polop wrote ...

is there a chip that youguys would reccomend that does all the timing and things for me, ie the only components are the chip the inductor and the diode, that will regulate anywere between 0 and 3amps ? these solutions although they inerest me more, get me so fustrated because i do not have any equipment to dest them (apart from a hardly working ddm)

jonny5 wrote ...

Hi polop!

Simpler is almost always better. Here's an idea that uses a single comparator and the control loop phase-shifts to make a high powered LED driver:



The buck topology keeps relatively constant current through the high-powered LED (simulated by two smaller LEDs in parallel)by comparing the voltage dropped across the current-sense resistor to a regulated reference voltage. Since the rail-to-rail comparator output cannot drive the PFET gate directly, the totem-pole 2n3904/2n3906 pair source and sink the necessary gate currents to turn the switch on and off very quickly. Be careful with the phase shifts adding up around the control loop - the buck inductor, "output" 4.7uF capacitor, and low-pass filter off of the current-sense resistor all contribute to the total phase shifts. You might want to play around with a dummy load before risking the awesome LEDs!

Here's the simulated LED current:



I'm excited to try this circuit (have to find good LED's first)!