Circuit and method for adjusting conduction period for energy recovery circuit

Abstract

The invention relates to a circuit and a method for adjusting a turn-on period for an energy recovery circuit. A period determination circuit is used for determining a conduction period for an energy recovery circuit, and comprises an indication circuit which is coupled to an inductor of the energy recovery circuit to receive an inductor voltage and is used for generating an indication signal according to the inductor voltage, and the indication signal reflects a state corresponding to a first conduction period of the energy recovery circuit; and the control signal generator is coupled to a switch of the energy recovery circuit and is used for generating a control signal with 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 an inductor and a switch coupled between the first capacitive element and the second capacitive element. The control signal generator determines a second conduction period according to the first conduction period and the indication signal.

Description

Technical Field

[0001] The present application relates to a circuit and a method for determining a conduction period for an energy recovery circuit. Background Art

[0002] Unless otherwise indicated, the practices described below are not prior art within the scope of the present application, and the contents of this paragraph should not be included in the prior art.

[0003] Energy recovery circuits using inductor-capacitor oscillation have been applied to driving circuits for driving capacitive loads, especially in the case where an alternating voltage is required (e.g., 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 another capacitive element, thereby recovering electrical energy to be stored in one of the capacitive elements.

[0004] During the on-time, if the on-time is long enough, the current decreases and eventually reaches zero. If the on-time is too long, a reverse current will be formed due to the oscillation characteristics of the inductor and capacitor.

[0005] The on-time cannot be too short, otherwise there will be residual charge (electric energy) that cannot be fully recovered. On the other hand, the on-time cannot be too long, otherwise it will form an unnecessary reverse current, as mentioned above. Therefore, determining the on-time for energy recovery becomes an important issue.

[0006] Furthermore, in some application scenarios, the size of the capacitor is not constant, making the determination of the on-time more challenging.

[0007] Therefore, how to determine the on-time for the energy recovery circuit is an important goal in the art. Summary of the invention

[0008] Therefore, the main purpose of the present application is to provide a circuit and method for determining the conduction period of an energy recovery circuit.

[0009] One 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 used 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 used to generate a control signal with 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. 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. BRIEF DESCRIPTION OF THE DRAWINGS

[0011] Figure 1 It is a schematic diagram of a period determination circuit coupled to an energy recovery circuit according to an embodiment of the present application.

[0012] Figure 2 The diagram shows an inductor current and an inductor voltage related to the voltage and the control signal when the on-time is too short.

[0013] Figure 3 The inductor current and inductor voltage are shown when the on-time is too long.

[0014] Figure 4 A period determination circuit is shown coupled to an energy recovery circuit according to an embodiment of the present application.

[0015] Figure 5 This is a schematic diagram of an indicator circuit according to an embodiment of the present application.

[0016] Figure 6 A schematic diagram of a capacitive element according to an embodiment of the present application is shown.

[0017] Figure 7 A period determination circuit is shown coupled to an energy recovery circuit according to an embodiment of the present application.

[0018] Figure 8 The waveforms of voltage, control signal, inductor current and inductor voltage are shown.

[0019] Fig. 9 A schematic diagram of a period determination circuit according to an embodiment of the present application is shown.

[0020] The reference numerals are described as follows:

[0021] 10,42: Energy recovery circuit

[0022] 20,34,44,54: Period determination circuit

[0023] L: Inductance

[0024] SW: switch

[0025] C1, C2: Capacitive components

[0026] V c1 ,V c2 :Voltage

[0027] V L ,V Lx ,V L1 ,V L2 : Inductor voltage

[0028] I L : Inductor current

[0029] 200,340,31,440,540: Indicator circuit

[0030] 202,342,442,542: Control signal generator

[0031] SW, SWx, SW1, SW2: control signals

[0032] IDS: Indicator Signal

[0033] T on : On-time

[0034] t off ,t off,1 ,t off,2 : Closing time

[0035] t rev : Reverse time

[0036] 310: Surge detection circuit

[0037] 312,512: Comparator

[0038] 314: Logic Circuits

[0039] 11: Membrane structure

[0040] 102: Petal pair

[0041] 101,103: Petals

[0042] SM: Modulated drive signal

[0043] ±SV: Demodulated driving signal

[0044] 101A,103A: Actuator

[0045] 40: Demodulation signal generator

[0046] t on,1 ,t on,2 : Opening time

[0047] TD: Time difference

[0048] 510: Time difference determination circuit TD pre : Scheduled time difference DETAILED DESCRIPTION

[0049] Figure 1 Schematic diagram of a period determination circuit 20 coupled to an energy recovery circuit 10 according to an embodiment of the present application. The energy recovery circuit 10 basically includes an inductor L and a switch SW, coupled between a first capacitive element C1 and a second capacitive element C2. The capacitive element can be a capacitor or an element with a certain capacitance value, and C1 / C2 can also represent its capacitance value.

[0050] The period determination circuit 20 is used to generate a control signal (also indicated 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 T for the switch SW or the energy recovery circuit 10 through the control signal SW. on .

[0051] In this application, switches and their control signals share the same symbols. In addition, nodes (in the circuit) and their voltages also share the same symbols.

[0052] Once the switch SW is turned on, the energy recovery circuit 10 can start the LC oscillation. Assuming that the first capacitive element C1 corresponds to a (first) voltage V c1 is greater than a (second) voltage V corresponding to the second capacitive element C2 c2 When (V c1 >V c2), at the first time (i.e. the initial moment when the switch SW is turned on), an inductor current I is formed from C1 to C2 L When the switch SW remains on, the inductor current I L The magnitude of the inductor current I L The direction of current turns to the reverse.

[0053] The purpose of the period determination circuit 20 is to determine or adaptively adjust the on period T on , so that it is optimized as much as possible. In one embodiment, the optimal conduction period T on It should be the longest period before the inductor current reverses. If the on-time is too short, it means that there is still residual charge in C1 at the end of the on-time. If the on-time is too long, it means that the switch SW is turned off after the inductor current reverses.

[0054] 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 V L The control signal generator 202 may be used to generate a control signal SW output to the switch SW.

[0055] The indicating circuit 200 can be configured to detect the inductor voltage V L To generate an indication signal IDS, wherein the indication signal IDS can reflect the current (first) conduction period (in terms of T on,n represents a state corresponding to the state, where T on,n represents the conduction period corresponding to the nth energy recovery operation. In one embodiment, the indication signal IDS may indicate the current conduction period T on,n Too short or too long.

[0056] The control signal generator 202 can generate a next / subsequent (second) conduction period (T on,n+1 ) for the switch SW, where T on,n+1 represents the on-period corresponding to the (n+1)th energy recovery operation, which is located after the nth energy recovery operation.

[0057] In one embodiment, when the indication signal IDS indicates the current conduction period T on,n If the on-time is too short, the control signal generator 202 may adjust the on-time, or more specifically, lengthen the on-time so that T on,n+1 >T on,n , and produces a longer conduction period T on,n+1 (i.e. T on,n+1 >T on,n) of the control signal SW. On the other hand, when the indication signal IDS indicates the current conduction period T on,n If the on-time is too long, the control signal generator 202 may adjust the on-time, or more specifically, shorten the on-time so that T on,n+1 <T on,n , and produces a conduction period with a shortened T on,n+1 (i.e. T on,n+1 <T on,n )’s control signal SW.

[0058] Figure 2 The conduction period T on Too short and voltage V c1 、V c2 and an inductor current I related to the control signal SW L and the inductor voltage V L .exist Figure 2 Inductor current I L Flow from C1 to C2 is considered positive. Figure 2 In (a), during the conduction period T on At the beginning, V c2 >V c1 , the inductor current flows from C2 to C1 and I L Assuming that the switch is coupled between the inductor L and the first capacitive element C1, if the conduction period T on If the switch SW is too short, the closing time ( Figure 2 China off denoted by V), some residual inductor current flows from C2 to L It should be noted that the node V L There is some parasitic capacitance, which is much smaller than C1, so the inductor current is off The node or inductor voltage V L Generates high / positive voltage spikes, such as Figure 2 As shown in (a).

