cell phone and i-pod charger from lithium battery

[roltex_rohit123]

I have just rebuild my laptop battery and the cells that i replaced with new ones still hold a good charge. laptop used to give me 20 min backup when i took out the cells. I want to utilise the cells in a backup charger circuit for my cell phone and I-pod. i measured the voltage in the cell charger and it was about 6 volts. i want to use 2 lithium cells in parallel. they give about 4.1-4.2 volts, when charged. how can i proceed for the circuit. I need a higher voltage 6 volts at 300mA. The cells I suppose might be holding about 0.5 amp charge each. I have plenty of these cells for use. i can charge my cell when power is not available and then recharge both cells and backup battery pack when power is available. which IC's and what components can i use?

 

[(*steve*)]

"Holding 0.5 amp charge" doesn't mean anything. Do you mean they hold 0.5 Ah? Or you can discharge them at 0.5A (and for how long?)?

Yes, you need to protect them from too high a charge, too low a charge, and excessive discharge current.

I would recommend that you find 2 batteries with similar capacity and place them in series, but charge them individually.

Current limited, fixed voltage (the voltage should drop to limit current) charging is acceptable for these batteries.

Connecting 2 in series enables you to use a simple voltage regulator to drop the voltage to 6V. You will need to ensure that the battery voltage does not drop too low or the batteries will be damaged.

There are simple chargers using an LM317. You could dedicate a single 317 to each cell.

 

[roltex_rohit123]

"Holding 0.5 amp charge" doesn't mean anything. Do you mean they hold 0.5 Ah? Or you can discharge them at 0.5A (and for how long?)?

Yes, you need to protect them from too high a charge, too low a charge, and excessive discharge current.

I would recommend that you find 2 batteries with similar capacity and place them in series, but charge them individually.

Current limited, fixed voltage (the voltage should drop to limit current) charging is acceptable for these batteries.

Connecting 2 in series enables you to use a simple voltage regulator to drop the voltage to 6V. You will need to ensure that the battery voltage does not drop too low or the batteries will be damaged.

There are simple chargers using an LM317. You could dedicate a single 317 to each cell.

I guess you didnt get what i meant.
I have lithium cells from an old laptop battery, holding good charge. the voltage in them is 4.1-4.2 volts. now i want to make a backup charger from 2 cells, to charge my cellphone. the ratings for the charger are 6 volts at 0.5 amperes/hr. now since these cells are also rechargable i would charge these cells when power is available from the mobile phone charger. this gives me an additional charging source when there is a power cut. i dont want to connect the cells in series because i dont have charger to charge 7.4 volts. lithium cells cannot be charged using LM317. it needs a specialised algorithm for charging cells or cells get damaged.

 

[(*steve*)]

No, I understand what you wrote and LiIon batteries *CAN* be charged from a current limited constant voltage source. It is not the optimum in terms of time, but it is safe.

The only caveat is that you should stop the charge when the charging current falls to 3% of the rated current. This can be done manually, or automatically.

Remember that the charger should ensure the same voltage (within 0.05V) per cell.

 

[NickS]

What voltage does your I-pod require(I thought they needed 5V)?

I would plan on spinning a PCB that has the following blocks
(1) Switching voltage regulator(step up from 4.2V to a regulated 5V)
(2) Li charging IC
(3) Misc Logic

I envision you have a charging IC smart enough to know when it is done and stop charging the batts. Hopefully it also has a logic output to indicate this state.

Know for the truth table
connected------------------------------operations
------------------------------------------------------------
Batt low voltage and
Ipod---------------------------------------do nothing

Batt low Volt and
EXT PWR------------------------------Charge batts

Batt Low Volt and
Ext PWR and
Ipod--------------------------------------Charge Ipod from EXT PWR

Batt charged and
EXT PWR and
Ipod--------------------------------------Charge Ipod from EXT PWR

Batt charged and
Ipod-------------------------------------Charge Ipod from Batt through switcher

 

[roltex_rohit123]

No, I understand what you wrote and LiIon batteries *CAN* be charged from a current limited constant voltage source. It is not the optimum in terms of time, but it is safe.

