The last article was about conventional diodes. There are many applications for various types of diodes. What they have in common are that they are made up of only two materials, a P (+) and a N
(-) material. Depending on the composition, a diode can be made to do a variety of functions.
The Zener diode. These have been used for a long time. They arevery affective in regulating voltage.
How does it work? Again, you can get as complicated as you want, but I am not up to that.
A diode allows current to flow in one direction only. A zener will do the same. However, if you use a zener in the reverse direction, it will not conduct current until you reach a specified voltage, then it will avalanche in conductivity.
Therefore, If you have a zener rated at 7 volts. It will not conduct current until you reach 7 volts. It will maintain the 7 volts very steady.
This is also a reason zeners are rated not only in voltage, but wattage. When the zener conducts it can not exceed the power of the diode. A 1 watt diode rated at 7 volts can not exceed .14 amps.
Therefore, your circuit design can not exceed this current because the zener will offer close to a short (near 0 ohms) when regulating.
Zeners are available from 1/4 watt to 50 watts. They come in a large variety of voltages. You can use two in series to obtain a higher regulating voltage. If you have a 7 volt and a 5 volt in series, they can be used as a 12 volt regulator.
Keep in mind that zeners regulate by shorting the circuit. Therefore, the circuit design has to be able to handle the short and so does the zener.
Common applications are regulating biasing voltages for amplifiers. It is common to see zeners in linear amplifiers for regulating the needed bias.
Zeners can be used in voltage dividers, transient protection (spark plug noise) and RF clamping to prevent over load of a sensitive RF amplifier.
If you want to try out a zener or want to know the unknown value, it is quite easy.
Connect a zener in series with a 1,000 ohm resister. Apply a reverse bias. One lead to the zener and one to the resistor. Use a variable DC power supply. Measure the voltage across the zener only. You will see the voltage increase to the value of the zener and no more.
Zeners are a small inexpensive device with a large variety of applications.
73,
Ralph WD0EJA
April 2019
BILAL COMPANY
