JP2005168163A - Zero crossing signal generation device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To output a zero crossing signal that is stable even if a conventional zero crossing signal erroneously detects zero crossing due to the warp of a waveform of a commercial AC power supply voltage, a noise component and the like. <P>SOLUTION: A first pulse signal is generated by comparing a first reference voltage and a commercial AC voltage. A second pulse signal is generated by comparing a second reference voltage larger than the first reference voltage and the commercial AC voltage. It is determined from the first pulse signal and the second pulse signal whether the commercial AC power supply voltage has less warpage and is properly zero-crossed or not, and the cycle of commercial AC power is detected. A third pulse signal having the detected cycle is generated, and a synchronous zero crossing signal is generated by synchronizing the first pulse signal and the third pulse signal. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a zero-cross signal generator for detecting a zero-cross point of a commercial AC power source and generating a zero-cross signal.

  Phase control is often used for devices that use a commercial AC power supply as input and control the conduction time, such as heater power control and lamp light intensity control (see Patent Document 1, for example).

  In this case, it is common to use a switch element of a thyristor, a triac, or a solid state relay, and determine the on-timing of the switch element based on the zero cross point of the commercial AC power supply.

  FIG. 12 shows a general phase control technique.

  12A shows a commercial AC voltage waveform, and V1 in FIG. 12 is a reference voltage. The reference voltage V1 is set in the vicinity of 0V. The reference voltage V1 is compared with the commercial AC voltage, and a signal that becomes Hi only during a period when the absolute value of the commercial AC voltage is lower than the reference voltage V1 is (b) a zero cross signal. . Then, (e) a drive signal is generated with reference to the rise of (b) the zero cross signal.

  FIG. 13 shows a method for generating (e) drive signals.

  In FIG. 13, (i) indicates the timer output (count value). The timer (b) starts to operate at the rising edge of the zero cross signal and is reset at the next rising edge.

(K) is a control value. The control value is a value that determines the conduction time of the phase angle control by feedback control of the device. (i) The timer output and the (k) control value are compared, and when the (i) timer output reaches the (k) control value, (e) the drive signal becomes Hi and the switch means is turned on. As a result, a current as shown in FIG. 12 (f) flows through the load. When the conduction time is extended by controlling the device, the (k) control value decreases, and conversely, when the conduction time is shortened, the (k) control value increases. In any case, (b) the rising timing of the zero-cross signal is a reference, and control is performed as to how much time is delayed from this timing to turn on the switch means.
Japanese Patent Laid-Open No. 10-115997

  However, since the ON timing of the switch means is determined based on (b) the rising timing of the zero cross signal, if the AC voltage waveform is distorted or the noise component increases, the rising timing of the zero cross signal is advanced or delayed, There is a problem that the phase control becomes unstable when the zero cross signal is converted into a plurality of pulses at one zero cross, or when the zero cross signal is output at a timing completely unrelated to the zero cross.

  FIG. 14 shows an example of an AC voltage waveform including a noise component. When an AC voltage waveform as shown in FIG. 14A is generated with the same configuration as in FIG. 12, an extra pulse is output separately from the original zero cross point as shown in FIG. 14B. End up. When a drive signal is to be generated based on this FIG. 14 (b) zero cross signal, (i) the timer output is reset by a significant pulse before reaching the control value (k) as shown in FIG. k) It is reset by the next true zero cross signal before reaching the control value.As a result, during the period when such a noise component is included, (e) no drive signal is generated, and no current flows in the load. The phenomenon of not flowing will occur.

  The present invention has been made for the purpose of solving the above-described problems, and solves the above-described problems, and generates a zero-cross signal that outputs a stable zero-cross signal even when the commercial AC power supply voltage is distorted or contains a noise component. Another object of the present invention is to provide a zero cross signal generator.

  For example, the following configuration is provided as one means for achieving the object.

