BJT Spike Protection Circuit for Inductive Load Outputs
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Solution Overview
Problem
Semiconductor devices, particularly ICs, are vulnerable to damage from spike voltages generated in external inductive load circuits, which can exceed the breakdown voltage of conventional Zener diodes, leading to high leakage current and power loss, making it difficult to manufacture effective spike voltage protection circuits with lower leakage current and breakdown voltage.
Innovation Solution
A protection circuit utilizing bipolar junction transistors (BJTs) connected in series is introduced, allowing for adjustable breakdown voltage and reduced leakage current, with the number of BJTs determining the breakdown voltage and on-state resistance, enabling effective spike voltage protection without the need for additional manufacturing steps or masks.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional Zener diodes are used for spike voltage protection, then breakdown voltage protection is provided, but leakage current and power loss increase
Solution Approach 1:
The protection circuit is segmented into multiple BJTs connected in series, where each BJT contributes a portion of the total breakdown voltage. This segmentation allows for better control of leakage current while maintaining the required protection voltage level, as each BJT operates at a lower individual voltage stress
Solution Approach 2:
The invention changes the fundamental parameter of the protection device from Zener diode to BJT, utilizing the BJT's breakdown characteristics. By adjusting the number of BJTs in series and their individual parameters, the circuit achieves both the required breakdown voltage and reduced leakage current compared to conventional Zener diodes
2Reliability
If the number of BJTs is increased to increase breakdown voltage, then spike voltage protection capability improves, but device complexity increases
Solution Approach 1:
The BJTs in the protection circuit serve multiple functions: they provide breakdown voltage protection, limit leakage current, and can be integrated with existing circuit elements. The same BJT structure is used for both protection and potential signal processing functions, reducing overall device complexity
Solution Approach 2:
The protection circuit merges the BJTs into the existing semiconductor device structure, sharing common substrates, doping regions, and manufacturing processes. This integration combines the protection function with the main device fabrication, avoiding additional discrete components and reducing overall complexity
3Reliability
If additional protection circuits are added to semiconductor devices, then spike voltage protection is improved, but manufacturing complexity and cost increase
Solution Approach 1:
The protection circuit is designed to be formed during the preliminary stages of semiconductor manufacturing, using the same doping and fabrication steps as the main device. The BJT structures are created before final device assembly, allowing the protection function to be built-in rather than added later
Solution Approach 2:
The invention merges the protection circuit fabrication with the main semiconductor device manufacturing process. Common steps including substrate preparation, doping, oxidation, and metallization are shared between the protection circuit and the main device, eliminating the need for separate manufacturing lines or additional masks
Data Source
AI summary
A semiconductor device is provided. The semiconductor device comprises an output circuit configured to be electrically connected between a driving circuit and an external load circuit, and a protection circuit electrically connected to the output circuit and the driving circuit. The protection circuit comprises a first transistor having a base electrode, a collector electrode and an emitter electrode and a second transistor having a base electrode, a collector electrode and an emitter electrode. The base electrode of the first transistor is electrically connected to the collector electrode of the second transistor.