MEAN WELL EUROPE B.V.
Langs de Werf 8, 1185 XT Amstelveen
The Netherlands
Tel: +31 (0)20 758 6000
Fax: +31 (0)20 758 6001
E-mail: info@meanwell.eu
Web: www.meanwell.eu
How to select a LED driver to DIM LED
Strip?
Introduction
LED dimming has advantages in terms of energy savings, enhanced ambience, improved light source
efficacy/ lifetime…etc. The dimming performance is mainly determined by the LED source and driver.
Generally speaking, the LED source can be simply divided into two categories: LED diodes only and LED
diode with resistor. Sometimes LED source is designed as a module which could have DC-DC converter
inside. However such complex module is not in the scope of article here. In case the LED source or
module is made from LED diodes only, the common dimming method is realized by adjusting the
amplitude of current fed into LED. Therefore the LED driver should be designed to meet such demand.
Mean Well HLG families is featured with current adjusting and is controlled by external dimmer with
signal of DC1-10V* or 10V pulse width modulation (PWM) or even just a simple resistor. Another
category of LED source is LED diode with resistor which is simply so called LED strip. LED strip is widely
used because its voltage is relatively fixed thanks to the present of resistor in serious with LED diode.
Therefore user or installer can just take any constant voltage source / LED driver to power the LED strip.
Yes LED strip is relatively easy to be powered by either 12 or 24V. But sometimes it would be tricky to
perform the dimming. This article shows the consequence of LED strip dimming using driver with
amplitude current adjusting. Some of the common dimming undesired behaviors are also discussed.
The best and easiest way of dimming an LED strip is using a dimmable LED driver which has output
PWM.
Common undesired behaviors when dimming an LED
It sounds to be an easy task to dim a light source. Actually there are several considerations needed
taken into account in case a good and smoothly dimming performance is expected. Otherwise the
undesired issues shown in the Table 1 could further lower the expectation.
Behavior
Dead travel
Flickering
Drop-out
Popcorn
Flashing
Ghosting
Pop-on
Visible steps
Description
Adjusting the dimmer without a corresponding change in light level
Small changes in light intensity
Lights turning off unexpectedly
Different turn-on times for each LED module on a dimmed circuit
Light source is intermittently on when it should be off
Light source is at a low-level on state when it should be off
Dimmer setting needs to be raised above its existing setting in
order to get light output at turn-on
Visible steps in light level while adjusting the dimmer
*Reference: LED Dimming: What you need to know by Michael Poplawski; DOE SSL Program 2012
Table 1. Common undesired behaviors in dimming
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Note: New series of MW LED Driver is featured with DC0-10V.
July 15
Tel: +31 (0)20 758 6000
Fax: +31 (0)20 758 6001
E-mail: info@meanwell.eu
Web: www.meanwell.eu
MEAN WELL EUROPE B.V.
Langs de Werf 8, 1185 XT Amstelveen
The Netherlands
Especially dead travel is quite often an issue when dim a LED strip using amplitude current dimmable
LED driver. It can work fine in case the LED driver is fully loaded as shown in the Figure 1(a). However
the user feels the light level is not corresponding increase in case LED driver is only partial loaded with
LED strip.
(a)
(b)
(c)
Figure 1. Mean Well amplitude current adjusting LED driver HLG-100 connected to LED strip at different
load (length) conditions: (a) full load(length) resulting in the best dimming performance; (b) 70%
load(length) implying non-perfect dimming experience due to small dead travel; (c) 30% load(length)
implying worst dimming result due to huge dead travel.
Output PWM resolving the dead travel
It may be criticized that the dead travel issue is gone in case the end application is always using the
LED driver at full load. Furthermore it makes less sense to pay a high wattage driver while it is used
only at much lower than its rated voltage. Yes it is a very straightforward thinking but may not be
realistic. It is due to the fact that LED strip is quite often used where the length cannot be predicted
precisely. For example, the decorative lighting used in a bar or restaurant. Therefore the solutions is
used the output PWM LED driver to realize the dimming instead of changing current amplitude. The
output light level is chopped depending on the duty cycle of dimming signal. Important parameters are
the dimming resolution and output PWM frequency. Minimal dimming level should be low to 0.1% in
order to achieve 8 bit dimming resolutions to fit most of applications. Output PWM frequency should
be as high as possible to prevent the flickering issue shown in Table 1. According to the literature, it is
suggested to keep at least higher than 1.25kHz in order to minimize the visual distractions*.
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Note: Reference: Designing to Mitigate the Effects of Flicker in LED Lighting by Brad Lehman and Arnold J. Wilkins 2014
the Effects of Flicker
MEAN WELL EUROPE B.V.
Langs de Werf 8, 1185 XT Amstelveen
The Netherlands
Tel: +31 (0)20 758 6000
Fax: +31 (0)20 758 6001
E-mail: info@meanwell.eu
Web: www.meanwell.eu
Conclusion
The best way to dim LED strip is using output PWM method which resolves the dead travel in the
commonly seen dimming issues. Mean Well offer PWM series with range 40~120Watt featuring analog
3 in one dimming (digital one: DALI is on the way) and IP67 protection is the suitable driver for the LED
strip applications.
Information in this document is subject to change without notice.
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