JP7640492B2 - Switching Power Supply Unit - Google Patents

Description

The present invention relates to a switching power supply device that rectifies and smoothes a commercial AC voltage to generate an intermediate voltage, and converts the intermediate voltage to a specified output voltage using a DC-DC converter.

As disclosed in Patent Document 1, for example, there has been a switching power supply device that includes a power conversion circuit that converts an input voltage into a predetermined output voltage, and controls the on/off of a switching element in the power conversion circuit so that an output voltage signal, which is a voltage signal that detects the output voltage, approaches a reference voltage. If the input power supply of this type of switching power supply device is a commercial AC power supply, it can be represented as switching power supply device 10 shown in Figure 8.

The switching power supply 10 is composed of a rectifier/smoothing circuit 12 that rectifies and smoothes a commercial AC voltage Vi (commercial frequency Fac) to output an intermediate voltage Vc, a DC-DC converter 14 that converts the intermediate voltage Vc to a predetermined output voltage Vo, and a switching control circuit 16 that feedback controls the on/off of a switching element 14a of the DC-DC converter 14 so that an output voltage signal Vo1, which is a voltage signal that detects the output voltage Vo, approaches a reference voltage Vref.

The inverter type of the DC-DC converter 14 is not particularly limited, but in order to ensure safety with respect to commercial AC power (e.g., to prevent electric shock accidents), an input/output isolated type converter is often selected.

The switching control circuit 16 is composed of an error amplifier circuit 18 that generates a first control signal Ver1, which is a voltage signal obtained by amplifying the difference between the output voltage signal Vo1 and the reference voltage Vref, and a drive pulse generation circuit 20 that pulse-width modulates the first control signal Ver1 to generate a drive pulse Vg for the switching element 14a.

The error amplifier circuit 18 is a so-called inverting amplifier circuit, and is configured to output a first control signal Ver1, which is the inverted and amplified voltage obtained by subtracting a reference voltage Vref from the output voltage signal Vo1, through an insulating means 18a.

The drive pulse generating circuit 20 is composed of a comparator 22 and a triangular wave generator 24. The triangular wave generator 24 is a block that generates a reference triangular wave Vosc of a predetermined frequency, and the frequency of the reference triangular wave Vosc becomes the switching frequency of the switching element 14a.

The comparator 22 receives the reference triangular wave Vosc at its inverting input terminal, receives the first control signal Ver1 at its non-inverting input terminal, and outputs a drive pulse Vg from its output terminal. In other words, during the period when the first control signal Ver1 is higher than the reference triangular wave Vosc, the drive pulse Vg is set to a high level to turn on the switching element 14a, and during the period when the first control signal Ver1 is lower than the reference triangular wave Vosc, the drive pulse Vg is set to a low level to turn off the switching element 14a.

Therefore, when the first control signal Ver1 drops, the drive pulse generating circuit 20 changes the time ratio between the high level and the low level of the drive pulse Vg in a direction that reduces the time ratio of the switching element 14a that is on, and when the first control signal Ver1 rises, the drive pulse generating circuit 20 changes the time ratio between the high level and the low level of the drive pulse Vg in a direction that increases the time ratio of the switching element 14a that is on.

Next, the operation of the feedback control of the switching power supply device 10 will be briefly explained. For example, if the output voltage Vo, which was held at the target value, rises slightly for some reason, the error amplifier circuit 18 detects that the output voltage signal Vo1 has become higher than the reference voltage Vref and lowers the first control signal Ver1, and the drive pulse generation circuit 20 changes the time ratio of the high level and low level of the drive pulse Vg in a direction that reduces the time ratio of the switching element 14a when it is on, so that the output voltage Vo falls and returns to the target value. On the other hand, if the output voltage Vo, which was held at the target value, falls slightly for some reason, the error amplifier circuit 18 detects that the output voltage signal Vo1 has become lower than the reference voltage Vref and raises the first control signal Ver1, and the drive pulse generation circuit 20 changes the time ratio of the high level and low level of the drive pulse Vg in a direction that increases the time ratio of the switching element 14a when it is on, so that the output voltage Vo rises and returns to the target value.

In this switching power supply device 10, the intermediate voltage Vc is not a completely DC voltage, but is a voltage in which a pulsating component Vrip of a frequency Fr corresponding to the commercial frequency Fac is superimposed on the DC component Vdc, resulting in the problem that an unnecessary low-frequency ripple component Vor that oscillates in approximately the same phase as the pulsating component Vrip is generated in the output voltage Vo.

