Electronics > Projects, Designs, and Technical Stuff

Polarity agnostic power supply

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mikerj:

--- Quote from: NiHaoMike on July 01, 2019, 10:04:08 pm ---How does the stock charging dock solve that problem? I would expect that there's a mechanical feature (might be subtle) to only allow it to connect one way or the internal circuit is reverse polarity protected and the dock simply alternates polarity until it detects a current draw.

--- End quote ---

In the absence of any other information I was assuming this was a DIY add-on rather than a replacement for the existing dock i.e. the pads would be connected to the existing micro USB charging port on the speaker.  If so then the only chance is to do something like you suggest, and if no reverse polarity protection then it may be possible to use a very low current to determine polarity before switching on the full charging voltage.

james_s:
If it's possible to put a schottky diode across the pads on the device then you could feed a small current and check for the relatively predictable voltage drop of the diode indicating that the polarity is backwards and reverse it. Of course there is also the issue of the device getting moved around on the pad once charging has already started, which could cause a sudden polarity reversal. The shunt diode may provide adequate protection though and you could detect the sudden voltage drop and reverse the polarity.

NiHaoMike:
How about a Qi upgrade kit for smartphones? There would be a small efficiency loss but it would eliminate contacts that could become dirty.

IconicPCB:
A quad MOSFET synchronous rectifier will replace the diode bridge with losses governed by drain source on resistance.

Boogami:

--- Quote from: mikerj on July 02, 2019, 07:22:46 pm ---
--- Quote from: NiHaoMike on July 01, 2019, 10:04:08 pm ---How does the stock charging dock solve that problem? I would expect that there's a mechanical feature (might be subtle) to only allow it to connect one way or the internal circuit is reverse polarity protected and the dock simply alternates polarity until it detects a current draw.

--- End quote ---

In the absence of any other information I was assuming this was a DIY add-on rather than a replacement for the existing dock i.e. the pads would be connected to the existing micro USB charging port on the speaker.  If so then the only chance is to do something like you suggest, and if no reverse polarity protection then it may be possible to use a very low current to determine polarity before switching on the full charging voltage.

--- End quote ---

Yes this is a DIY add-on rather a replacement for an existing dock.  I've attached a diagram, I cannot take a picture with the setup at the moment but this is basically what I have right now. In block 2 I have the bridge rectifier but I would like to have the circuit in block 1, if it's not possible than ok. I am thinking of a flexible circuit that can attach like those QI charging stickers placed on the back of the phone. 

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