Piezoelectric transformer driving circuit and method capable of automatically tracking resonant frequency

Abstract

The invention relates to the technical field of electronic transformer driving, in particular to a piezoelectric transformer driving circuit capable of automatically tracking resonant frequency, which comprises an LC series resonant circuit, an inductor, a capacitor, an inductor, a capacitor and a capacitor, the switching device is connected to the two ends of the capacitor in the LC series resonance circuit in parallel; the input end of the analog closed-loop control circuit is connected with the two ends of a capacitor in the LC series resonance circuit, and the analog closed-loop control circuit is used for sampling resonance voltage signals; the output end of the square wave generator is connected with the control end of the switching device and is used for outputting frequency-variable driving square waves; the analog closed-loop control circuit comprises a peak detection unit. Full-automatic frequency tracking is achieved, and the problem that an original fixed parameter circuit is poor in environment adaptability is thoroughly solved. No matter how the temperature and the load change, the circuit can automatically lock the resonance point, manual intervention is not needed, and the reliability and the robustness of the product are greatly improved.

Description

Technical Field

[0001] This invention relates to the field of electronic transformer drive technology, specifically to a piezoelectric transformer drive circuit, and particularly to a drive circuit and control method capable of automatically tracking the resonant frequency of a piezoelectric transformer to achieve efficient and stable operation. Background Technology

[0002] Piezoelectric transformers are widely used in various high-voltage power supply fields due to their advantages such as small size, light weight, and absence of electromagnetic interference. For example, Chinese invention patent CN101404462A discloses a piezoelectric transformer drive circuit, which converts DC voltage into intermittent half-sine wave voltage to drive the piezoelectric transformer through a specific LC series resonant circuit and switching devices. By fixing the ratio of LC parameters to the operating frequency (e.g., the resonant frequency is 1.5 times the operating frequency), the system reaches a fully resonant state, effectively reducing switching losses.

[0003] However, this solution has a significant drawback: its circuit parameters (inductance, capacitance, conduction time, etc.) are fixed. In practical applications, the resonant frequency of the piezoelectric ceramic material will drift with factors such as ambient temperature, mechanical load, and aging. Furthermore, piezoelectric transformers produced in different batches inherently exhibit parameter variations. The original patent's fixed-parameter drive circuit cannot adapt to these changes; once it deviates from the preset optimal operating point, the system becomes detuned, leading to a sharp drop in efficiency, unstable output, or even malfunction. This necessitates tedious manual tuning during production and limits the product's reliability and versatility.

[0004] Therefore, there is an urgent need in this field for a drive circuit that can automatically adapt to the above changes and always keep the system operating in the optimal resonance state. Summary of the Invention

[0005] The purpose of this invention is to overcome the shortcomings of the prior art and provide a piezoelectric transformer drive circuit and method with automatic resonant frequency tracking. This circuit can automatically and continuously adjust its operating frequency under a wide range of operating conditions to track the changes in the resonant frequency of the piezoelectric transformer, thereby always maintaining high power conversion efficiency.

[0006] To achieve the above objectives, the present invention provides the following technical solution: a piezoelectric transformer drive circuit with automatic resonant frequency tracking, characterized in that it comprises:

[0007] An LC series resonant circuit has its input terminal connected to a DC voltage and its output terminal connected to a piezoelectric transformer.

[0008] A switching device is connected in parallel across the two ends of the capacitor in the LC series resonant circuit;

[0009] Also includes:

[0010] The analog closed-loop control circuit has its input terminal connected to both ends of the capacitor in the LC series resonant circuit for sampling the resonant voltage signal; its output terminal is connected to the control terminal of the switching device for outputting a variable frequency drive square wave.

[0011] The analog closed-loop control circuit includes:

[0012] A peak detection unit is used to detect the peak value of the resonant voltage across the capacitor and output a DC voltage signal proportional to it.

[0013] A voltage comparison unit, whose input terminal is connected to the output terminal of the peak detection unit, is used to compare the DC voltage signal with a preset reference voltage and output an error signal.

[0014] A voltage-controlled oscillator unit has its input terminal connected to the output terminal of the voltage comparator unit and its output terminal connected to the control terminal of the switching device; the voltage-controlled oscillator unit is used to dynamically adjust the frequency of its output driving square wave according to the error signal.

[0015] Preferably, the peak detection unit consists of an operational amplifier circuit, a diode, and a holding capacitor.

[0016] Preferably, the voltage comparison unit is an integral comparator circuit, which includes an operational amplifier and an RC integral network for smoothing the error signal.

