constant-currentled-drivermosfetpwm
I have a set of LED panels that come with AC-DC constant current drivers. Is it acceptable to use a MOSFET to PWM the LED (MOSFET goes between the driver and the LED)?
Also the microcontroller that will be producing the PWM will use a different AC-DC power supply. Is it OK to common the ground rails from the LED driver and the microcontroller PSU, or is it advisable to use an optocoupler?
You can't force a constant current into a buck regulator. Think about it. Where would the extra power not used by the final load go?
So this question is really about what the constant current supply will do under low load, and if that is something the buck regulator can handle. What does the constant current supply do when open? If it goes to its maximum output voltage, and the voltage is less than the 48 V the buck regulator can handle, then all should be fine. If it shuts down or occasionally retries with pulses, then it won't work.
As often, the solution is to read the datasheets.
As expected, the answer is right there in your datasheet. Have a look at the schematic on page 8 (document page 5):
Do you see the "LED+" and "LED-" labels on the right hand side? Those correspond to the LED '+' and '-' terminals on the driver board. A constant current driver works by monitoring the feedback across a resistor, in this case "RSENSE," and changing the output voltage accordingly. You CAN connect multiple LEDs in series or parallel in between these leads, they would either share or split the output current. However, you CANNOT connect the negative terminal of one LED to one driver and its positive terminal to another driver. If you are using three drivers for an RGB LED, it CANNOT be common anode OR common cathode unless you want to put all three LEDs in parallel on the same driver, which would be pointless. You have to have three independent LED anodes and cathodes, one pair for each driver.
You CANNOT have a "shared ground" between your LEDS with this driver. You are confusing the LED ground (common cathode) with that of the power rail ground. They are NOT the same thing unless the LED is being driven some other way and its cathode is tied to the negative power rail.
Also, you mention in your question:
connect the positive output of the driver to the individual colors of the led and the negative output to the shared negative connector of the led
which would imply common cathode (shared negative), not common anode (shared positive) as you mentioned in a later comment. It seems as though you have absolutely no idea what you are doing or talking about... which is OK, it just means you need to learn to research these things on your own. It's hard to help if you don't even know how to ask an appropriate question.
Best Answer
It really depends on how the constant current driver has been designed.
simulate this circuit – Schematic created using CircuitLab
simulate this circuit
In any case the driver will most likely not appreciate the wildly fluctuating load, the best option would be to just control the setpoint of the driver.