From Selection To Commissioning: Master The Entire Process Of High-power Current Induction Resistors
introduction
In inverters, motor drives and industrial high-power power supplies, shunt resistors not only have to withstand constant current impacts of tens or even hundreds of amperes, but also maintain measurement stability for a long time. To achieve neither excessive heat generation nor provide precise current feedback, it is necessary to strive for excellence in every aspect, including selection, heat dissipation, PCB layout and calibration. This article will guide you to start from the characteristics of the device, break down the core design points, and combine real cases to help you master the application secrets of high-power current-sensing resistors throughout the process.
The core characteristics of high-power current induction resistors
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The common resistance is 0.1 mΩ - 2 mΩ, which can control the voltage drop caused by A current as high as 200 A within tens of millivolts, minimizing power consumption and system losses to the greatest extent.
High rated power
Plug-in or bigfoot SMD packages can provide continuous power carrying of 5 W - 30 W. When selecting the model, it is necessary to ensure that the rated power is ≥ the actual maximum heat generation power (I²R).
Excellent linearity
The linearity error is ≤ ±0.5%, ensuring a strict proportional relationship between the measured voltage and the actual current, which is convenient for signal amplification and digital processing.
Low temperature coefficient (TCR)
It is recommended to be ≤ ±25 ppm/°C, ensuring minimal resistance drift within the range of -40 °C to +85 °C, meeting the requirements of various environmental conditions.
Shock resistance and vibration resistance
Industrial and automotive-grade models need to pass the EC-Q200 certification and be capable of long-term stable operation under severe vibration and thermal cycling.
Key points of heat dissipation and thermal resistance design
The thermal resistance of the device itself
Pay attention to the RθJA (thermal resistance from junction to environment) and RθJC (thermal resistance from junction to shell) indicators. The lower the values, the easier the heat is to be conducted to the external heat dissipation medium.
PCB heat dissipation solution
Large copper foil area: Lay copper foil of ≥ 500 mm² at the bottom and on both sides of the shunt resistor to increase the heat diffusion rate.
Through-hole array: Multiple rows of through-holes are drilled beneath the copper foil to conduct heat to the inner or lower heat dissipation layer.
Multi-layer copper layer linkage: When using multi-layer PCBS, the heat dissipation layers can be connected in series to form highly efficient heat conduction channels.
External heat dissipation accessories
For high-power applications of ≥ 20W, lightweight aluminum heat sinks can be installed on the plug-in shunt resistors and combined with air ducts or micro fans to significantly reduce the junction temperature.
Temperature monitoring and protection
An NTC temperature sensor is placed near the shunt resistor to monitor the PCB temperature in real time. When it exceeds the safety threshold, a soft shutdown or fan speed increase is triggered.
PCB layout and routing techniques
The shortest and widest current loop
The power input, shunt resistor and load path are designed as "U" -shaped or "Π" -shaped large copper surfaces to reduce additional resistance and magnetic field interference.
Separate the measurement ground from the power ground
Set up a measurement ground (SGND) point to converge the signal lines at both ends of the shunt resistor here, completely isolating it from the high current ground (PGND) to prevent the ground loop voltage from affecting the measurement accuracy.
Differential amplifier pre-layout
Place the differential amplifier chip as close as possible to the shunt resistor to shorten the parasitic inductance and capacitance of the signal, and reduce common-mode interference and high-frequency noise.
Shielding and Filtering
For applications where the high-frequency noise of the switching power supply is relatively strong, a micro-difference common-mode inductor or RC filter can be installed beside the measurement line to smooth out the output signal.
Measurement accuracy calibration: OFFSET correction and temperature compensation
Hardware calibration (OFFSET adjustment)
Reserve a fine-tuning potentiometer interface at the input end of the amplifier. After the first board installation, adjust the output at zero current to 0 mV through the calibration circuit.
Software error compensation method
The reference value when there is no current is read by the built-in ADC of the MCU and stored in the non-volatile memory. Each time the power is turned on or recalibrated at regular intervals, the reference offset is dynamically deducted.
Temperature compensation algorithm
According to the TCR characteristic curve of the device, the data of the temperature sensor on the board is read in real time. The measured values are corrected linearly or by quadratic curve in the software to eliminate the influence of temperature drift.
Automatic verification and self-diagnosis
Design self-check mode: Regularly enter self-check when there is an open circuit or short circuit. Verify the consistency of the measurement channel through the internal electronic load or loopback circuit to ensure the reliability of the measurement link.
Real case: Practical Experience in Inverter and Motor drive systems
A certain industrial frequency converter project requires precise detection of the starting and braking processes of motors ranging from 0 to 300 A. The project team has selected the following solutions:
Device selection: 0.2m Ω, ±0.5% accuracy, TCR ±25 ppm/°C, rated power 15 W plug-in shunt resistor;
Thermal management: 800 mm² copper foil and a perforated array are laid at the bottom to direct heat to the multi-layer inner heat dissipation layer. Plug-in heat sinks combined with two 40mm micro fans;
PCB layout: The differential amplifier is adjacent to the shunt resistor input terminal, and the measurement ground is separately reflow to the MCU. The power supply ground and the measurement ground are zoned symmetrically.
Calibration strategy: Perform hardware OFFSET calibration for the first time at an ambient temperature of 25 ℃. Each time power is turned on, perform software reference sampling and linear temperature compensation based on the on-board thermistor.
Effect verification: In an environment ranging from -20 ℃ to +60 ℃, the system measurement error is always controlled within ± 0.5A, the temperature rise during heating is ≤ 40 ℃, and there is no drift after continuous operation for 1000 hours.
epilogue
The reliable application of high-power current-sensing resistors requires a full-process collaborative optimization from device selection, thermal management, PCB design to calibration algorithms. Through the above guidance and case analysis, we believe that you have mastered the key technologies for achieving high precision and high reliability. Act now - Optimize your current monitoring solution to safeguard the safety and performance of your equipment! If you need more model information or technical support, please feel free to contact our engineering team.