Drive circuit for piezoelectric ultrasonic transducer and ultrasonic transducer system

Abstract

To provide a drive circuit for an ultrasonic transducer and an ultrasonic transducer system improved in performance for efficiently detecting surrounding objects at a short distance.SOLUTION: In an ultrasonic transducer system 1, a drive circuit 2 of a piezoelectric ultrasonic transducer 4 includes: a transformer 21 having at least one primary winding 22, 22', and 22"; a switching unit having semiconductor switches 24' and 24" connected to at least one primary side winding via switching connecting portions A' and A"; a control unit 5 that operates to alternatively apply an operating voltage UB to at least one primary side winding or to disconnect the operating voltage UB; and a protection circuit 25 having a Zener diode ZD1 having a starting voltage (breakdown voltage) UZD that is electrically coupled to the switching connection portion and limits a switch-off voltage at the switching connection portion to a limiting voltage that corresponds in magnitude to at least twice the operating voltage UB.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a drive circuit for a piezoelectric ultrasonic transducer with improved protection against overvoltages due to the switching action of a transformer inductor. [Background technology]

[0002] Ultrasonic transducers are used for object detection and typically have a piezoelectric actuator that requires a high AC voltage of around 100 to 200 V for excitation. The voltage level of such a drive voltage is usually provided by voltage conversion using a transformer at the output stage.

[0003] In transmission mode, a periodic pulsed operating voltage is applied to the primary transformer, which converts it accordingly to the desired drive voltage. The excitation is pulsed for a simpler circuit design. In pulsed excitation of such a transformer, the operating voltage supplied on the primary is switched on or off. Pulsed excitation of a transformer results in a relatively high switch-off voltage due to the electrical energy stored in the inductance of the primary transformer winding. This effect is also known as the flyback effect.

[0004] The high switch-off voltage on the transformer primary due to the flyback effect must be limited to prevent damage to the drive circuit components. Normally, the energy in the primary inductance is dissipated through the diode and dissipated in the form of heat as power loss.

[0005] Ultrasonic transducer systems typically control an ultrasonic transducer in a transmit mode to emit an ultrasonic transmit signal and in a receive mode to receive a corresponding ultrasonic receive signal reflected from one or more surrounding objects. The propagation time of the resulting ultrasonic signal, along with other characteristics, is evaluated to obtain information about surrounding objects within the detection range of the ultrasonic transducer system. When switching from transmit to receive mode, the energy stored in the primary must be completely dissipated as quickly as possible to provide the sensitivity at the beginning of the receive mode as soon as possible after the end of the transmit mode. Establishing detection capability after the end of the transmit phase crucially determines the range at which the ultrasonic transducer system can detect nearby surrounding objects. Summary of the Invention [Problem to be solved by the invention]

[0006] An object of the present invention is to provide an ultrasonic transducer drive circuit and an ultrasonic transducer system that have improved performance for detecting surrounding objects at short distances more efficiently. [Means for solving the problem]

[0007] This problem is solved by a driving circuit for an ultrasonic transducer according to claim 1 and by an ultrasonic transducer system according to the independent claims. Further embodiments are set forth in the dependent claims.

[0008] According to one aspect, there is provided a drive circuit for a piezoelectric ultrasonic transducer in an ultrasonic transducer system, comprising: a transformer having at least one primary winding; a switching unit having a semiconductor switch connected to at least one of said primary windings via a switching connection; a control unit configured to alternately apply or de-apply an operating voltage to at least one of said primary windings; a protection circuit electrically coupled to said switching connection, the protection circuit comprising a Zener diode configured to limit the switch-off voltage at said switching connection to a limiting voltage corresponding in magnitude to at least twice the operating voltage; Includes.

[0009] The clamping voltage may be selected from the range of 100% to 150% of twice the operating voltage, in particular from the range of 105% to 130% of twice the operating voltage. Furthermore, the clamping voltage can be determined by selecting the turn-on voltage or breakdown voltage of the Zener diode. Preferably, the protection circuit is electrically coupled to at least one of the switched junctions in a non-capacitive manner.

[0010] In the drive circuit of an ultrasonic transducer, a transformer for the transmission mode is provided so that an ultrasonic transducer configured as a piezoelectric actuator can be driven with a high drive voltage. This is usually done using an AC voltage supplied by a pulsed operating voltage on the primary side of the transformer. The pulsed operating voltage is generated by applying or switching off the operating voltage using a suitable semiconductor switch, in particular a field effect transistor.

[0011] Due to the inductance of at least one primary winding of the transformer, when the operating voltage is turned off due to the electrical energy stored in the inductance, a significant voltage rise occurs at the terminals of the switched-on transformer. This voltage rise can lead to damage or destruction of components in the ultrasonic transducer system. Therefore, appropriate protection circuits are usually provided to limit the voltage rise after the primary winding is turned off.

