Piezoelectric Drive Circuit Slew Rate Control
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Solution Overview
Problem
Existing piezoelectric element drive circuits, such as those using H bridge circuits, result in high power consumption due to the application of rectangular drive signals that include unnecessary frequency components, which are not effectively suppressed, leading to inefficient operation and reduced battery life.
Innovation Solution
A piezoelectric element drive circuit incorporating an H bridge circuit, current detection resistance, differential amplifier circuit with a slew rate reducing low pass filter, and an inverter circuit, which moderates the rising and falling characteristics of control signals to produce step-like drive signals, thereby eliminating unnecessary frequency components and reducing power consumption.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If an H bridge circuit is used to generate drive signals, then the drive voltage is increased while power consumption is low, but the drive signals become rectangular waves that include unnecessary frequency components
Solution Approach 1:
The patent modifies the waveform parameters of the drive signal by introducing a slew rate limiting circuit that controls the voltage change rate. This transforms the rectangular wave into a waveform with moderated rising and falling edges, eliminating high-frequency harmonics while preserving the fundamental drive voltage capability provided by the H bridge circuit.
Solution Approach 2:
The patent introduces a slew rate limiting circuit as an intermediary component between the H bridge circuit and the piezoelectric element. This intermediary circuit shapes the drive signals by limiting their voltage change rate, thereby removing unnecessary frequency components before they reach the piezoelectric element, while allowing the H bridge circuit to maintain its voltage-doucing function.
2Power
If rectangular wave drive signals are applied to the piezoelectric element, then the drive voltage is high, but frequency components over a very wide range are included that do not contribute to substantial operation
Solution Approach 1:
The patent changes the temporal parameters of the drive signal by implementing slew rate limiting. This controls the rate of voltage change during transitions, effectively filtering out high-frequency components that do not contribute to piezoelectric element operation, while maintaining the voltage level necessary for effective driving.
Solution Approach 2:
The patent converts the harmful effect of sharp voltage transitions (which generate unnecessary harmonics) into a beneficial filtering mechanism. By deliberately limiting the voltage change rate, the circuit naturally attenuates high-frequency components that would otherwise consume power without contributing to useful work, turning a potential problem into a power-saving feature.
3Speed
If the drive signals have sharp voltage change rates, then the drive voltage is high and responsive, but frequency components over a very wide range are generated including harmonics that just consume electric power
Solution Approach 1:
The patent optimizes the voltage change rate parameter by implementing slew rate limiting. This sets an appropriate maximum rate of voltage change that is sufficient for effective piezoelectric element driving while avoiding excessively sharp transitions that generate harmful high-frequency harmonics, thereby reducing power consumption.
Solution Approach 2:
The patent introduces dynamic control of the voltage transition characteristics through the slew rate limiting circuit. The circuit adaptively manages the voltage change rate during switching transitions, balancing the need for responsive voltage changes with the need to minimize high-frequency content, thereby optimizing both performance and power efficiency.
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
The proposed circuit operates at low power consumption while maintaining high drive voltage for the piezoelectric element, significantly prolonging the life of the power source and ensuring efficient operation even when the resonance frequency varies.
Implementation Method 1
a piezoelectric element drive circuit configured to apply to a piezoelectric element two drive signals with opposite phases
Implementation Method 2
the H bridge circuit is a switch control circuit, the drive signals output from the H bridge circuit are each a rectangular wave
Implementation Method 3
because the drive signals output from the H bridge circuit are each a rectangular wave and the drive circuit is a self-excited circuit, a control signal input to the H bridge circuit again through feedback is also a rectangular wave
Data Source
AI summary
A piezoelectric element drive circuit includes an H bridge circuit, an LPF-attached differential amplifier circuit, an amplifier circuit, and an inverter circuit. First and second drive signals output from the H bridge circuit and having opposite phases are applied to a piezoelectric element. A voltage between opposite ends of a resistor connected to a first output terminal of the H bridge circuit is input to the LPF-attached differential amplifier circuit. A differential signal output from the LPF-attached differential amplifier circuit has a lower slew rate because harmonic components are suppressed by the function of a low pass filter. Accordingly, respective slew rates of first and second control signals input to first and second input terminals of the H bridge circuit are also reduced. Hence the first and second control signals are each provided as a signal having a step-like waveform and including harmonic components that have been suppressed.