JP2000139073A - Switching power supply circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To stabilize a DC output voltage and at the same time reduce the harmonic components of an input current accurately and stably over an entire operation range, to improve an input power factor by outputting a signal that is obtained by amplifying a current detection signal with a gain that changes continuously according to the change in a DC output voltage. SOLUTION: A DC output voltage error amplifier 71 obtains the error between a DC output voltage detection signal and a DC output voltage command signal, amplifies the error, and outputs an output voltage error amplification signal. A variable gain amplifier 72 outputs an input current command signal according to the output voltage error amplification signal and an input voltage detection signal. Also, a continuous type detection current gain adjustment circuit 81 inputs a current detection signal and a DC output voltage detection signal and outputs a detection current gain adjustment output signal. A current error amplifier 75 where the detection current gain adjustment output signal and an input current command signal are inputted amplifies the error between both of them and outputs a current error amplification signal. A PWM pulse signal generation circuit 76 inputs the current error amplification signal and outputs a PWM pulse signal for opening and closing a switch element 32.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a switching power supply circuit, and more particularly to a switching power supply circuit provided in an input circuit of a device using a commercial AC power supply as an input source.

[0002]

2. Description of the Related Art In recent years, a switching power supply circuit for supplying a DC voltage to a load while improving an input power factor has been applied to an input circuit of various power supply circuits using a commercial AC power supply as an input source for the purpose of shaping an input current waveform. Provided. Also, the switching power supply circuit has been receiving attention as means for reducing harmonic components contained in the input current. Such a switching power supply circuit operates such that the DC output voltage is stabilized at a predetermined target value according to circuit parameters or a control signal given from the outside. Above all, a circuit technique of actively changing a DC output voltage by a control signal, controlling power supplied to a load, and controlling an operation state of the load has become common. For example, if the load is a DC motor, and if it is desired to rotate the DC motor at higher speed or higher torque, a control signal may be provided to increase the DC output voltage. If it is desired to rotate the DC motor at a lower speed or a lower torque, a control signal may be given to reduce the DC output voltage.

[0003] Such a switching power supply circuit of variable DC output voltage has a converter circuit, and full-wave rectifies an input AC voltage and applies it to an inductor of the converter circuit. The inductor current flowing through the inductor is opened and closed by a switch element controlled based on the input current, and is converted into an alternating current of a predetermined voltage. This AC is rectified again and converted into a DC output voltage.

When the DC output voltage is changed, the current detection signal detected by the current detection circuit is adjusted by changing the gain of the gain adjustment circuit, and is transmitted to a control circuit that controls opening and closing of the switch element. The maximum value of the gain allowed for the gain adjustment circuit is determined based on the gradient when the inductor current decreases during the open period of the switch element. If the slope when the inductor current decreases becomes larger, the maximum value of the gain allowed for the gain adjustment circuit becomes smaller.
As shown in FIG. 8, the slope when the inductor current decreases during the open period of the switch element is proportional to the DC output voltage. That is, when transmitting the current detection signal to the control circuit, the change in the maximum value of the gain of the gain adjustment circuit
The ideal gain characteristic) changes in inverse proportion to the DC output voltage as shown in FIG.

In designing the switching power supply circuit, the gain of the gain adjustment circuit is determined on the assumption that the gradient when the inductor current decreases during the open period of the switch element is the largest, that is, the DC output voltage is the maximum. I do. Further, under the condition that the DC output voltage becomes smaller than the maximum value, the gain of the gain adjustment circuit needs to be designed with a margin. For example, in FIG. 9, the maximum value Vmax of the DC output voltage is reduced to a minimum value Vmin
Is designed as the operating range of the switching power supply circuit, at the minimum value Vmin, the maximum value of the gain allowed for the gain adjustment circuit is Gmax, but at the maximum value Vmax, the gain is Gh, which is half of the maximum value Gmax. Becomes As described above, when the DC output voltage is lower than the maximum value, the maximum value of the gain allowed for the gain adjustment circuit cannot be obtained at that voltage, and thus the maximum allowable current detection signal cannot be transmitted to the control circuit. . Therefore, the input current waveform cannot be made sufficiently close to the waveform of the desired input current command signal, resulting in a waveform far from the waveform of the desired input current command signal. As a result, there is a problem that the harmonic component of the input current cannot be sufficiently reduced and the input power factor cannot be improved.

