JP3759296B2 - Switching power supply - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
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]
[Prior art]
Conventionally, various types of switching power supplies are known. For example, Japanese Patent Laid-Open No. 9-56085 discloses that a charge / discharge circuit having a backup element made of a battery is connected to the secondary side of the conversion transformer provided in the power conversion circuit, and is generated in the secondary winding of the conversion transformer. When the backup element is charged using the induced voltage and the supply of the AC power supply voltage is stopped, the energy stored in the backup element is not passed through the conversion transformer, and the first converter circuit provided in the charging circuit And a power supply apparatus that supplies the converted electric power to a load.
[0003]
Japanese Patent Laid-Open No. 8-275521 discloses that a constant current circuit is connected to the secondary winding of a conversion transformer that constitutes a power conversion circuit, the battery is charged by the constant current circuit, and the charging voltage of the battery is supplied to the inverter during a power failure. And the power supply device which supplies electric power to a load from an inverter is disclosed.
[0004]
Japanese Patent Application Laid-Open No. 64-8836 discloses an uninterruptible power supply apparatus in which a storage battery is connected to the output side of a rectifier circuit that rectifies an AC power supply, and the storage battery is used as a power supply source in the event of a power failure.
[0005]
[Problems to be solved by the invention]
As can be seen from the above-mentioned prior art documents, this type of conventional switching power supply is provided with a converter that converts the power of the backup battery separately from the main converter that operates with the AC power supply voltage as an input, and switching between the two converters is possible. Thus, the configuration corresponds to a power failure of the AC power supply. In switching, the operation of the main converter is stopped, and instead, the operation of the backup converter that has been in a stopped state is started.
[0006]
However, a certain rise time is required for the backup converter that has been in a stopped state until it rises to an operating state in which the voltage that has been supplied can be supplied to the load. Due to the rising characteristics of the backup converter, the DC voltage supplied to the load is reduced during switching.
[0007]
An object of the present invention is to provide a switching power supply in which a DC output voltage supplied to a load at the time of switching between a main converter and a converter does not decrease.
[0008]
[Means for Solving the Problems]
In order to solve the above-described problem, a switching power supply according to the present invention includes a first converter, a second converter, and a control circuit.
[0009]
The first converter switches a DC voltage converted from an AC voltage, converts a switching output into a DC voltage, and supplies the DC output voltage to a load.
[0010]
The second converter switches the DC voltage supplied from the storage element, converts the switching output to a DC voltage, and supplies the DC output voltage to the load.
[0011]
The control circuit performs switching between the first converter and the second converter in response to a power failure or power recovery of the AC voltage, and the first converter and the second converter are simultaneously switched at the time of switching. Set the operating period.
[0012]
Since the first converter switches the DC voltage converted from the AC voltage, converts the switching output to the DC voltage, and supplies the DC output voltage for the load, the AC voltage is normally supplied. Can supply a DC output voltage to the load from the first converter.
[0013]
When the AC power supply fails, switching from the first converter to the second converter is performed. Thereby, instead of the first converter, the second converter starts operation. The second converter switches the direct current supplied from the storage element, converts the switching output into a direct current voltage, and supplies the direct current output voltage to the load. Thereby, a DC output voltage can be supplied to the load instead of the first converter.
[0014]
In switching from the first converter to the second converter, the control circuit sets a period in which the first converter and the second converter operate simultaneously. Therefore, the second converter starts operating while the first converter is operating. When the first converter stops operating, the second converter can be raised to a state where a predetermined DC voltage can be supplied to the load. For this reason, it is possible to avoid a decrease in the DC output voltage due to the rising characteristics of the second converter.
[0015]
When the AC power supply recovers, switching from the second converter to the first converter is performed. Also in this case, the control circuit sets a period in which the first converter and the second converter operate simultaneously. Therefore, when the first converter starts operating and the second converter stops operating while the second converter is operating, the first converter can supply a predetermined DC voltage to the load. You can stand up to the state. For this reason, it is possible to avoid a decrease in the DC output voltage due to the rising characteristics of the first converter.
[0016]
The DC voltage output from the second converter is desirably set lower than the DC voltage output from the first converter. This configuration is extremely effective as a means for preventing a transient drop in the DC output voltage when the AC power supply is switched due to a power failure or power recovery.
[0017]
As a means for setting a period for operating the first converter and the second converter at the same time, the control circuit can have a timer for setting such a period.
