Supplying power to BP on a LNK306, buck topology (was: 6.3V clamp on LNK306 not doing its job)

Hello.

Device is LNK306, a 5V buck converter topology, target current would be 250mA, standard 230Vac operation. Inductor is a 2.7mH, 0.6A. Feedback is opto derived. The converter does work, but I have a few issues with the IC itself.

I am trying to supply power to the LNK306 trough the BP pin. There is supposed to be a neat 6.3V clamp in there. The circuit that supplies the power sits at 8V and has an output resistance of 330ohm. I can see no clamping effect, the voltage on BP never drops to that level. I can still however observe that the no load input current of the whole supply is about 2.2mA, which causes the LNK306 to reach about 70degC @ 260Vrms input, no load.

If I force the voltage on BP to 15V (!) the input current under the same condtions (no load, 260Vrms) drops to virtually zero and the device no longer heats up. I can not reach the required power level if I don't supply power to BP and it puzzles me that I must hit the 15V input mark to do that.

Please advise.

EDIT: added schematic

Regards,

Iggy