JPH11146642A - Switching power supply - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a backup switching power supply capable of definitely identifying power failure and recovery. SOLUTION: An input circuit 1 converts an alternating current supply voltage Ein into a direct current voltage Vin, and outputs it. A first converter 3 switches a direct current voltage Vin supplied from the input circuit 1, and converts a switch output into a direct current voltage. A second converter 5 makes good use of energy supplied from an storage element 52 to supply a loud L with power during power failure, and makes good use of power supplied from an alternating current power supply e to charge the storage element 52 when power supply is restored. A control circuit 6 detects any failure of the alternating/current power supply e through the terminal voltage Vin of a smoothing capacitor 12, and recovery of power supply through the alternating current supply voltage Ein. The first converter 3 and the second converter 5 are controlled according to the detection signals.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to a switching power supply, and more particularly, to a switching power supply having a function of backing up by a storage element such as a battery.

[0002]

2. Description of the Related Art Various types of switching power supplies have been conventionally known. For example, Japanese Patent Application Laid-Open No. 9-56085 discloses that a charging / discharging circuit having a backup element composed of a battery is connected to a secondary side of a conversion transformer provided in a first converter, and a secondary winding of the conversion transformer is connected to the secondary winding. When the backup element is charged using the induced voltage generated and the supply of the AC power supply is stopped, the energy stored in the backup element is converted by the converter circuit provided in the charging circuit without passing through the conversion transformer. A power supply device that supplies converted power to a load is disclosed.

Japanese Patent Application Laid-Open No. Hei 8-275521 discloses a method in which a constant current circuit is connected to a secondary winding of a conversion transformer constituting a first converter, a battery is charged by the constant current circuit, and the charging voltage of the battery is reduced during a power failure. , Supply to the inverter,
A power supply device for supplying power from an inverter to a load is disclosed.

Japanese Unexamined Patent Publication (Kokai) No. 64-8836 discloses an uninterruptible power supply device in which a storage battery is connected to the output side of a rectifier circuit for rectifying an AC power supply, and the storage battery is used as a power supply source during a power failure.

[0005]

By the way, in this type of switching power supply, in the backup operation, a power failure of the AC power supply and a power recovery must be detected. 2. Description of the Related Art Conventionally, as a method of detecting a power failure and a restoration of an AC power supply, two methods are known: a method of detecting from a power supply voltage of an AC power supply and a method of detecting from a rise and fall of a terminal voltage of an input smoothing capacitor. The former is suitable for detecting a power failure and a power recovery when a plurality of devices are operated by one input system, because the power failure and the power recovery can be detected under a certain condition regardless of the load state. The latter is suitable for a case where, even if a power failure occurs, the operation of the device is continued without causing a power failure within a range in which the device can operate normally. For a switching power supply of a type that performs backup using a battery, the latter power failure and power recovery detection method is suitable.

However, in a battery backup type switching power supply, depending on the circuit system, power may be supplied to a load at the time of backup operation, and at the same time, an input smoothing capacitor may be charged. In such a case, the terminal voltage of the input smoothing capacitor rises despite the power failure. For this reason, in a configuration in which the power failure and the power recovery are detected from the terminal voltage of the input smoothing capacitor, there is a risk that the power failure may be erroneously recognized despite the power failure.

An object of the present invention is to provide a backup type switching power supply that can clearly identify a power failure and a power recovery.

[0008]

To solve the above-mentioned problems, a switching power supply according to the present invention includes an input circuit, a first converter, a second converter, and a control circuit. The input circuit includes a rectifier circuit and a smoothing capacitor, rectifies and smoothes an AC power supply voltage supplied to an AC input terminal, converts the AC power supply voltage into a DC voltage, and outputs the DC voltage.

The first converter switches a DC voltage supplied from the input circuit, converts a switching output into a DC voltage, and outputs the DC voltage.

[0010] The second converter supplies power to the load in place of the first converter by using energy supplied from a power storage element when the AC power supply fails, and the AC power supply When power is restored, the storage element is charged using the energy of the AC power supply.

The control circuit detects a power failure of the AC power supply from a terminal voltage of the smoothing capacitor, detects a power recovery from the AC power supply voltage, and detects the first converter and the second converter based on the detection signal. The control circuit detects the AC power supply voltage and supplies a control signal based on the detection signal to the first converter and the second converter in the steady operation in which the AC power for controlling the converter is supplied. At this time, a control operation is applied from the control circuit to the first converter and the second converter such that the first converter supplies power to the load and the second converter enters the charging mode.