[0006] As a technique for solving this problem, conventionally, Y. Z
hao et al, "Design of a Power Factor Correction Ci
rcuit with Wide Output Voltage Range ", Proceedings
ofthe Virginia Power Electronics Center Seminar,
The one described in 1997 is known. According to this, a detection current gain adjustment circuit having a gain characteristic that changes stepwise according to the DC output voltage is provided in the path of the input current detection signal, and the gain of the gain adjustment circuit with respect to the input current detection signal is adjusted according to the ideal gain characteristic. Get closer. Over a wide operating range of the switching power supply circuit, the gain of the gain adjustment circuit is close to the maximum gain allowed for the DC output voltage. As a result, it is possible to perform control for appropriately improving the input power factor from the input power source while stabilizing the DC output voltage.

Hereinafter, the conventional switching power supply circuit will be described with reference to the drawings. FIG. 10 is a circuit configuration diagram of a conventional switching power supply circuit. As shown in FIG. 10, an AC power supply 10A is connected to a rectifier circuit 20 via an input terminal 10, and an output terminal of the rectifier circuit 20 is connected to a converter circuit 30. The switch element 32 of the converter circuit 30 is opened and closed by the control circuit 70. The output of converter circuit 30 is supplied to load 63A via output terminal 63. A DC output voltage command unit 100 is connected to a DC output voltage command signal input terminal 90 of the control circuit 70.

[0008] The converter circuit 30 includes an inductor 31 connected in series to an output terminal of the rectifier circuit 20 and a rectifier circuit 2.
0, a switch element 32 connected in parallel via an inductor 31, an inductor 33 connected in series to the inductor 31, and a diode 33 connected to the switch element 32.
And a capacitor 34 connected in parallel via
A current detection circuit 40 that detects a current flowing through the rectifier circuit 20 and outputs a current detection signal is provided at a ground wiring portion of the rectifier circuit 20. A converter circuit 30 and an input voltage detection circuit 50 that detects a voltage of the rectification circuit 20 and outputs an input voltage detection signal are connected in parallel to an output terminal of the rectification circuit 20. A DC output voltage detection circuit 60 that detects a DC output voltage of the converter circuit 30 and outputs a DC output voltage detection signal is connected in parallel with the capacitor 34 of the converter circuit 30.

In the control circuit 70, a DC output voltage error amplifier 71 receives the DC output voltage detection signal and the DC output voltage command signal, obtains and amplifies an error between the two, and amplifies the output voltage error signal. Output as The variable gain amplifier 72 receives the output voltage error amplification signal and the input voltage detection signal as inputs and outputs an input current command signal. The discontinuous detection current gain adjustment circuit 73 receives the current detection signal and the DC output voltage detection signal as input, and amplifies or attenuates the current detection signal with a gain that changes discontinuously according to the DC output voltage. Outputs the gain adjustment output signal. The current error amplifier circuit 75 receives the input current command signal and the detected current gain adjustment output signal as inputs, and outputs a current error amplification signal obtained by amplifying an error between the two. The PWM pulse signal generation circuit 76 receives the current error amplification signal as an input and outputs a pulse width modulation signal (hereinafter, referred to as a PWM pulse signal) for opening and closing the switch element 32 of the converter circuit 30.

FIG. 11 is a circuit diagram of the discontinuous detection current gain adjustment circuit 73 of the control circuit 70. As shown in FIG. 11, the discontinuous detection current gain adjustment circuit 73 includes a resistor R1 connected in series to the input terminal of the current detection signal, a resistor R2 connected in parallel to the output side of the resistor R1, and a switch S1. The resistor R3 is connected to the resistor R4 via the switch S2. The logic circuit 74 sets two predetermined threshold values for the DC output voltage, and drives the switches S1 and S2 to open and close according to the magnitude of the DC output voltage.

