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220v LED DIMMER??

Discussion in 'LEDs and Optoelectronics' started by BlinkingLeds, Mar 16, 2013.

  1. BlinkingLeds

    BlinkingLeds

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    Feb 23, 2013
    Hi everyone!
    I found this circuit in my computer (i don't remember where i got it and when) and i was wandering if it's able to dim 220V LED BULBS? it seems possible by utilizing the common pwm technique. I'd looove the idea of dimming my led bulbs (with which i have been slowly replacing every cfl bulb that reached the end of it's life). If this circuit doesn't work, is there any other easy way to make led dimmers that would be not much larger that the standard triac/scr dimmers?
    Thanks in advance guys.
     

    Attached Files:

    Last edited: Mar 16, 2013
  2. Rleo6965

    Rleo6965

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    Jan 22, 2012
    The circuit seems will work. It has capacity of 600 watts.

    You can use NE555 Astable circuit with variable output pulse width.

    Just wondering that your unaware of that circuit diagram? Possibly sent by virus program.:D
     
    Last edited: Mar 17, 2013
  3. BlinkingLeds

    BlinkingLeds

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    Feb 23, 2013

    Yep it would be very funny if it was sent by a virus but it's probably from the time i was searching for something else and thought it was useful and saved it and then i completely forgot about it somehow.

    So i found a circuit about independent frequency and pulse width control , i never tested it but i hope it will work.

    http://www.instructables.com/id/Insanely-easy-independent-control-of-frequency-and/

    By the way if you now any better circuit that allows for independent pulse width and frequency control feel free to share ;) :)

    P.S. Actually the real question that i wanted to ask is : Will it work off the mains or do i need a 1:1 transformer?

    Oh and what's D1?
     
    Last edited: Mar 17, 2013
  4. Harald Kapp

    Harald Kapp Moderator Moderator

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    Nov 17, 2011
    This circuit will need an additional PWM generator to work (PWM input at the left). There are considerably less complex circuits for dimming.

    You'll have to look at the LED lamp's specifications. No every LED lamp is dimmable - regadless of the type of dimmer used.
     
  5. KrisBlueNZ

    KrisBlueNZ Sadly passed away in 2015

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    Nov 28, 2011
    The circuit in your first post has a number of problems and I wouldn't use it. Also it probably won't dim an LED light bulb. It depends how the LED light bulb is designed internally. If it contains a rectifier and capacitor, PWM control won't vary its brightness. Nor will phase angle control (SCR-type dimmer).

    Do you have a manufacturer and part number, or a link to the data sheet, for the LED light bulbs you're using?
     
  6. BlinkingLeds

    BlinkingLeds

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    Feb 23, 2013
    So this circuit will have the same result on my leds as an scr/triac dimmer (almost no dimming and intense flickering) ?

    i was hoping that i finally found a circuit that will be able to dim my bulbs but now i realize it won't work :( .

    Does anyone knows of a circuit that works? They do work with a VARIAC but that's out of the question for obvious reasons.

    Thanks everyone.
     
  7. KrisBlueNZ

    KrisBlueNZ Sadly passed away in 2015

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    Nov 28, 2011
    My guess would be that at a high duty cycle, you would see no dimming of the LED, and at low duty cycles, the LED might go out, or blink. It really depends on what's inside the LED light bulb. At very high duty cycles the circuit will stop working properly and I couldn't predict exactly what it would do.

    Short of a VARIAC, you may be able to use a DC voltage regulator. Probably a switching regulator, for efficiency. The voltage could be a problem though. What is the mains voltage where you live? (You might want to put your location in your profile; it can be helpful.)
     
  8. BlinkingLeds

    BlinkingLeds

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    Feb 23, 2013
    I have 220-240v so , no voltage regulator?
     
  9. KrisBlueNZ

    KrisBlueNZ Sadly passed away in 2015

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    You would need a switching regulator that would operate from 350 VDC! In other words, a mains-powered power supply with an output that can be varied over a wide range, and doesn't need to be isolated from the input.

    Try Googling high voltage buck converter power supply
    The first hit looks interesting:
    http://www.onsemi.com/pub_link/Collateral/AND8098-D.PDF
    Maximum output current is 100 mA which is 3W at 300VDC so if your LED bulbs are rated for more than 3W you need to look elsewhere.
    Rolling your own solution will probably work out expensive and time-consuming. Interesting... if you have the time. Are you sure there aren't already dimmers for LED bulbs available on the market?
     