Based on the control operation, the first converter switches the DC voltage supplied from the input circuit, converts the switching output into a DC voltage, and outputs the DC voltage. This DC output voltage is supplied to the load. In the second converter, the energy storage element is charged using the energy of the AC power supply.

Next, when the AC power supply fails, the terminal voltage of the smoothing capacitor included in the input circuit decreases. The control circuit detects a power failure of the AC power supply from the terminal voltage of the smoothing capacitor, and controls the first converter and the second converter based on the detection signal. At this time, a control operation is performed on the second converter from the control circuit such that the second converter supplies power to the load instead of the first converter. In the second converter, power is supplied to the load in place of the first converter using the energy supplied from the power storage element when the AC power supply is interrupted.

Next, when the AC power supply is restored, the control circuit detects the restoration from the AC power supply voltage, and supplies a control signal based on the detection signal to the first converter and the second converter. Control. At this time, the first
A control operation is performed so that the first converter supplies power to the load and the second converter enters the charging mode.

As described above, since the control circuit detects a power failure of the AC power supply from the terminal voltage of the smoothing capacitor and detects a power recovery from the AC power supply voltage, the smoothing capacitor constituting the input circuit is charged during the backup operation. Thus, even if the terminal voltage of the smoothing capacitor rises, a rise in the terminal voltage of the smoothing capacitor caused by the backup operation is not mistaken for power recovery. It is determined that the power is restored when the AC power supply voltage becomes normal.

[0016]

FIG. 1 is an electric circuit diagram of a switching power supply according to the present invention. As shown, the switching power supply according to the present invention includes an input circuit 1, a first converter 3, a second converter 5, and a control circuit 6.

The input circuit 1 converts an AC power supply voltage Ein supplied to the AC input terminals 71 and 72 into a DC voltage Vin and outputs it. The illustrated input circuit 1 includes a rectifier circuit 11 composed of a diode bridge or the like and a smoothing capacitor 12.

The first converter 3 includes a conversion transformer 32
, A switch element 33, and an output circuit 4.
The conversion transformer 32 includes a first winding 321 and a second winding 322. The first winding 321 constitutes a primary winding,
A DC voltage Vin is supplied from the input circuit 1.

The switching element 33 switches the DC voltage Vin supplied through the first winding 321.
The switch element 33 is typically constituted by a field effect transistor (FET), but may be another three-terminal switch element such as a bipolar transistor. The main electrode circuit of the switch element 33 is connected in series to the first winding 321 of the conversion transformer 32.

The output circuit 4 is connected to the second winding 322 and converts a switch output appearing on the second winding 322 into a DC voltage. The illustrated output circuit 4 constitutes a so-called forward converter circuit, and includes a switch element 33.
And the choke coil 4 is turned on when the switch element 33 is off.
3 includes a rectifier circuit composed of a diode 42 that emits the energy stored in 3, and an output smoothing capacitor 44. However, it is needless to say that the present invention is not limited to such a circuit configuration.

The second converter 5 includes a switching circuit 51,
And a storage element 52. The switching circuit 51 is configured such that the second converter 5 becomes the charging circuit CH or the discharging circuit D
H is switched. When switching to the charging circuit CH is performed, the power storage element 52 is charged using the electric power supplied from the AC power supply e. When switching to the discharge circuit DH is performed, power is supplied to the load L using the energy supplied from the storage element 52. The storage element 52 is
Typically, it is composed of a secondary battery. Or you may comprise with a capacitor.

In the embodiment, the switching circuit 51 is constituted by a switching element. One end of this switch element is connected to one end of power storage element 52, and the other end of the switch element is connected to one end of first winding 231. If the AC power supply e is normal or the power is restored, the switching circuit 5
1 is turned on. This allows
A charging circuit CH is formed. When the AC power supply e fails,
The switching elements of the switching circuit 51 are turned on and off. At this time, the main switch element 33 is kept conductive. The switching operation of the switch elements constituting the switching circuit 51 causes the conversion transformer 3
The second first winding 321 is excited, a switching output is transmitted from the first winding 321 of the conversion transformer 32 to the second winding 322, and converted into a DC voltage by the output circuit 4. This DC voltage is supplied from the output terminals 81 and 82 to the load L as the DC output voltage Vo.

