Lamp Dimmers - Leading and Trailing Edge
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- Опубликовано: 22 мар 2019
- A demonstration of the difference between leading edge dimmers and trailing edge dimmers using an oscilloscope.
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"It is NOT just a question of shoving wires together and seeing what happens" . No that's Big Clives channel :)
Haha, I occasionally kind-of do that as well on an experimental level, but I have my *_"Fun-Jiggery-Pokery Unit"_* in play to avoid big bangs. :D
-Wayne's Electrical.
_23rd March 2019, 17.08_
@@WaynesElectrical A good belt now and again does you good "keeps you on yer toes" as my old spark master used to say!
I got that out of my system when I was about 10 years old. Temporary blindness and a mild heart attack later and I stopped underestimating electricity... and became an electronics tinkerer for life. Weird how that works.
I often wondered why the leading edge dimmers buzzed and the trailing edge not. Very interesting to see on the oscilloscope and very informative mr JW.
Clean, concise, precise. Perfect delivery. A job well done.
Thank you JW for taking the time to explain about the generation of noise interference and the stark differences between leading edge, trailing edge and the use of various mode settings on dimmer controllers. Dim the light without the noise is like the message of salvation to a lost sinner. I appreciate your dedication and am grateful.
A decent quality dimmable LED lamp driver will be able to dim equally well on either Leading or Trailing Edge dimmer, since the mains waveform has absolutely nothing to do with the way that the LED dims itself (via it's own PWM). All it needs to know is how much of the duty cycle is at zero volts, and it doesn't care if that is leading of trailing.
The main issue is that Leading Edge dimmers are OK for inductive loads but causes multiple problems with Capacitive loads, since the sharp rise time creates a back EMF from (capacitive) light fittings that causing "ringing" and misfiring for the (usually very crude) Triac control circuit.
So, it's not that (all) LED lamps don't dim nicely on Leading Edge, but more that the Leading Edge dimmers are an el-cheapo solution that works great for Resistive (incandescent) and Inductive (LV halogen transformers) loads, but not on switchmode power supplies. The very best LED driver chips use complicated PFC and timing manipulation to present an almost "resistive looking" load, and this helps cheap Leading Edge dimmers cope with the non-resistive load.
I bought a decorative Edison style led bulb and it states on the box you need to use Trailing Edge. These bulbs have Chip On Board and run off mains AC.
@zoki kostadinov - it probably won't be the LED filament (as such), but more the driver circuits that are used in the new Osram bulbs. What I mean by that is that there is nothing particular about "filament LEDs" that can make a noise - they are just a different way to package the tiny LED dies in a thin line (often of glass or ceramic) rather than onto a flat PCB substrate like used for COB packages.
A triac-based dimmer (which your touch lamp will most certainly be) produces a very sharp switch on at the beginning of each mains frequency cycle. So in USA that would mean a considerable power pulse with a frequency of 120 Hertz. That sharp rise time of voltage can cause a sudden creation of magnetic fields on the driver PCB, and anything that's physically loose (eg: an inductive coil designed to suppress electrical noise) can "rattle" and create a buzz.
This is typified by a noise that will change in intensity depending on the dimmer setting. So it might buzz the worse at half dimming, yet quieten down at higher or lower settings.
A NICE EXPLANATION, VERY HELPFUL TO understand dimmer switch working.
Thank you for your videos, its nice for a fellow electrical engineer to refresh memory, you are brilliant!
The best explanation I have seen on this subject by a country mile!
Excellent video John. I work in the LED industry in a technical capacity and dimmers are one of the most confusing areas for the general public. If in doubt start with a varilight V-Pro, in default trailing edge mode it will dim most LED loads well. Available with capacity options up to 300w and is very inexpensive and widely available.
Thank you John. That was very enlightening , no pun intended.
Excellent demonstration as per usual from mr JW.......👍
Great vid as usual. You could also use this to show learners how electronic equipment distorts our sine wave, causing harmonic currents and poor power factor. It’s clear from the oscilloscope trace that both the electronic dimmer and the LED lamp distort the sine wave: a double whammy! 😊
Great choice of video John well done man.
very good visual demonstration of the operation of the dimmers
Thanks for the demonstration on dimmer switches
I enjoyed this video, sir. Very well executed, and thank you.
thank you for explaining leading edge and trailing edge in a light bulb and the types of bulbs they are uitable for in relation to dimmer switches and normal off and on switches. Your video has given me clarity to what type of dimmer switch to buy for my led bulbs, a VARILIGHT V Pro is perfect.
