Trailing-edge dimmers require the input voltage of the LED driver to fall to zero each half-cycle to enable the dimmer controller to energize its own supply rails. For a buck topology, when the input voltage falls below the output voltage, the switching circuit cannot draw any power from the AC rail and is therefore unable to bleed down the switch voltage. This blog highlights how dimmer type determines both the selection of damper and bleeder circuits in LED drivers, and the switching topology needed to optimize operation. The amplitude of the load ring is modulated by the surge protection capacitor C S , making the amplitude of the oscillation dependent on dimmer type. Dimming LEDs – The difference between leading and trailing edge. You must have JavaScript enabled in your browser to utilize the functionality of this website.
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Conversely trailing edge dimming cuts out the second half of each waves’ half cycle. Trailing edge dimmers are now the more popular of the two types. They have several advantages over leading edge dimmers including smoother control, soft start and silent running when in operation. MPLAB Mindi Analog Simulator reduces circuit design time and design risk by simulating analog circuits prior to hardware prototyping. The simulation tool uses a SIMetrix/SIMPLIS simulation environment, with options to use SPICE or piecewise linear modeling, that can cover a wide set of possible simulation needs.
Dimming LEDs – The difference between leading and trailing edge
With no capacitive or inductive elements, the incandescent bulb does oscillate when presented with the voltage step of a dimmed AC sine wave. Buck converters are very popular for LED lamp drivers due to their high efficiency and low component count.
The installed base of domestic dimmers supports the almost ideal resistance exhibited by the impedance of an incandescent bulb. For a trailing-edge dimmer if insufficient current is drawn to force a zero-crossing before the next half-line cycle, the dimmer may misfire, causing shimmer or flicker.
A simple RC bleeder is used across the input line or after the bridge rectifier. Our range of LED dimmers are changeable between trailing edge and leading edge modes but are set to trailing edge mode by default. For lower power LED lamps higher bleed is required. These devices are increasingly called upon to support LED replacement lamps, which offer challenges unanticipated by the designers of the dimmer systems, such as low current draw and very fast luminous response to minor power fluctuations.
In addition we also stock a range of Varilight dimmers which are recommended for dimming LED. If this is the case then you are using standard mains dimming. Buck converters in particular have challenges when supporting trailing-edge dimmers. Dimmnig ensures that the zero-crossing detector will turn on the switch at the beginning of the next voltage half-line cycle. Compact fluorescent bulbs also known as CFL or stick shape should be taken as non-dimmable unless stated on the bulbs packaging.
Dimming LEDs – The difference between leading and trailing edge
Input filtering and topology selection for LED replacement bulbs By Andrew Smith Power Integrations The installed base of domestic dimmers supports the almost ideal dimmimg exhibited by the impedance of an incandescent bulb. Often this can be found on their websites to download. For a buck topology, when the input voltage falls below the output voltage, the switching circuit cannot draw any power from the Lightceh rail and is therefore unable to bleed down the lighetch voltage.
A Buck-boost converter continues switching provides a low impedance to the input when the input voltage has fallen below output voltage, making this topology more suitable for trailing-edge dimmers. JavaScript seems to be disabled in your browser. There are two types of dimmer switch for mains dimming in your home; leading edge and trailing edge.
Leading-Edge vs. Trailing-Edge Dimmers | LED Journal
The national grid supplies AC alternating current Electricity to our homes, offices, restaurants, pubs and clubs.
Can it be dimmed? If you wish to dim your LED Light source you will need to make sure that your LED is dimmable, this will be clearly stated on the box and will look something like this:. However as technology has advanced to become more efficient and environmentally friendly, dimming has become more complicated.
The designer must allow sufficient margin give up efficiency in the damper circuit to work with as many dimmers as practicable. Trailing edge switches work best with LEDs. The MOSFET switch is driven by a controller which continually energizes the gate, making the dimmer less susceptible to current ringing.
