Circuit to Protect Mobile

[Thayne]

I have an extra Nexus 5 missing a bunch of parts (I used on my other mobile). I am making a Bluetooth amp with speakers from a broken JBL Charge and want to use the Nexus as a screen on the amp box. The charging component is fried, as is the speaker and some other parts. I can turn it on and use it with the other battery and it works fine until the battery dies. I want to hardwire the phone to power input in the amp box, but I am pretty sure that the charging unit and battery protect the phone from power fluctuations.

If that is true, is there a simple circuit I can build to protect the phone if I hardwire it to a power source? I just need the name of what this type of circuit is called. I can research it myself if no one has the time to tell me how.

Thanks!

 

[KlausST]

Hi,

the Nexus 5 comes with a power supply.
If powered from this wall wart, the Nexus 5 should operate without a battery.

Klaus

 

[Thayne]

Both the micro USB component and the component that the speaker is on are fried (the two removed parts bottom left). So I have to wire the mobile directly to the circled connection (see pic). Are you saying I can hardwire from the SMPS directly to that connection on the mobile? I understood that the charging control happened in the mobile. I thought I read that somewhere -- I could have read it wrong, or misunderstood.

Thanks

 

[KlausST]

Hi,

Are you saying I can hardwire from the SMPS directly to that connection on the mobile?

No.
If the mobile can´t be powered from the micro-USB (without charging circuit and without battery), then you should look to find a schematic.

Klaus

 

[Thayne]

I cannot find the specific schematic for my mobile. What is the type of circuit I need to build? Maybe there is a generic schematic that will work?

 

[d123]

Hi,

I can't help you with a schematic and risk a ridiculous wrong solution to a device I do not understand. I am also slow and stupid, I have finally understood the first post. Sorry.

If you think it will work, what better than a voltage regulator like an LDO or just a dirty little 5.1V zener diode as an overvoltage protection device (I'm not good with zeners so expert advice might help if that's a nasty solution here)?

Look at the charger and see the max output volts and output current it can do, and then check the micro-usb source can do the same, if so you could look for maybe an LDO that is extremely low dropout and can handle maybe double the estimated charging current of the phone. Phone chargers are just SMPS and nearly all are 5V, 200 to 600mA, from those I've seen. An SMPS IC might work. You need to know the input voltage needed to the phone and the output voltage from the charger.

All this said, I think besides quick solutions it would be a great idea to sit back and try to get info. about how the phones use charge from the battery. I hope you find a schematic, good luck. You want to power a phone from a supply but with no battery, I understand. I'd guess that phones may have multiple voltage regulators straight off the battery pins or only one main one and a few dependant lower voltage ones off the main one - I'd really tru to get a vague idea of that internal circuitry somehow. Sorry this hasn't been much help.

Silly question: have you tried to hunt down mobile repair technician websites or blogs, if they exist, or Samsung forum or modding forum things, if they exist? Without wanting you to waste time on a wild goose chase, I think some of them occasionally have threads where you can get lucky with a schematic or a helpful thread but that can be very hit and miss and even a frustrating waste of time, you never know though.