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Explore our precision-engineered transformer products designed specifically for switching power supply applications — delivering reliable performance across a wide frequency range.
A current transformer (CT) for switching power supplies (SMPS) is a specialized magnetic component designed to measure, monitor, and control electrical current within high-frequency power conversion circuits. Unlike conventional line-frequency transformers, SMPS current transformers operate at frequencies ranging from tens of kilohertz to several megahertz, making their core material selection, winding geometry, and insulation design critically important.
In a typical SMPS topology — whether flyback, forward, half-bridge, full-bridge, or LLC resonant — the current transformer serves multiple essential functions: it provides isolated current feedback to the PWM controller, enables overcurrent and short-circuit protection, and supports peak current mode control strategies that improve transient response and power factor correction (PFC).
Current transformers in SMPS circuits provide galvanic isolation between the high-voltage primary side and the low-voltage control circuitry, enabling safe, accurate current sensing at switching frequencies above 100 kHz — a capability that resistive shunts and Hall-effect sensors cannot match in terms of power loss and bandwidth simultaneously.
Designing a current transformer for SMPS applications demands a precise balance of magnetic, electrical, and thermal parameters. The following characteristics define a high-performance SMPS CT:
Six critical advantages that make current transformers indispensable in modern switching power supply design.
Provides complete electrical isolation between the power stage and control circuitry, protecting sensitive ICs and ensuring operator safety in AC-input designs.
Accurately reproduces current waveforms at switching frequencies from 20 kHz to over 2 MHz, enabling precise peak-current-mode control and PFC algorithms.
Enables cycle-by-cycle current limiting, protecting power MOSFETs and output diodes from catastrophic failure during overload or short-circuit conditions.
Compared to resistive shunts, CTs introduce minimal conduction loss into the primary circuit, improving overall SMPS efficiency — critical for 80 PLUS Titanium and similar certifications.
Modern ferrite-core SMPS CTs achieve high performance in extremely small packages — SMD variants as small as 4mm × 4mm — supporting ultra-thin and high-density power supply designs.
Engineered to maintain magnetic stability from −40°C to +125°C, ensuring reliable operation in automotive, industrial, and outdoor power systems without parameter drift.
Modern data centers demand power supplies with efficiency ratings above 96% (80 PLUS Titanium) and power densities exceeding 50 W/cm³. In these high-performance AC/DC rectifiers and DC/DC converters, current transformers are embedded in the primary switch leg of LLC resonant converters and phase-interleaved PFC stages. The CT provides real-time current feedback to the digital controller (DSP or FPGA), enabling adaptive dead-time control that minimizes switching losses across the full load range. Leading telecom infrastructure providers specify CTs with less than 0.5% amplitude error up to 1 MHz and isolation voltages of 3000 Vrms to meet ETSI EN 300 132 requirements.
On-board chargers for electric vehicles represent one of the most demanding SMPS applications for current transformers. Operating from a 400V or 800V DC bus, these bidirectional converters use CTs in both the AC/DC PFC stage and the isolated DC/DC stage (typically CLLC or DAB topology). The CT must withstand high dV/dt transients (>50 V/ns) without introducing common-mode noise into the current sense signal, which would corrupt the battery management system's (BMS) charge control algorithm. Automotive-grade CTs (AEC-Q200 qualified) with reinforced insulation (4000 Vrms) and operating temperatures up to +150°C are now standard requirements from Tier-1 automotive suppliers.
The global EV on-board charger market is projected to exceed USD 8.5 billion by 2030, driving unprecedented demand for automotive-qualified SMPS current transformers. Manufacturers capable of supplying AEC-Q200 compliant CTs with fast delivery and design support hold a significant competitive advantage.
Variable frequency drives (VFDs) and servo amplifiers rely on SMPS current transformers for both the internal power supply and the motor current feedback path. In the auxiliary SMPS powering gate drivers and control boards, CTs ensure stable operation even during regenerative braking events that cause DC bus voltage spikes. High-current CTs with primary current ratings from 50A to 500A and secondary outputs of 5A or 1V are used in the motor phase current sensing path, feeding the field-oriented control (FOC) algorithm with the accuracy needed for precise torque control.
String inverters and central inverters for photovoltaic systems use current transformers extensively in their MPPT (Maximum Power Point Tracking) boost converters and grid-tied inverter stages. The CT monitors inductor current for average current mode control, ensuring the grid injection current is sinusoidal and in phase with the grid voltage (unity power factor). In battery energy storage systems (BESS), bidirectional DC/DC converters use CTs for charge/discharge current monitoring with accuracy requirements of ±0.5% to comply with grid codes and battery warranty conditions.
The proliferation of GaN (Gallium Nitride) and SiC (Silicon Carbide) power devices has pushed switching frequencies in USB-C PD adapters and laptop chargers above 1 MHz. At these frequencies, traditional silicon-steel CTs are entirely unsuitable. Ultra-miniature ferrite-core CTs with primary single-turn construction and secondary turns of 100–300 are designed to fit within the tight PCB real estate of a 65W GaN charger. These components enable the Active Clamp Flyback (ACF) or quasi-resonant flyback controller to regulate output voltage and current with the precision demanded by the USB Power Delivery 3.1 specification (up to 240W).
