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I am working on DALI bus converter, using EFR32xx MCU(SiLAbs) for home usage. My question is following.. Is it possible to get DC voltage from DALI interface to supply MCU unit(3.3V) to avoid stuff battery or external DC voltage input? If i am not mistaken, DALI bus(master) supply is ISOLATED 16VDC 250mA maximum, it means, my slave device will get around 4mA in case, when all 64 devices will be connected to dali bus controller(master). Does anybody did the same, and if yes - can this connection diagram be provided?

Beforehand thanks Arsen

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Yes, you can draw some power from the DALI bus power supply. You simply need a diode and capacitor (assuming you know the polarity, or after a bridge rectifier if you cannot predict the polarity) so that you get a stabilised voltage even when there are messages on the bus. Follow this with a voltage regulator for your micro with a 3.3V output. DALI Bus powered circuit

D1-4 is the bridge rectifier for when you need polarity insensitivity, if used connect da1 and da2 to the bus. Otherwise, omit D1-4 and just connect D+ to your DALI bus +ve and D- to your DALI bus -ve. D6 is optional, protects regulator from transient overvoltages (EMC). R and C values given as starting points, you might need to experiment with values.

Whether you need an isolated DC-DC converter following the linear regulator depends on your application - whether there are user accessible metal parts or external connections galvanically connected to the micro. If it is has no other connections than the DALI bus and is in a sealed double insulated housing, you don't need an isolated DC-DC converter.

How much current you can draw depends on the power supply rating. The 250mA number is a maximum that the bus power supply is allowed to supply before it must go into current limit mode and reduce the voltage. You have to subtract the control gears and control devices requirements from the rating of the bus power supply to see what is left for your micro. Mains powered control gears are required to take no more than 2mA under all circumstances but bus powered control devices do not have such a restriction so you have to check their specification.

You should easily be able to draw 4mA for a micro, but don't neglect the linear regulator's quiescent draw which adds to that.

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  • \$\begingroup\$ Thank you very much for the quick responce! \$\endgroup\$ Apr 16, 2021 at 10:49
  • \$\begingroup\$ If I understood correct, I need to connect diode anode to "+" of bridge, then LC filter to cathode of diode(where C should be connect to "-" od bridge) and then it should go to ISOLATED DC-DC converter, correct? \$\endgroup\$ Apr 16, 2021 at 11:02
  • \$\begingroup\$ Updated answer with schematic and notes on isolation. \$\endgroup\$
    – Martin
    Apr 16, 2021 at 12:16

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