Circuit and method of adjusting conduction period for energy-recycling circuit

Abstract

A period determination circuit for determining the conduction period of an energy recovery circuit includes an indicator circuit coupled to an inductor of the energy recovery circuit to receive an inductor voltage, for generating an indicator signal based on the inductor voltage, reflecting the state corresponding to a first conduction period of the energy recovery circuit; and a control signal generator coupled to a switch of the energy recovery circuit, for generating a control signal having a second conduction period for use with the switch based on the indicator signal. The energy recovery circuit is coupled to a first capacitive element and a second capacitive element. The energy recovery circuit includes an inductor and a switch coupled between the first and second capacitive elements. The control signal generator determines the second conduction period based on the first conduction period and the indicator signal.

Description

Technical Field

[0001] This application refers to a circuit and method for determining the conduction period for an energy recovery circuit. Prior Art

[0002] Unless otherwise indicated, the methods described below are not prior art to the patent scope of this application, and the content of this paragraph should not be included in the prior art.

[0003] An energy recovery circuit using inductance-capacitance oscillation has been applied to a drive circuit for driving a capacitive load, especially in situations where a switched voltage is required (for example, see U.S. Patent No. 11,057,692, Application No. 18 / 396,678, and Patent No. 12,107,546), which has the benefit of reducing power consumption. Basically, the energy recovery circuit includes an inductor and a switch, coupled between a first capacitive element and a second capacitive element having a certain capacitance. During the conduction period, the energy recovery circuit can form a current flowing from one capacitive element to the other, thereby recovering electrical energy to be stored in one of the capacitive elements.

[0004] During the conduction period, when the conduction period is long enough, the magnitude of the current decreases and eventually reaches zero. If the conduction period is too long, due to the characteristics of inductance-capacitance oscillation, a reverse current will be formed.

[0005] The conduction period cannot be too short, otherwise there will be remaining charge (electrical energy) that cannot be fully recovered. On the other hand, the conduction period cannot be too long, otherwise an unnecessary reverse current will be formed, as described above. Therefore, determining the conduction period for energy recovery becomes an important issue.

[0006] Furthermore, in some application scenarios, the capacitance value is not constant, making the determination of the conduction period more challenging.

[0007] Therefore, how to determine the conduction period for an energy recovery circuit is an important goal in this field. Summary of the Invention

[0008] Therefore, the main objective of this application is to propose a circuit and method for determining the conduction period for an energy recovery circuit.

[0009] An embodiment of the present invention discloses a period determination circuit for determining a conduction period for an energy recovery circuit. The period determination circuit includes an indication circuit coupled to an inductor of the energy recovery circuit to receive an inductor voltage, and is configured to generate an indication signal according to the inductor voltage, wherein the indication signal reflects a state corresponding to a first conduction period of the energy recovery circuit; and a control signal generator coupled to a switch of the energy recovery circuit, and is configured to generate a control signal having a second conduction period for the switch according to the indication signal. The energy recovery circuit is coupled to a first capacitive element and a second capacitive element. The energy recovery circuit includes the inductor and the switch coupled between the first capacitive element and the second capacitive element. The control signal generator determines the second conduction period according to the first conduction period and the indication signal.

[0010] Another embodiment of the present invention discloses a period determination method for determining a conduction period for an energy recovery circuit. The period determination method includes receiving an inductor voltage corresponding to an inductor of the energy recovery circuit; generating an indication signal according to the inductor voltage, wherein the indication signal reflects a state corresponding to a first conduction period of the energy recovery circuit; determining a second conduction period according to the first conduction period and the indication signal; and generating a control signal having the second conduction period according to the indication signal for a switch of the energy recovery circuit. Wherein, the energy recovery circuit is coupled to a first capacitive element and a second capacitive element; wherein, the energy recovery circuit includes the inductor and the switch coupled between the first capacitive element and the second capacitive element. Brief Description of the Drawings

