JP2010239774A - Zero-cross detection device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a zero-cross detection device capable of executing power saving of a circuit well. <P>SOLUTION: In a zero-cross detection circuit 1, a diode bridge D1 which fully rectifies an AC current from an AC power supply 101 using four diodes is connected through a resistor R1. The AC current that has been fully rectified by the diode bridge D1 is flown to a circuit in which a J-FETQ1, a resistor R2, and a light emitting diode PC1a of a photocoupler PC1 are connected in series. The electric potential between the resistor R2 and the light emitting diode PC1a is input in the gate of J-FETQ1. A photocoupler input current If that flows through the light emitting diode PC1a is suppressed to be a current limit value or less due to the constant current characteristics of J-FETQ1. An inversion buffer IC1 outputs a zero-cross signal in accordance with whether the photocoupler input current If has increased up to a zero-cross signal threshold (a value smaller than the current limit value) or higher. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a zero-cross detection device capable of detecting a so-called zero-cross point where the absolute value of an alternating current from an alternating-current power supply is less than a predetermined threshold, and more particularly to a zero-cross detection device capable of saving power related to the circuit.

  Conventionally, a zero-cross detection device that detects a so-called zero-cross point as a timing when the absolute value of the alternating current becomes zero has been proposed. The detected zero cross point is applied to various controls in various electric devices, such as setting the heater ON / OFF timing. In addition, in this type of zero-cross detection device, it has been proposed to intermittently energize the zero-cross detection unit in order to reduce the energization to the zero-cross detection unit that detects the zero-cross point (see, for example, Patent Document 1). ).

JP 2000-282546 A

  However, the timing of the zero cross point is not known immediately after the power is turned on. For this reason, with the technique of the said patent document 1, power saving cannot be performed until the timing and period of a zero crossing point are acquired after power-on. The above technique cannot be applied even when the frequency of the AC power supply is unstable. Therefore, the present invention has been made for the purpose of providing a zero-crossing detection device capable of satisfactorily executing circuit power saving.

  In order to achieve the above object, the zero-cross detection device of the present invention includes a full-wave rectifying means for full-wave rectifying and outputting an alternating current, a light-emitting element that emits light based on the output of the full-wave rectifying means, and its light emission In a period in which the absolute value of the alternating current is less than a predetermined threshold based on the current output from the light receiving element of the photocoupler and the light receiving element that outputs a current corresponding to the light emitted from the element. A zero-cross pulse output means for outputting a corresponding zero-cross pulse, and an absolute value of a current that is full-wave rectified by the full-wave rectifier means and that is supplied to the light-emitting element is equal to or less than a current limit value set larger than the predetermined threshold value. And current limiting means for limiting the current to a current value.

  In the zero-cross detection device of the present invention configured as described above, when the light emitting element of the photocoupler emits light based on the output of the full wave rectification means, that is, the current subjected to full wave rectification, the light receiving element of the photocoupler Outputs a current corresponding to the emitted light. The zero cross pulse output means outputs a zero cross pulse corresponding to a period in which the absolute value of the alternating current is less than a predetermined threshold based on the current output from the light receiving element. For this reason, the center timing of this zero cross pulse can be detected as a zero cross point.

  Further, the current that is full-wave rectified by the full-wave rectifying means and is supplied to the light emitting element is equal to or less than a current limit value that is preset by the current limiting means so that the absolute value of the current is larger than the predetermined threshold value. To be limited. For this reason, in the present invention, power saving of the circuit related to input / output of the photocoupler can be executed immediately after the power is turned on, and the power saving can be executed even when the frequency of the AC power supply is unstable. . Therefore, in the present invention, power saving of the circuit can be performed extremely well. Further, in the present invention, only a current equal to or lower than the current limit value flows through the light emitting element, and a current having a maximum alternating current does not flow through the light emitting element. Therefore, it is possible to use a photocoupler having a small rated current. It becomes.

  Further, the zero-cross detection device of the present invention made to achieve the above object is a half-wave rectifier that outputs a half-wave rectified alternating current, a light-emitting element that emits light based on the output of the half-wave rectifier, A photocoupler including a light receiving element that outputs a current corresponding to light emitted by the light emitting element, and the half-wave rectified current is less than a predetermined threshold based on the current output from the light receiving element of the photocoupler. A half-wave pulse output unit that outputs a half-wave pulse corresponding to a certain period and a zero-cross point detection unit that detects a zero-cross point from the half-wave pulse may be provided.

  In the zero-cross detection device of the present invention configured as described above, when the light emitting element of the photocoupler emits light based on the output of the half-wave rectifier, that is, the half-wave rectified current, the light-receiving element of the photocoupler Outputs a current corresponding to the emitted light. The half-wave pulse output means outputs a half-wave pulse corresponding to a period during which the half-wave rectified current is less than a predetermined threshold based on the current output from the light receiving element. Then, the average of the half-wave pulse during the period H and the period L corresponds to a half cycle of the alternating current, and the zero cross points are arranged near both ends of the half-wave pulse. Therefore, the zero cross point detection means detects the zero cross point from the half wave pulse output from the half wave pulse output means.

