0
\$\begingroup\$

I work on a DALI lighting system for home usage and I design all DALI devices from scratch. In this system, also a sensor module will be implemented. Since it will draw only a negligible current (app. 4 mA), I thought it would be convenient to use DALI interface itself to power this device. Commercial products usually offer this feature, but I couldn't find any details on how exactly does it work.

Just to clarify, DALI logic levels are 9.5 - 22.5 V for HIGH level and -4.5 - 4.5 V for LOW level.

So what I need is some basic idea or schematic of circuit I can use to turn DALI interface into some sort of power supply.

\$\endgroup\$
2
\$\begingroup\$

You need diodes to charge up a capacitor from the DALI line when the voltage is high, so it will stay charged when the voltage goes low for short periods. It should be designed to work continuously at the lowest high voltage of 9.5V, but bear in mind that as the traffic increases, the average line voltage tends towards half of that. It won't quite reach half because during the stop condition and minimum interpacket spacing periods the line is at high level.

Also make sure your transmit transistor is on the DALI line side of the diode so that you are not shorting out your own power supply line directly when you transmit but are using the charged capacitor. Making the capacitor too big can be a problem because it will draw a surge current when the device is attached, one solution is to restrict the charging rate.

|improve this answer|||||
\$\endgroup\$
  • \$\begingroup\$ I'm trying to understand your advice. It makes sense, although I think I don't understand the circuit itself completely. Could you explain to me, how does it work? What is the purpose of Zener diode in the circuit? And where would you place the capacitor? Here is the schematic I'm using: mouser.com/images/microsites/lighting-addresable-fig-05.png \$\endgroup\$ – Rainy Mar 18 '15 at 10:27
  • \$\begingroup\$ That Microchip app note doesn't describe the circuit operation but a similar one from ST does, including a note about the zener. In your schematic, take a diode from the top of D4 pointing towards a capacitor, that junction is your positive of your supply derived from the bus, with the negative being the low side of the bridge. \$\endgroup\$ – Martin Mar 18 '15 at 12:50
  • \$\begingroup\$ Please do not forget that a compliant DALI device needs to tolerate application of mains to the DALI terminals. The test is long enough for the application of mains to be effectively / equivalent to forever, and the device must not be damaged. Making a device do this is not trivial. The schematic you reference will not be suitable. \$\endgroup\$ – quickly_now May 11 '16 at 7:41
  • \$\begingroup\$ @quickly_now Mains protection on the DALI terminals has always been optional. It is mentioned in IEC62386-101:2009 (Ed 1) as "optional over-voltage protection of the control interface" and in 101:2014 (Ed 2) as "over-voltage protection is optional but recommended for the highest rated voltage of the system". \$\endgroup\$ – Martin May 11 '16 at 8:08
0
\$\begingroup\$

DALI is ~16 V polarity-free at all times, and signalling is done by shorting the lines together to signal "LOW", for very brief intervals of time (very brief indeed since it uses Manchester encoding... however because of the Manchester encoding, during signalling it is on/off exactly half the time, but signal frames are also brief). Use a diode bridge, and there you go. 16VDC. Just do NOT place a cap between the DALI lines in front of the diode bridge, because you will screw up the signalling on the entire bus by storing energy that prevents the voltage from being pulled "LOW" when the lines are shorted (the IEC standard for the DALI PSU has timing requirements for how quickly the signal must be capable of changing, and prohibits capacitance directly between the lines). Place one after the diode bridge to clean the signal up, however. Maybe a ferrite or inductor too, if you'd like, for a low-pass L-filter. (I'd actually use a voltage regulator of some sort because there's a decent-sized range of valid DALI bus voltages)

|improve this answer|||||
\$\endgroup\$
  • \$\begingroup\$ Not quite "polarity-free at all times". The original EN60929 spec and the IEC62386-101 Ed 1 spec both have "optional polarity insensitive control interface", and it became very common but not universal or mandatory. IEC62386-101 Ed 2 makes polarity insensitivity mandatory, and it has always been required to mark the polarity of power supplies or polarity sensitive inputs. \$\endgroup\$ – Martin Oct 29 '15 at 13:50

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.