What is ethernet isolation tansformer

Your question was answered accurately by Andrew. Galvanic isolation is also part of the computer's internal protection. Any protection effective adjacent to the computer is already inside the computer. That includes this galvanic isolation provided by the transformer since typically destructive transients are common-mode.

Just another reas> Hi there,

They remove common-mode signals. They also help with EMI supression.

You can get large voltages between mains earth in different parts of a building (or opposite sides of a room even). Without the transformer, the sensitive input circuitry would need to deal with the common-mode signal.

If you're playing around with ethernet like this guy

you can get away without the transformers for the purpose of a table-top FPGA experiment, but not otherwise.

Doesn't the the transformer also provide a differential connection ?

Graham

Thanks Andrew and Tom.....BTW what is Galvanic isolation??

It simply means that there is no path for DC current, i.e. a metallic connection.

Hi,

"James T. White" wrote in news:43737dcb$0$10624$ snipped-for-privacy@news.hal-pc.org:

not really: it means that there is NO DIRECT PATH for any current at all!

Direct path means any kind of conductive (or semiconductive) material. By this definition, the magnetic coupling of a transformer provides galvanic insulation.

With regards to saftey standards (like ISO 60065 or UL1650 ...) the term galvanic insulation is mostly coupled to a clearly specified value of withstand voltage, that the insulation must keep without any wrong behaviour:

For a mains transformer (PRI to SEC) this is:

1500Vacrms or 2120Vdcpeak for basic insulation

3000Vacrms or 4240Fdcpeak for reinforced insulation

By this you can see, that also AC currents are not allowed to run directly from one side to the other. These tests are made with one probe connected to the (shorted) primary windings and the other probe connected to the (shorted) secondary windings.

Regards Michael