  In the present invention, since the current flows through the light receiving element only for a half-wave period, power saving of the circuit related to the output of the photocoupler can be executed immediately after the power is turned on, and the frequency of the AC power supply The above power saving can be executed even when is unstable. Therefore, in the present invention, power saving of the circuit can be performed extremely well.

  In many cases, electrical equipment has full-wave rectification means in the power supply device for full-wave rectification of the alternating current and outputting the full-wave rectified current to a load. In this case, a part or all of the half-wave rectifying means may constitute a part of the full-wave rectifying means in the power supply device.

  A full-wave rectifier circuit that full-wave rectifies the alternating current and outputs it to the load is normally a half-wave rectifier circuit that half-wave rectifies the positive half cycle and outputs it to the load, and a half-wave rectifier that half-wave rectifies the negative half cycle. And a half-wave rectifier circuit that outputs to a load. Thus, as the half-wave rectifying means for half-wave rectifying and outputting an alternating current to the light emitting element of the photocoupler in this way, full-wave rectifying means for outputting the full-wave rectified current to the load (for example, the full-wave rectifying means). When a part of the rectifier circuit (for example, the one half-wave rectifier circuit) is used, the configuration can be simplified and the manufacturing cost of the device can be reduced.

It is a block diagram showing the structure of the power supply circuit and heater control circuit to which the zero cross detection circuit as one form of this invention was applied. It is a circuit diagram showing the structure of the said zero cross detection circuit in detail. It is a time chart showing the change of various currents and signals in the circuit. It is a circuit diagram showing the structure of the other zero crossing detection circuit to which this invention was applied. It is a time chart showing the change of various currents and signals in the circuit. It is a circuit diagram showing an example of the rectification smoothing circuit of the said power supply circuit and a heater control circuit. It is a circuit diagram showing the modification of the circuit of FIG. 5 using the rectification smoothing circuit. It is a circuit diagram showing a zero cross detection circuit when there is no J-FET Q1.

[First Embodiment]
Next, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a block diagram showing a configuration of a power supply circuit and a heater control circuit 100 to which a zero-cross detection circuit 1 as an example of a zero-cross detection device of the present invention is applied. The power supply circuit and heater control circuit 100 is built in the laser printer, and is supplied with an AC current from an AC power supply 101 that is a general commercial power supply. The heater output output to the heater or the like is output.

  As shown in FIG. 1, the alternating current from the AC power source 101 is input to the rectifying / smoothing circuit 3, the zero-cross detection circuit 1, and the heater switching circuit 5. As will be described later, the zero-cross detection circuit 1 outputs a zero-cross signal as an example of a zero-cross pulse corresponding to a period in which the absolute value of the alternating current is less than a predetermined threshold (hereinafter referred to as a zero-cross signal threshold). The signal is input to a timer 7 and a microcomputer (hereinafter referred to as a microcomputer) 9 having a CPU, ROM, RAM and the like. In addition, the timing result of the timer 7 is also input to the microcomputer 9.

  The microcomputer 9 inputs a heater ON / OFF signal for switching ON / OFF of the fixing heater to the heater switching circuit 5 based on the zero cross signal, and the heater switching circuit 5 receives the heater ON / OFF signal. Based on this, it is switched whether or not an alternating current from the AC power source 101 is output to the fixing heater as a heater output. For this reason, for example, the occurrence of flicker can be suppressed by matching the ON / OFF timing of the fixing heater with the zero cross point of the alternating current.

  The rectifying / smoothing circuit 3 performs full-wave rectification and smoothing of the alternating current from the AC power supply 101 and inputs it to the high-frequency transformer 33 as an example of a load via the switching circuit 31. The switching circuit 31 generates a voltage suitable for driving the DC motor or the like in the secondary coil of the high-frequency transformer 33 by switching a current supplied to the primary coil of the high-frequency transformer 33. The voltage is rectified and smoothed by the rectifying / smoothing circuit 35 and output as a DC output to the DC motor or the like. The DC output is also input to the control circuit 37, and the control circuit 37 controls the switching timing by the switching circuit 31 so that the DC output becomes a voltage suitable for driving the DC motor or the like. .

