Patent Publication Number: US-11660637-B2

Title: Driving device

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims the priority benefit of Taiwan patent application serial no. 109107184, filed on Mar. 5, 2020. The entirety of the above-mentioned patent application is hereby incorporated by reference and made a part of this specification. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The invention relates to a driving device, and in particular, to a driving device configured to drive a transducer. 
     2. Description of Related Art 
     Ultrasonic waves are wave vibrations that exceed several times and even hundreds of times of human hearing, and ultrasonic cleaners use ultra high-frequency vibrations to clean objects. The ultrasonic cleaners use ultrasonic waves to pass through liquid and remove dirt and dust on material surfaces, holes, and gaps, and are widely used for cleaning glasses, contacts, jewels, watches, false teeth, electronic devices, and the like. 
     An ultrasonic cleaner generally uses a transducer (for example, a piezoelectric ceramic transducer) as a vibration source of the ultrasonic cleaner, and the transducer generates mechanical vibrations by applying an excitation signal of more than a frequency 20 kHz to the transducer. The transducer uses the piezoelectric effect to generate mechanical vibrations, and when an alternating current power is applied to the transducer, the transducer has mechanical waves in positive and negative directions. 
     Because the transducer is operated at a high frequency, a drive circuit configured to drive the transducer generates a switching loss in the high-frequency operation. Therefore, as can be seen, how to reduce the switching loss of the drive circuit in the high-frequency operation is one of the development emphases of the high-frequency drive circuit. 
     SUMMARY OF THE INVENTION 
     The invention provides a driving device having a low switching loss in a high-frequency operation. 
     The driving device of the invention is adapted to drive a transducer. The driving device includes a boost inductor, a rectifying circuit, and a resonance circuit. The boost inductor is configured to receive a first power via a first terminal of the boost inductor in a first mode, and provide a second power via a second terminal of the boost inductor. The rectifying circuit is coupled to the second terminal of the boost inductor. The rectifying circuit is configured to limit a transmission path of the second power. The resonance circuit is coupled to the transducer and the rectifying circuit. The resonance circuit is configured to store a stored electric energy from the second power in the first mode, so that the boost inductor does not provide the second power in the second mode, and drive the transducer by the stored electric energy in the first mode and the second mode. The first mode and the second mode are alternately operated. 
     Based on the above, the driving device stores the stored electric energy from the second power by the resonance circuit in the first mode, so that the boost inductor does not provide the second power in the second mode, and drives the transducer by the stored electric energy in the first mode and the second mode. Therefore, the boost inductor is operated in equivalence in a discontinuous conduction mode, so that the driving device has an effect of correcting power factors. In addition, zero voltage switching (ZVS) occurs when the driving device switches from the first mode to the second mode, thereby reducing a switching loss. 
     To make the features and advantages of the invention clear and easy to understand, the following gives a detailed description of embodiments with reference to accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG.  1    is a schematic circuit diagram of a driving device shown according to an embodiment of the invention. 
         FIG.  2    is an operation sequence diagram shown according to an embodiment of the invention 
         FIG.  3 A  to  FIG.  3 F  are respectively schematic diagrams of equivalent circuits of a plurality of modes of the driving device according to an embodiment of the invention. 
     
    
    
     DESCRIPTION OF THE EMBODIMENTS 
       FIG.  1    is a schematic circuit diagram of a driving device shown according to an embodiment of the invention. In the present embodiment, the driving device  100  is configured to drive a transducer PCT. The transducer PCT is, for example, a piezoelectric ceramic transducer. The driving device  100  includes a boost inductor LB, a rectifying circuit  110 , and a resonance circuit  120 . The driving device  100  is operated in a first mode and a second mode. The first mode and the second mode are alternately operated. In the present embodiment, the boost inductor LB receives a first power P 1  via a first terminal of the boost inductor LB in the first mode, and provides a second power P 2  via a second terminal of the boost inductor LB. The rectifying circuit  110  is coupled to the second terminal of the boost inductor LB. The rectifying circuit  110  is configured to limit a transmission path of the second power P 2 . 
     In the present embodiment, the resonance circuit  120  is coupled to the transducer PCT and the rectifying circuit  110 . The resonance circuit  120  stores a stored electric energy from the second power P 2  in the first mode, and makes the boost inductor LB not provide the second power P 2  in the second mode. In addition, the resonance circuit  120  drives the transducer PCT by the stored electric energy in the first mode and the second mode. 