[0018]
As another simultaneous operation period setting means, the control circuit operates the first converter until the switching pulse width reaches a maximum duty at the time of the AC voltage interruption, and at the time of power recovery, the control circuit switches the switching pulse of the first converter. It can also have a function of stopping the second converter after the width becomes smaller than the maximum duty.
[0019]
In this case, as a means for determining the maximum duty, the control circuit compares the voltage signal obtained by amplifying the error of the DC output voltage with respect to a reference value with a voltage signal for setting the maximum duty, It can have a function of determining the duty.
[0020]
The present invention further discloses specific means that is extremely effective for downsizing this type of switching power supply, particularly when it has a plurality of outputs.
[0021]
Other objects, configurations and advantages of the present invention will be described in more detail with reference to the accompanying drawings. The drawings are merely illustrative.
[0022]
DETAILED DESCRIPTION OF THE INVENTION
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 a first converter 1, a second converter 2, and control circuits 31 and 32.
[0023]
The first converter 1 switches the DC voltage converted from the AC voltage, converts the switching output to the DC voltage V21, and supplies the DC output voltage Vo to the load L. The output of the first converter 1 is connected to output terminals 71 and 72. An input circuit 4 is provided on the input side of the first converter 1. The input circuit 4 rectifies and smoothes the AC voltage Ein supplied from the AC power source e and supplies the DC voltage V11 to the first converter 1.
[0024]
Second converter 2 switches DC voltage V12 supplied from power storage element 20, converts the switching output to DC voltage V22, and supplies DC output voltage Vo for load L. When the supply of the AC voltage Ein to the first converter 1 is stopped, the DC output voltage Vo is supplied to the load L instead of the first converter 1. The power storage element 20 is formed of a battery or an electric double layer capacitor. The output of the second converter 2 is connected to output terminals 71 and 72.
[0025]
The control circuits 31 and 32 are supplied from the switching circuit 5 to the control signals S3 and S4. The switching circuit 5 has a power failure detection function, and supplies control signals S3 and S4 to the control circuits 31 and 32 in accordance with the AC voltage Ein so that the operations of the first converter 1 and the second converter 2 are performed. Switching is performed, and a period in which the first converter 1 and the second converter 2 operate simultaneously at the time of switching is set. In the drawing, the control circuits 31 and 32 are expressed as independent blocks, but may be integrated as one block. The control signals S1 and S2 are pulse width modulation (hereinafter referred to as PWM) control signals for the first converter 1 and the second converter 2. The switching circuit 5 may be integrated with the control circuits 31 and 32.
[0026]
Next, the operation of the switching power supply shown in FIG. 1 will be described with reference to the time chart of FIG.
[0027]
While the AC voltage Ein is normally supplied from the AC power source e (see FIG. 2A), the first converter 1 is connected to the DC voltage V11 converted from the AC voltage Ein (see FIG. 2B). ) Is switched (see FIG. 2C), the switching output is converted to the DC voltage V21, and the DC output voltage Vo is supplied to the load L. In FIG. 2C, a logical value 1 corresponds to a state in which the first converter 1 is operating, and a logical value 0 corresponds to a state in which the first converter 1 has stopped operating.
[0028]
Next, when the AC power source e fails at t0, the switching circuit 5 supplies the control signals S3 and S4 to the control circuits 31 and 32 according to the DC voltage V11. Then, the first converter 1 and the second converter 2 are switched by the control signals S1 and S2 supplied from the control circuits 31 and 32 to the first converter 1 and the second converter 2. Thereby, instead of the first converter 1, the second converter 2 starts operation. Second converter 2 switches DC voltage V12 supplied from power storage element 20, converts the switching output to DC voltage V22, and supplies DC output voltage Vo to load L.
[0029]
In switching from the first converter 1 to the second converter 2, the control circuits 31 and 32 set a period during which the first converter 1 and the second converter 2 operate simultaneously. In FIG. 2, a period ΔT1 from time t0 to time t1 is a period during which these operations are performed simultaneously. Accordingly, the second converter 2 starts operating while the first converter 1 is operating (see FIGS. 2C and 2E). As a result, the second converter 2 can be raised to a state where a predetermined DC voltage can be supplied to the load L by time t1 when the operation of the first converter 1 stops (see FIG. 2E). ). For this reason, it is possible to avoid a drop in the DC output voltage V21 due to the rising characteristics of the second converter 2. Assuming that the first converter 1 and the second converter 2 are simultaneously switched at t1 (see the dotted line display in FIG. 2 (e)), a transient drop Vd1 occurs in the DC output voltage V21. (See FIG. 2 (g)).
