JPH06245529A - Switching power supply - Google Patents

Abstract

PURPOSE:To provide a switching power supply, which can prevent the burning of a power-factor improvement circuit even when the power-factor improvement circuit is not operated and input currents are increased and cost of which is reduced. CONSTITUTION:A rectifier circuit 11 generates a rectifying output Er. In a step-up circuit 12, a first switching element 121 switches the rectifying output Er, and a step-up output Ei is generated through an inductor element 122. A capacitor 13 smooths the step-up output Ei, and generates a smoothing output Eo. In a control circuit 14, the first switching element 121 is supplied with a switching signal S2 so that the smoothing output Eo reaches aimed voltage while an interrupting signal S3 is output when the smoothing output Eo is made lower than a reference level Vref. An interrupting circuit 15 prevents charging to the capacitor 13 or discharge from the capacitor 13. In a switching circuit 2, a second switching element 21 switches the smoothing output Eo.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a switching power supply, and more particularly to a technique for preventing burnout of a circuit when a boost type power factor correction circuit does not work and the input current increases.

[0002]

2. Description of the Related Art The conventional switching power supply has a drawback that a large charging current flows in a short time and the power factor is bad because the capacitor is charged only when the rectified output voltage is higher than the charging voltage of the capacitor. In order to prevent such a drawback, in the process of boosting by using a switching element and an inductor element, a charging current is dispersed and made to flow so that the input AC voltage waveform and the AC current waveform have similar shapes, that is, a so-called boost type power factor. An improved circuit is disclosed in Japanese Patent Laid-Open No. 3-78469.

[0003]

However, the conventional switching power supply including the boost type power factor correction circuit has the following problems. (A) When the switching element fails in the open mode, the boosting action is lost, the power factor returns to the conventional power factor, and a large input current flows in the rectifier circuit, the booster circuit, and the like. For example, if the power factor before power factor improvement is 50%, the input current will be doubled. Therefore, the circuit may be burnt. (B) If the current capacities of circuit components are set so as not to cause burnout, the specifications will be overspecified due to a rare failure, and the cost will increase.

A first object of the present invention is to provide a switching power supply which can achieve power factor improvement without limiting the charging period of the capacitor.

A second object of the present invention is to provide a switching power supply which can supply a target DC voltage or AC voltage by switching the smoothed output.

A third object of the present invention is to provide a switching power supply capable of detecting a case where a switching element fails and cannot boost the rectified output.

A fourth object of the present invention is to provide an inexpensive switching power supply capable of preventing burnout of the circuit even when the power factor correction circuit does not work and the input current increases.

[0008]

In order to solve the above problems, the present invention is a switching power supply including a power factor correction circuit and a switching circuit, wherein the power factor correction circuit comprises:
Rectifier circuit, booster circuit, capacitor, control circuit,
A cutoff circuit, the rectifier circuit rectifies an alternating current input to generate a rectified output, and the booster circuit includes a first switching element and an inductor element, and the first switching element. An element and the inductor element are connected in series, both ends of a series circuit are connected to the rectifying circuit, the first switching element switches the rectified output, and a boosted output is generated through the inductor element, The capacitor smoothes the boosted output to generate a smoothed output, the control circuit has a reference level, a smoothed output signal based on the smoothed output is input, and the smoothed output becomes a target voltage. Such a switching signal is supplied to the switching element, and a cutoff signal is output when the smoothed output is lower than the reference level. A shall, said blocking circuit,
The cutoff signal is input to prevent charging to or discharge from the capacitor, the switching circuit includes a second switching element, and the second switching element switches the smoothed output. To do.

[0009]

The rectifier circuit rectifies an AC input to generate a rectified output, and the booster circuit has the first switching element and the inductor element connected in series, and both ends of the series circuit are connected to the rectifier circuit. The first switching element switches the rectified output and produces a boosted output through the inductor element, the capacitor smoothes the boosted output and produces a smoothed output, and the control circuit produces a smoothed output based on the smoothed output. Since a signal is input and a switching signal such that the smoothed output has a target voltage is supplied to the first switching element, the charging period of the capacitor is not limited as in the conventional case, and power factor improvement can be achieved. A switching power supply is obtained.

Since the second switching element of the switching circuit switches the smoothed output, a switching power supply capable of supplying a target DC voltage or AC voltage can be obtained.

The control circuit receives the smoothed output signal based on the smoothed output and outputs the cutoff signal when the smoothed output is lower than the reference level. Therefore, when the switching element fails and the rectified output cannot be boosted. Can be detected.

