Adding more leds to an existing LNK-306 design
For years, we have been producing a product that runs a string of 8-leds in two parallel strings of 4 in series at about 350mA total current. The circuit implements the LNK306 chip in a non-isolated format, as explained in AN-37. Our customer has recently Decided they want to double the amount of leds in the circuit. I figured keeping the output current the same, and doubling the output voltage would be the simplest means to achieve this.I have attached the updated schematic, as I thought it would work. I have only changed the size of the protective zener diode to 36V from 18V, and the voltage ratings of the Cfb capacitor to allow for a higher output voltage. I have retained the values of the Rsense resistor, and the bias network recommended. However, the circuit now goes into the classic .8sec reset condition. What should I be looking to change to correct this? I think I read I should be getting 1.65v at the FB pin, in reference to the Source pin. How long should this stay at 1.65v? Also, how can I possibly measure for the 49uA current limit? I tried to increase the Csense capacitor from 10uF @6.3v to a 22uF, no difference. I have also tried to increase the value of Cout from 1uF to 10uF, without any change. My sense resistor is 5.6-ohms, 1/2W. Any further info would be greatly appreciated, as always.