How to Test and Distinguish Zener Diodes?
- May 23, 2022
In electronics, Zener diode refers to a diode made to play the role of voltage stabilization. That is, the current can be changed in a large range while the voltage is basically unchanged by using the reverse breakdown state of the diode PN junction. Zener diodes are classified according to the breakdown voltage, and are mainly used as voltage regulators or voltage reference components. Therefore, it is very important in the electronic circuit. So daily maintenance, precautions for daily use, and fault detection are very necessary. Here, this note will introduce how to detect and distinguish the Zener diodes in detail.
How to Test Zener Diode with a Multimeter?
The resistance measurement method is generally more practical to measure the tube voltage regulation value below 10V, because the maximum voltage of the stacked battery is 9V from the analog multimeter we use.
The principle of the test is: through the multimeter RX10K block, the internal power supply is 9V at this time to make the internal PN junction of the diode to be in a reverse breakdown state, which will have a relatively small resistance.
Another way is using a multimeter to measure the forward and reverse resistance in the R×1k block. Normally, the reverse resistance is relatively large. If the needle swings or other abnormal phenomena are found, it indicates that the regulator tube has poor performance or even damage. The method of energizing in the road can also roughly measure the quality of the Zener tube. The method is to measure the DC voltage at both ends of the Zener tube with the DC voltage file of a multimeter. If the voltage close to regulation value, the diode is basically intact; if the voltage deviates too much from the nominal voltage regulation value or is unstable, the voltage regulator tube is damaged.
The disadvantage is that it can only measure the quality of Zener diodes below 10V, and can only be measured with an analog multimeter.
The diode block of the multimeter can also be used to measure the quality of the Zener tube. When measuring, adjust the multimeter's range switch to the diode position firstly, and then touch the positive and negative poles of the regulator tube with the red and black test pens. If the tube is normal, the multimeter will display a reading of about 0.700. Next, Change the two test pens. And measure the reverse resistance of the Zener tube. If it is a good tube, the reading will be "1"; if the positive and negative readings of the Zener tube are both "0.000" or both are "1" during the measurement, it means that the Zener tube is damaged.
This measurement method is relatively simple. We generally use the DC voltage file of the digital multimeter to directly measure the output voltage regulation value of the Zener diode. If the measured DC voltage result is equal to the voltage regulation value of the Zener diode, it means that this is stable. The pressure diode is working normally, which also shows that the diode is good.
For Zener diodes with higher regulated voltages, sometimes we can also use a megger to detect them. We connect the terminal of the megger to the diode and shake the handle of it according to the rated speed. When it is found that the megger is relatively stable at a certain value, it means that the quality of the Zener diode is good. If the swing is more severe, it means that the Zener diode is poor or is not a Zener diode.
We all know that the Zener diode works in a breakdown state, so you can use this feature to distinguish whether it is an ordinary diode or a Zener tube. Use a 500-volt megger, and its output terminal is connected in parallel with a multimeter, either digital or analog meter. Adjust the voltage of the multimeter to 500 volts, shake the megger to make the needles deflect in the positive direction, at this time, the red test lead is positive.
Then connect the two test leads to the two electrodes of the tested tube. If you know the electrodes of the tested tube in advance, connect the red test lead to the negative electrode of the tested tube, shake the megger, and the voltage value measured on the meter is regulator voltage value, that is the voltage stabilization value of the Zener tube. If you don’t know the electrodes of the tube under test, first shake the megger to see the voltage. If there is no voltage (0.5 volt), change the test lead and test again. This method is suitable for detecting Zener diodes below 200 volts. If the measured voltage exceeds 200 volts, it may not be a Zener diode.
Figure 1. Zener Diode Symbol
Zener diodes generally measure leakage on an oscilloscope. The reverse voltage is gradually applied to both ends of the Zener diode, and the leakage current of it gradually increases when it reaches the critical point. The higher the voltage, the greater the leakage current. Using a multimeter to measure the forward and reverse resistance of the Zener diode can only roughly judge its quality.
From the appearance point of view, the positive pole of the metal-encapsulated Zener diode tube body is flat, and the negative end is semicircular. One end of the plastic-encapsulated zener diode tube with a color mark is the negative pole, and the other end is the positive pole. For Zener diodes with unclear signs, you can also use a multimeter to determine its polarity. The measurement method is the same as that of ordinary diodes test, that is, use the multimeter R×1k block, connect the two test leads to the two electrodes of the Zener diode, and take measurement. finally, adjust the two meter pens to measure again. In the two measurement results, choosing the one with the smaller resistance value, the black test lead is connected to the anode of the Zener diode, and the red test lead is connected to the cathode of the Zener diode.