Since the cutoff circuit receives a cutoff signal and blocks charging or discharging of the capacitor, when the cutoff circuit is provided before the capacitor, for example, between the rectifier circuit and the booster circuit, There is no charging current to the capacitor through the booster circuit, and as a result, no current flows in the rectifier circuit, and burnout of the rectifier circuit and the like can be prevented. Also, if it is provided after the capacitor, for example, between the capacitor and the switching circuit, the discharge current from the capacitor disappears, so there is no charge current after the capacitor is charged by the rectified output, and the rectifier circuit burns out. Can be prevented. Further, even when the switching operation of the second switching element is stopped by the cutoff signal, the discharge current from the capacitor disappears, as in the case of being provided in the subsequent stage of the capacitor, so that burnout of the rectifier circuit and the like can be prevented.

As a result, the power factor correction circuit does not work, and a switching power supply capable of preventing the circuit from burning even when the input current increases can be obtained. In addition, it is not necessary to set the current capacity of the circuit component on the assumption of a failure, and an inexpensive switching power supply can be obtained.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows a first switching power supply according to the present invention.
2 is a circuit diagram of the embodiment of FIG. 2, and FIG. 2 is a diagram for explaining the operation of the power factor correction circuit in the first embodiment of the switching power supply according to the present invention. In the figure, 1 is a power factor correction circuit, and 2 is a switching circuit.

The power factor correction circuit 1 includes a rectifier circuit 11, a booster circuit 12, a capacitor 13, a control circuit 14, and a cutoff circuit 15.

The rectifier circuit 11 rectifies the AC input Ei,
It produces a rectified output Er. The booster circuit 12 is a chopper type booster circuit, and includes a first switching element 121.
And an inductor element 122. The first switching element 121 and the inductor element 122 are connected in series, and both ends of the series circuit are connected to the rectifier circuit 11. The first switching element 121 is composed of a field effect transistor or the like, is ON / OFF driven in the range of several kHz to several hundred kHz, and switches the rectified output Er. The inductor element 122 stores energy when the first switching element 121 is on and converts the stored energy into a flyback voltage Vf when it is off. As a result, the booster circuit 12 adds the flyback voltage Vf to the rectified output Er to generate a boosted output El. The capacitor 13 smoothes the boosted output El to generate the smoothed output Eo. The diode 123 prevents the backflow of the smoothed output Eo.

The control circuit 14 has a reference level Vref and receives a smoothed output signal S1 based on the smoothed output Eo. The reference level Vref is set higher than the peak value of the rectified output Er and lower than the target voltage Vs. The control circuit 14 supplies the switching signal S2 such that the smoothed output Eo becomes the target voltage Vs to the switching element 121, and outputs the cutoff signal S3 when the smoothed output Eo is lower than the reference level Vref. AC input is AC20
In one embodiment set to 0V, the target voltage Vs is 38
The reference level Vref is set to 0V and the reference level Vref is set to 350V.

The cutoff circuit 15 receives the cutoff signal S3 and blocks charging or discharging of the capacitor 13. In this embodiment, it is provided between the rectifier circuit 11 and the booster circuit 12, and cuts off the charging path to the capacitor 13. It consists of a three-terminal switch element, a relay, etc.

The switching circuit 2 includes a second switching element 21, and the second switching element 21 switches the smoothed output Eo. The switching circuit 2 is
It may be anything that switches a DC input, and is composed of a DC-DC converter, a DC-AC converter, or the like. The embodiment is a general D for obtaining a DC constant voltage output Vo.
It is a C-DC converter.

As described above, the rectifier circuit 11 rectifies the AC input Ei and produces the rectified output Er, and the booster circuit 12 has the first switching element 121 and the inductor element 122 connected in series. Both ends of the series circuit are connected to the rectifier circuit 11, and the first switching element 12
1 switches the rectified output Er, and the inductor element 1
22 generates a boosted output, the capacitor 13 smoothes the boosted output El and generates a smoothed output Eo, and the control circuit 14 receives the smoothed output signal S1 based on the smoothed output Eo and outputs the smoothed output. Since the switching signal S2 such that Eo becomes the target voltage Vs is supplied to the first switching element 121, the capacitor 13
As in the conventional case, the charging period is not limited to the case where the rectified output Er is higher than the charging voltage of the capacitor 13, and a switching power supply capable of achieving power factor improvement can be obtained.

Since the second switching element 21 of the switching circuit 2 switches the smoothing output Eo, a switching power supply capable of supplying a target DC voltage or AC voltage can be obtained.

