0
\$\begingroup\$

I'm using a Meanwell LDH-45B-350 Dali driver for currently 4 Bridgelux BXRE-30G0800-D-73 LEDs with forward voltage of 18v at 350mA. The problem is when I switch off the driver, the LEDs still glow a little bit.

I saw in the datasheet today this paragraph in really bad English:

  1. At dim off,LDH output voltage will drop to the same level as input voltage.To get luminaires complete dark, A please make luminaires are light off when they are driving by the input voltage.

The driver is fed by 24V, does this mean that with these LEDs there is no solution for this problem?

I got the B version and 24v supply because it can drive my 7 LEDs together. The A version can only drive 4.

\$\endgroup\$
11
  • 1
    \$\begingroup\$ "The problem is when I switch off the driver, the LEDs still glow a little bit." How do you switch off the driver? \$\endgroup\$ Nov 13 '19 at 8:00
  • \$\begingroup\$ Through DALI off command or brightness 0. If I lower the input voltage to 20V the LEDs go off. My power supply's aren't adjustable to 20v though. I'm not sure if there are din rail psu's for around 18-20v. \$\endgroup\$
    – Bart
    Nov 13 '19 at 8:25
  • \$\begingroup\$ It's a boost converter, so there is no good solution here. You need higher Vf of your LEDs, for example by using more of them in series or cheat with a diode but that will cost you efficiency. Can you just live with them glowing? \$\endgroup\$
    – winny
    Nov 13 '19 at 8:43
  • \$\begingroup\$ I am now using 4 LEDs in series. When complete it will be 7, will that be better? Also, j just replaced the PSU with a bench lab PSU at also 24v. This has stopped the glowing. So it is also related to the PSU. I have meanwell SDR 24vpsu's incoming. I hope these will do the trick then. \$\endgroup\$
    – Bart
    Nov 13 '19 at 8:59
  • \$\begingroup\$ Yes, seven in series should minimize or eliminate this issue for you. Try it! Oh! And at 24 V in and 18 V Vf, you are violating the specifications from the start. \$\endgroup\$
    – winny
    Nov 13 '19 at 14:52
0
\$\begingroup\$

The meaning of that statement is pretty clear, the minimum output voltage is the input voltage.

So to get less minimum brightness you can either use more LEDs in series or lower the input voltage (or both). Too few LEDs and they might be damaged.

The topology probably looks like this (from Wikipedia commons):

enter image description here

For minimum output, the switch is always open so the inductor and diode are in series to the output. It's possible the diode is actually another switch.

\$\endgroup\$
0
\$\begingroup\$

You could throw in a zener to take up the additional voltage, but it should be as low leakage as you can get. You'd be surprised how little current it takes to visibly light some LEDs.

\$\endgroup\$
0
\$\begingroup\$

This seems solved by replacing the cheap temporary chinese 24vdc power supply. I now have a meanwell sdr-120-24 powering the LDH module and all led's are completely off!

\$\endgroup\$
1
  • \$\begingroup\$ Sounds like the upstream power supply has bad low-load regulation or requires a minimum load for regulation and was rising high enough to start conducting through the boost supply's diode. Do you have a multimeter to check the cheap power supply's output voltage with no load? \$\endgroup\$ Nov 29 '19 at 18:10

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.