Im working on a project and i need 3v3,5v and 12V in this. I though smps circuits would be better than Linear Regulators. So i choose LM2676-adj IC. I designed schemetics for 3V3-3A SMPS and 12V-3A SMPS. Read all datasheet and get all recommended pieces from distributor. Printed the PCB and soldered on it. when i supply(16V) the Input on Pcb, i read 12.10V and 3.28V and its OK for me. But when load the circuit for get near of 3Ampere (3v3 - 1.5 ohm & 12v - 4.5 ohm) problems begin. I always read 1.2V from output of 3v3 smps and 11.90V from output of 12v smps.
Output of 3v3 smps is stabile at 1.2v but output of 12v smps is not stabile, its up to 16V and down to 6V by the time randomly.
Here is my all components list, Schemetics and Board images, What do you think about this problem, how i can handle it?
For 3v3 SMPS I use:
IC: 1x LM2676-ADJ, Inductor: 1x P0841, Output Cap: 2x 100uF (10V 1.1A(Irms)), Input Cap: 2x 4.7uF (50V 0.6A(Irms)), Boost Cap: 1x 10nF, Schottky: 1x 40V (3A), FeedBack Res: 1K & 1K74
For 12V SMPS:
IC: 1x LM2676-ADJ, Inductor: 1x PE54039S, Output Cap: 2x 47uF (20V 0.9A(Irms)), Input Cap: 2x 4.7uF (50V 0.6A(Irms)), Boost Cap: 1x 10nF, Schottky: 1x 40V (3A), FeedBack Res: 1K & 9K1