Lithium Ion charging ICs

[audioguru]

Can u recommend any such ICs?

Maxim-IC and other Western semiconductor manufacturers make battery charger ICs. I don't know which ones are available in your world.

 

[Mohamed Najiullah]

What we mean is that there is no need to have a battery between the cellphone and the regulator.

The cellphone has its own battery and charging control. If you supply it with 5 V it will charge, and it won't overcharge.

If you want to store power in a battery, and at a later time charge a cell phone from the battery, it is a lot more complicated.

That is exactly what we wish to do.. Charge the battery whenever power is available and use the battery to charge the mobile whenever necessary.. And thats y i need to know whether i have to regulate the current flowing from the LiPo battery to the mobile and if yes, how do i regulate it?

 

[Ubergeek63]

Maxim-IC and other Western semiconductor manufacturers make battery charger ICs. I don't know which ones are available in your world.

If you can afford it and do not need to worry about if you can get it tomorrow i suppose Maxim is ok... fact is they keep EVERYTHING on the books as active... even if they only run the silicon once a year!

the end result is something that is over priced and completely unavailable unless you happen to beat the rush when it comes off the assembly line!

Stick with TI or National, they are honest about when stuff is end of life or discontinued and much better bang for your buck!

If you insist on Maxim, avoid anything that is over 5 years old... for instance MAX232's current data sheet is on rev 15 from 1/06 and costs $3.30 from digikey... TI's version is $1.16, both in single piece quantity.

Maxim likes pushing new tech stuff out for a premium, like the Si-Ge RF chips, but once something is no longer a novelty it should not be gotten from Maxim! Problem is, they never bring the price down when the thing hits jelly bean status!

 

[MrAl]

Hi again,


Here is a basic design. You can decrease the first resistor to get more max current out to charge faster.
You can eliminate the parts associated with the blue LED if you dont need the LED indicator, which gives you an idea when the cell is charged.
Note that as is, the charge current is about 150ma or so, so the LM317 does not need a heat sink. If you increase the output current it will need a heat sink though.
Also, the LED is either a blue or white one, but possibly two red LEDs in series will also work ok.

 

[Hero999]

What cuts off the power when the cell is charged?

If the used fogets to disconnect it, then the battery will be trickle charged until it blows up.

 

[Mohamed Najiullah]

Hi again,


Here is a basic design. You can decrease the first resistor to get more max current out to charge faster.
You can eliminate the parts associated with the blue LED if you dont need the LED indicator, which gives you an idea when the cell is charged.
Note that as is, the charge current is about 150ma or so, so the LM317 does not need a heat sink. If you increase the output current it will need a heat sink though.
Also, the LED is either a blue or white one, but possibly two red LEDs in series will also work ok.

Thanx a ton.. Now one more question.. How do i control the current that is flowing out from the charged battery to the Mobile Phone. i.e the discharge speed? I heard that a rapid rate of discharge will also blow up the battery or make it completely useless...

And u've given 9v as the i/p supply but actually the supply will be a lot less at around 5v...

Can i use the same circuit with a different IC or do i have to change it?

And i'l also like to know the answer to Mr.Hero9999's question too...

 

[Mohamed Najiullah]

**broken link removed**

What would u say abt this IC? Or this one

LM3621 - Single Cell Lithium-Ion Battery Charger Controller [Discontinued]

Which one would be more suitable?

 

[audioguru]

The charger circuit in your cell phone needs an input of 5.0V. A Li-Po battery cell has a voltage that is too low so you need a regulated voltage stepup circuit to produce 5.0V. Maybe you can use two Li-Po cells in series then they feed an ordinary linear 5V regulator.

 

[MrAl]

Thanx a ton.. Now one more question.. How do i control the current that is flowing out from the charged battery to the Mobile Phone. i.e the discharge speed? I heard that a rapid rate of discharge will also blow up the battery or make it completely useless...

And u've given 9v as the i/p supply but actually the supply will be a lot less at around 5v...

Can i use the same circuit with a different IC or do i have to change it?

And i'l also like to know the answer to Mr.Hero9999's question too...

Hello again,

Are you saying you also want to control the charge from the battery to the phone?
The charger is made just for charging, that's about it. What you do with it after that
is up to you.

