Introduction of resistor selection experience

introduction of resistor selection experience

Introduction of resistor selection experience

1. Fixed resistor selection fixed resistors are available in a variety of types, the choice of which material and structure of the resistor, according to the specific requirements of the application circuit. The high-frequency circuit should choose a non-wirewound resistor with distributed inductance and small distribution capacitance, such as carbon film resistor, metal resistor and metal oxide film resistor.

Low-noise resistors, such as metal film resistors, carbon film resistors, and Wirewound resistors, should be used in high-gain small-signal amplification circuits rather than using synthetic carbon film resistors with large noise and organic solid resistors.

Wirewound resistors have large power, low current noise, high temperature resistance, but larger volume. Common Wirewound resistors are commonly used in low-frequency circuits or as bias resistors for current-limiting resistors, voltage-divider resistors, drain resistors, or high-power tubes. High-precision wirewound resistors are used in fixed attenuators, resistor boxes, computers, and various precision electronic instruments.

The resistor value of the selected resistor should be close to a nominal value of the calculated value in the application circuit, and the standard series of resistors should be preferred. The general circuit uses a resistor that allows an error of ±5%~±10%. Precision resistors should be used in precision instruments and in special circuits.

The rated power of the selected resistor, to meet the application circuit in the resistor power capacity requirements, generally should not arbitrarily increase or decrease the power of the resistor. If the circuit requirement is a power type resistor, then its power rating can be higher than the actual application circuit required power of one or more times.

2. Fuse resistors are selected with a fuse resistor with a protective function. The choice should consider its dual performance, according to the specific requirements of the circuit to choose its resistance and power parameters. It is necessary to ensure that it can be quickly fused during overload, and that it can work stably in normal conditions. If the resistance value is too large or excessive power, it can not protect the function.

3. Thermistor selection of the type and type of thermistor, and choose which kind of thermistor, should be based on the specific requirements of the circuit.

The positive temperature coefficient thermistor (PTC) is generally used for the starting circuit of refrigerator compressor, the degaussing circuit of color kinescope, the over-current overheat protection circuit of motor, the current-limiting circuit and the thermostatic electric heating circuit.

The thermistor used in the starting circuit of the compressor has mz-01~mz-04 series, MZ81 series, MZ91 series, MZ92 series and MZ93 series. According to the different types of compressors to choose the right to start the thermistor, in order to achieve the best starting effect.

The degaussing thermistor used in color TV and computer monitor has the MZ71~MZ75 series. According to the TV, monitor operating voltage (220V or 110V), operating current and degaussing coil specifications, such as the use of nominal resistance, the maximum starting current, the maximum operating voltage and other parameters meet the requirements of degaussing thermistor.

Low power current Limiting PTC Thermistor has mz2a~mz2d series, MZ21 series, the motor overheat protection PTC Thermistor has MZ61 series, should choose the nominal resistance, switching temperature, operating current and dissipation power parameters in line with the requirements of the application circuit model.

Negative temperature coefficient thermistor (NTC) is generally used in a variety of electronic products for microwave power measurement, temperature detection, temperature compensation, temperature control and voltage regulator, the selection should be based on the needs of the application circuit to choose the appropriate type and model.

The common NTC thermistors for temperature sensing are the MF53 series and the MF57 series, each with a variety of models (the same type, different types of NTC thermistors, and the same standard resistance) to choose from.

Commonly used for voltage regulator NTC Thermistor has MF21 series, RR827 series, etc., according to the application circuit design reference voltage value to select the thermal resistor regulator value and operating current.

NTC thermistors commonly used for temperature compensation and temperature control have MF11~MF17 series. Commonly used in temperature control and NTC Thermistor has MF51 series, MF52 series, MF54 series, MF55 series, MF61 series, mf91~mf96, MF111 series and many other. The MF52 series, MF111 series of NTC thermistors are suitable for temperature measurement and temperature control circuits in the -80℃~+200℃ range. The MF51 series, mf91-mf96 series NTC thermistors are suitable for temperature and temperature control circuits up to 300 ℃. The MF54 series, MF55 series NTC thermistors are suitable for temperature and temperature control circuits up to 125 ℃.

The MF61 series, MF92 series NTC thermistors are suitable for temperature measurement and temperature control circuits up to 300 ℃. When choosing temperature control thermistor, we should pay attention to whether the temperature control range of NTC thermistor conforms to the requirement of application circuit.

4. Varistors are selected for varistors mainly used in overvoltage protection circuits of various electronic products, which are available in various models and specifications. The main parameters of the selected varistor (including nominal voltage, maximum continuous operating voltage, maximum limit voltage, flow capacity, etc.) must meet the requirements of the application circuit, especially the nominal voltage to be accurate. The nominal voltage is too high, the varistor does not have overvoltage protection, the nominal voltage is too low, the varistor is prone to malfunction or be penetrated.

5. The selection of photosensitive resistor when selecting a photosensitive resistor, the spectral characteristic type of the photosensitive resistor in the application circuit should be determined first. If used in a variety of optoelectronic automatic control systems, electronic cameras and light alarms and other electronic products, you should select the use of visible light-sensitive resistors; if used in infrared signal detection and astronomy, military and other fields of the relevant automatic control system, you should choose the infrared light-sensitive resistor; if used in instruments such as ultraviolet detection, UV light-sensitive resistors should be selected.

After selecting the non-spectral pasture type of photosensitive resistor, the main parameters of the selected photosensitive resistor (including light resistance, dark resistance, maximum operating voltage, apparent current, dark current, rated power, sensitivity, etc.) should also be considered to meet the requirements of the application circuit.

6. When selecting the wet-sensitive resistor, the suitable type should be selected first according to the requirements of the application circuit. If used in washing machines, dryers and other household appliances for high humidity detection, can choose lithium chloride wet-sensitive resistor; if used in air conditioners, humidity and other household appliances for medium humidity detection, you can choose ceramic humidity-sensitive resistors; if used for meteorological monitoring, video recorder dew detection, etc., You can choose a polymer wet-sensitive resistor or selenium film humidity-sensitive resistor.

Ensure that the main parameters of the selected humidity-sensitive resistor (including humidity range, nominal resistance, operating voltage, etc.) meet the requirements of the application circuit.