JP5176551B2 - AC detection circuit and DC power supply device - Google Patents

Description

  The present invention relates to an AC detection circuit that detects a decrease in AC voltage, and more particularly to a technique that is effective when used in a DC power supply device that includes an AC-DC converter that generates a DC voltage from an AC power supply and has an AC detection function.

An electronic device such as a personal computer with a built-in microprocessor is equipped with an AC-DC converter that generates a DC voltage such as DC5V or 3V necessary for the operation of the microprocessor from AC100V. In an electronic device equipped with an AC-DC converter, if the AC voltage is cut off due to a power failure or lightning and the DC voltage on the secondary side decreases, the system may run out of control or important data may be lost. Therefore, an invention relating to a DC power supply device provided with a voltage monitoring unit for detecting a decrease in AC voltage has been proposed (see, for example, Patent Document 1).
JP-A-6-113455

  The voltage monitoring means in the invention of Patent Document 1 takes out the voltage from the center tap of the secondary coil of the AC-DC converter, rectifies it, shapes the waveform, and inputs it to the microcomputer as a rectangular wave pulse. In this case, it is possible to quickly determine that the AC voltage has been interrupted. However, the invention of Patent Document 1, there is a problem that really is detected delayed because it monitors the voltage on the secondary side.

  Thus, a technique has been developed in which the primary voltage is monitored to detect AC voltage interruption. As a technique for monitoring the primary side voltage and detecting AC voltage interruption, for example, as shown in FIG. 8, rectification diodes D1 and D2, voltage dividing resistors R1 and R2, and voltage after rectification There is a capacitor C2 that holds the voltage and notifies the microcomputer (CPU) of the voltage drop of the capacitor C2 by the photocoupler PC.

  The AC voltage interruption detection circuit of FIG. 8 cannot detect a decrease in AC voltage until the capacitance C0 between the power supply lines L1 and L2 is discharged, and therefore detects when the AC power supply is interrupted while C0 is sufficiently charged. There is a problem that it takes time to complete.

  The present invention has been made paying attention to the above-described problems, and an object of the present invention is to provide an AC detection circuit capable of quickly detecting and notifying AC power supply interruption or AC voltage drop. is there.

  In order to achieve the above object, the present invention provides a pulse detection circuit that detects an AC waveform of an input voltage from an AC power supply to generate a pulse, and determines that the AC power supply is cut off when the pulse disappears and changes the output. It is a thing. More specifically, a pulse generation circuit that detects an AC waveform of an input voltage from an AC power source to generate a pulse, a waveform generation circuit that generates a predetermined signal waveform by performing a charge / discharge operation according to the pulse, The AC detection circuit is configured by a pulse detection circuit including a comparator that compares the generated waveform with a predetermined reference voltage and outputs a signal indicating the presence or absence of a pulse.

  According to the configuration as described above, when the AC power supply is cut off, it is possible to output a signal notifying that the power supply is cut off. Therefore, in a DC power supply device having an AC-DC converter, it becomes possible to detect interruption of the AC power supply on the primary side and promptly notify a microcomputer or the like.

  Here, preferably, in addition to the pulse detection circuit, a low voltage detection circuit that monitors the AC voltage and changes the output when the AC voltage falls below a predetermined level is provided. It is configured to output a signal obtained by logically summing the outputs of the low voltage detection circuit. As a result, it is possible to detect and quickly notify the AC voltage drop as well as the interruption of the AC power supply.

  The low voltage detection circuit is connected to the output side of the buffer amplifier for smoothing the input waveform connected to the output of the buffer amplifier with a voltage that has been subjected to both-wave rectification or half-wave rectification by an element that rectifies the AC input voltage. And a comparator that compares a voltage smoothed by the capacitor with a predetermined reference voltage.

  According to the present invention, there is an effect that it is possible to realize an AC detection circuit capable of quickly detecting and notifying AC power supply interruption or AC voltage drop.

  DESCRIPTION OF EXEMPLARY EMBODIMENTS Hereinafter, preferred embodiments of the invention will be described with reference to the drawings.

  1 and 2 show a first embodiment of an AC detection circuit to which the present invention is applied. FIG. 2 shows a specific example of an internal circuit of an IC (semiconductor integrated circuit) 20 used in FIG. Show.

  As shown in FIG. 1, the AC detection circuit of this embodiment includes a rectifying diode D1 having an anode terminal connected to one power supply line L1 of a plug 10 connected to an AC power supply via a resistor R3, and the other A rectifying diode D2 having an anode terminal connected to the power line L2 via a resistor R4, a voltage dividing resistors R1 and R2 connected in series between a common cathode terminal of the diodes D1 and D2 and a ground point, and a resistor The circuit includes an AC detection IC 20 having a voltage input terminal IN connected to a coupling node between R1 and R2, and a pull-up resistor R0 connected between the output terminal OUT of the IC 20 and the power supply voltage VDD.

