JP5995186B2 - Zero cross detection circuit - Google Patents

Description

  The present invention relates to a zero-cross detection circuit, and more particularly to a circuit configuration suitable for reducing the consumption of a zero-cross detection circuit that detects a point where the voltage of an AC power supply becomes 0V.

For example, Patent Document 1 discloses a zero-cross detection circuit 342 shown in FIG. Referring to FIG. 1, zero cross detection circuit 342 accumulates electric power in electrolytic capacitor 392 when the absolute value of the AC power supply voltage is higher than a predetermined value, and supplies electric power when the absolute value of the AC power supply voltage is lower than the predetermined value. The current flows to the photocoupler 398 and zero crossing is detected. Therefore, when compared with a conventional zero-cross detection circuit in which current always flows when the voltage of the AC power supply is not 0 V, the zero-cross detection circuit 342 consumes less power.
However, in such a case, the driving time of the photocoupler 398 varies due to variations in electronic components and temperature characteristics. Therefore, it is necessary to take a margin in the energization time of the photocoupler 398 in order to reliably detect the point where the voltage of the AC power supply becomes 0V. As a result, there is a problem that the time during which a current flows through the photocoupler 398 becomes longer and the power consumption increases.

JP 2010-54306 A (page 18, FIG. 5)

  The present invention has been made in order to solve the above-mentioned problems, and an object of the present invention is to detect a zero-cross signal only for a short time as soon as the voltage of the AC power supply becomes 0 V, and to measure reduction in power consumption. is there.

According to the invention of claim 1, wherein in order to achieve the above object, a zero-cross detection circuit for detecting a zero-cross timing of the AC power source, a first photocoupler, for energizing the first photocoupler and oN / OFF switching element, and detects the zero-cross timing have groups Dzu the energized state of the first photocoupler, and a control unit for switching the oN / OFF state of the switching element, the first photo The coupler is energized when the switching element is in the ON state and the voltage of the AC power supply is positive, and the control unit turns on the switching element at a negative timing of the AC power supply voltage and turns on the switching element. The predetermined time is provided with a period during which it is not determined whether or not the first photocoupler is energized. Start the determination of the energization state whether photocoupler, characterized in that it OFF the switching element When energization is confirmed to the first photocoupler.
Therefore, it is possible to reduce the wasteful power consumption by energizing the first photocoupler only for the time necessary for taking in the zero cross signal without considering the variation of the electronic parts and the temperature characteristics. Furthermore, when the power plug is pulled out, the first photocoupler is energized immediately after the switching element is energized due to the charge accumulated in the capacitor or the like, and accordingly, the signal transition (edge) is taken into the control unit. Since the control unit does not detect the signal transition for a predetermined time, the captured signal transition is ignored. When the determination of the presence / absence of signal transition is started after a predetermined time, since the signal transition is not detected, the switching element continues to be turned on, and the charge accumulated in the built-in capacitor is changed to the first charge. It can be consumed by energizing the photocoupler. Therefore, the discharge after the power plug is unplugged is quick.

According to a second aspect of the present invention, the switching element is configured using a high breakdown voltage transistor, and includes a second photocoupler between the control unit and the high breakdown voltage transistor. To do.
Therefore, if a high-voltage photocoupler or a high-voltage photoMOSFET is used for the switching element, the second photocoupler is not necessary, but the high-voltage photocoupler or the high-voltage photoMOSFE is used.
T is expensive. By using a high breakdown voltage transistor for the switching element and turning on the high breakdown voltage transistor with a signal from the second photocoupler, a circuit can be configured with inexpensive electronic components.

  According to the present invention, it is possible to provide a control device that can shorten the energization time to a photocoupler for capturing a zero-cross signal and has a low-power-consumption zero-cross detection circuit.

It is a circuit diagram of the zero cross detection circuit 342 described in the patent document. It is a figure which shows the circuit structure of the zero cross detection circuit 500 in connection with this invention. It is a figure which shows the taking-in timing of a zero cross signal. It is a figure which shows the taking-in timing of a zero cross signal about another embodiment of this invention. It is a figure which shows the taking-in timing of a zero cross signal about another embodiment of this invention.

[Circuit configuration]
FIG. 2 is a diagram showing a circuit configuration of the zero-cross detection circuit 500 according to the embodiment of the present invention.

  Referring to FIG. 2, a zero-cross detection circuit 500 includes a first diode 501 whose cathode is connected to one end of an AC power source 520, a cathode connected to the other end of the AC power source 520, and an asode having a first one. And a second diode 511 connected to the anode of the diode 501.

  The zero-cross detection circuit 500 further includes a first photocoupler 521 including a light emitting diode 504 and a transistor 505, a capacitor 502 having one end connected to the anode of the light emitting diode 504, and the other end connected to the cathode of the light emitting diode 504, and a fourth resistor. 503. The capacitor 502 and the fourth resistor 503 are components for absorbing noise to the first photocoupler 521.

  The zero-cross detection circuit 500 further has a switching element 510 whose collector is connected to the cathode of the light emitting diode 504, an emitter connected to the anode of the second diode 511, one end connected to the emitter of the switching element 510, and the other end. Includes a resistor 512 connected to the base of the switching element 510, and 513 having one end connected to the other end of 512.

