Page 4 of 10 FirstFirst ... 23456 ... LastLast
Results 31 to 40 of 92

Thread: Single channel AC dimmer

  1. #31
    Join Date
    Dec 2011
    Posts
    7,092
    Post Thanks / Like

    Default Re: Single channel AC dimmer

    Quote Originally Posted by P. Short View Post
    By the way, why do you want to apply 36V to the guts of the device? Is it just tinkering, or do you have some plan behind not using the 110VAC power input?
    I was hoping to bypass the AC and control them with DC directly.

  2. #32
    Join Date
    May 2007
    Posts
    5,571
    Post Thanks / Like

    Default Re: Single channel AC dimmer

    I haven't been able to find any data on that 5-pin IC on the internet...the closest that I came across was in a family of parts with completely different packaging. In any case, did that 36V that you measure appear to be an AC or DC voltage?
    Phil

  3. #33
    Join Date
    Dec 2011
    Posts
    7,092
    Post Thanks / Like

    Default Re: Single channel AC dimmer

    35.3 Vac at each rectifier .

  4. #34
    Join Date
    May 2007
    Posts
    5,571
    Post Thanks / Like

    Default Re: Single channel AC dimmer

    OK, 35.5 VAC is presumably an rms value from a DVM, corresponding to a peak voltage of 50V and a p-p voltage of 100V. Without further understanding I wouldn't put any higher voltage a that point in the circuit than what you've already tried. Particularly since I'm totally unclear on what the MOSFET or the unknown IC are supposed to be doing.

    One interesting piece of information would be to know how the LEDs are arranged on the board. I'm guessing that there are some number of LEDs are in series to form what I'll call a chain, and that several of these chains are in parallel in each half of the LED array. This would provide information on how to drive the LEDs from some source other than the AC power line.
    Phil

  5. #35
    Join Date
    Dec 2011
    Posts
    7,092
    Post Thanks / Like

    Default Re: Single channel AC dimmer

    Quote Originally Posted by P. Short View Post
    OK, 35.5 VAC is presumably an rms value from a DVM, corresponding to a peak voltage of 50V and a p-p voltage of 100V. Without further understanding I wouldn't put any higher voltage a that point in the circuit than what you've already tried. Particularly since I'm totally unclear on what the MOSFET or the unknown IC are supposed to be doing.

    One interesting piece of information would be to know how the LEDs are arranged on the board. I'm guessing that there are some number of LEDs are in series to form what I'll call a chain, and that several of these chains are in parallel in each half of the LED array. This would provide information on how to drive the LEDs from some source other than the AC power line.
    Ok I will define what i see as 1 cluster which is tied to 1 of the 4 mosfets.

    There is 10 columns of 7 leds . If looking at the columns from left to right , the first 2 columns are in parallel and this continues for each group of 2 columns going to the right .

    So it appears that there are 2 groups of 35 leds in series per cluster .

  6. #36
    Join Date
    Dec 2011
    Posts
    7,092
    Post Thanks / Like

    Default Re: Single channel AC dimmer

    I'd bet the 5 pin ic is a voltage regulator

  7. #37
    Join Date
    May 2007
    Posts
    5,571
    Post Thanks / Like

    Default Re: Single channel AC dimmer

    Quote Originally Posted by angus40 View Post
    I'd bet the 5 pin ic is a voltage regulator
    Possibly, but I'm skeptical. Most regulators that I've come across have 3 pins, rather than 5. I'd bet that it's an op-amp or comparator, possibly operating on conjunction with the MOSFET as some sort of protection circuit in case of over-voltage or over-current.

    One thing that I've noticed in playing around with el-cheapo LED strings is that the human eye (or at least my eye) is sensitive to peak LED output at AC line frequencies, rather than the average LED output. Those parts might be a method to turn the LEDs on only around the peak of the AC line voltage. The benefit of this is that the energy that the LED has to dissipate is lessened by only driving them during part of the cycle the part of the cycle that determines the apparent brightness (i.e not dissipating power at times that don't affect the brightness sensed by the eyes), allowing the current through them to be increased and as therefor the apparent brightness. Just a guess, though, don't take this as gospel.

