A diode can conduct in two different modes: forward bias and reverse bias.
- Forward Bias: When a diode is forward-biased, it means that the voltage across the diode allows the current to flow easily through the diode. In this mode, the positive terminal of the voltage source is connected to the P-type material (anode), and the negative terminal is connected to the N-type material (cathode). This configuration reduces the potential barrier, allowing charge carriers (electrons and holes) to move across the junction and contribute to the flow of current.
In the forward-biased mode, the diode exhibits low resistance, and it allows a significant current to pass through. The voltage required to overcome the potential barrier and initiate conduction is typically around 0.6 to 0.7 volts for silicon diodes.
- Reverse Bias: When a diode is reverse-biased, the voltage across the diode opposes the flow of current. In this mode, the positive terminal of the voltage source is connected to the N-type material (cathode), and the negative terminal is connected to the P-type material (anode). This configuration increases the potential barrier, preventing the majority of charge carriers from crossing the junction.
In the reverse-biased mode, the diode exhibits high resistance, and only a small leakage current, called reverse saturation current, flows through. The voltage required to maintain this state is known as the reverse breakdown voltage. If the reverse bias voltage exceeds a critical value, the diode may undergo a breakdown, and a significant reverse current may flow.
In summary, a diode conducts in the forward-biased mode, allowing current to flow, and exhibits high resistance in the reverse-biased mode, limiting the current to a small leakage current unless the reverse breakdown voltage is exceeded. Understanding these modes is crucial for designing and analyzing electronic circuits that utilize diodes.