Power Electronics Lecture Notes

Linear vs. Power Electronics

• Linear Electronics
  • Devices operate in the ACTIVE region.
  • Power loss is high as the device is ON for the entire cycle.
  • Low efficiency.
  • Power rating: few milliwatts to few watts.
• Power Electronics
  • Devices operate in SATURATION and CUT OFF regions.
  • Less power loss as the device is not ON for the entire cycle.
  • High efficiency.
  • Power rating: few milliwatts to megawatts.

Power Electronic Devices

• Power Diode

  • Consists of P+, n–, and n+ layers.
  • Conducts current in one direction.
  • Features heavy doping for increased conductivity.
  • Handles high power and voltage.
  • Types: Standard Diodes, Fast Recovery Diodes, Schottky Diodes.

• Power BJT (Bipolar Junction Transistor)

  • Current controlled device with collector, base, and emitter.
  • Operates in active and saturation regions.
  • Used in amplification and switching applications.
  • High switching frequency and efficiency.
  • Applications: SMPS, power amplifiers, motor speed controllers.

• Power MOSFET (Metal Oxide Semiconductor Field-Effect Transistor)

  • Voltage-controlled device.
  • High switching speed and efficiency.
  • Simple gate driving circuit.
  • Applications: UPS, SMPS, motor control, power amplifiers.

• IGBT (Insulated Gate Bipolar Transistor)

  • Combines features of BJT and MOSFET.
  • High voltage and current handling capabilities.
  • Voltage-controlled with high input impedance.
  • Used in SMPS, UPS, motor drives, inverters.

• SCR (Silicon Controlled Rectifier)

  • Four-layer PNPN device with three junctions.
  • Operates in reverse blocking, forward blocking, and forward conduction modes.
  • Applications: DC motor speed control.

• GTO (Gate Turn-Off Thyristor)

  • Three-terminal device similar to SCR.
  • Can be turned on and off using gate signals.
  • Faster switching speed than SCR.
  • Applications: AC drives, DC choppers, induction heating.

Key Characteristics and Comparisons

• Power Diode Characteristics
  • V-I characteristics similar to signal diodes.
  • Reverse recovery time important for performance.
• Power BJT Characteristics
  • V-I output characteristics with distinct saturation regions.
  • Switching characteristics defined by delay, rise, and fall times.
• MOSFET Characteristics
  • Switching influenced by internal capacitance and gate drive impedance.
• IGBT Characteristics
  • V-I characteristics show relation of gate-emitter voltage to collector current.
  • Superior for high voltage and current applications compared to BJT and MOSFET.

Applications Overview

• Power devices used in power supplies, inverters, motor controllers.
• Specific applications: UPS, SMPS, AC/DC drives, solar inverters.

Advantages & Disadvantages

• BJTs: High switching frequency, low turn-on losses, but complex drive circuit.
• MOSFETs: Simple drive, high frequency, but high on-state voltage.
• IGBTs: High handling capability, simple gate drive, but lower switching speed than MOSFETs.
• SCRs & GTOs: Suitable for high power applications but complex control and commutation.

These notes summarize the key concepts and devices discussed in the Power Electronics module, highlighting the operational principles, characteristics, and applications of various power electronic devices.