Hacking the WS2811 for Arduino controlled project

Other Hardware Product Design
1

Hi Everyone! Thanks in advance for any and all help!

I need to use WS2811 ICs to drive slightly amplified loads in each of the three channels (R, G, and B). At 5V, the data sheet for WS2811 says that those channels will drive constant current of 18.5ma each (by design for one LED). What I want to do is have each channel drive about 80ma each (in addition to the 18.5ma synced by the IC). The plan is to have 4 LEDs in parallel on each of those channels at 20ma each (totaling 80ma each).

Here is a chicken scratch circuit (see attachment) I came up with for ONE CHANNEL (red) on the WS2811. This is just the circuit for the channel… yes there is more to it for the WS2811 itself and hooking up to the Arduino, but that part I’m confident I have right. The question is… is this going to work with a PNP transistor like I have here? Something about it feels wrong like I might be missing resisters somewhere or something. But the chip would basically be syncing the base of the PNP at a constant current of 18.5ma.

The following requirements are very specific and can’t be changed: Must use the WS2811 chip, must drive 4 - 20ma LEDs on each channel, and the circuit must be 5 volts.

Thanks!

pnp-transistor-concept.png
pnp-transistor-concept.png1059×950 121 KB

2

Why not just address each of the four the LEDS separately?
If a separate driver is really necessary, just plonk a resistor and FET on each output.

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The two things I’m trying to balance is cost and efficiency. I do have plans to drive much higher loads with mosfets for a different application. But mosfets are expensive. I want to replicate this design I’m showing here maybe as much as a few hundred times. I was hoping a cheap PNP could provide the amplification i needed. Addressing each led is also overkill because that means more WS2811 chips which is also expensive. I know the answer must be fairly simple here I’m just missing it.

4

You want a "current mirror" circuit.

Or just 4 WS2811's driven with the same data.