracy of the resistor.
3. Rated power: The maximum power that the resistor can dissipate during long-term operation under normal atmospheric pressure of 90-106.6 kPa and ambient temperature of -55℃ to +70℃.
4. Rated voltage: The voltage calculated from the resistance and rated power.
5. Temperature coefficient: The relative change in resistance caused by a 1°C change in temperature. The smaller the temperature coefficient, the better the stability of the resistor. A positive temperature coefficient indicates that the resistance increases with increasing temperature, while a negative temperature coefficient indicates that the resistance decreases with increasing temperature.
6. Aging coefficient: The percentage change in resistance value of a resistor under long-term rated power load. It is a parameter that indicates the lifespan of a resistor.
7. Voltage coefficient: Within a specified voltage range, the relative change in resistance for every 1 volt change in voltage.
Main parameters of inductors
The main parameters of an inductor include inductance, tolerance, quality factor, distributed capacitance, and rated current.
1. Inductance: Inductance, also known as self-inductance coefficient, is a physical quantity that represents the ability of an inductor to generate self-induction.
The inductance of an inductor depends primarily on the number of turns in the coil, the winding method, the presence or absence of a magnetic core, and the material of the core. Generally, the more turns the coil has and the denser the winding, the greater the inductance. Coils with a magnetic core have a larger inductance than those without; the higher the permeability of the magnetic core, the greater the inductance of the coil.
2. Allowable deviation: Allowable deviation refers to the permissible error between the nominal inductance value marked on the inductor and the actual inductance value.
Inductors used in circuits such as oscillation or filtering generally require high precision, with an allowable deviation of ±0.2% to ±0.5%; while coils used for coupling, high-frequency choke, etc., do not require high precision, with an allowable deviation of ±10% to 15%.
3. Quality Factor: The quality factor, also known as the Q value or figure of merit, is a key parameter for evaluating the quality of an inductor. It refers to the ratio of the inductive reactance to the equivalent loss resistance of an inductor when operating under AC voltage at a specific frequency. A higher Q value indicates lower losses and higher efficiency. The quality factor of an inductor is related to the DC resistance of the coil conductors, the dielectric loss of the coil frame, and losses caused by the core, shielding, etc.
4. Distributed capacitance: Distributed capacitance refers to the capacitance between the turns of the coil and between the coil and the magnetic core. The smaller the distributed capacitance of an inductor, the better its stability.
5. Rated Current: Rated current refers to the maximum current that an inductor is allowed to pass through when it is operating normally. If the operating current exceeds the rated current, the inductor will heat up, causing its performance parameters to change, and it may even burn out due to overcurrent.
Main characteristic parameters of capacitors
The main parameters of a capacitor include capacitance value, tolerance, rated operating voltage, and temperature coefficient.
1. Capacitance and Tolerance: The maximum allowable deviation between the actual capacitance and the nominal capacitance is generally divided into ±5%, ±10%, and ±20%. Precision capacitors have smaller allowable errors, while electrolytic capacitors have larger errors; they use different error grades.
2. Rated operating voltage: The maximum DC voltage that a capacitor can withstand to operate stably and reliably in a circuit for a long period of time, also known as withstand voltage. For devices with the same structure, dielectric, and capacitance, the higher the withstand voltage, the larger the size.
3. Temperature coefficient: Within a certain temperature range, the relative change in capacitance for every 1°C change in temperature. A smaller temperature coefficient is better.
4. Insulation resistance: This indicates the magnitude of leakage current. Generally, small-capacity capacitors have very high insulation resistance, ranging from hundreds to thousands of megaohms. Electrolytic capacitors typically have lower insulation resistance. Generally speaking, higher insulation resistance is better, as it indicates less leakage current.
5. Losses: The energy consumed by a capacitor due to heat generation per unit time under the influence of an electric field. These losses mainly come from dielectric loss and metal loss. They are usually represented by the loss tangent.
Main characteristic parameters of MOSFET
MOSFET is an abbreviation for Metal-Oxide Semiconductor Field Effect Transistor. It is a device made of three materials: metal, oxide (SiO2 or SiN), and semiconductor.
The main parameters of a MOSFET include ID, IDM, VGS, V(BR)DSS, RDS(on), and VGS(th).
1. ID: Maximum drain-source current. This refers to the maximum current allowed to flow between the drain and source of the field-effect transistor (FET) during normal operation. The operating current of the FET should not exceed ID. This parameter will decrease as the junction temperature increases.
2. IDM: Maximum pulsed drain-source current. This parameter decreases as junction temperature increases.
3. VGS: Maximum gate-source voltage.
4. V(BR)DSS: Drain-Source Breakdown Voltage. This refers to the maximum drain-source voltage that a field-effect transistor (FET) can withstand during normal operation when the gate-source voltage VGS is 0. This is a limiting parameter; the operating voltage applied to the FET must be less than V(BR)DSS. It has a positive temperature characteristic. Therefore, the value of this parameter under low-temperature conditions should be considered for safety.
5. RDS(on): Under specific VGS (typically 10V), junction temperature, and drain current conditions, the maximum drain-source impedance of the MOSFET when it is turned on. It is a very important parameter that determines the power dissipation of the MOSFET when it is turned on. This parameter generally increases with increasing junction temperature. Therefore, the value of this parameter under the highest operating junction temperature condition should be used for calculating losses and voltage drop.
6. VGS(th): Threshold voltage. When the applied gate control voltage VGS exceeds VGS(th), a connecting channel is formed between the surface inversion layers of the drain and source regions. In applications, the gate voltage at which ID equals 1 mA with the drain shorted is often referred to as the threshold voltage. This parameter generally decreases as the junction temperature increases.
7. PD: Maximum Power Dissipation. This refers to the maximum drain-source power dissipation allowed when the performance of the MOSFET remains unchanged. In practice, the actual power dissipation of the MOSFET should be less than PDSM with a certain margin. This parameter generally decreases as the junction temperature increases.
8. Tj: Maximum operating junction temperature. Typically 150℃ or 175℃. The operating conditions of the device design must avoid exceeding this temperature, and a certain margin should be allowed.
Compared to bipolar power MOSFETs, power MOSFETs have the following characteristics:
1. MOSFETs are voltage-controlled devices (bipolar devices are current-controlled devices), therefore no driver stage is needed when driving high currents, making the circuit simpler;
2. High input impedance;
3. Wide operating frequency range, high switching speed (switching time from tens to hundreds of nanoseconds), and low switching losses;
4. It has a superior linear range, and the input capacitance of a MOSFET is much smaller than that of a bipolar transistor, resulting in extremely high AC input impedance; it also has low noise, making it ideal for Hi-Fi audio equipment.
5. Multiple power MOSFETs can be used in parallel to increase the output current without the need for current sharing resistors.