[0059] Similarly, in Figure 2 In (b), during the conduction period T on At the beginning, V c2 <V c1 , the inductor current flows from C1 to C2 and I L Is a positive value. If the conduction period T on If the switch SW is turned off during the off time t off The positive residual inductor current will affect V L Generates low / negative voltage surges, such as Figure 2 as shown in (b).

[0060] on the other hand, Figure 3 Draw the conduction period T on The inductor current I L and the inductor voltage V L , that is, t off >t rev , where t off Represents the closing time of the switch, t rev Represents the reversal time of the inductor current (i.e., the time it takes for the inductor current to return to zero). Figure 3 (a) shows V c2 >V c1 In the case of conduction period T on At the beginning, the inductor current I L Flow from C2 to C1 (i.e. negative value); Figure 3 (b) shows V c1 >V c2 In the case of conduction period T on At the beginning, the inductor current I L Flows from C1 to C2 (i.e. positive value).

[0061] like Figure 3 As shown in (a), the positive reverse inductor current I L will be at time t off Upper inductor voltage V L Generates a negative surge. Figure 3 As shown in (b), the negative reverse inductor current I L will be at time t off Upper inductor voltage V L Produces a positive surge.

[0062] Depend on Figure 2 and Figure 3 It can be concluded that the conduction period T on If it is too short or too long, the voltage V c1 、V c2 and V L behavior to make inferences.

[0063] Figure 4 The embodiment of the present application shows that a period determination circuit 34 is coupled to an energy recovery circuit 10 (which is a part of a modulation signal generator 30, as 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 T for the energy recovery circuit. on , and coupled to the capacitive elements C1, C2 and the inductor L to receive the voltage V corresponding to C1 c1 , corresponding to the voltage V of C2 c2 , and the inductor voltage V L .

[0064] Furthermore, 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 surge is positive and at time t off V c1 >V c2 When the surge is negative and at time t off V c1 <V c2 When the current (first) conduction period T on,n On the other hand, the indication circuit 340 can generate an indication signal IDS to indicate that the surge is negative and at time t off V c1 >V c2 When the surge is positive and at time t off V c1 <V c2 When the current (first) conduction period T on,n Too long. Please note that the closing time of the switch is t off Corresponds to the surge time, or to the time when the surge reaches its peak.

[0065] Similar to 202, when the indication signal IDS received by the control signal generator 342 indicates the current conduction period T on,n If the on-time is too short, the control signal generator 342 may generate a signal with a longer on-time T on,n+1 (i.e. T on,n+1 >T on,n ) of the control signal SW; and when the control signal generator 342 receives the indication signal IDS indicating the current conduction period T on,n When the on-time T is too long, the control signal generator 342 may generate a signal with a shortened on-time T on,n+1 (i.e. T on,n+1 <T on,n )’s control signal SW.

[0066] Figure 5 3 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 can 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 V c1 and V c2 The logic circuit 314 may generate an indication signal IDS according to the detection result generated by the surge detection circuit 310 and the comparison result generated by the comparator 312 .

[0067] based on Figure 2 and Figure 3The period determination circuit 34 is suitable for an energy recovery circuit disposed in a driving circuit to drive an air pulse generating device (Air-Pulse Generating Device, APG Device) to generate an amplitude modulated ultrasonic air pressure variation (Amplitude-Modulated Ultrasonic AirPressure Variation) having an ultrasonic carrier frequency (see U.S. Patent No. 12,075,213). In other words, the period determination circuit 34 can be coupled to / applied to an energy recovery circuit disposed in a modulation signal generator disclosed in U.S. Patent Application No. 18 / 396,678, or an energy recovery circuit in a driving circuit disclosed in U.S. Patent No. 12,107,546, which is used to generate a modulated driving signal SM or a general double sideband with suppressed carrier (DSB-SC) signal.