  Reference numeral 30 denotes an AC-DC converter that includes a diode bridge circuit, a transformer, and the like and generates a DC voltage such as 5 V or 3 V from AC 100V. A capacitance C0 between the power supply lines L1 and L2 indicates an equivalent capacitance (primary smoothing capacitance + parasitic capacitance or the like) of the primary side circuit of the AC-DC converter 30. The AC-DC converter 30 and the AC detection circuit (IC20, R1 to R4, D1, D2) are mounted on a common printed wiring board (power supply board) to constitute a DC power supply device.

As shown in FIG. 2, the AC detection IC 20 includes a first comparator CMP1 having a hysteresis characteristic in which an input voltage Vin is applied to an inverting input terminal, and a switch MOSFET Q1 having a gate terminal connected to the output terminal of the comparator CMP1. And a constant current source I1 connected between the MOSFET Q1 and the power supply voltage terminal VDD, and a capacitor C1 connected between a coupling node N1 of Q1 and I1 and a ground point. The constant current source I1 charges the capacitor C1 with a constant current while Q1 is off. As a result, the potential V1 of the node N1 gradually rises, and when Q1 is turned on, the charge of the capacitor C1 is discharged and the potential V1 is rapidly lowered to generate a sawtooth. Therefore, the switch MOSFET Q1, the constant current source I1, and the capacitor C1 constitute a waveform generation circuit that performs a charge / discharge operation according to a pulse to generate a predetermined signal waveform.

  Further, the AC detection IC 20 includes a second comparator CMP2 having a hysteresis characteristic in which the potential V1 is applied to the non-inverting input terminal, an open drain output MOSFET Q2 having a gate terminal connected to the output terminal of the comparator CMP2, A constant current source I2, a diode D3, and voltage dividing resistors R5 and R6 that generate a reference voltage Vref1 applied to the non-inverting input terminal of the first comparator CMP1 and a reference voltage Vref2 applied to the inverting input terminal of the second comparator CMP2. The drain terminal of Q2 is connected to the output terminal OUT. Although not particularly limited, in this embodiment, the reference voltage Vref1 is generated by dividing the reference voltage Vref2 by resistors R5 and R6.

The first comparator CMP1 compares the input voltage Vin with the reference voltage Vref1, and when the input voltage Vin becomes higher than Vref1, the output falls to a low level to turn off the MOSFET Q1, and when Vin becomes lower than Vref1, the output becomes high. It operates to rise to the level and turn on Q1. When Q1 is turned on, the potential V1 of the node N1 changes to the ground potential because the charge of the capacitor C1 connected to the coupling node N1 between Q1 and I1 is extracted. The second comparator CMP2 compares the potential V1 of the node N1 with the reference voltage Vref2, and operates so that the output falls to a low level when V1 becomes higher than Vref2. Accordingly, the first comparator CMP1 functions as a pulse generation circuit that detects an AC waveform of the input voltage from the AC power source and generates a pulse. The capacitor C1 may be configured to be built in and connected to the IC chip.

  FIG. 3 shows an operation timing chart of the AC detection circuit of FIG. (A) is the AC input voltage, (B) is the voltage Vin after full-wave rectification input to the IC 20, (C) is the output of the first comparator CMP1, and (D) is the potential of the coupling node N1 between Q1 and I1. V1 and (E) are the output Vout of the IC (the same as the output of the second comparator CMP2).

  In the AC detection circuit of this embodiment, the first comparator CMP1 continues to detect the AC waveform and output a pulse even if the AC voltage drops somewhat as in the period T1 in FIG. The charge is periodically reset, the potential V1 of the node N1 does not become higher than Vref2, and the output Vout remains at the high level. On the other hand, when the AC waveform disappears as in the period T2, the first comparator CMP1 does not output a pulse, and the charge of the capacitor C1 is not reset. Therefore, V1 becomes higher than Vref2, and the output Vout changes to a low level, so that the interruption of the AC power supply can be notified to a CPU (microcomputer or microprocessor).

  4 and 5 show a second embodiment of the AC detection IC 20.

  In this embodiment, in addition to the pulse detection circuit 21 having the configuration shown in FIG. 2 in the AC detection IC 20, the low voltage detection circuit 22, the output of the pulse detection circuit 21, and the low voltage detection circuit 22. The OR gate circuit 23 is added to take the logical sum of the outputs and supply it to the gate terminal of the output MOSFET Q2. Although not particularly limited, external terminals P1 and P2 are provided in the IC 20 so that the capacitor C1 of the pulse detection circuit 21 and the capacitor C2 of the low voltage detection circuit 22 are connected as external elements. . The capacitor C2 is for smoothing the AC voltage subjected to both-wave rectification.