The control circuit 14 receives the smoothed output signal S1 based on the smoothed output Eo, and outputs the cutoff signal S3 when the smoothed output Eo is lower than the reference level Vref. Therefore, the first switching element 121 is used. When the inductor element 122 fails to generate the flyback voltage Vf and the smoothing output Eo drops to a voltage obtained by smoothing the rectified output Er, the booster circuit 12 cannot boost the rectified output Er. To detect. That is,
It detects that the power factor correction circuit has stopped working, and outputs the cutoff signal S3.

The cut-off circuit 15 receives the cut-off signal S3 and blocks the charging or discharging of the capacitor 13, so that the preceding stage of the capacitor 13, for example, the rectifying circuit 11 and the boosting circuit 12, is connected. If it is provided between them, the charging current Ic to the capacitor 13 disappears via the booster circuit 12 and the AC input current Ii does not flow to the rectifier circuit 11 either, so that burnout of the rectifier circuit 11 and the like can be prevented.

As a result, the switching power supply can be obtained which prevents the power factor correction circuit 1 from working and prevents the circuit from burning even when the AC input current Ii increases. In addition, it is not necessary to set the current capacity of the circuit component on the assumption of a failure, and an inexpensive switching power supply can be obtained.

The control circuit 14 outputs the cutoff signal S3 when the smoothing output Eo becomes lower than the reference level Vref for a certain period of time, taking into consideration the charging time of the capacitor 13 when starting the power supply, noise, and the like.

FIG. 3 is a diagram for explaining the operation of the power factor correction circuit in the second embodiment of the switching power supply according to the present invention. In the figure, the same reference numerals as those in FIG. 2 denote the same components. In this embodiment, a plurality of AC inputs having different rated voltages, for example, AC100V and AC200V can be shared. The circuit configuration is similar to that of the first embodiment shown in FIG. 3 with reference to FIG.
Will be explained.

A plurality of AC inputs having different rated voltages, for example, AC100V and AC200V are input to the rectifier circuit 11. The smoothing output Eo of the control circuit 14 is AC200V.
The switching signal S2 is supplied to the first switching element 121 so that the target voltage Vs corresponding to the AC input of is obtained. The reference level Vref is set to be higher than the peak value of the rectified output Er2 of the AC input (AC200V) having the highest rated voltage and lower than the target voltage Vs.

When an AC input of 200 V AC is input and the first switching element 121 fails in the open mode and the booster circuit 12 does not work, the smoothed output E
o drops to the voltage level indicated by reference sign a. The control circuit 14 outputs the cutoff signal S3 because the smoothed output Eo becomes lower than the reference level Vref. The same applies when an AC input of 100 V AC is input, and smoothing output E
o drops to the voltage level indicated by reference sign b, and the control circuit 14 outputs the cutoff signal S3.

As a result, even when a plurality of AC inputs are shared, an inexpensive switching power supply which can prevent the circuit from being burned due to a failure of the power factor correction circuit can be obtained.

FIG. 4 is a diagram for explaining the operation of the power factor correction circuit in the third embodiment of the switching power supply according to the present invention. In the figure, the same reference numerals as those in FIGS. 2 and 3 denote the same components. In this embodiment, a plurality of AC inputs having different rated voltages, for example, AC100V, AC2.
00V is shared, and when the AC input current is within the allowable current, it can operate as a switching power supply. The circuit configuration is similar to that of the first embodiment. Figure 1
4 will be described with reference to FIG.

A plurality of alternating current inputs having different rated voltages, for example, AC100V and AC200V are input to the rectifier circuit 11. In the control circuit 14, the smoothed output Eo is an AC input AC.
A switching signal S2 that provides a target voltage Vs corresponding to 200V is supplied to the first switching element 121. The reference level Vref is the highest AC input AC200.
Lower than the peak value of the rectified output Er2 according to V, and
Rectified output Er1 corresponding to the lowest AC input AC100V
It is set higher than the peak value of. For example, the reference level Vref is set to 170V.

FIG. 5 is a diagram showing how the AC input current changes depending on the relationship between the power factor and the AC input voltage.
The figure shows the ratio when the AC input current is 1 when the AC input is AC 100V and the power factor is 100%.
For example, if the power factor correction circuit 1 fails when the AC input is AC100V and the power factor is reduced to 50%, the AC input current is doubled. The same applies when the AC input is AC200V. The power factor correction circuit 1 operates normally and the power factor is 100.
%, The AC input current at AC200V is 0.5 times the AC input current at AC100V.

When the first switching element 121 fails in the open mode and the booster circuit 12 does not work when the input AC200V is input, the smoothed output Eo is indicated by reference numeral a, as in the second embodiment. Fall to the voltage level. In the control circuit 14, the smoothed output Eo is the reference level V
Since it is higher than ref, the cutoff signal S3 is not output. In this case, the AC input current Ii is doubled, but the AC input is A
The AC current is the same as when C100V and the power factor is 100%, and does not cause burnout of the circuit. The failure of the booster circuit 12 can be understood by the decrease of the smoothing output Eo, and the booster circuit 12
Since the switching power supply is not immediately shut off even if the failure occurs, the repair can be performed without affecting the control device using the switching power supply.