The operation of the conventional switching power supply circuit will be described below with reference to the drawings. The inductor current flowing through the inductor 31 of the converter circuit 30 increases during the closed period of the switch element 32 and decreases during the open period of the switch element 32. In order to increase the inductor current and the input current excluding the high-frequency component of the inductor current, a PWM pulse signal of a switching cycle having a large closing time ratio (hereinafter referred to as a duty ratio) may be continued. In the case of decreasing the duty ratio, a PWM pulse signal having a switching cycle with a small duty ratio may be continued. At the output end of the rectifier circuit 20, a DC voltage obtained by full-wave rectifying the voltage of the AC power supply is obtained. The input voltage detection unit 50 detects this DC voltage
1 and the input voltage detection signal divided by the resistor 52 is output to the variable gain amplifier 72.

On the other hand, a DC output voltage detecting section 60 converts a DC output voltage detection signal obtained by dividing the output voltage of the converter circuit 30 by resistors 61 and 62 into a DC output voltage error amplifier 71.
Is applied. The DC output voltage error amplifier 71 obtains and amplifies an error between the DC output voltage detection signal and the DC output voltage command signal output from the DC output voltage command unit 100.
The DC output voltage error amplifier 71 applies a DC output voltage error amplified signal to the variable gain amplifier 72. The variable gain amplifier 72 generates an input current command signal from the input voltage detection signal and the output voltage error amplification signal, and applies it to one input terminal of the current error amplifier 75. In this conventional example, a multiplier is used as the variable gain amplifier 72. Therefore,
The waveform of the input current command signal input from the variable gain amplifier 72 to the current error amplification circuit 75 is similar to the voltage waveform obtained by full-wave rectifying the voltage waveform of the AC power supply, and the error between the DC output voltage and the DC output voltage command signal is obtained. The peak value changes according to.

The current error amplification circuit 75 generates a PWM pulse signal by amplifying a current error amplification signal obtained by amplifying an error between the detection current gain adjustment output signal output from the discontinuous detection current gain adjustment circuit 73 and the input current command signal. Applied to the circuit 76. The PWM pulse signal generation circuit 76 adjusts the duty ratio of the PWM pulse based on the current error amplification signal. The control circuit 70 changes the duty ratio of the PWM pulse signal so that the input current waveform approaches the waveform of the input current command signal output from the variable gain amplifier 72.

In the discontinuous detection current gain adjusting circuit 73, when the DC output voltage is smaller than two predetermined thresholds, the logic circuit 74 includes the switch S1 and the switch S
Open 2 together. Assuming that the impedance of the current detection circuit 40, which is the current detection signal source, is sufficiently smaller than the resistances R1 and R2, and the impedance of the current error amplifier 75 to which the detection current gain adjustment output signal is applied is sufficiently larger than the resistances R1 and R2. Since the discontinuous detection current gain adjusting circuit 73 can be regarded as a voltage dividing circuit of the resistors R1 and R2, the gain G of the discontinuous detection current gain adjusting circuit 73 is
Is given by the following equation (1).

G = R1 / (R1 + R2) (1)

When the DC output voltage increases and exceeds the first threshold value, the logic circuit 74 determines this and closes the first switch S1. As a result, the resistor R3 becomes the resistor R2
And the discontinuous detection current gain adjusting circuit 7 is connected in parallel with the resistor R2 and the resistor R3.
The gain Ga of 3 is given by the following equation (2).

Ga = Ra / (R1 + Ra) (2)

When the DC output voltage increases and exceeds the second threshold value, the logic circuit 74 determines this and closes the second switch S2. As a result, the resistors R2, R3, R
4 are connected in parallel, and assuming that the parallel combined resistance value of the resistor R2, the resistor R3, and the resistor R4 is Rb, the gain Gb of the discontinuous detection current gain adjustment circuit 73 is given by the following equation (3).

Gb = Rb / (R1 + Rb) (3)

Since the resistance values have the relationship of R2>Ra> Rb, the relationship of gain is G>Ga> Gb, and the change of the gain of the discontinuous detection current gain adjusting circuit 73 with respect to the DC output voltage is shown in FIG. As shown in (1), the characteristic is such that it decreases stepwise in a discontinuous manner as the DC output voltage increases. As a result, a characteristic closer to an ideal gain characteristic can be obtained as compared with a case where the gain of the gain adjustment circuit is not adjusted according to a change in the DC output voltage.