First, the pulsating component Vrip and frequency Fr will be described. When the commercial AC power supply is single-phase, for example, as shown in FIG. 9(a), the rectifying and smoothing circuit 12 can be configured with a rectifying section 26 that full-wave rectifies the commercial AC voltage Vi (commercial frequency Fac) with four diodes, and a smoothing section 28 that is configured with a capacitor that smoothes the full-wave rectified voltage. In this case, as shown in FIG. 9(c), a pulsating component Vrip with a frequency Fr=2·Fac is generated in the intermediate voltage Vc. Also, as shown in FIG. 9(b), when the rectifying and smoothing circuit 12 is configured with the above-mentioned rectifying section 26 and a smoothing section 30 that is configured with a chopper circuit for power factor improvement, a pulsating component Vrip with a frequency Fr=2·Fac is generated in the intermediate voltage Vc.

When the commercial AC voltage is three-phase, for example, as shown in FIG. 10(a), the rectifying and smoothing circuit 12 can be composed of a rectifying section 32 that full-wave rectifies the commercial AC voltage Vi using six diodes, and the smoothing section 28 described above. In this case, as shown in FIG. 10(b), a pulsating component Vrip with a frequency Fr = 3·Fac is generated in the intermediate voltage Vc.

The pulsating component Vrip, which is the main cause of the low-frequency ripple component Vor, can be reduced by increasing the capacitor values of the smoothing sections 28 and 30. However, because the frequency Fr is low, many large-capacity capacitors are required, which leads to problems of larger equipment and higher costs.

Even if the pulsating component Vrip occurs, the low-frequency ripple component Vor can, in principle, be reduced by increasing the gain in the low-frequency band (band including frequency Fr) of the feedback control system of the output voltage Vo. However, if the gain in the band of frequency Fr is increased, the gain margin and phase margin of the feedback control system in the high-frequency band cannot be secured and oscillation occurs, so in practice, the gain in the band of frequency Fr must be kept low. Therefore, as shown in FIG. 11, it is not possible to generate an oscillation component of frequency Fr (a component that attempts to suppress the low-frequency ripple component Vor) corresponding to the pulsating component Vrip in the waveform of the first control signal Ver1, and a large low-frequency ripple component Vor occurs in the output voltage Vo.

Another possible method for reducing the low-frequency ripple component Vor is to modify the switching power supply 10 as shown in FIG. 12 as the switching power supply 10x. The switching power supply 10x is characterized in that the triangular wave generator 24 is changed to a unique triangular wave generator 24x, and the slope of the reference triangular wave Vosc is changed approximately in proportion to the intermediate voltage Vc. This modification performs feedforward control, which stabilizes the output voltage Vo by changing the on-time ratio of the main switching element 14a in response to changes in the intermediate voltage Vc, and can reduce the low-frequency ripple component Vor. This feedforward control technology is disclosed in Patent Document 2.

JP 2014-128110 A JP 2010-124524 A

As described above, it is difficult for the conventional switching power supply device 10 to reduce the low-frequency ripple component Vor of the output voltage Vo.

The conventional switching power supply device 10x performs feedforward control using the slope of the reference triangular wave Vosc, so in principle it can reduce the low-frequency ripple component Vor of the output voltage Vo. However, since the slope of the reference triangular wave Vosc also greatly affects the gain characteristics of the feedback control system, there is a problem that the gain characteristics of the feedback control system fluctuate periodically and become unstable due to the influence of the ripple component Vrip of the intermediate voltage Vc. In addition, as explained in Patent Document 2, feedforward control using the slope of the reference triangular wave Vosc requires special measures to avoid saturation of the transformer at low input voltages, and depending on the content of these measures, there are issues such as a decrease in power supply efficiency, so there are circumstances in which it is desirable to avoid using it in general-purpose power supplies that require a simple and inexpensive configuration or power supplies with a wide range of input voltages Vi.

The present invention has been made in consideration of the above background technology, and aims to provide a switching power supply device with a simple configuration that can easily reduce the low-frequency ripple components of the output voltage.

The present invention includes a rectifying and smoothing circuit that rectifies and smoothes a commercial AC voltage to output an intermediate voltage, a DC-DC converter that converts the intermediate voltage into a predetermined output voltage, and a switching control circuit that controls on/off of a switching element of the DC-DC converter so that an output voltage signal, which is a voltage signal obtained by detecting the output voltage, approaches a reference voltage,
the switching control circuit includes an error amplifier circuit that generates a first control signal, which is a voltage signal obtained by inverting and amplifying a voltage obtained by subtracting the reference voltage from the output voltage signal; a ripple component signal injection circuit that detects a ripple component of a frequency corresponding to a commercial frequency included in the intermediate voltage, and generates a second control signal in which a voltage signal obtained by inverting and amplifying the ripple component is added to the first control signal or a voltage signal obtained by non-inverting and amplifying the first control signal; and a drive pulse generation circuit that pulse-width modulates the second control signal to generate a drive pulse for the switching element;
The drive pulse generating circuit is a switching power supply device that changes the time ratio of the high level and low level of the drive pulse in a direction that reduces the on-time ratio of the switching element when the second control signal drops, and changes the time ratio of the high level and low level of the drive pulse in a direction that increases the on-time ratio of the switching element when the second control signal rises.

