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Background

I made a nice light for my electronics bench using a tunable LED strip and off-the-shelf driver. The strips have interleaved warm and cool LEDs, and is tunable by adjusting how much power is delivered to each color.

The driver I found is very versatile, in that it can be dimmed by a typical wall dimmer, or 0-10V signal, or PWM, etc. But it’s only a single channel, and what I really want is something with Z-wave control. I could put two of the drivers on my bench light, with a couple of Z-wave 0-10V control dimmers, but then those need an additional 24 V supply of their own.

Need

Having had no luck finding an off-the-shelf solution, I’d like to design my own, but I’m struggling to find appropriate ICs or reference designs, in part because there are so many lighting applications and I don’t know the terminology well enough (I do have an EE degree, though).

I want the following:

  • Mains-powered (e.g. 90 - 277 VAC)
  • Flicker-free
  • Compact
  • Controllable (e.g. from an MCU) output power, 0 - 100%
  • Not AC dimmable (no need to support dimming via triac or other means)
  • Easy to add a second (or more) independent output stages
  • Easy to add a low-power 5 VDC supply for MCU

When I go googling, I find things like “Offline controller for LED lighting with constant voltage primary- sensing and high power factor” (the ST HVLED001A). This already implies so many considerations in LED driving. But I suppose the first is, wouldn’t I prefer a (adjustable) constant-current driver, since LED output intensity is proportional to current? Or is that question really moot in this application?

Would it be best to design a 24 V SMPS and then just tack on buck converters?

I guess I’m asking for recommendations of topology, or terminology to use when searching IC websites. Or even part number recommendations.

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    \$\begingroup\$ What on earth is "Z-wave control"? \$\endgroup\$
    – Hearth
    Sep 30, 2023 at 0:29
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    \$\begingroup\$ @Hearth A standards for a wireless network over ~900 MHz. Low speed and meshed to reach long distances. \$\endgroup\$
    – winny
    Sep 30, 2023 at 7:28
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    \$\begingroup\$ Reading control either the output voltage or the output current precisely and reliably, an ST HVLED001A should do fine - but the only circuitry shared between multiple outputs is "bus voltage generation" (and possibly \$V_{CC}\$). In particular, you'd have separate not entirely trivial "magnetics". \$\endgroup\$
    – greybeard
    Sep 30, 2023 at 7:54
  • \$\begingroup\$ @greybeard I just now found this Linear part that does a better job showing what the flyback transformer should look like. I was a little overwhelmed earlier trying to find one. It seems Linear’s data sheets are better than ST’s. \$\endgroup\$
    – Rick
    Sep 30, 2023 at 9:43
  • \$\begingroup\$ You can buy meanwell constant current step down or step up drivers for a few dollars. These take low voltage DC and a brightness signal and apply a proportional current to LEDs. One per color channel and you can easily program the brightness/color temperature however you like. Use a common DC supply for all. \$\endgroup\$ Sep 30, 2023 at 13:30

1 Answer 1

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Due to Kruithof effect, for a pleasant light, illumination intensity (in lux) depends on color temperature.

For example, 3000K is nice at 200lux, but for 6000K to feel nice you need a lot more lux.

This means the usual CCT LED strips, which have the same number of warm and cool LEDs, are not an ideal solution. If you put enough strip length to have enough lux for 6000K to feel just right, then you have way too many warm LEDs, which is a waste of money.

It works better with one CCT strip and one cold white strip next to each other, resulting in 3x more cool white LEDs than warm white.

If you use a CCT strip alone, then there is the problem that most CCT drivers will not allow to use both colors at 100% brightness at the same time. If the driver allows it then the strip can output 2x the power at around 4000K by lighting both LED colors at 100%, which satisfies the Kruithof curve. This produces a light that is pleasant between the warm LEDs CCT and around 4000-4500 but not powerful enough for higher CCT. That's not necessarily a problem, ad 4500K is pretty good for fine work.

Anyway. Do if you DIY your controller it should be able to run both channels at full power and have a more powerful cold white channel.

An off the shelf RGB controller fits the bill. I use mine with 1800K, 2700K, and 5000K LEDs. No one ever said you had to use RGB LEDs only.

For flicker free operation it's more complicated as many controllers still use too low PWM frequency. But with 5kHz and above, there is zero visible flicker.

If you DIY you really don't need to build one SMPS per channel, or use buck converters. One supply with high frequency PWM channels will be absolutely fine.

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