# A PN Junction, acts as a _______

A PN Junction, acts as a _______

### Right Answer is: Unidirectional switch

#### SOLUTION

• A diode is a two-terminal device made of a p-n junction. It works like a unidirectional switch that allows current flow only in one direction.
• It is a conductor in the positive direction and an insulator in the negative direction.
• Once it starts conducting, its resistance is negligible. It is like a closed switch.
• The voltage and current relationship across a diode have three regions: the forward bias region, reverse bias region, and reverse breakdown region.

• When the voltage is larger than the forward bias voltage value (VF = 0.3 V for germanium diode, VF = 0.6 V to 0.7 V for a silicon diode),
• VD > VF, the diode becomes a conductor and acts as a closed switch. Hence, the current increases very fast indicating very low resistance at this device.
• In this region, the diode can be considered as a closed switch with negligible resistance and a small voltage drop of VF.
• When the diode is in the reverse bias region, VZ < VD < VF, then the diode acts as an insulator or open switch. In other words, it acts like a very large resistor.
• When the VD < VZ, the diode operates in the breakdown region and acts as a closed switch.
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