charge my phone from a LiPo battery

[mailint]

I would connect a 7.4V~11.1V LiPo battery pack to the miniUSB port (5V - 1.5A max) of my cellular phone to power and charge it.
I want the circuitry to be as small/light as possible since I would like to keep the whole thing in my pocket.

What solution do you suggest?

 

[matk95]

Well Firstly be very careful when conecting circuits to an expensive phone. and don't try this circuit till one of the expert people here say its ok

 

[audioguru]

You need a low-dropout voltage regulator since your battery is as low as only 7.4V.
Voltage regulators need the input capacitor and output capacitor that are shown on their datasheet.

You need a circuit to disconnect the Li-Po battery when its voltage becomes too low or it will be destroyed. It might even catch on fire.

 

[mailint]

Well Firstly be very careful when conecting circuits to an expensive phone. and don't try this circuit till one of the expert people here say its ok

I read that the LM7805 is a linear regulator and linear regulators dissipate the "voltage in excess" in heat. That would be a bad use of my LiPo battery and dangerous for my pocket. Isn't there a better solution?

 

[mailint]

You need a low-dropout voltage regulator since your battery is as low as only 7.4V.
Voltage regulators need the input capacitor and output capacitor that are shown on their datasheet.

Interesting, thanks!

I heard that if a switching regulator fails it lets the input voltage pass entirely and this would fry my phone.
What happens if a low-dropout regulator fails?

You need a circuit to disconnect the Li-Po battery when its voltage becomes too low or it will be destroyed. It might even catch on fire.

Ah, thanks for remembering this to me! What do you suggest me to use for this?

 

[audioguru]

I have used many low dropout regulators and have never had one fail.
It could go dead, it could short the input to ground then the Li-Po battery will catch on fire or it coud pass the input directly to its output which will also set the battery on fire.
An ordinary regulator could fail the same.

I have a $30.00 remote control helicopter. I got it free complete with AA alkaline batteries from Energizer battery company::
1) It automatically shuts off the charger when the Li-Po battery is fully charged.
2) It automatically disconnects the battery when it is discharged too low.
3) It automatically disconnecte the battery when the current is too high when its motor can't spin the blades.

It won't catch on fire because its designers thought of everything.

An older model made by the same company was recalled. Guess why? Because its Li-Po battery caught on fire.