[0030]
Next, when the AC power source e recovers at t2, the switching from the second converter 2 to the first converter 1 is performed. Also in this case, the control circuits 31 and 32 set a period during which the first converter 1 and the second converter 2 operate simultaneously. In FIG. 2, a period ΔT2 from t3 to t4 corresponds to this simultaneous operation period. Accordingly, at time t4 when the first converter 1 starts operating and the second converter 2 stops operating while the second converter 2 is operating, the first converter 1 is set to the load L at a predetermined time. The DC output voltage V21 can be supplied until it can be supplied.
[0031]
FIG. 3 is a diagram showing a more specific 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.
[0032]
The input circuit 4 converts the AC voltage Ein supplied to the AC input terminals 61 and 62 into a DC voltage V11 and outputs it. The illustrated input circuit 4 includes a rectifier circuit 41 formed of a diode bridge or the like and a smoothing capacitor 42.
[0033]
First converter 1 includes a power conversion circuit 11 and an output circuit 12. The power conversion circuit 11 includes a conversion transformer 13 and a switch element 14. The conversion transformer 13 includes a first winding 131 and a second winding 132, and the first winding 131 is supplied with the DC voltage V <b> 11 from the input circuit 4.
[0034]
The switch element 14 switches the DC voltage V11 supplied through the first winding 131. The switch element 14 is typically composed of 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 14 is connected in series to the first winding 131 of the conversion transformer 13.
[0035]
The output circuit 12 is connected to the second winding 132, converts the switch output appearing in the second winding 132 to the DC voltage V <b> 21, and supplies the DC output voltage Vo to the load L. The illustrated output circuit 12 constitutes a so-called forward first converter circuit, and a diode 121 that conducts when the switch element 14 is on, and a choke coil during the period when the switch element 14 is off. A rectifier circuit including a diode 122 that releases energy stored in 123 and an output smoothing capacitor 124 are provided. However, it goes without saying that the present invention is not limited to such a circuit configuration.
[0036]
Second converter 2 includes a power conversion circuit 21 and an output circuit 22. The power conversion circuit 21 includes a conversion transformer 23 and a switch element 24. Conversion transformer 23 includes a first winding 231 and a second winding 232, and first winding 231 receives supply of DC voltage V <b> 12 from power storage element 20.
[0037]
The switch element 24 switches the DC voltage V12 supplied through the first winding 231. The switch element 24 is typically composed of 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 24 is connected in series to the first winding 231 of the conversion transformer 23.
[0038]
The output circuit 22 is connected to the second winding 232, converts the switch output appearing in the second winding 232 into the DC voltage V 21, and supplies the DC output voltage Vo to the load L. The illustrated output circuit 22 forms a forward first converter circuit, and a diode 221 that conducts when the switch element 24 is on, and a choke coil 223 during a period when the switch element 24 is off. And a rectifier circuit composed of a diode 222 that discharges the energy stored therein. However, it goes without saying that the present invention is not limited to such a circuit configuration.
[0039]
Next, the operation of the switching power supply shown in FIG. 3 will be described with reference to the time chart of FIG. 2 again.
[0040]
While the AC voltage Ein is normally supplied from the AC power source e (see FIG. 2A), the AC voltage Ein is converted into the DC voltage V11 by the input circuit 4 (see FIG. 2B). The DC voltage V11 supplied from the input circuit 4 through the first winding 131 of the conversion transformer 13 is switched by the switch element 14 (see FIG. 2C). Since the output circuit 12 is connected to the second winding 132 of the conversion transformer 13, the switch output appearing in the second winding 132 is converted into a DC voltage V 21 by the output circuit 12. The DC voltage V21 is supplied to the load L as the DC output voltage Vo (see FIG. 2G), and the load current Io1 flows (see FIG. 2D).
[0041]
Next, when the AC power source e fails at t0, the control circuits 31 and 32 switch between the first converter 1 and the second converter 2 according to the DC voltage V11. Thereby, instead of the first converter 1, the second converter 2 starts operation. In the second converter 2, the DC voltage V <b> 12 supplied from the power storage element 20 through the first winding 231 of the conversion transformer 23 is switched by the switch element 24. Since the output circuit 22 is connected to the second winding 232 of the conversion transformer 23, the switch output appearing in the second winding 232 is converted into the DC voltage V 22 by the output circuit 22. The DC voltage V22 is supplied to the load L as the DC output voltage Vo (see FIG. 2G), and the load current Io2 flows (see FIG. 2F).
