Dimmer to end all dimmers - Page 1
Forum section: electronics / projects

author: djacobow
author_rank: Super Contributor
timestamp: January 08, 2014, 11:19:09 pm
content: I've recently completed a small project (well, mostly) to create a simple incandescent lamp dimmer that follows a short program and dims the light from a starting set point to an ending set point over a longish period.The application is putting the kids to bed with a light that almost imperceptibly slowly turns off.Did it with a triac, opto-triac driver H11AA1 opto ZC detector, and an Arduino, and a board I sent to Seed studio.Happy with it, but incandescents are on their way out and I am really keen learning more on power control, Internet of Things, etc, and would like to do this better.The next stage in "better" seems to be reverse phase control. The topology I see most is an IGBT or FET shorting the DC side of a bridge rectifier, where the AC side is connected in series with the load to the AC power source.The next next better is "true sine wave dimming, which is basically just PWM. I'm wondering, though, can this same topology work for PWM dimmingl? I would think something like 40kHz (above the range of human hearing). This should not be too much less efficient than reverse phase dimming (FET is switching more, but still mostly on or off, assuming its fast enough) and filtering back to a clean sine wave should be easy since 40kHz is so many octaves away from 60 Hz. And PWM allows me to get rid of the ZC detection entirely. This also allows me to get rid of some interrupt routines and just levergage the PWM hardware the uC. It sounds good if the circuit can be cheap and simple.An alternate approach would perhaps dispense with the bridge rectifier and instead use complementary FETs, driven by inverted signals (I think, though, that this would require the ZC detection again, though.)What are the gotchas here?What is the gold standard circuit for high-frequency PWM of AC mains yielding a scaled "copy" of AC mains?And can I buy this as a module already made?Regards,Dave J

author: nickm
author_rank: Regular Contributor
timestamp: January 09, 2014, 02:15:09 am
content: First thing is figure out the compatability of the lights you are switching to. Some LEDs won't work with adjusting the amplitude of the sine.As far as problems with changing the pure sine scheme switching losses might get you. 40kHz is in between the transition from IGBT to MOSFET territory.Answering the last two questions with a device not intended with this application. The easiest way to do what you want to do is buy a 70V or 100V audio amplifier and feed it with the signal you want to dim with. Just make a 60Hz sine wave with whatever controller you are using and gradually increase the amplitude to mimic the pure sine you're talking about. They might be fine with incandescents because they look like resistors but CFLs or LEDs might cause problems because they are non-linear loads. Actually now that I think about it do what the cheap 70V/100V manufacturers do and take a 4/8ohm amp and put a step up transformer on the output. 1:2.5 turns ratio should do it. It would be fun just to see how it performs. Redneck dimming.

author: johansen
author_rank: Super Contributor
timestamp: January 09, 2014, 04:21:23 am
content: you can make an AC buck converter with 4 switches.very painful to build and since you'll be limited to <50Khz, you will need a not very cheap inductor and capacitor on the output, as well as the input of the buck converter.

author: djacobow
author_rank: Super Contributor
timestamp: January 09, 2014, 04:35:58 am
content: Well, I understand that not all loads will be happy with all dimmer approaches. That's an unfortunate given. I would think, though that most loads would be happiest with the sine wave input, but I would not at all be surprised that some buck converter in an LED module is not.Most of the information on dimming comes from the theater lighting industry. Triac dimmers are known for being flickery, hard on bulbs, and noisy, both electrically and audibly -- the filaments will often "sing." Reverse phase control helps relieve this since the voltage rises sinusoidally, and is only cut off abruptly. I'm not entirely sure why this is better than the other way around, but consensus is that it is. Most of the "for LED" or "for CFL" dimmers you see use this method.The sine wave method obviously will have no high harmonics (if you filter them well) and that should be the easiest on incandescents for sure (and motors, etc) but yeah, who know what happens to power electronics downstream. However, I have tried dimming LED modules with the output of my variac, and the results were promising. So perhaps some of the LED drivers are happy with reduced voltage sine waves.The theater industry appears to be moving to sine wave dimming using PWM at super-audible frequencies. They may be much more incandescent-oriented, though than the rest of the world is heading.