The only caveat is that you should stop the charge when the charging current falls to 3% of the rated current. This can be done manually, or automatically.

Remember that the charger should ensure the same voltage (within 0.05V) per cell.

actually i dont have to do anything besides maintaining 6 volts and 0.5 amp. my cell phone charger has these specifications. the control unit is in the cell phone only. i just have to give the 6 volts at 0.5 amp. i have also build a wind generator from a stepper motor and CPU fan. it is used in trains where it starts operating from 65Kmph. the voltage from stepper motor goes to 50 volts but i want to regulate it at 6 volts again for cell charging. i am thinking of using 7806 for this purpose. but i have no idea of how to increase the voltage from the lithium battery pack.

 

[roltex_rohit123]

What voltage does your I-pod require(I thought they needed 5V)?

I would plan on spinning a PCB that has the following blocks
(1) Switching voltage regulator(step up from 4.2V to a regulated 5V)
(2) Li charging IC
(3) Misc Logic

I envision you have a charging IC smart enough to know when it is done and stop charging the batts. Hopefully it also has a logic output to indicate this state.

Know for the truth table
connected------------------------------operations
------------------------------------------------------------
Batt low voltage and
Ipod---------------------------------------do nothing

Batt low Volt and
EXT PWR------------------------------Charge batts

Batt Low Volt and
Ext PWR and
Ipod--------------------------------------Charge Ipod from EXT PWR

Batt charged and
EXT PWR and
Ipod--------------------------------------Charge Ipod from EXT PWR

Batt charged and
Ipod-------------------------------------Charge Ipod from Batt through switcher

i donot need a lithium ion charging IC. the whole unit is there inside the cellphone. i just want to give the voltage and current. the chargers are just adjusted for supplying 5.7 volts at 800ma (my nokia 7610 charger). it does not contain any ic. i also ran a NE555 timer from the charger. and also opened it to see the circuit. so i just need to incerase the voltage to 6 volts.

 

[(*steve*)]

i donot need a lithium ion charging IC. the whole unit is there inside the cellphone

In that case you need to explain again what you want to do, because you clearly DO NOT now "want to utilise the cells in a backup charger circuit for my cell phone and I-pod." If you did, then you'd need a way of charging them.

OK, OK, UNLESS you're thinking of connecting the laptop batteries to replace the battery in your iPhone?!?! Is that *really* what you mean?

 

[roltex_rohit123]

In that case you need to explain again what you want to do, because you clearly DO NOT now "want to utilise the cells in a backup charger circuit for my cell phone and I-pod." If you did, then you'd need a way of charging them.

OK, OK, UNLESS you're thinking of connecting the laptop batteries to replace the battery in your iPhone?!?! Is that *really* what you mean?

I explain it again fully:

I have rebuild my laptop battery. it has yeilded me 6 cells (old ones holding good charge). now i want to utilise them to make a backup charger for my cell phone.

now the batteries (from the laptop) are connected 2 in parallel. I have a seperate charger to charge them.

when i go for trek or there is a power failure at home, i want to charge my cell phone from the battery pack charger(from the laptop batteries) i want to make.

now the voltage of the batteries is 4.1-4.2 volts. i want 6 volts at 500ma for charging my cell phone ( these are the specs given on my cell phone charger).

I am not replacing ipod or cellphone battery with laptop batteries.

I want to build a circuit to convert the 4.2 volts to 6 volts at 500ma.

I want help regarding this. what ic can i use how should the circuit be?

hope i could explain it better this time.
Sorry for the mess i created before.
Thanks

 

[(*steve*)]

OK, the simplest way is to connect 2 in series and use a regulator to set the voltage to 6V.

For the greatest efficiency, a switchmode regulator could be used.

Another option is to use a boost switchmode regulator to get 6V from a single battery.

Any way you go, it would be advisable to have something check for low voltage on the cells and take steps to ensure the batteries are protected.

 

[roltex_rohit123]

OK, the simplest way is to connect 2 in series and use a regulator to set the voltage to 6V.

