Transformerless power supplies circuit, cheatsheet and questions

[StillTrying]

how did you simulate the spikes? Do I get it correctly that square wave is kind of a worse scenario than sine wave?

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]

how did you simulate the spikes? Do I get it correctly that square wave is kind of a worse scenario than sine wave?

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.

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]

how did you simulate the spikes? Do I get it correctly that square wave is kind of a worse scenario than sine wave?

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.

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

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.

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?

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.

[waste]

"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.

I did just that (added a switch), but the results were not spectacular The spikes (after the cap) were very short and even though I couldnt measure current, I can't really see the LEDs being damaged by it.

My aim is a) led protection (as they are not replaceable if they burn encased in concrete) b) low parts count. (consumption is pretty low anyhow less or close to a watt)

In my test circuit I went for an X2 of .22μF (so around 22mA peak to peak with no capacitor) and a 100μF/100V smoothing capacitor I had around. For extra protection I added a 20V 0.5W zener I also had around (the 6LEDs I used are a bit lower voltage than on LTspice, all together they run at 17.6V for 15mA) and a 1watt in rush resistor of 1K .  This created a quite a minuscule ripple of around 700mV and an average of 14mA. So in normal conditions this circuit will run for ever.

After 30 minutes of use I checked the temperature of the components with the scientific method of the back of my finger (after powering off) and none was over body temperature.

So to sum it up, bigger capacitors help with inrush currents, but not with spikes from other devices during operation. For that, a zener (better 1Watt)  or a MOV you used in your own circuits is a better solution.

Zeners are also quite nice for troubleshooting. If I have another failure and the LED dies first (that's the most accepted mode of failure from the people here), the zener will clamp the voltage to 20V and the capacitor won't blow.. I'm really troubled by the failure because at home I have 3-4 of these circuits running for years 24/7 no problems, and have given another 3-4 as presents in the last 2 years with no problems. Maybe my friend with the 2 dead ones lives in a particularly (electrically) noisy house



I'm really touched by your transistor idea, I remember reading about it in talking electronics and still use it from time to time when I need a specific amperage value from an LED. It was actually this type of circuit that made me understand that transistors are current regulating devices (before that I was treating them like Mosfets ie amplifiers/ switches)
http://www.talkingelectronics.com/projects/200TrCcts/200TrCcts.html


But I always thought of it as a current limiter solution for batteries and other voltage limited devices (like 5V power supplies). So  your idea is to use a bigger X2 capacitor (like a .33μF) and then current limit the LED's with the transistor. This way you can actually get away with a smaller capacitor.

extra bonus, the transistor circuit can also be used with low voltage power supplies.

I will play with ltspice a bit and report back, but for my current construction phase (I have promised 5 of these concrete cubes lol and want two for myself too) I will go without the transistor as most of the concrete cubes are ready (and have limited space for electronics) and I want to declutter my "lab" (i'm sure you have also experienced this urge)




thanks again for all the input.

[StillTrying]

The MOV circuit is not mine, it's an 11 year old 20 blue LED GU10 I 'opened.', I'll photo it if you want to see its simple construction.

I don't think voltage clamping gives all that much protection with only a small number of LEDs in series, because a small increase in the LED voltage gives a much larger increase in the LED current.

This is the best max. protection and min. components so far, - still using a transistor I'm afraid.
It limits the now 400V 1kV spikes to peaks of 40mA 55mA through the 5 LEDs. R4 (10R to 22R) is not essential, it just spreads the spike's dissipation around itself, the 33u and TR a little bit.
For long life I'd think you have to consider C1 and C2 losing about half of their capacitance, and the solder joints on TH LEDs seem to have a very high failure rate.
I don't think any of these simple circuits would survive a continuously arcing switch, even a MOV would eventually give up.

[waste]

I ve found the perfect candidate for a test. I want to install nightlights for our common workshop, a place with so much noise from switches and motors etc, that it will be a perfect test bed .

On the one night light I will use the "classic" circuit improved with a zener for clamping and a high voltage capacitor.

on the other one i will try your last circuit with the transistor. I have a question though. In the diagram you posted as also in the talking electronics page, http://www.talkingelectronics.com/projects/200TrCcts/200TrCcts.html#15
the LEDs are placed in the collector side of the transistor, while in your LTspice file you have put the LEDs on the base side of the transistor.

So in the LTspice file, if I get it correctly, the transistor doesn't regulate the LED current, just the overshoot current from the spikes.

For added protection I will also add a 1watt zener on your circuit, after thee capacitor

I will build both, hang them on the ceiling and see which one gives in first in this brutal environment (I designed them that way, that they will be easily replacable if/when fail occurs.

[StillTrying]

"while in your LTspice file you have put the LEDs on the base side of the transistor."
"if I get it correctly, the transistor doesn't regulate the LED current, just the overshoot current from the spikes."

Yes, in theory.

When the current through the LEDs and 22R reaches ~27mA the transistor starts to turn on and draw the extra current through its collector. In the plot added to post#31 I've increased the simulated mains spikes to 1kV causing the transistor to clamp 600mA.
Once you get up to about 20 LEDs in series the voltage change between running current and over current becomes larger so a simple zener or MOV voltage clamp works well enough. Good luck.