Meanwell Ldd-- what does PWM really do?

[oreo57]

I couldn't think of a better way to ask this..
First the article that brought the subject to light.. (I've already had the question in the back of my mind)
http://www.americanaquariumproducts.com/aquarium_lighting.html

Meanwell Ldd's dim using a PWM "signal" but the question is what about the output???
Is it "pulsed" as well or just ... what???
So do the LED's receive a chopped output at full strength simulation a reduced current or is it actually reduced based on the PWM signal??

Does that make sense??

if your Aquarium LED uses cooling fans, even if it an expensive LED, it good bet your LED fixture is either using the vastly inferior "Current Reduction" technology or is simply at the very least wasting energy as heat instead of light energy.
As well, electrical usage with "current reduction" is higher and considerably higher when lights are dimmed such as at night which adds considerably to operating costs of any light not utilizing PWM (which is most)

What is important to consider is that unlike fluorescent, incandescent, and other lighting types; very specific emitters require circuitry/drivers similar to your computer

.

So what do you think? Anyone scope the LDD output??

 

[n2585722]

PWM is pulse width modulation. The length of the positive pulse in this case determines the brightness. The cycle frequency remains the same. The duration of the positive pulse increases to brighten the LED's the low pulse duration will decrease as the positive pulse increases. The inverse will dim the LED's.

 

[oreo57]

PWM is pulse width modulation. The length of the positive pulse in this case determines the brightness. The cycle frequency remains the same. The duration of the positive pulse increases to brighten the LED's the low pulse duration will decrease as the positive pulse increases. The inverse will dim the LED's.

thanks but I understand that part..

in this case you are "pulsing" a 0 or 5V signal..

question is.. what is the driver doing w/ it??

Say the LED is running 1000mA.. is the "output" pulsed w/ the "input"?

Or does the pulse width just determine the ma out??

Say 50% duty cycle = 500mA..
or is it pulsing the 1000mA output 50% on/ 50% off.. "simulating" 500mA..

See the issue is if it just pulses the output the "quality" of the LED doesn't change..conversely if the LED sees a lower amp out it can change spectrum (usually minor)..

Only way I know of to verify this is either an oscilloscope or high speed camera..

 

[oreo57]

Err never mind ..found it........

http://www.ultimatereef.net/forums/showthread.php?p=6535081

controller:

OUTPUT:

At $7 so much for the "expensive circuitry" mentioned in that article........

 

[n2585722]

Have you checked this thread out? http://www.reefcentral.com/forums/showthread.php?t=2222702

 

[oreo57]

Have you checked this thread out? http://www.reefcentral.com/forums/showthread.php?t=2222702

I think I found the answer.. Your missing the point, to be perfectly frank.

Actually I had to go over that thread again.. Reading O=scopes aren't actually my thing..

But I can read..

During the ON time of the PWM control signal, the voltage is 13.4V and 8.8V during the OFF period.

However, it is pulsing the current like true PWM waveform, 1 amps during the ON time and 0 amps during the OFF time, like in the form below, current measured as voltage drop over 1 ohm resistor.

 

[n2585722]

OK, you are interested in color shift if it is not at full power. I don't think it is a big issue with LED's. It could go either way on the driver output whether it is pulsed or constant depending on the model and brand you choose. I would think that most would probably be pulsed current. I think that would be the less complex as far as circuitry. All you have to do is convert the input pulse to a pulse of output current. The LED may still exhibit some color shift with either type. I don't think it would be very much. I have used the LDD drivers and they seem to work with good results.