230V LED driver circuitry without inductor?

[T_guttata]

Hi

To drive LEDs from 230V you can take some sort of step down converter to get 12V DC: https://de.aliexpress.com/item/1005001988211867.html?spm=a2g0o.productlist.0.0.47c365de7iEc9N&algo_pvid=aa40d580-f666-4511-9ee0-b505de900e78&algo_exp_id=aa40d580-f666-4511-9ee0-b505de900e78-11&pdp_ext_f=%7B%22sku_id%22%3A%2212000018326482933%22%7D
Those designs usually need an inductor and a capacitor. You then need to control the current, for example with a resistor or dedicated IC.

There are as well some LED PCBs available which can be powered directly from 230V and judging from the pictures, they do not need any inductor or capacitor: https://de.aliexpress.com/item/32974901441.html?spm=a2g0o.productlist.0.0.67ab7315EfrFFx&algo_pvid=29b75736-800c-4a8a-9994-4dd945e341d3&algo_exp_id=29b75736-800c-4a8a-9994-4dd945e341d3-22&pdp_ext_f=%7B%22sku_id%22%3A%2266726861442%22%7D

Can anyone explain how that works or provide a circuit diagram? What is the "state of the art" way to drive LEDs directly from 230V?

Thanks!

[langwadt]

The LED is actually a larger number of LEDs in series so the forward voltage is close to the 230V supply

[T_guttata]

230/2.7 = 85 LEDs. Don't think they fit 85 LEDs on that PCB, if you count on the picture there are actually 24.

[mariush]

There's 24 leds in the pictures in your links, so that works out to around 80v ....

You have rectified AC output  so 120 times a second the output voltage goes from 0v to some high voltage and then down again - there's very low capacitance on the output so there's high voltage only for short periods of time, let's say 4ms out of every 8 ms (if we go with rectified 60 Hz AC) 
The leds in series need at least 80V to turn on, so the leds are off until the voltage goes up to 80v then that driver's pass transistor limits current and probably turns off once the voltage goes above some threshold ... so for example, the leds may only work between 80v..150v and then again on the 150v...80v  .... and since the driver doesn't work continuously, it has time to cool down.


Here's something that uses a similar driver chip, there's schematic at around 4 minutes in :

[T_guttata]

Thanks, I got the principle. Basically you just use a portion of the sine half wave.

Is this the state of the art way to drive LEDs from 230V? What's about efficiency?

[mariush]

There's some led driver chips which add leds (well, short out sections of the led strip) so that the forward voltage of the led chain is adjusted as the rectified dc sine wave peak changes.   

So you get 20v light up from 60v to 90v , then 30 leds from 90v to 120v and so on...

Best would be to use a buck driver (with inductor outside, mosfet and diode in driver chip or outside) as it also solves the power factor issue, allows dimming etc

[T_guttata]

Does anybody know the name of a quality chip? In the video, there is the SM2082 which seems to be a chinese chip.

[mariush]

Is it that hard to research chips on electronic distributor stores like Digikey, Mouser, Newark/Farnell, RS-Components, tme.eu etc?

digikey : https://www.digikey.com/en/products/filter/pmic-led-drivers/745

farnell : https://uk.farnell.com/c/led-lighting-components/led-driver-ics?searchref=searchlookahead

mouser : https://eu.mouser.com/Search/Refine?N=13413255

tme.eu  : https://www.tme.eu/ro/en/katalog/led-drivers_112848/

rs components : https://uk.rs-online.com/web/c/displays-optoelectronics/led-lighting-system-components/led-driver-ics/?sra=p

[T_guttata]

You are right, that's easy. What's more challenging is to filter the 7k chips. Maybe I should have asked differently: For what type or topology do I have to search?

[mariush]

All websites have filters.

If you want led drivers for AC lightning, you can probably rule out led drivers that work with maximum 5-10v input voltage, you can probably rule out led drivers with more than 2 channels, you can probably rule out boost / step-up drivers as you'd have a high voltage already ... that will narrow your selection a lot.
You can further filter by minimum and maximum current (ex you don't want chips that do max 10mA, when you plan to use 50mA leds), or by other things and not to forget, also by price per quantity (ex cheapest if you buy 100pcs)

Then, you can sort by other things like maybe quantity available in stock which may be a hint that part is popular (but these days lots of companies have low stocks of chips), or by maximum current the part can handle.

You would also end up with a small selection of companies that make those led drivers, and from there you could go to the websites of those companies  and some will have a catalogue of such chips or parametric search through these driver chips.