Buck-Boost Converter Control Circuit Stabilizing Quasi-Fixed Frequency
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Solution Overview
Problem
Existing switch control methods for buck-boost converters face instability due to mismatched phase angles and frequencies in variable frequency control, leading to complex control requirements and potential system instability.
Innovation Solution
A power stage circuit with a constant time control circuit and PWM control circuit that generates switch trigger signals to control the on/off states of switches S1 and S3, achieving constant off time or constant on time control with quasi-fixed frequency, stabilizing the system by ensuring fixed switching cycles.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If variable frequency control is used in buck-boost converter, then the control can adapt to different operating conditions, but the phase angles and frequency mismatch causes system instability and increased complexity
Solution Approach 1:
The patent implements constant on-time or constant off-time control for the switches, creating a periodic action pattern that ensures fixed switching cycles. This periodic control mechanism stabilizes the system by maintaining consistent timing relationships between switching events, thereby resolving the instability caused by variable frequency control while preserving adaptability through adjustable constant time parameters.
2Adaptability or versatility
If variable frequency control is used in buck-boost converter, then the control can adapt to different operating conditions, but the control complexity increases due to multiple components needed
Solution Approach 1:
The patent extracts and eliminates the complex frequency and phase angle control mechanisms from the control system. By removing these unnecessary components and focusing only on constant time control, the system achieves adaptability through simpler means, directly reducing control complexity while maintaining the ability to adapt to different operating conditions.
Solution Approach 2:
The control system uses the natural switching signals from the power stage circuit itself to generate the constant time control signals. This self-service approach eliminates the need for external frequency and phase control circuits, thereby simplifying the overall control architecture while preserving adaptability through the inherent characteristics of the power stage.
3Reliability
If constant time control is implemented with fixed switching cycles, then system stability is improved, but the frequency flexibility is reduced
Solution Approach 1:
The patent implements dynamics by allowing the constant time value (either on-time or off-time) to be adjusted based on operating conditions, while maintaining fixed switching cycles within each mode. This dynamic adjustment of the constant time parameter provides frequency flexibility and adaptability, whereas the fixed cycle within each constant time period ensures system stability.
Data Source
AI summary
An apparatus can include: (i) a power stage circuit including first, second, third, and fourth switches and an inductor; (ii) a constant time control circuit configured to generate a switch trigger signal according to switching signals of the first and third switches; (iii) a PWM control circuit configured to receive an input voltage signal via the input terminal, an output voltage via the output terminal, and the switch trigger signal, and to generate switching signals to control the first, second, third, and fourth switches; and (iv) the PWM control circuit being configured to turn on or off the first and third switches in response to the switch trigger signal being activated.