  The first comparison for generating a first pulse signal by comparing a first reference voltage and a commercial AC voltage in a zero cross signal generator for detecting a zero cross point of a commercial AC power source and outputting a zero cross signal. Means for comparing a second reference voltage larger than the first reference voltage with a commercial AC voltage and generating a second pulse signal; and a commercial based on the first pulse signal and the second pulse signal in the previous period Determine whether the AC power supply voltage has little distortion and is properly zero-crossed, detects the period (frequency) of the commercial AC power supply during the period of zero-crossing properly, and the commercial AC power supply detected by the period detection means Pulse signal generating means for generating a third pulse signal having the same period as the period, and so that a phase difference between the first pulse signal and the third pulse signal is a predetermined value or less. It has a synchronization means for adjusting the phase of the three-pulse signal and a synchronization zero-cross signal generation means for generating a synchronization zero-cross signal based on the phase-adjusted third pulse signal, and outputs the synchronization zero-cross signal as a zero-cross signal. And

  According to a second aspect of the present invention, the second comparison means has a time constant and is configured not to respond to short-term fluctuations in the commercial AC power supply voltage.

  In claim 3, the synchronization means performs a synchronization operation at a predetermined timing, and when the phase difference between the first pulse signal and the third pulse signal is a predetermined value or less over a predetermined number of pulses, It is characterized by determining that synchronization is complete.

  5. The method according to claim 4, further comprising a counting means for counting the synchronous zero-cross signal. When the count value reaches a predetermined value, the frequency detection operation and the synchronous operation are performed again to update the synchronous zero-cross signal. It is characterized by things.

  According to a fifth aspect of the present invention, when an update signal is input from the outside, the frequency detection operation and the synchronization operation are performed again to update the synchronization zero-cross signal.

  According to a sixth aspect of the present invention, there is provided an output signal selection means, wherein the frequency detection means monitors the false detection frequency of the first pulse signal, and if the false detection occurrence frequency is lower than a predetermined value, the first pulse is detected. When the zero-cross signal is selected and the false detection frequency is higher than a predetermined value, the synchronous zero-cross signal is selected as the zero-cross signal, and the selected signal is output as the zero-cross signal.

  In Claim 7, it has an output signal selection means, and has masked except near the zero cross point which the synchronous zero cross signal shows, and near the zero cross point which the synchronous zero cross signal shows, the first pulse signal and One of the synchronous zero-cross signals, which outputs the zero-cross signal first, is selected and output as the zero-cross signal.

  As described above, according to the present invention, the period of the commercial AC power supply voltage is detected in a situation where the commercial AC power supply voltage has little distortion and noise, and a pulse signal based on the detected period is generated. Further, this pulse signal is synchronized with the zero cross signal generated by comparing the commercial AC voltage and the reference voltage of the conventional method, thereby generating a synchronized zero cross signal. By outputting this synchronous zero-cross signal as the output of this zero-cross signal generator, a stable zero-cross signal can be obtained even when there is a false detection of the zero-cross signal in the conventional method due to distortion or noise of the commercial AC power supply. This makes it possible to realize a zero-cross signal generator capable of providing a signal.

  In addition, by selecting and outputting the conventional zero-cross signal and the synchronized zero-cross signal generated in this zero-cross signal generator, even if the true zero-cross point is not always constant due to frequency fluctuations of commercial AC power, it is real-time It is possible to provide a responsive and stable zero cross signal.

  In addition, by switching between the zero cross signal of the conventional method and the synchronous zero cross signal generated in this zero cross signal generator according to the erroneous detection situation of the zero cross signal by the conventional method, the true stability of the frequency of the commercial AC power supply is increased. Even if the zero cross point is not always constant and changes, the commercial AC power supply voltage can respond in real time to the above frequency fluctuations during periods when the commercial AC power supply voltage is low in distortion and noise components. It is possible to provide a stable zero-cross signal for many periods.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

  In the following description, the same or corresponding members as those in FIGS. 12, 13, 14, and 15 of the above-described conventional example are denoted by the same reference numerals, and the description thereof is omitted.

  1 to 8 are views showing a first embodiment of the present invention.

  1-8, the same code | symbol is attached | subjected to the same or equivalent member as FIGS. 12-15 of the above-mentioned prior art example, and the description shall be abbreviate | omitted.

  FIG. 1 is a block diagram showing the configuration of a zero cross signal generator of the present invention.

  In FIG. 1, reference numeral 1 denotes a commercial AC power supply, and a load 3 is connected to both ends of the AC power supply via switch means 2. Reference numeral 1 A zero-cross signal generator 1 (4) and a zero-cross signal generator 2 (5) are connected to both ends of the commercial AC power supply Vac, and a pulse signal is generated by comparing different reference potentials with AC power supply voltages. Output. Each output is input to the frequency detection unit 6, and the output of the zero cross signal generation unit 1 (4) is also output to the synchronization unit 8.

