Bipolar Transistors Passive-Off AC Coupling Prevent Turn-On
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Solution Overview
Problem
Bidirectional bipolar transistors face challenges in maintaining breakdown voltage and preventing gain degradation during the 'passive-off' mode, especially when control circuitry is inactive, leading to potential accidental turn-on and increased leakage currents.
Innovation Solution
The implementation of a passive-off circuitry that uses AC coupling with transient voltages on external terminals to prevent forward biasing of emitter junctions, employing drive transistors and a transient coupling circuit to limit voltage between emitter/collector regions and their corresponding base contact regions, ensuring the breakdown voltage is not degraded.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If the control circuitry is inactive during passive-off mode, then the device structure is simplified, but the breakdown voltage degrades and leakage currents increase due to accidental turn-on
Solution Approach 1:
The patent implements a self-service mechanism where the bipolar transistor automatically enters passive-off mode when the control circuitry is inactive. The emitter junction is designed to self-clamp through its inherent diode characteristics, preventing forward bias without requiring active control signals. This self-regulating behavior maintains breakdown voltage reliability while simplifying the control circuitry.
Solution Approach 2:
The patent applies preliminary anti-action by designing the emitter junction with a clamp circuit that preemptively prevents forward biasing before accidental turn-on can occur. The clamp circuit is pre-configured to counteract any transient voltages that might cause the emitter junction to forward bias, thereby preventing leakage current amplification and maintaining breakdown voltage integrity during passive-off mode.
2Productivity
If the emitter junction is allowed to forward bias during passive-off mode, then the device operates more efficiently, but the bipolar gain degrades the breakdown voltage
Solution Approach 1:
The patent applies local quality by creating different operational characteristics for different parts of the device. The emitter junction is designed with a clamp circuit that locally prevents forward biasing, while the collector junction maintains its normal bipolar operation. This localized control allows the device to maintain high breakdown voltage reliability at the emitter junction while preserving efficient bipolar conduction at the collector junction.
Solution Approach 2:
The patent segments the bipolar transistor operation into two independent junctions with different control strategies. The emitter junction is segmented to operate in diode mode with clamp protection during passive-off, while the collector junction is segmented to maintain bipolar gain during active operation. This segmentation allows independent optimization of each junction's behavior to resolve the contradiction between efficiency and breakdown voltage reliability.
3Reliability
If AC coupling is used to prevent forward biasing, then the breakdown voltage is maintained, but the device complexity increases
Solution Approach 1:
The patent merges the clamp circuit functionality directly into the emitter junction structure, combining the diode characteristics with the clamp protection in a single integrated element. This merging eliminates the need for separate passive-off circuitry components, thereby maintaining breakdown voltage reliability while minimizing the increase in device complexity. The clamp circuit shares the emitter junction's physical space and electrical nodes, reducing overall device complexity.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This solution effectively prevents breakdown voltage degradation and leakage current amplification, even when control circuitry is inactive, enhancing the reliability and efficiency of power conversion systems by maintaining high breakdown voltage and reducing on-resistance.
Implementation Method 1
AC coupling uses transient voltage on the external terminals to prevent forward biasing an emitter junction
Implementation Method 2
The passive turnoff circuit clamps each base contact region to less than a diode drop from the neighboring emitter/collector region, so that bipolar transistor operation is avoided
Implementation Method 3
By keeping the emitter junctions well away from turn-on, minority carrier injection is limited, and the gain of the bipolar transistor does not degrade the breakdown voltage
Data Source
AI summary
The present application discloses new approaches to providing “passive-off” protection for a B-TRAN-like device. Even if the control circuitry is inactive, AC coupling uses transient voltage on the external terminals to prevent forward biasing an emitter junction. Preferably the same switches which implement diode-mode and pre-turnoff operation are used as part of the passive-off circuit operation.