Dimming LED's

I just got this email from TridonicAtco. Seems like an expensive way to dim LED's. Any thoughts?

In regards to your LED enquiry, the answer is yes. In order to Dim LEDs you need to use PWM(pulse width modulation) to dim them. This means varying the duty cycle on the output of the power supply. We have dimming devices for either Dali, DSI, switchdim or 1-10V applications. All LEDs are dimmable using this method. In order to use a system like Cbus you will need to use a clipsal device called a Cbus to Dali gateway then use one of our DALI PWM dimmers and suitable LED power supply, depending on the voltage requirements of the LEDs being used. Please see attached LED catalogue for of these devices. LED K210,K211 and C003. Please feel free to contact me directly on the number below if you require further info.

 

LEDs are not an "simple" load - they require a constant current drive rather than a certain voltage...

To dim them you cannot simply vary the voltage, as this just changes their current draw and they don't like that.

What you MUST do is use the driver circuits that are recommended by the supplier. In other words, if you use Vossloh LEDs then use Vossloh drivers. Same for Osram, Philips, OptiLED, etc etc... The reason being that they all have different amounts of "on-board" control equipment (on the LED circuit board).

For dimming, it's pretty trivial to use a 0-10V analogue module. If you want them separately addressable then use DALI, but you have to trade off cost and complexity (not worth it in most applications).

The best way for really complex applications is probably DMX, but that adds a level of complexity that is not viable for most projects.

Osram's range (link to Osram.com) :

http://tinyurl.com/2q6gpn

 

Here my sugestions as a manufacturer of DALI and 0-10V devices, considered the costs and convenience:
if you want to dim a large quantity LED individually, DMX512 is recommended as one bus can dim 512 units.
but if you want to mix the usage of LED and fluorescent, using DALI LED transformer or 0-10V LED transformer may be the best choice.

 

I have an application that i'm designing at the moment which is a Home Cinema room with 4 groups of RBG LED Strips which will be slowly cycling through the same colour at the same time. Although each of the 4 groups can be turned on and off individually.

I looked at TridonicAtco and using 0-10V analogue outputs or DALI units, but i think the total length per supply was very short. Given my longest length with be ~10m i've found a suitable deisgn from Digilin using DMX and various Power supplies for the different lengths. Just waiting on a quote for all the parts.

I've read through the installation instructions and guides for the Cbus DMX Gateways but is there anything else on the programming of the Cbus Groups/DMX Slots thats helpful?

 

Yup you cant go wrong with the LED Xformer.

 

The easiest way to think about the DMX Gateway is as a 12-Channel dimmer, that outputs 12 DMX slot levels rather than dimmer channels.

A DALI line is good for 300m so DALI LED drivers could have been used with a C-Bus DALI Gateway too. The DMX Gateway is easier to configure though.

 

on my DMX drivers/controllers I have an option to use one of the DMX channels for dim level or strobe, so I've simple added a group. It's a little clunky as it dims 0 to 100% up to about 200 and above that it's strobe frequency but it works fine. So I have Red Green and Blue and dim/strobe on seperate channels.