Soft-Stop Overvoltage Protection Circuit for PFC Switching Power Supplies
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Solution Overview
Problem
Existing power factor correction type switching power supply units face challenges in achieving stable output voltage during transient response corrections, leading to potential overvoltage and inefficiency due to the interaction between transient response correctors and overvoltage protection circuits.
Innovation Solution
A power factor correction type switching power supply unit is designed with a transient response corrector circuit that includes a soft-stop overvoltage protection circuit and an overvoltage protection circuit, which prevent excessive inductor current and output voltage rises by controlling the switching element based on detected voltage thresholds, ensuring stable output voltage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If a transient response corrector circuit is used to swiftly raise the output voltage when it decreases, then the output voltage response speed is improved, but the output voltage may excessively rise causing overvoltage
Solution Approach 1:
The patent employs feedback control by detecting the output voltage level and using this information to control the switching element. When the output voltage decreases to or below a threshold, the control circuit activates the transient response corrector to raise the voltage, and when the voltage reaches a predetermined level, the control circuit stops the corrector operation to prevent overvoltage, thus maintaining stability while improving response speed.
Solution Approach 2:
The control circuit is designed to preemptively stop the transient response corrector operation when the output voltage reaches a predetermined level before excessive rise occurs. This preliminary action prevents overvoltage conditions while allowing the rapid voltage rise needed for good transient response characteristics.
2Speed
If the transient response corrector operation is not restricted, then the output voltage can be quickly restored, but excessive power is removed causing inefficiency
Solution Approach 1:
The transient response corrector operates periodically rather than continuously - it is activated when voltage drops below a threshold and deactivated when voltage reaches a predetermined level. This periodic operation allows quick voltage restoration when needed while avoiding continuous power removal that would cause inefficiency, thus resolving the contradiction between speed and energy loss.
3Speed
If the output voltage is allowed to rise freely during transient response, then the response characteristics are improved, but overvoltage protection is triggered causing switching element to stop
Solution Approach 1:
The patent changes the voltage threshold parameters used for control - specifically using a predetermined level for stopping the transient response corrector that is lower than the overvoltage protection trigger level. This parameter adjustment allows the output voltage to rise sufficiently for good transient response while preventing overvoltage protection activation, maintaining switching operation continuity.
Data Source
AI summary
A soft-stop overvoltage protection circuit, into which a soft-stop overvoltage detection voltage proportional to a direct current output voltage is input, reduces the output of a multiplier in accordance with the soft-stop overvoltage detection voltage when the soft-stop overvoltage detection voltage exceeds a first threshold value. An overvoltage protection circuit, a second threshold value higher than the first threshold value being set, compulsorily turns off a switching element by outputting an overvoltage detection signal when the soft-stop overvoltage detection voltage exceeds the second threshold value. The soft-stop overvoltage protection circuit compulsorily increases the output of a voltage error amplifier circuit on the output voltage decreasing. When the output of the voltage error amplifier circuit increases suddenly, and the output voltage rises excessively, the soft-stop overvoltage protection circuit decreases the output of the multiplier, thus curbing the rise of the output voltage.