author: johansen
author_rank: Super Contributor
timestamp: January 09, 2014, 05:49:22 am
content: it would appear to me from a quick googling that sine wave dimming refers to the 4 switch ac buck converter i described above.. but without the output capacitor and inductor.. this is complete blasphemy lol. might work for lightbulbs and motors but that's it."igbt dimming" appears to refer to be what you describe, cutting off the tailing end of the sine wave.. this should work with led and CFL bulbs.but by "work with" i mean: doesn't light on fire and or cut operating hours to less than 1000.there's no guarantee the led will actually dim properly.. it may sit and flicker, as some of mine do.

author: richard.cs
author_rank: Super Contributor
timestamp: January 09, 2014, 10:42:45 am
content: Leading edge dimmers (where you get the first part of a smoothly rising sine wave) are better for feeding rectifier-capacitor input loads and normally specified for CFLs and LEDs that contain switchers. Trailing edge (a conventional triac dimmer where you get a sharp rise and then the remainder of the sine wave) are very bad for these as it puts huge spikes of current into the input capacitors but are better for inductive loads where you don't want to have to suddenly interrupt the current (motors and iron core transformers).It is possible to do leading edge dimming with SCRs/Triacs (and historically it was often done this way for theatre lighting) but a mosfet in a diode bridge or a pair of source-source mosfets is probably easier. To make it work with SCRs you have one SCR with a bit of series resistance that turns on at the start of a cycle and another that shorts it out through a capacitor robbing enough current from the first to turn it off but then ceasing conduction itself once the capacitor charges. Fets are definately better.PWM on a since wave is much nicer and just gives you a lower amplitude sine wave after the filtering. It should work on any kind of load that can be dimmed. Note that some CFLs/LEDs will give constant output power for 90-260V in and go out entirely a little below that. They're just not dimmable by any technique. Also note that for rectifier-capacitor input loads all the dimming action happens in the first 90 degrees of the sine wave, it's largely immaterial how much of the downslope you get as the input capacitor is now charged.

author: Kjelt
author_rank: Super Contributor
timestamp: January 09, 2014, 11:08:12 am
content: Also note that a lot of intelligent dimmable led drivers do need a specific dimmertype for it to dim correctly.

author: djacobow
author_rank: Super Contributor
timestamp: January 09, 2014, 06:33:35 pm
content: Thanks for the replies folks. This is making me thing that it actually isn't possible to make the dimmer to end all dimmers, because each target light source likes something better. And now that we're in the world of CFLs and LEDs, and who knows how many variations in ballasts and driver circuits, there are really many many types of light sources.That said, it looks like the AC/AC converter concept is the most flexible. It can do sine wave dimmer (actually, this is more like wave-out-same-shape-as-wave-in dimming) but driven by the right software, could easily simulate reverse or forward phase angle dimming.I think right now lighting is in the midst of a big transition and when things settle down, hopefully standards will arise. It's actually not cool at all that each luminaire comes with a specific and limited list of dimmers it will work with, etc.

author: Codemonkey
author_rank: Regular Contributor
timestamp: January 09, 2014, 07:39:14 pm
content: You could just get a Philips hue kit. The protocol they use (ZigBee Light Link) has commands such as "Move to level" and one of the parameters is the time that the bulb should take to do the transition. So, you can for example send it a command saying move to a brightness of zero and take an hour to do so. You can also do the reverse and have a light that comes on gradually to wake you. The technology seems to be going the way of putting the dimmer in the bulb.

author: N2IXK
author_rank: Frequent Contributor
timestamp: January 09, 2014, 08:10:30 pm
content: Motorized Variac FTW!