Thank you for educating us!!! Great video! 😁
Way back in another life when I was a roadie on the pub and club circuit (at the bargain basement level, just beer money stuff really), I built a lighting rig that used small PAR 38 lamps, and ran them from a controller made from domestic dimmers. There were only two bulbs per channel and they were never on for more than a few minutes at a time, but looking back I'm surprised it never blew up! It was fine for a typical 15 foot wide stage, but used to make the occasional strange noise through the PA, and now I know why.
Ta muchly JW, old mystery solved! ;o)
Thank you for the oscilloscope display and your explanations of leading and trailing edge wave forms. Lutron in the US makes excellent dimmers with low end brightness of LED bulbs easily adjustable with a small dial while the lamp is on.
I just installed one of those new Lutron units today. (Which is why I'm revisiting this video!) It replaced an older, identical-looking Lutron dimmer that was made before LED and CFL light bulbs were common. It's likely from when my house was rewired sometime in the mid 90s. It worked well with the dimmable LEDs I had in the fixture, until it started intermittently flickering, however it never dimmed the LEDs as well as it could dim incandescents. The replacement has that extra adjustment on there, and that is great! Also, full brightness looks brighter to me. Overall, it's an improvement over the old one. Also, I did an "autopsy" on the old one, and found a loose connection on the input filtering capacitor. Sure, I could fix it, but I don't have any incandescent lights in my house anymore, so what would be the point?
Luving your work as per long may it continue ..... Thk you ......
Thanks for the video, nice to know what they actually do not that they just 'reduce the voltage' as your always told as an apprentice
Fantastic video John. The visual of the wave firm helps illustrate exactly what's gooding on with leading and trailing edge dimmers which is what I struggled a bit with. I'd love to know how you wired the switching though.
Excuse the typos...
Nicely explained 👍👏😀
Fantastic explanation
Finally I understand. Thank you.
If only we had school teachers that explained things like you do. We would have more quality, skilled engineers. Thank you 👍
Excellent excellent video JW! Thanks so much! Great scope BTW, those old tube types are still the best in my opinion for true viewing. I looked it up on the RS website since the PN is proudly displayed on the front of your scope and apparently, its "temporarily" out of stock lol.
Love that it is only temporarily out of stock.🤔
Great explanation from one sparky to another. Thumbs up from me John.
Great explanation John. Would it be possible for you to do a video on how you hooked up the oscilloscope and why there may be flames if you do it wrong?
It would indeed be good to know. Here is the quick why you don't do it;
Scopes are low voltage and low power test instruments and usually have a maximum input voltage of 50 volts. So that won't work with the mains levels.
The input is co-axial and the reference level is electrical earth. You would need to connect the neutral to the scope earth (which is internally connected to mains earth) and therefore make the scope case part of the mains circuit.
The potential energy that could be dissipated in the scope is beyond any safe design limits. This is covered by instrument category now. Few scopes are rated for anything but cat 1.
The correct way to do it is with differential (voltage) probes and current transformers which both cost a fortune.
I bet there is a voltage divider in the "brown wire" and as JW said the rig was being fed from an isolation tx, to get round the neutral to earth connection issue. The other option is to wire the scope with no earth in the plug. Then it really can go bang.
Keysight probably have a good video on how to test heigh energy circuits with scopes.
Excellent demo, but would you be willing to do a follow up video showing us what affect a "debuzzing coil" would have on the wave of the leading and trailing dimmers?
And another good one....thanks
V-Pro dimmers are the best dimmers I’ve ever used for LED, especially when u set them up properly.
John excellent video once again. I have a question can I connect two dimmer switches to one 6wLED light bulb?
No, but you can connect one dimmer and connect one or more additional controller to it.
www.varilight.co.uk/dimmers/v-pro-multi-point.php is one example.
Thanks. Keep going
would be fun to see current waveforms of those LED's
Would more or less be the same with Nick? As current is proportional to voltage
@@abdulseaforth6930 not so true. D letter in LED implies its nonlinearity, it generates harmonics. Typical current waveform of LED is sharp decaying spike both positive and negative according to voltage polarity
@@abdulseaforth6930 Only if the load is resistive (like a filament lamp). When you have a reactive load, current is no longer proportional to voltage anymore. Hook up a cheap power adapter with a fullwave bridge followed by a capacitor filter, then watch both voltage and current waveforms. They are not even closely similar.
Is there some power factor changes in the fancy o matic dimmer?
I haven't seen an oscilloscope.being used since the mid 70's when the computer engineer used to perform maintenance on the Computer I worked on. It used 10mb disks that weighed 20Kg (5 platers) and it had 64KB of RAM.