The pulsating flow component signal injection circuit can be composed of an operational amplifier that receives the first control signal at its non-inverting input terminal and outputs the second control signal from its output terminal, an input circuit consisting of a series circuit of a capacitor and a resistor connected between the inverting input terminal of the operational amplifier and the output terminal of the rectifying and smoothing circuit, and a feedback circuit consisting of a parallel circuit of a capacitor and a resistor connected between the output terminal and the inverting input terminal of the operational amplifier.

Particularly in the switching power supply of the present invention, the pulsating component signal injection circuit comprises a voltage dividing circuit which resistively divides the intermediate voltage to generate a stepped-down voltage, a pulse width modulation section which generates a rectangular wave voltage having a duty set based on the stepped-down voltage, a smoothing circuit which smoothes the rectangular wave voltage to generate a smoothed voltage proportional to the stepped-down voltage, an operational amplifier which receives the first control signal at its non-inverting input terminal and outputs the second control signal from its output terminal, an input circuit which is connected between the inverting input terminal of the operational amplifier and the output end of the smoothing circuit and which is composed of a series circuit of a capacitor and a resistor, and a feedback circuit which is connected between the output terminal and the inverting input terminal of the operational amplifier and which is composed of a parallel circuit of a capacitor and a resistor.

Alternatively, in the switching power supply device of the present invention, the pulsating flow component signal injection circuit is composed of a voltage dividing circuit that resistively divides the intermediate voltage to generate a step-down voltage, an AD converter that converts the step-down voltage into a step-down voltage signal that is a digital signal, a digital signal processing unit that generates a proportional voltage signal that is a digital signal corresponding to the step-down voltage based on the step-down voltage signal, a DA converter that converts the proportional voltage signal into a proportional voltage that is an analog voltage, an operational amplifier that receives the first control signal at a non-inverting input terminal and outputs the second control signal from an output terminal, an input circuit that is connected between the inverting input terminal of the operational amplifier and the output terminal of the DA converter and is composed of a series circuit of a capacitor and a resistor, and a feedback circuit that is connected between the output terminal and the inverting input terminal of the operational amplifier and is composed of a parallel circuit of a capacitor and a resistor.

In addition, for example , the power supply may include a rectifying and smoothing circuit that rectifies and smoothes a commercial AC voltage to output an intermediate voltage, a DC-DC converter that converts the intermediate voltage into a predetermined output voltage, and a switching control circuit that controls the on/off of a switching element of the DC-DC converter so that an output voltage signal that is a voltage signal of the output voltage approaches a reference voltage.
the switching control circuit includes an error amplifier circuit for generating a first control signal, which is a voltage signal obtained by non-inverting and amplifying a voltage obtained by subtracting the reference voltage from the output voltage signal; a ripple component signal injection circuit for detecting a ripple component of a frequency corresponding to a commercial frequency included in the intermediate voltage, and for generating a second control signal in which a voltage signal obtained by non-inverting and amplifying the ripple component is added to the first control signal or a voltage signal obtained by non-inverting and amplifying the first control signal; and a drive pulse generation circuit for pulse-width modulating the second control signal to generate a drive pulse for the switching element;
The drive pulse generating circuit changes the time ratio of the high level and low level of the drive pulse in a direction that reduces the on-time ratio of the switching element when the second control signal rises, and changes the time ratio of the high level and low level of the drive pulse in a direction that increases the on-time ratio of the switching element when the second control signal falls .

The switching power supply of the present invention is provided with a uniquely configured ripple component signal injection circuit, which performs feedforward control to reduce the on-time ratio of the main switching element when the ripple component of the intermediate voltage oscillates in the upward direction, and to reduce the on-time ratio of the main switching element when the ripple component oscillates in the downward direction. This makes it possible to easily solve the problem of low-frequency ripple components occurring in the output voltage due to the ripple component of the intermediate voltage, without significantly affecting the feedback control system.

In addition, the ripple component signal injection circuit injects the ripple component signal into the feedback control system at a position just before pulse width control is performed to generate the drive pulse (the input end of the drive pulse generation circuit), so it is extremely effective in changing the operation of the main switching element extremely quickly in response to changes in the ripple component.

