What circuits are resistors mainly used in?

Resistors, as the core components of electronic circuits, have applications that run through almost all electronic systems. From the perspective of circuit function classification, the main application areas and typical scenarios of resistors are systematically explained as follows:
1. Analog signal processing circuit
Operational amplifier feedback network: In an audio amplifier, the feedback resistor and input resistor form a proportional circuit to precisely control the amplification factor. For example, using a 10k Ω feedback resistor and a 1k Ω input resistor can achieve a 10 times voltage gain, while ensuring gain stability through resistance accuracy (such as 0.1%).
Filter design: In active filters, resistors and capacitors work together to form an RC time constant, which determines the cutoff frequency. When designing a 1kHz low-pass filter, using a 16k Ω resistor and a 10nF capacitor can accurately filter out high-frequency noise.
Sensor interface: In the platinum resistance temperature sensor (PT100) circuit, precision resistors form a bridge structure to convert temperature changes into millivolt level voltage signals, which are combined with instrumentation amplifiers to achieve a temperature measurement accuracy of 0.01 ℃.
2. Basic circuits of digital systems
Logic level conversion: In a 3.3V/5V hybrid system, a pull-up resistor (usually 4.7k Ω~10k Ω) ensures the integrity of the bus signal and prevents logic misjudgment caused by signal reflection.
ESD protection network: In the USB interface circuit, a 0 Ω resistor (actually a safety resistor) is connected in series to ensure normal signal transmission and to fuse and protect the downstream chip in the event of electrostatic shock.
GPIO protection: The input port of the microcontroller is often connected to a 10k Ω pull-down resistor to ensure that the pin maintains a certain level when suspended, avoiding false triggering.
3. Power management unit
LDO voltage regulator circuit: In a low dropout linear regulator, the feedback resistor voltage divider network (typical value 10k Ω+20k Ω) sets the output voltage and achieves 1% output accuracy through laser resistance adjustment technology.
DC-DC converter: In Buck circuits, an RC absorption network (such as 22 Ω+1nF) suppresses switch off spikes and limits voltage overshoot within a safe range.
Battery management system: In the lithium battery protection circuit, the detection resistor (milliohm level) monitors the charging and discharging current in real time, and cooperates with differential amplifiers to achieve overcurrent protection.
4. Radio frequency and communication circuits
Impedance matching network: In the RF front-end of 5G base stations, the 50 Ω characteristic impedance matching adopts a π - type resistor network (such as two 33 Ω series connected and one 100 Ω parallel connected), optimizing the S11 parameter to below -30dB.
Terminal resistor: At the end of the CAN bus, a 120 Ω terminal resistor eliminates signal reflections to ensure waveform integrity when the bus speed reaches 1Mbps.
Attenuator: In testing instruments, precision resistors form a stepped attenuation network (such as 10dB steps) to achieve signal conditioning in the dynamic range of -60dB to 0dB.
5. Special functional circuits
Heating control: In the temperature control module of the PCR instrument, thick film resistors (with a power density of 10W/cm ²) achieve a temperature control accuracy of 0.1 ℃ through PWM power adjustment.
Current sampling: In the motor driver, a copper wire resistor (0.1m Ω) is combined with an operational amplifier to form a current detection circuit, achieving millivolt level signal conversion in the 100A range.
Surge suppression: At the power input end, the varistor and PTC thermistor form a dual protection, which can withstand the 6kV surge impact specified in IEC61000-4-5 standard.
Modern electronic systems have higher requirements for resistors: carbon film resistors (self resonant frequency>1GHz) are used in high-frequency applications, thin film resistors (temperature drift<5ppm/℃) are used in precision measurement fields, and aluminum shell resistors (power up to 500W) are selected for high-power scenarios. These specialized developments have enabled resistors to continue to play a crucial role in emerging fields such as quantum computing and electric vehicles, confirming the irreplaceability of their "circuit cornerstone".