I don't see the advantage of adding another controller in front of a controller. Sounds like trouble. The specs for your CC device show that it should handle the ~18V of your power supply just fine, so I don't think you need anything additional.

I'm in agreement that switching power to the CC supply should be fine. It should power up or down quickly compared to the on or off time of the LED string, and it should not allow a transient surge to shoot through at startup or shutdown. It would be nice to confirm that, I suppose.

 

Tell us about your whole project. Maybe there are some short cuts.

 

Hello guys it has passed a lot of time...but i have been working on my project the whole time...so i found the right controler for LEDs that are connected to...the base is XLSEMI XL4005 i have been testing it its perfect for driving any leds up to current of 700mA for on and off and up to 1A for pwm all over that is just CC or CV no power to control it via PWM or on off feature built in within...so short cuts about project its big LED sign 10 A4-size letters controlled with ATmega328p over optoisolator to XL4005(tested and working fine) i bought Nichia LEDs they are simply the brightest leds i have ever seen just amazing...here is some design how it should it look, sign is 2000x300 mm.Any errors or better solutions please be kind to advise. Thank you for your time!

 

Between the LED's and ground would be the most common. However, you could put the mosfet in the positive supply line, but then you would need a different driver. I hope this drawing is clear. I am not very adept with Paint.

View attachment 73466

John

If you hang a MOSFET from the positive rail - its easier to use a P-channel type.

A high side N-channel would need gate drive that goes at least 6V higher than Vcc.