I'm trying to build a 12V-to-5V DC-DC Buck converter using the LM2576 IC.
This is the circuit recommended in the datasheet:
I've built it (without the optional ouput ripple filter) in a perfboard.
Now I'm doing some tests in it, and it works well when I draw little current from the output. For example, with a 40 Ohm test load, y get an output of 5V and 0.125 Amps, as expected.
But as I test the converter with smaller resistors as loads (20 ohm, 10 ohm, 5 ohm, etc) the output voltage drops from 5V to 4V, 3V, etc., till eventually I get an output voltage of 0V and no current! And also, as the output voltage drops, I start noticing a high frequency sound coming from the converter (from the inductor, I believe).
I don't really have a clue about what might causing this problem. The datasheet of the LM2576 IC says the IC can put up with up to 3 Amps.
Could it be a inductor problem? I've read that the inductor might saturate with high current. But I think that in case of saturation, I would have a ripple problem, not a current problem, am I right?
So, what could be the problem?