USB Power from Mobile Phone and Case
USB Power from Mobile Phone and Case
(OP)
Hello All, I am hoping for some help and/or direction with a project. I trying to create a product that incorporates an existing mobile phone accessory. I am starting with a phone case that holds a secondary external battery supply. Is the existing battery in the phone working simultaneously with the secondary battery in the case or do you deplete the existing phone battery and then charge it with the secondary battery?
I would like the accessory to draw power from the phone's battery, not the secondary battery. The accessory should draw power from the same USB that the external battery is plugged into.
I am a Mechanical Engineer and in the past I've stayed away from electronics as much as possible. I know I will need to do a fair amount of research for this idea and I'm hoping someone on here can at least point me in the right direction. Any advice or suggestions are greatly appreciated. Thanks, Dave.
I would like the accessory to draw power from the phone's battery, not the secondary battery. The accessory should draw power from the same USB that the external battery is plugged into.
I am a Mechanical Engineer and in the past I've stayed away from electronics as much as possible. I know I will need to do a fair amount of research for this idea and I'm hoping someone on here can at least point me in the right direction. Any advice or suggestions are greatly appreciated. Thanks, Dave.





RE: USB Power from Mobile Phone and Case
Exactly what happens when the external battery drops very low in voltage probably depends on the power management or DC-DC converter IC(s) used.
RE: USB Power from Mobile Phone and Case
There was a recent news article about a TV Tuner dongle that would attach to smart phones. The news article (not the most reliable source) indicated that the dongle designers had to include a power cable because the phones' socket wouldn't supply enough power.
This is probably going to be phone specific.
I believe that there's phantom power on the headphone socket. I've seen several audio I/O accessories that contain preamps that obviously need power.
RE: USB Power from Mobile Phone and Case
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RE: USB Power from Mobile Phone and Case
In regards to the proposed accessory... I can run the accessory using the external battery. However, I am hoping to run it off the phone's battery so that I can use the phone's battery meter and not need a separate meter for the external battery.
I have read in several places that the phone usb does not provide any power so I can only assume that those tuner dongles have a battery. I've also read that the audio jack provides little power and may not be enough for the accessory. I'm still researching but it looks like I might need to run the accessory from the external battery.
I would still like to get the internal battery and the external battery to stay at the same level which would require the battery to charge the phone continuously?... I'm not sure how realistic that is, I may need to have a separate meter for the external battery and make it a stand alone accessory. I'm going to play with the settings first to see if I can make external battery to continually charge the phone battery. If that fails I'll take it apart and see if I can bypass anything. As I said before, I'm a novice when it comes to electrical. I can make sense of the settings and play with that a bit. I'm a little overwhelmed when it comes to modifying circuit boards.
Any more helpful hints?
RE: USB Power from Mobile Phone and Case
Bill
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Jimmy Carter
RE: USB Power from Mobile Phone and Case
I thought that many gadgets have DC-DC converters inside, sometimes for providing 5Vdc outputs.
I assume that it depends on the specific phone under investigation. OP hasn't yet spilled the beans about which phone he's investigating (e.g. Apple, Android, other...). Most phones have a ton of technical data available on the 'net; if not from the OEM then from all the geeks tearing them apart.
RE: USB Power from Mobile Phone and Case
The accessory will be universal in concept but will probably need to be phone specific in application as it will need to be integrated into a case. I will most like start with the trusty iPhone as it's the most popular phone.
RE: USB Power from Mobile Phone and Case
I don't know if this is helpful, but a few years ago I worked on a piggyback battery idea for a handheld game system. If you just plugged the battery/charger into the adapter, it would constantly top off the game battery, not very efficiently. But it worked so that it would completely drain the external battery, then the system would go to the internal.
The charging current on the game system was proportional to the battery state. So if you measured that current, you could get an idea for the battery state. I haven't watched a phone charge, so it may or may not be similar. And even then, you'd probably need to spec a charging current vs. battery voltage that might vary between phones, batteries, etc.
Pulsing the current in could allow you to try to keep them at similar states of discharge.
RE: USB Power from Mobile Phone and Case
http://www.maximintegrated.com/app-notes/index.mvp... has a heap of information on battery charging and USB.
RE: USB Power from Mobile Phone and Case
I know that I will eventually hire an electrical engineer to create a custom pcb for my design but I would like to be able to hack the current pcb to prove out the design first. How hard or easy (or possible) is it to hack a pcb?