Hi, my first post here after reading lots of useful posts by others.
I'm hoping to learn how I can use a Meanwell LDD-700L constant current device in a circuit that employs a microcontroller and a Darlington array to choose among several LED series circuits that will be driven by the LDD. Here's the setup:
The microcontroller's GPIO pin is used to turn on one of the LED channels via a control pin of the Darlington array, and another GPIO pin of the microcontroller is used for PWM dimming using the LDD's DIM pin. I haven't been able to get this to work properly (i.e. nondestructively :-} ) due to what I think is a grounding problem with my circuit design.
The Darlington array and the microcontroller share a common ground. The LDD Vin- pin is used as ground for the PWM dimming signal from the microcontroller as indicated in the LDD documentation. My goal is to use one LDD to power each of the LED circuits (one at a time) and then to also use the microcontroller to use PWM to control the average power of the output of that circuit.
I'm unsure about two aspects of this: (i) the LDD uses Vin- for the ground reference of its DIM pin, and (ii) the LDD datasheet says that the Vout- terminal must not be connected to the Vin- terminal.
My problem is that the ground pin of the Darlington array has two roles: it serves as the return path of the constant current provided by the LDD Vout+ pin, and it also serves as the ground reference for the channel selection signal from the microcontroller. This then means that Vin- and Vout- are both connected (indirectly) to the microcontroller ground (i.e they are both connected together), violating the datasheet injunction against doing this. This setup works fine using a different buck power supply (e.g. a BuckPuck) where the danger of Vin- being connected to Vout- is not relevant.
I'd like to learn how I can modify the circuit to allow use of the LDD. I've thought about connecting the GPIO dimming pin and ground of the microcontroller to the input side of an optoisolator and then connecting the optoisolator's output to the DIM pin and Vin- pin of the LED. This would appear to isolate Vin- from Vout- of the LDD
Is this a reasonable solution, or would some other approach be used? Would it help if I posted a rough sketch of this circuitry?
Thanks, eeLight
I'm hoping to learn how I can use a Meanwell LDD-700L constant current device in a circuit that employs a microcontroller and a Darlington array to choose among several LED series circuits that will be driven by the LDD. Here's the setup:
The microcontroller's GPIO pin is used to turn on one of the LED channels via a control pin of the Darlington array, and another GPIO pin of the microcontroller is used for PWM dimming using the LDD's DIM pin. I haven't been able to get this to work properly (i.e. nondestructively :-} ) due to what I think is a grounding problem with my circuit design.
The Darlington array and the microcontroller share a common ground. The LDD Vin- pin is used as ground for the PWM dimming signal from the microcontroller as indicated in the LDD documentation. My goal is to use one LDD to power each of the LED circuits (one at a time) and then to also use the microcontroller to use PWM to control the average power of the output of that circuit.
I'm unsure about two aspects of this: (i) the LDD uses Vin- for the ground reference of its DIM pin, and (ii) the LDD datasheet says that the Vout- terminal must not be connected to the Vin- terminal.
My problem is that the ground pin of the Darlington array has two roles: it serves as the return path of the constant current provided by the LDD Vout+ pin, and it also serves as the ground reference for the channel selection signal from the microcontroller. This then means that Vin- and Vout- are both connected (indirectly) to the microcontroller ground (i.e they are both connected together), violating the datasheet injunction against doing this. This setup works fine using a different buck power supply (e.g. a BuckPuck) where the danger of Vin- being connected to Vout- is not relevant.
I'd like to learn how I can modify the circuit to allow use of the LDD. I've thought about connecting the GPIO dimming pin and ground of the microcontroller to the input side of an optoisolator and then connecting the optoisolator's output to the DIM pin and Vin- pin of the LED. This would appear to isolate Vin- from Vout- of the LDD
Is this a reasonable solution, or would some other approach be used? Would it help if I posted a rough sketch of this circuitry?
Thanks, eeLight
