I tested a diode model SB360 PFS which it showed about 0.15 forward voltage. The reverse voltage is zero. enter image description here Looking the diode specification I read that Vf is 0.49v to 0.68v. So my question is if this diode is faulty.

  • \$\begingroup\$ Zero, or out of range (0 to the left on the multimeter display.) \$\endgroup\$ – JRE Dec 27 '18 at 20:34
  • \$\begingroup\$ Assuming you are testing the diode correctly, I am going out on a limb and say that the diode is possibly shorted, which would be a typical fail mode if it is overloaded by sustained over-voltage or over-current. \$\endgroup\$ – user105652 Dec 27 '18 at 20:39
  • \$\begingroup\$ @JRE I did not understand your comment. Are you referencing to the reverse voltage ? If yes then it is zero. \$\endgroup\$ – Maverick Dec 27 '18 at 20:40
  • \$\begingroup\$ Test it in both directions. If you get the same reading then it is shorted. \$\endgroup\$ – Transistor Dec 27 '18 at 20:42
  • \$\begingroup\$ @Transistor please read the question. Diode is typically works as it supposed to work which means no reverse voltage but forward voltage is diverging from the typical 0.4v to 0.6v \$\endgroup\$ – Maverick Dec 27 '18 at 20:47

Assuming by "0" you actually mean "overrange", no that's quite normal (Edit: Yes, .OL stands for over-range). You have a fat 3A Schottky diode, and at 25°C the forward voltage at 10mA is typically around 270mV according to the datasheet.

Most multimeters put only about 0.5~1mA through the diode junction, so 150mV at that test current is plausible.

enter image description here

Note that the higher voltage rated diodes such as the SB360 have more forward drop than the lower-rated ones.

  • \$\begingroup\$ So you mean that the diode is not faulty right ? \$\endgroup\$ – Maverick Dec 27 '18 at 21:08
  • \$\begingroup\$ Almost surely not. \$\endgroup\$ – Spehro Pefhany Dec 27 '18 at 21:08

Probably not faulty. If it showing different values depending on which way you connect it, then it is still acting as a diode

Page 2 of the datasheet has a chart of forward voltage vs. forward current.

If your meter supplies less than 100mA, then the forward voltage will be below 0.2V - that's the bottom of the chart.

So, your measured 0.15V fits in. A typical multimeter won't push anything like 100mA through the diode test function.

If your multimeter is showing a 0 on the left of the display that means "out of range." The voltage required to make the diode conduct in reverse bias is more than the multimeter can supply.

  • \$\begingroup\$ Other diodes I tested my multimeter showed about 0.486v so that means that multimeter is able to supply more current than 100mA \$\endgroup\$ – Maverick Dec 27 '18 at 20:51

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.