  The zero cross signal generator 2 (5) has a time constant and is configured not to respond to short-term fluctuations in the commercial AC power supply voltage.

  Based on the pulse signals from the zero cross signal generation unit 1 (4) and the zero cross signal generation unit 2 (5), the frequency detection unit 6 has a period during which the zero cross operation is properly performed with little distortion and noise in the commercial AC power supply voltage. In this period, the period of the commercial AC power supply is detected, and the period information is output to the pulse signal generation unit 7 and the synchronous zero cross signal generation unit 9. The pulse signal generation unit 7 generates a pulse signal of that cycle based on the input cycle information and outputs it to the synchronization unit 8. The synchronizer 8 synchronizes the pulse signal from the pulse signal generator 7 with the zero cross signal based on the commercial AC voltage waveform generated by the zero cross signal generator 1 (4). The signal phase is adjusted. When the phase difference between the two falls within a predetermined value, the synchronization timing signal is used as the synchronization zero-cross signal generator 9.

  The synchronous zero cross signal generator 9 generates a synchronous zero cross signal based on the synchronous timing signal and outputs it as a zero cross signal. The phase control device of FIG. 1 uses the synchronization zero-cross signal output from the synchronization zero-cross signal generator 9 as a zero-cross signal, and determines the on-timing of the switch means based on the rise of this signal to perform phase control.

  The operation of each part will be described with reference to FIGS.

  In FIG. 2, the zero-cross signal generator 1 (4) and the zero-cross signal generator 2 (5) will be described. The zero cross signal generator 1 (4) generates the same signal as a signal conventionally called a zero cross signal. As shown in FIG. 2, the reference potential V1 near 0 V of the commercial AC power supply (a) Vac is compared with the commercial AC power supply (a) Vac, and as a result, only the period when the absolute value of the commercial AC voltage Vac is lower than the reference voltage V1. This signal becomes Hi, and the zero cross signal 1 in FIG. 2B is generated.

  On the other hand, the zero cross signal generator 2 (5) compares the reference potential 2 sufficiently larger than the reference potential V1 with the commercial AC power source (a) Vac. As a result, the commercial AC voltage as shown in FIG. A signal that becomes Hi is output only during a period when the absolute value of Vac is lower than the reference voltage V2. The reference voltage V2 is set so that the commercial AC power supply voltage is rated at (c) zero-cross signal 2 with a duty of about 50% and has a time constant, and the commercial AC power supply voltage due to noise or the like has a short period. It is configured not to respond to fluctuations.

  3 and 4 are diagrams for explaining the operation of the frequency detector 6.

  As shown in FIG. 2, the frequency detector 6 distorts the state in which only one pulse of the zero cross signal 1 is output in FIG. 2 (c) when the zero cross signal 2 is Hi into the commercial AC power supply voltage. And the noise is determined to be a period in which the zero cross operation is properly performed, and the noise component is included in the commercial AC power supply voltage as shown in FIG. 3 (a) Vac. As a result, (b) zero cross signal 1 As shown in FIG. 3 (c), when the zero-cross signal 2 is output during the period when the zero-cross signal 2 is Hi, the zero-cross operation is performed properly. Judge that it is not.

  Then, as shown in FIG. 4 during the period in which the zero-cross operation is properly performed, that is, the period when the commercial AC power supply voltage waveform is beautiful, the predetermined number of pulses (n) of the zero-cross signal 1 (n) and its cycle are measured. The period T (frequency f) of the commercial AC power supply is calculated from the average value.

  Of course, FIG. 4B may measure the period during which the zero-cross signal 1 is counted for a predetermined number of pulses (n), and calculate the cycle T (frequency f) of the commercial AC power supply from the measurement result.

  And the frequency detection part 6 outputs the calculated period information of the commercial AC power supply.

  FIG. 5 is a diagram illustrating the operation of the synchronization unit 8.