[0068] More specifically, Figure 6 A schematic diagram of a capacitive element C1 or a gas pulse generating device according to an embodiment of the present application is shown. The capacitive element C1 or the gas pulse generating device may include a membrane structure 11, the membrane structure 11 includes a petal pair 102, and the petal pair 102 includes petals 101 and 103. Figure 6 In the embodiment, the petal pair 102 can be driven by a modulated drive signal SM to perform common-mode motion, and driven by a demodulated drive signal ±SV to perform differential-mode motion, thereby realizing a combination of modulation and demodulation or on-site modulation and demodulation, that is, modulation and demodulation can be performed on the same part / position of the membrane structure.

[0069] Furthermore, the capacitive element C1 or the gas pulse generating device may include an actuator 101A disposed on the petal 101 and an actuator 103A disposed on the petal 103. Each actuator 101A and 103A may include a piezoelectric material, such as PZT (e.g., Lead Zirconate Titanate), which is disposed between an upper electrode and a lower electrode.

[0070] The detailed operation principle of the gas pulse generating device can be found in the description of US Pat. No. 12,075,213, which is omitted for simplicity. In short, the period determination circuit 34 can be coupled to a driving circuit for generating a modulated driving signal SM.

[0071] 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 US patent application 18 / 396,678, which is used to generate the demodulation driving signal ±SV.

[0072] For example, Figure 7 The embodiment of the present application shows a period determination circuit 44 coupled to an energy recovery circuit 42 (which is a part of a demodulation signal generator 40). The period determination circuit 44 includes an indication circuit 440 and a control signal generator 442. Generally speaking, the indication circuit 440 can receive an inductor voltage V Lx and a control signal SWx, and generates the indication signal IDS accordingly. The control signal generator 442 can generate a control signal for the switch SWx, x=1 or 2. Similarly, the connection between the energy recovery circuit 42 and the period determination circuit 44 is omitted for simplicity.

[0073] The demodulation signal generator 40 (energy recovery circuit 42) can be used to generate the demodulation driving signal ±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 switches SW1 and SW2 in the energy recovery circuit 42.

[0074] exist Figure 7 In the embodiment, the first capacitive element C1 coupled to the energy recovery circuit 42 may be an actuator 101A disposed on the petal 101 , and the second capacitive element C2 coupled to the energy recovery circuit 42 may be an actuator 103A disposed on the petal 103 .

[0075] Figure 8 Display voltage V c1 and V c2 , control signals SW1 and SW2, inductor current I L , and the inductor voltage V L1 and V L2 waveform. Figure 8 The waveform shown can be obtained through simulation or experiment. More specifically, Figure 8 (a) shows the waveforms of the control signals SW1 and SW2, which have a plurality of different closing times t off,2 , Figure 8 (b) shows the closing time t off,2 The inductor voltage V responds to the control signal SW2 L2 waveform.

[0076] It is worth noting that, in one embodiment, during the conduction period, a voltage V cx When V is lower than the other, the switch SWx is turned off to terminate. For example, at the end of the n-1th energy recovery operation, the switch SW1 is turned off due to V c1 <V c2At the end of the nth energy recovery operation, the switch SW2 is turned off due to V c2 <V c1 Therefore, the on-time T of the n-1th energy recovery operation is on Can be obtained by off,1 -t on,2 The conduction time T of the nth energy recovery operation is determined by on Can be obtained by off,2 -t on,1 Decision. Note that t on / off,x Indicates the on / off time of the switch SWx.

[0077] It is worth noting that the on-time T on By delaying the closing time t off,x To lengthen, or by closing the time t in advance off,x To shorten (assuming the opening time t on,x unchanged situation).