Reminds me of the old BBC 2 OU programs. Nice.
I think the flat part of the LED waveform is the "turn on" voltage of the LED string (about 2.5V per LED), so LED current only occurs when voltage exceeds baseline voltage.
It would be interesting to see waveforms when driving non-dimmable LEDs.
Flat part is the internal power supply voltage of the LED power supply, as the mains voltage drops below this the diode bridge in the dimmer, used for the IGBT inside, disconnects the incoming voltage and the voltage on the suppression capacitor holds up the voltage for a while. Would be interesting to see with a regular incandescent or halogen in parallel with the LED though that discharges this.
Very nice demo though, and also the scope trace brightening up as the beat between the mains frequency and the camera rolling shutter moves down the display. You can see the actual data being read out at the edges of the brightening line of the refreshed phosphor in the way it jumps into sections at around the zero crossing.
Great presentation! Would it be possible to ask for an explanation on how dimmable LEDs work - for instance why doesn’t the power supply in the LED just continue to provide the same, constant voltage / current it is set to, and then shut off when the dimmer is turned down to low?
A dimming driver is specifically designed to detect the incoming waveshape and convert that to a certain led current or PWM current.
@@rowifi Makes sense. Thanks!
Don't you think it would be a good idea if LED bulbs were marked with details of the dim switch mode with which they are designed to operate? The data sheets supplied with these bulbs, if any, provide little information about the dimmer switches with which they are compatible. The data sheets offer lack the technical information.
I have encounter LED bulbs that are designed to operate with leading edge dimmers. The clue is in their weight, they tend to be heavier as they include large inductors. In my experience, the adjustment range and stability( tendency to flash) of LED bulbs leaves a lot to be desired when compared to the operation that was available with incandescent filament bulbs.
John, I noticed you mentioned the use of an isolating transformer to decouple the common earth but what is in the probe lead? It could be just resistors to bring the 240 down to a suitable test voltage but there maybe more lurking in there....
PS I'm still waiting for the day I'm not entertained and informed by one of your videos.
subscribed
Is there a quick way to determine whether a dimmer is leading or trailing edge type without an oscilloscope?
Very odd waveform on the 5W dimmable LED but of course as mentioned not the resistive type load for crystal clear signals
Thanks!
This is brilliant. Similar style to the comedian Simon Evans
Great explanation JW a much misunderstood subject. Try explaining this to customers and they look at you blank 😂 the number of people who fit led lamps and wonder why they flicker is amazing. Another one is fitting MR12 style 12V led lamps on halogen 60VA transformers flickery antics.. Or burned out Leds.
Thanks John that was really interesting. I find dimming LED GU10 lamps to be a nightmare. Any more than between 4 - 6 per single trailing edge dimmer you seem to get a horrible buzzing sound. Is this something you've encountered? Thanks.
Yes - it all depends on what type of electronics are in the lamps, and how the dimmer actually does the dimming. Some combinations are far better than others.
Hiya John, the way
that second dimmer
started and ramped
up is rather similar to.......
.........The speed controller in that Russell Hobbs vacuum cleaner I have.
If I turned that right up and applied power, the motor doesn't just instantly scream-up, but kind-of "soft starts" up to its top speed.
Similarly, the speed selection dial is also not "direct acting." I can whip-up the dial to the top and back down again really quickly, and unlike a variac, the motor does not 'follow' where the speed selection knob goes to. It's a bit like me telling something what speed I want the motor to go to, and then it tweaks-in the speed.... in rather-much the same way as me telling someone to rapidly turn a variac up-and-down by rapid-fire shouting a variety of random voltage settings on the variac to another person in another room. :D
Sinewaves on dimmers..... Ooooh, choppy-choppy. :D
That's where a variac is *_Muuuuuuch better. :D_*
Request...... dial-up one of those LED lamps on a variac and see how it behaves with a reduced voltage and a sinewave which hasn't been massacared by electronic hocus-pocus.
Thanxx for showing,
-Wayne's Electrical.
_23rd March 2019, 17.00_
Dimmable LED lamps use switchmode power supplies inside. The input voltage is largely irrelevant, and they provide the same power and light output in a range approx. 85V to 260V. So it is pointless connecting them to a Variac… it will do nothing whatsoever to the light output.
Triacs cutting current only in zero cross passings.An inderesting device i didn't know until recently that exists is called Gate Turn Off,GTO in short that can open and close in any random ac phase.But i havent found any commercial type for less than 1KA as far.
I want flames.....oh wait, wrong channel😂
Your a Muppet. Why would you want smoke and flames in your house? Keep your dickhead comments to yourself because no one is interested in your pea sized brain. I see dumb people.
