Power Electronics Lecture Series: Power BJ

Symbol, Structure, and Characteristics

Introduction to Power BJ

Power BJ is a bipolar junction transistor used in power electronics.
It has three terminals: base, emit, and collector.
The symbol for N p configuration is depicted with an arrow head towards the emit terminal.
Power BJ is designed to handle high power and has a larger cross-sectional area.
We will focus on N p transistor for internal analysis and comparison with normal BJ.

Power BJ has three layers: n plus, p, and n minus.
The collector drift region is added for handling high breakdown voltage.
The cross-sectional area and doping level are increased for power handling capacity.
The symbol remains the same as normal BJ, but with additional layers.
The structure is crucial for efficient power operation.

Power BJ exhibits different modes in the output characteristics.
These modes include cutoff, active, quasi-saturation, and hard saturation.
Cutoff mode occurs when both junctions are reverse biased.
Active mode functions as an amplifier and is not extensively covered in power electronics.
Quasi-saturation offers advantages like lower on-state resistance and quick turn-off, making it suitable for high-frequency applications.
Hard saturation has lower resistance and power loss but is used for low-frequency operation.