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- AUGUST NEWS LETTERISOTRON 20 A WORK HORSE FOR 20 METERS DIODES This is a very common term, even among folks that are not in electronics. These devices are used in automotive, generators, solar panels, HVAC and many other applications. What is it? Mostly a two material solid state device. A "P" and a "N" material. Simply it allows electrical current to flow in one direction only. If reversed it will not conduct. Sort of like a check valve in a plumbing system. Water will flow in one direction, but not the reverse direct. Why do we need it? One basic reason is to change an alternating current (AC) to a direct current (DC). The latter is what most of our equipment operates on. There are several ways to use diodes to make the AC to DC change. There are 1/2 wave rectifiers (what the diode does) that will allow 1/2 the wave of an alternating current to flow, but eliminate the 2nd half the AC cycle. There are full wave rectifiers using two to four diodes. This allows 1/2 of the alternating current to flow down a wire. Then it reverses the polarity of the other 1/2 wave to flow in the same direction. This makes a more stable direct current. The most common power supply diode is the silicon diode. These can be acquired for very low power to hundreds of amps such is used in welders. One interesting characteristic is the voltage it take to get the diode to conduct in the forward direction. For silicon diodes it takes .7 volts across the diode to start conducting. Voltages lower than this will not conduct. What is the advantage? If you look at your Digital Multi Meters (DMM) you will see a resistance mode. When you select this mode (several selections), you will be able to measure the value of resistors, capacitors (for short) or inductors without turning on the diode and giving you an improper reading because the meter uses less than .7 volts to make the measurement. To check the diode, there is a selection on the meter specifically for this. It may have a symbol of a diode. The diode symbol tells you the polarity. The pointed end of the triangle with a line is the cathode or negative side. The back of the triangle is the anode or positive end. This is usually marked on the diode. Small diodes have a line around the diode that indicates the cathode side. On the bigger diodes that use a stud and heat sinks, it is best to confirm polarity with your DMM. There are many applications diodes can be used in. Later articles will describe more on this. 73, Ralph WD0EJA 03-19 BILAL COMPANY 137 MANCHESTER DR. FLORISSANT, CO. 80816 U.S.A PH/FX: 719/687-0650 |
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