  The pulse signal generation unit 7 generates period information from the frequency detection unit 6, that is, a pulse signal having the same frequency as that of the commercial AC power supply, and inputs the pulse signal to the synchronization unit 8. The synchronization unit 8 also receives the zero-cross signal 1 based on the commercial AC voltage waveform generated by the zero-cross signal generation unit 1 (4), and the pulse signal from the pulse signal generation unit 7 is synchronized with the zero-cross signal 1. Thus, the phase of the pulse signal from the pulse signal generator 7 is adjusted. At this time, since the zero-cross signal 1 may change the pulse width or include an erroneous zero-cross pulse, after the phase adjustment, the phase shown in FIG. When the phase difference Δt between the adjusted pulse signal and FIG. 5 (c) zero-cross signal 1 falls below a predetermined value, it is determined that the synchronization is completed, and (d) a phase-adjusted pulse signal is output together with the synchronization completion signal. . Then, the synchronous zero cross signal generation unit 9 generates and outputs a pulse signal having a period based on the period information from the frequency detection unit 6 using the phase-adjusted pulse signal as a trigger, and this signal becomes a synchronous zero cross signal.

  The synchronization zero cross signal generation unit 9 continues to output pulse signals with the same period and the same phase until the next synchronization completion signal is input. Therefore, once the synchronization is completed, a stable synchronized zero-cross signal can always be output even when the commercial AC voltage is distorted or an accurate zero-cross signal is not generated by a conventional method due to noise components or the like.

  In FIG. 1, reference numeral 10 denotes a control unit of a device incorporating the present zero-cross signal generator. The control unit 10 operates a timer based on the synchronous zero-cross signal, and based on the input control signal, the method described in FIG. The drive signal is generated by The drive signal is supplied to the switch means 2 to control the conduction time of the commercial AC power supplied to the load 3.

  As a result, even if the commercial AC voltage is distorted as shown in FIG. 6 (a) Vac or includes a noise component, an accurate zero cross signal cannot be generated by the conventional method as shown in FIG. 6 (b) zero cross signal 1. FIG. 6D shows that the drive signal is generated based on the synchronous zero-cross signal (e), so that a stable load (f) is supplied to the load. As a result, stable phase control can be performed. Become.

  Further, as described above, the zero-cross signal generation unit 2 (5) has a time constant and is configured not to respond to short-term fluctuations in the commercial AC power supply voltage.

  Therefore, as in (a) Vac in FIG. 7, even if (a) Vac changes for a short time across the reference potential V2, the output of the zero-cross signal generation unit 2 (5) is the same as that in FIG. However, the pulse is as shown in FIG. As a result, (b) even though the zero-cross signal 1 is not erroneously detected, the frequency detector 6 has a lot of distortion in the commercial AC power supply voltage waveform, and a proper zero-cross operation is not performed. Therefore, (b) it is prevented that the zero cross signal 1 is detected as being erroneously detected.

  Furthermore, the frequency of the commercial AC power supply is not always constant and may vary.

  Therefore, as shown in FIG. 8, when the power supply of the device incorporating the zero cross signal generator is turned on, the series of operations described above (the period of the commercial AC power supply is detected => the pulse signal based on the detected period is used. Generation => synchronize the pulse signal with the zero cross signal 1 obtained from the AC power supply voltage waveform => synchronous zero cross signal output), and after the synchronous zero cross signal is output, count the number of pulses of this synchronous zero cross signal, When the count reaches a predetermined value, an update signal is output, the above operation is performed again, and the frequency and phase of the synchronous zero cross signal are updated.

  At that time, even if the update signal is output, the synchronization unit of FIG. 8 completes the synchronization operation, and the synchronization zero cross signal generation unit 9 continues to output the pulse signal of the current frequency and phase until the synchronization completion signal is output. Then, at the timing when the synchronization completion signal is output, the frequency and phase of the synchronization zero cross signal are updated.

  As a result, a stable synchronous zero-cross signal can be output, and a device incorporating this zero-cross signal generator can perform more stable phase control.

  The update signal may be input from the outside, and can be updated at an arbitrary timing in accordance with the state of the device in which the zero cross signal generator is built.

  9 and 10 are diagrams showing a second embodiment of the present invention.

  9 and 10, the same or corresponding members as those in FIGS. 1 to 8 of the first embodiment and FIGS. 12 to 15 of the conventional example are denoted by the same reference numerals, and the description thereof will be omitted.

  The zero-cross signal generator of FIG. 1 described in the first embodiment always outputs a pulse signal generated inside the zero-cross signal generator as a zero-cross signal. However, in the present embodiment, a commercial AC voltage and a reference voltage are output by a conventional method. This is a mode in which the zero cross signal generated by the comparison and the synchronous zero cross signal generated inside the zero cross signal generator are selectively output, and the zero cross signal is output.