  Next, FIG. 2 is a circuit diagram showing in detail the configuration of the zero-cross detection circuit 1. As shown in FIG. 2, in the zero cross detection circuit 1, the AC power supply 101 includes a diode bridge D <b> 1 as an example of a full-wave rectification unit that performs full-wave rectification of the alternating current from the AC power supply 101 using four diodes. Connected through a device R1. The alternating current that has been full-wave rectified by the diode bridge D1 passes through a J-FET (junction FET) Q1, a resistor R2, and a light emitting diode PC1a (an example of a light emitting element) of a photocoupler PC1 as an example of a current limiting unit. A circuit connected in series in the direction is energized. The anode of the light emitting diode PC1a is also connected to the gate of the J-FET Q1.

  Therefore, a voltage corresponding to the voltage drop in the resistor R2 is applied between the gate and source of the J-FET Q1, and the photocoupler input current If flowing through the light emitting diode PC1a is a current determined according to the resistance value of the resistor R2. It is suppressed below the limit value. That is, the photocoupler input current If is limited by the constant current characteristic when the gate and the source of the J-FET Q1 are connected. For this reason, the photocoupler input current If is limited to a current limit value or less with a peak cut as shown in FIG.

  In the case of the zero-cross detection circuit without the J-FET Q1 shown in FIG. 8A, the photocoupler input current If changes as shown in FIG. 8B because there is no J-FET Q1.

  Returning to FIG. 2, in the phototransistor PC1b (an example of a light receiving element) of the photocoupler PC1, the collector is connected to the DC power source Vcc via the resistor R3, and the emitter is grounded. The potential of the collector of the phototransistor PC1b is input to an inverting buffer IC1 as an example of a zero cross pulse output unit, and the inverting buffer IC1 outputs the above-described zero cross signal as follows.

  That is, as the photocoupler input current If increases, a larger amount of current flows through the phototransistor PC1b, and the potential input to the inverting buffer IC1 decreases. For this reason, in the inverting buffer IC1, when the photocoupler input current If exceeds the zero cross signal threshold value determined according to the voltage of the DC power supply Vcc, the characteristics of the inverting buffer IC1, the characteristics of the photocoupler PC1, and the resistance value of the resistor R3, , H signals are output, and when the photocoupler input current If falls below the zero cross signal threshold, an L signal is output. The relationship between the zero cross signal threshold and the current limit value is set so that the current limit value is larger than the zero cross signal threshold by appropriately setting the resistance values of the resistors R2 and R3. Yes.

  For this reason, as shown in FIGS. 3A and 3B, the period t1 in which the zero cross signal is L is included in the range of the period t2 in which the photocoupler input current If is not limited. For this reason, it is possible to detect the center timing of the period t1 as a zero cross point as in the conventional case where the current limitation is not performed. The above-described microcomputer 9 executes various controls based on this zero cross point.

  In this embodiment, since the photocoupler input current If is limited to be equal to or less than the current limit value, power saving in the zero-cross detection circuit 1 can be performed immediately after the power is turned on. The above power saving can be executed even when the frequency is unstable. In the present embodiment, only a current equal to or less than the current limit value flows through the light emitting diode PC1a of the photocoupler PC1, and the maximum current of the alternating current does not flow through the light emitting diode PC1a. It is also possible to use the coupler PC1.

[Second Embodiment]
Next, a zero cross detection circuit 11 as a second embodiment of the zero cross detection device will be described with reference to the circuit diagram of FIG. The zero cross detection circuit 11 is also connected in the same manner as the zero cross detection circuit 1 as shown in FIG. As shown in FIG. 4, in the zero cross detection circuit 11, the AC power supply 101 is connected in parallel with the light-emitting diode PC1a of the photocoupler PC1 and the reverse voltage protection diode D2 as an example of the half-wave rectifying means with the polarities reversed. The connected circuit is connected via a resistor R5. That is, the light-emitting diode PC1a and the reverse voltage protection diode D2 constitute a half-wave rectifier, and the light-emitting diode PC1a performs two functions of the light-emitting element of the photocoupler PC1 and half-wave rectification. Therefore, as shown in FIG. 5B, the half-wave rectified photocoupler input current If is applied to the light emitting diode PC1a, and the collector current Ic of the phototransistor PC1b of the photocoupler PC1 is also the photocoupler input current. It changes in proportion to If.

  On the other hand, the phototransistor PC1b of the photocoupler PC1 is connected to a resistor R3 and an inverting buffer IC1 as an example of a half-wave pulse output means, similarly to the zero cross detection circuit 1 described above. In this case, the output of the inverting buffer IC1 is input as a half-wave identification signal as an example of a half-wave pulse to the microcomputer 9 or the like as an example of a zero cross point detection unit. The microcomputer 9 detects a zero cross point as follows.

  That is, as shown in FIG. 5C, when the photocoupler input current If exceeds the above-mentioned zero cross signal threshold, the half wave identification signal becomes H, and when the photocoupler input current If becomes less than the zero cross signal threshold, the half wave identification. The signal becomes L. The microcomputer 9 acquires the period t3 when the half-wave identification signal is H and the period t4 when the half-wave identification signal is L via the timer 7, and detects the zero cross point as follows.