1 is a circuit diagram showing one embodiment of a switching power supply device. 2 is a diagram illustrating an example of the operation of the pulsating flow component signal injection circuit of FIG. 1 and a method for setting constants. 2 is a time chart showing operational waveforms of each part of the switching power supply device of FIG. 1 . 1 is a circuit diagram showing a switching power supply device according to a first embodiment of the present invention; 4 is a time chart showing operational waveforms of each part of the switching power supply device of the first embodiment; FIG. 11 is a circuit diagram showing another embodiment of a switching power supply device. 7 is a time chart showing operational waveforms of each part of the switching power supply device of FIG. 6 . FIG. 1 is a circuit diagram showing an example of a conventional switching power supply device. 1A and 1B are circuit diagrams showing an example of a general rectifying smoothing circuit, and FIG. 1C is a time chart showing the waveform of an intermediate voltage. 1A is a circuit diagram showing an example of a general rectifying smoothing circuit, and FIG. 1B is a time chart showing a waveform of an intermediate voltage. 9 is a time chart showing operational waveforms of each part of the switching power supply device of FIG. 8 . FIG. 11 is a circuit diagram showing another example of a conventional switching power supply device.

< One form of switching power supply device >
An embodiment of a switching power supply device will be described below with reference to Figures 1 to 3. Here, components similar to those of the conventional switching power supply device 10 are given the same reference numerals and descriptions thereof will be omitted.

As shown in the circuit diagram of FIG. 1, a switching power supply 34 of this embodiment has many features in common with the switching power supply 10 as a whole, but a major difference is that a pulsating current component signal injection circuit 36 is added to the switching control circuit 16.

The pulsating flow signal injection circuit 36 has an operational amplifier 38. An input circuit 40 consisting of a series circuit of a capacitor C1 and a resistor R1 is connected between the inverting input terminal of the operational amplifier 38 and the output terminal of the rectifying and smoothing circuit 12, and a feedback circuit 42 consisting of a parallel circuit of a capacitor C2 and a resistor R2 is connected between the inverting input terminal and the output terminal of the operational amplifier 38. The non-inverting input terminal of the operational amplifier 38 is connected to the output terminal of the error amplifier circuit 18, and the output terminal of the operational amplifier 38 is connected to the non-inverting input terminal of the comparator 22 of the drive pulse generation circuit 20.

2, in the ripple signal injection circuit 36, the first control signal Ver1 output by the error amplifier circuit 18 is input to the non-inverting input terminal of an operational amplifier 38, which is one input end, and the intermediate voltage Vc (=DC component Vdc+ripple component Vrip) is input to one end on the input circuit 40 side, which is the opposite input end, and the second control signal Ver2 is output from the output terminal of the operational amplifier 38, which is the output end. The second control signal Ver2 can be expressed as the following equations [1] and [2].
Ver2=(1+Z2/Z1)・Ver1−(Z2/Z1)・Vc...[1]
Ver2≒(1+Z2/Z1)・Ver1−(Z2/Z1)・Vrip...[2]
Here, Z1 is the combined impedance of the capacitor C1 and resistor R1 of the input circuit 40, and Z2 is the combined impedance of the capacitor C2 and resistor R2 of the feedback circuit 42. Equation [2] is obtained by substituting Vc=Vdc+Vrip into equation [1] and then eliminating Vdc coupled by the capacitor C1 from the equation.

The values of R1, C1, R2, and C2 that determine the impedances Z1 and Z2 are adjusted individually according to the circumstances of the power supply device, but it is preferable to adjust them so that R1>>(ωC1) ^-1 and R2<<(ωC2) ^-1 are satisfied at the frequency Fr [frequency corresponding to the commercial frequency] of the pulsating component Vrip, and set them so that almost no phase delay occurs, as shown in formula [3]. Furthermore, if adjustment is made so that R1>>R2 is satisfied, the setting will be as shown in the following formula [4].
Ver2≒(1+R2/R1)/Ver1-(R2/R1)/Vrip...[3]
Ver2≒ Ver1－(R2/R1)・Vrip...[4]
In the case of the switching power supply device 34, since the pulsating component Vrip of the intermediate voltage Vc is several tens of volts and the first control signal Ver1 is several volts, it is necessary to step down the pulsating component Vrip to a level that can be injected into the first control signal Ver1. Therefore, it is preferable to adjust the pulsating signal injection circuit 36 so as to satisfy the condition R1>>R2 and set it to the formula [4].

In this way, the pulsating signal injection circuit 36 detects the pulsating component Vrip of the frequency Fr contained in the intermediate voltage Vc, generates a second control signal Ver2 by adding a voltage signal obtained by non-inverting and amplifying the first control signal Ver1 with an amplification factor of 1 and inverting and amplifying the pulsating component Vrip, -(R2/R1) · Vrip, and outputs it to the downstream drive pulse generation circuit 20.

