{"id":6603,"date":"2025-07-21T00:00:00","date_gmt":"2025-07-21T00:00:00","guid":{"rendered":"https:\/\/lp.szlogic.cn\/glossary\/turns-ratio-in-lan-transformers\/"},"modified":"2026-06-22T08:54:07","modified_gmt":"2026-06-22T08:54:07","slug":"turns-ratio-in-lan-transformers","status":"publish","type":"post","link":"https:\/\/resources.l-p.com\/pt\/glossary\/turns-ratio-in-lan-transformers","title":{"rendered":"What is the Turns Ratio in LAN Transformers?"},"content":{"rendered":"
\"What<\/figure>\n\n\n\n

\ud83e\uddf2<\/strong>Understanding the Turns Ratio in Ethernet Magnetics<\/h2>\n\n\n\n

The turns ratio<\/strong> in LAN transformers\u2014also known as Ethernet magnetics<\/a>\u2014is a critical design parameter that defines the relationship between the number of windings (turns) on the primary side<\/strong> (PHY side) and the secondary side<\/strong> (cable side) of the transformer. It is typically represented as a ratio such as 1:1<\/strong> or 2.5:1<\/strong>, and it directly affects signal integrity, impedance matching, and Power over Ethernet (PoE) compatibility in Ethernet applications.<\/p>\n\n\n\n

\ud83e\uddf2<\/strong>Why Does the Turns Ratio Matter in LAN Transformers?<\/h2>\n\n\n\n

1. Impedance Matching<\/strong><\/h3>\n\n\n\n

The primary purpose of the transformer in an Ethernet circuit is to provide impedance matching<\/strong> between the PHY (Physical Layer IC) and the twisted-pair cabling (usually 100 \u03a9 differential impedance). A 1:1 turns ratio typically maintains this impedance balance, ensuring minimal signal reflection and maximum power transfer.<\/p>\n\n\n\n

2. Voltage and Current Conversion<\/strong><\/h3>\n\n\n\n

A non-1:1 turns ratio allows for adjustment of voltage and current levels. For example, a 2.5:1 turns ratio<\/strong> steps down the voltage by a factor of 2.5 while increasing the current proportionally, which is beneficial in PoE<\/strong><\/a> (Power over Ethernet)<\/strong> applications where different voltage levels must be supported across isolation barriers.<\/p>\n\n\n\n

3. Signal Isolation and Protection<\/strong><\/h3>\n\n\n\n

All Ethernet transformers<\/a>, regardless of their turns ratio, provide galvanic isolation<\/strong> (commonly 1500 Vrms) between the PHY and the external Ethernet cable. This helps protect sensitive ICs from voltage surges, ground loops, and EMI<\/a>.<\/p>\n\n\n\n

\ud83e\uddf2<\/strong>Common Turns Ratio Configurations<\/h2>\n\n\n\n
\n\n<\/colgroup>

Application Type<\/p><\/th>

Typical Turns Ratio<\/p><\/th>

Notes<\/p><\/th><\/tr>

10\/100BASE-T Ethernet<\/p><\/td>

1:1<\/p><\/td>

Standard for legacy Ethernet<\/p><\/td><\/tr>

1000BASE-T (Gigabit)<\/p><\/td>

1:1 or Center-tap<\/p><\/td>

Optimized for full-duplex signaling<\/p><\/td><\/tr>

PoE \/ PoE+ (802.3af\/at)<\/p><\/td>

2.5:1 or higher<\/p><\/td>

Supports higher voltage on cable side<\/p><\/td><\/tr>

Multi-gig Ethernet (2.5G\/5G\/10G)<\/p><\/td>

Depends on PHY<\/p><\/td>

Requires careful matching & shielding<\/p><\/td><\/tr><\/tbody>\n<\/table>\n<\/figure>\n\n\n\n

\n

\ud83d\udccc Example: LINK-PP\u2019s <\/span>LP5019NL<\/a> 1G LAN transformer uses a 1CT:1 turns ratio for compatibility with IEEE 802.3u and 802.3ab standards.<\/span><\/p>\n<\/blockquote>\n\n\n\n

\"Turns<\/figure>\n\n\n\n

\ud83e\uddf2<\/strong>How to Select the Correct Turns Ratio?<\/h2>\n\n\n\n

Choosing the right turns ratio depends on multiple system-level factors:<\/p>\n\n\n\n