DEFERENCE BETWEEN DOIODE AND ZENER

Simply we can say that a Diode is a semiconductor device, which consists of two semiconductor layers. That means a Diode is the simplest semiconductor device and it consists of two semiconductor layers (one P-type and one N-type) connected to each other. Therefore, diode is a PN junction. Diode has two terminals known as the anode (the P-type layer) and cathode (the N-type layer). Diode allows current to flow through it, only in one direction that is anode to cathode. This direction of current is marked on its symbol with an arrow head. Since diode restricts the current to only one direction, it can be used as a rectifier. The full bridge rectifier circuit, which is made of four diodes can rectify an alternative current (AC) to a direct current (DC). The diode starts acting as a conductor when a small voltage is applied in the direction of anode to cathode. This voltage drop (known as the forward voltage drop) is always there when a current flow happens. This voltage is usually about 0.7V for normal silicon diodes. Although, diode allows current flows from anode to cathode, things change when a very large voltage (called breakdown voltage) is applied in the direction of cathode to anode (N to P). In this case, diode is damaged permanently (due to avalanche breakdown) and becomes a conductor allowing a huge cathode to anode current. Where a Zener diode is a special type of diode, which possesses some other features that cannot be found in normal diodes. Designers select them according the requirement of the application. A Zener diode is made by doing a little adjustment to a normal diode. As mentioned in previous paragraph, a normal diode will conduct a large reverse current and becomes permanently damaged when a large reverse voltage is applied. Zener diode will also conduct a large reverse current, but the device will not be damaged. This is achieved by changing the way of doping the PN junction and this reverse voltage is called the ‘Zener voltage’. Therefore, Zener diode can conduct in both ways. If the anode to cathode voltage is higher than forward voltage drop (about 0.7V), it will conduct in forward direction, and it will conduct in reverse direction, if the reverse voltage is equal to zenor voltage (may be any value ex: -12V or -70V).