I think he is referring to photonic induction as a joke. No need to insult him
@@philrichmond7567
Calm the f down. And it's you're.
Haha. Occasionally just like me.... John also wants flaaaaaames!
In fact, a couple of vids
back, he was talking about
a dodgy lead which......
........didn't have a fuse in the plug and probably had aluminium conductors.
If I am right in saying this, there may be a possibility soon that John may very-well have that cord out in the garden and give it a *_RIIIIIIIGHT BEATING_* with a good degree of current, just so we can see what happens.
You never know, if John's in the mood...... There may be flaaaaaames. :D
Here's hoping for flaaaaames. In fact, it's been a little while since I got something up in flaaaaames, so something is due-in to cop an unfortunate caning from my variac. Let's see what pops-and-flashes I can get up to and how large the flaaaaames go. :D
-Wayne's Electrical.
_23rd March 2019, 17.18_
@@philrichmond7567 firstly this was clearly a reference to big clives channel, and secondly its you're not your. ruclips.net/video/DK95r1Q-Tlg/видео.html
I found your video of great interest, the different arrays of light bulbs & dimmer switches on the market can be very confusing. Some dimmer switches are sold as Suitable for LED bulbs. Some LED bulbs are sold as Dimmable.
My question would be: Could I use a dimmer switch suitable for LED bulbs, where the Led bulbs were standard Non dimmable? & conversely. Could I use a standard dimmer switch where LED bulbs are classed as Dimmable? Or, would both the dimmer switch and LED Bulbs have to be LED Dimmable? This is a question which I have been asked a lot.
I am currently using, a standard dimmer on a five lamp pendant, with 5 *42w halogen bulbs. I am now down to only one bulb working, as each one has individually blown over a short course of time. Am wondering if a trailing edge dimmer would solve the problem.
For the best results use dimmable LEDs and a dimmer designed for LEDs.
Dimmable LEDs and a standard dimmer may work, but there could be problems.
Non-dimmable LEDs will not work with any dimmer.
I had a leading edge dimmer burn up when I tried to change halogens to LED. Any idea why that happens?
Hi J W. Quick question. I want to buy a step down from 12v to 5v 1A only one I can find is a 12v to 5v 3A. Will the extra 2 amps burn or damage my device ? Only my device is saying it's 5v 1A
Many thanks Mick
3A is just the maximum it can supply, not a problem using items less than 3A.
@@jwflame Thank you J W much appreciated
Not to detract from the video, but I'd use an external trigger off mains before the dimmer to keep the trace still and triggering regardless of what you do with the switch.
Strange the way the voltage to the first LED was above zero even after the dimmer had turned off. Adjusting the scope so the 0V point was in line with the graticle would make this clearer. The second (filament type) LED was much closer to zero after the turn off point. This would result in the second LED dimming to a lower level. Connecting a true RMS meter (with a high enough frequency response to cope with the harmonics) would be interesting as well.
Hello, if I use led lamps on an installation with a leading edge dimmer, will they work ok if I leave that on full power and not turn it down? Or will I have to remove it?
They might work, but it's not a good idea, as a lot of dimmers are still partially dimmed even when set to maximum. The LEDs could eb damaged.
Better to just replace with a normal switch, or a dimmer that's suitable for LEDs. If dimming, the LEDs themselves must be dimmable as well.
@@jwflame Thank you
How to choose between leading and trailing edge mode on a inline dimmer switch that's capable of both?
Just use whichever works best with the LED lamps you have got.
@@jwflame yes but where is the switch? to choose between the two options? Is it a tiny mini button or..? Thanks in advance
I would have been happy with one buzzes and one doesn't but cool to know why as well!
Those extra bits of distortion in the waveform can become audible given the right bulb, and is the primary reason I never liked this style of dimmer. You used to could find dimmers that were auto-transformer based, and they didn't have these issues at all.
I doubt that leading vs trailing edge makes any real difference for EMI. Either way, you've chopping the waveform by multiplying it with a variable duty cycle square wave. Multiplying in the time domain is equivalent to convolution in the frequency domain, and the transform of the pure sine wave is just a delta function at ±line frequency.
What you're left with is the transform of the square wave shifted by the line frequency. The phase of the modulating square wave again just shows up as a shift in the phase angle in the frequency domain. The power spectrum itself is unaffected by the phase of the transform.
I understand that you cannot connect 2x dimmers (2 way) for the same circuit , what would then happen?
It just won't work - if one dimmer is turned down, the second dimmer only gets the tiny amount of power from the first one, so the light stays off.
