Buck-Boost Converter Control Circuit Bootstrap Voltage Refresh
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Buck-boost power converters face issues with bootstrap voltage refresh during light or no-load conditions, leading to oscillations and disturbances in output voltage when the inductor current crosses zero, especially in pulse skipping mode, due to insufficient charge in bootstrap capacitors.
Innovation Solution
A control circuit that includes a logic control module to receive pulse skipping and zero-crossing indication signals, allowing the second and third power switches to turn on when the buck-boost power converter enters pulse skipping mode and the inductor current crosses zero, ensuring the bootstrap capacitors are charged promptly without oscillation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the bootstrap capacitors are charged during pulse skipping mode when inductor current crosses zero, then the bootstrap voltage is refreshed, but oscillations occur at the switching nodes causing output voltage disturbance
Solution Approach 1:
The control circuit detects the inductor current zero-crossing point in advance and triggers the bootstrap capacitor charging operation at this specific moment. By performing the charging action preliminarily at the zero-crossing point rather than continuously or at random moments, the circuit ensures bootstrap voltage refresh while minimizing disruption to the switching nodes and output voltage stability.
2Use of energy by moving object
If the power switches are kept off during pulse skipping mode to reduce power consumption, then energy efficiency improves, but the bootstrap capacitors cannot be charged properly
Solution Approach 1:
During pulse skipping mode, instead of keeping power switches continuously off or continuously on, the control circuit implements periodic switching actions. Specifically, at the detected inductor current zero-crossing point, the circuit briefly activates the appropriate power switch to charge the bootstrap capacitor, then returns to the off state. This periodic action ensures bootstrap voltage refresh occurs intermittently while maintaining overall low power consumption.
3Reliability
If the bootstrap voltage is refreshed continuously to ensure adequate charging, then the bootstrap capacitors maintain sufficient voltage, but oscillations and disturbances occur at the switching nodes
Solution Approach 1:
The control circuit incorporates feedback mechanisms to detect the inductor current status and the bootstrap voltage level. By monitoring the inductor current zero-crossing point and the actual bootstrap voltage condition, the control circuit intelligently determines when charging is needed and triggers the charging operation only at appropriate moments. This feedback-based control ensures bootstrap voltage adequacy while avoiding unnecessary switching actions that would cause oscillations and disturbances at the switching nodes.
Data Source
AI summary
A buck-boost power converter and a control circuit for the buck-boost converter. The buck-boost power converter includes a first power switch and a second power switch coupled in series between an input port and a reference ground, and a third power switch and a fourth power switch coupled in series between an output port and the reference ground. The control circuit receives a pulse skipping control signal and a zero-crossing indication signal, and controls the second power switch and/or the third power switch to turn on when the pulse skipping control signal controls the buck-boost power converter to enter into a pulse skipping mode and the zero-crossing indication signal indicates that an output inductor current of the buck-boost power converter crosses zero.