One of the problems with my diode overflow is that some kinds of diodes are not marked, except for the cathode lead, in particular, zener diodes. These have been the bane of my existence, as if I don't mark them somehow (usually with tape and a sharpie) I will never remember or know what the zener voltage is. You see, zeners aren't color coded like resistors and inductors, they don't have helpful numbers like capacitors, and they rarely -- if ever -- have any component numbers marked on their shiny, tubular bodies.
After a few different angles of attack, I think I have found the best way to not only determine the zener's breakdown voltage of an unidentified zener independent of changes in the supply voltage, and, in the same fell stroke, am able to determine if a zener diode is fried or otherwise faulty.
If you have a box, compartment, bag, or drawer full of unidentified zeners that you haven't been able to use for sake of identification, this instructable will be right up your alley. It could easily become a standard part of your electronic testing and measurement arsenal due to its simplicity and ease of use.
Go to the next step and let's begin!
Step 1: Zener Diodes
DiodesA diode is a two-lead semiconductor that acts as a one-way gate to electric current flow. When a diode's anode lead is made more positive in voltage than its cathode lead -- known as forward biasing -- current is permitted to flow through the device. However, if the polarities are reversed (that is, the cathode is made more positive than its anode) -- a condition known as reverse biasing -- the diode will act to block the flow of electrons.
Diodes are used in circuits that convert, or rectify, AC voltage into DC voltage. They are also commonly found in voltage-multiplier circuits, voltage-shifting circuits, voltage-clamping circuits, and voltage regulator circuits. For a novel design showing what you can do with regular old diodes, check out my instructable Make a Solar Panel Using Diodes!
CharacteristicsForward Voltage (Vf): Current flows in the direction of the arrow (from anode to cathode) provided the voltage across the diode, the forward voltage, exceeds its junction threshold voltage.
Junction Threshold Voltage: In many cases, the p-n junction composing the diode has a 0.6V threshold, while other special types of diodes, like germanium diodes exhibit 0.2V thresholds, and Schottky diodes often can be found with 0.4V thresholds. Don't carve these values in stone though, as production values may skew these thresholds off by upwards of a volt.
Forward Biasing: When the diode's anode is more positive in voltage than its cathode
Reversed Biasing: When the diode's anode is more negative in voltage than its cathode.
Note my hand drawings below to see this graphically represented. Keep in mind that not all diode junctions are p-n junctions, specifically Shottkys which use a metal junction.
Peak Current Rating (Iomax): Also called Max Forward Current, this is the maximum current that must flow through the diode for safety reasons, lest you burn it out.
Peak Inverse Voltage (PIV) Rating: When reverse biased and the reverse voltage is negative, this negative voltage must be less than the peak inverse voltage rating of the diode.
Kinds of DiodesAs mentioned, there are numerous types of diodes to be found and that are useful in various projects you may work on. Here are some of the top ones and a brief description of what they do.
Rectifier diodes: These diodes are used to rectify (convert) AC voltage and current into DC voltage and current.
Signal/Switching diodes: Often used in circuits where small currents and high frequencies are involved, like radio and RF.
Fast recovery diodes: Ultrafast switching diodes used to conduct reactive load current and rectify AC, among other uses.
Schottky diodes: Using a metal conductor junction, these diodes have a lower Vf and are commonly found in voltage clamping and transistor saturation modulation circuits.
Germanium diodes: These have a low reverse resistance value giving a lower forward volt drop across the junction but have a higher forward resistance value because of their small junction area.
LEDs: Ah the light-emitting diode. The blinken light favorites of all of us.
Zener DiodesZener diodes, instead of acting like a one-way gate to current flow, act as a two-way gate for current flow. In the forward direction it's easy to break through, often 0.5 - 0.7V like a standard diode. But, in the reverse direction, current can flow but it's harder to push open. The voltage required is equal to the zener's breakdown voltage. This breakdown voltage can be anywhere from 1.8V to upwards of 200V. Power ratings vary.
Breakdown Voltage (Vz): The voltage required to push open and flow current in the reverse direction. This is, arguably, the primary characteristic you look for in a zener diode (outside of maybe power ratings).
Zener Diode Application Examples
1. Line regulation
2. Load regulation
3. Split supply from a non-tapped transformer
4. Waveform modification and limiter
5. Voltage shifter
6. Voltage regulator booster
7. Overvoltage protection