Figure 2. Zener Diode Regulator
Generally, color code Zener diodes are marked with models and parameters, and detailed information can be found in the component manual. They are small in size, low in power, and mostly within 10V, so they are easily broken down and damaged. The appearance of them is very similar to the color code resistor, so it is easy to make mistakes. The color ring on the Zener diode represents two meanings: one represents the number, and the other represents the number of decimal places (usually the color ring Zener diode takes one decimal place, expressed in brown). It can also be understood as the magnification: ×10 (the -1 power), the number corresponding to the specific color is the same as the color code resistors).
The forward characteristic of the Zener tube is similar to that of an ordinary diode; the reverse voltage is smaller than the breakdown voltage (regulated value) and is in an open state, which is also similar to an ordinary diode.
First set the multimeter to the R×1k gear, and measure the positive and negative poles of the diode according to the aforementioned method; then connect the black test lead to the cathode of the tested diode and the red test lead to the anode of the diode. The measured value is the reverse resistance of the PN junction, which is very high. At his time, the hands do not deflect. Then switch the multimeter to the R×10k gear. If the needle is deflected to the right by a certain angle, it means that the measured diode is a Zener diode; if the needle does not deflect, it means that the measured diode may not be a Zener diode (Note: The above method is only suitable for the voltage stabilizer diode whose voltage is lower than the battery voltage of the multimeter at R×10k gear).
The principle of the above measurement method is that the battery voltage in the multimeter's R×10k gear is much higher than that of the R×1k gear. If the voltage stabilization value of the Zener diode is lower than the battery voltage, the R×10k gear is used to measure the voltage. The PN junction of the diode will have breakdown, showing that the resistance reading drops a lot. The reverse withstand voltage of ordinary diodes is relatively high, and the battery voltage in the meter of R×10k is not enough to make it reverse breakdown. In addition, if the voltage regulation value of the Zener diode is higher than the battery voltage of the meter, the needle will not deflect, therefore the type of the tested diode cannot be distinguished by the above method.
Figure 3. Zener Diode Voltage Regulator Circuit
1. How do you identify a 12v zener diode?
Note place a diode across the meter probes. One way they'll read a low voltage (under 1V). The other way, if they read less than 18V then the diode is likely to be a zener diode. The voltage you see on the multimeter is the zener diode voltage.
2. How do you know if a Zener diode is bad?
Measure the reverse-biased voltage on the Zener diode by switching the multimeter probes. Place the positive lead on the marked or cathode side, and the negative lead on the unmarked or anode side. You should get a reading indicating infinite resistance or no current flow.
3. What is the difference between a diode and a Zener diode?
A diode is a semiconductor device which conducts in one direction only. A Zener diode is a semiconductor device which conducts in forward biased as well as reversed biased.
4. What happens when a Zener diode is shorted?
What happens when a zener diode is shorted? The zener normally fails SHORT circuited in reverse bias, but before it get short circuited, its terminal voltage goes up, that is it behaves like open circuit for few seconds and then goes to short circuit permanently.
5. How do you test a Zener diode?
Measure the resistance between the terminals 1/4/5/8 and one of the four earth terminals 2/3/6/7. At each of the terminals 1/4/5/8 the zener diodes should have an extremely high resistance and probably the measuring instrument will not show any reaction for a healthy zener barrier.
6. Why is a Zener diode reverse biased?
Zener diode is a heavily doped diode. ... When the Zener diode is reverse biased the junction potential increases. As the breakdown voltage is high this will provide high voltage handling capacity. As the reverse voltage is increased, the reverse current increases drastically at a certain reverse voltage.
7. What happens when zener diode is forward biased?
When forward biased voltage is applied to the zener diode it allows large amount of electric current and blocks only a small amount of electric current. Zener diode is heavily doped than the normal p-n junction diode. Hence, it has very thin depletion region.
8. How do I know my SMD Zener diode?
The pin of voltage regulation SMD diode is also divided into positive and negative poles as the general-purpose SMD diode, which can generally be identified according to the mark on the package, such as the diode symbol, the length of the lead, color wheels, color spots.