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LM2596 14V to -12V negative buck problem

Other Parts Discussed in Thread: LM2596

Hi TI

Im trying to design a -12V negative output from a 14V positive battery power supple, with the intention to drive the negative supply to an Audio OpAmp. Following to datasheet and adding circuit to change the ON/OFF to active high this was apparently succesfull.

However, as soon I apply any load to the output of the converter, the output drives to maximum current draw, only limeted by the LM2596 to approx. 3,4A, and the input voltage drops to far below 5V. This continues even after I have removed the load again. The circiut ofcouse get very hot and after I turn off the power supply, I most wait a few minutes waiting for the circiut to cold down, otherwise the circiut will drive to shortcut again, even without load Applied. I have attached the circiut. Hoping for a reply

The coil has a value of 33uH

  • You will need a bypass capacitor across the VIN and GND pins of the regulator.  I would try an Al of about 100uF in parallel with a ceramic of about 10uF.  Also, you mentioned your input supply was being pulled down; maybe the current limit is set too low on your input supply.

    FD