  The low voltage detection circuit 22 includes a buffer amplifier AMP1 to which an input voltage Vin is applied to a non-inverting input terminal, a MOSFET Q3 having a gate terminal connected to an output terminal of the amplifier AMP1, a MOSFET Q3, and a ground point GND. And a capacitive element C2 connected between a coupling node N2 of Q3 and R7 and a ground point.

  Further, the low voltage detection circuit 22 includes a third comparator CMP3 having a hysteresis characteristic in which the potential V2 of the coupling node N2 is applied to the inverting input terminal. The reference voltage Vref2 is applied to the non-inverting input terminal of the comparator CMP3 and output. The signal is input to the OR gate circuit 23, and the output of the OR gate circuit 23 is applied to the gate terminal of the open drain output MOSFET Q2.

  The buffer amplifier AMP1 operates the MOSFET Q3 so that the potential V3 matches the input voltage Vin by feeding back the potential V3 of the coupling node N3 of Q3 and R7 to the inverting input terminal. Thus, the inverting input terminal of the buffer amplifier AMP1 operates so that the same voltage as the input voltage Vin is input. At this time, since the capacitor C2 is connected to the node N2 connected to the node N3, a smoothed voltage V2 as shown in FIG. 6C appears at the node N2. This voltage V2 is input to the inverting input terminal of the third comparator CMP3.

  Since the low voltage detection circuit 22 compares the voltage V3 and the reference voltage Vref2 by the third comparator CMP3, the low voltage detection circuit 22 detects a state in which the AC voltage has slightly decreased as in the period T1 in FIG. As shown in FIG. 6F, the output Vout can be changed to a low level. In the AC detection circuit of the second embodiment, as shown in the period T2 in FIG. 6B, when the AC voltage stops changing, the pulse detection circuit 21 detects the change and changes the output Vout to the low level. Therefore, it is possible to detect both a decrease and interruption of the AC voltage.

  If only the low voltage detection circuit 22 is provided, the buffer amplifier AMP1 is not provided and the same operation is possible only by the third comparator CMP3 and the capacitor C2. However, since the pulse detection circuit 21 is provided, the buffer amplifier AMP1 is omitted. Then, the input of the pulse detection circuit 21 is also averaged, so that the pulse cannot be detected. Therefore, the buffer amplifier AMP1 is indispensable in this embodiment. Further, in the circuit of FIG. 5, the nodes N2 and N3 are directly connected, but a low-pass filter may be configured by connecting them via a resistor and the resistor and the capacitor C2.

  Further, in the AC detection IC 20 of FIG. 5, the capacitors C1 and C2 are configured to be connected as external elements. However, these capacitors are elements formed on the same semiconductor chip as the comparator and the amplifier. May be used.

  FIG. 6 shows the timing when both the pulse detection circuit 21 and the low voltage detection circuit 22 are in operation. For inputting a signal for selecting one of the detection circuits from the outside. A terminal or a register may be provided so as to selectively operate, or a fuse element may be provided so that one of the detection circuits can be set not to operate. Note that the AC-DC converter can supply energy to the secondary side to some extent even during the period in which the AC voltage is reduced, such as T1 in FIG. 6, so that only the low-voltage detection circuit 22 can stop its operation. It is also possible.

  In the AC detection IC of FIG. 5, since terminals P1 and P2 for connecting the capacitors C1 and C2 as external elements are provided, the terminal P1 is connected to the ground potential by using a pull-down resistor. The detection circuit 21 can be set not to operate. In addition, the low voltage detection circuit 22 can be set not to operate by connecting the terminal P2 to the power supply voltage using a pull-up resistor.

  FIG. 7 shows a modification of the AC detection circuit. In this modification, half-wave rectification is performed by omitting the resistor R4 and the diode D2 connected to the power supply line L2. Even in this way, it is possible to detect a decrease and interruption of the AC voltage. The configuration of the AC detection IC 20 may be the same as that shown in FIG. Similar to FIG. 7, a modification using the half-wave rectification type and the same AC detection IC 20 as that of FIG. 2 is also conceivable.

  Although the invention made by the present inventor has been specifically described based on the embodiment, the present invention is not limited to the above embodiment. For example, in the AC detection IC of FIGS. 2 and 5, a circuit for generating the reference voltage Vref2 is provided in the IC, but a terminal for receiving the reference voltage Vref2 generated outside the chip is provided. May be.