Medical-grade SMPS for patient-connected equipment (IEC 60601-1, 2× MOPP) require current transformers with exceptional isolation integrity — typically 5000 Vrms or higher — and ultra-low leakage current (<10 µA). CTs in these applications serve both the primary-side current sensing for the resonant controller and the secondary-side output current monitoring for the overcurrent protection circuit. The combination of high isolation and high bandwidth is uniquely achievable with custom-wound ferrite-core CTs, making them irreplaceable in Class II medical device power supplies.
The SMPS current transformer market is undergoing rapid transformation driven by electrification, digitalization, and miniaturization megatrends.
The global current transformer market was valued at approximately USD 3.2 billion in 2023 and is forecast to grow at a CAGR of 6.8% through 2030, with the SMPS segment representing the fastest-growing sub-category. Several converging technology trends are reshaping product requirements:
| Trend | Impact on SMPS CT Design | Timeline |
|---|---|---|
| GaN & SiC Power Devices | Requires CTs with bandwidth >2 MHz and <5 ns propagation delay | Now – 2027 |
| EV & Bidirectional Charging (V2G) | Bidirectional CT designs with AEC-Q200 qualification | 2024 – 2028 |
| AI Data Center Power Density | Ultra-compact CTs for 48V bus architectures, >1 kW/cm³ | 2024 – 2030 |
| Digital Power Management (DPWM) | CTs with digital output (Σ-Δ modulator interface) replacing analog burden resistors | 2025 – 2030 |
| Renewable Energy Expansion | High-current CTs (500A+) for MW-scale solar and BESS inverters | Now – 2030 |
| Miniaturization & Integration | Integrated CT + controller modules in single SMD package | 2026 – 2030 |
From a commercial perspective, the shift toward domestic supply chain resilience in North America and Europe is creating opportunities for Asian manufacturers — particularly those in China's Pearl River Delta manufacturing cluster — to establish long-term supply agreements with Tier-1 electronics OEMs. Manufacturers offering rapid prototyping, custom winding services, and full qualification testing (including HALT/HASS) are commanding premium pricing and preferred supplier status.
The adoption of automated winding machines and AI-driven quality inspection systems is enabling leading CT manufacturers to achieve Cpk >1.67 on critical parameters such as turns ratio, DCR, and inductance — meeting the Six Sigma quality standards demanded by automotive and medical customers.
Dong Guan Golden Eagle Coil Co. Ltd., founded in 2007, is a diversified sole proprietorship integrating research and development, production, sales, and industry-trade. It has been providing high-quality products and services to industry giants such as HUAWEI, XIAOMI, DJI, SIEMENS, TDK, Samsung, BOSE and others.
Research and development and production are based on market and customer needs, committed to technological innovation and enhancing the overall manufacturing capability of precision components in the enterprise.
DongGuan Golden Eagle Coil Co. Ltd. is a diversified sole proprietorship integrating research and development, production, sales, and industry-trade. It has been providing high-quality products and services to industry giants such as HUAWEI, XIAOMI, DJI, SIEMENS, TDK, Samsung, BOSE and others.
Our SMPS current transformers and precision magnetics power products from the world's most recognized technology brands.
Our commitment to quality and innovation is recognized through extensive industry certifications, patents, and awards — ensuring every SMPS current transformer meets the highest global standards.
Selecting the optimal current transformer for a switching power supply requires a systematic engineering approach. The following step-by-step guide outlines the key decision points:
Identify the switching frequency of your SMPS topology. For frequencies below 200 kHz, standard MnZn ferrite cores (e.g., PC40, PC95 material) provide excellent performance. For 200 kHz to 2 MHz, select NiZn ferrite or nanocrystalline materials with lower core loss at high frequencies. For GaN-based designs above 2 MHz, consider air-core or ultra-thin ferrite tape-wound cores.
Calculate the peak primary current in your switch leg, including startup and fault conditions. The CT primary is typically a single conductor (1 turn) passing through the core for high-current applications, or a few turns of heavy-gauge wire for lower currents. Ensure the core does not saturate at the maximum peak current, with a safety margin of at least 20%.
Choose a turns ratio (N) such that the secondary current (Isec = Ipri / N) produces a voltage across the burden resistor (Vburden = Isec × Rburden) within the input range of your PWM controller's current sense pin — typically 0.5V to 1.5V at peak current.
Match the CT isolation voltage to your safety standard. IEC 62368-1 Class II requires 3000 Vrms for reinforced insulation. Medical IEC 60601-1 2× MOPP requires 4000 Vrms or higher. Automotive AEC-Q200 applications may require 4000 Vrms with partial discharge testing.
Choose between through-hole (THT) for high-power designs requiring robust mechanical mounting, or SMD for compact, high-density PCB layouts. Confirm that the CT package fits your PCB footprint and that the primary conductor clearance meets your creepage and clearance requirements.
In SMPS current transformers, the core must be reset during the off-time of the switching cycle to prevent DC flux accumulation and eventual saturation. A reset diode or active reset circuit across the secondary winding is essential for duty cycles above 50%. Failure to implement proper core reset is the most common cause of CT saturation failure in production SMPS designs.
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