How to design a smps based battery charger?

[--BawA--]

Sunnyskyguy, i gone through the datasheet of uc3842 , and found that the peak current in primary can be set by following relation Ipk= 1v/ Rsense . so my question is if current in the primary can be limited by Rsense(R37) , don't you think the secondary side current will also be limited then .
so again the same question arises , if the value of R37 is chosen such that the max secondary current is limited to 10Amps ,then why this R19 is needed?

 

[FvM]

Of course the primary peak current limitation translates to a maximum output current, but it depends on input voltage, output voltage and other parameters, e.g. temperature. It's not the kind of battery current limit you are asking for in post #30 and it's not easily adjustable. But may be suficient for some applications.

 

[--BawA--]

FvM , sir please see the schematics in post #33, red_alert has solved the problem of current adjustments using an OPAMP with variable gain using a pot, so do i still need a current sensing network in the output section ?

 

[red_alert]

You don't need a very accurate current to charge a battery. My oppinion is that you can rely on primary current limiting.

However, if your budget is not so tight, you could buy the cheapest Arduino board to implement any charging alghorithm you like, by only reading the output voltage and current. You could also set any alarm, generate buzzing signals, flash LEDs, perform data logging and so on.

 

[FvM]

You don't need a very accurate current to charge a battery. My oppinion is that you can rely on primary current limiting.

Maybe it's sufficient. But the relation between primary peak current and secondary average current depends on many parameters, e.g. input voltage, CCM or DCM operation, output voltage, in DCM also transformer inductance. Making the primary current limit variable is another problem, varying CS gain also changes controller loop gain, adding a variable limit for the feedback amplifier output doesn't work over a wide current range.

 

[vikasbly44]

dear...

Target voltage can be adjusted by trimmer or pot P1 ,that can be set in the range of about 12 - 16V. Adjust with the voltmeter connected to the output without battery connected. Voltmeter can also be built into the charge...