An LED lamp load does not exhibit incandescent-like pure resistance, and so, when presented with a step voltage the EMI filter and the bulk capacitance of the switching stage will cause an oscillation in the input current I F see figure 3. Log in to Reply. Trailing-Edge Dimmers zoe says: For this reason, buck-boost converters and tapped-buck drivers with ICs, which switch through the whole line cycle as the LYTSwitch-4 from Power Integrations, can pull down the dimmer voltage after it turns off and are therefore better able wdge support trailing-edge dimmers.
They have several advantages over leading edge dimmers including smoother control, soft start and silent running when in operation. In contrast, buck-boost, tapped-buck and flyback converters can draw current for the entire switching cycle.
There are two types of mains dimmer; leading edge and trailing edge collectively known as phase cutting dimmers. One Response to Leading-Edge vs. Buy dimmable LEDs from well-known brands such as Philips or Osram as they are likely to have been tested and compatible with a wider range of dimmers. Sign Up for Our Newsletter:
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The dimming of lights has always been very popular, as it is a quick and easy way to alter the ambience of a room.
When it comes to updating your dimmable lights to the more energy efficient LEDs, what are the things we need to be aware of? How do we know what dimmers and lights bulbs we need?
Hopefully, this quick guide will give you a good basis of understanding of the different products on the market and which ones you will need.
DIFFERENT TYPES OF DIMMING
When it comes to lighting, there are different dimming options to consider, each with different benefits and different functions. There are two types of dimming modules, leading and trailing edge, which we will look at below.
LEADING EDGE
These dimmers were originally used for dimming incandescent and halogen lamps. Due to their original use, these dimmers have a high minimum load, making them less useful for low energy lighting such as LEDs.
USING LEADING EDGE DIMMERS WITH LEDS
The high minimum load requirements of leading edge dimmers mean you can struggle to meet this minimum with LED lamps and their low power consumption. Because of this you would have to use several LED lamps on one dimmer in order to meet the minimum load requirements of a leading edge dimmer.
Due to LEDs being more energy efficient, thereby producing more light with far less electricity, you could end up with more lighting than you need by using a leading edge dimmer set up. It is best to upgrade your dimmer switch to a newer trailing edge dimmer, which allows you to control lower wattage loads such as LEDs.
TRAILING EDGE
These more modern dimmers have many benefits over the leading edge type. These improvements include smoother dimming with less buzzing and interference. Trailing edge dimmers have a much lower minimum load than the leading edge, making them far more suitable for powering LEDs.
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USING TRAILING EDGE DIMMERS WITH LEDS
The 10% rule is very important when using trailing edge dimmers with LEDs. Although a 400W trailing edge dimmer may be able to power 400W of incandescent lamps with ease when it comes to LEDs the maximum load is only 10% of this. This means, with our 400W dimmer example, the maximum load would only be 40W worth of LEDs.
The main benefit of trailing edge dimmers is that they are able to control lower wattage loads. This means you do not have to worry about meeting the high minimum load of leading edge dimmers and can instead just use the amount of LEDs required for your lighting needs.
HOW DO I DIM LEDS?
When dimming LED lamps, there are many things to consider:
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- Check the new LED lamps are dimmable before purchasing
- Ensure your current dimmers are compatible with your new LED lamps
- Well-known brands, such as Crompton, tend to have been tested with a wider range of dimmers
- Establish the minimum and maximum loads of the dimmer. This will allow you to know how many lights are needed on the circuit
- It is recommended, to ensure the best quality dimming, that old leading-edge dimmers are replaced with the trailing edge
- Ensure the maximum load of the dimmer (remembering the 10% rule for trail edge dimmers) is not exceeded by the total wattage of the LED lamps
- Make sure you have a combination of dimmable lamps and dimmer modules that work together, before purchasing
- You can guarantee compatibility by using Chip-On-Board fittings, such as the D-Lux LED Downlights with their electronically matched dimmer