The failure of the diode is mainly manifested by open circuit, short circuit and unstable voltage regulation. Among the three types of faults, the former fault shows an increase in the power supply voltage; the latter fault appears as the power supply voltage goes low to zero volts or the output is unstable. Then the failure of the diode
Judgment of common faults of diodes:By testing the voltage across the Zener diode on the road, the fault characteristic of the Zener diode can be judged.
Open circuit
After the diode is opened, the voltage across it will rise, so it is not difficult to make a judgment.
2. Short circuit
A short-circuit fault occurs in the diode, and the voltage across it drops to zero volts.
3. The voltage regulation value is unstable
Poor diode quality can cause unstable output voltage. When measuring the voltage across the Zener diode with the DC voltage of the multimeter, you will find that the voltage is high or low.
How to use a multimeter to detect the quality of ordinary diodes:1. Identify the positive and negative poles of the diode. One end of the white line is the negative pole and the other end is the positive pole.
2. Turn the knob on the multimeter to the on/off position and insert the red and black test leads into the correct position of the multimeter.
3. Connect the red test lead to the positive pole of the diode and the black test lead to the negative pole. Then observe the reading, if it is full (ie shows 1), the diode is broken. If there is a reading, exchange the test leads. If there is still a reading that does not overflow, the diode is broken.
4. If it is a light-emitting diode, if the diode is normal, you can see a weak light, and the long foot is the positive pole.
1. Discriminating between positive and negative electrodes
In terms of appearance, the positive end of the metal-packed Zener diode body is planar, and the negative end has a semi-circular shape. One end of the plastically sealed diode body printed with a color mark is a negative electrode, and the other end is a positive electrode. For the Zener diode with unclear mark, the polarity can also be judged by a multimeter. The measurement method is the same as that of the ordinary diode. That is, using the multimeter R&TImes; 1k file, the two test leads are respectively connected to the two electrodes of the Zener diode, and one is measured. After the result, the two test leads are measured again. In the two measurement results, the resistance value is smaller, the black meter is connected to the positive pole of the Zener diode, and the red meter is connected to the cathode of the Zener diode.
If the positive and negative resistances of the Zener diode are measured to be small or infinite, the diode is broken or open circuit damaged.
2. Voltage measurement
Use 0~30V continuously adjustable DC power supply. For the Zener diode below 13V, the output voltage of the regulated power supply can be adjusted to 15V, and the positive pole of the power supply is connected in series with a 1.5kΩ current limiting resistor. The negative pole is connected, the negative pole of the power supply is connected to the positive pole of the Zener diode, and the voltage value across the Zener diode is measured by a multimeter, and the measured reading is the steady voltage value of the Zener diode. If the regulation voltage of the Zener diode is higher than 15V, the regulated power supply should be adjusted to 20V or more.
Test power can also be supplied to the Zener diode with a megger below 1000V. The method is:
Connect the positive end of the megohmmeter to the negative pole of the Zener diode. After the negative end of the megohmmeter is connected to the positive pole of the Zener diode, shake the megohmmeter handle at a uniform speed as specified, and monitor the voltage across the Zener diode with a multimeter. The value (the voltage of the multimeter should be determined according to the magnitude of the stable voltage). When the indication voltage of the multimeter is stable, this voltage is the stable voltage of the Zener diode.
If the steady voltage value of the measured Zener diode is high or low, the diode is unstable.
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