[0011] FIG. 1 is a schematic diagram of a period determination circuit coupled to an energy recovery circuit according to an embodiment of the present application. FIG. 2 illustrates an inductor current and an inductor voltage related to a voltage and a control signal when the conduction period is too short. FIG. 3 illustrates an inductor current and an inductor voltage when the conduction period is too long. FIG. 4 illustrates a period determination circuit coupled to an energy recovery circuit according to an embodiment of the present application. FIG. 5 is a schematic diagram of an indication circuit according to an embodiment of the present application. FIG. 6 illustrates a schematic diagram of a capacitive element according to an embodiment of the present application. FIG. 7 illustrates a period determination circuit coupled to an energy recovery circuit according to an embodiment of the present application. FIG. 8 illustrates waveforms of a voltage, a control signal, an inductor current, and an inductor voltage. FIG. 9 shows a schematic diagram of a period determination circuit during an embodiment of the present application. Embodiment

[0012] FIG. 1 is a schematic diagram of a period determination circuit 20 coupled to an energy recovery circuit 10 during an embodiment of the present application. The energy recovery circuit 10 basically includes an inductor L and a switch SW, which are coupled between a first capacitive element C1 and a second capacitive element C2. The capacitive element can be a capacitor or an element having a certain capacitance value, and C1 / C2 can also represent its capacitance value.

[0013] The period determination circuit 20 is used to generate a control signal (also denoted as SW) to the switch SW of the energy recovery circuit 10. In other words, the period determination circuit 20 can determine a conduction period Ton for the switch SW or the energy recovery circuit 10 through the control signal SW.

[0014] In the present application, the switch and its control signal share the same symbol. In addition, the nodes (in the circuit) and their voltages also share the same symbol.

[0015] Once the switch SW is turned on and activated, the energy recovery circuit 10 can initiate an inductor-capacitor oscillation. Assuming that a (first) voltage Vc1 corresponding to the first capacitive element C1 is greater than a (second) voltage Vc2 corresponding to the second capacitive element C2 (i.e., Vc1 > Vc2), an inductor current IL is formed from C1 to C2 at a first time (i.e., the initial instant when the switch SW is turned on). When the switch SW remains on, the magnitude of the inductor current IL gradually decreases to zero, and then the current direction of the inductor current IL turns reverse.

[0016] The purpose of the period determination circuit 20 is to determine or adaptively adjust the conduction period Ton to make it as optimal as possible. In one embodiment, the optimal conduction period Ton should be the longest period before the inductor current turns reverse. A too short conduction period means that there is still residual charge in C1 at the end of the conduction period. A too long conduction period means that the switch SW is turned off after the inductor current reverses.

[0017] The period determination circuit 20 includes an indication circuit 200 and a control signal generator 202. The indication circuit 200 is coupled to the inductor L of the energy recovery circuit 10 to receive an inductor voltage VL from the inductor L. The control signal generator 202 can be used to generate an output control signal SW to the switch SW.

[0018] The indication circuit 200 can generate an indication signal IDS according to the inductor voltage VL. Among them, the indication signal IDS can reflect a state corresponding to the current (first) conduction period (denoted as Ton,n) of the energy recovery circuit 10, where Ton,n represents the conduction period corresponding to the nth energy recovery operation. In an embodiment, the indication signal IDS can indicate that the current conduction period Ton,n is too short or too long.

[0019] The control signal generator 202 can generate a control signal SW with the next / subsequent (second) conduction period (denoted as Ton,n+1) according to the indication signal IDS for the switch SW, where Ton,n+1 represents the conduction period corresponding to the (n + 1)th energy recovery operation, which is after the nth energy recovery operation.

[0020] In an embodiment, when the indication signal IDS indicates that the current conduction period Ton,n is too short, the control signal generator 202 can adjust the conduction period, or more specifically, lengthen the conduction period so that Ton,n+1 > Ton,n, and generate a control signal SW with the lengthened conduction period Ton,n+1 (i.e., Ton,n+1 > Ton,n). On the other hand, when the indication signal IDS indicates that the current conduction period Ton,n is too long, the control signal generator 202 can adjust the conduction period, or more specifically, shorten the conduction period so that Ton,n+1 < Ton,n, and generate a control signal SW with the shortened conduction period Ton,n+1 (i.e., Ton,n+1 < Ton,n).