According to the principle described above, the switching power supply circuit of FIG. 11 amplifies or attenuates a current detection signal with a gain approaching an ideal gain characteristic, as compared with a switching power supply circuit having no detection current gain adjustment function. . As a result, control is performed to improve the input power factor from the input power supply while stabilizing the DC output voltage over a wide operating range of the switching power supply circuit.

[0022]

The above conventional switching power supply circuit has a function of improving the input power factor while stabilizing the DC output voltage, and the DC output voltage is variable. However, when trying to automatically adjust the gain of the gain adjustment circuit with respect to the detection current according to the change in the DC output voltage, the change in the gain of the discontinuous detection current gain adjustment circuit 73 is discontinuous, and at the switching point. The state of the discontinuous detection current gain adjustment circuit 73 changes rapidly. Accordingly, there has been a problem that the operation becomes unstable or a minute change in the DC output voltage occurs, which adversely affects the load.

An object of the present invention is to provide a switching power supply circuit that stably stabilizes a DC output voltage, reduces harmonic components of an input current accurately and stably over the entire operation range, and improves an input power factor. With the goal.

[0024]

A switching power supply circuit according to the present invention includes a rectifier circuit for rectifying an AC voltage supplied from an AC power supply, and a rectifier circuit connected to an output terminal of the rectifier circuit. A switching circuit that performs a switching operation at a high frequency and outputs a smoothed DC output voltage, a current detection circuit that detects an output current of the rectifier circuit and outputs a current detection signal, and detects an output voltage of the rectifier circuit An input voltage detection circuit that outputs an input voltage detection signal, a DC voltage detection circuit that detects a DC output voltage output by the converter circuit, and outputs a DC output voltage detection signal, and a voltage value of the DC output voltage. It has a DC output voltage command section for outputting a DC output voltage command signal for commanding, and a control circuit for controlling a switching operation of the converter circuit. A DC output voltage error amplifier that receives the DC output voltage detection signal and the DC output voltage command signal, obtains an error between the two, amplifies and outputs the amplified output voltage error signal, A continuous type having a current detection signal and the DC output voltage detection signal as inputs, and a detection current gain adjustment output signal obtained by amplifying or attenuating the current detection signal and having a gain that continuously changes according to the DC output voltage. A detection current gain adjustment circuit, a variable gain amplifier that receives the output voltage error amplification signal and the input voltage detection signal and outputs an input current command signal, and the input current command signal and the detection current gain adjustment output signal. As an input, a current error amplifier circuit that amplifies the error between the two and outputs a current error amplified signal, and the current error amplified signal as an input and And having a PWM pulse signal generating circuit for outputting a PWM pulse signal for opening and closing the switching elements of the inverter circuit.

Since this switching power supply circuit has a continuous detection current gain adjustment circuit, a detection characteristic that amplifies or attenuates the current detection signal with a gain characteristic that continuously changes in accordance with a change in the DC output voltage. A current gain adjustment output signal can be output. Therefore, the harmonic component of the input current can be reduced accurately and stably over the entire operation range while stabilizing the DC output voltage, and the input power factor can be improved.

Preferably, the continuous detection current gain adjustment circuit linearly reduces the level of the detection current gain adjustment output signal in accordance with an increase in the DC output voltage. Further, it is preferable that the continuous detection current gain adjustment circuit decreases the detection current gain adjustment output signal linearly with a gradient changing at a predetermined threshold value in accordance with an increase in the DC output voltage. Preferably, the continuous detection current gain adjustment circuit decreases the detection current gain adjustment output signal in inverse proportion to an increase in the DC output voltage. Further, the variable gain amplifier preferably has a multiplier.

[0027]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of a switching power supply circuit according to the present invention will be described below with reference to the drawings.

Embodiment 1 FIG. 1 is a block diagram showing a configuration of a switching power supply circuit according to Embodiment 1 of the present invention.
The same parts as those of the conventional switching power supply circuit are denoted by the same reference numerals and described. In FIG. 1, the switching power supply circuit according to the first embodiment includes an AC power supply 10 </ b> A connected to a rectifier circuit 20 that performs full-wave rectification via an input terminal 10, and a rectifier circuit 2.
The output terminal of 0 is connected to the converter circuit 30. A current detection circuit 40 is provided on the ground wiring side of the rectifier circuit 20, and an input voltage detection circuit 50 is provided on an output terminal of the rectifier circuit 20. A DC output voltage detection circuit 60 is provided at an output terminal of the converter circuit 30. The switch element 32 of the converter circuit 30 is opened and closed by the control circuit 80. The output of converter circuit 30 is supplied to load 63A via output terminal 63. The control circuit 80 includes a DC voltage command unit 100 connected to a DC output voltage command signal input terminal 90 for outputting a DC output voltage command signal.

