SgtWookie,

I tried to calculate the R values for the input to the MOSFET - assuming I need individual ones for each string of LEDs - following your method from an earlier post...

I'm only looking at the white LEDs for now, I can apply the same process to the blues.

MCU source/sink = 25mA per pin
25mA/6 FETs = 4.16mA each
12V/4.16 = 2.88ohm

Using a 3ohm resistor = 12/3 = 4mA x 6 = 24mA total (may be better to use 2 pins to spread the load, 3 strings on each ??)
Power = 12v x 0.004 = 0.048W (use 0.125W)

I'm not sure about calculating Rsense in this circuit as i don't know how the circuit will look with 6 separate LED strings.

If you have a chance I would really appreciate your thoughts on this and the questions I annotated in the jpeg above.

Thanks,

Simon

 

I've been trying to figure out this circuit for a few weeks and this is where I am at. Please can someone take a look and guide me on the component values for the resistor prior to the MOSFET (R9) and the RSense resistor in the current feedback loop (R1). Is the inductor correctly rated ?

I may not use the 12HV615, hence the inclusion of the 5V regulator.

I will now be using a 12v, 30A PSU so I can run everything from the same supply (white and blue LED arrays, etc).

Thanks.

 

Hi
Go for a new power supply and drive 3 banks of 9 on seperate series chains.Running high power led's in parrallel is not recomended.the variation in light output will also be noticable.What about heatsinks, those led's are going to need some serious heatsink probably fan cooled.

 

Simon,
Sorry, I've been quite busy, and this is going to take some time to go through again.

 

SgtWookie,

If you're buried with things, please don't worry - it was not my intention to add to the pressure !

Last night I found another possible solution, I posted the project at Freelancer.com and several people have already bid on the project...this may be better anyway as I feel a little out of my depth, especially with the coding ! Although I will say, since I first posted my original circuit I am now hooked on PICs and have been busy playing with my PICKit2 and have built simple circuits on my breadboard - yes, the blinking LED...everyone's first project ! That is all down to you - thank you !

 

12V/4.16A= 2.89 ohms. 12V/4.16mA= 2890 ohms. A huge difference.
12V/3 ohms= 4A, not 4mA. another huge difference.