  The switching element 510 is composed of an NPN bipolar high voltage transistor, which is cheaper than a high voltage photocoupler or a high voltage photo MOSFET (Metal-Oxide-Semiconductor Field-Effect Transistor). Is a base resistance of the switching element 510, and a resistance 513 is a resistance for voltage stabilization between the base and the emitter of the switching element 510.

The zero-cross detection circuit 500 further includes a second photocoupler 522 including a transistor 514 and a light-emitting diode 515 whose emitter is connected to the other end of 513, a resistor 516 whose one end is connected to the cathode of the light-emitting diode 515, The transistor 517 whose emitter is connected to the other end of the resistor 516, the resistor 518 whose one end is connected to the emitter and reference voltage of the transistor 517, the other end is connected to the base of the transistor 517, and the other end of the resistor 518 And a resistor built-in transistor 523 including a resistor 519 connected to the end.
The resistor 516 is a current limiting resistor, the resistor 518 is a resistor for stabilizing the voltage between the base and the emitter of the built-in transistor 517, and the resistor 519 is a base resistor of the built-in transistor 517.

  The zero-cross detection circuit 500 further includes a resistor 506 having one end connected to the power supply potential and the other end connected to the collector of the transistor 505, and a resistor 507 connected to the other end of the resistor 506 and the collector of the transistor 505. Including. Resistors 506 and 507 are current limiting resistors.

  The zero-cross detection circuit 500 is further connected to the other end of the resistor 507 so as to capture the zero-cross signal, and is connected to the other end of the resistor 519 so as to send a signal for controlling the ON / OFF state of the transistor 523 with built-in resistor. A CPU (Central Processing Unit) 508 as a control unit is included.

[Operation]
Referring to FIG. 2, the zero-cross detection circuit 500 having the above-described configuration operates as follows.

  The CPU 508 turns on / off the output signal to the transistor with built-in resistor 523, so that the transistor with built-in resistor is turned on / off. When the resistor built-in transistor 523 is turned on / off, the second photocoupler 515 is turned on / off. When the second photocoupler 515 is turned on / off, the switching element 510 is turned on / off.

  When the switching element 510 is in the ON state and the voltage of the AC power supply is positive, the first photocoupler 521 is turned on. When the first photocoupler 521 is turned on, the voltage of the input signal to the CPU 508 decreases from the power supply voltage to the reference voltage, and the CPU 508 detects the zero cross signal.

  The second diode 511 is not energized when the voltage of the AC power source is negative, and prevents reverse voltage application to the switching element 510.

  FIG. 3 is a diagram illustrating an AC power supply, a signal output for the CPU 508 to capture a zero-cross signal, and a timing at which the CPU 508 detects the zero-cross signal. 2 and 3, the CPU 508 predicts an arbitrary time during which the voltage of the AC power supply is negative by a built-in timer, and outputs a signal to the resistor built-in transistor 523 (T1). When the resistor built-in transistor 523 is turned on in response to the signal from the CPU 508, the second photocoupler 522 and the switching element 510 are also turned on (T1). The first photocoupler 521 is turned on and consumes power from the time when the switching element is in the ON state and the voltage of the AC power supply changes from negative to positive (T2) and exceeds the Vf of the light emitting diode 504 (T3). . When the first photocoupler 521 is turned on, the voltage of the input signal to the CPU 508 decreases from the power supply voltage to the reference voltage, so that the CPU 508 determines that the zero cross signal has been detected. When the CPU 508 determines that the zero cross signal has been detected, the CPU 508 turns off the output signal to the resistor built-in transistor 523 (T4). When the output signal to the resistor built-in transistor 523 is turned OFF, the first photocoupler 521 is also turned OFF, and power is not consumed. The hatched portion (between T3 and T4) of the AC power supply waveform is a portion where the first photocoupler 521 is energized and consumes power in order to detect the zero cross signal.

  The operation described with reference to FIG. 3 is an operation in the normal mode when the CPU 508 is in a standby state. The CPU also controls driving of a load such as an electric heater (not shown). In a standby state that does not require control of the load, the normal mode described in FIG. 3 is used to reduce power consumption in the zero-cross detection circuit. Do the operation in. On the other hand, when the load is controlled, a zero-cross signal at the time of falling when the voltage of the AC power supply changes from positive to negative is taken in, and the operation is performed in a high detection mode that further improves the detection accuracy of the zero-cross timing.

  Specifically, the CPU 508 keeps the switching element 510 driven at all times, so that the switching element is turned on even after detecting that the current has flown through the first photocoupler, and the voltage of the AC power supply is positive. It is possible to detect the zero-crossing timing by the input of the CPU 508 rising at the falling edge that changes from negative to negative.

