Current limiting IC needed for Battery Charging

[danymogh]

Hello everyone,

I'm working on a project where I need to charge a small lipo from a voltage source of 10V-110V and use it in my low-power circuit.
The source voltage may change at any time but it is either of these values: 10v DC,50v DC,110v AC.
I mainly need to charge my lipo at the 50v state which is what the source voltage will be most of the time.
now I need an IC or circuit that can supply me with no more than 5mA of current at the 50v source voltage to charge my lipo battery.
in on.

here is a simple diagram.

Code: [Select]

 __________        _______________________
|	   |      |Circuit or IC	  |    |
|10v DC or |      |to limit current at	  |    |lipo charger that can
|50v DC or |======|1-5mA for lipo charging|====|charge the lipo at 5ma
|110vAC    |      |in 50vDC state and shut|    |and provide power to
|Source____|      |down at other values___|    |the rest of the circuit

it doesn't matter if the lipo charger can limit the current internally. I can put a LDO before it to bring down the voltage.

the only important thing here is that the source can provide more than 5mA but I Should NOT use more than 5mA at that state.

[shapirus]

It sounds like your current limiter has to be a CC-CV buck-boost DC to DC converter (placed after a bridge rectifier, since you can have both AC and DC on the input). You can then attach the battery directly to it.

Anything other than that, you will have to deal with potentially big heat dissipation issues.

[danymogh]

@shapirus Thanks for the reply.

Why buck-boost? isn't just buck converter enough? my circuit voltage is 3.3v or 5v.
also can you recommend any IC for this?
the current to charge the batteries is very limited. my goal is not to charge the batteries as fast as possible but rather keep them charged over a long period of time. when the input line voltage is at 50v , the main circuit is idle and charging batteries. only at 10v and 110v the charger is disconnected and the circuit starts to perform some tasks on the mainline (some measurements).

[Konkedout]

If the input voltage can be either above or below the output voltage, then that points to a buck boost.

But...do those different input voltages all connect to the same input terminals or can they be connected differently?

I do not recommend that hobbyists work with mains AC directly.   It is too dangerous for amateurs.   Even now I would not do it casually.  But laptop AC/DC power adapters (or other "wall warts") are inexpensive and safe.

From your original post, I am confused as to what is your battery voltage.  But the AC input power adapter could give you 18V and you could buck the 50V DC down to 18V.  You could boost the 10V input to 18V.  And then regulate the 18V input to your battery voltage at that point.

I have been designing power supplies (including many AC-DC) since 1980 but I need a refresh on what is LiPo and what is your battery voltage?

[inse]

I assume it’s a single LiPo cell, so boosting would not be necessary.
If you are only drawing 5mA, a switching regulator is almost overkill as the max power dissipation is only ~0.75W at 110VAC.
How about something like the attached circuit - a 5mA limiter followed by a 4.1V shunt regulator?
The 5mA will always be drawn regardless of battery charge state.
Resistor values need to be determined…

[shapirus]

Why buck-boost?

Because this made me think so:

I mainly need to charge my lipo at the 50v state

I thought that you wanted to charge a 50V battery, and obviously that would need a buck-boost converter.

But if I was wrong and your battery's max charging voltage is below the minimum input voltage, then yes of course you'll only need a buck (step-down) converter.

So, what's your battery's final charging voltage and what's the current that you want to charge it with during the CC stage?

also can you recommend any IC for this?

I would use a ready-made converter (e.g. from Aliexpress), I think. It may be difficult to find one that supports that wide of an input voltage range, though, so I'm not sure on that part.

...unless the charging current is really small (a few milliamps), as explained in the post above: in that case you can get away with a simple linear regulator.