Diode question: Determining type?

Question

How can I tell if a diode is zener or not?

Answer 1

Easy:  it is.

*All* diodes -- indeed, all P-N junctions, including the ones in transistors -- behave like zener diodes:  at a certain reverse voltage, they become constant-voltage devices  (i.e. their resistance decreases as current increases to maintain a constant voltage across the terminals).  Zener diodes are just deliberately designed to do this at a particular voltage and safely withstand the power thus dissipated.  Rectifier diodes are designed so the breakdown voltage  (note, it's only the behaviour that breaks down:  catastrophic failure will only result if the device's safe power dissipation limit is exceeded)  is higher than will be encountered in normal operation; as long as it's above a certain value, nobody really cares what it actually is.  And LEDs are built from a material which glows when electrons cross the junction.  But they *all* exhibit this constant-voltage property!

To measure the voltage at which this happens, you need to reverse-bias the diode from a current-limited supply and measure the voltage across the diode .....  if it suddenly stops increasing despite you turning up the power supply, then you've found the breakdown voltage.

Note also that it's quite possible to use zener diodes as rectifiers; as long as you are careful never to exceed the breakdown voltage, they will do the job.  They aren't even especially lossy when forward-biased.

Answer 2

Place diode in series with 1k resistor

Apply positve voltage to resistor which is connected to

cathode or stripe on diode. increase  voltage to find breakdown voltage of zener while measuring across

the diode.  if the votage does not suddenly increase

it is not a zener