In Ethernet networking and signal transmission, the electrical performance of a LAN transformer plays a critical role in maintaining stable, interference-free communication. One of the most important parameters in magnetic components—especially Ethernet Transformers —is Open Circuit Inductance (OCL).
In this article, we explain what OCL is, why it matters, how it's measured, and how it applies directly to the performance of LINK-PP’s LAN magnetics solutions.
🔍What Is OCL?
Open Circuit Inductance, abbreviated as OCL, refers to the inductance measured on one winding of a transformer when all other windings are left open (unconnected). This value reflects how much magnetic energy the coil can store under unloaded conditions, which directly impacts signal coupling, noise suppression, and compliance with Ethernet standards such as IEEE 802.3.
In Ethernet applications, OCL is essential for ensuring:
Efficient signal transmission across differential pairs
Common-mode noise rejection
Stable impedance matching
Proper isolation between PHY and magnetics
🔧How Is OCL Measured?
OCL is typically measured using an LCR meter under specific test conditions, most commonly:
Test frequency: 100 kHz
Signal level: 100 mVrms
DC bias current: 8 mA (or as specified)
It is essential that all secondary windings are left open during the test, allowing the meter to read the magnetizing inductance of the primary winding without the influence of mutual coupling.
🎯Applications and Performance Impact
A well-designed Ethernet transformer with appropriate OCL ensures smooth signal transmission in high-speed Ethernet environments such as:
10/100/1000Base-T/2.5/5/10G networks
PoE/PoE+ Ethernet applications
Industrial and automotive Ethernet systems
In these systems, OCL is directly tied to:
Performance Factor | Impact of OCL |
|---|---|
Signal Integrity | High OCL preserves waveform fidelity |
EMI/Noise Suppression | OCL acts as a low-pass filter for common-mode noise |
Compliance with IEEE Specs | Meeting OCL thresholds is mandatory |
Magnetizing Current | Higher OCL leads to lower core excitation current |
⚖️OCL vs. Leakage Inductance
While both are inductance parameters, they represent different behaviors in transformers:
Parameter | Definition | Test Setup |
|---|---|---|
OCL | Inductance with other windings open | Secondary open |
Leakage Inductance | Inductance when other windings are shorted | Secondary shorted |
Understanding both values is critical when evaluating transformer performance across frequency ranges.
🏆 LINK-PP’s OCL-Optimized LAN Magnetics
As a trusted manufacturer and long-term OEM supplier to companies like Texas Instruments, Intel, and Cisco, LINK-PP provides a diverse portfolio of LAN transformer magnetics engineered with tightly controlled Open Circuit Inductance (OCL) specifications. These components ensure superior signal integrity, EMI suppression, and compliance with IEEE Ethernet standards.
Explore our collection:
🔗 LINK-PP LAN Transformer Magnetics
Some featured Products include:
LP84822ANL – 48-Pin 1000Base-T PoE+ Magnetics Transformer
OCL: 350μH Min @100kHz, 0.1V, 8mA DC Bias
Ideal for gigabit PoE+ Ethernet applications requiring high isolation and robust performance.LP72423ANL – Single-Port 10GBase-T Magnetic Module
OCL: 200μH Min @100kHz, 100mA
Designed for high-speed 10G networks, ensuring signal clarity under high current conditions.LPJG0926HENL – RJ45 Connector with Integrated 1000Base-T Magnetics for PoE+
Inductance OCL:
350μH Min @100kHz, 0.1V, 8mA DC Bias
120μH Min @100kHz, 0.1V, 18mA DC Bias
A compact magnetic RJ45 module combining PoE+ support and optimized inductance for stable Ethernet transmission.
All LINK-PP magnetics are 100% OCL-tested (not batch-tested), ensuring consistent quality and reliable electrical performance across every unit shipped.
✅ Conclusion
Open Circuit Inductance (OCL) is a foundational parameter in evaluating Ethernet transformer performance, directly influencing signal integrity, EMI behavior, and IEEE compliance. For designers and engineers, understanding how OCL is measured and how it affects key transmission metrics is essential when selecting LAN magnetics for high-speed and PoE-enabled networks. LINK-PP’s commitment to precision OCL testing and product consistency positions its LAN transformers as a reliable choice across diverse Ethernet applications—from industrial automation to data center infrastructure.
FAQ
What does OCL mean in Ethernet transformers?
OCL stands for open circuit inductance. You measure it with the secondary winding open. It shows how well your transformer stores energy for Ethernet signals.
Why should you care about OCL values?
You need the right OCL value to keep your Ethernet network stable. Low OCL can cause data loss. LINK-PP transformers list OCL clearly for easy selection.
How do you find the OCL value for a transformer?
Check the datasheet from LINK-PP or other trusted brands. Look for OCL at 100 kHz and 25°C. This helps you match the transformer to your network needs.
