Ac input detection circuit

Abstract

To attain reduction in standby power of an AC input detection circuit.SOLUTION: Rectification elements (diodes D1 and D2) rectify AC input, a resistive element R1 for voltage division and current limitation steps down output voltages from the rectification elements, and a capacitive element (capacitor C1) is charged with an output current from the resistive element R1. A detection signal generation element generates a detection signal indicating that a voltage level of the AC input shifts from a non-detection level to a detection level in response to an inversion of a switching element to a conductive state. A shunt regulator is adopted as the switching element.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to an AC input detection circuit that detects the presence or absence of an AC input to a primary side circuit of an AC / DC converter in a switching power supply circuit. [Background technology]

[0002] FIG. 2 is a circuit diagram showing the configuration of a conventional AC input detection circuit.

[0003] In this AC input detection circuit, the AC input voltage Vin1 applied between AC input terminal T1p and ground terminal T1n is full-wave rectified by diodes D1 and D2 (rectifier elements). That is, during the positive half-wave input period, diode D1 performs half-wave rectification, and during the negative half-wave input period, diode D2 performs half-wave rectification. A DC voltage (rectified voltage) Vin2, which is a repeating mountain-shaped pulsating current every half cycle, appears at the cathode connection point P1 common to both diodes D1 and D2. A DC current caused by this pulsating DC voltage Vin2 flows through a voltage divider circuit VD, which is composed of a series circuit of a resistor element R1 for voltage division and current limiting and a capacitor C1 for voltage division and smoothing. Capacitor C1 is charged to a voltage level Vcap corresponding to the AC input voltage Vin1.

[0004] Next, the AC input voltage Vin1 is set to the predetermined design voltage (V S ) or less (i.e., a voltage level that does not reach the voltage required for normal operation of the equipment), and S ) will be explained in order.

[0005] (1) AC input voltage Vin1 is the design voltage (V S ) below the non-detection level The charging voltage Vcap of the capacitor C1 is equal to the design voltage (V S ) corresponding to the specified voltage (V K ) or less, the base-emitter voltage (V BE) is the forward voltage (V F ) less than ((V F ) does not exceed the design voltage (V S ) and below the non-detectable level.

[0006] (2) AC input voltage Vin1 is the design voltage (V S ) detection level exceeds The charging voltage Vcap of the capacitor C1 is the design voltage (V S ) corresponding to the specified value (V K ), the charging voltage Vcap causes the current output from the capacitor C1 to be supplied to the base of the transistor Q1 via the resistor R2. In this case, the voltage across the resistor R3, i.e., the base-emitter voltage (V BE ) is the forward voltage (V F ), the transistor Q1 turns on and becomes conductive. As a result, a potential difference occurs between both ends of the resistor element R4, the light-emitting diode LE of the photocoupler PC1 operates, and the phototransistor PT becomes conductive in conjunction with this. This conduction of the phototransistor PT operates the detection circuit section (not shown), and the voltage level of the AC input becomes the detection level (design voltage (V S ) and above) to indicate that an AC input of the desired voltage level is being supplied. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Japanese Patent Application Laid-Open No. 2014-155266 Summary of the Invention [Problem to be solved by the invention]

[0008] In the prior art, a bipolar transistor Q1 is used as the AC input detection element to detect whether the AC input voltage Vin1 is at the detection level. However, because this bipolar transistor Q1 is used, its drive must depend on a large current supplied from the high-voltage circuit (AC input side).

[0009] Specifically, to turn on transistor Q1, its base-emitter voltage (V BE ) to the forward voltage (V F ), and to achieve this, a large current must be supplied to the base of transistor Q1 from the high-voltage circuit (AC input side) via resistor element R1, which divides the voltage and limits the current.

[0010] As a result, power loss increases, and the standby power consumption of the AC input detection circuit increases.

[0011] The present invention aims to solve the problems observed in the conventional example. [Means for solving the problem]

[0012] The present invention solves the above problems by taking the following measures.

[0013] The AC input detection circuit according to the present invention comprises: a rectifying element for rectifying the AC input voltage; a voltage dividing resistor element that reduces the output voltage from the rectifier element; a voltage dividing capacitance element that charges an output current from the voltage dividing resistance element; a shunt regulator that is non-conductive when the output current of the voltage-dividing capacitance element is equal to or less than a predetermined value, and that is conductive when the output current of the voltage-dividing capacitance element exceeds the predetermined value; and a detection signal generating element that generates a detection signal indicating that the voltage level of the AC input has transitioned from a non-detection level to a detection level in response to the shunt regulator being inverted to a conductive state.

[0014] According to the above-described configuration of the present invention, the following effects are exhibited.

[0015] When the AC input voltage level transitions from the non-detection level to the detection level, the voltage between both terminals of the voltage-dividing capacitance element exceeds the specified value, the current flowing into the reference terminal of the shunt regulator increases, the shunt regulator becomes conductive, and the detection signal generating element operates in conjunction with this.