The converter circuit 30 includes an inductor 31 connected in series to the output terminal of the rectifier circuit 20, a switch element 32 connected in parallel to the output terminal of the rectifier circuit 20 via the inductor 31, and a serial connection to the inductor 31. , And a capacitor 34 connected in parallel with the switch element 32 via the diode 33. In the control circuit 80, the DC output voltage error amplifier 7
1 receives the DC output voltage detection signal and the DC output voltage command signal as input, finds and amplifies an error between the two, and outputs it as an output voltage error amplified signal. The variable gain amplifier 72 receives the output voltage error amplification signal and the input voltage detection signal as inputs and outputs an input current command signal.
The continuous detection current gain adjustment circuit 81 receives the current detection signal and the DC output voltage detection signal as inputs and outputs a detection current gain adjustment output signal. Current error amplifier 75
Receives the input current command signal and the detected current gain adjustment output signal, amplifies the error between the two, and outputs a current error amplified signal. PWM pulse signal generation circuit 76
Is a P for inputting the current error amplified signal and driving the switching element 32 of the converter circuit 30 to open and close.
It outputs a WM pulse signal.

The switching power supply circuit according to the first embodiment has a discontinuous detection current gain adjusting circuit 7 shown in FIG.
As an alternative to 3, a continuous detection current gain adjustment circuit 81 that outputs a detection current gain adjustment output signal that amplifies or attenuates the current detection signal with a gain that continuously changes according to the DC output voltage is used. ing.

FIG. 2 is a circuit diagram showing the configuration of the continuous detection current gain adjustment circuit 81 which is a characteristic part of the switching power supply circuit of the first embodiment. FIG. 3 is a graph illustrating a gain characteristic of the detection current gain adjustment circuit with respect to a DC output voltage in the switching power supply circuit according to the first embodiment. The continuous detection current gain adjustment circuit 81 of the first embodiment receives a voltage-current conversion circuit 84 that converts a DC output voltage input via a buffer 83 into a control current Icont, and receives a current detection signal and a control current Icont. And a multiplier IC as a variable gain internal amplifier for outputting a detection current gain adjustment output signal.
(BA6110 manufactured by ROHM). In the continuous detection current gain adjustment circuit 81, the input DC output voltage is converted in the buffer 83 into a DC voltage proportional to a negative coefficient that decreases with an increase in the DC output voltage. Then, the voltage-current conversion circuit 84 converts the DC current into a control current Icont that is proportional to the DC output voltage by a negative coefficient and inputs the control current Icont to the multiplier IC 82. On the other hand, the current detection signal of the switching current is input to the multiplier IC82, and is output as a detection current gain adjustment output signal as a value obtained by multiplying the control current Icont. The level of the output detection current gain adjustment output signal decreases linearly as the DC output voltage increases. Therefore, as shown in FIG. 3, the continuous detection current gain adjustment circuit 81 outputs a detection current gain adjustment signal with a gain characteristic close to an ideal gain characteristic in a practical output voltage range of the switching power supply circuit. be able to.

Next, the operation of the switching power supply circuit according to the first embodiment will be described. At the output terminal of the rectifier circuit 20, a voltage waveform obtained by full-wave rectifying the voltage waveform of the AC power supply is obtained.
The input voltage detection circuit 50 outputs to the variable gain amplifier 72 an input voltage detection signal having a similar voltage waveform obtained by dividing this voltage by the resistors 51 and 52. On the other hand, the output voltage detected by the DC output voltage detection circuit 60 is divided by the resistors 61 and 62 and input to the DC output voltage error amplifier 71 as a DC voltage detection signal. The DC output voltage error amplifier 71 obtains an error between the DC voltage detection signal and the DC output command signal output from the DC output voltage command section 100 and amplifies the output voltage error amplified signal generated by the variable gain amplifier 72.
Output to

