Slow fade-in circuit

mandag den 28. september 2020 kl. 22.41.59 UTC+2 skrev John Larkin:

te

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

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

le LEDs contain this circuit or something similar. It has PFC correction as well as an algorithm to decode the RMS input from a conventional TRIAC dim mer to a current drive for the LED.

od is a 700mA CC on a low wattage bulb.

bay, replace the slider with an LDR, and control it with a cheap Arduino or something. Any more effort than that isn't worth it.

I assume they have switched to much longer strings of LEDs so they don't ha ve to drop much voltage

te

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

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

le LEDs contain this circuit or something similar. It has PFC correction as well as an algorithm to decode the RMS input from a conventional TRIAC dim mer to a current drive for the LED.

od is a 700mA CC on a low wattage bulb.

bay, replace the slider with an LDR, and control it with a cheap Arduino or something. Any more effort than that isn't worth it.

My point was not to use the LM3450, but to justify using this piece of crap :

Get it?

Probably so. The fake Edison lamps have a *lot* of LEDs in series.

There is some common, ultra-cheap current limiter IC. I can't recall the part number.

I wonder if a soft start circuit would work for this. My 3.5 HP router has a lovely startup action instead of the big unnerving jerk when you pull the trigger

You mean the lockout, or the converter? You can manufacture a universal-input bulb for 100-220 VAC for one thing. You can accommodate (some?) triac dimmers. Here's a data sheet:

This one doesn't lock out exactly but it senses low mains voltage and enters a power-saving mode, though the context is supposed to be either near the zero-crossings of the mains, and/or when it's being fed a leading-edge chopped waveform with a relatively high peak but low RMS.

So not sure exactly what would happen if it was fed from just an inline thermistor.

The "best" way to do it if a switcher is going to be used is to have high-voltage LEDs that have a string integrated into a common substrate and use a boost rather than a buck or buck-boost, and boost the rectified mains up to say 400 from 270.

Boosts are just simpler and more efficient in this context than bucks or buck-boosts.

And ideally have no electrolytic filter caps in the circuit, or no caps at all, even. There are research papers to that effect idk if it's done in any commercial products, though.

This chip drives series-parallel strings with current regulators but tracks the mains voltage, turning them all on at the peak and less on the slopes. Decent efficiency with no magnetics and would probably work OK with a thermistor limiter.

http://

The 12VDC supply is provided by an MP9488GS-P Buck regulator. U1 integrate s the 0V differential signal provided by R1 - R4 with a time constant deter mined by R5 and C1. C2 provides a delay, keeping the output of U1 high unt il C2 is charged to 6V by R4 (~2ms). Once C2 is charged, the output of U1 slowly decreases from ~10V to ~2V over a period of 5 seconds. U2 inverts t he slope of the signal from U1 and produces a necessary offset. Its output changes from 4.5V to 12V over the same 5 second time period. The 555 time r X1 operates as a short pulse generator, creating pulses a few microsecond s wide approximately every 8 milliseconds. Transistor Q1 prevents X1 from generating any pulses until C2 is charged to ~1.4V by R8, allowing time for the 12V buck converter to settle before X1 begins operation. X2 is config ured as a variable pulse width monostable timer triggered by Q2 from the sh ort pulses produced by X1. The output of X2 is held high by the internal f lip flop until the voltage across C6 rises to be greater than Control volta ge, which is the output of U2. Initially, the output of U2 is within 1/2 v olt of the Trigger voltage, so the voltage across C6 reaches this value ver y quickly. As time passes, the Control voltage increases, causing the outp ut of X2 to remain high longer and longer, increasing the duty cycle to nea r 100%. The output of X2 drives Q3, causing M1 to turn on whenever X2 is h igh.

"Hmm. We?re having trouble finding that site.

We can?t connect to the server at http."

That was a typo. I deleted the old message and replaced it. Try the new o ne.

it turns out LED light bulbs can work on 170VDC, then I have cobbled together a circuit I think might work. Please take a look at the link below and see if any o f you can find any issues with this.

supply is provided by an MP9488GS-P Buck regulator. U1 integrates the 0V differential signal provided by R

For want of a micro controller the kingdom was lost.

I thought about using a PIC. They take time to boot, though. I could supply power full time, but I am sort of avoiding that.

Yea they "boot" in like half a microsecond.

And how long does the buck regulator take to come up?

That has not been my experience. I haven't done a huge amount of work with PICs, and I have never created a design with one, but the ones I have used (DMX and WS3811 Pixelnet controllers) take several secomds.

I have set the startup delays for about 50 milliseconds. According to the circuit emulator I am using, that is enough for the start-up transients to settle and the control capacitors to charge to their working values. If I set the holdoffs lower than that, I get some instability which might cause some noticeable flicker when the circuit is first energized.

There are 2 ways that can go:

1. Little to no flicker & low pf
2. Good pf & heavy flicker

NT