The control circuit 6 detects a power failure of the AC power supply e from the terminal voltage Vin of the smoothing capacitor 12, and detects a power recovery from the AC power supply voltage Ein. Then, control signals S1 and S2 based on the detection signal are supplied to the first converter 3 and the second converter 5 for control. The illustrated control circuit 6 includes a rectifier circuit 61, comparators 62 and 63, reference voltage sources Vr1 and Vr2, a flip-flop 64, and a control unit 65. The rectifier circuit 61, the comparator 62 and the reference voltage source Vr1 are connected to an AC voltage E supplied from an AC power source e.
Monitor in and detect power outage. The rectifier circuit 61 is configured by a diode rectifier bridge circuit. The comparator 62 converts the rectified voltage supplied from the rectifier circuit 61 into a reference voltage source V
The power failure of the AC power supply e is detected by comparing the reference voltage with the reference voltage of r1.

The comparator 63 and the reference voltage source Vr2 detect the restoration of the AC power supply e. The comparator 63 compares the terminal voltage Vin of the smoothing capacitor 12 with a reference value supplied from the reference voltage source Vr2, and detects the restoration of the AC power supply e when the terminal voltage Vin reaches a certain level.

When a power failure detection signal is supplied from the comparator 62 to the reset terminal R, the flip-flop 64 supplies a signal S5 corresponding to the signal to the control unit 65 from the output terminal Q. When the power recovery detection signal of the AC power supply e is supplied from the comparator 63 to the set terminal S, a signal inverted from that in the case of the power failure detection is supplied to the control unit 65 from the output terminal Q. The control unit 65 controls the switch element 33 and the second converter 5 of the first converter 3 based on the power failure detection and power recovery detection signals S5 supplied from the flip-flop 64.

The control circuit 6 further includes a DC output voltage Vo
Alternatively, detection signals S3 and S4 of the output current I0 are input,
In this type of switching power supply, general output stabilization control and overcurrent protection are performed.

Further, in the embodiment, the diode 34 is provided in a circuit loop including the smoothing capacitor 1212 and the first winding 321 of the conversion transformer 32. Further, a resistor 35 is connected in parallel with the diode 34.

Next, the operation will be described. In the normal operation in which the AC power supply e is supplied, the control circuit 6 detects the AC power supply voltage Ein, and supplies control signals S1 and S2 based on the detection signal to the first converter 3 and the second converter 5. Control. At this time, control is applied from the control circuit 6 to the first converter 3 so that the first converter 3 supplies the load L with power determined by the current Io and the DC output voltage Vo. A control operation is performed on the second converter 5 so as to be in the charging mode.

First, the first converter 3 switches the DC voltage Vin supplied from the input circuit 1, converts a switching output into a DC voltage, and outputs the DC voltage. This DC output voltage Vo is supplied to the load L from the output terminals 81 and 82. In second converter 5, power storage element 52 is charged using the energy of AC power supply e.

Next, when the AC power supply e fails, the terminal voltage Vin of the smoothing capacitor 12 included in the input circuit 1 decreases. The control circuit 6 detects a power outage of the AC power supply e from the terminal voltage Vin of the smoothing capacitor 12, and supplies a control signal based on the detection signal to the first converter 3 and the second converter 5 to control.

At this time, a control operation is performed from the control circuit 6 to the second converter 5 such that the second converter 5 supplies electric power to the load L instead of the first converter 3. In the second converter 5, power is supplied to the load L in place of the first converter 3 by using the energy supplied from the power storage element 52 when the AC power supply e fails.

Next, when the AC power supply e is restored from the power failure, the control circuit 6 detects the restoration from the AC power supply voltage Ein, and outputs a control signal based on the detection signal to the first converter 3 and the second converter 3. Is supplied to the converter 5 for control. At this time, the first converter 3 applies a load L to the first converter 3 and the second converter 5 from the control circuit 6.
, And a control operation is performed so that the second converter 5 enters the charging mode.

Here, in the case of the embodiment, since the resistor 35 is provided, a circuit is configured to charge the smoothing capacitor 12 constituting the input circuit 1 through the resistor 35 during the backup operation. Vin
Rises. As described above, the control circuit 6 controls the AC power supply e.
Is detected from the terminal voltage Vin of the smoothing capacitor 12 and the power recovery is detected from the AC power supply voltage Ein.
Even if n rises, the rise of the terminal voltage Vin of the smoothing capacitor 12 due to the backup operation is not mistaken for power restoration. The power restoration is determined when the AC power supply voltage Ein becomes normal.

In the embodiment, the switching power supply according to the present invention includes a diode 34 in a circuit loop including the smoothing capacitor 12 and the first winding 321 of the conversion transformer 32.
Is provided.