For the greatest efficiency, a switchmode regulator could be used.

Another option is to use a boost switchmode regulator to get 6V from a single battery.

Any way you go, it would be advisable to have something check for low voltage on the cells and take steps to ensure the batteries are protected.

i guess now i could explain better.. you are right,the stepdown idea is the most advisable, but i have a charger to charge only a single cell at a time and the chargers are quite costly. a $20 charger is 50 times costly over here. so i dont want to spend more money on buying another charger. also i could remove the cells an charge them individually, but it would require removing cells everytime and charging them one by one.my charger is 1 ampere it can charge 2 parallel cells at a time. so i opted for parallel mode.
i have PCB mounted cells so i need not worry about the voltage stuff.

now comes the part of your precious guidance.

i dont know much about switch mode power supply and boost switchmode regulator. i have just studied the basics of SMPS. can you suggest me some components i could use like ic part numbers and other required components. i will try to design the circuit under your guidance..

 

[NickS]

Well I think National has a good web tool for designing one. Plus they let you roll between different designs to see the impact or tradeoffs of various changes to the circuit. When you are finished they give you a parts list with pricing and schematic.

There is another tool I have heard of made by Linear tech called switcher cad. I have not used this one but I hear good things about it too.

But perhaps I am geting ahead of myself. If you can't get a PCB made then these might not work for you. You may need an already built module that you can just wire into place.
perhaps like the one pictured below from TI. which is available HERE for $20 which is steep but if you can't make your own board its the best way to go(in my opinion)

 

[roltex_rohit123]

I dont want to buy a readymade one. i want to make one for myself. i can get a pcb etched. i just wanted to learn about SMPS designs.hop you could tell me the best among tth ones i posted or one you know better than those.

 

[NickS]

....hop you could tell me the best among tth ones i posted or one you know better than those.

I am confused. I don't see that you have posted any SMPS parts. I see you mentioned one linear reg(LM317) which is not the same thing.

What I tried conveying in the last post was that National semiconductors has a web based tool for generating a SMPS circuit. You tell it what range of input voltages and the desired output voltage/current then it spits out several options. Following which you can configure the switching frequency and layout size to your liking. It then spits out data on thermal issues, efficiency and of course the schematic/BOM. All in all it is quite easy to use and it gives you more freedom in your design.

You clearly just want us to suggest a part #, but SMPS can be complicated to build correctly so I would suggest you go through the web bench design process. It will make the recommendation you are looking for here.

go here --> http://www.national.com/analog/all_products#software

 

[roltex_rohit123]

ohh i'm sorry that post might not have actually got posted.. i'm giving you the part numbers now. please tell me which one would be the best?

TPS61220
LTC3458L
LTC3423
LTC3499.

 

[NickS]

ohh i'm sorry that post might not have actually got posted.. i'm giving you the part numbers now. please tell me which one would be the best?

TPS61220
LTC3458L
LTC3423
LTC3499.

Did you read the basic specs on these parts when you chose them?
TPS61220: Vin 0.7-5.5, Vout 1.8-5.5V, Iout = 50mA
LTC3458L: Vin 1.5-6, Vout 2-7.5V, Iout = 1.4A
LTC3423: Vin 0.5-5.5, Vout 1.5-5.5V, Iout = 1A
LTC3499: Vin 2-6, Vout 1.8-6V, Iout = 750mA

Based on what you have posted previously 2 of these are absolutely out and one is marginal. I stand by my previous post.

 

[roltex_rohit123]

Did you read the basic specs on these parts when you chose them?
TPS61220: Vin 0.7-5.5, Vout 1.8-5.5V, Iout = 50mA
LTC3458L: Vin 1.5-6, Vout 2-7.5V, Iout = 1.4A
LTC3423: Vin 0.5-5.5, Vout 1.5-5.5V, Iout = 1A
LTC3499: Vin 2-6, Vout 1.8-6V, Iout = 750mA

Based on what you have posted previously 2 of these are absolutely out and one is marginal. I stand by my previous post.