The question of what happens when an Li-ion cell is charged indefinitely comes up now
and then. The answer is a bit unclear, but the main point is that Li-ion batteries should
NEVER be charged and then left alone for ANY time length. The reason for this is because
most problems occur during the charge period. That means you CAN NOT leave the cell
alone regardless of what charger you are using, so you can simply remove the cell when
it is done charging. You can calculate the time required if you like and then take it off,
or include the blue LED and that will tell you.
What happens to the current in chargers like this when the cell gets charged is that the
current reduces lower and lower, until the output current is almost nothing at all.
Typically it goes down to 50ma, then 40ma, then 20ma, then 10ma, then 5ma, and it
will remain at some low current like that for some time. The cell does not explode or
catch fire though, as the way these circuits are connected as the cell voltage rises the
current decreases more and more, so that the final voltage can never get past the
4.200 volt level no matter how long you leave it on charge.
It's always still a good idea however to take it off charge at something like C/10, so
keep that in mind, and also NEVER leave it alone and go away.
If you have any doubts about any chargers, then dont build one and simply buy one
off the web. There are many out there offered for reasonable prices.

 

[audioguru]

Experts always say to turn off the charger when the charging current of a Lithium battery gets low. They say that trickle charging a lithium battery must never be done. look at www.batteryuniversity.com .
Your circuit must limit the charging voltage to 4.2V per cell, the battery cell does not limit the voltage and is a fire hazzard if charged to a higher voltage.

 

[DirtyLude]

An MCP73833 costs less than a dollar. If you can manage to solder the tiny package, there's not much reason to play with schematics with a bunch of passives. I made up a little board for one.

This isn't mine, it's somebody else's. LiPoly charging with MCP73833

I'd like to use some of the Maxim chips, but for some reason Digikey doesn't carry Maxim.

 

[MrAl]

Experts always say to turn off the charger when the charging current of a Lithium battery gets low. They say that trickle charging a lithium battery must never be done. look at www.batteryuniversity.com .
Your circuit must limit the charging voltage to 4.2V per cell, the battery cell does not limit the voltage and is a fire hazzard if charged to a higher voltage.

Hi there audioguru,


Yes that is definitely correct. It's not exactly relevant here though, because that charger
i posted does not "trickle charge" the cell. That's one of the things that comes up in the
discussions of chargers like this, and because it does not trickle charge the cell voltage is
always limited to less than 4.200v (assuming it is set correctly of course).
I always recommend 4.15v instead of 4.20v too to make sure people dont set it too high
accidentally with meters that dont read accurately.

It's true that a charger that trickle charges a cell will damage it at the very least, but this
charger does not trickle charge the cell. That's the difference.

BTW i have used this exact charger many times and another one that is similar for years
with no problems. As i always say too though, the user should always be present
when the cell is being charged just in case anything goes wrong. There's always the chance
that the IC chip burns out during a charge too. The only way around that is to have a
backup charge monitor, which i also installed on my charger but that requires a PIC chip
and algorithm which complicates the design quite a bit. With the PIC chip the current and
voltage can be monitored continuously and the circuit turned off if the current or voltage
goes too high, or even if the voltage is too low.

 

[Hero999]

But your circuit float charges the cell, I doubt the cell current will ever completely decay to zero so there'll always be a small current plating the electrodes in the cell.

If safely charging a lithium ion cell was as simple as limiting the current to 0.5C, then float charging at 4.15V per cell then surely lots of charges on the market would do it that way, instead of having to rely on complicates ICs which sense the current dropping and disconnecting the cell when it drops to something like 0.05C.

 

[MrAl]

Hi there Hero,


I wont argue that it is better to have the circuit disconnect completely when the end of charge is reached, but as you probably know sometimes these apps are just taken too literally and that leads to a much more complicated design. For a commercial charger, we might want to build in some sort of disconnecting mechanism but for a home charger it's a waste of time and energy, unless of course you dont mind doing this.
As i said before, we have to be around when the cell is charging anyway, so we wont be far when the cell gets what we might call "fully charged".
Also, you can't overthink this problem either...which is easy to do by ignoring one or two features of this charger and other chargers like it.
Keep in mind that originally before Li-ion chargers/cells were so popular designers used to think that you had to supply a constant current to the cell in order to charge it. That was another case of misunderstanding what the spec's really meant.