  FIG. 9 is a block diagram showing the configuration of the present embodiment.

  The output of the synchronous zero cross signal generator 9 is input to the selector 11. The selection unit 11 also receives the zero cross signal 1 generated by comparing the commercial AC voltage generated by the zero cross signal generation unit 1 (4) with the reference voltage. Then, at every zero cross timing of the commercial AC voltage, the synchronous zero cross signal that is the output of the synchronous zero cross signal generation unit 9 and the zero cross signal 1 that is the output of the zero cross signal generation unit 1 (4) are selected and output as a zero cross signal. ing.

  The operation of the selection unit 11 will be described with reference to FIG.

  FIG. 10H shows a pulse indicating a true zero cross point of a commercial AC waveform. The true zero cross point is not always constant and slightly changes depending on the frequency stability of the commercial AC power supply. On the other hand, FIG. 10B shows the output of the zero cross signal generation unit 1 (4).

  (B) The zero cross signal 1 may cause the commercial AC power supply voltage to be distorted, an extra pulse output due to the influence of noise components, the pulse width may change, or no pulse may be output at all. (D) is a synchronous zero-cross signal which is an output of the synchronous zero-cross signal generator 9. (D) The synchronous zero-cross signal is a pulse signal generated inside the zero-cross signal generator and always operates with a stable cycle and pulse width.

  The selection unit 11 is masked except for the period during which the synchronous zero-cross signal is output and the time including the predetermined time ti before and after the stable zero-cross signal based on the stable synchronous zero-cross signal. It has become. The shaded area in (i) in FIG. 10 is the mask period.

  By this mask processing, (b) an erroneous pulse of the zero cross signal 1 can be ignored. Then, during the period in which the mask is released, (b) the zero cross signal 1 or (d) the synchronous zero cross signal, whichever pulse is output first, is selected and output as the zero cross signal. As a result, in FIG. 10 (i), (d) is the same at the mask release timing of A, but (d) is the same at B, and (b) is further increased at C where the true zero cross point is slightly advanced. (B) In D where the zero-cross signal 1 has not been output, (d) is selected, and as a result, (j) a selection unit output pulse is generated, and this signal is output as the output of the zero-cross signal generator.

  This function makes it possible to output a stable zero-cross signal in synchronization with the zero-cross point of the commercial AC power supply.

  FIG. 11 is a diagram showing a second embodiment of the present invention.

  11, the same or corresponding members as those in FIGS. 1 to 8 of the first embodiment, FIGS. 9 and 10 of the second embodiment, and FIGS. 12 to 15 of the conventional example are denoted by the same reference numerals. Shall be omitted.

  The zero cross signal generator of FIG. 1 described in the first embodiment always outputs a pulse signal generated inside the zero cross signal generator as a zero cross signal.

  The present embodiment monitors the zero-cross signal false detection situation of the zero-cross signal generated by comparing the commercial AC voltage and the reference voltage by the conventional method, and the zero-cross signal and zero-cross signal generator according to the conventional method is detected by the erroneous detection situation. This is a mode in which the generated synchronous zero-cross signal is selectively output and the zero-cross signal is output.

  FIG. 10 is a block diagram showing the configuration of the present embodiment.

  As shown in FIG. 3, the reference numeral 16 period detection unit in FIG. 10 determines whether the commercial AC power supply voltage has little distortion and noise and whether the zero-cross signal according to the conventional method is output properly. Therefore, the situation in which the zero-cross signal (output of the zero-cross signal generation unit 1) according to the conventional method is erroneously detected is monitored, and the erroneous detection occurrence state is output to the selection unit 12 as an erroneous detection state signal.

  When the frequency of occurrence of erroneous detection is small in response to the erroneous detection status signal, the selection unit 12 generates the conventional zero-cross signal 1 based on the comparison between the commercial AC voltage and the reference voltage generated by the zero-cross signal generation unit 1 (4). Is output as the output of the zero cross signal generator, and when the frequency of occurrence of erroneous detection increases to a predetermined value or more, the synchronous zero cross signal output from the synchronous zero cross signal generator 9 is selected to generate the zero cross signal. Output as device output.

