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I need to convert a digital signal generated from a microcontroller GPIO (0-3.3V) to a high-power (15-40W) current signal to drive an LED chip for illuminance, where the signal frequency can range from 1kHz to 1MHz.

The goal is to utilize the optical channel for data transmission while fulfilling the constraints of regular illumination. Digital data will be encoded in the LED with on-off keying at a high frequency and at the same time maintain a flicker-free and stable illuminance, so the current must be very stable.

How should I design the circuit?

Will the below design using a constant current driver, a voltage-controlled SPDT work? The clock signal in the diagram is supposed to be

enter image description here

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  • \$\begingroup\$ The frequency impacts the amount of data that can be piggybacked. So in general the higher the better. I put a 1MHz limit here because that's the limit on the receiver end. \$\endgroup\$ Commented Aug 9, 2023 at 15:06
  • \$\begingroup\$ Why not say "optical data transfer" instead of illuminance? Please also supply the data sheet for the LED. \$\endgroup\$ Commented Aug 9, 2023 at 15:08
  • \$\begingroup\$ Both requirements are important, illuminance is like the constraint, while optical data transfer is the quantity to be optimized. Let me rephrase the question to clarify that. \$\endgroup\$ Commented Aug 9, 2023 at 15:11
  • \$\begingroup\$ I am not absolutely sure, but I am assuming the LED chip is not the most important part here, as I would want to make the design work for a large variety of LED chips, but I will probably be using the Cree XLamp CHA0825 for this particular implementation which can be found here cree-led.com/?s=cha0825 \$\endgroup\$ Commented Aug 9, 2023 at 15:15
  • \$\begingroup\$ @greybeard Was going to comment the same but what if you would sense only in the blue spectrum? The blue light wound shine though the phosphor and go on-off before the phosphor would react. \$\endgroup\$ Commented Aug 9, 2023 at 15:31

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Typically this is done by shunting the LED. The current source doesn't care, of course (as long as it responds fast enough to changes in load voltage, anyway; this is not a guarantee, and depends on design), and it saves one pole off your example (as the LED doesn't need to be open-circuited when "off").

Actually, it's an improvement, not to open-circuit the LED, but to discharge it -- device capacitance and stored charge will cause it to continue glowing for some time (100s ns? µs?) if left alone, but shorting it out solves that.

schematic

simulate this circuit – Schematic created using CircuitLab

(drawn with default component types only; just showing topology)

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  • \$\begingroup\$ Thanks for the answer. It also solves my problem to find a low-cost SPDT that can handle the power. \$\endgroup\$ Commented Aug 9, 2023 at 15:42

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