Next, the operation of the switching power supply device 34 will be described. First, assuming that the pulsating voltage Vrip is not generated in the intermediate voltage Vc, the operation of the feedback control of the switching power supply device 34 will be briefly described. For example, if the output voltage Vo, which was held at the target value, rises slightly for some reason, the error amplifier circuit 18 detects that the output voltage signal Vo1 has become higher than the reference voltage Vref, and the first control signal Ver1 is lowered. The first control signal Ver1 passes through the pulsating component injection circuit 36 and is input to the drive pulse generation circuit 20, which changes the time ratio of the high level and low level of the drive pulse Vg in a direction that reduces the time ratio of the switching element 14a when it is on, so that the output voltage Vo drops and returns to the target value. Conversely, if the output voltage Vo, which had been held at the target value, drops slightly for some reason, the error amplifier circuit 18 detects that the output voltage signal Vo1 has become lower than the reference voltage Vref and raises the first control signal Ver1, which passes through the pulsating component injection circuit 38 and is input to the drive pulse generation circuit 20, which then changes the time ratio of the high level and low level of the drive pulse Vg in the direction of increasing the time ratio of the switching element 14a being on, causing the output voltage Vo to rise and return to the target value. The above operation is basically the same as in the case of the conventional switching power supply unit 10.

The actual operation of the switching power supply 34, that is, the operation when a large ripple component Vrip (frequency Fr) occurs in the intermediate voltage Vc, is shown in Figure 3. Since the gain of the error amplifier circuit 18 in the low frequency band including the frequency Fr is kept low, the waveform of the first control signal Ver1 hardly generates an oscillation component of the frequency Fr corresponding to the ripple component Vrip (a component that tries to suppress the low frequency ripple component Vor).

The pulsating component signal injection circuit 36 receives the intermediate voltage Vc and the first control signal Ver1, and generates a second control signal Ver2 in which the voltage signal -(R2/R1)·Vrip, which is the inverted and amplified version of the pulsating component Vrip, is added to the first control signal Ver1. Therefore, the waveform of the second control signal Ver2 sometimes oscillates downward when the pulsating component Vrip oscillates upward, and sometimes oscillates downward when the pulsating component Vrip oscillates upward.

When the second control signal Ver2 oscillates downward (when the pulsating component Vrip oscillates upward), the drive pulse generating circuit 20 changes the time ratio of the high level and low level of the drive pulse Vg in a direction that reduces the on-time ratio of the switching element 14a. Therefore, the output voltage Vo cannot rise in phase with the pulsating component Vrip and is maintained at a substantially constant value. Conversely, when the second control signal Ver2 oscillates upward (when the pulsating component Vrip oscillates downward), the time ratio of the high level and low level of the drive pulse Vg is changed in a direction that increases the on-time ratio of the switching element 14a. Therefore, the output voltage Vo cannot fall in phase with the pulsating component Vrip and is maintained at a substantially constant value. Therefore, the low-frequency ripple component Vor is hardly generated.

In order to achieve Vor ≒ 0, it is necessary to set the magnitude of the voltage signal - (R2/R1) Vrip, which corresponds to the ripple component Vrip, to an appropriate value, but this can be easily optimized by adjusting the values of resistors R1 and R2.

As described above, the switching power supply 34 is provided with a predetermined pulsating component signal injection circuit 36, and thereby performs feedforward control in which the on-time ratio of the main switching element 14a is reduced when the pulsating component Vrip of the intermediate voltage Vc oscillates in the upward direction, and the on-time ratio of the main switching element 14a is reduced when the pulsating component Vrip oscillates in the downward direction. This solves the problem of low-frequency ripple component Vor occurring in the output voltage Vo due to the influence of the pulsating component Vrip of the intermediate voltage Vc, without significantly affecting the feedback control system.

In addition, the ripple component signal injection circuit 36 injects the ripple component signal -(R2/R1)・Vrip at a position in the feedback control system just before pulse width control is performed to generate the drive pulse Vg (at the input end of the drive pulse generation circuit 20), so the operation of the main switching element can be changed extremely quickly in response to changes in the ripple voltage Vrip, which is very effective.

<One embodiment of the switching power supply device of the present invention >
Next, an embodiment of the switching power supply device of the present invention will be described with reference to Figures 4 and 5. Here, the same components as those of the switching power supply device 34 described above are given the same reference numerals and the description thereof will be omitted.

As shown in the circuit diagram of FIG. 4, the switching power supply 44 of this embodiment has many features in common with the switching power supply 34, but differs in that a new pulsating voltage injection circuit 46 is provided in the switching control circuit 16 instead of the pulsating component signal injection circuit 36 described above.

The pulsating voltage injection circuit 46 includes a voltage divider circuit 48, a pulse width modulation unit 50, and a smoothing circuit 52. The pulse width modulation unit 50 is a block that performs digital signal processing, and is provided within a digital processor that operates at low voltage.

The voltage divider circuit 48 resistively divides the intermediate voltage Vc, which is a high voltage of several hundred volts, to generate a low voltage (step-down voltage Vc1) that can be handled by the pulse width modulation unit 50 in the digital processor. The pulse modulation unit 50 generates a square wave voltage Vp (peak value V1) with a duty D set based on the step-down voltage Vc1. The smoothing circuit 52 smoothes the square wave voltage Vp to generate a smoothed voltage Vc2 proportional to the step-down voltage Vc1. Therefore, the smoothed voltage Vc2 can be expressed as in Equation [5].
Vc2=D・V1=k2・Vc1=k2・(k1・Vc)=k1・k2(Vdc+Vrip) ・・・・・・［5］
Here, k2 is a proportionality coefficient of D·V1 to Vc1, and k1 is a voltage division ratio of the voltage divider circuit 40.