  As a result, even if the true zero cross point is not always constant due to the stability of the frequency of the commercial AC power supply, etc., the commercial AC power supply voltage responds in real time to the above frequency fluctuations during periods when distortion and noise components are low. It is possible to output a stable zero-cross signal during a period when the commercial AC power supply voltage is distorted and has a lot of noise components.

The figure which shows the structure of the zero cross signal generator in the 1st Embodiment of this invention. The figure explaining the operation | movement in the 1st Embodiment of this invention. The figure explaining the operation | movement in the 1st Embodiment of this invention. The figure explaining the operation | movement in the 1st Embodiment of this invention. The figure explaining the operation | movement in the 1st Embodiment of this invention. The figure explaining the operation | movement in the 1st Embodiment of this invention. The figure explaining the operation | movement in the 1st Embodiment of this invention. The figure explaining the operation | movement in the 1st Embodiment of this invention. The figure which shows the structure of the zero cross signal generator in the 2nd Embodiment of this invention. The figure explaining the operation | movement in the 2nd Embodiment of this invention. The figure which shows the structure of the zero cross signal generator in the 2nd Embodiment of this invention. The figure explaining the conventional zero cross signal generation method. The figure explaining the conventional zero cross signal generation method. The figure explaining the conventional zero cross signal generation method. The figure explaining the conventional zero cross signal generation method.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Commercial AC power supply 2 Switch means 3 Load 4 Zero cross signal generation part 1
5 Zero cross signal generator 2
6 cycle detection unit 7 pulse signal generation unit 8 synchronization unit 9 synchronization zero cross signal generation unit 10 control unit 11 selection unit 12 selection unit 16 cycle detection unit

Claims (7)

  In a zero-cross signal generator for detecting a zero-cross point of a commercial AC power supply and outputting a zero-cross signal, first comparison means for comparing a first reference voltage with a commercial AC voltage and generating a first pulse signal, and the first reference A second comparison means for generating a second pulse signal by comparing a second reference voltage larger than the voltage with the commercial AC voltage, and the commercial AC power supply voltage is less distorted properly based on the first pulse signal and the second pulse signal in the previous period. A period detecting means for determining whether or not zero crossing is performed and detecting the period (frequency) of the commercial AC power supply during a period of zero crossing properly, and a third having the same period as the period of the commercial AC power supply detected by the period detecting means A pulse signal generating means for generating a pulse signal, and a phase of the third pulse signal so that a phase difference between the first pulse signal and the third pulse signal is a predetermined value or less. A zero-cross signal generator characterized by having a synchronizing means for adjusting and a synchronizing zero-cross signal generating means for generating a synchronized zero-cross signal based on a phase-adjusted third pulse signal, and outputting the synchronized zero-cross signal as a zero-cross signal .   The zero cross signal generator according to claim 1, wherein the second comparison unit has a time constant and does not respond to a short-time fluctuation of the commercial AC power supply voltage.   The synchronization means performs a synchronization operation at a predetermined timing, and determines that the synchronization is completed when the phase difference between the first pulse signal and the third pulse signal is equal to or less than a predetermined value over a predetermined number of pulses. The zero-cross signal generator according to claim 1 or 2, characterized by the above-mentioned.   2. The counter according to claim 1, further comprising a counting unit that counts the synchronous zero-cross signal, and when the count value reaches a predetermined value, the frequency detection operation and the synchronous operation are performed again to update the synchronous zero-cross signal. 4. A zero cross signal generator according to any one of items 1 to 3.   4. The zero-cross signal generator according to claim 1, wherein when an update signal is input from the outside, the frequency detection operation and the synchronization operation are performed again to update the synchronization zero-cross signal. 5.   An output signal selection means, wherein the frequency detection means monitors the frequency of erroneous detection of the first pulse signal, and if the frequency of occurrence of erroneous detection is lower than a predetermined value, the first pulse is selected as a zero-cross signal and erroneous detection 6. The zero-cross signal generator according to claim 1, wherein when the frequency is higher than a predetermined value, the synchronous zero-cross signal is selected as a zero-cross signal, and the selected signal is output as a zero-cross signal. Output signal selection means is provided and masked except for the vicinity of the zero cross point indicated by the synchronous zero cross signal, and in the vicinity of the zero cross point indicated by the synchronous zero cross signal, the first pulse signal or the synchronous zero cross signal is first. 6. The zero-cross signal generator according to claim 1, wherein the one that outputs a zero-cross signal is selected and output as a zero-cross signal.

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