Meter check of a diode

Chapter 3.2 Meter check of a diode

Lessons In Electric Circuits Volume III – Semiconductors Book
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Lessons In Electric Circuits Volume III – Semiconductors Book

  • 3.2. METER CHECK OF A DIODE103VDIDforward-biasreverse-biasforwardreversebreakdown!0.7VFigure 3.8:Diode curve: showing knee at 0.7 V forward bias for Si, and reverse breakdown.• The voltage dropped across a conducting, forward-biased diode is called the forward volt-age. Forward voltage for a diode varies only slightly for changes in forward current andtemperature, and is fixed by the chemical composition of the P-N junction.• Silicon diodes have a forward voltage of approximately 0.7 volts.• Germanium diodes have a forward voltage of approximately 0.3 volts.• The maximum reverse-bias voltage that a diode can withstand without “breaking down”is called the Peak Inverse Voltage, or PIVrating.3.2Meter check of a diodeBeing able to determine the polarity (cathode versus anode) and basic functionality of a diodeis a very important skill for the electronics hobbyist or technician to have. Since we knowthat a diode is essentially nothing more than a one-way valve for electricity, it makes sensewe should be able to verify its one-way nature using a DC (battery-powered) ohmmeter as inFigure 113,3.9. Connected one way across the diode, the meter should show a very low resistanceat (a). Connected the other way across the diode, it should show a very high resistance at (b)(“OL” on some digital meter models).Of course, to determine which end of the diode is the cathode and which is the anode, youmust know with certainty which test lead of the meter is positive (+) and which is negative (-)when set to the “resistance” or “Ω” function. With most digital multimeters I’ve seen, the redlead becomes positive and the black lead negative when set to measure resistance, in accor-dance with standard electronics color-code convention. However, this is not guaranteed for allmeters. Many analog multimeters, for example, actually make their black leads positive (+)