Motorcycle cell phone battery charger

[ElectronicsDevil]

Hi Friends,
I am a newbie to electronics and really this electronics is getting interesting and interesting.
I want to build a portable battery charger for my cell phone.
Can anybody suggest how should i proceed, Because bike battery is having great voltage fluctuations. If you have a schematic ready then please please give it to me.
Rating of battery charger: 5V, 0.7A
Battery of motorcycle : 12V

 

[MikeMl]

What's wrong with just using a 12V DC car charger designed for your cell phone? They will tolerate a wide range of input voltages. If you are not burning out your headlight/turn/running lights, then the voltage fluctuation on your bike is well within the input range of a standard cell phone charger.

 

[ElectronicsDevil]

Hi Mike.. Thanks for replying..
where can I get the schematics of the charger & referance for such DC to DC regulator.

 

[MikeMl]

This chip is used in about 90% of the commercial 12Vdc input cell phone chargers, as well as power supplies for MP3s, XMRadio, etc. Last time I need a special voltage, I bought a retired 5V cell phone charger at a "garage sale" for $0.50, opened it up, changed one resistor, and I was good to go.

 

[Hero999]

I'm surprised they used an SMPS, I'd just go for the LM7805, the circuit is on the datasheet which can be found using Google.

 

[MikeMl]

I'm surprised they used an SMPS, I'd just go for the LM7805, the circuit is on the datasheet which can be found using Google.

The ~1A cigar-plug 12V to 5V adapters run cool; no detectable heat. If they used a linear regulator, they would get stinking hot.

 

[AlainB]

Here is my setup for my PDA. The fan is overkill.

https://www.electro-tech-online.com/threads/pocket-pc-car-charger.99495/