1. Selection of Fixed Resistors

There are various types of fixed resistors, and the selection of which material and structure of resistor to use should be based on the specific requirements of the application circuit. For example, for high-frequency circuits, non-inductive resistors with small distributed inductance and capacitance should be selected, such as carbon film resistors, metal resistors, and metal oxide film resistors. For high-gain small-signal amplification circuits, low-noise resistors such as metal film resistors, carbon film resistors, and wire wound resistors should be used, and resistors with larger noise such as composite carbon film resistors and organic solid resistors should not be used.

Wire wound resistors have high power, low current noise, and high temperature resistance, but they have a larger volume. Ordinary wire wound resistors are commonly used in low-frequency circuits or as current limiting resistors, voltage divider resistors, discharge resistors, or bias resistors for high-power tubes. High-precision wire wound resistors are mostly used in fixed attenuators, resistance boxes, computers, and various precision electronic instruments.

When selecting resistors, nominal values close to the calculated values in the application circuit should be selected, and standard series resistors should be preferred. The allowable error of resistors used in general circuits is ±5% to ±10%. Precision resistors should be used in precision instruments and special circuits. The rated power of the selected resistor should meet the requirements of the power capacity of the resistor in the application circuit, and the power of the resistor should not be arbitrarily increased or decreased. If the circuit requires a power resistor, its rated power can be higher than the actual power required by the application circuit by 1 to 2 times.

2. Selection of Fuse Resistors

Fuse resistors are resistors with protective functions. When selecting them, their dual performance should be considered, and the resistance value and power parameters should be selected according to the specific requirements of the circuit. It is necessary to ensure that it can quickly fuse under overload conditions and can work stably for a long time under normal conditions. A resistance value or power that is too large cannot provide protection.

3. Selection of Thermistor Resistors

There are many types and models of thermistor resistors, and the selection of which thermistor resistor to use should be based on the specific requirements of the circuit. For example, positive temperature coefficient thermistor resistors (PTC) are generally used in refrigerator compressor starting circuits, color cathode ray tube demagnetization circuits, motor overcurrent and overheating protection circuits, current limiting circuits, and constant temperature electric heating circuits.

In compressor starting circuits, commonly used thermistor resistors include the MZ-01 to MZ-04 series, MZ81 series, MZ91 series, MZ92 series, and MZ93 series. Suitable thermistor resistors can be selected according to different types of compressors to achieve the best starting effect.

The demagnetization thermistor resistors used in color televisions and computer monitors include the MZ71 to MZ75 series. Thermistor resistors with nominal resistance values, maximum starting currents, and maximum working voltages that meet the requirements can be selected based on the working voltage (220V or 110V), working current, and specifications of the demagnetization coil of the television or monitor.