Teach you how to use a multimeter to detect the quality of ordinary diodes

　　The main faults of diodes are open circuit, short circuit and unstable voltage regulation. Among these three faults, the former fault is manifested by the increase of power supply voltage; the latter fault is manifested by the power supply voltage dropping to zero volts or the output being unstable.

　　Judgment of common faults of diodes:

　　By testing the voltage across the Zener diode while power is on, the nature of the Zener diode fault can be determined.

　　1. Open circuit

　　When the diode is open, the voltage across it will increase, and it is not difficult to make a judgment based on this.

　　2. Short circuit

　　When a diode fails as a short circuit, the voltage across it drops to zero volts.

　　3. The voltage stabilization value is unstable

　　Poor quality diodes can lead to unstable output voltage. When the voltage across the Zener diode is measured using the DC voltage range of a multimeter, it is found that the voltage fluctuates.

　　How to use a multimeter to detect the quality of ordinary diodes:

　　1. Identify the positive and negative poles of the diode. The end with 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 positions 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 overflows (i.e., it displays 1), the diode is broken. If there is a reading, swap the test leads. If there is still a reading but it is not overflowing, the diode is broken.

　　4. If it is a light-emitting diode, if the diode is normal, you can see a faint light, and the longer leg is the positive pole.

　　Summary of using a multimeter to measure the quality of diodes

　　1. Detection of Zener Diode

　　1. Identification of positive and negative electrodes

　　From the appearance point of view, the positive end of the metal packaged Zener diode body is flat, and the negative end is semicircular. The end with a color mark printed on the plastic packaged Zener diode body is the negative pole, and the other end is the positive pole. For Zener diodes with unclear markings, you can also use a multimeter to determine their polarity. The measurement method is the same as that of ordinary diodes, that is, use the multimeter R&TImes;1k gear, connect the two test leads to the two electrodes of the Zener diode respectively, and after measuring a result, swap the two test leads for measurement. In the two measurement results, the one with smaller resistance value, the black test lead is connected to the positive pole of the Zener diode, and the red test lead is connected to the negative pole of the Zener diode.

　　If the forward and reverse resistances of the Zener diode are measured to be very small or infinite, it means that the diode has been broken down or damaged by an open circuit.

　　2. Measurement of voltage stabilization value

　　Use a 0~30V continuously adjustable DC power supply. For voltage regulator diodes below 13V, the output voltage of the voltage regulator can be adjusted to 15V. Connect a 1.5kΩ current limiting resistor in series to the positive pole of the power supply and then connect it to the negative pole of the voltage regulator diode to be measured. Connect the negative pole of the power supply to the positive pole of the voltage regulator diode. Then use a multimeter to measure the voltage value across the voltage regulator diode. The measured reading is the voltage regulator value of the voltage regulator diode. If the voltage regulator value of the voltage regulator diode is higher than 15V, the voltage regulator should be adjusted to more than 20V.

　　A megohmmeter with a voltage lower than 1000V can also be used to provide a test power supply for the Zener diode. The method is:

　　Connect the positive terminal of the megohmmeter to the negative terminal of the Zener diode, and then connect the negative terminal of the megohmmeter to the positive terminal of the Zener diode. Then shake the handle of the megohmmeter at a prescribed uniform speed. At the same time, use a multimeter to monitor the voltage across the Zener diode (the voltage range of the multimeter should depend on the size of the stable voltage value). When the voltage indicated by the multimeter is stable, this voltage value is the stable voltage value of the Zener diode.

　　If the measured stable voltage value of the Zener diode fluctuates, it means that the diode is unstable.