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ZENER DIODE TESTER
ABSTRACT
The testing of zener diodes requires a variable dc power supply. A typical test circuit can be constructed, as shown in figure 4-19. In this circuit, the variable power supply is used to adjust the input voltage to a suitable value for the zener diode being tested. With the zener diode connected no current will flow until the voltage across the diode is equal to the zener voltage. If the diode is connected in the opposite direction, current will flow at a low voltage, usually less than 1 volt. Current flow at a low voltage in both directions indicates that the zener diode is defective. Before you start to test any zener diode, you must first understand the marking or part number and then look for the voltage ratings. Refer to my article about how to read the zener diode data. Once you know the zener diode voltage from your favorite data book such as the Philip ECG semiconductor master replacement guide then it is easy to check with your meter to see if it leak, open or shorted.
Sometimes a normal signal glass type diode you may think is a zener diode thus you will not get the exact measurement. If you have confirmed that the diode you want to measure is zener diode then you can proceed to use my method to accurately test it. For your knowledge, a zener diode with 2.4 volt to 12 volt should have two readings when test with an analog meter set to times 10K ohm range. But these readings are not shorted reading.when you put your meter probes across the zener diode of 2.4 volt using the times 10 k ohm range, one way will show a full scale reading (red probe to cathode and black probe to anode) which mean the pointer will point towards the 0 ohms scale, if you now connect the probe the other way (black probe to cathode and red probe to anode) the pointer will point to around 2- 4 ohms!
If both ways of testing cause the pointer to point to 0 ohm, then the zener diode is considered shorted. When you measure a 5.1 volt zener diode, as usual one way will point to zero ohms while the other way will show a higher resistance which is in the 20 to 60 ohms. These are the characteristic of a good working zener diode and don’t think that the meter shows two reading means the zener diode is faulty.
Sometimes a normal signal glass type diode you may think is a zener diode thus you will not get the exact measurement. If you have confirmed that the diode you want to measure is zener diode then you can proceed to use my method to accurately test it. For your knowledge, a zener diode with 2.4 volt to 12 volt should have two readings when test with an analog meter set to times 10K ohm range. But these readings are not shorted reading.when you put your meter probes across the zener diode of 2.4 volt using the times 10 k ohm range, one way will show a full scale reading (red probe to cathode and black probe to anode) which mean the pointer will point towards the 0 ohms scale, if you now connect the probe the other way (black probe to cathode and red probe to anode) the pointer will point to around 2- 4 ohms!
If both ways of testing cause the pointer to point to 0 ohm, then the zener diode is considered shorted. When you measure a 5.1 volt zener diode, as usual one way will point to zero ohms while the other way will show a higher resistance which is in the 20 to 60 ohms. These are the characteristic of a good working zener diode and don’t think that the meter shows two reading means the zener diode is faulty.