  10. BlinkingLeds

    BlinkingLeds

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    Feb 23, 2013
    I can't find a dimmer for standard led bulbs and most of my bulbs are from 10-20w. i would like to build something myself ... if i knew how that is. I thought of using a voltage regulator but i can't find any that has an input over 350v.
     
  11. KrisBlueNZ

    KrisBlueNZ Sadly passed away in 2015

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    Oops! 100 mA at 300V is 30W, not 3W!

    So the Motorola app note I linked to might be the answer. Except that the NCP1052 is not available from Digikey. I suspect it's obsolete. But the app note might give you some ideas. Also have a look at the other search results.
     
  12. KrisBlueNZ

    KrisBlueNZ Sadly passed away in 2015

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    Looks like there are lots of possibilities on Digikey. Go to their product index and select "Integrated Circuits -> PMIC - AC DC Converters, Offline Switchers". Narrow down the selection using the input voltage range and the output power rating, and by checking the "In Stock" box. Choosing power ratings from 30W to 60W and voltages of 350V and higher cuts your options down to 95 parts.

    Then sort ascending on price for quantity=1. The very first one is similar to what you need. http://www.digikey.com/product-detail/en/FSFM300N/FSFM300N-ND/2078266 Fairchild FSFM260/300N. It's designed to perform many of the functions needed in an off-line (mains-powered) power supply, in power supplies for LCD TVs and so on. It uses current mode flyback operation, which I've personally used a lot and found to work well. It's highly integrated and cheap. But it's not designed for variable output voltage, and can't cleanly be adapted to work as an LED dimmer. It also needs a transformer, which you would have to make by hand. This can be a black art and should be considered NSFN (Not Suitable for Newbies).

    In any case, we're now getting into an area where I feel uncomfortable advising you further. This is because this is a mains-powered application and I don't want anyone to try to hold me responsible for anyone's death or injury because of a mistake you made. If you want that kind of assurance from me, you'll have to get me to your place so I can watch over your shoulder.
    I seriously suggest you pay for an appointment to talk to an experienced local registered electrician, about as much as possible, including personal safety when working with mains equipment, safe design and construction for mains-connected equipment, specific characteristics of the design(s) you are considering, considerations relating to the wiring from the switch to the light socket (which would be carrying DC instead of AC), fire risks, insurance issues, isolation and insulation requirements, whether it's legal for an unqualified person to build his own light dimmer for installation into his house wall, and any and all related matters, including ones I didn't think of and mention specifically above.

    With that said, if you want to continue, do that Digikey search, note down all the manufacturers, and go to each one's web site in turn and look for switching power supply components with suitable characteristics. The data sheets often have a general application circuit design with real-world figures so you can see whether they might be suitable or not, so you should be able to eliminate many of them for various reasons.

    Unfortunately, most switching power supply devices are designed for fixed output supplies, and cannot necessarily be made fully adjustable from 0% to 100% output voltage. A search on dimmers might produce more useful results.

    I would also find out as much as you can about the internal design of the LED lights you're using, and the technology trend in general, so you don't put a lot of effort into something that soon becomes obsolete because LED light bulb technology changes.

    Good luck!

    Kris
     
    Last edited: Mar 19, 2013
  13. BlinkingLeds

    BlinkingLeds

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    Feb 23, 2013
    Hi, thanks for your reply.
    I've build the whole electrical installation in my house (fuses, wires in the walls, everything) so i do have some experience. Ok if a switching power supply is not such a good approach what about using a fet as an VCR (voltage controlled resistor)?

    In a previous circuit i made (ir led / phototransistor) the fet's resistance varied proportionally to the gate's voltage which in turn was proportional to the ir light that hit the phototransistor. What if i use that feature so i would wire the fet just as in the circuit in my first post but i use a potentiometer instead of the photocoupler so that I may vary the gate’s voltage?.
     
    Last edited: Mar 19, 2013
  14. BlinkingLeds

    BlinkingLeds

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    Feb 23, 2013
    also if i may ask what program, are you using to draw those lovely schematics you post everywhere?
     