When an AC input of 100 V is input, if the first switching element 121 fails in the open mode and the booster circuit 12 does not work, the smoothed output Eo is the same as the reference numeral b. To the voltage level indicated by. The control circuit 14 outputs the cutoff signal S3 because the smoothed output Eo becomes lower than the reference level Vref. The cutoff circuit 15 receives the cutoff signal S3 and the capacitor 1
The charging path to 3 is blocked to prevent the AC input current Ii from doubling.

As a result, it is possible to obtain a switching power supply that prevents the circuit from being burnt out due to a failure of the power factor correction circuit and does not unnecessarily stop the power supply.

FIG. 6 is a circuit diagram of a fourth embodiment of the switching power supply according to the present invention. In the figure, the same reference numerals as those in FIG. 1 denote the same components.

The cutoff circuit 15 is provided between the capacitor 13 and the switching circuit 2 and cuts off the discharge path from the capacitor 13. In this case, since the discharge current Id from the capacitor 13 disappears, the charging current Ic disappears after the capacitor 13 is charged by the rectified output Er,
Burnout of the rectifier circuit 11 and the like can be prevented.

FIG. 7 is a circuit diagram of the fifth embodiment of the switching power supply according to the present invention. In the figure, the same reference numerals as those in FIG. 1 denote the same components.

The switching circuit 2 is a general forward type converter. Reference numeral 22 is a transformer, 23 is an output circuit, and 24 is an output control circuit. The second switching element 21 switches the smoothing output Eo via the transformer 22, and the output circuit 23 rectifies and smoothes the switching output to obtain a DC constant voltage output Vo. Output control circuit 24
Is a switching signal S22 to which a smoothed output signal S21 based on the constant voltage output Vo is input to obtain a target constant voltage output.
Is supplied to the second switching element 21.

The cutoff circuit 15 cuts off the switching signal S22 to the second switching element 21, stops the switching operation of the switching circuit 2, and turns off the capacitor 1
Prevents discharge from 3. Also in this case, as in the fourth embodiment, the discharge current Id from the capacitor 13 disappears, so that the charging current Ic disappears after the capacitor 13 is charged by the rectified output Er, and burnout of the rectifier circuit 11 and the like is prevented. it can.

FIG. 8 is a circuit diagram of a sixth embodiment of the switching power supply according to the present invention. The figure shows the part of the power factor correction circuit, and the switching circuit connected to the subsequent stage is omitted. Actually, the switching circuit shown in FIG. 1 is connected. In the figure, the same reference numerals as those in FIG. 1 denote the same components. Reference numeral 14 is a control circuit.

The control circuit 14 includes a target setting circuit 16, an error detection circuit 17, a current detection circuit 18, a differential amplifier circuit 191, and a pulse width control circuit 192.

The target setting circuit 16 includes a reference voltage signal generator 160, and has a rectified output signal S4 and a smoothed output signal S5.
Are input, and a first output signal S6 and a second output signal S7 are output. The reference voltage signal generator 160 generates a reference voltage signal S60. The first output signal S6 is obtained from the reference voltage signal S60. The second output signal S7 is obtained from the smoothed output signal S5. One of the first output signal S6 and the second output signal S7 changes so that the smoothed output Eo becomes higher than the rectified output Er by following the increase and decrease in the entire voltage range of the rectified output Er. FIG. 9 is a characteristic diagram showing an example of the first output signal S6. The first output signal S6 follows the rectified output signal S4 and is set so that the smoothed output Eo is larger than the rectified output Er. The same applies to the second output signal S7.

The error detection circuit 17 uses the first output signal S
6, the second output signal S7 and the rectified output signal S4 are input, the first output signal S6 and the second output signal S7 are compared, and the error detection signal S having a similar waveform to the rectified output signal S4.
8 is output. Specifically, the error amplification circuit 172 compares the first output signal S6 and the second output signal S7 and outputs the error signal S9, and the multiplication circuit 174 outputs the error signal S9.
And the rectified output signal S4 are multiplied to obtain an error detection signal S8. The error amplification circuit 172 and the multiplication circuit 174 can be configured by a differential amplification circuit using an operational amplifier, a multiplication circuit, or the like.

The current detection circuit 18 includes the inductor element 12
The current flowing in 2 is detected and a current detection signal S10 is output.