[0021] FIG. 2 shows an inductor current IL and an inductor voltage VL related to voltages Vc1, Vc2, and the control signal SW when the conduction period Ton is too short. In FIG. 2, the inductor current IL flowing from C1 to C2 is regarded as positive. In FIG. 2(a), at the start of the conduction period Ton, Vc2 > Vc1, the inductor current flows from C2 to C1, and IL is negative. Assuming that the switch is coupled between the inductor L and the first capacitive element C1, if the conduction period Ton is too short, then during the off-time of the switch SW (denoted as toff in FIG. 2), there is a part of the remaining inductor current flowing from C2 to the node labeled VL. It should be noted that there is some parasitic capacitance at the node VL, which is much smaller than C1, so the inductor current will generate a high / positive voltage spike on the node or the inductor voltage VL at time toff, as shown in FIG. 2(a).

[0022] Similarly, in Figure 2(b), at the start of the conduction period Ton, Vc2 < Vc1, the inductor current flows from C1 to C2 and IL is positive. If the conduction period Ton is too short, then during the turn-off time toff of the switch SW, the positive residual inductor current will generate a low / negative voltage spike on VL, as shown in Figure 2(b).

[0023] On the other hand, Figure 3 shows the inductor current IL and the inductor voltage VL when the conduction period Ton is too long, i.e., toff > trev, where toff represents the turn-off time of the switch and trev represents the inductor current reversal time (i.e., the time when the inductor current returns to zero). Figure 3(a) shows the situation where Vc2 > Vc1, and at the start of the conduction period Ton, the inductor current IL flows from C2 to C1 (i.e., negative); Figure 3(b) shows the situation where Vc1 > Vc2, and at the start of the conduction period Ton, the inductor current IL flows from C1 to C2 (i.e., positive).

[0024] As shown in Figure 3(a), the positive reverse inductor current IL will generate a negative spike on the inductor voltage VL at time toff. As shown in Figure 3(b), the negative reverse inductor current IL will generate a positive spike on the inductor voltage VL at time toff.

[0025] It can be determined from Figures 2 and 3 that whether the conduction period Ton is too short or too long can be inferred based on the behaviors of the voltages Vc1, Vc2, and VL.

[0026] Figure 4 shows that during a first embodiment of the present application, the period determination circuit 34 is coupled to the energy recovery circuit 10 (which is part of a modulation signal generator 30, described in detail later), and the connection between the circuits 10 and 34 is omitted for simplicity. The period determination circuit 34 can be used to determine the conduction period Ton for the energy recovery circuit and is coupled to the capacitive elements C1, C2, and the inductor L to receive the voltage Vc1 corresponding to C1, the voltage Vc2 corresponding to C2, and the inductor voltage VL.

[0027] Further, the period determination circuit 34 may include an indication circuit 340 and a control signal generator 342. The indication circuit 340 may generate an indication signal IDS to indicate that the current (first) conduction period Ton,n is too short when the surge is positive and Vc1 > Vc2 at time toff, or when the surge is negative and Vc1 < Vc2 at time toff. On the other hand, the indication circuit 340 may generate an indication signal IDS to indicate that the current (first) conduction period Ton,n is too long when the surge is negative and Vc1 > Vc2 at time toff, or when the surge is positive and Vc1 < Vc2 at time toff. Note that the turn-off time toff of the switch corresponds to the surge time, or the time when the surge reaches its peak.

[0028] Similar to 202, when the indication signal IDS received by the control signal generator 342 indicates that the current conduction period Ton,n is too short, the control signal generator 342 may generate a control signal SW with an extended conduction period Ton,n+1 (i.e., Ton,n+1 > Ton,n); and when the indication signal IDS received by the control signal generator 342 indicates that the current conduction period Ton,n is too long, the control signal generator 342 may generate a control signal SW with a shortened conduction period Ton,n+1 (i.e., Ton,n+1 < Ton,n).

