Hysteretic Buck-Boost Converter Segmentation
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Solution Overview
Problem
Buck-Boost converters face inefficiencies due to high inductance current ripple, increased resistive losses, and complex voltage mode control requirements, particularly in wearable applications where line transient response is critical and power consumption needs to be minimized.
Innovation Solution
A hysteretic Buck-Boost converter system employing separated Buck and Boost pulses, monitored by a derivative of the output voltage and a difference with a reference voltage, using comparators and a logic and timers block to define operation modes and switch activation, reducing inductance current ripple and quiescent power consumption.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If traditional Buck-Boost converter operation is used with 4 switches changing state at each cycle, then the converter can achieve output voltages lower or higher than input voltage, but switching loss increases to 2 times of typical Buck or Boost converter
Solution Approach 1:
The patent segments the Buck-Boost operation into separate Buck and Boost phases, where each phase uses only 2 switches instead of 4. During Buck operation, switches M1 and M2 are used; during Boost operation, switches M3 and M4 are used. This segmentation reduces switching loss by half while maintaining the ability to achieve both buck and boost voltage conversion.
2Adaptability or versatility
If traditional Buck-Boost operation is used, then voltage conversion is achieved, but average inductance current becomes significantly higher than load current (IL=ILOAD/(1−D)), leading to increased resistive losses
Solution Approach 1:
The patent divides the operation into separate Buck and Boost modes, allowing the inductor to operate more efficiently in each mode. In Buck mode, the inductor current is closer to load current; in Boost mode, the duty cycle is optimized to reduce current. This segmentation reduces the average inductance current and associated resistive losses compared to traditional continuous Buck-Boost operation.
3Ease of operation
If Voltage Mode control is used for Buck-Boost converter, then output voltage control is achieved, but complex feedforward techniques are needed to improve line transient response
Solution Approach 1:
The patent employs hysteretic control with feedback from the output voltage to directly control the switching of Buck and Boost phases. The control circuit monitors the output voltage and adjusts the duty cycles of Buck and Boost modes accordingly, eliminating the need for complex feedforward techniques while achieving excellent line transient response. The hysteresis window provides inherent stability and simplicity.
4Adaptability or versatility
If traditional Buck-Boost operation is used with high inductance current ripple, then voltage conversion is achieved, but efficiency decreases and quiescent power consumption increases
Solution Approach 1:
The patent segments the operation into distinct Buck and Boost phases with separate switch sets, allowing each phase to operate with optimized current waveforms. This reduces inductance current ripple compared to traditional continuous Buck-Boost operation, thereby improving efficiency and reducing quiescent power consumption, especially in low-current wearable applications.
Data Source
AI summary
Circuits and methods to achieve a hysteretic buck-boost converter system, separating buck and boost pulses based on monitoring a difference between the output voltage of the buck-boost converter and a reference voltage (error voltage) or alternatively based on monitoring additionally coil current or load current or both currents have been disclosed. The performance of the buck-boost converter can be further improved by using an optional output voltage change block monitoring if the output voltage rises or falls. The buck-boost converter disclosed has a very simple topology without a modulator block, which is regulating the duty cycle and without frequency compensation.