[0078] The falling time / falling edge (falling edge) of the control signal SW2 and the inductor voltage V L2 There is a time difference between the rise times of Figure 8 As can be seen from (b), when the switch SW2 is closed earlier, the time difference TD increases; and when the switch SW2 is closed later, the time difference TD decreases. In one embodiment, the period determination circuit 44 can obtain / have a pre-stored predetermined time difference TD pre (before the demodulation signal generator 40 operates) After the energy recovery circuit 42 completes the n-th energy recovery operation, the period determination circuit 44 can obtain a time difference TD corresponding to the n-th energy recovery operation. n The period determination circuit 44 can compare the time difference TD n Time difference TD pre .

[0079] If TD n >TD pre t (indicates the closing time of switch SW2 off,2 Too early, or equivalent to the conduction time T on,n The indication circuit 440 generates an indication signal to indicate that the switch SW2 is closed or turned on too early. on,n is too short, and the control signal generator 442 will delay the closing time t for the next / subsequent (such as the n+1th or n+2th) energy recovery operation. off,2 , or equivalently increase the on-time T on To make T on,(n+1) >T on,n or T on,(n+2) >T on,n.

[0080] If TD n <TD pre t (indicates the closing time of switch SW2 off,2 Too late, or equivalent to the conduction time T on,n The indication circuit 440 generates an indication signal to indicate that the switch SW2 is closed or turned on too late. on,n is too long, and the control signal generator 442 will advance the closing time t for the next / subsequent (such as the n+1th or n+2th) energy recovery operation. off,2 , or equivalently shorten the on-time T on To make T on,(n+1) <T on,n or T on,(n+2) <T on,n .

[0081] Scheduled time difference TD pre It can be obtained through simulation or experiment, which can be an optimized time difference TD in terms of optimized power loss or optimized efficiency. According to experience, the predetermined time difference TD pre The range is 15 to 30 nanoseconds.

[0082] Fig. 9 The schematic diagram of a period determination circuit 54 according to an embodiment of the present application is shown. 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.

[0083] The indicating circuit 540 includes a time difference determining circuit 510 and a comparator 512. The time difference determining circuit 510 can receive the inductor voltage V Lx and control signal SWx. Generally speaking, Fig. 9 Inductor voltage V Lx Can represent V L1 or V L2 , and the control signal SWx can represent SW1 or SW2, where V Lx is a node coupled between the inductor L and the switch SWx. Lx and the control signal SWx, the time difference determination circuit 510 can determine the time difference TD or TD corresponding to the nth (current / first) energy recovery operation. n The comparator 512 can compare the time difference TD / TD n Time difference TD preThe 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 SWx for the next / subsequent (eg, the n+1th or n+2th) energy recovery operation.

[0084] In short, the present invention can adaptively adjust the energy recovery period (ie, the conduction period) to meet the needs of capacitive loads with different capacitance values.

[0085] The above descriptions are only preferred embodiments of the present invention. All equivalent changes and modifications made according to the claims of the present invention should fall within the scope of the present invention.

Claims

1. A period determination circuit for determining a conduction period for an energy recovery circuit, the period determination circuit comprising: An indication circuit is coupled to an inductor of the energy recovery circuit to receive an inductor voltage and is used 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; as well as a control signal generator coupled to a switch of the energy recovery circuit, for generating a control signal having a second conduction period for the switch according to the indication signal; Wherein, 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.

2. The period determination circuit according to claim 1, in, The indicating circuit includes a surge detection circuit; The surge detection circuit is coupled to the inductor to receive the inductor voltage.

3. The period determination circuit according to claim 2, in, The indication circuit generates the indication signal according to the polarity of a surge detected by the surge detection circuit.