     It is worth mentioning herein that, because the driving device  100  makes the boost inductor LB not provide the second power P 2  in the second mode, the boost inductor LB is operated in equivalence in a discontinuous conduction mode, so that the driving device  100  has an effect of correcting power factors. In addition, zero voltage switching (ZVS) occurs when the driving device  100  switches from the first mode to the second mode, thereby reducing a switching loss. 
     In the present embodiment, the driving device  100  further includes a filter  130 . The filter  130  receives an external power VAC, and filters out noise of the external power VAC to provide the first power P 1 . Further, the external power VAC is an alternating current power. The filter  130  filters out high-frequency noise of the external power VAC to provide the first power P 1 . That is, based on the configuration of  FIG.  1   , the first power P 1  may be regarded as the external power VAC obtained after the high-frequency noise is filtered out. 
     The circuit configuration is further described in detail. The resonance circuit  120  includes a first power switch S 1 , a second power switch S 2 , a series inductor LS, a first capacitor C 1 , and a second capacitor C 2 . A first terminal of the first power switch S 1  is coupled to a second terminal of the boost inductor LB via the rectifying circuit  110 . A control terminal of the first power switch S 1  is configured to receive a first control signal CS 1 . A first terminal of the second power switch S 2  is coupled to a second terminal of the first power switch S 1 . A second terminal of the second power switch S 2  is coupled to a reference low potential (for example, is grounded). A control terminal of the second power switch S 2  is configured to receive a second control signal CS 2 . According to design requirements, the first control signal CS 1  and the second control signal CS 2  may be generated from a control signal generator (not shown). A first terminal of the series inductor LS is coupled to the second terminal of the first power switch S 1 . A second terminal of the series inductor LS is coupled to one of power electrodes of the transducer PCT. A first terminal of the first capacitor C 1  is coupled to the first terminal of the first power switch S 1 . A second terminal of the first capacitor C 1  is coupled to the other one of the power electrodes of the transducer PCT. A first terminal of the second capacitor C 2  is coupled to the second terminal of the first capacitor C 1 . A second terminal of the second capacitor C 2  is coupled to the reference low potential. 
     The first power switch S 1  and the second power switch S 2  may be respectively implemented by one of a metal-oxide-semiconductor field-effect transistor (MOSFET), a bipolar transistor (BJT), and an insulated gate bipolar transistor (IGBT). The first power switch S 1  and the second power switch S 2  of the present embodiment are respectively implemented by an n-type MOSFET. Therefore, the first power switch S 1  may be conducted according to the first control signal CS 1  at a high voltage level. The first power switch S 1  may be disconnected according to the first control signal CS 1  at a low voltage level. The second power switch S 2  may be conducted according to the second control signal CS 2  at a high voltage level. The second power switch S 2  may be disconnected according to the second control signal CS 2  at a low voltage level. 
     In the present embodiment, the rectifying circuit  110  includes a first diode D 1  and a second diode D 2 . A cathode of the first diode D 1  is coupled to the first terminal of the first power switch S 1 . An anode of the first diode D 1  is coupled to the second terminal of the boost inductor LB. A cathode of the second diode D 2  is coupled to the anode of the first diode D 1 . An anode of the second diode D 2  is coupled to the reference low potential. 
     In the present embodiment, the filter  130  includes a filter inductor LF and a filter capacitor CF. A first terminal of the filter inductor LF is used as one of power pins connected to the external power VAC, and a second terminal of the filter inductor LF is coupled to the first terminal of the boost inductor LB. A first terminal of the filter capacitor CF is coupled to the first terminal of the boost inductor LB and the second terminal of the filter inductor LF. A second terminal of the filter capacitor CF is used as the other one of the power pins connected to the external power VAC. The second terminal of the filter capacitor CF is further coupled to the second terminal of the first power switch S 1 . Therefore, the first terminal of the filter inductor LF and the second terminal of the filter capacitor CF are used as two input terminals of the filter  130 . The second terminal of the filter inductor LF is used as an output terminal of the filter  130 . 
     It is worth mentioning herein that, the resonance circuit  120  of the present embodiment includes a first power switch S 1  and a second power switch S 2 . Therefore, compared with four power switches in the prior art, the present embodiment has an advantage of reducing the quantity of power switches. 
     The operation process of the driving device is described next. Referring to  FIG.  2    and  FIG.  3 A  together,  FIG.  2    is an operation sequence diagram shown according to an embodiment of the invention.  FIG.  3 A  to  FIG.  3 F  are respectively schematic diagrams of equivalent circuits of a plurality of modes of the driving device according to an embodiment of the invention. 