author: djacobow
author_rank: Super Contributor
timestamp: January 10, 2014, 08:28:42 pm
content: Unrelated to this question and project, I've been replacing a lot of lighting in my home with LED retrofits and discovering that the dimmers (simple triac phase control) don't work all that well. One one circuit, I bought a new top-of-the-line Lutron LED-compatible dimmer that _SPECIFICALLY_ listed my LED lights as compatible. Well, the dimmer works nicely, but the fixtures buzz.Sorry, that's just unacceptable to me. And it makes me angry that the only way you can determine what works is through trial and error.I honestly had not thought about household lighting very much until about a month ago and I can tell you for sure now, the situation is f*k'd up. There are no standards. There are no promises. Every fixture has a different driver circuit, and nobody will even tell you what "secret" circuit they have in their dimmer.I have a feeling that the new buzzing from my lights is because the fancy new dimmer does reverse phase angle and as a result has a sharp turn off each cycle, resulting in a voltage spike. Should I need a snubber on a lighting circuit? No. I should not. It should have been in the dimmer.

author: johansen
author_rank: Super Contributor
timestamp: January 11, 2014, 06:37:32 am
content: Quote from: djacobow on January 10, 2014, 08:28:42 pmno, the buzzing is from the current flowing through the wire.. hook up a CT to your scope and make sure your beverage is well out of arms reach....

author: Kjelt
author_rank: Super Contributor
timestamp: January 11, 2014, 10:02:53 am
content: Quote from: djacobow on January 10, 2014, 08:28:42 pmThere are good and bad retrofit dimmable led lamps out there. That said I personally find that if you really change the lighting in your home to led you are much better off also changing the way you controll the lights. That means no more AC dimming but PWM DC dimming in the lamp or driver itself and controlling it with the appropriate dimming protocol (Dali/DMX/RS232/KNX/IP etc.). It wíll not be easy if you don't have a wooden house with wood and plaster walls like in the US. Here I have the same problem, all concrete and bricks and changing the layout is almost not done. Alternatives are RF controlled lamps (Zigbee) but they are expensive. The modern/new houses that are build with a nice budget are already future prove, each AC outlet, each lampfixture outlet, every and each electric outlet have their own seperate cable tube to the central power installation in the house.

author: djacobow
author_rank: Super Contributor
timestamp: January 11, 2014, 08:25:48 pm
content: Ah! This makes sense. The dimmer I have is a Lutron Maestro C*L unit, which I naively assumed used reverse phase angle because it's "for LEDs. But it appears to be a normal triac dimmer with who knows what special magic. The Lutron dimmer with reverse phase control is called their "ELV" line. It's really expensive: $105. Going from a triac to an IGBT and bridge rectifier shouldn't cost that much, but...Anyway. I may or may not spring for it.Quote from: johansen on January 11, 2014, 06:37:32 am

author: djacobow
author_rank: Super Contributor
timestamp: February 19, 2014, 09:08:32 pm
content: I'm back with more dimming experiments and questions. :-)First, I made a PCB for a simple triac dimmer that can be controlled by an AVR. Uses the H11AA1 and non-ZC detecting triac drivers and -- for incandescent lights -- it works great. It's cool because I can control it over a wireless network using NRF24L01 and similar. CFLs won't dim (even the kind that claim to dim with conventional dimmers) and I don't quite understand it. But looking at the current waveforms, it appears that the drivers for CFLs will pull a big spike of current every cycle the instant they can and so it's not surprising that they don't care how delayed the turn on. (Which makes me wonder why they work with "better" triac dimmers.Another issue is that some lightbulbs "sing" and buzz. The noise can be annoying. I'm sure the electrical noise is even worse.So... I'm revisiting the sine wave dimming concept. I've created the circuit below in LTspice and it seems to work, but I'm noticing that producing a filtered sine wave output requires some, umm, pretty "special" passive components.If I want to run the PWM at 5 kHz and, say, want filter with a knee at ~1 kHz, I need 1uF capactors that can withstand 120 Vac (250V caps) are easy enough to come by, but 10mH inductors that can handle amps ... not seeing it.Doing a Google image search on sine wave dimmers shows some theater equipment with truly massive filtering inductors.I could up the frequency at which I drive the FET to make the filter easier, but then that gets harder to drive with my rather high impedance super janky "power supply."Pic below attached. Sorry it's more vertical than horizontal. Bad planning while make the schematic.Thoughts and ideas welcome. I don't like breadboarding AC powered projects, so when I have enough confidence that this will work well enough for experimenting, I'll do a PCB.

