LEM LF1005-S/SP36 Current Transducer – LF Series

LEM LF1005-S/SP36 — Closed-Loop Hall Effect Current Transducer for High-Power Industrial Control Loops

In high-power drive and converter architectures, the integrity of the current feedback path is not a secondary concern — it is the foundation upon which closed-loop control stability is built. The LEM LF1005-S/SP36 is a closed-loop Hall effect current transducer rated for a nominal primary current of ±1005 A, housed in LEM’s SP36 PCB through-hole package. It occupies the current measurement node between the power stage and the DSP/FPGA control board, delivering a galvanically isolated, bandwidth-stable secondary current signal that the control algorithm can act upon with deterministic confidence.

Within LEM’s LF Series product family, the LF1005-S/SP36 is positioned for high-current industrial applications: variable frequency drives (VFDs) above 200 kW, large-format solar inverters, traction auxiliary converters, and high-power UPS systems. The SP36 package integrates the primary conductor aperture, the Hall element, the compensation winding, and the signal conditioning circuit into a single PCB-mountable assembly — eliminating the mechanical complexity of external current transformers and reducing the BOM footprint of the power electronics design.

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Technical Parameters

Hardware Logical Analysis

The LF1005-S/SP36 operates on the closed-loop flux compensation principle, which is architecturally distinct from open-loop Hall effect designs. In an open-loop transducer, the Hall element output is amplified directly and presented as the measurement signal — a topology that is inherently susceptible to temperature-induced drift of the Hall coefficient and to magnetic hysteresis in the core material. The LF1005-S/SP36 eliminates both error sources through active flux nulling.

The primary conductor passes through the SP36 aperture, generating a magnetic flux in the ferromagnetic core. A Hall element positioned in the core air gap detects any residual flux. The Hall element output drives a compensation amplifier, which forces a secondary current through the compensation winding wound on the same core. This secondary current generates an opposing magnetic flux that continuously nulls the core flux to zero. The measurement output is the secondary current itself — which, by Ampere’s law, is proportional to the primary current with a ratio defined by the turns count. Because the core operates at near-zero flux at all times, the measurement is independent of core permeability variation, temperature coefficient of the Hall element, and magnetic remanence.

The SP36 package integrates the compensation winding, the Hall element, and the signal conditioning ASIC on a single PCB-mountable assembly. The 36 mm × 36 mm primary aperture accommodates bus bars up to that cross-section, which at 1005 A nominal corresponds to a current density of approximately 7.8 A/mm² for a 130 mm² copper bus bar — well within standard industrial bus bar design practice.

From an EMC perspective, the closed-loop topology provides inherent immunity to external magnetic fields. Because the compensation circuit actively nulls the core flux, stray fields from adjacent conductors or transformers produce a compensation response rather than a measurement error. The SP36 package also incorporates a shielded housing that attenuates capacitively coupled high-frequency interference from the primary conductor — a critical consideration in PWM inverter environments where dV/dt on the primary bus can exceed 10 kV/µs.

The 3 kV_rms isolation barrier between primary and secondary circuits is implemented through the physical separation of the primary aperture and the secondary PCB circuitry, with the ferromagnetic core serving as the coupling medium. This architecture meets the reinforced insulation requirements of IEC 61010-1 for measurement circuits in Category III environments, making the LF1005-S/SP36 suitable for direct connection to 690 V AC industrial distribution systems.

System Integration Benefits

• Deterministic current feedback latency: The ≤1 µs response time ensures that the current feedback signal reaches the DSP control loop within a single PWM switching period at frequencies up to 20 kHz, preserving the phase margin of the current regulator and preventing limit-cycle oscillation.
• DC and AC measurement in a single device: Unlike current transformers, which are inherently AC-coupled and cannot measure DC components, the LF1005-S/SP36 measures DC, AC, and pulsed waveforms with equal accuracy — essential for DC bus monitoring in active front-end drives and battery storage inverters.
• Elimination of shunt resistor power dissipation: At 1005 A, a 100 µΩ shunt dissipates 101 W continuously. The LF1005-S/SP36 introduces negligible primary impedance, reducing thermal management requirements in the power stage and improving overall system efficiency.
• Galvanic isolation simplifies control board design: The 3 kV_rms isolation barrier eliminates the need for optocoupler-based isolation amplifiers between the current sense point and the DSP analog input, reducing component count and potential failure modes in the signal chain.
• Wide bandwidth supports harmonic analysis: The DC–100 kHz bandwidth allows the control system to observe current harmonics up to the 2000th order at 50 Hz fundamental, enabling real-time harmonic compensation algorithms in active power filter applications.
• PCB integration reduces mechanical assembly complexity: The SP36 through-hole package mounts directly to the power electronics PCB, eliminating the cable harnesses, mounting brackets, and connector interfaces required by panel-mount transducers — reducing assembly time and vibration-induced failure modes.
• Standardized secondary current output: The proportional secondary current output is compatible with standard burden resistors and differential ADC input stages without additional signal conditioning, simplifying firmware development and reducing analog front-end BOM cost.
• Thermal stability across industrial temperature range: The −25°C to +85°C operating range covers the full ambient temperature envelope of industrial enclosures without derating, including outdoor installations in temperate and subtropical climates.
• RoHS compliance enables global market access: Full compliance with RoHS 2011/65/EU eliminates regulatory barriers for equipment exported to the European Union, United Kingdom, and markets with equivalent substance restrictions.
• 12-month warranty reduces lifecycle cost: The 12-month warranty from date of shipment provides procurement teams with a defined risk window for warranty claims, simplifying total cost of ownership calculations for MRO and capital equipment budgets.

Quality Assurance & Global Logistics

Every LEM LF1005-S/SP36 unit supplied through siemensplc.com is sourced from verified supply chain channels with full traceability to LEM’s manufacturing facilities in Switzerland and China. Incoming inspection includes part marking verification against LEM’s official date code and lot number format, package integrity assessment, and cross-reference against LEM’s authorized distributor documentation. Certificate of Conformance (CoC) is available upon request for all shipments.

Shipments originate from our warehouse in Xiamen, China — a major international logistics hub with direct access to DHL Express, FedEx International Priority, and UPS Worldwide Express services. Standard export documentation — commercial invoice, packing list, and certificate of origin — is prepared for all international orders. For orders requiring CITES, CE Declaration of Conformity, or customs pre-clearance documentation, our logistics team coordinates directly with the freight forwarder to minimize customs dwell time at the destination port.

Typical transit times from Xiamen: Europe 3–5 business days, North America 3–5 business days, Southeast Asia 1–3 business days, Middle East 4–6 business days. All shipments include real-time tracking and are covered by cargo insurance. ESD-safe packaging with desiccant is standard for all electronic components.

Contact Information

Email: [email protected]
WhatsApp: +86 18359268345
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Location: Xiamen, China
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