MeanWell 3-in-1 dimming
2) I need dimming to be 0% when microcontroller is powered off.


This becomes a bit non-standard immediately. If the driver outputs 0 % even at say 0.7 V, you may be able to cheat around this with a BJT pulling itself up until your MCU can take over and somehow defeat that. A NC relay comes to mind too if you can accept that.

If 0 V is required on the DIM pin when your MCU is not powered, this is an expensive and obscure solution but solid-state.







simulate this circuit &ndash; Schematic created using CircuitLab

You need negative voltage to turn off the depletion MOSFET, but the Vishay VOM1271 can be used "upside down". Again, obscure and expensive solution.