The variable gain amplifier 72 generates an input current command signal from the input voltage detection signal output from the input voltage detection unit 50 and the output voltage error amplification signal output from the DC output voltage error amplifier 71, and generates a current error amplification signal. Output to the circuit 75. The current error amplification circuit 75 calculates an error between the input current command signal and the detection current gain adjustment output signal output from the continuous detection current gain adjustment circuit 81 described above,
This error is amplified and output to the PWM pulse signal generation circuit 76 as a current error amplified signal. The PWM pulse signal generation circuit 76 outputs a PWM pulse signal for opening and closing the switching element 32 of the converter circuit 30 based on the current error amplification signal. In this way, control is performed to change the duty ratio of the switching element so that the input current waveform approaches the waveform of the input current command signal.
As described above, the switching power supply circuit according to the first embodiment has a function of automatically and continuously adjusting the gain of the continuous detection current gain adjustment circuit 81 with respect to the current detection signal in accordance with the DC output voltage. . Therefore, the conventional switching power supply circuit, in which the gain changes discontinuously in accordance with the DC output voltage, does not cause a problem such as unstable operation at the time of gain switching or a small fluctuation of the DC output voltage. Further, the gain characteristic of the continuous detection current gain adjustment circuit 81 is obtained in accordance with a change in the DC output voltage with characteristics close to ideal gain characteristics. As a result, the harmonic component of the input current can be reduced accurately and stably over the entire operation range while the DC output voltage is stabilized, and the input power factor can be improved.

Embodiment 2 A switching power supply circuit according to Embodiment 2 of the present invention replaces the continuous detection current gain adjusting circuit 81 of the switching power supply circuit according to Embodiment 1.
A continuous detection current gain adjustment circuit 81A is used which decreases the detection current gain adjustment output signal linearly at a predetermined threshold value in accordance with an increase in the DC output voltage. Hereinafter, the continuous detection current gain adjustment circuit 81A which is a characteristic portion will be described.

FIG. 4 is a circuit diagram of a continuous detection current gain adjustment circuit 81A according to a second embodiment of the switching power supply circuit of the present invention. FIG. 5 is a graph illustrating a gain characteristic with respect to a DC output voltage in the switching power supply according to the second embodiment. The continuous detection current gain adjustment circuit 81A in the switching power supply circuit according to the second embodiment converts a DC output voltage input via a buffer 83 into a threshold generation circuit 86 using a parallel circuit of a Zener diode and a resistor, and a threshold generation circuit 86. A voltage-current conversion circuit 84 that converts a DC voltage input through a circuit 86 into a current and outputs a control current Icont, and inputs a current detection signal and a control current Icont and outputs a detection current gain adjustment output signal. And a variable gain amplifier 82 as an internal amplifier. According to the continuous detection current gain adjustment output circuit 81A, the buffer 83 converts the DC voltage into a DC voltage proportional to a negative coefficient that decreases as the DC output voltage increases. In the threshold generation circuit 86, the magnitude of the proportionality constant changes with the Zener voltage of the Zener diode as a threshold depending on the magnitude of the DC output voltage proportional to the negative coefficient. In the voltage-current conversion circuit 84,
This DC voltage is converted into a current to obtain a control current Icont.
In the variable gain amplifier 82, the current detection signal is multiplied by the control current Icont and output as a detection current gain adjustment output signal.

The detected current gain adjustment output signal thus generated is proportional to the DC output voltage by a negative coefficient, and the magnitude of the proportionality constant is determined by the magnitude relationship between the predetermined threshold value and the DC output voltage. change. Therefore, the continuous detection current gain adjustment circuit 81A exhibits an amplification effect having a gain characteristic that decreases linearly with a gradient at a predetermined threshold value as the DC output voltage increases. Here, an example is shown in which a multiplier IC, BA6110, is used as the variable gain amplifier 82. As a result, as shown in FIG. 5, a gain characteristic closer to an ideal gain characteristic can be realized in the entire range of the DC output voltage as compared with the switching power supply circuit of the first embodiment. Therefore, there is no problem such as the unstable operation at the time of gain switching of the conventional switching power supply circuit in which the gain changes discontinuously with respect to the change of the DC output voltage, or the occurrence of minute fluctuation of the DC output voltage. As a result, the harmonic component of the input current can be reduced accurately and stably over the entire operation range while the DC output voltage is stabilized, and the input power factor can be improved.

