Hi. I'm planning to build a lighting array using the 3W RGB leds from dealextreme.
The plan is to wire one of these "Quality AMC7135 350mA Regulated Circuit Board for DIY Flashlights 20-Pack" to each cathode to limit the current.
Hoping someone with more experience could say if the circuit makes sense before I order all the parts. I'm not sure what switching transistors to use as I want to control groups of up to about 10 leds in parallel at a time, which would need to drain a lot of current. Any suggestions?
Here is a paint sketch ( :D )of my circuit idea to drive them.
What are those circles on the schematic? They can't be the AMC7135 350mA Regulated Circuit Board because these have two connections and the boards have three.
They are meant to be the AMC7135. Reading the data sheet it seems they the AMC7135 needs the 5V input and a capacitor on the led cathode. The led would then be pwm through the 5V input to the AMC7135 as shown below for one of the cathodes.
Would this work? Would I need the 1uF input capacitance used in the data sheet between 5V and ground?
Cheers for your help :)
First off the capacitor should be across the supply not the FET output.
Fitting it on the cathode will just reduce the off switching time and put excessive current through the output FET when you turn it on.
However if you do fit at the correct position on the supply, it will kill the PWM pulses.
Due to the band gap reference in the chip lowering the voltage, using filtered PWM would not appear to offer a solution.