Testing a Diode

 A diode can be tested by checking the forward-to-reverse-resistance ratio indicates the ability of the diode to pass current in one direction and block current in the other direction.

      A germanium diode has a low forward-resistance of several hundred ohms. The reverse resistance is high, greater than 100,000 ohms. Silicon diodes have a higher forward and reverse resistance than germanium. An ohmmeter test of a diode should show a low forward resistance and a high reverse resistance.

      The polarity of the terminals in an ohmmeter appears at the leads of ohmmeter: Red is positive and black is negative or common. If the positive ohmmeter lead is connected to the anode of the diode and the negative lead to the cathode, the diode is forward biased. Current should then flow through the diode and the meter should indicate a low resistance. If the meter leads are reversed, the diode is reverse biased. Little current should flow and the meter should measure a high resistance.

      If a diode shows both low forward and low reverse resistance, it is probably shorted. If the diode measure both high forward and high reverse resistance, then it is probably opened.

      An accurate diode test ca be made with most types of ohmmeters. The forward resistance voltage must be larger than the barrier voltage of the diode (0.7 V for silicon and 0.3 V for germanium) for conduction to take place.

      An ohmmeter can also be used to determine the cathode and anode of unmarked diode. When there is a low reading, the positive lead is connected to the anode and the negative lead is connected to the cathode.

Characteristics of Diode

Did you fully understand what diode is? Can you explain the difference between cathode and anode? Did you know that  it has  Characteristics?, here it is:

1. The process of converting alternating current into direct current is called Rectification.
2. The small silicon diodes are used as low-current rectifiers.
3. When employed as a rectifier, the point-contact diode is less efficient than the junction diode.
4. One of the most common uses for semiconductor diodes is rectifiers in power supplies.
5. A heat-equipped diode has much higher current rating than an identical diode which is not so equipped.
6. The large silicon diodes are used as high current and high voltage rectifiers.
7. Silicon diodes have a higher forward-to-reverse resistance ratio, and much smaller than the selenium of the same voltage and current characteristics.
8. The temperature coefficient for higher voltage units is positive for the very-low voltage unit is negative.
9. Heat sink is used to reduce the rise in junction temperature as the current is raised.
10. Zener diode is a semiconductor device used as voltage regulator.
11. One of the most important characteristics of the zener diode is its temperature coefficient.
12. The most common use of any regulator circuits is to minimize output variations with respect to variations in input, temperature, and load requirements.
13. Silicon diodes that are designed for a specific value of reverse breakdown voltage are called Zener diodes.
14. A silicon diode is used as half-wave rectifiers, and a very small germanium diode is used as detector.
15. Point-contact diodes are extensively used detectors in R-F circuits, because of their low shunt capacitance feature.
16. Connect two or more diodes in series, to increase the voltage rating.
17. Zener diodes are also called voltage-reference diodes and avalanche diodes.
18. Compared with germanium, silicon is used in almost all solid-state devices because it can operate at higher temperature and has less leakage current.
19. Reverse voltage is applied at the N-cathode side, since the zener diode is a PN junction.
20. Usually, general-purpose silicon diode has maximum forward current ratings of 1A and 200 to 400v reverse breakdown voltage.

What is Diode?

Basically, solid-state diode is a semiconductor device (consisting of two electrodes) that permits the flow of current in only one direction. It is simplest electronic component of semiconductors family.

Diode is an electronic device that allows the flow of current in only one direction. Generally, diodes are classified into three categories:  a) the signal diode, b) the rectifiers diode, and the regulator diode. When they are used in signal circuits, they are called “signal diodes”. When they are used for the conversion of AC to DC they are called “rectifiers”. When they used for controlling voltage they are called “regulator diodes”. Zener diodes are especially designed for controlling voltage.