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120kHz oscillation in received DALI signal
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ocset:

--- Quote ---I would probably have gone with the original (more or less) and just stacked a couple of diode junctions in series with the base connection (And maybe reduced the bottom resistor a bit or added a second one between the diodes and the base).

--- End quote ---
Thanks, that sounds like the best shot for us. The diode junctions will help because eg 1n4148's have very little leakage, so the leakage thats coming through the zener wont be able to get through the stackjed diodes so easily.
And for that bit of leakage that does get through, the lower value base_emitter resistor will bleed it away.
Thanks.

I am hoping, in the first instance, that we can solve it by  just putting a 3k9 across the dali bus (post bridge) and also by reducing base_emitter resistor to 1k (that means we have to reduce the top resistor to 2k2  so as to reduce the potential divider effect)....these changes we can do without re-spinning the board.
If it doesnt work, then we will have to come in with the diodes on the re-spun board, , and also possibly a base_emitter capacitor of some 1nF.
ocset:
The attached (pdf schem and LTspice sim) are all the possible ways of fixing this DALI comms (Tx and RX) circuit.....we hope we only have to resort to circuit "A"
ocset:
by the way, the following circuit also works fine, but we dont want a bulky opto in there as we dont need the isolation.
(ltspice and pdf attached)
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