The differential amplifier circuit 191 has an error detection signal S8.
Also, the current detection signal S10 is input, both signals are compared, and a differential signal S11 that causes the current detection signal S10 to follow the error detection signal S8 is output.

The pulse width control circuit 192 uses the differential signal S1.
1 is input and the first signal is input to minimize the differential signal S11.
Signal S12 for controlling the switching element 121 of
Is supplied to the first switching element 121.

As described above, in the booster circuit 12, the first switching element 121 is driven on / off at the frequency f2 higher than the frequency f1 of the AC input Ei, and the inductor element 122 is connected in series with the switching element 121. Both ends of the series connection circuit are connected to the output end of the rectifier circuit 11, the anode of the diode 123 is connected to the series connection point of the first switching element 121 and the inductor element 122, and the cathode is connected to the capacitor 13. Therefore, the energy stored in the inductor element 122 when the first switching element 121 is turned on causes the flyback voltage Vf when the first switching element 121 is turned off.
Then, the flyback voltage Vf is superimposed on the rectified output Er, and the boosted output El higher than the rectified output Er is supplied to both ends of the capacitor 2.

The target setting circuit 16 uses the reference voltage signal S60.
A rectified output signal S4 and a smoothed output signal S5 are input, and a first output signal S6 and a second output signal S7 are output.
Output signal S6 of the second reference voltage signal S60 is
Is obtained from the smoothed output signal S5, one of the first output signal S6 and the second output signal S7 follows the increase / decrease in the entire voltage range of the rectified output Er, and the smoothed output Eo is The error detection circuit 17 receives the first output signal S6, the second output signal S7, and the rectified output signal S4 and changes the rectified output Er to be higher than the first output signal S6 and the second output signal S7. Since the output signal S7 is compared and the error detection signal S8 having a waveform similar to the rectified output signal S4 is output, when the reference voltage signal S60 is changed, the second output signal S7 becomes the first output signal S6. Change following
The smooth output Eo also changes at the same time. In addition, the smoothed output signal S
When 5 is changed, the second output signal S7 is controlled to match the first output signal S6, and the smoothing output Eo changes in the process of matching. This satisfies the requirement that the smoothed output Eo is higher than the rectified output Er, which is the requirement for power factor improvement.

The current detection circuit 18 includes the inductor element 12
2 outputs a current detection signal S10, the differential amplifier circuit 191 compares the error detection signal S8 and the current detection signal S10, and causes the current detection signal S10 to follow the error detection signal S8. The pulse width control circuit 192 supplies the control signal S12 for controlling the first switching element 121 so as to minimize the differential signal S11 to the first switching element 121. Therefore, the smoothed output Eo is the first output signal S
6 is adjusted to a voltage corresponding to 6 and the AC input current I
i changes following the AC input voltage Ei, becomes equal to a resistance load when viewed from the AC power supply, and the power factor can be improved.

When the AC input voltage Ei drops and the rectified output Er drops, the smoothing output Eo also drops, so that the first switching element 12 is boosted to boost the voltage.
1 can be reduced, and the power loss of the first switching element 121 can be reduced.

The target setting circuit 16 can be configured to change the smoothed output signal S5 according to the rectified output signal S4. FIG. 10 is a circuit diagram showing a specific example of the target setting circuit in that case. In the figure, the same reference numerals as those in FIG. 8 denote the same components. Below, FIG.
10 will be described with reference to FIG. Reference numeral 160 is a reference voltage signal generator, and 164 is a smoothing output adjuster. Terminal 165
The rectified output Er is applied between the terminal 1 and the terminal 166, and the terminal 1
The smoothed output Eo is applied between 67 and the terminal 166.

The reference voltage signal generator 160 outputs the smoothed output E
A reference voltage Vk serving as a reference for increasing or decreasing o is generated and output as a first output signal S6. Reference voltage Vk is battery B
It is gained by 1. The positive electrode of the battery B1 is connected to the terminal 168. The reference voltage Vk may be obtained by forming a DC constant voltage circuit and dividing the DC constant voltage with a resistance voltage dividing circuit.

