Buck Converter Dynamic Impedance Control for Over-Current
Solution Overview
Problem
Synchronous buck converters face efficiency limitations when operating with a forward biased body diode, particularly due to current limit violations, which can lead to suboptimal performance and reliability.
Innovation Solution
The technique involves switching the operating mode of the buck converter when a current limit threshold is detected, commanding the switch with a forward biased body diode to a low impedance mode, allowing efficient current conduction and mode transitions between buck and boost operations, thereby preventing body diode conduction and managing over-current limits.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the buck converter operates with a forward biased body diode during current limit violations, then the converter can handle over-current conditions, but the efficiency of the buck converter is reduced
Solution Approach 1:
The patent applies dynamics by making the impedance of the power switches adjustable rather than fixed. The controller dynamically changes the impedance state of the switches based on operating conditions - maintaining low impedance for efficient current conduction during normal operation, and switching to high impedance when body diode conduction is detected during over-current events. This dynamic adaptation allows the system to optimize between efficiency and over-current protection capability.
Solution Approach 2:
The patent changes the electrical parameters (impedance) of the power switches based on detected operating conditions. When a body diode becomes forward biased during current limit violations, the controller modifies the impedance parameters of the switches to prevent harmful body diode conduction while maintaining the ability to handle over-current conditions. This parameter adjustment resolves the contradiction by optimizing performance for different operational states.
2Loss of energy
If the switch impedance is kept low for efficient current conduction, then the converter efficiency is improved, but the switch may be unable to block reverse voltage during body diode conduction
Solution Approach 1:
The patent implements dynamic impedance control where the power switches operate in different impedance states depending on the operational phase. During normal buck operation, switches maintain low impedance for efficient current conduction. When body diode conduction is detected (indicating reverse voltage conditions), the controller dynamically switches the impedance to high state, enabling the switches to block reverse voltage effectively. This temporal separation of impedance states resolves the contradiction between conduction efficiency and voltage blocking capability.
Solution Approach 2:
The patent employs periodic monitoring and switching actions where the controller continuously detects body diode conduction conditions and periodically adjusts switch impedance states accordingly. This periodic control mechanism ensures that low impedance is maintained during efficient conduction phases while high impedance is activated during voltage blocking phases, resolving the apparent contradiction through time-based separation of functions.
Data Source
AI summary
Techniques for a sinking and sourcing power stage are provided. In an example, a power stage circuit can include a first power transistor configured to couple to a first input power rail, a second power transistor configured to couple to a second input power rail, an output node configured to couple to a load and to couple the first power transistor in series with the second power transistor between the first and second input power rails, and a controller configured to operate the first and second power transistors in a first mode to source current to the load and to operate the first and second power transistors in a second mode to sink current from the load.