[0017] Preferably, the voltage-controlled oscillator unit uses a linear voltage-controlled oscillator chip, whose output frequency is linearly related to the control voltage.

[0018] Preferably, the preset reference voltage value corresponds to the voltage value that the peak detection unit should output when the piezoelectric transformer drive circuit is in full resonance.

[0019] A method for controlling the output voltage of a piezoelectric transformer drive circuit with automatic resonant frequency tracking, the method comprising the following steps:

[0020] S1: The peak voltage is sampled in real time across the capacitor in the LC series resonant circuit by the peak detection unit.

[0021] S2: The peak voltage is compared with a preset reference voltage by the voltage comparison unit to generate an error signal;

[0022] S3: The error signal is converted into a square wave signal of a certain frequency through the voltage-controlled oscillator unit, and the square wave signal is used to drive the switching device.

[0023] S4: Through steps S1 to S3, a negative feedback closed-loop control system is formed, so that when the resonant frequency of the piezoelectric transformer changes due to external conditions, the operating frequency of the drive circuit is automatically adjusted to rematch and lock at the current resonant frequency of the piezoelectric transformer, maintaining the full resonance state.

[0024] Compared with the prior art, the beneficial effects of the present invention are:

[0025] Fully automatic frequency tracking: This completely solves the problem of poor environmental adaptability of the original fixed-parameter circuits. Regardless of changes in temperature or load, the circuit can automatically lock the resonant point without manual intervention, greatly improving the reliability and robustness of the product.

[0026] Maintaining high efficiency: Since the system always operates in a resonant state, the zero-voltage switching condition of the switching devices is maintained, resulting in low switching losses and high overall conversion efficiency.

[0027] Simple and reliable hardware: The entire control loop is composed of classic analog discrete components or general-purpose ICs, without the need for microprocessors and software programming. The circuit structure is simple, the cost is low, and the debugging is convenient. It is especially suitable for technical teams to quickly realize industrialization, and it has good long-term stability.

[0028] High versatility: This circuit can automatically adapt to the optimal operating point for different piezoelectric transformers with varying parameters, simplifying the production process and improving product consistency and yield. Attached Figure Description

[0029] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0030] Figure 1 This is a block diagram of the overall structure of the piezoelectric transformer drive circuit according to an embodiment of the present invention.

[0031] Figure 2 This is a circuit diagram of a specific embodiment of the simulated closed-loop control circuit of the present invention.

[0032] Figure 3 This is a waveform diagram illustrating the automatic frequency tracking and locking process during the operation of this invention. Detailed Implementation

[0033] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0034] Please see Figures 1 to 3 The present invention provides a technical solution:

[0035] Example:

[0036] See Figure 1 The piezoelectric transformer drive circuit with automatic resonant frequency tracking provided by the present invention mainly includes three parts: power stage circuit, analog closed-loop control circuit and piezoelectric transformer.

[0037] The power stage circuit is similar to that in the prior art publication CN101404462A, including: an LC series resonant circuit (composed of an inductor L1 and a capacitor C1 connected in series) with the input terminal connected to a DC voltage VIN, and a switching device Q1 (such as a MOSFET) connected in parallel across the resonant capacitor C1. The input terminal of the piezoelectric transformer is connected in parallel across the capacitor C1.

[0038] The core improvement of this invention lies in the analog closed-loop control circuit. (See also...) Figure 2 Specifically, it includes:

[0039] Peak detection unit: Composed of operational amplifier U1A, diode D1, and capacitor C2. Operational amplifier U1A is configured as a voltage follower to sample the voltage UC across capacitor C1 using high impedance. Diode D1 and capacitor C2 form a basic peak detection circuit, maintaining the peak voltage of UC and outputting a smooth DC voltage Vpeak. Resistor R1 provides a discharge path for capacitor C2.

[0040] Voltage Comparison Unit: This unit consists of operational amplifier U1B and its peripheral resistors R2 and R3, and capacitor C3, forming an integral comparator. Its inverting input is connected to the peak voltage Vpeak, and its non-inverting input is connected to a preset reference voltage Vref generated by a resistor divider network (R4, R5). This unit compares Vpeak and Vref, integrates the difference, and outputs a slowly varying control voltage Vctrl. This integral characteristic ensures smooth system regulation and avoids frequency jitter.

[0041] Voltage-controlled oscillator unit: A general-purpose voltage-controlled oscillator chip U2 (such as MAX038 or ICL8038) is used. Its frequency control input is connected to a voltage Vctrl, and its output OUT generates a square wave signal DRV with a frequency proportional to Vctrl. This signal directly controls the gate of the switching transistor Q1 through the drive resistor R6.

