Electronics > Projects, Designs, and Technical Stuff

Low power PoE

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SiliconWizard:

--- Quote from: GeorgeOfTheJungle on December 10, 2019, 05:26:18 pm ---
--- Quote from: SiliconWizard on October 12, 2019, 02:29:05 pm ---Thanks.

I thought that true PoE would be the only way, but just wanted to see if there was any possibility with non-PoE networks.

And yes, unfortunately, PoE was not really designed for very low-power devices, so in the case of low-power, there's a significant waste of energy. That sucks.

--- End quote ---

I'm interested in this too. Did you find a solution?
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Nope, I've given up on PoE so far.


--- Quote from: GeorgeOfTheJungle on December 10, 2019, 05:26:18 pm ---I'm reading this pdf (attached). See "Power Disconnection Scenarios" it's very interesting  :-+

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Thanks for this app note. It's short and informative.


--- Quote from: GeorgeOfTheJungle on December 10, 2019, 05:26:18 pm ---It seems there's a lower current threshold of about 7.5mA which at 48V would be 360mW, but the PSE waits 300..400 ms before shutting power down. If you can manage to draw power in pulses of >10mA with 20% duty cycle and a period of less than that it won't shut down, and that would be 10e-3*48*0,2 ~= 96mW. Not sure if I'm understanding that right?

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I think you are. This seems to be exactly what the "DC modulation" paragraph and figure show.


--- Quote from: GeorgeOfTheJungle on December 10, 2019, 05:26:18 pm ---Another thing I don't know (I have zero experience with PoE) is if the PSE will keep trying to power up again and again in a loop after a/the first no power disconnection event/shutdown. Do you happen to know?

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I don't know for sure, but I think it will cycle forever indeed. (See: "3   The PoE Provision Process ")

--- Quote --- Upon disconnection, voltage and power shut down. Right afterwards, the cycle is restarted (1).
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Note that the cycle itself restarts. It won't "power up" the device again after a disconnection event. It will first start again with the detection process. So one way you could implement your device so that if you want it to shut down at some point and never get powered again, you could just programmatically disconnect the required detection resistor.

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