[0029] FIG. 5 is a schematic diagram of an indication circuit 31 according to an embodiment of the present application. The indication circuit 31 can be used to implement the indication circuit 340. The indication circuit 31 may include a surge detection circuit 310, a comparator 312, and a logic circuit 314. The surge detection circuit 310 can be used to detect whether a surge occurs and determine the polarity of the surge when a surge occurs. The comparator 312 can be used to compare Vc1 and Vc2. The logic circuit 314 can generate an indication signal IDS based on the detection result generated by the surge detection circuit 310 and the comparison result generated by the comparator 312.

[0030] Based on the content of FIGS. 2 and 3, the period determination circuit 34 is applicable to the energy recovery circuit provided in the drive circuit for driving an Air-Pulse Generating Device (APG Device) to generate an Amplitude-Modulated Ultrasonic Air Pressure Variation having an ultrasonic carrier frequency (please refer to U.S. Patent No. 12,075,213). That is to say, the period determination circuit 34 can be coupled to / applied to the energy recovery circuit provided in the modulation signal generator disclosed in U.S. Patent Application No. 18 / 396,678, or the energy recovery circuit in the drive circuit disclosed in U.S. Patent No. 12,107,546, which is used to generate the modulation drive signal SM or generate a Double Sideband with Suppressed Carrier (DSB-SC) signal.

[0031] More specifically, FIG. 6 illustrates a schematic diagram of the capacitive element C1 or an air-pulse generating device of an embodiment of the present application. The capacitive element C1 or the air-pulse generating device may include a membrane structure 11, and the membrane structure 11 includes a flap pair 102, and the flap pair 102 includes flaps 101 and 103. In the embodiment of FIG. 6, the flap pair 102 can be driven by a modulation drive signal SM to perform a common-mode motion, and driven by a demodulation drive signal ±SV to perform a differential-mode motion, thereby realizing the combination of modulation and demodulation or in-situ modulation and demodulation, that is, modulation and demodulation can be performed on the same part / position of the membrane structure.

[0032] Furthermore, the capacitive element C1 or the air-pulse generating device may include an actuator 101A provided on the flap 101 and an actuator 103A provided on the flap 103. Each of the actuators 101A and 103A may include a piezoelectric material, such as PZT (for example, Lead Zirconate Titanate), which is disposed between the upper electrode and the lower electrode.

[0033] For the detailed operating principle of the air-pulse generating device, reference can be made to the description of U.S. Patent No. 12,075,213, which will not be elaborated here for the sake of simplicity. Briefly, the period determination circuit 34 can be coupled to the drive circuit used to generate the modulation drive signal SM.

[0034] On the other hand, the period determination circuit of the present application can also be coupled to / applied to the energy recovery circuit disposed in the demodulation signal generator disclosed in U.S. Patent Application No. 18 / 396,678, which is used to generate the demodulation drive signals ±SV.

[0035] For example, FIG. 7 shows a period determination circuit 44 of an embodiment of the present application coupled to an energy recovery circuit 42 (which is part of a demodulation signal generator 40). The period determination circuit 44 includes an indication circuit 440 and a control signal generator 442. Generally, the indication circuit 440 can receive an inductor voltage VLx and a control signal SWx, and generate an indication signal IDS based thereon. The control signal generator 442 can generate control signals for the switches SWx, where x = 1 or 2. Similarly, the connection between the energy recovery circuit 42 and the period determination circuit 44 is omitted for simplicity.

[0036] The demodulation signal generator 40 (energy recovery circuit 42) can be used to generate the demodulation drive signals ±SV, as described in U.S. Patent Application No. 18 / 396,678. Different from U.S. Patent Application No. 18 / 396,678, the demodulation signal generator 40 of the present application further includes a period determination circuit 44, which can be used to generate control signals SW1 and SW2 for the switches SW1 and SW2 in the energy recovery circuit 42.

[0037] In FIG. 7, the first capacitive element C1 coupled to the energy recovery circuit 42 can be the actuator 101A disposed on the flap 101, and the second capacitive element C2 coupled to the energy recovery circuit 42 can be the actuator 103A disposed on the flap 103.

