if someone unsoldered the on/off pin and put an NPN transistor with Collector on the pin, and the emitter soldered down to the pad of the board could I effectively get PWM control? I would use the input to the buck converter for powering the PWM 555 circuit.
http://www.ebay.com/itm/DC-DC-LM259...238205?hash=item41a00f66fd:g:7nEAAOSwEgVWSYuw
thanks( i realize I need to regulate the 555 chip power down under 15 V)

 

Thats a Lm2596 variable regulator chip, just set the desired voltage and feed that to the 555 circuit.

 

sorry dodgy, i didn't explain the whole picture.
This is an LED Driver, and I am going to set the current output to a level appropriate for the LED and I want to add PWM dimming to the unit.
I understand that just adjusting the current level of the LM2596 isn't the best choice because the color can shift when I get down in the 5%-40% light output range.
My reading seem to indicate setting 600ma for a 750ma rated LED is OK but then I need to start PWM dimming to avoid color shift.
The question is how to best achieve PWM with the LM2596 board. I hope to not add a Mosfet if I can avoid it.
thanks and have a great weekend.