author: johansen
author_rank: Super Contributor
timestamp: February 19, 2014, 10:01:33 pm
content: Inductors are great until you calculate Joules per dollar......I mean dollars per mJsome IGBTs are up to the task at 30Khz.most large motor inverters run at 2,4, and 8Khz, but they use the inductance of the motor as the filter.One last thing: the issue with CFLs is even worse when you include the inductance between the cfl and the triac.that's one of the reasons the cfl doesn't dim, resonant charging beyond the peak ac line votlage..

author: ahakman
author_rank: Regular Contributor
timestamp: March 08, 2014, 12:01:07 am
content: Oooh, you had my hopes up with the topic title, and then when I read the thread, you just got stuck on the same things I did.I also tired to simulate the output filter in spice for a "sinewave dimmer" and found it difficult to come up with anything that was very independent of the load. Was going to try some different filter topologies, but never got around to it. Shame too, because I'd really like to replace my X10 stuff with something more reliable, but like you, realized building a universal dimmer seems to be quite the feat not knowing what kind of bulb with what kind of driver you might end up with in the near future. I already have the control / network side of things done, in the form of something like the JeeLabs Jeenodes. I use almost the same hardware, but completely different scratch built firmware that's not arduino dependent for better performance, and because I enjoy low level coding. I also did completely custom PCB layouts that contains everything I need for each node, not in the modular arduino type approach, so a USB attached 'base node', and so far RGB controller, and eventually AC mains powered wall switch, and "lamp module" type nodes.http://imgur.com/a/MP8WnReally would be nice if there was a standard to dim new tech lights like CFLs and LED fixtures the proper way (on the DC side of the fixture in the case of LEDs) without having to hack it into each one yourself. Oh well, for now I can build and control as many channels of RGB led controllers as I care for, at least after I get back to that project and do a new PCB layout for the different radio I switched to now that the RF12 is EOL, and to fix some other "rev 1" type issues!http://youtu.be/qjKS70O8DNk

author: NiHaoMike
author_rank: Super Contributor
timestamp: March 08, 2014, 02:09:36 am
content: Best bet, if you're using LEDs, is to put a switching PSU and microcontroller in the fixture and use wireless or PLC for the control signals. Then put a transmitter in the control.Dimmable CFLs (and even the regular ones, though to a much lesser extent) will dim by reducing the supply voltage, but many LED bulbs will not. They specifically look for the phase angle control. They don't make much noise when dimmed so no point using some other form of control.

author: djacobow
author_rank: Super Contributor
timestamp: March 08, 2014, 04:57:03 am
content: Dimming LEDs, if I control the fixture, is not that difficult, though it may be the most feasible way to dim stuff "in the future."But we are living in a transitional time, and so I am still interesting in dimming existing plug loads. It occurs to me that with the FET (or IGBT) shorting a bridge rectifier topology, along with a ZC detecting circuit, one can actually delivery any of the three dimming techniques discussed here (forward phase control, reverse phase control, and PWM/sine wave). I think the passives would be slightly different, certainly for the sine wave dimming there is a need to do some serious filtering, but basically the bridge and the right FET can deliver all three.So I think I'm going to either dead bug or maybe do a simple board to experiment with this and I'l report back with any learning.The one thing that is stopping me from doing this right now is that I'm not sure how to drive the FET. I want to control it through an optoisolator, but those are open collector, so I can pull down from the opto, but I'll need a positive voltage supply to pull it up. I'm not sure the best way to do this. It occurs to me that I can use the drain voltage itself, but that will go away when the FET is on.

author: gxti
author_rank: Frequent Contributor
timestamp: March 08, 2014, 05:49:53 am
content: Lutron costs so much you think they'd just bribe the lamp manufacturers to agree on a protocol where they could control the bulbs through the wiring, and let them sort it out. Can't be much more complicated than making a good "dimmable" bulb in the first place.

