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| Transformer and circuit protection products | |||
Ethernet is the most widespread wired communication method in use today. In each Ethernet port, a transformer provides isolation between the drive circuitry and communication lines. The transformer is often robust enough to protect vulnerable circuitry, but may have some weakness in resisting isolation flashover and heating due to the current that is flowing in the primary coil. Bourns provides a range of transformer and circuit protection products for such applications. The PT61020 to P61024 series of Ethernet transformers is designed for long haul gigabit 10/100/1000Base-T full duplex applications. Devices support four pairs of Category 5 UTP (Unshielded Twisted Pair) cables. Compliant with IEEE802.3ab, they can satisfy single 100A 2µs/10μs intra-building impulse requirements without damage.  If the Ethernet transformer can support IEC 61000-4-5 impulse tests without failure, protection is only required on the secondary side of the transformer to protect the Ethernet IC from the energy transfer before the transformer saturates. Such protection must support the energy transfer from the transformer without letting through too much voltage and overstressing the Ethernet IC. A bridge diode network would clamp any positive or negative transients to the power supply lines. The Bourns CDSOT23-SR724 steering diode array contains two bridge networks to protect single Tx/Rx data ports. Suitable for 1000Base Ethernet applications, the device offers a low capacitance of 3pF typical. Supplied in a compact surface mount SOT23-6 package, it can withstand a maximum impulse current of 12A 8µs/20μs. Forward voltage is 2V with a 1A impulse.  TVS (Transient Voltage Suppressor) diodes are also considered in secondary protection. It is important to determine the energy transfer across the windings so that a TVS diode can be suitably selected for the application. The CDSOT23-SRV05-4 steering Diode/TVS array combination contains two bridge networks and TVS diode to protect Tx/Rx data ports. Capacitance is typically 3.5pF, and the devices are designed for maximum pulse handling of 43A, 8µs/20μs impulse. Also supplied in an SOT23-6 package, they are suitable for 10/100/1000Base-T Ethernet applications. For increased current capability, the Bourns CDNBS08-PLC03-6 (6V) or CDNBS08-PLC03-3.3 (3.3V) are good alternatives to protect a single pair up to 95A 8µs/20μs. These can be used at the primary side as well as the secondary side of the transformer. If more robust protection on the primary side is required, a Gas Discharge Tube (GDT) can be used on the primary side of the transformer directly after the RJ45 socket. The Bourns 2035-09-SM GDT can be used for metallic protection, while the 2038-xx-SM GDT can also be used to protect the transformer isolation against excessive longitudinal voltages. Bourns also supplies a series of ChipGuard® ESD protectors based on MultiLayer zinc oxide Varistor (MLV) technology, designed to protect high speed data/communications ports such as 10/100MB and 1GB Ethernet applications. Features
For further information, including a copy of Bourns Ethernet and PoE Protection Technical Article and details of how to obtain Samples, please click here |
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