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Refering to my previous question, I want to drive a bunch of High power LED drivers (Datashsheet AL8860WT-7) With a Pixel-IC (Datashsheet P9813).

This is my concept: enter image description here

My project so far: connecting the R, G or B Pin of the Pixel-IC directly to the driver does not work, as these pins seem to need some kind of a Pullup or other things which I simply don't know. This is the from the P9813 Datasheet: enter image description here The resistor RB seem to work like a Pullup in this case, but I can't figure out, how this would work with the AL8860 Driver. This Driver needs a PWM signal > 2.5V to switch the load with full current. When I connect the P9813 with the pullup-resistor (RB=2.2k) shown above, I get a constant voltage of about 1V at the drivers' input with a ripple of about 0.1V. This is the circuit so far: enter image description here

I would be very happy to figure out:

  • Do I have to use a transistor to switch the driver?
  • if no: What do I have to change?
  • if yes: would I rather use a bipolar transistor or a mosfet? these cheap levelshifting modules for example often use BSS138 mosfets for I2C stuff etc... Unfortunately I have these only in a SOT-23 package laying arround and its a pain to get these tiny chips working on a breadboard.

Your advice will be highly appreciated!

edit: I have successfully used a Bipolar transistor to get the driver to work with the P9813, but with a inverted signal. So I thought I'll use two transistors to invert the signal twice.

This is my latest schematic: enter image description here Would this work ?

kokospalme
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  • So in your previous question the problem was that the "MCU" was actually a constant current LED driver? And your goal is to take the 10 or 20 mA drive current and turn that into a 0-2.5v control signal for a second LED driver? Is that right – user1850479 Jul 16 '23 at 20:50
  • No, in my previous question the mcu was given a pwm signal to the driver. Now it's a Pixel-IC that is producing the pwm signal (4500hz btw) for the driver. – kokospalme Jul 17 '23 at 07:50
  • Can you show an actual circuit diagram of the connections? The constant current outputs on your driver just pull current to ground, they don't produce a voltage, so you need to provide a voltage source (the pull up to VCC). Voltage should be VCC-current * resistance. – user1850479 Jul 17 '23 at 15:57
  • schematic has been added :) – kokospalme Jul 18 '23 at 07:36

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