[SOLVED] want to convert CV smps to CC also

[maheshjalgaonkar]

sir i am studying SMPS develop a smps with 12 v now want to convert it to 300 mA current. so i want to know what are the methods to do this operation. i tried it with BC 547 and 1 sense resister but as temp rises (resister) current decrease. help me please

 

[goldsmith]

Hello my friend
Can you give me more explanation about your clear purpose?
Best Wishes
Goldsmith

 

[maheshjalgaonkar]

at output of smps i connect tl 431 for voltage regulation. now i want to add the circuit which will control the current flow. when load is more then it has to give same current but decrease the voltage

 

[goldsmith]

Again Hi
It is very simple. but it depends on your schematic. anywhere , you have two main way : 1- hiccup method. 2- off current . and hiccup is better way.
you should get some sample from current and compare it with a voltage ( current reference ) and then the result of this comparison , should cut your PWM signal.
For better help , you should attach your schematic.
Best Regards
Goldsmith

 

[maheshjalgaonkar]

here is my schematic.

 

[goldsmith]

So as i understood , you are using a continuous fly back converter . at first step , for limiting , you can use current mode ICs , those have current limiters at the primary of the transformer . anywhere , you should use a series resistor , with your primary , and get the voltage across that and do comparing between that and a low value DC voltage , and when the voltage across the current sense resistor become higher than the current reference voltage , thus your comparator or opamp can give a positive voltage to you , that you can give this voltage to your feed back pin , thus , the IC , will think that the out put voltage is high and will try to cut the voltage . and with this fast action , the current will be constant ( at your desired current ) as well as .
Good luck
Goldsmith

 

[maheshjalgaonkar]

but i dont want to use current limiter at primary side want to used it at secondary side

 

[goldsmith]

If you limit the current of primary , naturally the current of secondary will limit.
Respectfully
Goldsmith

---------- Post added at 16:16 ---------- Previous post was at 16:15 ----------

Don't forget the relationship between the primary current and secondary current.