High-Current Sensing Technology and Operating Condition Adaptation Solutions

I. Core Performance Requirements for New Energy Charging Piles

The circuit control requirements of new energy charging piles are primarily reflected in four key aspects: high-current carrying capacity, precision control, environmental adaptability, and structural integration. The specific specifications are as follows:

① Current and Power: DC fast charging piles operate at working currents ranging from 60A to 200A, with instantaneous peak currents reaching 2 to 3 times the rated value. Components must be capable of handling 5W to 20W of power. AC slow charging piles operate at working currents ranging from 16A to 32A, requiring components to handle 3W to 8W of power.

②  Accuracy and TCR: The control error for charging current must be ≤ ±2%. This necessitates resistors with an accuracy of ≥ 0.1%, a Temperature Coefficient of Resistance (TCR) of ≤ ±10ppm/℃, and a resistance drift of ≤ 0.1% over a wide temperature range (-20℃ to +70℃).

③  Environmental Adaptability: Components must withstand high and low-temperature cycling, water ingress, dust contamination, salt spray corrosion, and power grid electromagnetic interference (EMC) without experiencing package damage or performance degradation.

④ Structural Requirements: Surface-mount device (SMD) packages ranging from 0805 to 4527 are required to facilitate automated assembly. They must also feature a parasitic inductance of < 3nH to meet the compact layout and high-frequency signal transmission needs of modern charging piles.

II. Technical Shortcomings of Traditional Resistors and Milliohm Alloy Resistor Solutions

① Three Core Shortcomings of Traditional Resistors

① -1: Insufficient High-Current Carrying Capacity: Standard alloy resistors have a low power rating (≤5W) and are prone to burnout under high-current conditions exceeding 60A, making them unsuitable for fast-charging requirements.

① -2: Excessive Accuracy and TCR Deviation: Conventional metal film resistors typically offer an accuracy of only 1% to 5% and a TCR of ≥50ppm/℃. They exhibit significant resistance drift over a wide temperature range, causing charging current control errors to exceed allowable limits, thereby compromising charging efficiency and battery safety.

① -3: Poor Environmental Adaptability: Traditional resistors often feature basic packaging with weak waterproof and dustproof capabilities. They are susceptible to oxidation and corrosion in outdoor environments with rain and salt spray. Furthermore, their high parasitic inductance makes them vulnerable to power grid electromagnetic interference, leading to distorted control signals.

② Targeted Solutions with Milliohm Alloy Resistors

② -1: High-Current Carrying Solution: Utilizing high-conductivity alloy materials and electron beam welding technology, the chip's cross-sectional area and heat dissipation path are optimized to enhance power density. This achieves a power coverage of 5W to 20W with a 1.5x power derating margin, meeting the demands of high-current fast charging.

② -2: Precision Control Solution: Through independently developed alloy formulations and precision processing techniques, the resistors achieve an accuracy of 0.1% to 1% and a TCR of ±5 to ±10ppm/℃, with a resistance drift of ≤ 0.1% over a wide temperature range. This ensures the charging current control error remains ≤ ±2%.

② -3: Environmental Adaptation Solution: Encased models feature an epoxy resin seal to provide robust protection against moisture, dust, and salt spray corrosion. A low parasitic parameter design (inductance < 3nH) ensures the component passes EMC testing and possesses strong anti-electromagnetic interference capabilities.

② -4: Integration and Adaptation Solution: The standardized SMD packaging is compatible with automated assembly processes and integrates seamlessly with mainstream power chips and control modules without requiring circuit layout adjustments, thereby reducing research and development costs.

III. Operating Condition Adaptation Advantages

①  Adaptation to High-Current Fast-Charging Conditions

The charging process in new energy DC fast-charging piles is characterized by long duration and high power, making components susceptible to thermal degradation. Milliohm alloy resistors, through optimized packaging structures and heat dissipation paths, can withstand instantaneous surges and effectively disperse heat. This prevents burnout and performance degradation caused by prolonged high-power charging, making them ideally suited for high-current fast-charging applications.

②  Adaptation to Harsh Outdoor Environment

② -1:  Salt Spray Protection: The molding compound incorporates anti-corrosive additives, enabling the resistors to pass salt spray testing (≥500 hours). This makes them suitable for deployment in high-salinity environments such as coastal areas and highway service zones.

② -2: Electromagnetic Protection: The low parasitic inductance (<3nH) design minimizes electromagnetic interference caused by grid fluctuations and surrounding equipment, ensuring stable charging control signals.

③  Adaptation to Compact Layout Conditions

The limited board space within a charging pile's power modules and main control boards imposes strict miniaturization requirements on components. The standardized SMD design is compatible with automated assembly processes and requires no additional mounting space, perfectly meeting the compact layout demands of modern charging piles.

IV. Technical Selection Guide ： Selection Methodology and Considerations

①  Three-Step Selection Process

• Step 1: Determine Power Rating and Package Based on Charging Current

  • For 60A~100A: Select 10W~12W (2725 package)

  • For 100A~200A: Select 15W~20W (4527 package)

  • For 16A~32A: Select 3W~8W (2010/2512 package)

• Step 2: Determine Specifications Based on Accuracy Requirements

  • For core charging circuits and BMS (Battery Management System) interface circuits: Select 0.1% accuracy with ±5ppm/℃ TCR

  • For standard safety protection circuits: Select 1% accuracy with ±10ppm/℃ TCR

• Step 3: Determine Type Based on Installation Environment

  • For outdoor exposed applications and coastal salt spray environments: Select encased (molded) type

  • For indoor compact layouts: Select high-power open-frame type (requires accompanying heat dissipation structure)

②  Key Considerations

• Maintain a 1.5x power derating margin to accommodate instantaneous peak current surges during fast charging and prevent component thermal degradation;

• Prioritize products with low parasitic inductance (<3nH) for core circuits to minimize electromagnetic interference affecting charging control;

• Conduct high-temperature aging tests (≥1000 hours) and compatibility validation prior to mass production to ensure proper matching with power modules and IGBTs.