Next, the operation of the diode 34 will be described. Assuming that the diode 34 is not provided, in the backup operation, when the energy supplied from the power storage element 52 is switched and supplied to the conversion transformer 32, the AC power input side at the preceding stage of the first converter 3 This causes a loss in that energy that becomes a load on the converter 5 and should be supplied to the original load L is consumed on the AC power supply input side.

At the start of the backup operation, a charging current flows through the smoothing capacitor 12 constituting the input circuit 1. At the start of the backup operation (at the time of a power failure), the terminal voltage of the smoothing capacitor 12 is low, and the charging current has a magnitude that cannot be ignored.

In a circuit loop including the smoothing capacitor 12 and the first winding 321 of the conversion transformer 32, a diode 3
When the power supply 4 is provided, the AC power supply does not become a load of the second converter 5 and the overcurrent limiting operation is not added.

Next, the operation of the resistor 35 connected in parallel with the diode 34 will be described. First, a case without the resistor 35 will be described. In this type of switching power supply, the output capacitance of the switch element 33 and the conversion transformer 3
Parasitic capacitance Cs due to the line capacitance 2 and the like occurs. Therefore, the parasitic capacitance Cs is charged by the flyback voltage when the switch element 33 is turned off, according to the resonance characteristics of the resonance circuit formed by the parasitic capacitance Cs and the inductance of the first winding 321 of the conversion transformer 32, The terminal voltage rises to the peak value of the flyback voltage. If the parasitic capacitance Cs is represented by the output capacitance of the switch element 33 for simplicity of description, the rise in the voltage between the terminals of the parasitic capacitance Cs causes the voltage V between the main electrodes of the switch element 33 to increase.
ds rises to the peak value of the flyback voltage.

In this case, a diode 34 is inserted as a means for preventing the unstable operation from occurring at the start of the backup operation, and the charging voltage appearing at the terminal of the parasitic capacitance Cs has the opposite polarity to the diode 34. In addition, there is no path for discharging the charge accumulated in the parasitic capacitance Cs. Therefore, the voltage across the parasitic capacitance Cs substantially maintains the peak value of the flyback voltage while the switch element 33 is off. Therefore, the switching element 33 is turned on in a state where the peak value of the high flyback voltage is applied, so that the switching loss increases. Further, switching noise also occurs.

On the other hand, if the resistor 35 as described above is provided, the electric charge accumulated in the parasitic capacitance Cs can be discharged through the resistor 35 during the OFF period of the switch element 33.
It is possible to reduce the voltage between the main electrodes when the switch element 33 is turned on, reduce the switching loss, and suppress the generation of noise.

FIG. 2 is an electric circuit diagram showing another embodiment of the switching power supply according to the present invention. In the figure, the same components as those shown in FIG. 1 are denoted by the same reference numerals. The second converter 5 shown in the embodiment includes a switching circuit 51, a third winding 323 provided in the conversion transformer 32, and a power storage element 52. The switching circuit 51 is configured such that the second converter 5
The switching is performed so as to be H or the discharge circuit DH. When switching to the charging circuit CH is performed, the electric storage element 52 is charged by the electric power supplied from the third winding 323. When switched to the discharge circuit DH, the energy supplied from the storage element 52 is switched and supplied to the third winding 323.

The switching circuit 51 is composed of one field effect transistor (FET). The FET constituting the switching circuit 51 is connected such that the main electrode circuit constituted by the drain and the source is in series with the circuit including the third winding 323 and the electric storage element 52. FET
Is driven, its main electrode circuit constitutes the discharge circuit DH, and when the FET is not driven, the source. The drain-to-drain diode 53 forms a charging circuit CH. When the main switch element 33 is turned on, the diode 53 has a directionality that is forward with respect to the induced voltage VF appearing in the third winding 323 of the illustrated polarity (shown by a black circle in the figure). ing. As the switching circuit 51, an FET
Other switch elements can be used. in this case,
What is necessary is just to connect the diode 53 in parallel with the switch element. However, when the switching circuit 51 is configured by an FET, as described above, the source of the FET. Since the charging circuit CH can be configured using the inter-drain diode 53, the circuit configuration can be simplified.

In the switching power supply shown in FIG.
First when power is supplied from AC power supply e
The operation of converter 3 is the same as that of the embodiment shown in FIG. 1, but the operation of second converter 5 is slightly different.

