I need a simple circuit design for a slow fade-in AC dimmer. In a dark theater, suddenly turning on the lights is a somewhat unpleasant experience. I want a simple circuit compatible with 110 volt dimmable LED lights that will slowly ramp the light output over a period of about 5 seconds or so. I have found a number of simple designs that would work for 12VDC LEDs, but none for 110VAC dimmable LED lights.
Slow fade-in circuit
Started by ●September 23, 2020
Reply by ●September 23, 20202020-09-23
n Wednesday, September 23, 2020 at 2:08:15 PM UTC+10, rhor...@gmail.com wrote:> I need a simple circuit design for a slow fade-in AC dimmer. In a dark theater, suddenly turning on the lights is a somewhat unpleasant experience. I want a simple circuit compatible with 110 volt dimmable LED lights that will slowly ramp the light output over a period of about 5 seconds or so. I have found a number of simple designs that would work for 12VDC LEDs, but none for 110VAC dimmable LED lights.There is a fairly straight-forward solution, but it isn't going to be al that simple. You need to synthesise a 60Hz AC waveform that can move up to 110V RMS over 5 seconds. The Baxandall Class-D oscillator lets you generate such an AC waveform fairly easily. http://sophia-elektronica.com/Baxandall1959JM.pdf It's usually used at frequencies above 60Hz, but the kind of centre-tapped power transformer you'd need is easily available for 60Hz operation. Modern versions use MOSFET switches, rather than the bipolar transistors, which were all that was available when Baxandall wrote the paper. You'd need a fairly high current choke to feed the centre tap, and you'd have to pulse-width-modulate the DC you fed into it to get the five second ramp ramp you want. The inductor is going to be a pretty effective low pass filter, so adjusting the width of string of pulses in a 1kHz pulse stream would be all you'd need to do, and your could do that with a very simple and cheap microcontroller. That would be 5000 pulses, so the "on" period would go up by 0.2usec from pulse to pulse. That implies a timing clock that's running at 5MHz or faster, which wouldn't be hard to get. There are lots of other ways of doing it, and you can probably buy something off the shelf - there's lots of stuff available for theater lighting and that's been true for many years - but finding something small and cheap might take time. -- Bill Sloman, Sydney
Reply by ●September 23, 20202020-09-23
On 9/23/2020 12:08 AM, rhor...@gmail.com wrote:> I need a simple circuit design for a slow fade-in AC dimmer. In a dark theater, suddenly turning on the lights is a somewhat unpleasant experience. I want a simple circuit compatible with 110 volt dimmable LED lights that will slowly ramp the light output over a period of about 5 seconds or so. I have found a number of simple designs that would work for 12VDC LEDs, but none for 110VAC dimmable LED lights. >You can buy a "DMX dimmer" box off the shelf: <https://www.amazon.com/American-Dp-415-Channel-Dimmer-Pack/dp/B000FVZUMM> paired with a control box (or PC interface) you can set up fade in/out programs synced to external triggers as you like. DMX is a communications standard for theater and stage lighting control.
Reply by ●September 23, 20202020-09-23
On Tuesday, September 22, 2020 at 9:08:15 PM UTC-7, rhor...@gmail.com wrote:> I need a simple circuit design for a slow fade-in AC dimmer. In a dark theater, suddenly turning on the lights is a somewhat unpleasant experience. I want a simple circuit compatible with 110 volt dimmable LED lights that will slowly ramp the light output over a period of about 5 seconds or so. I have found a number of simple designs that would work for 12VDC LEDs, but none for 110VAC dimmable LED lights.LED fixtures that take 110VAC are all different types and designs, and while some come with dimmer options, not all do. There are also different types of "12VDC" lamps, none of which (to my knowledge) is a simple LED. You could, however, operate a servo motor to lower a shade over a panel, or rotate a polarizer, i.e. ignore the electronic range of such devices by... ignoring the electronic parts.
Reply by ●September 23, 20202020-09-23
On Tuesday, September 22, 2020 at 11:46:41 PM UTC-5, Bill Sloman wrote:> n Wednesday, September 23, 2020 at 2:08:15 PM UTC+10, rhor...@gmail.com wrote: > > I need a simple circuit design for a slow fade-in AC dimmer. In a dark theater, suddenly turning on the lights is a somewhat unpleasant experience. I want a simple circuit compatible with 110 volt dimmable LED lights that will slowly ramp the light output over a period of about 5 seconds or so. I have found a number of simple designs that would work for 12VDC LEDs, but none for 110VAC dimmable LED lights. > There is a fairly straight-forward solution, but it isn't going to be al that simple. You need to synthesise a 60Hz AC waveform that can move up to 110V RMS over 5 seconds. > > The Baxandall Class-D oscillator lets you generate such an AC waveform fairly easily. > Modern versions use MOSFET switches, rather than the bipolar transistors, which were all that was available when Baxandall wrote the paper. > > You'd need a fairly high current choke to feed the centre tap, and you'd have to pulse-width-modulate the DC you fed into it to get the five second ramp ramp you want. > > The inductor is going to be a pretty effective low pass filter, so adjusting the width of string of pulses in a 1kHz pulse stream would be all you'd need to do, and your could do that with a very simple and cheap microcontroller. That would be 5000 pulses, so the "on" period would go up by 0.2usec from pulse to pulse. That implies a timing clock that's running at 5MHz or faster, which wouldn't be hard to get.I'm sorry, I should have provided more details. First of all, this is for a home theater, not a public performance / movie theater. It doesn't need to drive a lot of power: maybe 50 watts @ 120V. Secondly, it needs to be small. This has to fit in the top bell of a ceiling fan, and one that already has a wifi controller in it. A "standard" dimmer circuit with the potentiometer replaced by a VCO should work without resorting to a large transformer.> There are lots of other ways of doing it, and you can probably buy something off the shelf - there's lots of stuff available for theater lighting and that's been true for many years - but finding something small and cheap might take time.
