Low-Cost Current Sensing Solution: Precision Shunt Replaces Traditional Low-Voltage Current Transformers
I. Solution Background
Facing the urgent demand for low-cost current sensing in industrial control, energy metering, and overcurrent protection applications, traditional electromagnetic current transformers (CTs) and Hall sensors present pain points such as high material costs (especially for >30A specifications) and complex manufacturing processes. This solution employs a four-terminal manganin shunt resistor + optimized signal chain design to achieve extreme cost control in high-volume application scenarios.
II. Core Solution Design
- Sensing Unit
- Precision Four-Terminal Manganin Shunt Resistor
- Replaces traditional CT core and coil structure.
- Key Parameters: 50μΩ-5mΩ resistance range (customized per current rating), Temperature Coefficient <50ppm/°C.
- Four-terminal structure eliminates contact resistance error (Kelvin connection).
- Signal Processing Chain
- Low-Drift Instrumentation Amplifier (INA)
- Utilizes devices with <0.5μV/°C offset voltage drift (e.g., AD8237, INA826).
- Gain Error <0.1%, CMRR >120dB (suppresses common-mode interference).
- Integrated EMI filtering reduces peripheral circuitry.
- Isolation Optimization
- Switched Capacitor Isolator (e.g., ADI isoPower®)
- Replaces traditional CT's magnetic isolation structure.
- Supports >5kV DC isolation voltage.
- 40% lower power consumption, cost only 60% of optocoupler solutions.
- Mechanical Design
- Injection-Molded Plastic Housing
- Eliminates metal shielding layers and potting process.
- Maintains IP54 protection rating (dustproof and water splash resistant).
- Standardized pluggable terminals for automated assembly.
III. Cost Advantage Analysis (vs. Traditional Solution)
|
Item |
Traditional CT Solution |
This Shunt Solution |
Reduction/Increase |
|
100A Sensor BOM Cost |
$8.2 |
$1.7 |
**79%↓** |
|
Daily Production Line Capacity |
5,000 pcs |
22,000 pcs |
**340%↑** |
|
Calibration Time/Piece |
45 sec |
8 sec |
**82%↓** |
|
High-Current Spec Premium |
300% |
20% |
- |
IV. Typical Technical Specifications
- Accuracy: 1% FS (@25°C), 2% FS (@-40°C~+85°C)
- Bandwidth: DC~50kHz (superior to traditional CT's 10kHz limit)
- Rated Current: 15-300A (>300A recommended using parallel shunt arrays)
- Power Consumption: <15mW (no self-heating impact)
- Response Time: <1μs (significant advantage in overcurrent protection scenarios)
V. Application Scenario Adaptation
- Smart Meter Internal Measurement
- Suitable for energy metering below Class 1.
- Busbar current sampling (paired with Σ-Δ ADC).
- Motor Drive Control Systems
- Three-phase inverter phase current detection.
- Cost-sensitive BLDC controllers.
- Overcurrent Protection Devices
- Breaker trip current detection.
- Response speed improved by 50x.
- Solar Inverters
- String current monitoring (DC side).
- Eliminates traditional CT's residual flux error issue.
VI. Implementation Key Points
- Thermal Management Design
- Copper pour heat dissipation (PCB acts as heat sink).
- Rule to follow: ≥4mm² copper pour per 1A current.
- EMC Optimization
- Differential trace length matching ≤10mm.
- π-filter at instrumentation amplifier front end.
- Mass Production Control
- Fully automated laser resistor trimming calibration.
- Temperature compensation coefficient firmware programming.
- Dynamic load testing (replaces traditional burn-in process).
Solution Limitations:
- Not suitable for >600V strong isolation scenarios (requires reinforced isolation solution).
- Significant copper losses at currents >500A (recommend magnetic solution).