The smoothing output adjusting section 164 is provided with a rectified output signal S
The voltage division ratio of the resistor that divides the smoothed output Eo is changed according to 4, and the divided voltage is output as the second output signal S7.
This embodiment has a diode D1, a capacitor C1, resistors R1 to R6, an operational amplifier IC1 and a battery B2. The diode D1 and the capacitor C1 are connected in series, and both ends of which are connected in series are terminals 165 and 166.
Connected to. The resistors R1 and R2 are connected in series, and both ends of which are connected in series are connected to the capacitor C1. The connection point between the resistor R1 and the resistor R2 is connected to the negative input terminal of the operational amplifier IC1, and the divided voltage Vin obtained by dividing the rectified output Er is supplied to the operational amplifier IC1. The battery B2 is connected to the positive input terminal of the operational amplifier IC1 and supplies the reference voltage Vk to the operational amplifier IC1.
The resistor R3 is connected between the output terminal and the negative input terminal of the operational amplifier IC1. One end of the resistor R4 is an operational amplifier I
It is connected to the output end of C1 and the other end is connected to the connection point of the resistors R5 and R6. The resistors R5 and R6 are connected in series, and both ends of the series connection are connected to the terminals 167 and 166. The connection point of the resistors R5 and R6 is connected to the terminal 169, and the divided voltage VR6 obtained by dividing the smoothed output Eo is supplied as the second output signal S7. The operational amplifier IC1 constitutes an inverting amplifier circuit, and
As shown in FIG. 1, the output voltage Vout decreases as the divided voltage Vin increases. Therefore, the terminal voltage VR of the resistor R5
When the rectified output Er increases, that is, when the output voltage Vout decreases, the voltage 5 increases due to an increase in the current flowing through the resistor R4.
Further, the terminal voltage VR5 of the resistor R5 decreases due to the decrease in the current flowing through the resistor R4 when the rectified output Er decreases, that is, when the output voltage Vout increases. Therefore, the divided voltage VR6 of the resistor R6 decreases as the terminal voltage VR5 increases and increases as the terminal voltage VR5 decreases if the smoothed output Eo is constant.

The error detection circuit 17 connected in the subsequent stage has the divided voltage VR6 at the terminal 169 and the reference voltage Vk at the terminal 168.
Therefore, the change in the divided voltage VR6 substantially changes the first output signal S6, and the smoothed output Eo is finally adjusted to the target voltage. That is, when the rectified output Er increases, the divided voltage VR6 decreases,
When the smoothing output Eo is increased and the rectified output Er is decreased in the process of equalizing the divided voltage VR6 with the reference voltage Vk, the divided voltage VR6 is increased and the divided voltage VR6 is changed to the reference voltage Vk.
The smoothing output Eo is reduced in the process of equalizing. As a result, the smoothed output Eo is adjusted to be higher than the rectified output Er, and the same effect as that of the embodiment shown in FIG. 8 can be obtained.

The target setting circuit 16 can also be configured to change the reference voltage signal S60 according to the rectified output signal S4. FIG. 12 is a circuit diagram showing a specific example of the target output voltage setting circuit. In the figure, the same reference numerals as those in FIGS. 8 and 10 denote the same components. Hereinafter, description will be given with reference to FIGS. 8, 10 and 12.

The reference voltage signal generator 160 changes the reference voltage Vk according to the rectified output signal S4 and outputs the first output signal S6. In this embodiment, the diode D1 and
Capacitor C1, resistor R1 and resistor R2, resistor R7
And a battery B3, and a resistor R5 and a resistor R6. A diode D1, a resistor R1 and a resistor R2 are connected in series, and both ends of the series connection circuit are connected to terminals 165 and 16 respectively.
It is connected to 6. The capacitor C1 is connected in parallel to the series circuit of the resistor R1 and the resistor R2. The resistor R2 generates a divided voltage Vin obtained by dividing the rectified output Er. Resistance R
7 and the battery B3 are connected in series, and both ends of which are connected in series are connected to the resistor R2. One end of the resistor R7 is terminal 1
The reference voltage Vk is supplied to the terminal 168. The reference voltage Vk becomes a voltage as shown in FIG. 13 from the relationship between the divided voltage Vin and the voltage Vr of the battery B3. That is, when the divided voltage Vin is higher than the voltage Vr,
Current flows from the resistor R1 to the battery B3, and the voltage Vr
When the divided voltage Vin is lower than the voltage Vr, the current flows from the battery B3 to the resistor R2 and becomes lower than the voltage Vr.

The smoothing output adjusting unit 164 has resistors R5 and R6 and divides the smoothing output Eo by resistance. The connection point of the resistors R5 and R6 is connected to the terminal 169, and the divided voltage VR6 is output to the terminal 169 as the second output signal S7.

Since the error detection circuit 17 connected in the subsequent stage operates so as to match the first output signal S6 and the second output signal S7, the second output signal S7 changes to the first output signal S6. And the smoothed output Eo is finally adjusted to the target voltage. As a result, it is possible to obtain the same effect as that of the embodiment shown in FIG.

The control circuit 14 outputs the cutoff signal S3 when the smoothed output signal S5 is lower than the reference level Vref.
The cutoff circuit 15 receives the cutoff signal S3 and cuts off the charging path to the capacitor 13.