    Edit - regarding that 5-pin part, it might be something like LMV731L, which comes in both an SOT23-5 and SC70-5 package, which are both little things like those in your photo. And I would bet on linear comparators being available in those packages as well.
    Last edited by P. Short; 06-12-2021 at 08:21 PM. Reason: Add last paragraph, some grammar changes
    Phil

  8. #38
    Join Date
    Dec 2011
    Location
    UK S80 postcode
    Posts
    1,535
    Post Thanks / Like

    Default Re: Single channel AC dimmer

    Hi, it looks like:
    U1 is a PM2014 mains Voltage LED current limiter / driver.
    http://www.power-micro.com/bookpic/201832992822124.pdf
    The resistors and capacitors are support for above.
    Q1 is a CSD-4N unidirectional thyristor.
    https://www.chinahao.com/Product/559...power_scr_hxw/

    It looks very much like the 35 series LEDs are straight across the rectified mains and are being pulse width modulated (PWM) by the components above. It is likely that they are being run at quite a high current for a short period of time. Something like 100mA but only for 10 to 20% of the half wave.

    Unfortunately 35V ‘DC’ is not going to be enough to light a series string of 35 LEDs whit a forward voltage of say 3V each. 35LEDs * 3V = 105V which is what you would need to get them to conduct. Even if you went up that high with the voltage the PM2014 may not turn on the thyristor as it is current limiting by delaying the ‘on’ time during the half cycle to current limit. There is also the issue that thyristors once switched on will stay on until the voltage is removed, that’s why we always delay the ‘on’ time as we can’t switch them off. With unsmoothed rectified AC the voltage drops to zero every cycle and the thyristor switches off. Replacing this with a smoothed DC would mean the thyristor once switched on would stay on and be unable to provide any current limiting (magic smoke scenario).

    This would explain why the off the shelf PWM module didn’t work as you are stacking two forms of PWM, it should be posable to PWM the whole module but you would need a very specific PWM module that acts over a very specific range say between 90V -> peek -> 90V. Full, 50% & off is easier as that could be done with diodes and a thyristor but would have a 60Hz flicker.
    Last edited by Barnabybear; 06-13-2021 at 08:10 AM.

  9. #39
    Join Date
    May 2007
    Posts
    5,571
    Post Thanks / Like

    Default Re: Single channel AC dimmer

    Thanks, Barnabybear.

    Based on what you described and my own experimenting, I think that the Renard controllers are so limited that they would only allow crude dimming of those LED Floods. I suspect that this is also true of the AC dimmer library that Angus tried. I have controller designs that I'm bench-testing that I think have the necessary fine degree of control, but that is likely as far as i will go with them.

    I would also hesitate to say anything more without having one of those floods in hand and making some voltage and current waveform observations.
    Last edited by P. Short; 06-13-2021 at 10:18 AM.
    Phil

  10. #40
    Join Date
    Dec 2011
    Posts
    7,092
    Post Thanks / Like

    Default Re: Single channel AC dimmer

    Quote Originally Posted by Barnabybear View Post
    Hi, it looks like:
    U1 is a PM2014 mains Voltage LED current limiter / driver.
    http://www.power-micro.com/bookpic/201832992822124.pdf
    The resistors and capacitors are support for above.
    Q1 is a CSD-4N unidirectional thyristor.
    https://www.chinahao.com/Product/559...power_scr_hxw/

    It looks very much like the 35 series LEDs are straight across the rectified mains and are being pulse width modulated (PWM) by the components above. It is likely that they are being run at quite a high current for a short period of time. Something like 100mA but only for 10 to 20% of the half wave.

    Unfortunately 35V ‘DC’ is not going to be enough to light a series string of 35 LEDs whit a forward voltage of say 3V each. 35LEDs * 3V = 105V which is what you would need to get them to conduct. Even if you went up that high with the voltage the PM2014 may not turn on the thyristor as it is current limiting by delaying the ‘on’ time during the half cycle to current limit. There is also the issue that thyristors once switched on will stay on until the voltage is removed, that’s why we always delay the ‘on’ time as we can’t switch them off. With unsmoothed rectified AC the voltage drops to zero every cycle and the thyristor switches off. Replacing this with a smoothed DC would mean the thyristor once switched on would stay on and be unable to provide any current limiting (magic smoke scenario).

    This would explain why the off the shelf PWM module didn’t work as you are stacking two forms of PWM, it should be posable to PWM the whole module but you would need a very specific PWM module that acts over a very specific range say between 90V -> peek -> 90V. Full, 50% & off is easier as that could be done with diodes and a thyristor but would have a 60Hz flicker.
    Thank you both for figuring this fixture out . I think these floods are purpose built as work lights where they are mounted in pairs .
    I had read a little about AC leds requiring components for particular timings and current/voltages but was maybe wishful in thinking to control these like a simple dumb r,g or b element .Should there be a method to dim these that worked for this hobby would be great as they are an affordable flood light solution.



    A side note , I learned a few new things from playing with this flood . Powering a Esp module form AC via a ultra-compact power module 3W 5V rather than the standard AC-DC power supply .

Page 4 of 10 FirstFirst ... 23456 ... LastLast

Bookmarks

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •