Emitter-Switching Transistor Drive Circuit for Stable Saturation
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Solution Overview
Problem
Existing driving circuits for emitter-switching configurations face challenges in maintaining suitable saturation levels across a wide range of collector currents, leading to excessive dissipation and inaccurate control during turn-off, especially when dealing with variable collector current applications.
Innovation Solution
A driving circuit that includes an IGBT driving device and a driving bipolar transistor, maintaining the base-collector junction of the bipolar transistor at a voltage next to zero, ensuring stable saturation conditions and reducing dynamic voltage drop, allowing for efficient control of the saturation level and enabling the use of recirculation diodes in full-bridge configurations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If a conventional driving circuit with Zener diode and electrolytic capacitor is used, then the circuit can store energy during turn-off, but the saturation level becomes unstable when collector current varies widely, leading to excessive dissipation and inaccurate control
Solution Approach 1:
The patent introduces a driving bipolar transistor as an intermediary device between the control signal and the main power transistor. This driving transistor actively regulates the base current to the HV transistor, ensuring stable saturation level regardless of collector current variations. The intermediary transistor acts as a current buffer that maintains consistent base-collector junction voltage, resolving the instability issue while preserving energy storage functionality.
Solution Approach 2:
The patent dynamically adjusts the base current parameter to the HV transistor through the driving bipolar transistor. By changing the base current in response to collector current variations, the circuit maintains optimal saturation levels across different operating conditions. This parameter adjustment prevents excessive dissipation and ensures accurate control, directly addressing the reliability issue.
2Speed
If the base current is increased to improve turn-on speed, then the saturation voltage decreases, but the storage time increases excessively during turn-off
Solution Approach 1:
The patent employs periodic control of the base current through the driving bipolar transistor. During turn-on, the driving transistor provides sufficient base current to achieve fast saturation. During turn-off, the driving transistor rapidly reduces and reverses the base current, extracting stored charge and reducing storage time. This periodic adjustment of base current optimizes both turn-on speed and turn-off performance without excessive storage time.
Solution Approach 2:
The driving bipolar transistor provides feedback control by sensing the collector current and adjusting the base current accordingly. This feedback mechanism ensures that the base current is optimized for each operating condition, achieving fast turn-on when needed while preventing excessive charge storage that would prolong turn-off time. The feedback loop maintains optimal saturation levels dynamically.
Data Source
AI summary
A driving circuit for an emitter-switching configuration of transistors having first and second control terminals connected to the driving circuit, forms a controlled emitter-switching device having in turn respective collector, source and gate terminals. The driving circuit comprises a driving block coupled between the collector terminal and the source terminal of the controlled emitter-switching device and connected to the first control terminal of the emitter-switching configuration. Further advantageously, the driving block comprises at least one IGBT driving device coupled between the collector terminal and the first control terminal of the emitter-switching configuration and having, in turn, a third control terminal, as well as a driving bipolar transistor, coupled between the collector terminal and the first control terminal of the emitter-switching configuration for controlling a saturation condition of said bipolar transistor of said emitter-switching configuration maintaining a base-collector junction thereof at a voltage next to zero and having, in turn, a fourth control terminal.