Third Embodiment A switching power supply circuit according to a third embodiment of the present invention has a gain characteristic that decreases in inverse proportion to an increase in the DC output voltage instead of the continuous detection current gain adjustment circuit 81 of the first embodiment. A continuous detection current gain adjustment circuit 81B that outputs a detection current gain adjustment output signal is used. Hereinafter, the continuous detection current gain adjustment circuit 81B which is a characteristic portion will be described. FIG. 6 is a circuit diagram showing a continuous detection current gain adjustment circuit 81B according to a third embodiment of the switching power supply circuit of the present invention. FIG. 7 is a graph illustrating a gain characteristic of the continuous detection current gain adjustment circuit 81B according to the third embodiment. The continuous detection current gain adjustment circuit 81B of the third embodiment includes a buffer 83 for inverting the polarity of the input DC output voltage, and a DC output voltage for which the polarity is inverted, which is the output of the buffer 83, converted into a current to control the current I.
A voltage-current conversion circuit 84 that generates a cont, an internal amplifier 87 that receives a current detection signal and outputs a detection current gain adjustment signal, and a multiplier IC that is a variable gain amplifier that generates a variable gain by using the control current Icont (BA611
0) 82. The output of the multiplier IC 82 is connected to the input of the internal amplifier 87, and the input of the multiplier IC 82 is connected to the internal amplifier 8.
7 respectively.

The detection current gain adjustment circuit 81B in the switching power supply circuit of the third embodiment uses a multiplier IC82 which is a variable gain type amplifier having a gain proportional to the DC output voltage in the feedback section of the internal amplifier 87. Accordingly, the continuous detection current gain adjustment circuit 81B exhibits an amplifying action having a gain characteristic that is inversely proportional to the DC output voltage. Here, the above multipliers IC and B are used as variable gain amplifiers.
The example using A6110 was shown. The continuous detection current gain adjustment circuit 81B of the third embodiment adjusts the gain of the detection current gain adjustment output signal so as to decrease in inverse proportion to the increase in the DC output voltage. As a result, as shown in FIG. 7, a detection current gain adjustment circuit having a gain characteristic extremely close to an ideal gain characteristic in the entire range of the DC output voltage can be realized. Therefore, the conventional switching power supply circuit in which the gain changes discontinuously with respect to the change in the DC output voltage does not cause a problem such as unstable operation at the time of gain switching or a minute change in the DC output voltage. As a result, it is possible to stably stabilize the DC output voltage, reduce the harmonic components of the input current accurately and stably over the entire operation range, and improve the input power factor.

[0039]

As described above, the switching power supply circuit of the present invention replaces the conventional discontinuous detection current gain adjustment circuit with a current detection with a gain that continuously changes in response to a change in the DC output voltage. A continuous detection current gain adjustment circuit that outputs a detection current gain adjustment output signal that amplifies or attenuates a signal is used. Therefore, the switching power supply circuit of the present invention has a function of automatically and continuously adjusting the gain of the continuous detection current gain adjustment circuit with respect to the current detection signal according to the DC output voltage. In the switching power supply circuit of the present invention, the operation becomes unstable at the time of gain switching or a minute fluctuation of the DC output voltage of the conventional discontinuous detection current gain adjustment circuit in which the gain changes discontinuously with respect to the change of the DC output voltage. Can solve problems such as the occurrence of As a result, the switching power supply circuit of the present invention can stably stabilize the DC output voltage, reduce the harmonic components of the input current accurately and stably over the entire operation range, and improve the input power factor.

[Brief description of the drawings]

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

FIG. 2 is a circuit diagram of a detection current gain adjustment circuit in the switching power supply circuit according to the first embodiment of the present invention.

FIG. 3 is a graph showing gain characteristics of a detection current gain adjustment circuit in the switching power supply circuit according to the first embodiment of the present invention.

FIG. 4 is a circuit diagram of a detection current gain adjustment circuit in a switching power supply circuit according to Embodiment 2 of the present invention.

FIG. 5 is a graph illustrating gain characteristics of a detection current gain adjustment circuit in the switching power supply circuit according to the second embodiment of the present invention.

