LNK306 issue

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Hello,

We have been using the LNK306 in a flood/spot work lamp design for quite some time now. The unit basically remains powered, and the output is switched between either a flood lamp string, or a single spot led of the same current rating.  We have the optional diodes in place to protect the circuit from over-voltage protection while it is in the no-load position on the switch.  All seems okay, except our customer has inquired about eliminating the delay that often occurs when turning either of the loads on.  I assume this is because it is somewhere in the 800mS time between pulses of the auto shut-down mode, and it has to detect the proper sense voltage condition before putting the circuit into normal operation mode.  Is there any means as to elliminate this with the switching of the two loads and an center off position as configured?  Thanks.

Hello,

I guess the issue isn't so much the delay, as it is the fact that when switching the unit on, it flashes once, then delays 800mS, then comes on as it should.  Is the first flash an indication that there is an over-current situation from the output cap charging?  Please see attached schematic.  Thanks.

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LS1728-1B_SCH.pdf36.69 KB

It looks like the there is an over-current condition at startup and the FB skips for more than 50ms triggering an 800ms auto-restart.

In AN37, it was advised to put a soft-start capacitor across RFB. However, that was for a CV output. You can try adding it too, but I would also try adding capacitor across R1 if it does not work on R3.

You may also try to increase the BP capacitor C2.