A diode’s forward voltage drop is the voltage that occurs when current passes through it. It is independent of current and varies by diode type. Forward bias allows current flow, while reverse bias does not and can cause damage. Different diodes have different forward voltage drops.
A diode forward voltage refers to the voltage drop that occurs when an electric current passes through a diode in an electrical circuit. It is generally independent of the amount of current flowing through the diode and will be the same for a given diode family. For silicon diodes, which are generally the most common, the forward voltage drop of the diode is about 0.7 volts (V).
Diodes are devices that pass electric current in only one direction and therefore can be thought of as a sort of one-way valve for electrons. When the electrons move in the correct direction to pass through the diode, the diode is said to be forward biased. Therefore, the forward voltage drop of the diode is also known as the forward bias voltage drop.
Diodes work by having a small piece of doped semiconductor material sandwiched between their electrodes, which pass electrons in one direction but not the other. This material has two zones, the n-zone, rich in negatively charged electrons, and the p-zone, poor in electrons. The p-zone can be thought of as having positive holes that can accept electrons from the n-zone. When the two zones are brought together to form a pn-junction, electrons transfer from the n-zone to the p-zone until all electrons in the n-zone available for use as current carriers are depleted and the pn-junction becomes an insulator.
If fresh electrons are injected into the depleted n-zone, while being removed from the saturated p-zone, electric current will flow through the junction. This is what happens when the diode is forward biased. The electrons must be pushed by a voltage with sufficient force to cross the p-n junction, and this push is the source of the diode’s forward voltage, or forward bias voltage drop.
If the polarity of the circuit is reversed and an attempt is made to inject electrons into the p-zone while removing them from the n-zone, the diode is said to be reverse-biased and will not flow current. If this reverse bias voltage exceeds a certain value – the maximum reverse voltage – the diode could fail and pass large currents, in a process known as reverse voltage breakdown. The diode will then be permanently damaged.
As stated, different types of diodes have different forward voltage drops. The forward voltage drop of a simple light emitting diode (LED) can range from 1.4 to 4 V, depending on the type. For the Schottkey diode, the forward voltage drop is usually only 0.2V.
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