[0016] A shunt regulator is a switching element that supplies a sufficiently small current to its reference terminal when transitioning from a non-conducting state to a conducting state. In the present invention, a shunt regulator that supplies a sufficiently small current for switching control is used as a switching element to replace the conventional bipolar transistor. This reduces power loss in the voltage-dividing resistor element in a voltage-dividing circuit consisting of a resistor element and a capacitor element. As a result, standby power can be reduced.

[0017] Preferably, a rapid discharge line for rapidly discharging the charge of the voltage-dividing capacitance element is provided between the reference terminal of the shunt regulator and the high-side terminal of the detection signal generating element, and a diode for preventing backflow is inserted in the rapid discharge line. This configuration provides the following advantageous effects. Although a larger voltage-dividing resistance element requires more time for discharging from the voltage-dividing capacitance element, rapid discharge can be achieved via the rapid discharge line when the AC input is off. [Effects of the Invention]

[0018] According to the present invention, the standby power consumption of the AC input detection circuit can be reduced. [Brief explanation of the drawings]

[0019] [Figure 1] FIG. 1 is a circuit diagram showing the configuration of an AC input detection circuit according to an embodiment of the present invention; [Figure 2]Circuit diagram showing the configuration of a conventional AC input detection circuit DETAILED DESCRIPTION OF THE INVENTION

[0020] The AC input detection circuit of the present invention having the above configuration will now be described in detail with reference to specific examples.

[0021] In FIG. 1 showing the configuration of an AC input detection circuit in an embodiment of the present invention, R1, R2, R3, R4, R5, and R6 are resistive elements, C1 is a capacitor for dividing and smoothing voltage, D1 and D2 are rectifying diodes (rectifying elements), D3 is a diode for preventing backflow, ZD1 is a Zener diode, IC1 is a shunt regulator, PC1 is a photocoupler consisting of a light-emitting diode LE and a phototransistor PT, HL is a high-side line, LL is a low-side line, VL is a voltage detection line, and KL is a rapid discharge line.

[0022] The cathodes of diode D1 (rectifier element), whose anode is connected to input terminal T1p on the high-potential side of AC, and diode D2 (rectifier element), whose anode is connected to input terminal T1n on the low-potential side, are commonly connected at connection point P1. A series circuit, in which a voltage-dividing and current-limiting resistor element R1 and a voltage-dividing and smoothing capacitor C1 (capacitor element) are connected at voltage-divider connection point P2, is connected between the cathode common connection point P1 and the low-side line LL, and the resistor element R1 and capacitor C1 constitute a voltage-divider circuit VD.

[0023] A Zener diode ZD1 is connected between both terminals of the voltage dividing and smoothing capacitor C1. The Zener diode ZD1 has its anode connected to the low-side line LL and its cathode connected to the voltage detection line VL (on the voltage dividing connection point P2 side). The Zener diode ZD1 is used for protection against overvoltage application.

[0024] In this embodiment, a shunt regulator IC1 is used as the AC input detection element instead of the conventional bipolar transistor Q1.

[0025] A series circuit of resistors R5, R4, and shunt regulator IC1 is connected between the high-side line HL and the low-side line LL. One end of resistor R5 is connected to the high-side line HL, and the other end is connected to one end of resistor R4, the other end of which is connected to the cathode of shunt regulator IC1. The anode of shunt regulator IC1 is connected to the low-side line LL, and the reference terminal RT is connected to the voltage detection line VL (resistance division point P3 side).

[0026] The resistor R3 is connected between a connection point P3 between the resistor R2 and the reference terminal RT and the low-side line LL.

[0027] The anode of the light-emitting diode LE in the photocoupler PC1 is connected to the junction of the resistor elements R5 and R4, and the cathode is connected to the junction of the resistor element R4 and the cathode of the shunt regulator IC1. The collector of the phototransistor PT in the photocoupler PC1 is connected to the high-side line HL via the resistor element R6, and the emitter is connected to the low-side line LL.

[0028] Furthermore, a rapid discharge line KL for rapidly discharging the charge of capacitor C1 is provided between the high-side line HL and a connection point (resistance division point) P3 of resistor elements R2 and R3 on the voltage detection line VL, and a backflow prevention diode D3 is inserted in the rapid discharge line KL. The backflow prevention diode D3 has an anode connected to a portion of the voltage detection line VL between resistor element R2 and reference terminal RT and a cathode connected to the high-side line HL. The rapid discharge line KL with the backflow prevention diode D3 inserted therein is provided for rapidly discharging the charge of voltage dividing and smoothing capacitor C1.

[0029] Next, the operation of the AC input detection circuit configured as above will be described.