author: SimpCirc
author_rank: Newbie
timestamp: March 08, 2014, 07:10:17 am
content: It's a shame you can't just use a circuit that slowly increases resistance to the LED's. Simple, no flicker, and cheap. But that would require altering the bulbs yourself and using something similar to the X10 equipment or a signal piggy back through the mains supply. Shame a variac or variac simulator won't work cause more than likely the LED Bulbs have a Voltage Regulator of some kind in them that would output that voltage until it cutout. The singing and buzzing is common on frequency controllers, simple voltage and amperage control does away with that, or has in my experience. Heres hoping you can find a solution to this issue.

author: ahakman
author_rank: Regular Contributor
timestamp: March 09, 2014, 01:58:03 am
content: Quote from: SimpCirc on March 08, 2014, 07:10:17 amYou don't want to do that at all - resistor => burning lots of power in heat that you have to get rid of somewhere. Might as well just stick to incandescents if you're going to do that.

author: ahakman
author_rank: Regular Contributor
timestamp: March 09, 2014, 02:07:47 am
content: Quote from: djacobow on March 08, 2014, 04:57:03 amYeah, that would be the best to be able to use any of the 3 methods. I think the IGBT might be the best bet, as I was reading an application guide before about using IGBTs for dimming, and you can do lots of good stuff with a few passives, like controlling the dv/dt of the gate to slow down the di/dt of the load current if doing reverse phase dimming, so less RF filtering is required, short circuit detection and shutdown, so no fuses are required, etc etc. Let me see if i can find that app note again...http://www.datasheetcatalog.com/datasheets_pdf/A/N/5/1/AN518.shtmlweird that it doesn't seem to show up on ST's website anymore.

author: johansen
author_rank: Super Contributor
timestamp: March 09, 2014, 02:11:44 am
content: Quote from: ahakman on March 09, 2014, 02:07:47 amslowing dv/dt of the gate down isn't exactly an option because that's heat burned up in the igbt.also, lagging edge phase control might work for led lighting and resistive loads, but that's it.once you throw a lagging load on it you're going to blow up the igbt's snubber circuitry with a *LOT* of power.an ac buck converter doesn't have that issue, but then you need an expensive inductor on the output.

author: tom66
author_rank: Super Contributor
timestamp: March 09, 2014, 02:26:57 am
content: Instead of the opto and associated driver circuit, consider an optoisolated gate driver, like FOD3182.You could get 250kHz with that. 50kHz is probably a good limit as most high voltage FETs have high gate charge so your power dissipation will increase too much.

author: djacobow
author_rank: Super Contributor
timestamp: March 09, 2014, 05:27:19 pm
content: Oh, cool, thanks Tom. I think I will try that. I was doing some more simulations with just the pull-down opto and a resistor pullup and it was clear that forward and reverse phase control would work just fine, but that PWM probably was not going to work. This part could make that work better.Going to order some now. Too bad I put in the order for the HV FETs and other components last night. :-(-- dave j>Instead of the opto and associated driver circuit, consider an optoisolated gate driver, like FOD3182.>You could get 250kHz with that. 50kHz is probably a good limit as most high voltage FETs have high gate charge so your power dissipation will increase too much.

author: ahakman
author_rank: Regular Contributor
timestamp: March 09, 2014, 07:41:57 pm
content: Quote from: johansen on March 09, 2014, 02:11:44 amI didn't really remember that right - if you read that app note, they slow down the dI/dt by putting a small inductor on the emitter of the IGBT - best to read the app note, and not listen to the person that read it 6 months ago and forgot all the details

author: johansen
author_rank: Super Contributor
timestamp: March 09, 2014, 08:09:30 pm
content: Quote from: ahakman on March 09, 2014, 07:41:57 pmlol, that's even worse.

author: ahakman
author_rank: Regular Contributor
timestamp: March 09, 2014, 10:22:32 pm
content: Quote from: johansen on March 09, 2014, 08:09:30 pmHowso? It's not changing the Ron of the device, it's just slowing down the current pulse.

