24V Dual CCT LED Strip DC Dimming

[larryqiann]

Hi

I recently purchased a bunch of this really high CRI LED strip. It runs on 24V and has two colour channels to allow it to be CCT tunable. The 24V are common, and the grounds are separate.

The obvious solution to dimming/controlling these is to use a N-channel MOSFET to switch them on and off at a high frequency. However, I do not want the light output to have any flicker, and I'm looking for ways to dim them while maintaining a constant DC voltage with minimal ripple. One way would be to use some DC power supplies that accept sinking current, but that might be difficult to find.  Furthermore, the dimming needs to be controlled from a microcontroller or PC, and should ideally have 12-bit dimming support to enable continuous dimming.

Would there be any way to design a circuit to achieve this? I was thinking about putting a inductor and then a capacitor before the low side switch on each channel, so that the current stays continuous during the off-cycle by charging the capacitor up, which would be discharged by the MOSFET on cycle. Does this sound like a feasible approach? Is there a proper name for this type of circuit?

Thanks!

[Prehistoricman]

I recently purchased a bunch of this really high CRI LED strip. It runs on 24V and has two colour channels to allow it to be CCT tunable. The 24V are common, and the grounds are separate.

The obvious solution to dimming/controlling these is to use a N-channel MOSFET to switch them on and off at a high frequency. However, I do not want the light output to have any flicker, and I'm looking for ways to dim them while maintaining a constant DC voltage with minimal ripple.

Are you sure the CRI and colour temperature are constant with lower voltages? I recently came across an LED COB that produced much warmer white when underpowered. By using PWM, you are making the LED act as if it's running at full power but not all of the time, so you get the correct colour temperature.

If you're only concerned about visible flicker, then just turn up the frequency of the switching.

I was thinking about putting a inductor and then a capacitor before the low side switch on each channel, so that the current stays continuous during the off-cycle by charging the capacitor up, which would be discharged by the MOSFET on cycle. Does this sound like a feasible approach? Is there a proper name for this type of circuit?

Yes, a buck convertor! Almost... what do you mean by "discharged by the MOSFET"?