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Transformerless power supplies circuit, cheatsheet and questions

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StillTrying:

--- Quote from: waste on February 07, 2019, 10:30:20 pm ---how did you simulate the spikes? Do I get it correctly that square wave is kind of a worse scenario than sine wave?
--- End quote ---

I've added the .asc to the graphs post, it's very rough!

"Capacitive droppers are current regulated, which is exactly why I find them so sexy for the LEDs."

The cap drops the smooth sine wave, but any fast edges go straight through the cap, leaving the 470R and 33u cap/LEDs to do nearly all of the spike's dissipation.

Cliff Matthews:

--- Quote from: StillTrying on February 08, 2019, 12:25:27 pm ---
--- Quote from: waste on February 07, 2019, 10:30:20 pm ---how did you simulate the spikes? Do I get it correctly that square wave is kind of a worse scenario than sine wave?
--- End quote ---

I've added the .asc to the graphs post, it's very rough!

"Capacitive droppers are current regulated, which is exactly why I find them so sexy for the LEDs."

The cap drops the smooth sine wave, but any fast edges go straight through the cap, leaving the 470R and 33u cap/LEDs to do nearly all of the spike's dissipation.

--- End quote ---
Might this be the prime reason why so many "guaranteed for 20-years" LED bulbs last for approximately 2-days after the average bloke throws out his proof of purchase receipt?

StillTrying:
"Might this be the prime reason why so many "guaranteed for 20-years" LED bulbs last for approximately 2-days"

I don't know. I bought some coloured GU10 1W or 3W LED bulbs about 11 years ago, a lot of the time I was switching them on and off by twisting them in the sockets, so quite a bit of flickering and arcing.
Red, Green and Yellow are still OK, White has been on for about 7 years and is now very dim.
Blue only lasted about 2 months before going VERY dim, but I kept it - just in case! I can't really see the few components in the glass neck, so I'll squash it in a vise. :)

Squashed.

waste:

--- Quote from: StillTrying on February 08, 2019, 12:25:27 pm ---
--- Quote from: waste on February 07, 2019, 10:30:20 pm ---how did you simulate the spikes? Do I get it correctly that square wave is kind of a worse scenario than sine wave?
--- End quote ---

I've added the .asc to the graphs post, it's very rough!

"Capacitive droppers are current regulated, which is exactly why I find them so sexy for the LEDs."

The cap drops the smooth sine wave, but any fast edges go straight through the cap, leaving the 470R and 33u cap/LEDs to do nearly all of the spike's dissipation.

--- End quote ---

Aha! gotcha. So a an appropriate zener diode even if it's higher rated than the Vf of the LED's will help ease the stress on the capacitor

The problem with my live circuit is I have to create spikes myself (using a switch probably) as the 2 transformers will act as filters for the circuit :)


--- Quote from: Cliff Matthews on February 08, 2019, 02:26:07 pm ---
--- Quote from: StillTrying on February 08, 2019, 12:25:27 pm ---
The cap drops the smooth sine wave, but any fast edges go straight through the cap, leaving the 470R and 33u cap/LEDs to do nearly all of the spike's dissipation.

--- End quote ---
Might this be the prime reason why so many "guaranteed for 20-years" LED bulbs last for approximately 2-days after the average bloke throws out his proof of purchase receipt?

--- End quote ---

There are many reasons LED die so quickly . First off the 20.000 hours rating goes for those red/green 3-5mm LEDs with top 20mA, on the others your milage may vary :) Then you have issues with the power supplies failing, but mostly with what I have seen the problem lies into bad heat management. Not only because of smaller spaces and smaller heatsinks, but also because the manufacturer wants to push as many watts as they can into the same amount of LED's, and that way they overdrive them creating even more heat in the process.

Like StillTrying said, lower rated LED's tend to survive more. I had a 8watt GU10 failing after a month (I was sure it was going to end that way), but his 3watt siblings still go on with no problems.

To my experience these new "filament " LEDs in sensible Wattages (4-6watts) tend to be quite sturdy

StillTrying:
"The problem with my live circuit is I have to create spikes myself (using a switch probably) as the 2 transformers will act as filters for the circuit"

Having another switch between the transformers and cap dropper will probably do.

Are you going for maximum LEDs protection, minimum components, or maximum efficiency.

Using a 2N3904 as a constant current generator provides quite a bit of switch on and off current protection for the LEDs, Green. Blue is the mW dissipation in the 2N3904.
It would still need some HV ~50V clamping across the 33u to survive very bad switch offs.

In my endless flashing LEDs experiments I've put 500-800mA through 5mm LEDs for a few us at a time, unfortunately I don't know how well they survive 200-300mA for a few ms at a time.

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