[0042]
In switching from the first converter 1 to the second converter 2, the control circuits 31 and 32 set a period during which the first converter 1 and the second converter 2 operate simultaneously. This point has already been described with reference to FIGS.
[0043]
That is, the first converter 1 and the second converter 2 operate simultaneously during a period ΔT1 from t0 to t1. For this reason, it is possible to avoid a decrease in the DC output voltage V0 due to the rising characteristics of the second converter 2.
[0044]
Further, when the AC power source e is restored at time t2, the first converter 1 and the second converter 2 operate simultaneously in a period ΔT2 from time t3 to time t4.
[0045]
The DC voltage V22 output from the second converter 2 is desirably set lower than the DC voltage V21 output from the first converter 1. According to this configuration, it is possible to continue supplying the current Io1 to the load L by the first converter 1 using the accumulated charge of the smoothing capacitor 42 at the time of a power failure of the AC voltage Ein. Then, as the DC voltage V11 given by the terminal voltage of the smoothing capacitor 42 decreases (see FIG. 2B), the supply of the current Io1 from the first converter 1 to the load L gradually decreases (FIG. 2). (See (d)).
[0046]
On the other hand, the current Io2 supplied from the second converter 2 to the load L gradually increases (see FIG. 2 (f)), and finally, the second converter 2 goes to the load L. It will bear all of the power supply. At this time t1, the first converter 1 is stopped. Therefore, at the time of switching, the transient drop Vd1 (see FIG. 2G) in the DC output voltage Vo can be reliably prevented by using the charge accumulated in the smoothing capacitor 42.
[0047]
When power is restored, switching from the second second converter 2 to the first first converter 1 is performed by an operation opposite to the above-described operation.
[0048]
As means for setting a period during which the first converter 1 and the second converter 2 are operated simultaneously, the control circuits 31, 32 or the switching circuit 5 can have a timer for setting such a period.
[0049]
As another simultaneous operation period setting means, the control circuits 31 and 32 operate the first converter 1 until the switching pulse width reaches the maximum duty at the time of a power failure of the AC voltage Ein, and the first converter 1 at the time of power recovery. It is also possible to have a function of stopping the second converter 2 after the switching pulse width becomes smaller than the maximum duty.
[0050]
In the field of switching power supplies, it is common to apply PWM control to the switch elements 14 and 24 by the control circuits 31 and 32 in order to stabilize the DC output voltage Vo. The PWM control in the switching power supply is such that when the DC output voltage Vo decreases, the ON period (hereinafter referred to as duty) of the switch elements 14 and 24 is extended, and when the DC output voltage Vo increases, the duty decreases. It is a method. In this case, the maximum duty is set for proper operation and protection of the switching power supply, and the switch elements 14 and 24 operate within the range of the maximum duty. The maximum duty corresponds to an extreme operation state for stabilizing the outputs of the first converter 1 and the second converter 2.
[0051]
In a preferred aspect of the present invention, at the time of a power failure of the AC voltage Ein, the control circuit 31 operates the first converter 1 until the switching pulse width reaches the maximum duty. This means that at the time of a power failure, the first converter 1 is switched to the second converter 2 after the output stabilizing ability is fully exhibited.
[0052]
When power is restored, the second converter 2 can be stopped after the switching pulse width of the first converter 1 becomes smaller than the maximum duty. This means that the switching from the second converter 2 to the first converter 1 is performed after the first converter 1 enters the output stabilization operable region. If the DC voltage V22 output from the second converter 2 is set to a value higher than the DC voltage V21 output from the first converter 1, it is assumed that the AC power source e is restored. As a result, the second converter 2 still continues to operate.
[0053]
In this case, as means for determining the maximum duty, the control circuits 31 and 32 compare the voltage signal obtained by amplifying the error of the DC output voltage Vo with respect to the reference value and the voltage signal for setting the maximum duty. , The maximum duty can be determined.
[0054]
FIG. 4 shows a specific example thereof. The control circuit 31 illustrated in FIG. 4 includes an error amplifier 301, a reference voltage source 302, a comparator 303, a maximum duty setting voltage source 304, a triangular wave oscillator 305, and a comparator 306.
[0055]
The error amplifier 301 amplifies the error of the DC output voltage Vo with respect to the reference voltage source Vr1 supplied from the reference voltage source 302, and supplies the error amplification signal S5 to the comparator 303.