author: johansen
author_rank: Super Contributor
timestamp: March 10, 2014, 02:41:09 am
content: Quote from: ahakman on March 09, 2014, 10:22:32 pmand when you turn the igbt off, where does the energy stored in that inductor go?

author: ahakman
author_rank: Regular Contributor
timestamp: March 10, 2014, 03:09:36 pm
content: Quote from: johansen on March 10, 2014, 02:41:09 amRather than trolling the thread for answers, maybe try actually reading the app note - it should be pretty obvious from the circuit diagrams and waveforms on pages 2 and 3

author: johansen
author_rank: Super Contributor
timestamp: March 10, 2014, 07:06:09 pm
content: it is pretty obvious.it goes into the IGBT.then again, at 100 or 120 hz switching, who cares.

author: JimmyM
author_rank: Regular Contributor
timestamp: March 11, 2014, 12:36:21 am
content: Is there any reason that it has to drive a household bulb?What about one of these 30W LED/power supply combos...http://www.ebay.com/itm/New-LED-High-Power-Driver-Power-Supply-driver-30W-LED-SMD-Chip-Light-Cool-White-/251469755079?pt=LH_DefaultDomain_0&hash=item3a8cc3f2c7and a floor lamp with a plastic globe something like this...http://www.ebay.com/itm/Laurel-Floor-Lamp-with-Mushroom-Glass-Globe-Chrome-Original-/131135833045?pt=LH_DefaultDomain_0&hash=item1e884e03d5Mount the LED on a heatsink/fan like this... with a resistor to slow down the fan so it isn't noisy.http://www.ebay.com/itm/AMD-CPU-heatsink-and-fan-/261416083496?pt=US_CPU_Fans_Heatsinks&hash=item3cdd9ce028You could hack the power supply (Rsense look like it right on the back) to send your own current feedback to it using an op-amp and a filtered PWM output from an arduino as the reference to the op-amp that sends the correct voltage back as the feedback. Thus allowing for variable current control.Just a thought.

author: djacobow
author_rank: Super Contributor
timestamp: March 15, 2014, 11:43:56 pm
content: As I've said before, if I am to "own" the luminaire as well as the dimming circuit, this is an easy problem. There are a plenty of ways to drive and dim an LED.What I am after is a near-universal base circuit that I can use to drive and dim and number of lamps and lamp types. I don't mind customizing hardware and software on a per-lamp basis, but it would be nice to have a board that could suit a bunch.Actually, that's just what I'm doing now. I've simulated the heck out of a FET shorting the DC output of a bridge rectifier, and it looks like it works quite well. I can easily drive the FET as a reverse or forward phase angle dimmer. It also seems to work OK for PWM up to a few kHz or so. I'm sure it could go faster if I had a better FET driver circuit, but I want to keep things simple for now.I'm a little leery of hitting 'send' on this PCB, though, as I feel like maybe that FET is going to ring to high heaven and make enough EMI to qualify as an electronic jammer. On the other hand, my FET driver doesn't move that quickly, so maybe it won't be too bad. I guess the best way to find out is to try it. I /may/ breadboard it, but I don't like to breadboard mains circuits. Also, I hate sticking TO220s and other thick pin parts into my breadboards. They do not seem to like it. :-)

author: electrodacus
author_rank: Super Contributor
timestamp: March 16, 2014, 12:16:48 am
content: There is not possible to make a dimer to end all dimersUnless you build some sort of plastic and metal eating nanobots that can multiply fast track and end all dimmers.Maybe I'm not that funny but is not possible to do a universal dimer there are to many an different AC and DC light bulbs and tubes used today.Since LED's have in my opinion the chance to replace soon almost all other types one idea will be to separate the wires that are used for lighting and deliver low voltage DC to the light fixtures.I live offgrid so is no problem for me everything in the house is wired (not completely still working on that new house) for 24V DC and I will have a CAT 6 cable going everywhere.But you can also use the two wires that transmit power to communicate with whatever is connected on the other side.Someone will probably come up with a new standard for lighting similar to what I try to explain that will easily convert the old existing infrastructure. Is possible since the LED's are way more efficient that old incandescent that the wire can transport the power at low DC voltage.It makes no sense to add so much complexity to each LED light source just to work on main AC.