The pulsating voltage injection circuit 46 also includes an amplifier circuit that is configured with the operational amplifier 38, input circuit 40, and feedback circuit 42, similar to those described above. However, one end of the input circuit 40 is connected to the output end of the smoothing circuit 52, not the output end of the rectifying smoothing circuit 12.

In the case of the pulsating voltage injection circuit 46, the smoothed voltage Vc2 (= k1 k2 Vc) is input to one end of the input circuit 40, so Vc in equation [1] is replaced with k1 k2 Vc, and Vrip in equations [2] to [4] is replaced with k1 k2 Vrip. However, since k1 k2 Vrip is a sufficiently low voltage in this case, it is preferable to adjust the values of R1 and R2 so that R1 does not become >> R2, and set it to equation [3].

In this way, the pulsating signal injection circuit 46 detects the pulsating component Vrip of the frequency Fr contained in the intermediate voltage Vc, generates a second control signal Ver2 by adding a voltage signal -(R2/R1)·k1·k2·Vrip obtained by inverting and amplifying the pulsating component Vrip to the voltage signal (1+R2/R1)·Ver1 obtained by non-inverting and amplifying the first control signal Ver1, and outputs it to the downstream drive pulse generation circuit 20.

Next, we will explain the operation of the switching power supply device 44. The feedback control operation of the switching power supply device 44 (operation when it is assumed that the pulsating voltage Vrip is not generated in the intermediate voltage Vc) is similar to that of the switching power supply device 34, so the explanation will be omitted.

The actual operation of the switching power supply 34, that is, the operation when a large ripple component Vrip (frequency Fr) occurs in the intermediate voltage Vc, is shown in Figure 5. Since the gain of the error amplifier circuit 18 in the low frequency band including the frequency Fr is kept low, the waveform of the first control signal Ver1 hardly generates an oscillation component of the frequency Fr corresponding to the ripple component Vrip (a component that tries to suppress the low frequency ripple component Vor).

The pulsating component signal injection circuit 46 receives the intermediate voltage Vc and the first control signal Ver1, and generates a second control signal Ver2 which is the sum of the pulsating voltage signal -(R2/R1)·k·Vrip obtained by inverting and amplifying the pulsating component Vrip, and the voltage signal (1+R2/R1)·Ver1 obtained by non-inverting and amplifying the first control signal Ver1. Therefore, the waveform of the second control signal Ver2 sometimes oscillates downward when the pulsating component Vrip oscillates upward, and sometimes oscillates downward when the pulsating component Vrip oscillates upward.

When the second control signal Ver2 oscillates downward (when the pulsating component Vrip oscillates upward), the drive pulse generating circuit 20 changes the time ratio of the high level and low level of the drive pulse Vg in a direction that reduces the on-time ratio of the switching element 14a. Therefore, the output voltage Vo cannot rise in phase with the pulsating component Vrip and is maintained at a substantially constant value. Conversely, when the second control signal Ver2 oscillates upward (when the pulsating component Vrip oscillates downward), the time ratio of the high level and low level of the drive pulse Vg is changed in a direction that increases the on-time ratio of the switching element 14a. Therefore, the output voltage Vo cannot fall in phase with the pulsating component Vrip and is maintained at a substantially constant value. Therefore, the low-frequency ripple component Vor is hardly generated.

In order to achieve Vor ≒ 0, the voltage signal -(R2/R1) k1 k2 Vrip, which corresponds to the ripple component Vrip, must be set to an appropriate value, but this can be easily optimized by adjusting the values of resistors R1 and R2 and coefficients k1 and k2.

As described above, the switching power supply 44 can provide the same operational effects as the switching power supply 34. Furthermore, the pulsating flow component signal injection circuit 46 is provided with the pulse width modulation section 50 and the smoothing circuit 52, which work together to generate the analog smoothed voltage Vc2, providing even more excellent effects .

The pulse width modulation unit 50 is a block that is provided within a digital processor and performs digital signal processing. By combining it with the smoothing circuit 52, it becomes possible to generate the smoothed voltage Vc2 with high resolution without using an expensive high-speed digital processor, and the intermediate voltage Vc can be detected with high accuracy.

The operation of the pulse width modulation unit 50 can be freely set by rewriting the program, so that, for example, it can be set to an operation mode that "performs operations to inject a pulsating flow component signal" under normal circumstances, and switched to another operation mode when a specific situation occurs. Therefore, by providing this pulsating flow component signal injection circuit 46, it becomes possible to perform feedforward control for a different purpose when a specific situation occurs, or to control a protective operation that reduces the output voltage Vo when an abnormality occurs, allowing for highly intelligent and advanced control.