     As shown in  FIG.  2    and  FIG.  3 A , at a time point t 0 , the first power switch S 1  is conducted according to the first control signal CS 1  at the high voltage level. A voltage difference VGS 1  between a control terminal (gate) and a second terminal (source) of the first power switch S 1  is a high voltage level. A voltage difference VDS 1  between a first terminal (drain) and the second terminal (source) of the first power switch S 1  is a low voltage level. The second power switch S 2  is disconnected according to the second control signal CS 2  at the low voltage level. A voltage difference VGS 2  between a control terminal (gate) and a second terminal (source) of the second power switch S 2  is a low voltage level. A voltage difference VDS 2  between a first terminal (drain) and the second terminal (source) of the second power switch S 2  is a high voltage level. The driving device  100  starts to be operated in the first mode MD 1  at the time point t 0 . The filter circuit  130  receives the external power VAC, and filters out noise of the external power VAC to provide the first power P 1 . 
     At the time point t 0 , the filter circuit  130 , the boost inductor LB, the diode D 1 , and the conducted first power switch S 1  form an energy loop LP 1 . Therefore, the boost inductor LB receives the first power P 1  via the energy loop LP 1  and provides the second power P 2 . In a first time interval (a time interval between the time point t 0  and a time point t 1 ) of the first mode MD 1 , a boost inductor current value ILB of the boost inductor LB rises. In the first time interval of the first mode MD 1 , the first capacitor C 1 , the conducted first power switch S 1 , the series inductor LS, and the transducer PCT form an energy loop LP 2 . The electric energy stored in the first capacitor C 1  is provided to the series inductor LS and the transducer PCT via the energy loop LP 2 . When the boost inductor current value ILB rises to a maximum value at the time point t 1 , the first power switch S 1  is disconnected according to the first control signal CS 1  at the low voltage level. 
     As shown in  FIG.  2    and  FIG.  3 B , at the time point t 1 , the first power switch S 1  is disconnected. Therefore, the filter circuit  130 , the boost inductor LB, the diode D 1 , and a parasitic capacitor PC 1  of the first power switch S 1  form an energy loop LP 3 . Therefore, the parasitic capacitor PC 1  of the first power switch S 1  stores the electric energy of the second power P 2 . In this case, the boost inductor current value ILB starts to drop. In a second time interval (a time interval between the time point t 1  and a time point t 2 ) of the first mode MD 1 , the first capacitor C 1 , the parasitic capacitor PC 1  of the first power switch S 1 , the series inductor LS, and the transducer PCT form an energy loop LP 4 . The electric energy stored in the first capacitor C 1  and the series inductor LS is provided to the parasitic capacitor PC 1  of the first power switch S 1  and the transducer PCT via the energy loop LP 4 . Therefore, the voltage difference VDS 1  between the first terminal (drain) and the second terminal (source) of the first power switch S 1  gradually rises. In the second time interval (the time interval between the time point t 1  and the time point t 2 ) of the first mode MD 1 , a parasitic capacitor PC 2  of the second power switch S 2 , the series inductor LS, the transducer PCT, and the second capacitor C 2  form an energy loop LP 5 . The electric energy stored in the series inductor LS and the second capacitor C 2  is also provided to the parasitic capacitor PC 2  of the second power switch S 2  and the transducer PCT via the energy loop LP 5 . Therefore, the voltage difference VDS 2  between the first terminal (drain) and the second terminal (source) of the second power switch S 2  gradually drops. 
     As shown in  FIG.  2    and  FIG.  3 C , at the time point t 2 , when the electric energy of the parasitic capacitor PC 2  of the power switch S 2  is released completely at the time point t 2 , the voltage difference VDS 2  between the first terminal (drain) and the second terminal (source) of the second power switch S 2  drops to 0 V. An intrinsic diode PD 2  of the second power switch S 2  is conducted. In a third time interval (a time interval between the time point t 2  and a time point t 3 ) of the first mode MD 1 , the filter  130 , the boost inductor LB, the first diode D 1 , the first capacitor C 1 , the second capacitor C 2 , and the intrinsic diode PD 2  of the second power switch S 2  form an energy loop LP 6 . The electric energy of the second power P 2  is provided to the first capacitor C 1  and the second capacitor C 2  via the energy loop LP 6 . The boost inductor current value ILB continuously drops. The series inductor LS, the transducer PCT, the second capacitor C 2 , and the intrinsic diode PD 2  of the second power switch S 2  form an energy loop LP 7 . The electric energy stored in the series inductor LS is provided to the transducer PCT via the energy loop LP 7 . The boost inductor current value ILB drops to 0 A at the time point t 3 . 
