Thanks for reply, my first post was not totally accurate, because I did use your exact circuitry in OSPi circuit, like the attached file. So LM2596 is adjustable version, and I am using a combination of a Zener diode and 10 ohm resistor just like your design, but output volt on pin2 is 1.8V. so either LM2596 is bad, or some other component. I am ordering some more LM2596 from DIGIKEY to try them out. The first 10 that I bought was from Ebay very cheap, may be they were all bad. I would appreciate any troubleshooting guide.