< Other forms of switching power supply device >
Next, another embodiment of the switching power supply device will be described with reference to Figures 6 and 7. Here, the same components as those of the switching power supply device 34 described above are given the same reference numerals and the description thereof will be omitted.

As shown in the circuit diagram of FIG. 6, in this form of switching power supply device 54, the error amplifier circuit 18, the ripple component signal injection circuit 36 and the drive pulse generating circuit 20 of the switching power supply device 34 are replaced with a new error amplifier circuit 56, a ripple component signal injection circuit 58 and a drive pulse generating circuit 60, respectively.

The error amplifier circuit 56 generates a first control signal Ver1, which is a voltage signal obtained by non-inverting and amplifying the voltage obtained by subtracting the reference voltage Vref from the output voltage signal Vo1. In other words, the difference between this and the error amplifier circuit 18 described above is that the difference voltage (Vo1-Vref) is amplified non-invertingly rather than invertingly.

The pulsating component signal injection circuit 58 detects the pulsating component Vrip of the frequency Fr contained in the intermediate voltage Vc, and generates a second control signal Ver2 by adding a voltage signal +A·Vrip obtained by non-inverting and amplifying the pulsating component Vrip to the first control signal Ver1 (which may be a voltage signal obtained by non-inverting and amplifying the first control signal Ver1). In other words, the difference from the above-mentioned pulsating component signal injection circuit 36 is that the pulsating component Vrip is amplified non-invertingly rather than amplified.

The drive pulse generating circuit 60 is a circuit that generates a drive pulse Vg for the switching element 14a by pulse width modulating the second control signal Ver2. When the second control signal Ver2 falls, the time ratio of the high level and low level of the drive pulse Vg is changed in a direction that reduces the on-time ratio of the switching element 14a, and when the second control signal Ver2 rises, the time ratio of the high level and low level of the drive pulse Vg is changed in a direction that increases the on-time ratio of the switching element 14a. The difference from the drive pulse generating circuit 20 described above is that when the second control signal Ver2 falls/rises, the on-time ratio of the switching element 14a is not increased/decreased, but is decreased/increased.

Next, the operation of the switching power supply device 54 will be described. First, assuming that the pulsating voltage Vrip is not generated in the intermediate voltage Vc, the operation of the feedback control of the switching power supply device 54 will be briefly described. For example, if the output voltage Vo, which was held at the target value, rises slightly for some reason, the error amplifier circuit 56 detects that the output voltage signal Vo1 has become higher than the reference voltage Vref and raises the first control signal Ver1. The first control signal Ver1 passes through the pulsating component injection circuit 58 and is input to the drive pulse generation circuit 60, which changes the time ratio of the high level and low level of the drive pulse Vg in a direction that reduces the on-time ratio of the switching element 14a, so that the output voltage Vo drops and returns to the target value. Conversely, if the output voltage Vo, which had been held at the target value, drops slightly for some reason, the error amplifier circuit 56 detects that the output voltage signal Vo1 has become lower than the reference voltage Vref and lowers the first control signal Ver1. The first control signal Ver1 passes through the pulsating component injection circuit 58 and is input to the drive pulse generation circuit 60, which then changes the time ratio of the high level and low level of the drive pulse Vg in the direction of increasing the time ratio of the switching element 14a being on, so that the output voltage Vo rises and returns to the target value.

The actual operation of the switching power supply 34, that is, the operation when a large ripple component Vrip (frequency Fr) occurs in the intermediate voltage Vc, is shown in Figure 7. Since the gain of the error amplifier circuit 56 in the low frequency band including the frequency Fr is kept low, the waveform of the first control signal Ver1 hardly generates an oscillation component of the frequency Fr corresponding to the ripple component Vrip (a component that tries to suppress the low frequency ripple component Vor).

The pulsating component signal injection circuit 58 receives the intermediate voltage Vc and the first control signal Ver1, and generates a second control signal Ver2 in which the pulsating voltage signal +A·Vrip, which is the non-inverted amplified version of the pulsating component Vrip, is added to the first control signal Ver1 (which may be a voltage signal that is the non-inverted amplified version of the first control signal Ver1). Therefore, the waveform of the second control signal Ver2 sometimes oscillates upward when the pulsating component Vrip oscillates upward, and sometimes oscillates downward when the pulsating component Vrip oscillates downward.

