CC & CV for battery charger..

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hi,

 

I need to design a battery charger for my apllication 12V,10A .. Actually ,the charger should provide constant current ifthe battery voltage is below some level.. Otherwise it should provide CV to the battery. i read some papers in PI application notes,there it is specified CC & CV using two opamp output tied together using diode to generate a current signal..

 

1) Either of CC & CV should be in the loop,how its possible using opamp .. how one loop gets active and other one lost. 

2) In application notes,its driving optocoupler, but i need error voltage at the output rather than current,how to acheive it..

 

Please tell me the operation.. i am struggling lot in that two loop feedback...

Which part or part family will you select for your application?

I didn't pick any device for my application.I am in bit confusion,the feeedback loop section.. once it cleared, i will pick suitable part for my application.

 

So please clarify that, how current loop and voltage loop gets tied at output and how either of loop gets active and other one saturated...?

Please see the attached document explains the CC/CV operation. If you refer to PI app note which has difference topology and can not be explained by this document,  you can forward me the file or your document #.

Ya. The document you have attached is the one which i refered earlier.... In fig 5 (page no 6), the two opamp outputs are tied together and given into optocoupler..  you might know about battery charger, it will have CC and CV mode. for the battery level below some point,it will be operate in CC and otherwise CV. either of two loop will be in active at a time. 

 Other one will be saturated.. but how the operation . i dont need any equation for that. theoritical concept is enough.. i want to design a battery charger. i should know about the two loop OR-ing function.

 pls explain it and also let me know suitable part for 12V,10A battery charger. 

Refer to the DN-14 fig 5, if the load current is not high enough, which means the voltage drop on R6(current sensing resistor) is not high enough to active the U4A, in other words U4A pin 3 voltage is not higher than pin 2 voltage, D7 is not conduct, it is not constant current mode but constant voltage mode. At this mode U4B conduct and regulat the constant voltage.

Once current increase to certain level, votlage drop on R6 is higher than set pin 2 votlage, U4A conduct and opto current is flowing through D7 and U4A. Vo voltage can not hold anymore until it drops too low (~2V) to source sufficient optocoupler current.

So to be simple, the two loop switching point is set by load current value, R6 and U4A pin 2 voltage.

Page 1-5 of DN-14 starts with a circuit using similar control scheme. If you read through it and understand the first case, fig 1,  it helps you to understand fig 5.

This external control loop is independent of what control part you are using. You can use it in any flyback circuits. TOP switch can be an candidate for your 120W application.