[0038] FIG. 8 shows the waveforms of voltages Vc1 and Vc2, control signals SW1 and SW2, inductor current IL, and inductor voltages VL1 and VL2. The waveforms shown in FIG. 8 can be obtained through simulation or experiment. More specifically, FIG. 8(a) shows the waveforms of control signals SW1 and SW2, which have multiple different off-times toff,2, and FIG. 8(b) shows the waveform of the inductor voltage VL2 in response to the control signal SW2 under each off-time toff,2.

[0039] It should be noted that, in one embodiment, the conduction period can be terminated by turning off the switch SWx when one of the voltages Vcx is lower than the other. For example, at the end of the (n - 1)th energy recovery operation, the switch SW1 is turned off because Vc1 < Vc2; at the end of the nth energy recovery operation, the switch SW2 is turned off because Vc2 < Vc1. Therefore, the conduction time Ton of the (n - 1)th energy recovery operation can be determined by toff,1 - ton,2, and the conduction time Ton of the nth energy recovery operation can be determined by toff,2 - ton,1. Note that ton / off,x represents the on / off time of the switch SWx.

[0040] It should be noted that the conduction time Ton can be lengthened by delaying the turn-off time toff,x, or shortened by advancing the turn-off time toff,x (assuming the turn-on time ton,x remains unchanged).

[0041] There is a time difference, denoted as TD, between the falling time / edge of the control signal SW2 and the rising time of the inductor voltage VL2. As can be seen from Figure 8(b), when the switch SW2 is turned off earlier, the time difference TD increases; when the switch SW2 is turned off later, the time difference TD decreases. In one embodiment, the period determination circuit 44 can obtain / have a predetermined time difference TDpre (before the demodulation signal generator 40 operates). After the energy recovery circuit 42 completes the nth energy recovery operation, the period determination circuit 44 can obtain a time difference TDn corresponding to the nth energy recovery operation. The period determination circuit 44 can compare the time difference TDn with the predetermined time difference TDpre.

[0042] If TDn > TDpre (indicating that the turn-off time toff,2 of the switch SW2 is too early, or equivalently, the conduction time Ton,n is too short), the indication circuit 440 generates an indication signal to indicate that the switch SW2 is turned off too early or the conduction time Ton,n is too short, and the control signal generator 442 will delay the turn-off time toff,2 for the next / subsequent (such as the (n + 1)th or (n + 2)th) energy recovery operation, or equivalently, lengthen the conduction time Ton so that Ton,(n + 1) > Ton,n or Ton,(n + 2) > Ton,n.

[0043] When TD n < TD pre (indicating that the turn-off time t off,2 of switch SW2 is too late, or equivalently, the conduction time T on, n is too long), the indication circuit 440 generates an indication signal to indicate that switch SW2 turns off too late or the conduction time T on, n is too long, and the control signal generator 442 will advance the turn-off time t off,2 for the next / subsequent (such as the (n + 1)-th or (n + 2)-th) energy recovery operation, or equivalently, shorten the conduction time T on so that T on,(n + 1) < T on, n or T on,(n + 2) < T on, n.

[0044] The predetermined time difference TD pre can be obtained through simulation or experiment, and it can be an optimized time difference TD in terms of optimizing power loss or optimizing efficiency. According to experience, the predetermined time difference TD pre can be selected between 15 and 30 nanoseconds.

[0045] FIG. 9 shows a schematic diagram of the period determination circuit 54 during an embodiment of the present application. The period determination circuit 54 can be used to implement the period determination circuit 44. The period determination circuit 54 includes an indication circuit 540 and a control signal generator 542.

[0046] The indication circuit 540 includes a time difference determination circuit 510 and a comparator 512. The time difference determination circuit 510 can receive the inductor voltage V L x and the control signal SW x. Generally, in FIG. 9, the inductor voltage V L x can represent V L1 or V L2, and the control signal SW x can represent SW1 or SW2, where V L x is the node coupled between the inductor L and the switch SW x. According to the inductor voltage V L x and the control signal SW x, the time difference determination circuit 510 can determine the time difference TD or TD n corresponding to the n-th (current / first) energy recovery operation. The comparator 512 can compare the time difference TD / TD n with the predetermined time difference TD pre, and the comparison result of the comparator 512 can be regarded as an indication signal IDS. According to the indication signal IDS, the control signal generator 542 can update the control signal SW x for the next / subsequent (such as the (n + 1)-th or (n + 2)-th) energy recovery operation.

