Programmable LED drivers now...

[dpcarls1598]

I have a failed driver in a 4” by 4’ fixture in a restroom. I removed the driver and it’s an OSRAM constant current driver but it says “PRE-PROGRAMMED AT THE FACTORY FOR 596 mA”.
Looking online, I can get the driver from my supplier and the software is free but I need some sort of programming module and tray or something. I haven’t looked at that cost but this seems to be a lot of work for a driver replacement. The driver is 400-1100mA or something like that and it doesn’t say what it’s programmed to as a default but this kind of makes me mad. More cost for servicing something simple.
im trying to see if my supplier has access to a programmer or knows someone who has one but this just seems rediculous.

 

[LarryFine]

Can a standard (constant-voltage) driver be used?

It may end up being cheaper to replace the light.

 

[n1ist]

A constant voltage driver won't work (it likely will kill the LEDs). If you can find a constant current driver rated at 600mA (or programmed to 600mA) with a high enough compliance voltage, it will work.

The drivers are programmable since the fixture manufacturer can stock one driver and program it depending on the fixture they are building at the time - different configurations or types of LEDs have different current specs.

/mike

 

[LarryFine]

I'm thinking of all the LED lighting I've installed that used 12vdc power supplies, and the current merely couldn't exceed the supply's capacity.

 

[winnie]

LEDs are considered 'current driven' devices, in that very small changes in voltage around the 'proper' voltage will cause huge changes in current. So to properly drive LEDs you either need a power supply designed to regulate current or you need to put some sort of current limiting element in series with the LED so that it will work reasonably with a voltage source power supply.

Many inexpensive LED strips use resistors as the current limiting element. Nicer ones have a built in simple linear regulator. You apply 12V to these devices and you are good to go, but only because of the built in current limiting element. For higher efficiency fixture manufacturers get rid of the current limiting element and instead use a current regulated power supply/driver.

To dig deeper: every electrical element has a voltage vs current curve. The common installations that we do have loads where small changes in voltage cause similarly small changes in current, so you can tolerate deviations in your supply voltage. At the same time we design for very 'stiff' voltage sources. So your 120V incandescent lamp will work fine over the range of 110-130V (dimmer at 110V, brighter and shorted lived at 130V, but it works reasonably.).

The voltage/current curve of an LED is very different. The current starts out low and climbs 'exponentially', and if you look at a graph it pretty much looks like it stays near zero and then suddenly takes off. Make your supply voltage to the LED 5% low and you are at perhaps 20% rated output, make it 5% high and you are probably at 250% rated output. (See page 8 of https://www.lumileds.com/uploads/404/DS120-pdf for an example)

And the 'correct' voltage changes with temperature. So to build an LED system using a stiff voltage supply means carefully matching the supply voltage to the LED, with very tight tolerances (no room for manufacturing variation) and then have to adjust things for temperature.

If instead you design your power supply to have a regulated _current_ output, things are easy. The supply automagically adjusts its output voltage to maintain correct current to the LEDs.

-Jon