Continue to Site

Welcome to EDAboard.com

Welcome to our site! EDAboard.com is an international Electronics Discussion Forum focused on EDA software, circuits, schematics, books, theory, papers, asic, pld, 8051, DSP, Network, RF, Analog Design, PCB, Service Manuals... and a whole lot more! To participate you need to register. Registration is free. Click here to register now.

Register Log in

cellphone charger circuit

Status
Not open for further replies.
P

poxkix

Member level 5
Joined
Aug 20, 2011
Messages
87
Helped
0
Reputation
0
Reaction score
0
Trophy points
1,286
Activity points
1,948
I want to design a circuit for a cellphone charger. I have found lots of circuits in the net but I can't find a suitable output enough to charge a 3.7v cell phone battery. I tried using 7805 regulator because it is the closest to 3.7v, how do I make the 5v output lower to 3.7v? By the way the power source is a 12v battery 100A. Thanks
 


mister_rf said:
A simple charger for Lithium-ion (Li-Ion) and lithium polymer (Li-Pol) cells here:
**broken link removed**

---------- Post added at 16:36 ---------- Previous post was at 16:33 ----------

A charger project using the MCP73841 charge management controller chip:

MCP73841Li ion li polymer battery charger electronic project circuit diagram | Electronics Projects Circuits Diagrams and Schematics
Click to expand...

Waw! How do you get this stuff? I didn't find this in the net. I will try this.
By the way, I'm afraid that the transistor used is not available in my country. Is there an equivalent transistor that I can use?
 

The choice of that transistor is not critical at all, almost any small signal NPN transistor will do the trick.
 

mister_rf said:
The choice of that transistor is not critical at all, almost any small signal NPN transistor will do the trick.
Click to expand...

I have a 2222N transistor. Can that replace the current one? I'm searching for the LM317 in electronics shop I just hope they have one.
 

I can't get the trimmer connection. How is it wired?
 

The circuit is for charging a Lithium battery, not for powering a phone that already has a charging circuit inside.
 

Audioguru said:
The circuit is for charging a Lithium battery, not for powering a phone that already has a charging circuit inside.
Click to expand...

So this circuit cannot charge a phone? What exactly should I look for? I'm trying to make a 'phone charger' where its power source is 5v or 12v.:???:
 

I was pretty convinced you are trying to charge the LiPol ‘battery’ outside the mobile phone. :-D
Usual phone chargers do not require a very accurate voltage output. A large number of phones accept USB charging mode, and it’s OK to supply let’s say 5V up to 7V to the phone, (maximum 300-400mA load current ), so try using any 5V IC power supply.
 

mister_rf said:
I was pretty convinced you are trying to charge the LiPol ‘battery’ outside the mobile phone. :-D
Usual phone chargers do not require a very accurate voltage output. A large number of phones accept USB charging mode, and it’s OK to supply let’s say 5V up to 7V to the phone, (maximum 300-400mA load current ), so try using any 5V IC power supply.
Click to expand...

Really? It will not damage a phone supplied by a 5v supply? Because usually the information on a phone battery is 3.7v.

I bought a a usb charger. The one where we insert it to a computer to charge a phone. But I'll use it in a different way. The usb charger will be supplied by another source.

My source is a 12v battery, so typically I should lower this down by using 7805. So the output now is 5v. How do I acquire the 300 - 400mA load current?
 

Normally the USB charger will limit the necessary current, so you don’t need to change anything. Check in the USB adapter specification the maximum positive voltage applied to the input which will be accepted by the unit, to be sure the 12V battery it’s safe for it.
 

poxkix said:
I want to design a circuit for a cellphone charger. I have found lots of circuits in the net but I can't find a suitable output enough to charge a 3.7v cell phone battery. I tried using 7805 regulator because it is the closest to 3.7v, how do I make the 5v output lower to 3.7v? By the way the power source is a 12v battery 100A. Thanks
Click to expand...

Can you check the mobile charger (the one you plug on the wall mains), there should be a label with the rating of the voltage and current .
If we know the voltage that the mobile expects it would be easier to give you an answer.
 

alexan_e said:
Can you check the mobile charger (the one you plug on the wall mains), there should be a label with the rating of the voltage and current .
If we know the voltage that the mobile expects it would be easier to give you an answer.
Click to expand...

I checked it out. I just realized. It is really 5v. Exact output -> 5.1v .07A. Now I think it is really safe to use 5v. My problem now is how do I get that .07A:???:
 

You don't need to provide the same current, this is just the max current that the specific charger can provide, the internal circuit will get as much as it needs so you can easily use a 5v 1A

0.07A is very low are you sure it is not 0.7A?

Alex
 

alexan_e said:
You don't need to provide the same current, this is just the max current that the specific charger can provide, the internal circuit will get as much as it needs so you can easily use a 5v 1A
0.07A is very low are you sure it is not 0.7A?
Alex
Click to expand...

Hhhmmm. Okay. The 5v source will be coming from a 7805 regulator. I know its output is 5v but how do I know the ampere?
I'm sorry. It is 0.7A. I just want to clarify something. The ampere is the one determining how long to take the phone to charge? Lets say the cellphone battery is rated with 950mAH.
With a 5v 1A. Does it mean that charging will be more faster?
 

7805 can provide about 1A assuming that the power source can provide it and that you are not exceeding the consumption limits that can create too much heat which triggers the protection.
The battery charging current does control the duration of the charge but in this case you are not in control of the charge current, this is controlled from the internal phone circuit.
 

alexan_e said:
7805 can provide about 1A assuming that the power source can provide it and that you are not exceeding the consumption limits that can create too much heat which triggers the protection.
The battery charging current does control the duration of the charge but in this case you are not in control of the charge current, this is controlled from the internal phone circuit.
Click to expand...

Okay. I got that. Would it be better if I will use 4 7805 regulators? This project of mine consists of 4 DIY cellphone chargers. Or just one 7805 for all of the 4 chargers? And the main source is just 1 7v 100A golf car battery.

I just read the datasheet it has an output current of 1.5A. With this value, how long does it take to charge a 950mA battery?

I'm a bit confused about what you said. In bold letters.
 

I mean that your external power supply will just provide the 5v to the internal charger, the charging is controlled by this internal circuit so even if you connect a 5v/10A source the internal charger will still use a small percentage of this current to load the battery.

Lithium battery charges in constant current and constant voltage stages ( ), the value of the constant current is not controlled by you but from the phone manufacturer and the circuit/code he has implemented internally.

7805 has a typical voltage drop of 2v so you will need 7v input min. in order to get 5v output , if the input is lower then the output will drop.
I would suggest four regulators so that the consumption on the regulators is shared too, you will get up to 2v*1A=2W on each regulator so you will probably be OK even without any heatsink but a small heatsink would weep the regulators cooler.
 

Status
Not open for further replies.

Similar threads

Part and Inventory Search

Welcome to EDABoard.com

Sponsor

Back
Top