As a result, the current flowing through the first switching element 121 at the time of boosting is reduced, the power loss of the first switching element 121 is reduced, and the power factor correction circuit does not work and the input current increases. An inexpensive switching power supply that can prevent circuit burnout can be obtained.

FIG. 14 is a circuit diagram of a seventh embodiment of the switching power supply according to the present invention. In the figure, the same reference numerals as those in FIG. 1 denote the same components.

The booster circuit 12 includes a first switching element 121, an inductor element 122, and a diode 12
3, 124 and a resistor 125. The inductor element 122 is composed of a flyback transformer. The primary windings of the first switching element 121 and the inductor element 122 are connected in series, and both ends of the series circuit are connected to the rectifier circuit 11. Inductor element 122
The secondary winding of the capacitor 1 through the diode 123
Connected to 3. First switching element 121
Is composed of a field effect transistor or the like, is supplied with the switching signal S13, and switches the rectified output Er. The inductor element 122 stores energy in the primary winding when the first switching element 121 is on, converts the stored energy into a flyback voltage Vf1 when the first switching element 121 is off, and outputs the flyback voltage Vf1 as a boost output from the secondary winding. To do. Flyback voltage Vf1 is diode 1
It is supplied to the capacitor 13 via 23. The capacitor 13 smoothes the flyback voltage Vf1 and outputs the smoothed output E.
produces o. The flyback voltage Vf1 is the rectified output Er.
Set higher than. The diode 123 prevents the backflow of the smoothed output Eo. The diode 124 and the resistor 125 are connected in series, and form a charging circuit from the rectifying circuit 11 to the capacitor 13. The charging circuit charges the capacitor 13 through a route different from that of the booster circuit 12 when the switching power supply is started, and improves the starting characteristic.

The switching circuit 2 includes a second switching element 21, an inductor element 22, and a diode 25.
And a capacitor 26 and a control circuit 27.
The inductor element 22 is composed of a flyback transformer. The primary windings of the second switching element 21 and the inductor element 22 are connected in series, and both ends of the series circuit are connected to the capacitor 13. Inductor element 2
The secondary winding of 2 is connected to the capacitor 2 via the diode 25.
Connected to 6. The second switching element 21 is
The switching signal S14 is supplied to switch the smoothed output Eo. The inductor element 22 stores energy in the primary winding when the second switching element 21 is on, and stores the stored energy in the flyback voltage Vf2 when it is off.
Then, the flyback voltage Vf2 is output from the secondary winding. The flyback voltage Vf2 is supplied to the capacitor 26 via the diode 25. The capacitor 26 smoothes the flyback voltage Vf2 and outputs a direct current constant voltage Vo.
To get

The control circuit 27 receives the output voltage signal S15 corresponding to the constant voltage output Vo, and the switching signals S13 and S1 which make the constant voltage output Vo the target output voltage.
4 is output. The switching signals S13 and S14 are synchronized, the frequency is set to several kHz to several hundred kHz, and the pulse width at the time of ON is changed. When the constant voltage output Vo is lower than the target output voltage, the pulse width when turned on is widened.

Energy stored in the inductor element 122 during the on-time of the first switching element 121,
The energy stored in the inductor element 22 during the on-time of the second switching element 21 is set to be equal. Specifically, the average value of the rectified output Er is Eav, the inductance of the primary winding of the inductor element 122 is L1, the inductance of the primary winding of the inductance element 22 is L2, the first switching element 121, and the second switching element. When the on-time of 21 is Ton, (Eav * Ton) ² / (2 * L1) ≥ (Eo * Ton) ² / (2 * L2) (1). The range of the inequality sign is the smooth output E
It is set so that o does not become excessively high. As a result, the energy supplied from the inductance element 122 to the capacitor 13 and the energy supplied from the capacitor 13 to the inductor element 22 are balanced, and the smoothed output Eo is made constant.

The capacitor 13 is charged by the rectified output Er.
Is not limited to a value higher than the smoothed output Eo, and the AC input voltage Ei is dispersed over the entire time region in accordance with the fluctuation of the constant voltage output Vo. As a result, the distortion of the AC input current Ii is reduced, and the power factor is improved.

The control circuit 27 receives the smoothed output signal S1 based on the smoothed output Eo, judges that the booster circuit 12 is abnormal when the smoothed output signal S1 is lower than the reference level Vref, and the switching signal S13, Stop S14.

As a result, by balancing the amount of charge to the capacitor 13 and the amount of discharge from the capacitor 13, the current flowing through the first switching element 121 is suppressed to the necessary minimum, and the power loss of the first switching element 121 is reduced. It is possible to obtain an inexpensive switching power supply which can prevent the circuit from burning even when the power factor correction circuit does not work and the input current increases, while reducing the power consumption.

