Hello,
Made PoE PD circuit as attached, but it doesn't work properly.
Could you review attached schematic and let me get the result?
Regards,
Nicky
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Hello,
Made PoE PD circuit as attached, but it doesn't work properly.
Could you review attached schematic and let me get the result?
Regards,
Nicky
Hi Thomas,
Customer has some questions as below
1. There are 2 kinds of EVM. One is buck, the other is flyback.
Could you let me know the difference between 2 EVM and which one is more stable?
And the difference between isolated design and non-isolated design.
2. There are about 500mV ripple without load. (see Attached).
Is this ripple is normal? Could you let me know normal ripple level of PoE PD without load?
3. If customer wants to use Gb ethernet, does she need to change the circuit?
If yes, how she can make it?
Regards,
Nicky
Hi Nicky,
To answer your questions:
1. A non-isolated buck design would have a shared ground plane between the RTN plane & the converter outuput (-Vout rail). An inductor is used to store energy for the power conversion.
An isolated flyback design works the same way as a buck converter, but instead of an inductor, a transformer is used to store energy. Transformers provide isolation between the RTN plane and the -Vout rail by transferring energy between 2 inductors, magnetically.
For more information about the differences between these two topologies, I recommend TI's "World of Power" Series: training.ti.com/world-power
The main difference between the two topologies is that the isolation of the ground planes prevents conducted emissions from the noisy power converter from traveling to the ethernet input where it may interfere with data signals. For design recommendations on isolated design, I recommend this app note: www.ti.com/.../slua469.pdf
Buck converters are generally used at type 1 power applications because the noise generated from the converter is smaller in magnitude.
2. I will take a measurement of the EVM and let you know.
3. To use gigabit ethernet, she will just need properly terminate the data side of the ethernet transformer and connect it to a gigabit PHY. This power level should not interfere with the designers ability to get gigabit speeds.
Thanks,
Tom