  Next, another embodiment of the present invention will be described with reference to FIG. FIG. 4 shows an energization waveform from an AC power source, a signal output to the transistor 523 with a built-in resistor so that the CPU 508 captures the zero-cross signal, and a period during which the CPU 508 waits for the zero-cross signal (in order from the top). FIG. 6 is a diagram illustrating a period in which a transition signal can be detected and a signal transition state from the first photocoupler 521 input to the CPU 508. The CPU 508 detects the zero cross timing by the signal transition from the first photocoupler 521. The CPU 508 outputs a signal to the resistor built-in transistor 523 at the timings T1 and T6, and then provides a period (non-detection period) until the predetermined period T5 and T7 is ignored even if the signal transition is taken into the CPU 508. In this period, a sufficient margin is provided from the timing T3 at which the signal transition is actually taken, and if the power plug is inserted, the signal transition is not taken between T1 and T5 and T6 and T7. The value is If the power plug is inserted, even if a signal is output to the resistor built-in transistor 523 during the period T1, the zero cross signal transition is actually input to the CPU 508 at the timing T3, and at the timing T4. The output of the signal to the resistor built-in transistor 523 is stopped, and the current consumption to the first photocoupler 521 is cut off. When the power plug is removed as shown in FIG. 4, the AC voltage is held by the capacitor 600 between the phases of the AC power supply shown in FIG. When the CPU 508 outputs a signal to the resistor built-in transistor 523 at the timing T6 while the AC voltage is held, the signal transition is taken in the non-detection period of the CPU 508 at the timing T6. After that, since the signal transition is not taken into the CPU 508 after T7, the CPU 508 keeps waiting for the signal transition and keeps turning on the transistor 523 with a built-in resistor. Therefore, the first photocoupler consumes the electric charge accumulated in the built-in capacitor by energization, and the discharge after the power plug is pulled out is quick in the period from T6 to T8.

  Next, still another embodiment of the present invention will be described based on FIG. FIG. 5 shows an energization waveform from an AC power supply, a signal output to the transistor 523 with a built-in resistor so that the CPU 508 captures a zero-cross signal, and a first photocoupler 521 input to the CPU 508 in order from the top. It is a figure which shows the signal transition state from. The CPU 508 detects the zero cross timing by the signal transition from the first photocoupler 521. The CPU 508 outputs a signal to the resistor built-in transistor 523 at timings T1, T4, and T7. If the power plug is inserted, the zero cross signal transition is input to the CPU 508 at the timing of T2 and T5. For example, the zero cross timing is newly detected after detecting the previous zero cross timing at the time of T5. Since the detection interval (T5-T2) until this is longer than a predetermined time set in advance, output of the signal to the resistor built-in transistor 523 is stopped at the timing of T6. Note that the predetermined time set in advance is about 90% of one cycle of the AC power source, and if the AC power source is 50 Hz, about 90% of 20 ms and the AC power source is 60 Hz. For example, a time of about 90% of 16.7 ms is set. Whether the frequency of the AC power supply is 50 Hz or 60 Hz is determined depending on whether the zero-cross timing detection period at the beginning of energization is 20 ms or 16.7 ms.

  On the other hand, when the power plug is removed after T6 as shown in FIG. 5, the AC voltage is held by the capacitor 600 between the phases of the AC power supply in FIG. If the CPU 508 outputs a signal to the resistor built-in transistor 523 at the timing T7 while the voltage is held, the signal transition is taken into the CPU 508 at the timing T7, and a new zero cross timing is detected after the previous zero cross timing is detected. Since the detection interval (T7-T5) until detection is shorter than a predetermined time set in advance, the CPU 508 continues to output the signal to the resistor built-in transistor 523, thereby continuing to turn on the switching element 510. Therefore, the first photocoupler consumes the electric charge accumulated in the built-in capacitor by energization, and the discharge after the power plug is pulled out is quick in the period from T7 to T8.

DESCRIPTION OF SYMBOLS 500 ... Zero cross detection circuit 501 ... 1st diode 502 ... Capacitor 503 ... Resistance 504 ... Light emitting diode 505 ... Transistor 506 ... Resistance 507 ... Resistance 508 ... CPU (control part)
510... Switching element (high voltage transistor)
511 ... second diode 512 ... resistor 513 ... resistor 514 ... transistor 515 ... light emitting diode 516 ... resistor 517 ... transistor 518 ... resistor 519 ... resistor 520 ... AC power supply 521 ... first photocoupler 522 ... second photocoupler 523 ... Transistor with built-in resistor 524 ... Resistor 600 ... Capacitor

Claims (2)

A zero cross detection circuit for detecting the zero cross timing of an AC power source ,
A first photocoupler;
A switching element for ON / OFF for energizing the first photocoupler,
Detects the zero-cross timing have groups Dzu the energized state of the first photocoupler, and a control unit for switching the ON / OFF state of the switching element,
The first photocoupler is energized when the switching element is in an ON state and the voltage of the AC power supply is positive,
The controller turns on the switching element at a negative timing of the voltage of the AC power supply, and provides a period during which a predetermined time does not determine whether or not the first photocoupler is energized after turning on the switching element .
A zero-cross detection circuit which starts determining whether or not the first photocoupler is energized after a predetermined time and turns off the switching element when energization to the first photocoupler is confirmed . The switching element is configured using a high voltage transistor,
A second photocoupler is provided between the control unit and the high breakdown voltage transistor;
The zero-cross detection circuit according to claim 1.