4. The period determination circuit according to claim 3, in, When the surge is positive and a first voltage corresponding to the first capacitive element is greater than a second voltage corresponding to the second capacitive element at a time corresponding to the surge, the indication circuit generates the indication 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 according to claim 3, in, When the surge is negative and a first voltage corresponding to the first capacitive element is less than a second voltage corresponding to the second capacitive element at a time corresponding to the surge, the indication circuit generates the indication 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 according to claim 3, in, When the surge is negative and a first voltage corresponding to the first capacitive element is greater than a second voltage corresponding to the second capacitive element at a time corresponding to the surge, the indication circuit generates the indication 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 according to claim 3, in, When the surge is positive and a first voltage corresponding to the first capacitive element is less than a second voltage corresponding to the second capacitive element at a time corresponding to the surge, the indication circuit generates the indication 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 according to claim 1, in, The indicating 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; The indication circuit generates the indication signal according to the inductor voltage, the first voltage and the second voltage.

9. The period determination circuit according to claim 8, in, The indication circuit compares the first voltage with the second voltage and generates the indication signal according to a comparison result between the first voltage and the second voltage.

10. The period determination circuit according to claim 1, in, The energy recovery circuit is arranged in a driving circuit for generating a general double-sideband suppressed carrier signal.

11. The period determination circuit according to claim 1, in, The energy recovery circuit is arranged in a driving circuit for driving a gas pulse generating device.

12. The period determination circuit according to claim 1, in, The energy recovery circuit is arranged in a driving circuit, and the driving circuit is used to drive a gas pulse generating device to generate an amplitude modulated ultrasonic gas pressure change with an ultrasonic carrier frequency.

13. The period determination circuit according to claim 1, in, The indicating circuit obtains a time difference according to 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; The indication circuit generates the indication signal according to a comparison result between the time difference and the predetermined time difference.

14. The period determination circuit according to claim 13, in, When the time difference is greater than the predetermined time difference, the indication circuit generates the indication signal so that the control signal generator determines that the second conduction period is longer than the first conduction period.

15. The period determination circuit according to claim 13, in, When the time difference is less than the predetermined time difference, the indication circuit generates the indication signal so that the control signal generator determines that the second conduction period is shorter than the first conduction period.

16. The period determination circuit according to claim 1, in, The energy recovery circuit is arranged in a driving circuit, and the driving circuit is used to drive a gas pulse generating device to form an opening.

17. The period determination circuit as claimed in claim 1, wherein the indicating circuit comprises a comparator.

18. The period determination circuit according to claim 17, in, The comparator receives a first voltage and a second voltage and is used for comparing the first voltage with the second voltage.

19. The period determination circuit according to claim 17, in, The comparator receives a time difference and a predetermined time difference, and is used to compare the time difference with the predetermined time difference.

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

21. The period determination circuit according to claim 1, in, The first capacitive element includes a first actuator disposed on a first petal in a membrane structure; The second capacitive element includes a second actuator disposed on a second flap in the membrane structure.

22. The period determination circuit according to claim 1, in, 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 a conduction period for an energy recovery circuit, the period determination method comprising: receiving an inductor voltage corresponding to an inductor of the energy recovery circuit; An indication signal is generated 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 According to the indication signal, a control signal having the second conduction period is generated 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; The energy recovery circuit includes the inductor and the switch coupled between the first capacitive element and the second capacitive element.

24. The period determination method as claimed in claim 23, wherein the step of generating the indication signal according to the inductor voltage comprises: performing a surge detection operation according to the inductor voltage; and The indication signal is generated according to the polarity of a surge detected in the surge detection operation.

25. The period determination method as claimed in claim 23, wherein the step of generating the indication signal according to 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 The indication signal is generated according to a comparison result between the first voltage and the second voltage.

26. The period determination method as claimed in claim 23, wherein the step of generating the indication signal according to the inductor voltage comprises: Obtaining a time difference according to the inductor voltage and a first control signal having the first conduction period; comparing the time difference with a predetermined time difference; and The indication signal is generated according to a comparison result between the time difference and the predetermined time difference.

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