Question

You test a diode with an ohmmeter. The two readings indicate a very low value of resistance. The diode is probably __________.

Answer 1

Answer:

  shorted

Explanation:

A diode is a device that passes current much better in one direction than in the reverse direction.

Ohmmeter test

Conceptually, an ohmmeter applies a voltage to the device under test and reports the current through the device on a scale calibrated in ohms. It typically has a low enough open-circuit voltage, and a high enough internal resistance so as to avoid damage to parts under test.

A "continuity" tester may have an open-circuit voltage of a few tens of millivolts and/or a short-circuit current of a few microamps, so as to properly detect continuity and avoid contact damage in "dry" circuits. Such a tester is virtually useless for diode testing.

An ohmmeter suitable for diode testing will generally have an open-circuit voltage of a few volts, and a short-circuit current of a few milliamps. When such a meter is used to test a diode, it will indicate a few kilohms (or less) in the "forward" direction, and several 10s or 100s of megohms in the reverse direction.

Low-resistance readings

If the "forward" resistance reading is unusually low (a few ohms), the diode may be damaged. If both forward and reverse readings are unusually low, the diode my be considered to be shorted.