[0056]
The comparator 303 compares the error amplification signal S5 supplied from the error amplifier 301 with the triangular wave supplied from the triangular wave oscillator 305, and supplies a PWM signal that stabilizes the DC output voltage Vo to the switch element 14. To do. The reference voltage Vr2 is supplied from the maximum duty setting voltage source 304 to the comparator 303. The pulse width obtained by comparing the reference voltage Vr2 with the triangular wave supplied from the triangular wave oscillator 305 determines the maximum duty.
[0057]
The comparator 306 compares the error amplification signal S5 supplied from the error amplifier 301 with the reference voltage Vr2 supplied from the maximum duty setting voltage source 304, and the error amplification signal S5 has reached the maximum duty, or Determine if it is less than the maximum duty.
[0058]
At the time of a power failure of the AC voltage Ein, the control circuit 31 operates the first converter 1 until the switching pulse width reaches the maximum duty, and therefore detects whether the error amplification signal S5 has reached the maximum duty. When it is determined that the maximum duty has been reached, the control circuit 31 stops the operation of the first converter 1.
[0059]
FIG. 5 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 in FIGS. 1 and 3 are denoted by the same reference numerals. In this embodiment, the conversion transformer 13 and the output circuit 12 constituting the first converter 1 are shared by the first converter 1 and the second converter 2. The conversion transformer 13 has a third winding 133.
[0060]
Second converter 2 includes a switching circuit 25, a third winding 133, and a storage element 20. The switching circuit 25 performs switching so that the second converter 2 becomes the charging circuit CH or the discharging circuit DH. When switched to charging circuit CH, second converter 2 charges power storage element 20 with electric power supplied from third winding 133. When switched to the discharge circuit DH, the energy supplied from the storage element 20 is switched and supplied to the third winding 133.
[0061]
The illustrated switching circuit 25 is configured by a parallel circuit of a diode 26 and a switch element 24 formed of a three-terminal element. The diode 26 configures a charging circuit CH, and the switch element 24 configures a discharge circuit DH. . More specifically, when the main switch element 14 is turned on, the diode 26 is in a forward direction with respect to the induced voltage appearing in the third winding 133 having the indicated polarity (shown by a black circle in the figure). Oriented to be
[0062]
The switch element 24 is configured by a three-terminal element, and the main electrode circuit is connected to the discharge circuit DH including the third winding 133 and the storage element 20 so as to enter in series. A three-terminal element suitable for the switch element 24 is an FET. When the switch element 24 is an FET, the source of the FET. Since the drain-to-drain diode can be used as the diode 26, the circuit configuration of the switching circuit 25 can be further simplified. The power storage element 20 is typically composed of a battery that is a secondary battery. Or you may comprise with a capacitor | condenser.
[0063]
When the first converter 1 is operating, the second converter 2 is switched by the switching circuit 25 to become the charging circuit CH. When switched to the charging circuit CH, the storage element 20 is charged by the electric power supplied from the third winding 133 of the conversion transformer 13. Therefore, the storage element 20 is charged by the voltage induced in the third winding 133 of the conversion transformer 13 by the switching operation of the power conversion circuit 11. In the circuit configuration shown in the embodiment, the diode 26 is in order with respect to the induced voltage appearing in the third winding 133 having the indicated polarity (shown by a black circle in the figure) when the main switch element 14 is turned on. Therefore, charging of the storage element 20 through the diode 26 is performed during the ON period of the main switch element 14.
[0064]
Next, at the time of a power failure of the AC power source e, the second converter 2 is switched to the discharge circuit DH. When switched to the discharge mode, the storage element 20 becomes a power supply source. Second converter 2 switches the energy supplied from power storage element 20 and supplies it to third winding 133. The third winding 133 is a winding of the conversion transformer 13 and is inductively coupled to the second winding 132 of the conversion transformer 13, and is obtained by switching energy supplied from the power storage element 20. When the winding of the third winding 133 is excited by the current, the energy is transmitted from the third winding 133 to the second winding 132. Since the output circuit 12 is connected to the second winding 132 of the conversion transformer 13, the switching output of the second converter 2 appearing in the second winding 132 is converted into the DC voltage V 21 by the output circuit 12, A DC output voltage Vo is supplied to the load L.
[0065]
As is apparent from the above description, in the embodiment shown in FIG. 5, the second converter 2 is mainly composed of the components that should be originally provided in the switching power supply, that is, the conversion transformer 13 and the output circuit 12. Is shared with the first converter 1 and the energy of the electric storage element 20 is supplied to the load L. Therefore, the number of parts can be reduced and the miniaturization can be achieved.
