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I want to create a multiple Channel Current Sink which is switchable. I already have 2 designs, but i am not realy happy with both of them. Maybe some of you guys have a Idea how to improve one or a totally different idea. The main idea is to trigger LED for a specific period of time with a defined current.

Number 1: Idea 1

This is the one with the internal Multiplexer.I know what you will probably think about the Mux in the control loop. But my intention is to Shut down the DAC to 0 so there is no Voltage Output of the OPA. Also i want to preload the Rset to around 1 mA to shut down all errors and offsets. Later i want to out this error out by just put 1 mA more on the DAC Output.

Number 2: Idea 2

This is the one with the external MUX and a dummy Load. The dummy load starts the circuit and later i switch one led channel on and take the dummy laod off. The sink is most of the time on. Here is my problem that the FET´s are floating at the beginning and if a LED fails or burns through they are not on a specific voltage level.

So to put it all together: Problem number 1: MUX in control circuit Problem number 2: Floating FETs

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  • \$\begingroup\$ Would it be acceptable to control the LED brightness with PWM rather than a controlled DC current? \$\endgroup\$ – The Photon Apr 4 at 20:05
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The circuits you show are not multichannel in the sense that you are controlling the current in each LED independently and in parallel.

Instead you are controlling the sum of the current through both LEDs with no assurance that the current split between them is equal.

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  • \$\begingroup\$ I just want one LED to be on at a Time, so practically i want to switch the led channels. \$\endgroup\$ – Valentin Huppertz Apr 5 at 7:43

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