Diode Basics Cheatsheet
Shared 11/27/2025•107 views
Diode Structure and Symbol A diode is formed by joining P-type and N-type semiconductor materials. P-Type Material: Majority Carriers: Holes (+) Connected to the Anode (A) terminal. N-Type Material: Majority Carriers: Electrons (-) Connected to the Cathode (K) terminal. Depletion Region: A region at the P-N junction where mobile charge carriers (holes and electrons) have diffused across the junction, leaving behind immobile ionized donor and acceptor atoms. Acts as an insulator when unbiased or reverse-biased. Diode Symbol: Triangle points from Anode (P-side) to Cathode (N-side). Current flows in the direction of the triangle (Anode to Cathode) when forward biased. Diode Biasing Conditions 1. Forward Bias Condition: Anode voltage is greater than Cathode voltage ($V_A > V_K$). Specifically, $V > V_{threshold}$. A positive voltage is applied to the P-type material (Anode) and a negative voltage to the N-type material (Cathode). Effect: The external voltage opposes and reduces the width of the depletion region. Majority carriers (holes from P-side, electrons from N-side) gain enough energy to cross the now-thinner depletion region. Results in Significant Current Flow (Anode to Cathode). 2. Reverse Bias Condition: Cathode voltage is greater than Anode voltage ($V_K > V_A$). Specifically, $V A negative voltage is applied to the P-type material (Anode) and a positive voltage to the N-type material (Cathode). Effect: The external voltage adds to the built-in potential, increasing the width of the depletion region. Majority carriers are pulled away from the junction, preventing current flow. Results in Negligible (Leakage) Current . I-V Characteristic Curve Plots Diode Current ($I$) versus Diode Voltage ($V$). Forward Bias Region ($V > 0$): Initially, very little current flows until the voltage reaches the threshold voltage ($V_{th}$), also known as the "knee voltage" . For silicon diodes, $V_{th}$ is typically around $0.7V$. Once $V > V_{th}$, the diode current increases exponentially with voltage. Reverse Bias Region ($V Only a very small, constant reverse leakage current flows, almost independent of voltage. If the reverse voltage increases beyond a certain point, the diode enters the Breakdown Region . In the breakdown region, the reverse current increases rapidly, potentially damaging the diode if not limited.