[0066]
In addition, the backup operation by the second converter 2 can be easily realized by selecting the switch element 24 and the main switch element 14 constituting the switching circuit 25.
[0067]
Also in the embodiment shown in FIG. 5, the switching circuit 5 switches the operation of the first converter 1 and the second converter 2 in accordance with the AC voltage Ein, and the first converter 1 and the second converter 2 are switched at the time of switching. The period during which the two converters 2 operate simultaneously is set.
[0068]
FIG. 6 is an electric circuit diagram showing another embodiment of the switching power supply according to the present invention. In this embodiment, the switching power supply shown in FIG. 5 is applied to a multi-output type switching power supply. A plurality of n second windings 132 are provided, and output circuits 91 to 9n are individually provided in each of the second windings 132. In the illustrated multi-output type switching power supply, the storage element 20 is charged in the same manner as in the embodiment of FIG.
[0069]
Next, when the second converter 2 is switched to the discharge circuit DH by the switching circuit 25, the second converter 2 switches the energy supplied from the power storage element 20 to the third winding 133. Supply. Since the third winding 133 is inductively coupled to the second winding 132 of the conversion transformer 13, the third winding 133 is generated by the current obtained by switching the energy supplied from the power storage element 20. Energy is transmitted from the third winding 133 to each of the n second windings 132 provided. Since each of the n second windings 132 is connected to the same number n of output circuits 91 to 9n, switching of the second converter 2 appearing in each of the n second windings 132 is performed. Outputs are converted into DC output voltages Vo1 to Von by output circuits 91 to 9n, respectively, and supplied to a load L.
[0070]
As is apparent from the above description, even in a multi-output type switching power supply, only one second converter 2 needs to be provided. For this reason, a small backup type switching power supply that does not require an increase in the number of components even when multiple outputs are used can be obtained. Also in the embodiment shown in FIG. 6, the switching circuit 5 switches the operation of the first converter 1 and the second converter 2 in accordance with the AC voltage Ein, and the first converter 1 and the second converter 2 are switched at the time of switching. The period during which the two converters 2 operate simultaneously is set.
[0071]
【The invention's effect】
As described above, according to the present invention, it is possible to provide a switching power supply in which the DC output voltage supplied to the load does not decrease when switching between the main first converter and the second converter.
[Brief description of the drawings]
FIG. 1 is a block diagram showing an embodiment of a switching power supply according to the present invention.
FIG. 2 is a time chart for explaining the operation of the switching power supply according to the present invention.
FIG. 3 is an electric circuit diagram showing an embodiment of a switching power supply according to the present invention.
FIG. 4 is an electric circuit diagram of a control circuit used in the switching power supply according to the present invention.
FIG. 5 is an electric circuit diagram showing another embodiment of the switching power supply according to the present invention.
FIG. 6 is an electric circuit diagram showing still another embodiment of the switching power supply according to the present invention.
[Explanation of symbols]
1 First converter
2 First converter
20 Power storage element
31, 32 Control circuit
4 Input circuit
5 Switching circuit

Claims (5)

A switching power supply including a first converter, a second converter, and a control circuit,
The first converter switches a DC voltage converted from an AC voltage, converts a switching output to a DC voltage, and supplies a DC output voltage to a load.
The second converter switches the DC voltage supplied from the storage element, converts the switching output to a DC voltage, and supplies the DC output voltage to the load.
The control circuit performs switching between the first converter and the second converter in response to a power failure or power recovery of the AC voltage, and the first converter and the second converter are simultaneously performed at the time of switching. An operation period is set, and the first converter is operated until the switching pulse width reaches a maximum duty when the AC voltage is interrupted, and when the AC voltage is restored, the first converter is operated. Stopping the second converter after a switching pulse width becomes smaller than the maximum duty;
Switching power supply. A switching power supply according to claim 1,
The switching power supply, wherein the DC voltage output from the second converter is set lower than the DC voltage output from the first converter. A switching power supply according to claim 1 or 2,
The control includes a timer, and the switching power supply sets a period during which the timer operates the first converter and the second converter simultaneously. A switching power supply according to claim 1,
The switching power supply, wherein the control circuit determines a maximum duty by comparing a voltage signal obtained by amplifying an error of the DC output voltage with respect to a reference value and a voltage signal for setting a maximum duty. A switching power supply according to any one of claims 1, 2, 3 or 4,
Including a conversion transformer for transmitting the switching output to the load side,
The conversion transformer is a switching power supply shared by the first converter and the second converter.

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