[0030] The AC input voltage Vin1 applied between the AC input terminal T1p and the ground terminal T1n is full-wave rectified by diodes D1 and D2, and a rectified voltage Vin2 with a mountain-shaped pulsating current appears at the common cathode connection point P1 of both diodes D1 and D2 every half cycle. The rectified voltage Vin2 is significantly dropped by resistor R1, charging capacitor C1 with a relatively small current, and a voltage that smooths the rectified voltage Vin2 appears at voltage-divider connection point P2 as the charging voltage Vcap of capacitor C1.

[0031] (1) AC input voltage Vin1 is the design voltage (V S ) below the non-detection level The current output from the voltage dividing and smoothing capacitor C1 due to the charging voltage Vcap is supplied to the reference terminal RT of the shunt regulator IC1 via the resistor element R2 (flows to the voltage detection line VL). However, when the AC input voltage Vin1 is equal to or greater than the design voltage (V S ), the current output from capacitor C1 and supplied to reference terminal RT is small (the voltage applied to reference terminal RT is less than the reference voltage), and shunt regulator IC1 remains non-conductive. As a result, light-emitting diode LE and phototransistor PT in photocoupler PC1 do not operate, and no detection signal is generated to indicate that the level of AC input voltage Vin1 has transitioned from the non-detection level to the detection level.

[0032] (2) AC input voltage Vin1 is the design voltage (V S ) is at a detection level that exceeds The charging voltage Vcap of the voltage dividing and smoothing capacitor C1 is the above-mentioned design voltage (V S ) corresponding to the specified value (V K), the current output from capacitor C1 and flowing into the reference terminal RT of shunt regulator IC1 increases (the voltage applied to reference terminal RT becomes equal to or greater than the reference voltage), causing the shunt regulator IC1, which had been in a non-conductive state until then, to reverse and turn on, switching it to a conductive state. As a result, a potential difference occurs between both ends of resistor element R4, which activates the light-emitting diode LE of photocoupler PC1, which in turn activates phototransistor PT. This conduction of phototransistor PT activates the detection circuit (not shown), causing the AC input voltage level to exceed the detection level (design voltage (V S ) or greater), a detection signal is generated indicating that an AC input at the desired voltage level is being supplied.

[0033] In this case, the current supplied from capacitor C1 to reference terminal RT via voltage detection line VL to turn on shunt regulator IC1 can be sufficiently small, suppressing power loss and reducing the standby power of the AC input detection circuit.

[0034] As an example, the present embodiment will be compared with the conventional example, with the same conditions: R1: 100 [kΩ], C1: 47 [μF], and Zener voltage: 6.2 [V].

[0035] In the conventional example, when the resistance element R2 is configured to 1 kΩ (an example of low impedance), a bipolar transistor Q1 is used as the AC input detection element, and therefore a large current of 44 μA is required as the drive current passing through the resistance element R2.

[0036] In contrast to this, in this embodiment, since a shunt regulator IC1 is used as the AC input detection element, a high impedance resistor element R2 having a resistance value of 47 kΩ (as an example) may be used, in which case the drive current passing through resistor element R2 can be as weak as 2 μA (reduced to about 1 / 20).

[0037] On the other hand, while the drive current can be reduced, it takes longer to discharge capacitor C1. Therefore, a quick discharge line KL is provided to quickly discharge the charge in capacitor C1. This allows capacitor C1 to be quickly discharged when the AC input is turned off. A backflow prevention diode D3 is inserted in the quick discharge line KL to prevent charge from flowing from the high side line HL through the quick discharge line KL into the voltage detection line VL. [Industrial Applicability]

[0038] The present invention can provide an AC input detection circuit that can reduce standby power consumption. [Explanation of symbols]

[0039] D1, D2 Diode (rectifier) D3 Reverse current prevention diode R1 Resistor element for voltage division and current limiting C1: Voltage dividing and smoothing capacitor (capacitance element) ZD1 Zener diode IC1 Shunt regulator PC1 Photocoupler (detection signal generating element) RT Reference Terminal KL Rapid Discharge Line

Claims

1. a rectifying element for rectifying the AC input voltage; a voltage dividing resistor element that reduces the output voltage from the rectifier element; a voltage dividing capacitance element that charges an output current from the voltage dividing resistance element; a shunt regulator that is non-conductive when the output current of the voltage-dividing capacitance element is equal to or less than a predetermined value, and that is conductive when the output current of the voltage-dividing capacitance element exceeds the predetermined value; and a detection signal generating element that generates a detection signal indicating that the voltage level of the AC input has transitioned from a non-detection level to a detection level in response to the shunt regulator reversing to a conductive state.

2. 2. The AC input detection circuit according to claim 1, wherein a rapid discharge line for rapidly discharging the charge of the voltage dividing capacitance element is provided between the reference terminal of the shunt regulator and the high-side terminal of the detection signal generating element, and a diode for preventing backflow is inserted in the rapid discharge line.

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