[0042] The working principle of this invention is as follows:

[0043] The system is powered on and begins operation. Assume that initially, the operating frequency does not match the resonant frequency of the piezoelectric transformer.

[0044] The peak detection unit continuously monitors the peak voltage Vpeak across capacitor C1.

[0045] The voltage comparator compares Vpeak with Vref. The value of Vref is set to the peak voltage that the system is expected to reach in the fully resonant state.

[0046] If the current Vpeak < Vref, it indicates that the system is detuned and inefficient. The comparator output Vctrl begins to increase.

[0047] After the voltage-controlled oscillator receives the increased Vctrl, the frequency of its output square wave DRV increases accordingly.

[0048] The change in operating frequency alters the impedance characteristics of the LC circuit and the piezoelectric transformer. The system "searches" along the resonance curve until it finds a frequency point where Vpeak is equal to or very close to Vref. At this point, the system enters a locked state, achieving full resonance.

[0049] If the resonant frequency of the piezoelectric transformer decreases due to increased temperature, the system will detect the drop in Vpeak and reduce the operating frequency through the aforementioned feedback mechanism to re-track the new resonant point.

[0050] Figure 3 This locking process is illustrated schematically. Before time t1, the operating frequency deviates, and the peak resonant voltage is relatively low. Starting from time t1, the closed-loop control takes effect, the operating frequency begins to change, the peak resonant voltage gradually increases, and stabilizes at its maximum value after time t2, at which point the system enters the locked state.

[0051] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A piezoelectric transformer drive circuit with automatic resonant frequency tracking, characterized in that, include: An LC series resonant circuit has its input terminal connected to a DC voltage and its output terminal connected to a piezoelectric transformer. A switching device is connected in parallel across the two ends of the capacitor in the LC series resonant circuit; Its characteristic is that it further includes: The analog closed-loop control circuit has its input terminal connected to both ends of the capacitor in the LC series resonant circuit for sampling the resonant voltage signal; its output terminal is connected to the control terminal of the switching device for outputting a variable frequency drive square wave. The analog closed-loop control circuit includes: A peak detection unit is used to detect the peak value of the resonant voltage across the capacitor and output a DC voltage signal proportional to it. A voltage comparison unit, whose input terminal is connected to the output terminal of the peak detection unit, is used to compare the DC voltage signal with a preset reference voltage and output an error signal. A voltage-controlled oscillator unit has its input terminal connected to the output terminal of the voltage comparator unit and its output terminal connected to the control terminal of the switching device; the voltage-controlled oscillator unit is used to dynamically adjust the frequency of its output driving square wave according to the error signal.

2. The piezoelectric transformer drive circuit with automatic resonant frequency tracking according to claim 1, characterized in that, The peak detection unit consists of an operational amplifier circuit, a diode, and a holding capacitor.

3. The piezoelectric transformer drive circuit with automatic resonant frequency tracking according to claim 1, characterized in that, The voltage comparison unit is an integral comparator circuit, which includes an operational amplifier and an RC integral network, used to smooth the error signal.

4. The piezoelectric transformer drive circuit with automatic resonant frequency tracking according to claim 1, characterized in that, The voltage-controlled oscillator unit uses a linear voltage-controlled oscillator chip, whose output frequency is linearly related to the control voltage.

5. A piezoelectric transformer drive circuit for automatic resonant frequency tracking according to any one of claims 1 to 4, characterized in that, The preset reference voltage value corresponds to the voltage value that the peak detection unit should output when the piezoelectric transformer drive circuit is in full resonance.

6. A method for controlling the output voltage of a piezoelectric transformer drive circuit with automatic resonant frequency tracking as described in claim 1, characterized in that, The method includes the following steps: S1: The peak voltage is sampled in real time across the capacitor in the LC series resonant circuit by the peak detection unit. S2: The peak voltage is compared with a preset reference voltage by the voltage comparison unit to generate an error signal; S3: The error signal is converted into a square wave signal of a certain frequency through the voltage-controlled oscillator unit, and the square wave signal is used to drive the switching device. S4: Through steps S1 to S3, a negative feedback closed-loop control system is formed, so that when the resonant frequency of the piezoelectric transformer changes due to external conditions, the operating frequency of the drive circuit is automatically adjusted to rematch and lock at the current resonant frequency of the piezoelectric transformer, maintaining the full resonance state.

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