Another alternative design

Ideas and questions about MintyBoost kits

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shawkie
 
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Another alternative design

Post by shawkie »

I have the Solar Charger which I really like and the MintyBoost which I don't. My main issue with it is that it doesn't seem to have any kind of current limiting. It does have various tweaks which try to get various types of device to go into their charging modes. This generally means will try to pull 1.5A or more. But then there seems to be no protection for the MintyBoost or the battery. If you're using a small Li-ion battery (a 750mAh CR123A in my case) then that's probably not good. In my case I want to limit the output current to 0.5A which is the minimum allowed by the USB dedicated charging port (DCP) specification. This is because my solar panel is only 3W and I'd like it to provide most of the power with the battery just providing top-up to get to this 0.5A minimum. I've had a bit of a search and the best thing I could come up with was the Texas Instruments TPS2500. This integrates the boost converter and a current limiting USB power switch into a single IC.

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adafruit_support_bill
 
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Re: Another alternative design

Post by adafruit_support_bill »

You could limit current like many USB ports do - with a polyfuse.

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shawkie
 
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Re: Another alternative design

Post by shawkie »

I think a polyfuse is really an emergency protection device (like a traditional fuse). I believe that what will happen is the device will try to draw 1.5A and the polyfuse will "blow". That isn't what I want. I want the MintyBoost (or alternative) to continue operating but reduce the voltage until the current drops down to 0.5A. If you look at the BC1.2 specification it has graphs of allowed voltage vs current load curves for a dedicated charging port (DCP). Basically, it either has to go all the way to 1.5A without shutting down or it has to gracefully reduce the voltage to 2.0V (but it mustn't start doing this before reaching 0.5A). And it mustn't shutdown in the middle of the "operating range" (which is basically the (2.0 - 5.0)V by (0 - 1.5)A box).

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