  First, by calculating the average value of the length of the period t3 and the length of the period t4, the interval between zero cross points, that is, the zero cross period t5 can be calculated. Further, when t4-t3 is divided by 4, the time t6 from the fall of the half-wave identification signal to the zero cross point can be calculated. Furthermore, the time from the fall of the half-wave identification signal to the next zero cross point can be calculated by adding the calculated t5 and t6. The microcomputer 9 executes various controls based on the zero cross point calculated in this way.

  In the present embodiment, since current flows only through the half-wave period in the phototransistor PC1b of the photocoupler PC1, power saving in the zero-cross detection circuit 11 can be performed immediately after the power is turned on. The above power saving can be executed even when the frequency of the current is unstable. Further, in the present embodiment, the number of diodes can be reduced from four to one as compared with the case where the diode bridge D1 is used as in the zero-cross detection circuit 1, and the manufacturing cost can be reduced. .

[Modifications of Second Embodiment and Other Modifications]
Further, such a zero-cross detection circuit 11 can be integrated with the rectifying / smoothing circuit 3 (see FIG. 1) as follows. That is, the rectifying / smoothing circuit 3, for example, as illustrated in FIG. 6, a diode bridge D 3 as an example of a full-wave rectifying unit connected to the AC power source 101, and an alternating current that has been full-wave rectified by the diode bridge D 3. And a smoothing capacitor C1 for smoothing.

  Therefore, as shown in FIG. 7, by using one diode D3a of the four diodes constituting the diode bridge D3 instead of the reverse voltage protection diode D2, the zero crossing similar to that in FIG. The detection circuit 11 can be configured. Also in this case, similarly to the circuit of FIG. 4, the current flows through the phototransistor PC1b only during the half-wave period, so that power saving can be performed in the same manner, and the zero cross point can be calculated in the same manner.

  Further, in this case, the reverse voltage protection diode D2 is not necessary, so that the configuration can be further simplified and the manufacturing cost of the device can be further reduced. Further, in this case, since no current flows through the reverse voltage protection diode D2, power can be saved more satisfactorily. In the example of FIG. 7, if a resistor R5 (see FIG. 4) is inserted between the diode D3a and the AC power supply 101, power is consumed by the current flowing through the load of the full-wave rectifier circuit. A resistor R7 was inserted between the cathode of the light emitting diode PC1a and the anode of the diode D3a.

  In addition, the present invention is not limited to the above-described embodiment, and can be implemented in various forms without departing from the gist of the present invention. For example, as in the embodiment shown in FIGS. 4 to 7, in the zero cross detection circuit configured so that only a half wave of the alternating current flows through the light emitting diode PC1a, the current is further limited by the above-described J-FET Q1 or the like. May be. The present invention can also be applied to various electric devices other than laser printers.

DESCRIPTION OF SYMBOLS 1,11 ... Zero cross detection circuit 3 ... Rectification smoothing circuit 5 ... Heater switching circuit 7 ... Timer 9 ... Microcomputer 100 ... Power supply circuit and heater control circuit 101 ... AC power supply C1 ... Smoothing capacitor D1, D3 ... Diode bridge D2 ... Reverse Voltage protection diode D3a ... Diode Q1 ... J-FET
IC1 ... Inversion buffer PC1 ... Photocoupler PC1a ... Light emitting diode PC1b ... Phototransistor

Claims (3)

Full-wave rectification means for full-wave rectification and output of alternating current; and
A photocoupler comprising: a light emitting element that emits light based on the output of the full wave rectifying means; and a light receiving element that outputs a current corresponding to light emitted by the light emitting element;
Zero-cross pulse output means for outputting a zero-cross pulse corresponding to a period in which the absolute value of the alternating current is less than a predetermined threshold based on the current output by the light receiving element of the photocoupler;
Current limiting means for limiting the absolute value of the current that is full-wave rectified by the full-wave rectifying means and that is passed through the light-emitting element to a current limit value that is set to be greater than the predetermined threshold;
A zero-cross detection device comprising: Half-wave rectification means for half-wave rectifying and outputting alternating current; and
A photocoupler comprising: a light-emitting element that emits light based on the output of the half-wave rectifier; and a light-receiving element that outputs a current corresponding to the light emitted by the light-emitting element;
Half-wave pulse output means for outputting a half-wave pulse corresponding to a period in which the half-wave rectified current is less than a predetermined threshold based on the current output from the light receiving element of the photocoupler;
A zero cross point detecting means for detecting a zero cross point from the half-wave pulse;
A zero-cross detection device comprising:   The part or all of the half-wave rectifying means constitutes a part of full-wave rectifying means for full-wave rectifying the alternating current and outputting the full-wave rectified current to a load. The zero-cross detection device according to 2.

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