Reply by ●September 23, 20202020-09-23
> There are lots of other ways of doing it, and you can probably buy something off the shelf - there's lots of stuff available for theater lighting and that's been true for many years - but finding something small and cheap might take time.I have been looking, and there are a number of off-the-shelf 12VDC solutions for small LEDs, but I have found nothing, yet for 120VAC
Reply by ●September 23, 20202020-09-23
On Wednesday, September 23, 2020 at 12:29:14 AM UTC-5, bitrex wrote:> On 9/23/2020 12:08 AM, rhor...@gmail.com wrote: > > I need a simple circuit design for a slow fade-in AC dimmer. In a dark theater, suddenly turning on the lights is a somewhat unpleasant experience. I want a simple circuit compatible with 110 volt dimmable LED lights that will slowly ramp the light output over a period of about 5 seconds or so. I have found a number of simple designs that would work for 12VDC LEDs, but none for 110VAC dimmable LED lights. > > > You can buy a "DMX dimmer" box off the shelf: > > <https://www.amazon.com/American-Dp-415-Channel-Dimmer-Pack/dp/B000FVZUMM> > > paired with a control box (or PC interface) you can set up fade in/out > programs synced to external triggers as you like. DMX is a > communications standard for theater and stage lighting control.See above. This is not for stage lighting. As it happens, I am extremely familiar with DMX as well as PixelNet and ArtNet. These are not good solutions, here. The unit needs to be smaller than a pack of gum - about the size if a Raspberry Pi Zero, and it only needs to slow the increase of the light intensity. Nothing else.
Reply by ●September 23, 20202020-09-23
On Wednesday, September 23, 2020 at 12:39:09 AM UTC-5, whit3rd wrote:> LED fixtures that take 110VAC are all different types and designs, and while some come with dimmer > options, not all do.I am aware, thanks. Non-dimmable bulbs do not work well with dimmers. 'Big surprise. It is easy enough to buy dimmable LED bulbs.> There are also different types of "12VDC" lamps, none of which (to my knowledge) > is a simple LED.Many are. As a matter of fact, I just installed a 12V wifi dimmer on my 12V LED strips lining the stair step in my theater. I already have wifi control of the ceiling lights. I just need them to come up slowly when turned on. A VCO feeding a Triac / Diac pair should work, but I am unsure of details.> You could, however, operate a servo motor to lower a shade over a panel, or > rotate a polarizer, i.e. ignore the electronic range of such devices by... ignoring the electronic parts.No, no, no. That is going off the rails. All I need is a circuit with a slowly charging capacitor that changes the duty cycle of a Triac.
Reply by ●September 23, 20202020-09-23
On Wednesday, September 23, 2020 at 1:20:28 AM UTC-7, rhor...@gmail.com wrote:> On Wednesday, September 23, 2020 at 12:39:09 AM UTC-5, whit3rd wrote: > > LED fixtures that take 110VAC are all different types and designs, and while some come with dimmer > > options, not all do. > I am aware, thanks. Non-dimmable bulbs do not work well with dimmers. 'Big surprise. It is easy enough to buy dimmable LED bulbs.No, that's not the only option; you can get LED light fixtures that accept low-voltage controls, and safely wire in something that does the brightness slew limiting that you want. <https://www.superbrightleds.com/moreinfo/led-panel-light/2ft-x-2ft-recessed-led-steel-troffer-light-40w-5000-lumens-dimmable/5837/> The dimmer input accepts a zero-to-ten-volt signal.
Reply by ●September 23, 20202020-09-23
On 23/09/2020 05:08, rhor...@gmail.com wrote:> I need a simple circuit design for a slow fade-in AC dimmer. In a > dark theater, suddenly turning on the lights is a somewhat unpleasant > experience. I want a simple circuit compatible with 110 volt > dimmable LED lights that will slowly ramp the light output over a > period of about 5 seconds or so. I have found a number of simple > designs that would work for 12VDC LEDs, but none for 110VAC dimmable > LED lights.Why don't you just get a standard mains dimmer compatible with your dimmable lights and remember to wind the wick up slowly. It doesn't need to be an automatic ramp up if you are the only one using it. -- Regards, Martin Brown