current mode contoller for flyback converter

[Chap7979]

Good day
To start, I'm new and a novice to power electronics!! I build a flyback converter and the control circuit used a open loop controller. I'm using a input of 220V 50Hz and the output I need to achieve is 15.8V 1.3A for a 20W LED. I'm using the discontinious mode flyback converter. The problem is that I need a close loop controller to regulate my current to achieve the 1.3A and currently its looking like a UC3843 chip. I have no idea how to progress with this ic as I dont have any knowledge on this field. Could anyone please help me out!! I'm using a switching frequency of 100kHz. Any info on how to continue with this problem, how to connect the chip will be appreciated
Regards
Novice

---------- Post added at 12:44 ---------- Previous post was at 12:43 ----------

sorry my input vary between 207Vrms and 253V rms thus the duty ratio must change accordingly.

 

[goldsmith]

Hey gentleman!
Hi
Why you don't use UC3844 or UC3845? these are some good current mode ic for your purpose!
Best lucks
Goldsmith

 

[Chap7979]

Hi any useful info regarding the UC3844 or UC3845 will be helpful.Damn I thought this controller would be a piece of cake, but I'm battling to find any info that will help me to solve my problem

 

[ea.arun]

hi,

can you try this app note...this gives a detailed application information about UC3843.....also some application circuits which can be altered for your requirements...

http://www.soloelectronica.net/PDF/AppNote03.pdf

let us know if you ned something specific.......

 

[Chap7979]

Good day and thanks for the fast reply. I'm looking for the formulas to achieve the close loop control. I've realised that I'll need a optocoupler to keep the circuit isolated but still need the formula to determine my close loop control values.

 

[Chap7979]

Ok after spending the whole week trying to figure out how the controller work I realise that my first post was not good. Here is my new try. I've put a small resistor in series with the LEDs and took the voltage over the resistor to a gain opamp and then to a optocoupler. The values at the optocoupler as the current at the resistor varies is as follow. When the current is 1.3A at the LEDs the voltage at optocoupler is 3.5V(I can vary that value if needed) at 1.4A the value is 4V and at 1.2A 3V. Now I need the duty ratio to change as this voltage change. Hope this is a better description on my problem to design the controller. Any advise will really be appreciated.