PWM Converter Loop Recovery After Dropout Saturation
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Solution Overview
Problem
Current mode PWM converters experience slow recovery from fault conditions like dropout, leading to undesirable large transients and output overshoot due to saturation of state variables, particularly the error amplifier.
Innovation Solution
A method and apparatus that dynamically preset the error output of the error amplifier to a state closest to its recovery state, preventing overshoot by sampling the peak voltage and applying an offset voltage to avoid saturation, thus accelerating recovery from fault conditions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If the converter operates during dropout condition, then the duty cycle becomes saturated to 100%, but the error amplifier becomes saturated and recovery becomes slow
Solution Approach 1:
The patent applies preliminary action by detecting the dropout condition before full saturation occurs and proactively adjusting the duty cycle to prevent complete saturation of the error amplifier. This early intervention allows the converter to recover faster when the dropout condition ends, avoiding slow recovery from deep saturation while maintaining output stability.
Solution Approach 2:
The patent implements dynamics by making the duty cycle adjustable and dynamic rather than fixed at 100% during dropout. The duty cycle is dynamically modified based on the detected dropout condition, allowing the error amplifier to operate in a less saturated state, which enables faster recovery when normal operation resumes while maintaining reliable output control.
2Power
If the duty cycle is saturated to 100% during dropout, then the converter maintains maximum power transfer, but large transients and output overshoot occur during recovery
Solution Approach 1:
The patent applies preliminary anti-action by detecting the dropout condition and preemptively modifying the duty cycle to prevent complete saturation. This counteracts the tendency toward excessive saturation that would cause large transients and output overshoot during recovery, while still maintaining adequate power transfer during the dropout condition through controlled duty cycle adjustment.
Solution Approach 2:
By detecting dropout conditions early and adjusting the duty cycle before full saturation occurs, the system prevents the harmful transients and overshoot that would occur during recovery. This preliminary adjustment maintains sufficient power transfer while avoiding the extreme saturation that leads to output instability.
3Productivity
If the error amplifier is allowed to saturate fully, then the converter responds maximally to dropout, but recovery time increases significantly
Solution Approach 1:
The patent applies preliminary action by detecting the dropout condition and proactively adjusting the duty cycle to prevent complete error amplifier saturation. This early modification maintains adequate fault response through controlled duty cycle adjustment while significantly reducing recovery time by avoiding deep saturation that would require lengthy recovery.
Solution Approach 2:
The patent implements dynamics by making the duty cycle adjustable based on detected dropout conditions. This dynamic adjustment allows the system to maintain effective fault response through controlled duty cycle modification while preventing the complete saturation that would extend recovery time, achieving both responsive fault handling and rapid recovery.
Data Source
AI summary
A method for dynamic enhancement of loop response upon recovery from fault conditions includes detecting a fault condition in response to a programmed output voltage of a Pulse Width Modulation (PWM) converter decreasing below an input voltage of the PWM converter. A peak voltage is sampled at the end of at least one of a plurality of clock cycles of the PWM converter in response to detecting the fault condition, wherein the peak voltage is proportional to a sensed current conducted through a transistor. An error output of an error amplifier is preset to an error value determined by the peak voltage. A PWM driver is controlled with the error value to drive the transistor. An output load is charged to the programmed output voltage with the transistor in response to the input voltage increasing above the programmed output voltage.