0

I'm working on a power stage (LED driver) that could manage 4 different LEDs color string. Each string is composed by 6 LEDs in serie. See the image to have a better idea:

enter image description here enter image description here

The schematic is composed by different components, and I can not consider to make 4 different circuit for each color.

To drive these strings I need at least 20.4 V in output and a maximum current of 30 mA.

Do you know a demultiplexer that has this specification?

  • Vcc>21V
  • Iout_max >= 30mA

Otherwise, is there another idea to manage 4 different color with only 1 driver?

Thank you very Much

Edit: Thanks Everybody for the feedback. Here you will find the schematic of the output:enter image description here

The flag Out+ indicates the output of the driver (the source of a P-mosfet). Below you will find the forward voltage of a single LED when the current is 20mA:

  • Red: 2.1 V
  • Green: 3.1 V
  • Blue: 3.1 V
  • White: 3.15 V

The LEDs are connected by common cathod.

The goal is to add a component between Out+ and the colors, in order to select which string has to be ON. Please, note that only one string at a time remain ON.

Cheers

Edit V2:

I found this high speed analogic switch: DG411 Datasheet: https://www.mouser.ch/datasheet/2/427/dg411hs-1815624.pdf

Could this be a elegant solution?

LucaMon
  • 43
  • 5
  • 1
    Please provide a schematic showing how the LEDs are connected, as well as links to the manufacturer's datasheets for the LEDs. – Elliot Alderson Jul 12 '21 at 15:47
  • There are power shift registers like the TPIC6C595. If you really want a demux, combine a logic device with stronger drivers. – CL. Jul 12 '21 at 19:03
  • Please do the schematic, they are a lot more symbols then colors and almost all of us understand them. Frizzy pictures do not count. At this point there are probably a hundred or more answers to your question, please narrow it down with details like voltages and loads. – Gil Jul 12 '21 at 19:41
  • Why do you need to connect these things directly to a demultiplexer? Why can't you put a transistor switch on each string and connect the switch gates to a demultiplexer? You are trying to solve this problem the wrong way IMO – user253751 Jul 13 '21 at 08:17

2 Answers2

0

I think you are trying to solve this problem the wrong way. You don't need a high-power demultiplexer.

And 21V, 30mA is barely high-power anyway. It's only high-power relative to logic circuits. Anything designed to handle power will have no trouble handling that.

What you do need is a component to turn each string on and off, and then a separate component that demultiplexes. In fact, if you have 4 output pins available, you don't even need the demultiplexer. Just build it like this:

schematic

simulate this circuit – Schematic created using CircuitLab

(please ignore that I didn't delete the automatic numbering from every LED. The LED numbers are irrelevant.)

Use a logic-level MOSFET - pay attention to the gate voltage so that it turns on properly when the controller outputs a high signal. Some MOSFETs require quite high gate voltages to turn on all the way. Although at only 30mA, maybe it doesn't even matter very much.

user253751
  • 11,998
  • 2
  • 21
  • 37
0

Thanks a lot for your answer @user253751

I will probably do this way, with a little change:

The cathodes of the load are in common, and this can not be changed. So, I will put the mosfet before the string, with this configuration:

enter image description here

With the Opamp, I'm sure that the voltage turn on the mosfet.

LucaMon
  • 43
  • 5