  In the AC detection IC of the embodiment, the constant current source I1 charges the capacitor C1 and discharges C1 when the switch element Q1 is turned on to generate a waveform signal (sawtooth wave) input to the comparator CMP2. However, the capacitor C1 may be rapidly charged when the switch element Q1 is turned on, and the charge of the capacitor C1 may be gradually discharged by the constant current source I1 to generate an inverted triangular waveform signal.

  In the above description, the example in which the present invention is applied to a DC power supply device including an AC-DC converter has been described. However, the present invention is not limited to the present invention, and is widely used for devices that want to detect a decrease in AC voltage. Can do.

FIG. 1 is a schematic configuration diagram showing a first embodiment of an AC detection circuit to which the present invention is applied. FIG. 2 is a circuit diagram showing a specific example of an AC detection IC constituting the AC detection circuit of FIG. FIG. 3 is a timing chart showing the operation of the AC detection circuit of FIG. FIG. 4 is a schematic configuration diagram showing a second embodiment of an AC detection circuit to which the present invention is applied. FIG. 5 is a circuit diagram showing a specific example of an AC detection IC constituting the AC detection circuit of FIG. FIG. 6 is a timing chart showing the operation of the AC detection circuit of FIG. FIG. 7 is a schematic configuration diagram showing a modification of the AC detection circuit to which the present invention is applied. FIG. 8 is a schematic configuration diagram showing an example of a conventional AC detection circuit.

Explanation of symbols

10 plug 20 AC detection IC
21 Pulse detection circuit 22 Low voltage detection circuit 30 AC-DC converter D1, D2 Rectifier (rectifier diode)
CMP1 to CMP3 comparator AMP1 buffer amplifier I1, I2 constant current source

Claims (6)

A pulse generation circuit that detects an AC waveform of an input voltage from an AC power supply and generates a pulse; a waveform generation circuit that generates a predetermined signal waveform by performing a charge / discharge operation according to the pulse; e Bei a reference voltage and a first comparator for outputting a signal indicating the presence or absence of a pulse by comparing,
The pulse generation circuit includes a second comparator that outputs a pulse signal by comparing a voltage obtained by rectifying an AC input voltage from an AC power supply with a rectifying element and a predetermined reference voltage,
The waveform generation circuit includes a constant current source for supplying a constant current, a capacitor element that can be charged by a current from the constant current source, and ON / OFF control by the output of the second comparator to charge / discharge the capacitor element. An AC detection circuit comprising switch means that can be controlled . The pulse generation circuit, the waveform generation circuit, and the first comparator are formed as a semiconductor integrated circuit on one semiconductor chip, the capacitor element is an external element, and the semiconductor integrated circuit includes the second comparator. The AC detection circuit according to claim 1, wherein an external terminal connected to one of the input terminals is provided, and the capacitive element can be connected to the external terminal. A pulse detection circuit that detects an alternating current waveform of an input voltage from an AC power supply to generate a pulse, determines that the AC power supply is shut off when the pulse disappears, and changes an output;
A low voltage detection circuit that monitors the AC voltage and changes the output when the AC voltage falls below a predetermined level;
And is configured to output a logical sum of the output of the pulse detection circuit and the output of the low voltage detection circuit ,
The pulse detection circuit includes a pulse generation circuit that detects an AC waveform of an input voltage from an AC power source and generates a pulse; a waveform generation circuit that generates a predetermined signal waveform by performing a charge / discharge operation according to the pulse; A first comparator that compares the generated waveform with a predetermined reference voltage and outputs a signal indicating the presence or absence of a pulse ;
The pulse generation circuit includes a second comparator that outputs a pulse signal by comparing a voltage obtained by rectifying an AC input voltage from an AC power supply with a rectifying element and a predetermined reference voltage,
The waveform generation circuit includes a constant current source for supplying a constant current, a capacitive element that can be charged by a current from the constant current source, and an ON / OFF control performed by an output of the second comparator to charge / discharge the capacitive element And an AC detection circuit comprising switch means capable of controlling The AC detection circuit according to claim 3 , wherein the operation of at least the low voltage detection circuit of the pulse detection circuit and the low voltage detection circuit can be stopped by an external setting . The low-voltage detection circuit includes a buffer amplifier for the voltage rectified by the AC input voltage rectifying device from the AC power source as input, and the capacitor for smoothing an input waveform connected to the output side of the buffer amplifier, The AC detection circuit according to claim 4, further comprising a third comparator that compares a voltage smoothed by the capacitive element with a predetermined reference voltage. An AC detection circuit according to any one of claims 1 to 5 , and an AC-DC converter having a transformer and receiving an alternating current input voltage from an AC power source and converting the alternating current voltage into a direct current voltage and outputting the same. Is provided on the primary side of the transformer.

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