[0047] In short, the present invention can adaptively adjust the energy recovery period (i.e., the conduction period), and can meet capacitive loads with different capacitance values. The above are only the preferred embodiments of the present invention. All equivalent changes and modifications made according to the scope of the patent application of the present invention shall fall within the scope of the present invention.

[0048] 10,42: Energy recovery circuit 20,34,44,54: Period determination circuit L: Inductor SW: Switch C1,C2: Capacitive element V c1,V c2: Voltage V L,V L x,V L1,V L2: Inductor voltage I L: Inductor current 200,340,31,440,540: Indicator circuit 202,342,442,542: Control signal generator SW,SW x,SW1,SW2: Control signal IDS: Indicator signal T on: Conduction period t off,t off,1,t off,2: Turn-off time t rev: Reverse time 310: Surge detection circuit 312,512: Comparator 314: Logic circuit 11: Membrane structure 102: Flap pair 101,103: Flap SM: Modulation drive signal ±SV: Demodulation drive signal 101A,103A: Actuator 40: Demodulation signal generator t on,1,t on,2: Opening time TD: Time difference 510: Time difference determination circuit TD pre: Predetermined time difference

Claims

1. A period determination circuit for determining the conduction period for an energy recovery circuit, the period determination circuit comprising: an indicator circuit coupled to an inductor of the energy recovery circuit to receive an inductor voltage, for generating an indicator signal based on the inductor voltage, wherein, The indication signal reflects a state corresponding to a first conduction period of the energy recovery circuit; and a control signal generator, coupled to a switch of the energy recovery circuit, is used to generate a control signal having a second conduction period for the switch based on the indication signal; wherein the energy recovery circuit is coupled to a first capacitive element and a second capacitive element; wherein the energy recovery circuit includes an inductor and the switch coupled between the first capacitive element and the second capacitive element; wherein the control signal generator determines the second conduction period based on the first conduction period and the indication signal.

2. The period determination circuit as described in claim 1, wherein, The indicator circuit includes a spike detection circuit; wherein the spike detection circuit is coupled to the inductor to receive the inductor voltage.

3. The period determination circuit as described in claim 2, wherein, The indicator circuit generates the indicator signal based on the polarity of a surge detected by the surge detection circuit.

4. The period determination circuit as described in claim 3, wherein, When the surge is positive and at a time corresponding to the surge, the first voltage corresponding to the first capacitive element is greater than the second voltage corresponding to the second capacitive element, the indicator circuit generates the indicator signal so that the control signal generator determines that the second conduction period is longer than the first conduction period.

5. The period determination circuit as described in claim 3, wherein, When the surge is negative and at a time corresponding to the surge, the first voltage corresponding to the first capacitive element is less than the second voltage corresponding to the second capacitive element, the indicator circuit generates the indicator signal so that the control signal generator determines that the second conduction period is longer than the first conduction period.

6. The period determination circuit as described in claim 3, wherein, When the surge is negative and at a time corresponding to the surge, the first voltage corresponding to the first capacitive element is greater than the second voltage corresponding to the second capacitive element, the indicator circuit generates the indicator signal so that the control signal generator determines that the second conduction period is shorter than the first conduction period.

7. The period determination circuit as described in claim 3, wherein, When the surge is positive and at a time corresponding to the surge, the first voltage corresponding to the first capacitive element is less than the second voltage corresponding to the second capacitive element, the indicator circuit generates the indicator signal so that the control signal generator determines that the second conduction period is shorter than the first conduction period.

8. The period determination circuit as described in claim 1, wherein, The indicator circuit is coupled to the first capacitive element and the second capacitive element to receive a first voltage corresponding to the first capacitive element and a second voltage corresponding to the second capacitive element; wherein, the indicator circuit generates the indicator signal based on the inductor voltage, the first voltage and the second voltage.

9. The period determination circuit as described in claim 8, wherein, The indicator circuit compares the first voltage with the second voltage and generates the indicator signal based on a comparison result between the first voltage and the second voltage.

