How to Identify Zener Diode Voltage and Current Ratings When Markings Are Unreadable

Zenor diods are tiny parts and the value is not readable. Can you suggest a method to identify the voltage/ current ratings of a zener diode?

Then how do you even know it's a diode?

(Assuming it is a Zener:)
If you have a multimeter with a diode test function, a zener diode will show the normal approx. 0.5V to 0.75V in forward bias.
To test in reverse bias, to find the Zener voltage, put a resistor in series with it to limit maximum possible current to about 1mA, a voltmeter across it, and progressively increase the voltage across the two components.
If/when the voltage across it stops increasing, that would be the Zener voltage.
Simplest way to guess power rating is to then compare it with known similar diodes of the same type and size.

To elaborate on Frank's fine treatment of this topic: Since the Zener, when reverse biased, will not start allowing any reasonable current to flow until it reaches the avalanche voltage, you only need to limit the current for a volt or two above the Zener knee, so a 1K resistor will limit the current to around 1 ma when the overall voltage is 1 volt above the Zener voltage.

Just be sure to begin with a voltage around 1 or 2 volts and slowly increase it from there.

It should be marked, either on the diode or on the box it came in. If you can't find the mark, then you have to measure it yourself.

Take the zener diode, a battery or DC power supply, and a resistor. Wire them all in series, with the NEG (cathode) end of the diode closer to the POSitive side of the battery or power supply.

Connect your voltmeter across the diode, and slowly increase the power supply output voltage while watching the meter.

You'll see the voltage across the diode increase slowly, tracking the power supply, until you reach the Zener voltage. At that point, the voltage across the diode won't increase any more; it'll just stay there at its 'reverse breakdown' voltage, which is the Zener voltage.

(If the voltage across the diode goes to around a volt and won't go any higher, the polarity is wrong. Reverse either the diode or else the power supply.)

You probably want a wild guess at what the value of the resistor should be. That's difficult to specify if I don't know the power rating of the Zener diode you're testing. I'm going to make the following suggestion completely in the blind: Select the resistor to limit the series current to 30 mA even if you have to crank the power supply up to 50 volts. R = 50/.03 = 1.5 to 2 K-ohms, rated for a couple of watts.

Reghu

You test the Zenor like a regular diode. the rating should be marked on the diode itself.....

By "rating" do you mean _zener voltage_? If so, that is rarely marked on the diode. In fact, in most cases only the part number, and perhaps a manufacturer's code are marked on the diode, and in the case of many SMD packages, not even that.

With the part #, if you look it up it should give you the voltage and the current rating... Internet

Ah, so, by "rating" you mean "part number", then.

yes, with that part number(example).. Type in the part number in your computer ( internet) and it will come up with the rating ,current and voltage

Got it?????

There should be a part number on the diode itself.... With this number you should identify the rating of the component ....