Switching Power Supply Slope Voltage Control for Load Responsiveness
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Solution Overview
Problem
Conventional switching power supply devices with reverse current cut-off functions experience large fluctuations in error voltage when load increases rapidly, leading to poor responsiveness.
Innovation Solution
Incorporating a slope voltage generating circuit that increases the slope voltage during the on period of the output transistor and maintains it at an offset level during the off period, enhancing the error voltage stability and responsiveness.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If a reverse current cut-off function is implemented to increase efficiency in light load, then efficiency is improved, but the fluctuation range of error voltage increases resulting in poor load responsiveness
Solution Approach 1:
The slope voltage is preliminarily raised to an offset level before the rapid load increase occurs. When the synchronous rectifying transistor is forcibly turned off due to reverse current detection, the slope voltage is already at the offset level corresponding to the output voltage, which preliminarily compensates for the upcoming error voltage fluctuation and enables faster responsiveness to load changes.
Solution Approach 2:
The slope voltage is made dynamic by switching between reset level and offset level based on the operational state. During the off period of the output transistor, the slope voltage is raised to the offset level corresponding to the output voltage, creating a dynamic adjustment that adapts to load conditions and reduces error voltage fluctuation range.
2Reliability
If the synchronous rectifying transistor is forcibly turned off to detect reverse current, then reverse current protection is improved, but error voltage stability deteriorates
Solution Approach 1:
The slope voltage is preliminarily adjusted to the offset level before the forced turn-off of the synchronous rectifying transistor. This preliminary action ensures that when reverse current detection occurs and the transistor is forcibly turned off, the slope voltage is already positioned to minimize error voltage fluctuation, thereby maintaining error voltage stability while preserving reverse current protection functionality.
Solution Approach 2:
The slope voltage generating circuit dynamically adjusts the slope voltage level based on the state of the synchronous rectifying transistor. When the transistor is turned off, the slope voltage is raised to the offset level, creating a dynamic compensation mechanism that stabilizes error voltage while allowing the forced turn-off operation for reverse current protection.
Data Source
AI summary
A switching power supply device includes a switching output circuit, an error amplifier, a slope voltage generating circuit, a PWM comparator, a logic circuit, a switch driving circuit, and a reverse current detection circuit. The slope voltage generating circuit increases a slope voltage from a reset level with a gradient corresponding to an input voltage during an on period of the output transistor, and maintains the slope voltage at an offset level corresponding not to the reset level but to an output voltage during an off period of the output transistor.