What is the difference between a forward biased diode and a reverse biased diode?

Differences Between Forward-Biased and Reverse-Biased Diodes

Forward-biased diodes and reverse-biased diodes have significant differences in their operating principles and applications. Here are the main distinctions:

Forward-Biased Diode 

Operating Principle

• Voltage Direction: Forward bias refers to connecting the anode (positive terminal) of the diode to the positive terminal of the power supply and the cathode (negative terminal) to the negative terminal of the power supply.

• Conduction State: When the applied voltage exceeds the diode's threshold voltage (typically 0.6V to 0.7V for silicon diodes, 0.2V to 0.3V for germanium diodes), the diode conducts, allowing current to flow.

• IV Characteristics: In forward bias, the IV characteristic curve shows exponential growth, with current increasing rapidly as voltage increases.

Applications

• Rectification: Converting alternating current (AC) to direct current (DC).

• Clamping: Limiting the amplitude of signals.

• Circuit Protection: Preventing damage from reverse voltage.

Reverse-Biased Diode 

Operating Principle

• Voltage Direction: Reverse bias refers to connecting the anode (positive terminal) of the diode to the negative terminal of the power supply and the cathode (negative terminal) to the positive terminal of the power supply.

• Cut-off State: In reverse bias, the diode is typically in the cut-off state and does not allow current to flow. This is because the built-in electric field prevents the majority carriers from moving.

• Reverse Breakdown: When the reverse voltage exceeds a certain value (known as the breakdown voltage), the diode enters the reverse breakdown region, where the current increases sharply. For regular diodes, the breakdown voltage is usually high, but for Zener diodes, the breakdown voltage is designed to be used for voltage regulation.

Applications

• Voltage Regulation: Zener diodes operate in the reverse breakdown region to regulate voltage in circuits.

• Switching: Utilizing the reverse blocking characteristic of diodes as switching elements.

• Detection: In radio receivers, using the nonlinear characteristic of diodes for signal detection.

Summary of Main Differences

Voltage Direction:

• Forward Bias: Anode connected to the positive terminal of the power supply, cathode connected to the negative terminal.

• Reverse Bias: Anode connected to the negative terminal of the power supply, cathode connected to the positive terminal.

Conduction State:

• Forward Bias: Conducts when the voltage exceeds the threshold voltage, allowing current to flow.

• Reverse Bias: Typically in the cut-off state, blocking current unless the breakdown voltage is exceeded.

IV Characteristics:

• Forward Bias: IV characteristic curve shows exponential growth.

• Reverse Bias: IV characteristic curve is nearly flat before the breakdown voltage and rises sharply beyond it.

Applications:

• Forward Bias: Rectification, clamping, circuit protection.

• Reverse Bias: Voltage regulation, switching, detection.