I took your advice and designed a circuit using LM3478MM IC. but since i dont know anything about SMPS circuits i wanted to know whether this circuit is a smps type.



Thanks for the help

 

[NickS]

The abbreviation you are using "SMPS" stands for Switch Mode Power Supply. That may seem ambiguous but it is in comparison to a Linear power supply.

Linear supplies can be very nice in many applications where you only need to drop a few volts and at a low current consumption, or you may require low noise power. But as you increase the drop/current draw they become more inefficient. All that aside Linear supplies only go from high voltage to lower voltage so they are useless to you because you need to move up in the voltage world.

A SMPS comes in two flavors Buck/Boost. The basic operations are similar they both switch power on and off rapidly(this creates noise and gives the name switching power supply more meaning). With a Buck converter on brings a high voltage down by only passing in to out for a short time per cycle and integrating/storing the energy in LC output components.

A Boost converter uses the inductor property that current cannot change instantly in an inductor. So each cycle the the swicth saturates an inductor and then cuts off the current causing a voltage spike(which can go much, much higher than the input voltage). Then a diode holds that higher potential on a cap while the switcher repeats the process.

So now that we have gone over that look at your schematic and you will see that LM3478 is turning M1 on and off to saturate L1 and then D1 catches the voltage spike and stores the charge in Cout. Its a beautiful thing!

One more thing. Make sure you use the output capacitor they tell you to. Especially in SMPS all caps are not equal and you can have wildly different results just by switching Cout. It comes down to a delicate balance of thermal performance, ESR, Leakage and a few other parameters and no lower ESR is not ALWAYS better(I made that mistake before)

So there is my my cliffs notes, cliff notes version.
Hope it helped and good luck to you on your design.

By the way I thought you said that you needed 6V out, why does your design say 5V out?

 

[roltex_rohit123]

The abbreviation you are using "SMPS" stands for Switch Mode Power Supply. That may seem ambiguous but it is in comparison to a Linear power supply.

Linear supplies can be very nice in many applications where you only need to drop a few volts and at a low current consumption, or you may require low noise power. But as you increase the drop/current draw they become more inefficient. All that aside Linear supplies only go from high voltage to lower voltage so they are useless to you because you need to move up in the voltage world.

A SMPS comes in two flavors Buck/Boost. The basic operations are similar they both switch power on and off rapidly(this creates noise and gives the name switching power supply more meaning). With a Buck converter on brings a high voltage down by only passing in to out for a short time per cycle and integrating/storing the energy in LC output components.

A Boost converter uses the inductor property that current cannot change instantly in an inductor. So each cycle the the swicth saturates an inductor and then cuts off the current causing a voltage spike(which can go much, much higher than the input voltage). Then a diode holds that higher potential on a cap while the switcher repeats the process.

So now that we have gone over that look at your schematic and you will see that LM3478 is turning M1 on and off to saturate L1 and then D1 catches the voltage spike and stores the charge in Cout. Its a beautiful thing!

One more thing. Make sure you use the output capacitor they tell you to. Especially in SMPS all caps are not equal and you can have wildly different results just by switching Cout. It comes down to a delicate balance of thermal performance, ESR, Leakage and a few other parameters and no lower ESR is not ALWAYS better(I made that mistake before)

So there is my my cliffs notes, cliff notes version.
Hope it helped and good luck to you on your design.

By the way I thought you said that you needed 6V out, why does your design say 5V out?

actually i just lost the cell phone nokia 7610 which had 5.7 volts at 800ma charger. now i have spice m-5151 which has charger of 5 volts 500ma. i charge it from USB also. but still i want to design the circuit. now i want to make 5 volts and 6 volts both. but my preference is 5 volts now. your national sem. software is magic. it designs the circuit itself. we can refine it.
so does it mean that the circuit is a SMPS?? otherwise i want to build a smps to save power from my cells.

 

[NickS]

Yes it is SMPS. You can probably use the same circuit to make both chargers. I am betting it is only a few resistor changes to change the output level. You may even be able to integrate a switch to go between output settings.