10. The period determination circuit as described in claim 1, wherein, The energy recovery circuit is housed within a drive circuit used to generate a general double sideband with suppressed carrier (DSB-SC) signal.

11. The period determination circuit as described in claim 1, wherein, The energy recovery circuit is located within a drive circuit used to drive an air-pulse generating device.

12. The period determination circuit as described in claim 1, wherein, The energy recovery circuit is located within a drive circuit that drives an air pulse generator to generate an amplitude-modulated ultrasonic air pressure variation with an ultrasonic carrier frequency.

13. The period determination circuit as described in claim 1, wherein, The indicating circuit obtains a time difference based on the inductor voltage and a first control signal having the first conduction period; wherein the indicating circuit compares the time difference with a predetermined time difference; wherein the indicating circuit generates the indicating signal based on a comparison result between the time difference and the predetermined time difference; wherein the time difference is the difference between a fall time of the first control signal and a rise time of the inductor voltage.

14. The period determination circuit as described in claim 13, wherein, When the time difference is greater than the predetermined time difference, the indicator circuit generates the indicator signal, causing the control signal generator to determine that the second conduction period is longer than the first conduction period.

15. The period determination circuit as described in claim 13, wherein, When the time difference is less than the predetermined time difference, the indicator circuit generates the indicator signal, causing the control signal generator to determine that the second conduction period is shorter than the first conduction period.

16. The period determination circuit as described in claim 1, wherein, The energy recovery circuit is located within a drive circuit, which drives a gas pulse generating device to form an opening.

17. The period determination circuit as described in claim 1, wherein the indication circuit includes a comparator.

18. The period determination circuit as described in claim 17, wherein, The comparator receives the first voltage and the second voltage, and uses them to compare the first voltage with the second voltage.

19. The period determination circuit as described in claim 17, wherein, The comparator receives a time difference and a predetermined time difference, and uses it to compare the time difference with the predetermined time difference; wherein the time difference is the difference between a fall time of a first control signal and a rise time of the inductor voltage.

20. The period determination circuit as described in claim 1, wherein, The first capacitive element includes a first actuator disposed on a membrane structure.

21. The period determination circuit as described in claim 1, wherein, The first capacitive element includes a first actuator disposed on a first lobe within a membrane structure; wherein the second capacitive element includes a second actuator disposed on a second lobe within the membrane structure.

22. The period determination circuit as described in claim 1, wherein, The energy recovery circuit includes a first switch coupled between the first capacitive element and the inductor, and a second switch coupled between the second capacitive element and the inductor.

23. A period determination method for determining an on-time for an energy recovery circuit, the period determination method comprising: receiving an inductor voltage corresponding to an inductor of the energy recovery circuit; and generating an indication signal based on the inductor voltage, wherein, The indication signal reflects a state corresponding to a first conduction period of the energy recovery circuit; a second conduction period is determined based on the first conduction period and the indication signal; and a control signal having the second conduction period is generated based on the indication signal for use with a switch of the energy recovery circuit; wherein the energy recovery circuit is coupled to a first capacitive element and a second capacitive element; wherein the energy recovery circuit includes an inductor and a switch coupled between the first capacitive element and the second capacitive element.

24. The period determination method as described in claim 23, wherein the step of generating the indication signal based on the inductor voltage comprises: performing a surge detection operation based on the inductor voltage; and generating the indication signal based on the polarity of a surge detected in the surge detection operation.

25. The period determination method as described in claim 23, wherein the step of generating the indication signal based on the inductor voltage comprises: comparing a first voltage corresponding to the first capacitive element with a second voltage corresponding to the second capacitive element; and generating the indication signal based on a comparison result between the first voltage and the second voltage.

26. The period determination method as described in claim 23, wherein the step of generating the indication signal based on the inductor voltage comprises: obtaining a time difference based on the inductor voltage and a first control signal having the first conduction period; comparing the time difference with a predetermined time difference; and generating the indication signal based on a comparison result between the time difference and the predetermined time difference; wherein, The time difference is the difference between the fall time of the first control signal and the rise time of the inductor voltage.

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