Multimeter to detect the polarity and goodness of ordinary diodes

A multimeter to detect the polarity and quality of ordinary diodes.

Detection principle: According to the unidirectional conductivity of the diode, the diode has good forward resistance and large reverse resistance; the larger the difference between the two values, the better. If the phase is similar, the performance of the diode is not good or has been damaged.

When measuring, use the "ohm" block of the multimeter. Generally use Rx100 or Rxlk block instead of Rx1 or Rx10k block. Because the current of the Rxl block is too large, it is easy to burn out the diode. The internal power supply voltage of the Rxlok block is too large and it is easy to break down the diode.

Measurement method: connect the two meter rods to the two electrodes of the diode respectively, and read out the measured resistance value; then measure the rod once and then measure it once, and record the second resistance value. If the difference between the two resistances is very large, the diode performance is good; and according to the rod connection method (referred to as the forward connection) when the measurement resistance is small, it is determined that the anode of the diode is connected to the black rod. Connected to the red bar is the negative pole of the diode. Because the positive pole of the internal power supply of the multimeter is connected to the “—” jack of the multimeter, the negative pole of the internal power supply is connected to the “+” jack of the multimeter.

If the resistance of the two measurements is small, the diode has been broken down; if the resistance of the two measurements is large, it means that the inside of the diode has been disconnected: the resistance of the two measurements is not much different, indicating that the diode performance is not good. In these cases, the diode cannot be used.

It must be pointed out that since the volt-ampere characteristics of the diode are non-linear, different resistance values ​​are measured when measuring the resistance of the diode with different electrical blocking of the multimeter; in actual use, the current flowing through the diode is larger, and thus the diode is presented. The resistance value will be smaller.

2. Detection of special types of diodes.

1 Zener diode. A Zener diode is a diode that operates in a reverse breakdown region and has a stable voltage. The measurement of polarity and performance is similar to that of ordinary diodes. The difference is that when using the Rxlk block measurement diode of the multimeter, the reverse resistance is measured. In this case, convert the multimeter to In the Rx10k file, if the multimeter pointer is deflected to the right by a large angle, that is, the reverse resistance value is greatly reduced, the diode is a Zener diode; if the reverse resistance is substantially unchanged, the diode is a normal diode instead of Zener diode. The measuring principle of the Zener diode is: the internal battery voltage of the multimeter Rxlk block is small, and usually does not cause the breakdown of the ordinary diode and the Zener diode, so the reverse resistance measured is large. When the multimeter is switched to Rx10k, the voltage of the battery in the multimeter becomes very large, causing reverse breakdown of the Zener diode, so its reverse resistance drops a lot, because the reverse breakdown voltage of the common diode is higher than that of the Zener diode. Much, so the ordinary diode does not break down, and its reverse resistance is still large.

2 Light-emitting diode LED (Light EMitting Diode). Light-emitting diode (LED) is a special diode that converts electrical energy into light energy. It is a new type of cold light source, which is often used in level indication and analog display of electronic equipment. It is often made of compound semiconductors such as arsenication and phosphating. The color of the light-emitting diode depends mainly on the material of the semiconductor used, and can emit four kinds of visible light such as red, orange, yellow and green. The outer casing of the light-emitting diode is transparent, and the color of the outer casing indicates its luminous color. The LED operates in the forward region and its forward-on (on) operating voltage is higher than that of a normal diode. The larger the forward voltage is, the brighter the LED is. However, it should be noted that the applied forward voltage cannot make the LED exceed its maximum operating current to avoid burning the tube. The detection method of the light-emitting diode mainly adopts the Rx10k block of the multimeter, and the measurement method and the performance of the performance thereof are the same as those of the ordinary diode. However, the forward and reverse resistances of LEDs are much larger than those of ordinary diodes. When measuring the forward resistance of the LED, it can be seen that the diode has a slight luminescence.

3 photodiodes. Photodiodes, also known as photodiodes, are special diodes that convert light energy into electrical energy, and have a glass-embedded window on the shell to accommodate light. The photodiode operates in the reverse working area. When there is no light, the photodiode is the same as the ordinary diode, the reverse current is very small (generally less than o.1uA), the reverse resistance of the phototube is very large (tens of megaohms or more); when there is illumination, the reverse current increases significantly. The reverse resistance drops significantly (several thousand ohms to tens of kilo ohms), ie the reverse current (called photocurrent) is proportional to the illumination. Photodiodes can be used for light measurement and can be used as an energy source (photocell). It is widely used as a sensor device in optoelectronic control systems. The detection method of the photodiode is basically the same as that of the ordinary diode. The difference is that there is a large difference in reverse resistance between light and no light: if the measurement results are not much different, the photodiode is damaged or the diode is not a light-emitting diode.