Anti-Series MOS Switch Circuit for Reverse Recovery Reduction
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
High-frequency switching systems face performance limitations due to the 'reverse recovery current' phenomenon in MOS transistors, leading to high power dissipation and operational issues, especially when using diodes for switching.
Innovation Solution
A power switch circuit comprising two MOS transistors in an anti-series arrangement with a common source and gate, where the gate is connected to the drain of either transistor based on current direction, significantly reducing reverse recovery current and power dissipation by minimizing diode activation during switching.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If MOS transistors with high BVdss are used in high-frequency switching systems, then the switching capability is improved, but reverse recovery current peaks occur causing high power dissipation
Solution Approach 1:
The patent divides the single switching function into two separate MOS transistors (M1 and M2) operating in complementary half-cycles. Each transistor handles only one polarity of current flow, preventing the reverse recovery phenomenon that occurs in single-transistor designs. This segmentation allows high-frequency operation without the harmful reverse recovery current peaks that cause power dissipation.
Solution Approach 2:
The patent inverts the conventional approach by using two transistors in an anti-series configuration where each transistor is reverse-biased during its non-conducting half-cycle instead of forward-biased. This inversion prevents the storage of minority carrier charges that would otherwise cause reverse recovery current when the transistor switches off, thereby eliminating the main source of power dissipation in high-frequency switching.
2Ease of operation
If diodes are used for switching in MOS transistors, then the switching function is achieved, but reverse recovery current peaks occur leading to high power dissipation
Solution Approach 1:
The patent changes the operating parameters of the MOS transistors by configuring them in an anti-series arrangement with reverse bias during non-conduction. This parameter change transforms the switching mechanism from diode-based (which suffers from reverse recovery) to MOS-based with reverse-biased body diodes, eliminating the reverse recovery current peaks while maintaining the switching function.
3Loss of energy
If anti-series MOS transistor arrangement is used, then reverse recovery current is reduced, but voltage drop across switch increases
Solution Approach 1:
The patent employs dynamic control of the anti-series transistor pair through complementary gate drive signals that are synchronized with the input signal polarity. This dynamic operation ensures that only one transistor conducts at a time during each half-cycle, minimizing the effective on-resistance and voltage drop while maintaining the benefit of eliminated reverse recovery current.
Data Source
AI summary
A bi-directional switch circuit includes first and second transistors having their control electrodes coupled at a first common node and the current paths coupled at a second common node in an anti-series arrangement. First and second electrical paths coupled between the first common node and the first and second transistors, respectively, include first and second switches switchable between a conductive state and a non-conductive state. A third electrical path between the first and second common nodes includes a third switch switchable between a conductive state and a non-conductive state. The third switch is coupled with the first and second switches by a logical network configured to switch the third switch to the conductive state with the first and second switches switched to the non-conductive state, and to the non-conductive state with either one of the first and second switches switched to the conductive state.