Slow fade-in circuit

On a sunny day (Sat, 26 Sep 2020 14:42:14 -0700) it happened snipped-for-privacy@highlandsniptechnology.com wrote in :

Here is my take, untested:

C2 sets fade-in time.

Disadvantage: needs pulse tranasformer (10 cent upwards from China).

The UTJ circuit is from around 1966 or so, For triggering I think most triacs are fine when triggered positive with negative voltage across those. No idea if it dims all LED lights, my cheap Chinese LED bulbs use a capacitor as current limit in series with a bridge with the LEDs in it directly on the mains, no other parts, should work.

Wave form drawings should explain.

Other disadvantage is the series resistor for the 12V, but it basically only charges the cap, the PNP is a linear current source to charge the cap, not many mA needed

You can replace the resistors on the PNP with a pot for brightness adjustment.

Circuit resets at each zero crossing of the mains and causes a trigger pulse sooner (brighter) or later (dimmer) in each half cycle.

Would a ISDN transformer work as pulse transformer ;-)?

g it would require great thermal contact to be effective in slowing interio r heat-up, most THs aren't a good shape for that. Laser slice them? :)

closer to the point where it dims, ie lower mains v, and Xc + Rth is going to be larger at any time during warm up. And if you really must you could slow it yet again with a PTC Thermistor across the bulb.

That is fun! Do NTCs, PTCs have lifetime, number of uses limits? (I know I could search on DK... but that's work. :^)

George H.

On Wednesday, September 23, 2020 at 12:08:15 AM UTC-4,

eater, suddenly turning on the lights is a somewhat unpleasant experience. I want a simple circuit compatible with 110 volt dimmable LED lights that w ill 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 n one for 110VAC dimmable LED lights.

Can't you just use an Alexa (Amazon Echo) compatible light bulb and run a q uick script?

Each bulb is addressable.

Yes, the shadow mask degaussing coil around CRT color tubes was often fed by a PTC/NTC thermistor combo. Mostly reliable but switching on and off repeatedly before they had reached thermal equilibrium was said to kill them.

piglet

Were they separated or thermally coupled?

why would anyone design that into an LED lamp? What for?

NT

Life was not infinite, but a colour tv where one had failed was uncommon. However bear in mind that TVs were generally cost sensitive machines, if you run your thermistor half as hot the metallisation does not oxidise.

I'm trying to remember. I think there were both separate -istors & then 3 legged blocks. I'm not sure it makes much difference, the short heatup time isn't going to transfer significant heat from one to the other.

NT

It's common for them to have a bridge rectifier and a linear IC voltage regulator. Or even some passive-part current limiters.

Thermally coupled in one packaged three terminal module.

piglet

OK, the OP's home theater is ~ a TV.

I made this thermistor pressure sensor, kinda a pirani gauge*.. but just a lm317 current source into a ~10 k NTC and measure the voltage. It works from atm. down to ~0.1 torr.. it's sensitive (on the high pressure end) to the outside (vacuum can) temperature.

George H.

So I'm guessing not made anymore.. or not for less than $1. George h.

I did some testing, and the dimmable LED bulb I used did not turn on with

Meanwhile, pending testing, I am leaning toward a PWM oscillator with a vol tage controlled duty cycle fed by a simple voltage integrator, pending the results of the high voltage testing. It is already clear a simple AC or DC voltage ramp is not going to work well. Pity

I am sorry, but I am having a very hard time making out your diagram. It is very dim, and no offense intended, but the writing is not very legible.

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.

quick script?

Well, that is a thought. I am using Google Home, but that is an insignific ant detail. The advantage would be the color temperature could be controll ed as well as the intensity. They are fairly expensive (~$60 for a 4 pack) every time one needs to be changed, but hopefully that would not be very o ften. I would need to bypass the existing controller, which is an idea tha t doesn't thrill me much.

I will need to consider this. I also need to do a little testing with one of my smart dimmers.

PTCs definitely do; the motor start circuit in my fridge konked out a few years back, and (1) GE parts department didn't have any stock, (2) it was available on eBay only after I identified the 120V version (Chinese electricity is 220V, and there's a LOT of 220V motor-start PTC aka "relay" available). Before the part came in the mail, I'd been tripping over ice chests in the kitchen for almost a week.

PTCs, though, ARE cheap; I got half a dozen spares.

If'n you want a light to come up slow, resistive can work for you, but not if you want it to dim gently as well.

On a sunny day (Sun, 27 Sep 2020 17:22:01 -0700 (PDT)) it happened " snipped-for-privacy@gmail.com" wrote in :

Yes, my apologies, should have taken into account many of you earthlings still have simpler display system. Do have a much higher resolution original, but just to simplify things it is just an unijunction transistor generating trigger pulses for a triac. If you type unijunction transistor triac trigger circuit in google and then select 'images' you see plenty of examples. The charge current in the timing capacitor sets the firing angle. These days (but I still have some UJTs here) I would likely use a small PIC micro-controller and use it comparators to detect zero crossing of the mains, and do the fade-in in software, generate the trigger pulse in software, maybe add a transistor to drive the pulse transformer.

As to the LED light circuit diagrams, here is the circuit of the ones I bought on ebay from China:

oltage controlled duty cycle fed by a simple voltage integrator, pending th e results of the high voltage testing. It is already clear a simple AC or DC voltage ramp is not going to work well. Pity

no such thing is clear, but a current ramp-up works much better.

NT

drop it in ice :)

, let alone 3, but I am game to look at anything.

with up to 450V input and 300ma output. It only requires 13 external compon ents, all of which can be 1206 SMDs except for a small inductor. This makes a trailing edge MOSFET based dimmer using a 555 practical. It's $2.24, but I can handle that.

According to a summary published in one of the industry mags, the dimmable LEDs contain this circuit or something similar. It has PFC correction as we ll as an algorithm to decode the RMS input from a conventional TRIAC dimmer to a current drive for the LED.