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I have 10 strings of LEDs, string 1 to string 6 have 4 LEDs in series, S7 and S8 have 3 LEDs in series, and S9, S10 have 6 LEDs in series. Each LED has a forward voltage of 3.2 V on average.

I'm going to use a constant current driver that will drive these strings one at a time at a rated current of 250 mA, so I need an IC that can control the strings.

I have chosen a CC LED driver and MAX4656ETA+T SPST switch and have attached a high-level schematic. Please let me know if this is feasible. Error in schematic the COM is connected to V- not V+.

SPST Switch

CC Driver

High Level Schematicenter image description here

I have other implementations with different parts, please consider sharing your opinion on that too

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  • \$\begingroup\$ In your "high level schematic" you appear to switch the LED cathodes to V+? That should be ground. And why not use a simple transistor or logic level FET to do the switching? \$\endgroup\$
    – Unimportant
    Commented Nov 30, 2021 at 10:16
  • \$\begingroup\$ Not everyone can access file storage sites (blocked by wonderful IT), if you post your schematic into the question, then more people can respond. \$\endgroup\$
    – Aaron
    Commented Nov 30, 2021 at 17:40
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    \$\begingroup\$ Why not use small MOSFETs as switches? That would be cheaper than the MAX chip... \$\endgroup\$
    – bobflux
    Commented Dec 1, 2021 at 12:23
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    \$\begingroup\$ You don't need a FET driver for slow switching on the low side, as shown in the schematic. Also this chip specs a max VCC of 36V, not 48V. \$\endgroup\$
    – bobflux
    Commented Dec 1, 2021 at 12:32
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    \$\begingroup\$ Also I have no idea what you want to do: in one question you mention analog dimming, but what is the range of current for this dimming? Or is it PWM dimming? If so, what frequency? etc \$\endgroup\$
    – bobflux
    Commented Dec 1, 2021 at 12:40

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Your idea doesn't seem bad just odd. Yes you could use multiple of those switches to switch the common cathode but you may be better off looking for an IC that has multiple switches in one.

The biggest issue is that you Constant Current boost led driver is designed for 350 mA and can only trim between 75% to 120% (if you get the model with the on board trim). That's 265mA on the low end, which is above your 250mA target.

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  • \$\begingroup\$ The problem is you don't have IC's that are multichannel, rated for 300mA continuous current or the rated voltage is less than what is required. Initial stages I was fixated on Analog Demux and Multichannel SPST switches but after I realized this is not panning out I researched and found a few load switch parts that do the job, like mouser.in/datasheet/2/609/LT3965_3965_1-1716272.pdf from Linear that is tailored for my requirement and also I have considered ST's st.com/resource/en/datasheet/l9026.pdf IC load switch intended for inductive load too. \$\endgroup\$
    – JAGADISH K
    Commented Dec 1, 2021 at 8:12
  • \$\begingroup\$ I have made a BOM comparison too, I had considered using 3 channel 14 linear buck CC drivers that cost 1.46$ too, plus these LEDs are in a circular array so I have considered Boost cc driver for ease of routing. You can find that approach in the following post I made electronics.stackexchange.com/questions/597207/… \$\endgroup\$
    – JAGADISH K
    Commented Dec 1, 2021 at 8:16
  • \$\begingroup\$ The 75% to 120% limitation is only there if you use the onboard trimmer, page 2 figure 2 shows the graph of Output Voltage vs. Output current, the current can be varied linearly when the control voltage is beyond 1.7V roughly. \$\endgroup\$
    – JAGADISH K
    Commented Dec 1, 2021 at 8:24
  • \$\begingroup\$ electronics.stackexchange.com/questions/597207/… electronics.stackexchange.com/questions/597194/… please have look at this too \$\endgroup\$
    – JAGADISH K
    Commented Dec 1, 2021 at 8:27

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