FIG. 6 is a circuit diagram of a detection current gain adjustment circuit in a switching power supply circuit according to Embodiment 3 of the present invention.

FIG. 7 is a graph showing gain characteristics of a detection current gain adjustment circuit in the switching power supply circuit according to Embodiment 3 of the present invention.

FIG. 8 is a graph showing a change in a gradient when the inductor current decreases during an open period of the switch element with respect to a change in a DC output voltage in a conventional switching power supply circuit.

FIG. 9 is a graph showing an ideal gain characteristic of a detection current gain adjustment circuit with respect to a change in a DC output voltage in a conventional switching power supply circuit.

FIG. 10 is a block diagram showing a configuration of a conventional switching power supply circuit.

FIG. 11 is a circuit diagram of a discontinuous detection current gain adjustment circuit in a conventional switching power supply circuit.

FIG. 12 is a graph showing a gain characteristic of a discontinuous detection current gain adjustment circuit in a conventional switching power supply circuit.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 Input terminal 20 Rectifier circuit 30 Converter circuit 31 Inductor 32 Switching element 33 Diode 34 Capacitor 40 Current detection circuit 50 Input voltage detection circuit 60 DC output voltage detection circuit 63 Output terminal 80 Control circuit 71 DC output voltage error amplifier 72 Gain variable amplifier 81 , 81A, 81B Continuous detection current gain adjustment circuit 75 Current error amplification circuit 76 PWM pulse signal generation circuit 82 Multiplier IC (BA6110) 83 Buffer 84 Voltage-current conversion circuit 86 Zener diode 87 Internal amplifier 90 DC output voltage command signal input Terminal 100 DC output voltage command signal generator

Continued on the front page F term (reference) 5H006 AA02 CA00 CB01 DA02 DA04 DB02 DB05 DC02 DC04 DC05 5H730 AA18 AS13 BB14 CC01 EE07 EE24 FD01 FD11 FD41 FG05 FG25 FG26

Claims (5)

[Claims] 1. A rectifier circuit for rectifying an AC voltage supplied from an AC power supply, connected to an output terminal of the rectifier circuit, performing a switching operation at a frequency higher than the frequency of the AC voltage, and outputting a DC output voltage. A converter circuit; a current detection circuit that detects an output current of the rectifier circuit and outputs a current detection signal; an input voltage detection circuit that detects an output voltage of the rectifier circuit and outputs an input voltage detection signal; Detects the DC output voltage output by the circuit,
A DC voltage detection circuit that outputs a DC output voltage detection signal; a DC output voltage command unit that outputs a DC output voltage command signal that commands a voltage value of the DC output voltage; the DC output voltage detection signal and the DC output voltage A DC output voltage error amplifier that receives a command signal as an input, obtains an error between the two, and amplifies and outputs the amplified output voltage error signal; and the current detection signal and the DC output voltage detection signal as inputs, A continuous detection current gain adjustment circuit that outputs a detection current gain adjustment output signal that amplifies or attenuates the detection signal and has a gain that changes continuously according to the DC output voltage; and the output voltage error amplification signal and the input. A variable gain amplifier that receives a voltage detection signal as an input and outputs an input current command signal; and the input current command signal and the detection current gain adjustment. A current error amplifier circuit that receives a power signal as an input and outputs a current error amplifier signal of an error between the two, and a pulse width modulation signal that receives the current error amplifier signal as an input and opens and closes a switch element of the converter circuit. And a PWM pulse signal generating circuit that outputs the following. 2. The continuous detection current gain adjustment circuit according to claim 1,
2. The switching power supply circuit according to claim 1, wherein the level of the detection current gain adjustment output signal is decreased linearly as the DC output voltage increases. 3. The continuous detection current gain adjustment circuit according to claim 1,
2. The level of the detection current gain adjustment output signal is reduced in a linear manner with a gradient changing at a predetermined threshold value in accordance with an increase in the DC output voltage.
3. The switching power supply circuit according to item 1. 4. The continuous detection current gain adjustment circuit according to claim 1,
2. The switching power supply circuit according to claim 1, wherein a level of the detection current gain adjustment output signal is reduced in inverse proportion to an increase in the DC output voltage. 5. The switching power supply circuit according to claim 1, wherein the variable gain amplifier has a multiplier.