  15. KrisBlueNZ

    KrisBlueNZ Sadly passed away in 2015

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    Sure. What worries me are the things you may not know that you don't know. That's one reason why electrical safety inspectors exist!
    Actually a switching power supply lS a good approach. A linear regulator wastes significant power, which gets converted to heat. Here are a few ROUGH calculations for a linear regulator.

    LED light bulb rated at 20W, 325 VDC. Current 62 mA. Assuming no active circuitry inside the LED bulb, internal resistance = 5300 ohms. Dimmed to about half voltage, 160 VDC. Current 30 mA. Voltage dropped across dimmer 165V. Power dissipation in dimmer = 5W.

    Dissipating 5W on a small circuit board inside a mostly enclosed box within your wall could be a problem. Even if it's achievable, there is a fire risk and probably an issue with insurance.

    That's the general idea of a linear regulator.

    So far I've been assuming that running these LED light bulbs from a variable DC voltage will allow them to be dimmed smoothly over a wide range. This isn't necessarily true.

    I think your next step should be to sacrifice an LED lamp and see what's inside it. Take some photos and draw up a diagram, and post it here.

    The dense monochrome diagrams are done with a very old commercial EDA program called OrCAD/SDT III printing to a GIF file driver. That program is very quick to use and it's easy to add custom component images, but it doesn't have circuit simulation; it's a "schematic capture" package only.

    The other diagrams I post here, often with oscilloscope traces, are done with LTSpice, which is a free (see http://www.linear.com) schematic capture program with simulation. It supports a limited range of components, but for small designs, the simulation feature is great.
     
  16. BlinkingLeds

    BlinkingLeds

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    Feb 23, 2013
    Hi i have posted the photos as requested.
    It was an 20w led bulb but it came broken , half of the leds didn't light up so i opened it and found that the cheapo pcb and solder lost the connection with the capacitor so i soldered it and it worked ok but i couldn't re-connect the pcb to the e27 base so i made this little round "lamp" with a piece of wood it isn't very pretty but it works :).
     

    Attached Files:

  17. KrisBlueNZ

    KrisBlueNZ Sadly passed away in 2015

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    OK, I'm glad you drew up the schematic of the LED lamp, because that design WILL NOT work from DC anyway!

    It uses the two 800 nF capacitors to convert the AC mains voltage into a current. If you supply it with DC, the capacitors will just charge up and the current will drop to zero.

    To dim these LED light bulbs, you need a variable AC voltage at roughly mains frequency. A Variac is a good solution. An electronic solution would be a high-voltage square-wave generator (the AC doesn't have to be sinusoidal). To keep the LEDs running within their limits, and to prevent interference being emitted from the wiring, I would use a current generator, rather than a voltage generator.

    The circuit would need to generate alternating positive and negative current into a load consisting roughly of a capacitor and resistor in series. The duty cycle would be 50% and some trick would be needed to keep the average DC output voltage at zero. The current would determine the LED brightness.

    I'll have a think about it and see if I can come up with a design. Does ANYONE ELSE have any suggestions?
     
  18. BlinkingLeds

    BlinkingLeds

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    Feb 23, 2013
    But if i use the diagram in post #1 it will not be getting dc it's output will still be ac.
     
  19. KrisBlueNZ

    KrisBlueNZ Sadly passed away in 2015

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    Nov 28, 2011
    That's true. But there are problems with that circuit. Specifically the way the gate supply voltage is derived, and with PWM over house wiring.

    I found the original circuit with its description, at http://www.extremecircuits.net/2010/06/dimmer-with-mosfet.html

    The description specifies incandescent bulbs only. I doubt it would work well with any other type of bulb. I don't even think it will work properly with incandescents! Read the full text for details.

    Edit: I like your rebuilt bulb! It looks to me like the original bulb construction points most of the light outwards, instead of downwards. Your way makes more sense. Are there three circuit boards in each bulb? Do you think hot melt glue is a safe way to hold them to your base board?
     
    Last edited: Mar 20, 2013
  20. BlinkingLeds

    BlinkingLeds

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    Feb 23, 2013
    I don't intend to use the circuit with pwm and optocoupler instead i will just use a potentiometer at the fet's gate.

    The hot glue is just to hold it so it could not vibrate or something. to hold each of the 12 led pcbs in place i have 4 screws that press the edges so it can't fall down :)

    as you say there are 3 separate circuits 2 "power supply" pcbs gives power to 5 led pcbs
    each and the other one gives power to the other 2 led plates and the center circular led plate
     
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