     As shown in  FIG.  2    and  FIG.  3 D , at the time point t 3 , when the boost inductor current value ILB drops to 0 A, the driving device  100  conducts the second power switch S 2  according to the second control signal CS 2 , and switches from the first mode MD 1  to the second mode MD 2 . The voltage difference VGS 2  between the control terminal (gate) and the second terminal (source) of the second power switch S 2  is a high voltage level. The voltage difference VDS 2  between the first terminal (drain) and the second terminal (source) of the second power switch S 2  keeps at the low voltage level. In this case, because the boost inductor current value ILB is 0 A, the boost inductor LB is a non-conducted state in equivalence. Therefore, the boost inductor LB starts not to provide the second power P 2  at the time point t 3 , and the driving device  100  performs ZVS at the time point t 3  to reduce a switching loss of switching from the first mode MD 1  to the second mode MD 2 . In a fourth time interval (a time interval between the time point t 3  and a time point t 4 ) of the second mode MD 2 , the second capacitor C 2 , the transducer PCT, the series inductor LS and the conducted second power switch S 2  form an energy loop LP 8 . The electric energy stored in the second capacitor C 2  is provided to the transducer PCT and the series inductor LS via the energy loop LP 8 . 
     Incidentally, according to the dropping speed of the boost inductor current value ILB, the time point t 3  may be close to the time point t 2 . 
     It should be noted herein that, in the first mode MD 1 , a series inductor current value ILS of the series inductor LS is greater than 0. In the second mode MD 2 , the series inductor current value ILS of the series inductor LS is less than 0. That is, a current direction in which the electric energy stored in the resonance circuit  120  flows through the transducer PCT in the first mode MD 1  is opposite to a current direction in which the electric energy flows through the transducer PCT in the second mode MD 2 . 
     As shown in  FIG.  2    and  FIG.  3 E , at the time point t 4 , the driving device  100  disconnects the second power switch S 2  according to the second control signal CS 2 . The parasitic capacitor PC 1  of the first power switch S 1 , the first capacitor C 1 , the transducer PCT, and the series inductor LS form an energy loop LP 9 . The electric energy stored in the series inductor LS and the parasitic capacitor PC 1  of the first power switch S 1  is provided to the first capacitor C 1  and the transducer PCT via the energy loop LP 9 . The series inductor LS, the parasitic capacitor PC 2  of the second power switch S 2 , the second capacitor C 2 , and the transducer PCT form an energy loop LP 10 . The electric energy stored in the second capacitor C 2  and the series inductor LS is provided to the parasitic capacitor PC 2  of the second power switch S 2  and the transducer PCT. When the electric energy stored in the parasitic capacitor PC 1  of the first power switch S 1  is released completely at a time point t 5  (the voltage difference VDS 1  drops to 0 V), the intrinsic diode PD 1  of the first power switch S 1  is conducted. 
     As shown in  FIG.  2    and  FIG.  3 F , the intrinsic diode PD 1  of the first power switch S 1  is conducted. Therefore, the series inductor LS, the intrinsic diode PD 1  of the first power switch S 1 , the first capacitor C 1 , and the transducer PCT form an energy loop LP 11 . The electric energy stored in the series inductor LS is provided to the first capacitor C 1  and the transducer PCT via the energy loop LP 11 . When the first power switch S 1  is conducted according to the first control signal at a time point t 6 , to switch from the second mode MD 2  to the first mode MD 1 , and the boost inductor LB returns to a conducted state in the first mode MD 1 . Next, return to the implementation content shown in  FIG.  2    and  FIG.  3 A . 
     Incidentally, the time point t 6  may be advanced or delayed to adjust a conducted time of the boost inductor LB, thereby correcting power factors. That is, the time point t 6  may be equal to the time point t 5  or later than the time point t 5 . Therefore, based on the adjustment of the time points t 3  and t 6 , at least one of a work cycle of the first power switch S 1  and a work cycle of the second power switch S 2  is less than 50%. Therefore, as can be seen, the driving device  100  makes the boost inductor LB be operated in equivalence in a discontinuous conduction mode, so that the driving device  100  can have effects of correcting power factors and reducing a switching loss of a drive circuit in a high-frequency operation. 
     Based on the above, the driving device of the invention is operated in equivalence in the discontinuous conduction mode by using the boost inductor, so that the driving device has the effect of correcting power factors. In addition, ZVS occurs when the driving device switches from the first mode to the second mode, thereby reducing the switching loss. 
     Although the invention is described with reference to the above embodiments, the embodiments are not intended to limit the invention. A person of ordinary skill in the art may make variations and modifications without departing from the spirit and scope of the invention. Therefore, the protection scope of the invention should be subject to the appended claims.