Bridge Output Circuit Dead Time Control via OFF State Detection
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Solution Overview
Problem
In half bridge circuits, the dead time required to prevent simultaneous turning on of high and low side transistors leads to deviations in output duty from the designated input signal duty, especially at higher frequencies, affecting the reliability of load driving.
Innovation Solution
A bridge output circuit with voltage-controlled transistors, OFF detection circuits, and an output control circuit that performs transition operations based on signal changes and acquired analog signals representing dead time, ensuring precise control of transistor states to minimize duty deviation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If dead time is introduced to prevent simultaneous turning on of high and low side transistors, then reliability is improved, but output duty precision deteriorates
Solution Approach 1:
The patent implements feedback by detecting the actual OFF state of transistors through OFF detection circuits and using this information to dynamically adjust the dead time period. The output control circuit monitors transistor states and feeds this information back to modify subsequent dead time durations, enabling precise compensation for duty cycle deviations caused by dead time effects.
Solution Approach 2:
The patent transforms the static, fixed dead time approach into a dynamic, adaptive system. The dead time period is no longer constant but varies based on real-time transistor OFF state detection results. This dynamic adjustment allows the system to optimize both reliability (by maintaining adequate dead time when needed) and duty precision (by reducing dead time when transistors are already safely OFF).
2Reliability
If dead time is extended to ensure reliable transistor switching, then reliability is improved, but response speed deteriorates
Solution Approach 1:
The patent makes the dead time duration dynamic rather than static. By continuously monitoring transistor OFF states and adjusting dead time accordingly, the system achieves fast switching response when conditions permit while maintaining extended dead time for reliability when needed. This dynamic approach resolves the contradiction between switching speed and reliability.
Solution Approach 2:
The system performs self-adjustment by automatically detecting transistor states and modifying dead time without external intervention. The OFF detection circuits and output control circuit work autonomously to optimize switching parameters in real-time, enabling the system to self-regulate between speed and reliability based on actual operating conditions.
3Object-generated harmful factors
If dead time is increased to prevent through current, then harmful factors are reduced, but output duty accuracy deteriorates
Solution Approach 1:
The patent uses feedback from OFF detection circuits to monitor whether transistors are truly OFF before extending dead time for through current prevention. This feedback mechanism ensures that dead time is only extended when actually necessary for safety, rather than being applied unconditionally. Consequently, the system suppresses through current harmful effects while minimizing the impact on output duty accuracy.
Solution Approach 2:
The patent dynamically changes the dead time parameter based on detected transistor states and through current risk assessment. When through current risk is detected, dead time is extended; when risk is low, dead time is reduced to maintain duty accuracy. This parameter adaptation resolves the contradiction between harmful factor suppression and precision maintenance.
Data Source
AI summary
A bridge output circuit includes: a voltage-controlled first transistor provided between a first power supply terminal and an output terminal; a voltage-controlled second transistor provided between the output terminal and a second power supply terminal having a potential lower than the potential of the first power supply terminal; a first OFF detection circuit detecting whether the first transistor is in an OFF state based on a gate voltage of the first transistor; a second OFF detection circuit detecting whether the second transistor is in an OFF state based on a gate voltage of the second transistor; and an output control circuit performing a first source transition operation of turning off the second transistor and then turning on the first transistor, and then performing a second source transition operation of turning off the first transistor and then turning on the second transistor.