Lipo Charging Schematics

[silverfox0786]

Hi guys

i am working on a project and i know the theory behind it but am a little confused how to lay out the schematics for it

I have a Lipo Battery 3.7V
I have a Lipo Charger, Cut off Voltage 4.2v

I have an appliance that runs on 5V and has a battery backed 3V save module on it (hence the battery)

I had an umm an an arr

and decided i want to use the battery power to keep the save and use the Lipo charger to charge it via USB connector rather than internal on the fly charging

what i want to do is this

how do i connect the battery to the Lipo Charger and the save module's + and - points and have them separate so no clashing occurs

i think diodes are needed but i cant figure out how to place them

any help is appreciated

silverfox07862016-03-22 13:37:07

 

[Macro]

see here for info, just nick what you want from their circuit.

 

[silverfox0786]

Cheers mike i shall have a read

funily enough i did see that site and kinds dismissed it

 

[Macro]

well, the bit with the mosfet and diode is probably what you need.

 

[silverfox0786]

Thanks Mike, i had a quick read and am not sure its what i need or then i think im just reading teh whole article wrong

The article talks about switching between Battery and Source IN

i dont want that,

my Source in will stay a steady 5V in and will be provided now and again when needed via a USB 5V cable

The part i need to figure out is how i can when i am occasional charging the battery with the source, to stop any clashing between the input charging voltage leaking itself to the actual 3V circuit

i need to isolate the source output charging going into the battery and the battery going to the load

 

[Macro]

ah, so power the unit from the battery whilst charging the battery

now I am not sure that is actually possible ... unless someone else knows differently

 

[silverfox0786]

im hoping someone will know because its defo possible

after all a mobile phone takes a 5v input to charge a 3.7V Lipo battery and it never uses the input power, always the battery

right to the point that if ever you drain your battery completely and plug in the charger, it will not switch on until there is enough juice in the battery to start the phone

 

[Macro]

I'm going to say it's not possible. (there is one way, but I don't think anyone does it ...)

a (normal) battery has two connections, + and -

to charge it you have to supply more power to it than it supplies (say 5v for a 4.8v battery stack)

there is no way that you can feed the 4.8v from the battery whilst the same two connectors have 5v from the power supply.

the only reason that a phone does not properly power up is down to the OS - they normally wait until there is enough power in the battery to 'shut it down cleanly' if the mains power was withdrawn - it is running from the power to draw the picture of the battery and shows the charge status

* it should be possible to rapidly switch between charge and use by quickly switching between the two - no idea if anything actually does that though!

 

[silverfox0786]

The only other thing i can think of then is to use a switch to isolate the circuitm but then that defeats the battery backed save feature

The other option is to use a DC to DC voltage regulator to drop the 5V to 3.3v and use the source when charging with a switch to disable the battery from going to the load

or then last option is to try modify teh actual circuit of the load to use some other method

currently its using a 6116 and a battery

maybe a Dallas DS1220
silverfox07862016-03-22 22:22:17

 

[Macro]

I used a DS1210 on the latest multigame PCB. It also sorts out the /OE to put the chip into low power mode.

 

[silverfox0786]

have you got a schematic of some sort to do this

the DS1220 seems like a nice idea

 

[Macro]

I took the circuit from here

it has to be /CS (not /OE as I said before) to put the 6116 into low power mode. (see Here for that bit)

fortunately I got the PCB right even if I typed it wrong the first time!

 

[silverfox0786]

cheers

i shall have a look into this