With both dimmers turned to full, either one might be able to dim the light, but one of them would have to be at full to allow the other one to actually do anything. Even that might not work as some dimmers are not at 100% even when set to maximum, and the distorted waveform from one could easily stop the other one from working properly.
@@jwflame got it
Most modern LED bulbs with built-in electronic ballast might not be dimmed with either type of dimmer topologies.
Very interesting to see the waveform for the three modes, especially with the altered waveform when driving the LED.
Mode 3 on the v-pro dimmers is meant to be for Varilight's dimmable CFLs but there's little information as to what the actual difference is. www.varilight.co.uk/technical-section/digiflux-mode.php
I have a UK plug in dimmer that makes light bulbs whistle like cheap SMPS._
I have a quick thinking, using these dimmers for leds. And do have a theory . but correct me if I am wrong.
With two diodes and two capacitors (polarity ones, so the charge will be reversed by AC waves)
Two sets of : One diode and one capacitor in series. And then this in parallel.
______ |----------|>|-----| |------| ___________
. |----------|
These "dimmable" LED lamps NEED to see the sharply chopped up mains waveform. The IC inside the driver uses the "off period" to calculate what duty cycle of PWM to supply to the LED chips. For example, an off period of 50% might equate to PWM of 30% power to the LED, which would provide an appearance of "50% brightness". If you smooth out the waveform, the LED driver has no way of determining what "dimming level" is required.
@@johncoops6897 With that assumption the classic dimmers should work fine as they are generating spikes too on the trailing side of each wave. So there is something different in play on this.
@@johncoops6897 The idea of my design to smooth out spikes was more for leds without drivers, like strips and cobs. Ofcourse in combination with full bridge rectifier (no boom) and current restricting resistors.
@@imgertberg5344 - we are discussing MAINS POWERED dimmers. The corresponding LED lamps don't work like you seem to think. They don't use resistors for current limiting, as that is a poor solution for Extra Low Voltage and even worse for mains power. You cannot (directly) dim ANY kind of mains powered LED lamp by varying the power by using a wave chopping dimmer... it just doesn't work (if it did, then the manufacturers would do it that way).
The "spikes" that you discuss are a non-issue - a dimmable LED lamp uses them then smooths it's own output, whilst a non-dimmable lamp is non-dimmable no matter what you do to it .
Seems like the leading edge dimmer had a much deeper set of "gubbins" in the back. Expect it needs a 35mm box to get it in.
Leading Edge Vs. Trailing Edge. Their at the gate, and their Off! (Sorry) PS. Any chance to put a scope on old auto transformer dimmer Vs. even older Salt Water dimmers? Ref: database.theatrestrust.org.uk/resources/images/show/7075-salt-water-dimmer-at-the-alexandra-palace-theatre
Looks like the LED bulb didn’t have a proper star grounding system! 😆 Just kidding, of course. It does look like your AC mains has a bit of clipping, though; the peaks of the sine waves were a little... soft.
It's fairly typical :p
@@AnnaVannieuwenhuyse Flat tops are usually caused by dc power supplies drawing more current at the peak of the waveform to charge their reservoir capacitors and pulling the supply down. I once monitored the shape early in the morning at work, before many supplies had been switched on. There was a good sinewave at first which deteriorated as more and more dc power supplies were switched on as the day began.
@@stephenwebb1481 sure.
And it's fairly typical.
@@AnnaVannieuwenhuyse and will probably get worse.
@@stephenwebb1481 that's not relevant to my original comment. Nobody asked for unsolicited advice on arbitrary unasked questions.
But I like smoke and flames... 😈
Your a Muppet. Why would you want smoke and flames in your house? Keep your dickhead comments to yourself because no one is interested in your pea sized brain. I see dumb people.
@@philrichmond7567 wow Phil, that's quite harsh.
Haha. Occasionally just like me.... John also wants flaaaaaames!
In fact, a couple of vids
back, he was talking about
a dodgy lead which......
........didn't have a fuse in the plug and probably had aluminium conductors.
If I am right in saying this, there may be a possibility soon that John may very-well have that cord out in the garden and give it a *_RIIIIIIIGHT BEATING_* with a good degree of current, just so we can see what happens.
You never know, if John's in the mood...... There may be flaaaaaames. :D
Here's hoping for flaaaaames. In fact, it's been a little while since I got something up in flaaaaames, so something is due-in to cop an unfortunate caning from my variac. Let's see what pops-and-flashes I can get up to and how large the flaaaaames go. :D
-Wayne's Electrical.
_23rd March 2019, 17.24_