[0012] Immediately after the primary winding of a transformer is switched off, the potential at the other transformer terminals corresponding to the primary winding remains constant, rather than switched, so that the switched-on transformer terminal normally has twice the operating voltage. Without further measures, if the current flow from the primary winding is strongly restricted or prevented, the switch-off voltage of the primary winding will continue to rise due to the electrical energy stored in the winding.

[0013] According to the above-described drive circuit, the protection circuit is coupled to the switching connection of at least one primary winding and includes a Zener diode. The Zener diode's turn-on voltage (breakdown voltage) is designed to be at least twice the operating voltage at which the primary winding switches. By setting the Zener diode's turn-on voltage to a value at least twice the operating voltage, the switch-off voltage of the primary winding can be effectively prevented from rising above the voltage threshold defined by the turn-on voltage. In this way, firstly, the voltage of the primary winding is limited to protect other components, and secondly, this voltage can be selected to ensure optimal energy dissipation in interactions with surrounding components.

[0014] Due to the specific drain of the current of the switched-off phase by the protection circuit, less electrical energy remains in the transformer during the transition from the transmit mode to the receive mode, so that the swing-out process at the end of the transmit mode is significantly shortened, so that any ultrasonic receive signals received by the ultrasonic transducer are not superimposed by any swing-out signals after the end of the transmit mode, or are superimposed for a shorter time, and can therefore be detected in an improved manner.

[0015] The operating voltage can be buffered by a buffer capacitance, to which the protection circuit can be coupled via a leakage resistor. This provides a rechargeable battery for the high switch-on current required at the beginning of the primary winding switch-on process. This reduces the current demand of the drive circuit by returning the energy dissipated during switch-off to the supply circuit.

[0016] Furthermore, the protection circuit may be coupled to the at least one switching connection via a diode, in particular directly via the diode, so that when a voltage difference occurs between the at least one switching connection and the Zener diode, a charge flow occurs from or to the at least one switching connection, limiting the voltage change at the at least one switching connection.

[0017] In this way, the protection circuit can be decoupled by connecting it in series with a diode, reducing the capacitive input to the protection circuit's switching transformer terminals or the transformer primary winding. Furthermore, the series connected diode allows biasing of the Zener diode, minimizing switching inertia.

[0018] Furthermore, a storage capacitor is electrically connected in parallel with the Zener diode to compensate for its capacitance. This improves the intermediate storage of electrical energy dissipated after the primary winding is turned off, making it available for use in the next switching cycle, i.e., the next time the primary winding is turned on. The Zener diode's starting voltage is deliberately selected to be more than twice the operating voltage, so that as the switch-off voltage increases, the current flowing through the primary winding can flow into the storage capacitor. This continues until the Zener diode's breakdown voltage is reached. The current then continues to flow through the Zener diode until the breakdown voltage falls below the Zener diode again. However, at the same time, the voltage on the secondary side also increases as the flow continues.

[0019] The storage capacitance is particularly useful in combination with a diode in series with the protection circuit, isolating the protection circuit from the transformer windings. In this way, the diode isolates the capacitance formed by the Zener diode and the storage capacitance from the transformer circuit and applies a bias voltage that increases switching speed.

[0020] Furthermore, the increased capacitance to absorb the dissipated charge means that the Zener diode capacitance no longer has a significant effect on the switching speed, and at the same time, it allows the storage of energy backflowing from the transformer, which is then fed back to the buffer capacitance battery via the leakage resistor.

[0021] In one embodiment, the transformer alternately connects and disconnects the two primary windings from the operating voltage, so that the operating voltage is always supplied to only one of the primary windings.

[0022] The corresponding switched connections of the primary winding can in particular be connected to a protection circuit via respective diodes.

[0023] According to a further aspect, a piezoelectric ultrasonic transducer; a drive circuit as described above, the secondary winding of which is connected to the ultrasonic transducer; An ultrasonic transducer system is provided that includes: [Brief explanation of the drawings]

[0024] Hereinafter, the embodiments will be described in more detail with reference to the accompanying drawings. [Figure 1] FIG. 1 is a diagram showing a schematic circuit diagram of an ultrasonic transducer system including a drive circuit. [Figure 2] FIG. 2 shows a signal-time diagram of the voltage signal of the drive circuit. DETAILED DESCRIPTION OF THE INVENTION

[0025] 1 shows an ultrasonic transducer system 1 including a driver circuit 2 for the transmit mode of the ultrasonic transducer system 1 and a receiver circuit 3 for the receive mode of the ultrasonic transducer system 1. The driver circuit 2 and receiver circuit 3 are connected to an ultrasonic transducer 4. The receiver circuit 3 is shown only schematically and the actual design details are not described here.

