DER-289 - short circuit protection
I have tried DER-289 circuit modified for 22V, 480mA (for wide range of amount of LEDs possibility) with EF20 core and LNK406 (spreadsheet attached).
Modification of circuit: R24=56,9K, R22=39,0K for required current, C7=22uF/50V for better bias voltage filtration, C10+C11=1uF/400V to minimize AC line ripple, C8=100nF/630V for better PF with less power (10,6W).
Everything worked very well but short circuit protection works only during startup (auto-restart mode).In case of short circuit during normal operation, transformer is emitting audio noise (it's normal - core saturation) and DC bias voltage doesn't go below 6,4V. To force auto-restart mode with R17=174K, it is needed max. 5.4V (in case of short circuit AC envelope at bias winding is about 3,0V but "hard" spikes charging bias bulk capacitor C7 to more than 6.4V).
Changing minimum current feedback resistor R17 to 220K didn't help.
I also tried to supply R17 from "independent" zener circuit as in DER-263 (R7,R10,VR5) but it didn't help.Unconnection of whole constant current opto circuit (daughter board) with R17 connected to V bias didn't help.It follows that the protection does not work even with reference design feedback circuit.
BTW: I think there is a mistake in daughter board layout in Q1 position does not match with schematic sheet - inverted collector with emitter.
Thank for help.