During a normal operation, the second converter 5 is switched by the switching circuit 51 so as to be the charging circuit CH. When switching to charging circuit CH is performed, power storage element 52 is charged by electric power supplied from third winding 323 of conversion transformer 32. Therefore, during the normal operation, the switching operation of the first converter 3
The storage element 52 is charged by the voltage induced in the third winding 323 of the conversion transformer 32. In the circuit configuration shown in the embodiment, when the main switch element 33 is turned on, the diode 53 is configured to have a forward polarity with respect to an induced voltage appearing in the third winding 323 having the illustrated polarity (shown by a black circle in the figure). Since the power storage device 52 is oriented so as to be in the same direction, charging of the power storage device 52 through the diode 53 is performed during the ON period of the main switch device 33.

Next, the rectifier circuit 61
When the voltage is detected by the comparator 62 and the reference voltage source Vr1, a control signal S2 based on the power failure detection signal is supplied from the control circuit 6 to the second converter 5, and the second converter 5 switches to the discharge circuit DH. Can be When the mode is switched to the discharge mode, power storage element 52 becomes a power supply source. Second converter 5 switches the energy supplied from power storage element 52 and supplies the switching energy to third winding 323. The third winding 323 is a winding of the conversion transformer 32 and is inductively coupled to the second winding 322 of the conversion transformer 32, and thus is obtained by switching the energy supplied from the power storage element 52. When the current excites the winding of the third winding 323, the energy is transmitted from the third winding 323 to the second winding 322. Since the output circuit 4 is connected to the second winding 322 of the conversion transformer 32, the switching output of the second converter 5 appearing in the second winding 322 is converted by the output circuit 4 into a DC output voltage Vo. , Load L.

As is clear from the above description, in the case of the embodiment shown in FIG. 2, most of the second converter 5 is a component that should be provided in the switching power supply, that is, the conversion transformer. Since the energy of the storage element 52 is supplied to the load L by sharing the output circuit 32 and the output circuit 4, the number of components can be reduced and the size can be reduced.

Further, the backup operation by the second converter 5 can be easily realized by selecting the switch element constituting the switching circuit 51 and the main switch element 33.

FIG. 3 is an electric circuit diagram showing still another embodiment of the switching power supply according to the present invention. In the figure, the same components as those shown in FIGS. 1 and 2 are denoted by the same reference numerals. In this embodiment, the control circuit 6
Has a function of operating the first converter after a certain period of time has elapsed from the time when the restoration of the AC power supply voltage Ein is detected.

The smoothing capacitor 12 included in the input circuit 1
The terminal voltage Vin cannot immediately return to a steady value just after the power is restored. Therefore, in this embodiment, the first converter 3 is operated when a certain period of time elapses after the power recovery is detected and the terminal voltage Vin of the smoothing capacitor 12 returns to a steady value or a level close to the steady value. is there. Specifically, a delay circuit 66 is provided between the comparator 62 and the flip-flop 64.

[0050]

As described above, according to the present invention, it is possible to provide a backup switching power supply that can clearly identify a power failure and a power recovery.

[Brief description of the drawings]

FIG. 1 is an electric circuit diagram showing an embodiment of a switching power supply according to the present invention.

FIG. 2 is an electric circuit diagram showing another embodiment of the switching power supply according to the present invention.

FIG. 3 is an electric circuit diagram showing still another embodiment of the switching power supply according to the present invention.

[Explanation of symbols]

 71, 72 AC input terminal 3 First converter 31 Input circuit 32 Conversion transformer 321 First winding 322 Second winding 323 Third winding 4 Output circuit 5 Second converter 51 Switching circuit 52 Energy storage element 6 Control circuit

Claims (2)

[Claims] An input circuit, a first converter, and a second converter.
A switching power supply including a converter and a control circuit, wherein the input circuit includes a rectifier circuit and a smoothing capacitor, rectifies and smoothes an AC power supply voltage supplied to an AC input terminal, and converts the AC power supply voltage into a DC voltage. The first converter switches a DC voltage supplied from the input circuit, converts a switching output into a DC voltage and outputs the DC voltage, and the second converter outputs a power failure In this case, the energy supplied from the storage element is used to supply power to the load in place of the first converter, and when the AC power is restored, the energy is supplied using the energy of the AC power. The control circuit detects a power failure of the AC power supply from a terminal voltage of the smoothing capacitor, and detects a power recovery from the AC power supply voltage, based on the detection signal. A switching power supply for controlling the first converter and the second converter. 2. The switching power supply according to claim 1, wherein the control circuit operates the first converter after a lapse of a predetermined time after detecting the restoration of the AC power supply voltage. Switching power supply.