[0026] The ultrasonic transducer 4 has a piezoelectric actuator that can be driven with a high piezoelectric voltage of 100 V to 200 V in the ultrasonic frequency range, and outputs an ultrasonic transmission signal in transmission mode. In reception mode, the ultrasonic transmission signal is reflected by one or more surrounding objects to generate an ultrasonic reception signal, which changes the capacitance that can be detected by the reception circuit 3.

[0027] The driver circuit 2 and receiver circuit 3 are generally operated alternately in a transmission mode and a reception mode via a control unit 5 . The drive circuit 2 comprises a transformer 21 coupled on the secondary side to the ultrasonic transducer 4 .

[0028] The transformer 21 has two primary windings 22 and one secondary winding 23. The primary winding 22 is alternately energized in each case with a pulsed operating voltage corresponding to the desired drive frequency of the emitted ultrasonic transmission signal. The primary winding 22 is energized at a first supply potential U B (operating voltage). In particular, the first supply potential U B Coupling to can be via a resistor R2 and a capacitor C4 providing capacitance to the second supply potential GND, in particular to ground potential.

[0029] The first first switching connection A' of the primary winding 22' is connected to the second supply potential GND via a first semiconductor switch 24', and the second second switching connection A" of the primary winding 22" is connected to the second supply potential GND via a second semiconductor switch 24". The semiconductor switches 24', 24" are alternately operated by the control unit 5 according to respective control signals S', S" according to an operating frequency for opening and closing, so that the first and second primary windings 22', 22" are alternately energized, and the other of the first and second primary windings 22', 22" is connected to the first supply potential U B and the second supply potential GND.

[0030] The secondary winding 23 is connected to the ultrasonic transducer 4 and can be buffered by a buffer capacitor CR1. Since a high switching current occurs when an operating voltage is applied to the primary windings 22', 22", the first power supply voltage can be buffered by a buffer capacitor C2 which acts as a rechargeable battery with a high initial current after the switch-on process of either of the primary windings 22', 22".

[0031] The switching junctions A', A" of the first and second primary windings 22', 22" are connected to the protection circuit 25 via respective diodes D1, D2. The forward direction of the diodes D1, D2 corresponds to a positive voltage between the switching junctions A', A" and the protection circuit 25, respectively.

[0032] The protection circuit 25 comprises a Zener diode ZD1 connected by diodes D1, D2 to the switching junctions A′, A″ and to the second supply potential GND. The start-up voltage (breakdown voltage) U ZD corresponds to a voltage set to at least twice the operating voltage, in particular between 100% and 150%, preferably between 105% and 130% of twice the operating voltage. The activation voltage of the Zener diodes thus defines the limiting voltage of the voltage at the switching connections A', A".

[0033] The alternating operation of the primary windings 22′, 22″ causes the first supply potential U , at the switching connections A′, A″ of the primary windings 22′, 22″, after the semiconductor switches 24′, 24″ are turned off (the respective semiconductor switches are opened). B A switch-off voltage or cut-off potential is generated which corresponds to approximately twice the potential of the second supply potential GND (called the second supply potential GND). The switch-off potential (minus the diode voltage) is applied to the protection circuit 25 by the diodes D1, D2. The limit of the voltage rise in the primary winding 22', 22" of the transformer 21 or the electronic semiconductor switches (transistors, FETs, ...) 24', 24" connected thereto is the start-up voltage U of the Zener diodes. ZDand the diode forward voltage of diode D1 or D2. If Zener diode ZD1 is used without diodes D1 and D2, the voltage rise limit will be equal to the start-up voltage of Zener diode ZD.

[0034] The protection circuit 25 limits the corresponding cut-off potential to the potential of the activation voltage of the Zener diode ZD1. Without the Zener diode ZD1, the cut-off potential would continue to rise because the stored electrical energy would cause a current to flow through the primary winding 22', 22", which would either counteract the first supply potential VB or lead to a sudden increase in the voltage on the corresponding switched connection A', A".

[0035] The Zener diode ZD1 limits the voltage rise to the operating voltage. It is preferable that a storage capacitor is connected in parallel with the Zener diode ZD1. This parallel connection increases the charge storage capacity, which takes over part of the dissipated charge from the switched-off primary windings 22', 22", and charges up to a voltage level corresponding to the start-up voltage of the Zener diode ZD1.

[0036] The protection circuit 25 can supply charge from the storage capacitor C1 to the first supply potential VB, particularly to the buffer capacitor C2, via the leak resistor R1 connected to the first supply potential VB, and can supply charge corresponding to the high initial current during the subsequent switching operation. In this way, by storing part of the electrical energy discharged when the corresponding primary winding is turned off in the storage capacitor C1 and the buffer capacitor C2, it can be used for the subsequent switching operation corresponding to the required high initial current, thereby reducing the current required by the drive circuit 2.

