Power Factor Correction Circuit Overshoot Suppression
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Solution Overview
Problem
Conventional power factor correction circuits face challenges in suppressing overshoot during momentary AC input halts, managing output voltage changes due to sudden input or load changes, and resetting the soft-start function without increasing system costs.
Innovation Solution
A power factor correction circuit with an error signal generation unit, oscillation unit, zero current detection unit, drive signal generation unit, and input interruption detection unit, which controls the slope of the triangular wave signal to manage the boost chopper's switching element, ensuring stable output voltage and soft-start operation during AC input interruptions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the error amplifier output voltage is clamped to discrete clamp voltages to suppress overshoot, then the maximum on-width of the boosting converter is limited, but the output voltage cannot be smoothly changed in response to input power restoration, reducing output power
Solution Approach 1:
The clamp voltage is changed from a discrete, fixed value to a continuously variable value that changes dynamically in response to the output voltage of the error amplifier. This allows the clamp voltage to adapt smoothly to changing operating conditions, particularly during input power restoration, thereby maintaining both overshoot suppression and full output power capability.
Solution Approach 2:
The invention changes the parameter of clamp voltage from a fixed discrete value to a variable parameter that can take on multiple values based on the error amplifier output. This parameter change enables the system to optimize performance across different operating conditions, resolving the contradiction between limiting on-width for overshoot suppression and maintaining output power.
2Reliability
If the soft-start function is activated during momentary AC input halt to suppress overshoot, then the switching element on-width is limited, but the soft-start function cannot be reset when control IC power supply voltage does not drop to UVLO threshold
Solution Approach 1:
The invention replaces the conventional UVLO-based reset mechanism with a new detection mechanism that monitors the AC input voltage directly. This substitution allows the soft-start function to be reset based on actual input voltage conditions rather than control IC power supply voltage, enabling proper reset even when the power supply voltage remains above the UVLO threshold during momentary halts.
Solution Approach 2:
The invention introduces an intermediary detection mechanism that monitors the relationship between input voltage and error amplifier output to determine when to reset the soft-start function. This intermediary detection layer provides more accurate control than direct UVLO monitoring, allowing the system to distinguish between genuine power failures and momentary halts that require soft-start reset.
3Reliability
If the error amplifier responsiveness is enhanced to meet user demands for voltage stability, then the error amplifier responds faster to load changes, but overshoot and excessive undershoot occur during momentary halts
Solution Approach 1:
The invention introduces feedback control that monitors the error amplifier output voltage and compares it with the clamp voltage. When the error amplifier output exceeds the clamp voltage (indicating potential overshoot), the feedback mechanism activates to limit the output, thereby suppressing overshoot and excessive undershoot while maintaining the enhanced responsiveness benefits.
Solution Approach 2:
The invention applies preliminary anti-action by pre-establishing clamp voltage limits before overshoot can occur. The clamp circuit is designed to activate when the error amplifier output approaches dangerous levels, preventing overshoot before it happens rather than correcting it after the fact. This preliminary protection maintains voltage stability without the harmful effects of excessive responsiveness.
Data Source
AI summary
A power factor correction circuit includes an error signal generation unit configured to output an error signal obtained by amplifying a difference between an output voltage and a referential voltage. A pulse width modulation unit is configured to receive the error signal to generate a pulse width modulation signal to control an on-time of a switching element. An input interruption detection unit is configured to detect an interruption state of an AC input voltage. When the input interruption detection unit detects an input interruption state, the input interruption detection unit causes the pulse width modulation unit to shorten the on-time of the switching element.