author: johansen
author_rank: Super Contributor
timestamp: March 16, 2014, 12:28:52 am
content: Quote from: djacobow on March 15, 2014, 11:43:56 pmthere's no good way to do that, you need to build an AC switch buck converter, or you have to deal with the residual energy stored in the inductance of the load, being dumped into either the igbt, or mosfet, every time it turns off.since triacs turn off at zero current, they don't have that problem..but they can't drive capacitive loads, except through an inductor.. and round and round you go.so if you include a beefy turn off snubber, you can drive led and incandescent lights, and that's about it.if you want a legit dimmer, you need an ac buck converter and that also needs an inductor for capacitive loads... otherwise you are relying on the inductance of the downstream wires to limit the inrush current.... at say, 10khz.. damn that smoke smells good.so anyhow, don't throw out the ac buck converter because its complicated, you can easily drive the 4 switch mosfet/igbt converter through a single transformer with two isolated secondaries, or you can use two FWB rectifiers and two switches, at the expense of 4 diode drops.

author: djacobow
author_rank: Super Contributor
timestamp: March 16, 2014, 12:48:03 am
content: Johansen,Thanks for the post. Obviously, universal is not possible. Mostly I want to deal with incandescents, say up to 150 W, CFLs that claim to be dimmable, and LEDs that are AC powered and also claim to be dimmable. If you've bought dimmers at the hardware store lately, you I'm sure know that a simple triac dimmer works at least "meh" on all three, but that smarter ones that do forward phase and use other tricks to soft start or current limit do a bit better, depending on the ballast/driver involved.I'm not sure I understand your point about the snubber. I am including a snubber diode between the drain and source of the FET. Won't that absorb the energy in any inductance in the circuit? Unlike a triac dimmer where the snubber needs to be an RC, here we have the switching device living in a rectified world, so the freewheel diode seems adequate to let the current bleed away. I'm sure I'm missing something. Maybe that diode needs a small power resistor in series to absorb most of that energy, rather than letting the diode take it.

author: johansen
author_rank: Super Contributor
timestamp: March 16, 2014, 01:15:05 am
content: you get the diodes for free with a mosfet, but that diode only protects against reverse voltage.by turn off snubber i mean a diode connected to the drain, charging a capacitor connected to the source, with a resistor across it.the resistor will heat up according to the turn off current flowing^2 multiplied by the inductance of the load*switching frequency/2but the capacitor prevents that turn off current from exploding the igbt, and at turn off the capacitor will take the full load current for a few microseconds.

author: djacobow
author_rank: Super Contributor
timestamp: April 03, 2014, 10:37:53 am
content: I put together the first iteration of the FET based aribtrary waveform dimmer tonight.+ It works, and I was able to make it do "true" PWM at various frequencies, forward phase, and reverse phase dimming.- I had to make a board bodge. I hate that I can never get a board exactly right the first time.* It seems to dim ballasted LED bulbs better than the triac dimmer, definitely in forward angle mode, but surprisingly, also in reverse angle mode* I don't have a differential probe to really examine the mains voltage circuits. Pity. I tried doing poor mans differential with the math functions, but that was ugly. Actually, on my old analog scope invert+add wasn't too bad.* When doing PWM, the power dissipated in the snubber goes way up when the frequency is high. This was expected -- why I made room for a large resistor on the board, but I didn't have one to populate. I smoked a little 1/4W resistor doing PWM at 25 kHzI built the board to take either a 4N25 pulling down the FET gate, and a simple resistor pulling it up, or a FOD3182, which I haven't tried yet. I'm somewhat surprised the circuit works as is, considering my awful gate supply circuit( rect+ <--> diode <--> resistor <--> zener12V || cap <--> rect-)Anyhoo, not exactly the dimmer to end all dimmers, but a fun board to experiment on. I want to try dimming a transformer powered halogen tomorrow.-- dave j

author: ahakman
author_rank: Regular Contributor
timestamp: April 04, 2014, 11:42:20 am
content: Is that some kind of current transformer you have wound around the load hot wire?

