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EEE 345 Power Electronics Lecture 2: Diodes and Semiconductor Switches
Semiconductor Switches Semiconductor switching –fundamental switching (50-60 Hz) and high frequency PWM switching (e.g., 10, 100 kHz, 1 MHz) Switches –uncontrolled (diodes) and controlled Controlled –full-controlled and half-controlled Voltage-controlled and current-controlled devices Ideal switch: ON state –short circuit; OFF state –open Avoid confusion when telling “the switch is open” or “the switch is closed”
Power Diode - 1 A PN-junction comprised of two semiconductor materials –P- and N-types Two diode electrodes are respectively called Anode (A) and Cathode (K) From basic semiconductor physics, diode Ampere-Volt characteristics Diode is a passive (uncontrolled) device and its state is defined by an external circuit Diode normal states are ON (forward current conductance) or OFF (reverse voltage blocking) If the reverse voltage exceeds diode rated voltage, the breakdown occurs Breakdown phenomenon is utilized in special Zener diodes used for spike protection and voltage stabilization DVDiForwardConductanceReverseBlockingBreakdownRV
Power Diode - 2 Diode models: a –ideal b –offset (ideal diode + voltage source) c –offset + slope (ideal diode + voltage source + resistance) According to ideal diode model (a), a diode is represented by short circuit in forward direction and by open circuit in reverse one Diode offset model (b) accounts for diode voltage drop in forward direction Accounting for slope adds series resistance
Power Diode - 3 Diode reverse recovery is a dynamic phenomenon at turn-OFF Reverse recovery understanding is required for high frequency switching