Diodes are semiconductor materials that behave like switches. They are open to electricity in one direction and short-circuited in the other, meaning that current is allowed to flow in only one direction. Silicon and germanium are two materials they are often made from.
The symbol for a diode is an arrow to show the direction current flow is allowed. A diode placed in a circuit this way is known as forward-biased. A diode with current flow in the wrong direction is called reverse-biased. Ordinary reverse-biased diodes will finally allow current when there is too much current flowing the wrong way. When this happens, they are destroyed.
Things You'll Need
- Silicon diode, such as a 1N4001
- Jumper wires
Measure the forward-biased voltage on the diode by placing the multimeter on the diode setting. Put the positive or red lead on the anode side of the diode, which is unmarked. Place the negative or black lead on the cathode side of the diode, which is marked by a stripe. An undamaged silicon diode will read 0.5 to 0.7 when it is forward-biased.
Measure the reverse-biased voltage on the diode by switching the multimeter probes. Place the positive or red lead on the marked or cathode side of the diode. Place the negative or black lead on the unmarked or anode side of the diode. You should get a reading indicating an overload or no current flow.
Attach a 3- to 9-volt battery to the circuit board. Add a 330 ohm to 1k ohm or more resistor to the positive lead. Connect the anode side of the diode to the free end of the resistor and the other end to the negative terminal of the battery. Note that the diode is in series with the battery and resistor.
Measure the voltage across the resistor by placing the multimeter on a low DC voltage setting, and by placing a lead across each side of the resistor.
Calculate the current in the circuit using Ohm's Law I = V/R, where V is the voltage from the battery, I is the current, and R is the value of the resistor. This mathematical model assumes the diode is ideal and behaves like a switch, so that the load is only across the resistor.
Measure the voltage across the diode. Note that the diode behaves like a 0.7 V battery.
Tips & Warnings
- Diodes are very delicate. Never exceed the manufacturer's recommended currents in the forward- or reverse-biased directions. Always exercise caution when building electrical circuits to avoid burning yourself or damaging your equipment.
- Electronic Principles; Albert Malvino; 1999
- Getting Started in Electronics; Forrest Mims III; 2000
- Photo Credit Mamun2a/Commons, Wikimedia.org, Dr. C
How to Wire in a Diode
Diodes are active electronic components, constructed from semiconductor material (such as germanium or silicon), and treated with chemical impurities such as boron...
How to Wire a Bridge Rectifier
A bridge rectifier converts alternating current (AC) to direct current (DC). All electronic devices that plug directly into a wall receptacle use...
How to Test Diodes in Circuit
A diode is a bipolar semiconductor that only allows current to pass in one direction. The positive terminal of a diode is...
How to Add a Diode to Reduce Voltage
A diode conducts electricity in one direction, from its positive terminal (anode) to its negative terminal (cathode). A diode will not fully...
How to Wire Diodes
A diode acts like a one-way valve for electricity. Connect the diode in one direction and current will flow through the diode....
How to Connect a Wedding Veil to Your Hair Combs
A wedding veil needs to be connected to your hair combs in a very particular way to avoid trouble later on. Connect...