[0070]

As described above, according to the present invention, the following effects can be obtained. (A) It is possible to provide a switching power supply that can achieve power factor improvement without limiting the charging period of the capacitor. (B) A switching power supply capable of supplying a target DC voltage or AC voltage can be provided by switching the smoothed output. (C) It is possible to provide a switching power supply that can detect a case where the switching element fails and the rectified output cannot be boosted. (D) It is possible to provide an inexpensive switching power supply that can prevent the circuit from burning even when the power factor correction circuit does not work and the input current increases.

[Brief description of drawings]

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

FIG. 2 is a diagram for explaining the operation of the power factor correction circuit in the first embodiment of the switching power supply according to the present invention.

FIG. 3 is a diagram for explaining the operation of the power factor correction circuit in the second embodiment of the switching power supply according to the present invention.

FIG. 4 is a diagram for explaining the operation of the power factor correction circuit in the third embodiment of the switching power supply according to the present invention.

FIG. 5 is a diagram showing how the AC input current changes depending on the relationship between the power factor and the AC input voltage.

FIG. 6 is a circuit diagram of a fourth embodiment of the switching power supply according to the present invention.

FIG. 7 is a circuit diagram of a fifth embodiment of the switching power supply according to the present invention.

FIG. 8 is a circuit diagram of a sixth embodiment of the switching power supply according to the present invention.

FIG. 9 is a characteristic diagram showing an example of a first output signal.

FIG. 10 is a circuit diagram showing a specific example of a target setting circuit configured to change a smoothed output voltage signal.

FIG. 11 is a characteristic diagram of an inverting amplifier circuit.

FIG. 12 is a circuit diagram showing a specific example of a target setting circuit configured to change a reference voltage signal.

FIG. 13 is an input / output characteristic diagram of a reference voltage generator.

FIG. 14 is a circuit diagram of a seventh embodiment of the switching power supply according to the present invention.

[Explanation of symbols]

 1 Power Factor Correction Circuit 11 Rectifier Circuit 12 Booster Circuit 121 First Switching Element 122 Inductor Element 13 Capacitor 14 Control Circuit 15 Breaker Circuit 2 Switching Circuit 21 Second Switching Element Ei AC Input Er Rectified Output El Boosted Output Eo Smoothed Output S1 Smoothed output signal S2 Switching signal S3 Cutoff signal Vref Reference level

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁵ Identification code Office reference number FI technical display location H02M 7/06 A 9180-5H

Claims (7)

[Claims] 1. A switching power supply including a power factor correction circuit and a switching circuit, wherein the power factor correction circuit includes a rectifier circuit, a booster circuit, a capacitor, a control circuit, and a cutoff circuit. The rectifier circuit rectifies an AC input to generate a rectified output, the booster circuit includes a first switching element and an inductor element, and the first switching element and the inductor element are Serially connected, both ends of the series circuit are connected to the rectifier circuit, the first switching element switches the rectified output, and generates a boosted output through the inductor element, and the capacitor is the boosted output. Are smoothed to generate a smoothed output, and the control circuit has a reference level and receives a smoothed output signal based on the smoothed output. Supplying a switching signal such that the smoothed output becomes a target voltage to the switching element, and outputting a cutoff signal when the smoothed output is lower than the reference level. A signal is input to prevent charging of the capacitor or discharge of the capacitor, the switching circuit includes a second switching element, and the second switching element switches the smoothed output. Is a switching power supply. 2. The switching power supply according to claim 1, wherein the reference level is set higher than a peak value of the rectified output and lower than the target voltage. 3. The rectifier circuit receives a plurality of AC inputs having different rated voltages, and the control circuit has the target voltage corresponding to the AC input having the highest smoothing output of the rated voltage. The switching power supply according to claim 2, wherein the switching power supply is set to: 4. The rectifier circuit receives a plurality of AC inputs having different rated voltages, and the control circuit has the target voltage corresponding to the AC input having the highest smoothing output of the rated voltage. Set lower than the peak value of the rectified output corresponding to the AC input having the highest reference level, and set higher than the peak value of the rectified output corresponding to the lowest AC input. 1. The switching power supply described in 1. 5. The switching power supply according to claim 1, wherein the cutoff circuit is provided between the rectifier circuit and the booster circuit and cuts off a charging path to the capacitor. . 6. The switching power supply according to claim 1, wherein the cutoff circuit is provided between the capacitor and the switching circuit and cuts off a discharge path from the capacitor. 7. The switching power supply according to claim 1, wherein the cutoff circuit stops the switching operation of the switching circuit and prevents discharge from the capacitor.