Lm2576 cannot generate -5V

[Tùng Nguy]

I am using LM2576 to generate +/- 5V from a battery 9V.

I use diode zener 7.5v in the circuit.
I can generate 5V from the 9V battery. However, I am unable to generate -5V. So what is the solution. I really appreciate your help.

 

[FvM]

However, I am unable to generate -5V.

Means exactly what? The circuit basically works, I've used it quite often.

 

[Tùng Nguy]

It means that I cannot get the output is -5V. I just take 0.5V instead of -5 V..Could you see my schematic again. I do not know why I am wrong

 

[FvM]

I presume you know that the circuit is also shown in the datasheet, thus it's supposed to work. I see two possible problems
- zener diode voltage of UVLO circuit to high, doesn't start at all
- 9V-battery is unable to supply the start-up current, battery voltage collapses

You may want to exchange the 2200 µF output capacitor with the 330 µF input capacitor which should improve the startup behaviour. Better use a newer Simple-Switcher with soft-start feature (e.g. LM2673) instead of the pretty old LM2576.