rdr195
Sir,
we made a 14w dimmable driver using rdr195. It is working fine. But the current changes from 505ma to 695ma for an input variation 90 to 265V.Is it possible to make it universal input with a single value feedback resistor. Please suggest some thing to make the output current variation within 5%.
Thanks
Stalin.
评论
Thank you very much for the reply.I tried using two V-pin resistors and the circuit improved a little bit. Magnetic coupling of bias winding is ok.
I am going to try with closed loop feedback for tighter CC regulation.
Suppose I am going to use the same ckt with input range 90 to 130v. I need the output current should not exceed a limit say 540ma when increasing the line voltage beyond 130v. Please suggesta solution for maintaing the output current limit upto 540 ma even after increasing the voltage upto 220v.
Stalin.
The solution presented in DER296 is able to tightly control the output current regardless of the input voltage.
However, please take note the circuit in DER296 is for non-isolated application. You need to add an opto-coupler for isolated design.
It is OK to use single value of feedback resistor on your design. The table shown on RD-195 only suggests that it may be required to tune FB resistor depending on which line voltage you want to optimize current regulation.
In order to improve output current regulation, you may try first to implement two V-pin resistors (3.9Mohms upper and 1.4Mohms lower, instead of using 4Mohms (please refer to fig.8 of linkswitch-ph datasheet for example). This solution will usually improve current regulation over line.
Second, please ensure that you have tight magnetic coupling between secondary and bias windings, since the feedback is sensed through the bias windings.
Third, if you still require much tighter regulation, you may implement a closed-loop feedback that will directly sense the output current and will provide much tighter CC regulation. Please check DER-296 to give you an idea how it is implemented.