Piezoelectric Transformer Ripple Control via Drive Frequency Feedback
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Solution Overview
Problem
Conventional high-voltage power supplies using piezoelectric transformers suffer from unnecessary circuit oscillations and output ripple, which can degrade image quality in electrophotographic image forming apparatuses due to the reliance on voltage-controlled oscillators that control drive frequency and extend the duration of the rising edge for higher voltages.
Innovation Solution
A high-voltage power supply system that includes a piezoelectric transformer, a digital drive frequency generating part, a voltage detection part, and a control part, where the drive frequency is directly controlled to achieve the desired output voltage quickly, reducing ripple and oscillations by using a feedback control system with specific time constants to manage the switching of drive frequencies and voltage detection.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If the drive frequency is changed to control the output voltage of the piezoelectric transformer, then the output voltage can be increased, but output ripple and circuit oscillations occur
Solution Approach 1:
The patent implements a feedback control system where the output voltage is detected and fed back to control the drive frequency. The control part adjusts the drive frequency based on the detected output voltage to maintain stable operation and eliminate ripple. This closed-loop feedback mechanism ensures that the piezoelectric transformer operates at the optimal frequency point, preventing the generation of harmful oscillations while maintaining the desired output voltage level.
Solution Approach 2:
The patent utilizes parameter changes by dynamically adjusting the drive frequency within a specific range (155 kHz to 165 kHz) to control the output voltage. By changing the drive frequency parameter and maintaining it within an optimal range, the system can regulate output voltage without entering regions that generate excessive ripple or oscillations. This parameter optimization resolves the contradiction between achieving high voltage and avoiding harmful oscillations.
2Power
If the VCO controls the duration of the rising edge by controlling the rate of change of drive frequency, then the voltage can be increased, but the duration of the rising edge becomes longer
Solution Approach 1:
The patent employs dynamic control of the drive frequency by the control part, which can rapidly adjust the frequency based on feedback. This dynamic adjustment capability allows the system to achieve the desired output voltage while controlling the rising edge duration. The control part can change the drive frequency at an optimized rate, preventing excessively long rising edges while still achieving the target voltage level, thus resolving the contradiction between voltage magnitude and rising edge duration.
3Device complexity
If a piezoelectric transformer is used instead of a wire-wound electromagnetic transformer, then the size and efficiency are improved, but unnecessary circuit oscillations and ripple are generated
Solution Approach 1:
The patent uses feedback control to detect and compensate for the harmful oscillations and ripple generated by the piezoelectric transformer. The voltage detection part monitors the output and feeds this information back to the control part, which adjusts the drive frequency to minimize oscillations. This feedback mechanism allows the system to maintain the compact size and high efficiency of the piezoelectric transformer while eliminating the harmful side effects through active control.
Solution Approach 2:
The patent optimizes the drive frequency parameter within a specific range (155 kHz to 165 kHz) to minimize harmful oscillations while maintaining the advantages of the piezoelectric transformer. By carefully selecting and controlling the operating frequency parameter, the system achieves both compact size/high efficiency and low ripple/oscillation performance, resolving the contradiction between transformer type benefits and harmful emissions.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach significantly reduces unnecessary circuit oscillations and output ripple, improving the quality of formed images by shortening the rising edge time and optimizing the control of drive frequencies, thereby enhancing the efficiency and stability of the high-voltage power supply.
Implementation Method 1
piezoelectric transformer outputs a voltage in accordance with a supplied drive frequency
Implementation Method 2
A rectification part is connected to an output side of the piezoelectric transformer
Data Source
AI summary
A high-voltage power supply comprises the following components. A piezoelectric transformer outputs a voltage in accordance with a supplied drive frequency. A rectification part is connected to an output side of the piezoelectric transformer. A drive frequency generating part generates the drive frequency supplied to the piezoelectric transformer. A voltage detection part detects an output voltage of the piezoelectric transformer or the rectification part. A control part controls the drive frequency generating part such that a drive frequency corresponding to the output voltage detected by the voltage detecting part is generated. A first time constant, which is a time constant of the control part, is smaller than a second time constant, which is a time constant of a control target including the piezoelectric transformer and the rectification part. A third time constant, which is a time constant of the voltage detecting part, is smaller than the second time constant.