[0037] The diodes D1, D2 have the advantage of decoupling the capacitance of the Zener diode ZD1 and any storage capacitance C2 from the switched junctions A', A'', thereby reducing the capacitance input to the switching of the transformer 21. The Zener diode of the protection circuit 25 is also biased across the leakage resistor R1 so that its switching inertia is reduced. The diodes decouple this part of the protection circuit from the primary winding and enable this biasing.

[0038] In addition, the protection circuit 25 quickly dissipates electrical energy from the primary windings 22', 22", leaving less electrical energy remaining in the transformer 21. This shortens the swing-out from the transformer-ultrasonic transducer combination, especially after the end of the transmission operation, and the inductance of the secondary winding 23 and the capacitance of the piezoelectric actuator of the ultrasonic transducer 4 form an oscillator circuit. This prevents the ultrasonic reception signals from overlapping due to the ongoing swing-out from the formed oscillator circuit, improving performance in short-range object detection.

[0039] 2 shows a signal time diagram illustrating the operation of the driver circuit 2 for one of the switching connections A'. After the respective semiconductor switch 24' is turned off (controlled by a low level control signal S'), the voltage on the switching connection A' immediately drops to twice the operating voltage, 2×U B and then, due to the energy dissipation in the protection circuit 25, the current flow decreases while the clamping voltage U G It can be seen that the voltage at the switched junction A' rises to U and remains there until the energy stored in the transformer is dissipated. B The entire circuit must be configured so that the voltage drop across the switched junction A' occurs before the next pulse of the control signal S' is applied. [Explanation of symbols]

[0040] 1. Ultrasonic Transducer System 2. Drive circuit 3 Receiver circuit 4 ultrasonic transducers 5 Control Unit 21 Transformer 22, 22', 22” primary winding 23 Secondary winding 24', 24" Solid State Switch 25 Protection circuit U B Operating voltage, first supply potential R1 Leak resistance R2 resistance C1 Storage Capacity C2 Buffer Capacity C4 capacity GND 2nd supply potential A', A" switch connection D1, D2 diodes ZD1 Zener diode

Claims

1. A driving circuit (2) for a piezoelectric ultrasonic transducer (4) in an ultrasonic transducer system (1), comprising: a transformer (21) having at least one primary winding (22, 22', 22''); a switching unit comprising a semiconductor switch (24', 24") connected to at least one of said primary windings (22, 22', 22") via a switching connection (A', A"); - at least one of said primary windings (22, 22', 22") is alternately supplied with an operating voltage (U Ｂ a control unit (5) configured to apply or decouple the a clamping voltage (U ) electrically coupled to said switching connection (A', A") and which limits the switch-off voltage at said switching connection (A', A") to a voltage which corresponds in magnitude to at least twice said operating voltage; Ｇ a protection circuit (25) having a Zener diode (ZD1) limiting a drive circuit including:

2. The clamping voltage (U Ｇ ) is the operating voltage (U Ｂ ) in the range of 100% to 150% of twice the operating voltage, in particular in the range of 105% to 130% of twice the operating voltage, The drive circuit of claim 1 .

3. The clamping voltage (U Ｇ ) is the starting voltage or breakdown voltage (U ＺＤ ) is determined by selecting 3. The drive circuit according to claim 2.

4. the protection circuit (25) is coupled, in particular directly, to at least one of the switching connections (A', A") via diodes (D1, D2), which, when a voltage difference occurs between at least one of the switching connections (A', A") and a Zener diode (ZD1), cause a charge flow from or to at least one of the switching connections (A', A") in order to limit voltage changes at at least one of the switching connections (A', A"); A drive circuit (2) according to claim 3.

5. the protection circuit (25) is electrically coupled to at least one of the switching connections (A', A") in a non-capacitive manner; 5. The drive circuit according to claim 4.

6. The protection circuit (25) has a storage capacitance (C1) electrically connected in parallel with the Zener diode (ZD1).

6. The drive circuit according to claim 5.

7. The operating voltage is buffered by a buffer capacitance (C2), and the protection circuit (25) is coupled to the buffer capacitance (C2) via a leakage resistor (R1). The drive circuit of claim 1 .

8. The transformer (21) operates at an operating voltage (U Ｂ ) and has two primary windings (22, 22', 22") that are alternately connected and disconnected from the operating voltage (U Ｂ ) is always applied to one of the primary windings (22, 22', 22"); The drive circuit of claim 1 .

9. 9. The drive circuit according to claim 8, wherein the corresponding switched connections (A', A") of the primary windings (22, 22', 22") are connected to the protection circuit (25), in particular via respective diodes (D1, D2).

10. a piezoelectric ultrasonic transducer (4), - a drive circuit (2) according to any one of claims 1 to 9, in which the secondary winding (23) of the transformer (21) is connected to the ultrasonic transducer (4); An ultrasonic transducer system (1) comprising:

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