author: SL4P
author_rank: Super Contributor
timestamp: April 04, 2014, 12:07:23 pm
content: While it's not a hacker solution - take a look atwww.COOLON.COM.AUThey make a distributed lighting control system that is particularly smart.Their programmable controllers are clever in themselves, and use simple DMX over a pair to many daisy-chained controllers which are luminaire specific (LEDs, incandescent, fluoro etc).Well designed and engineered, they are used for everything from homes, offices, street and architectural lighting. And they design / manufacture all their own products in house.

author: djacobow
author_rank: Super Contributor
timestamp: April 04, 2014, 02:57:18 pm
content: It was an attempt at one. I really wanted to see the current in the load on the scope, so I tried this. It did not work at all, which surprised me given the probe's high impedance. Perhaps I had way too few turns. I have some real CTs but I was too lazy at the moment to try one out.Quote from: ahakman on April 04, 2014, 11:42:20 am

author: djacobow
author_rank: Super Contributor
timestamp: April 04, 2014, 03:05:08 pm
content: Looks interesting. I'm weighing whether I want to pursue any of this commercially at all. My original idea, I think as stated in the original post, was to make something to help kids get to sleep; it was to work with their own lamps.Generally, I think with lighting, the retrofit market has to be many times as big as the new construction market, and a lot of these engineered solutions seem more tailored for the latter. (or at least for significant renovation). A wireless solution seems attractive for the former, though products so far seem 1/2 cooked. It probably does make sense for the control to be in the luminaire itself, but that may not be appealing to homeowners who want to be able to swap it out without changing their control system. Because of that, my money is on a future system that is still generic as the fixture/wiring interface. (Maybe not as generic as "neutral and hot" but at least a standard.) Because of that, I think wireless controlled switches, sockets, and wall boxes will come.The doodad I've built right now is controlled by an Arduino, and has two provisions for wireless, neither of which I've tried yet. The first is an NRF24L01 on the SPI bus. The second is to pull the Ard and plug in a SparkCore. The Spark is on order.Quote from: SL4P on April 04, 2014, 12:07:23 pm

author: Richard1303
author_rank: Newbie
timestamp: October 23, 2024, 01:11:48 pm
content: Dear Djacobow,Sorry to dig up this subject… and sorry in advance for the GoogleTrad because I am French and my English is not very good and the length of my message.I would like to know if you achieved your end with this project?I'm looking for schematics, parts list and design details for a similar project.I would like to dim an 8W 230V LED bulb the right way. (https://eprel.ec.europa.eu/screen/product/lightsources/765808?navigatingfrom=qr). Until now I was using an oxo dimmer (https://www.oxolight.com/product-page/simoun-2) because I had it on hand but I quickly understood that it was not suitable, I later learned that an IGBT solution would be more suitable.For my project, I need to be able to control this bulb in DMX and I was planning to use an arduino.I did find very simple diagrams, but surely too simple, and some people on forums warned me that there was a big electrical risk in simply connecting the IGBT to a DMX interface, that it would be very difficult to isolate the control part from the power part.Do you have a procedure to follow, perhaps some diagrams that I could draw inspiration from?The equipment needed to implement this project?I don't have a great theoretical knowledge of electronics but I am a good copier, in the past I was able to carry out several projects by taking inspiration and combining what had already been done by others people.Thank you very much for educating me a little more. I have attached a diagram on which I based myself to get started (it may not be suitable at all) I would like to clarify that this project is not intended for commercial use, obviously.

author: KerimF
author_rank: Frequent Contributor
timestamp: October 23, 2024, 04:16:09 pm
content: Quote from: djacobow on March 08, 2014, 04:57:03 amOnce I was in a hurry to drive the floating FET.I simply added a small ready-made 12V SMPS to power the gate driver of the FET (N-MOSFET).