Buck Converter Control for Stable Transition to 100% Duty
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Solution Overview
Problem
Buck DC-to-DC converters experience significant output voltage fluctuations during transitions between normal operation mode and 100% duty operation mode, failing to meet accuracy specifications due to input voltage drops close to output voltage.
Innovation Solution
A power converter with a switching circuit, comparator circuits, and a mode control logic that adjusts the switch control signal to extend the on-time of the high side switch in the second operation mode, allowing seamless transition and minimizing output voltage fluctuations by determining the end of on-time based on feedback and ramp voltage signals.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the converter operates in normal operation mode with periodic chopping, then the output voltage is regulated below input voltage, but during transition to 100% duty mode the output voltage experiences large fluctuations
Solution Approach 1:
The patent implements dynamic operation mode switching between normal chopping mode and 100% duty mode based on the relationship between input and output voltages. The converter dynamically adjusts its operating characteristics to maintain stability during transitions, resolving the contradiction between reliable voltage regulation and adaptability to different operating conditions.
Solution Approach 2:
The patent changes the duty cycle parameter from periodic chopping (less than 100%) to 100% duty mode when the input voltage approaches the output voltage. This parameter change allows the converter to adapt to different voltage conditions while maintaining output stability, resolving the transition fluctuation issue.
2Ease of operation
If the high side switch remains at on state during 100% duty mode, then the output voltage equals input voltage, but the transition causes significant voltage fluctuation
Solution Approach 1:
The patent prepares for the transition to 100% duty mode by monitoring the input-output voltage relationship in advance. When the input voltage approaches the output voltage, the controller proactively switches to 100% duty mode, preventing the output voltage from dropping and maintaining accuracy throughout the transition.
Solution Approach 2:
The patent uses feedback from the output voltage and input voltage comparison to control the switching mode. The controller continuously monitors voltage levels and adjusts the duty cycle accordingly, ensuring that the transition to 100% duty mode occurs at the optimal moment to maintain output voltage accuracy.
Data Source
Figure 1
Figure 2~3
Figure 4~5(b)
AI summary
There is provided a power converter 1, comprising: a switching circuit 3 for converting an input voltage VIN into an output voltage VOUT, comprising a high side switch 5, a low side switch 7, and a switching node SW between the high side switch 5 and the low side switch 7; a first comparator circuit 15 configured to receive a reference voltage signal VREF and a feedback voltage signal indicative of the output voltage 'FB+injection', and to generate a first comparing signal PWM based upon a comparison of the feedback voltage signal and the reference voltage signal; a second comparator circuit 51 configured to receive a ramp voltage signal 49 based upon an integration of a phase signal 25 from the switching node, and an emulated output voltage signal 43 based upon the phase signal, and to generate a second comparing signal XSHOT based upon a comparison of the ramp voltage signal and the emulated output voltage signal; a mode control circuit 23 configured to generate a state indication signal PATH indicative of whether a ratio of the output voltage to the input voltage exceeds a predetermined threshold ratio; and a logic circuit 39 configured to generate a switch control signal 40, 42 for controlling the switching circuit 3 based upon the first comparing signal PWM, the second comparing signal XSHOT and the state indication signal PATH. The switch control signal is configured to cause the switching circuit to transition from a first operation mode to a second operation mode in response to a change of value of the state indication signal PATH indicating that the ratio rises across the predetermined threshold ratio. The switch control signal 40, 42 is configured such that: during the first operation mode, an end of on-time of the high side switch 5 in each switching cycle of the high side switch 5 is determined by the second comparing signal XSHOT, and during the second operation mode, an end of on-time of the high side switch 5 in each switching cycle is determined by the first comparing signal PWM