LED Driver Dimming Simulation

[merymery]

Hello everyone, I am working on SEPIC LED driver for my university project, I designed my LED driver in the simulation program. I used resistance as a load. I run it under PWM control by giving square waves from the signal generator. I get the output values I want in my simulation. Should I change the resistance value and duty value for LED dimming? I looked at the V-i characteristic graph from my LED catalog and entered the resistance value corresponding to the voltage-current values, calculated the new D value for the SEPIC converter according to the V value on V-i graph. When I enter the duty and resistance value in my simulation program, I cannot obtain the desired current and voltage value. I could not be sure whether my technique is wrong. This is my first experience with a Led driver, did I go the wrong way? I will be glad if you help 

[sigma_xi]

Setting a fixed duty cycle is not going to work well. Usually LEDs are driven by a constant current. To do so, connect the LED in series with a current sensing resistor to your SEPIC output. Use the voltage across the resistor as feedback to automatically control the duty cycle of your driver.

[Zero999]

You need to control the current through the LED, not the voltage. Redesign your SEPIC converter so it regulates the current, rather than the voltage, by taking the feedback from a current sense resistor. Dimming can be implemented by PWMing the SEPIC converter on and off, at a much lower frequency, or by adjusting the LED current.