To make the point about overcharging or trickle charging more clear, let me ask you this:
If you had a cell that measured 4.000v would you mind putting it on a charger that put out 10ma? In other words, that would be a very small current relative to the usual current it would normally be charged at like 500ma or 750ma or even 1000ma. Now 10ma would be too slow of course so we wouldnt want to wait around,
but it would charge at least a little right? So would you mind charging at this level if it didnt take so long?

The point being that with this charger, if set right, can never overcharge the cell, but that's not the only point either. The user HAS to be there or else they are already taking a chance of something going wrong when they are not around. Thus, they can check now and then for the blue LED or even connect a buzzer too, or simply time the charge process and take the cell off of charge after a certain time expires. I've been doing this for years now and it works just fine for a home charger.
As i said, a commercial charger may want to build this into it but even then if the voltage level is set UNDER the top max level for the cell then it should be just fine
as the current goes way down and the voltage levels off at a comfortable 4.150v which is a safe level. That also extends the life of the cell.

 

[audioguru]

Pure metallic Lithium is very dangereous like magnesium (flares and fireworks). It burns with a very hot white flame. Water on it makes it hotter.
Li-Ion and Li-Po battery cells have no pure metal Lithium. They use ions. But the ions are plated into pure metallic Lithium if the cells are overcharged.

 

[Hero999]

Hi there Hero
To make the point about overcharging or trickle charging more clear, let me ask you this:
If you had a cell that measured 4.000v would you mind putting it on a charger that put out 10ma? In other words, that would be a very small current relative to the usual current it would normally be charged at like 500ma or 750ma or even 1000ma. Now 10ma would be too slow of course so we wouldnt want to wait around,
but it would charge at least a little right? So would you mind charging at this level if it didnt take so long?

I see you point but I'd be tempted to stick a comparator in there to cut the power off when the current falls below a certain point.

Wikipedia does say something about leaving the voltage connected indefinitely so it might be all right for some types of cell.

Charging is usually stopped when the current goes below 0.03C but it can be left indefinitely depending on desired charging time.

Lithium-ion battery - Wikipedia, the free encyclopedia

What about cell with a voltage of less than 3V? It's recommended to charge at la lower current, typically 0.1C.

If the voltage is below 2.5V the charger shouldn't even attempt to recharge it an the battery should be discarded.

The charger circuit you've posted is only suitable for use by those who know what they're doing, not the average clueless user.

I'm sure a couple of comparators could be used to reduce the charging current at 3V and disable the charger if the voltage is below 2.5V.

 

[audioguru]

The charger circuit you've posted is only suitable for use by those who know what they're doing, not the average clueless user.

Battery charger ICs are designed by many engineers who discuss EVERY catastrophe and eliminate them all. They are used in many consumer products.
Why not use one?

 

[danrogers]

ive recently joined a company in the uk who specialise in battery management systems lithium cells are EXTREMELY dangerous. They have to be monitored very accurately and charging/discharging needs to be calibrated properly for the amount and type of cells you are using. Equaliseation between the cells also needs to be carried out.

A system we produce is capable of monitoring 14 cells, (currents, voltages and temperatures) and can be used in bigger systems over CANbus. Its an incredibly complicated bit of kit and alot of engineering time has gone into delevoping it.

on that note i would advise you to use some off the shelf bm ic's for texas instruments!

 

[MrAl]

Hello again,


Yes the user who uses the LM317 type charger has to know enough not to charge at full current if the cell is below about 3v or so.

It also depends on what kind of cell the user is using, protected or unprotected.

The charger circuit you've posted is only suitable for use by those who know what they're doing, not the average clueless user.

I'm sure a couple of comparators could be used to reduce the charging current at 3V and disable the charger if the voltage is below 2.5V.

Well, at least you have graduated from "that charger doesnt work" to "Suitable for use by those who know what they are doing".

Yes comparators can easily be added, if you think you need that. I havent needed it since the first quarter of 2002.

I've worked with other people on a charger that charges at up to 3 amps, and we added everything including cutout and
under voltage detection. It took a heck of a lot more parts than the LM317 charger.

 

[Hero999]

Battery charger ICs are designed by many engineers who discuss EVERY catastrophe and eliminate them all. They are used in many consumer products.
Why not use one?

Because proprietary ICs often go obsolete.

Keeping to standard components such as the LM317 means there's a much lower risk of anything becoming hard to get hold of.