When the second control signal Ver2 oscillates in the upward direction (when the pulsating component Vrip oscillates in the upward direction), the drive pulse generating circuit 60 changes the time ratio of the high level and low level of the drive pulse Vg in a direction that reduces the on-time ratio of the switching element 14a. Therefore, the output voltage Vo cannot rise in phase with the pulsating component Vrip and is maintained at an approximately constant value. Conversely, when the second control signal Ver2 oscillates in the downward direction (when the pulsating component Vrip oscillates in the downward direction), the time ratio of the high level and low level of the drive pulse Vg is changed in a direction that increases the on-time ratio of the switching element 14a. Therefore, the output voltage Vo cannot fall in phase with the pulsating component Vrip and is maintained at an approximately constant value. Therefore, the low-frequency ripple component Vor is hardly generated.

In order to achieve Vor≒0, the voltage signal +A・Vrip, which corresponds to the ripple component Vrip, must be set to an appropriate value, but this can be easily optimized by adjusting the value of the amplification factor A.

As described above, the switching power supply device 54 can also provide the same operational effects as the switching power supply device 34 described above .

The switching power supply device of the present invention is not limited to the above embodiment.

The switching power supply device 44 shown in FIG. 4 is configured to provide a voltage divider circuit 48, a pulse width modulation unit 50, and a smoothing circuit 52 in the pulsating component signal injection circuit 46 to enable highly intelligent control, and the output voltage Vc2 of the smoothing circuit 52 is input to the input circuit 40. However, this portion may be changed to a voltage divider circuit 48, an AD converter, a digital signal processing unit, and a DA converter, and the output voltage Vc2 of the DA converter may be input to the input circuit 40. In this case, the AD converter converts the step-down voltage Vc1 generated by the voltage divider circuit 48 into a step-down voltage signal that is a digital signal, the digital signal processing unit generates a proportional voltage signal that is a digital signal corresponding to the step-down voltage Vc1 based on the step-down voltage signal, and the DA converter converts the proportional voltage signal into the proportional voltage Vc2 that is an analog voltage.

When generating voltage Vc2 using a DA converter, improving the resolution of voltage Vc2 becomes an issue. However, by applying the dithering technology described in Patent No. 6368696 by the applicant of this application, for example, the resolution of voltage Vc2 can be easily improved, making it possible to detect intermediate voltage Vc with high accuracy without using an expensive high-speed digital processor.

Additionally, the pulsating current component signal injection circuit 58 described above is one example of a pulsating current component signal injection circuit for the switching power supply device 54 , and although a preferred specific example is not shown, it can be freely configured by appropriately combining known circuits.

10, 34, 44, 54 Switching power supply device 12 Rectification smoothing circuit 14 DC-DC converter 14a Switching element 16 Switching control circuit 18, 56 Error amplifier circuit 20, 60 Drive pulse generation circuit 36, 46, 58 Pulsating component signal injection circuit 38 Operational amplifier 40 Input circuit (capacitor C1, resistor R1)
42 Feedback circuit (capacitor C2, resistor R2)
48 Voltage dividing circuit 50 Pulse width modulation section 52 Smoothing circuit
D Duty of square wave voltage
Vc Intermediate voltage
Vc1 Step-down voltage
Vc2 smoothing voltage
Vdc DC component of intermediate voltage
Ver1 First control signal
Ver2 Second control signal
Vg drive pulse
Vi Commercial AC voltage
Vo output voltage
Vo1 output voltage signal
Vp Square wave voltage
Vref Reference voltage
Vrip Pulsating component of intermediate voltage

Claims (2)

a rectifying and smoothing circuit which rectifies and smoothes a commercial AC voltage to output an intermediate voltage, a DC-DC converter which converts the intermediate voltage into a predetermined output voltage, and a switching control circuit which controls on/off of a switching element of the DC-DC converter so that an output voltage signal which is a voltage signal obtained by detecting the output voltage approaches a reference voltage,
The switching control circuit includes:
an error amplifier circuit that generates a first control signal, which is a voltage signal obtained by inverting and amplifying a voltage obtained by subtracting the reference voltage from the output voltage signal;
a pulsating component signal injection circuit that detects a pulsating component of a frequency corresponding to a commercial frequency included in the intermediate voltage, and generates a second control signal in which a voltage signal obtained by inverting and amplifying the pulsating component is added to the first control signal or a voltage signal obtained by non-inverting and amplifying the first control signal;
a drive pulse generating circuit that generates a drive pulse for the switching element by pulse-width modulating the second control signal;
The pulsating flow component signal injection circuit comprises a voltage dividing circuit which resistively divides the intermediate voltage to generate a stepped-down voltage, a pulse width modulation section which generates a square wave voltage having a duty set based on the stepped-down voltage, a smoothing circuit which smoothes the square wave voltage to generate a smoothed voltage proportional to the stepped-down voltage, an operational amplifier which receives the first control signal at a non-inverting input terminal and outputs the second control signal from an output terminal, an input circuit which is connected between the inverting input terminal of the operational amplifier and an output terminal of the smoothing circuit and which is made up of a series circuit of a capacitor and a resistor, and a feedback circuit which is connected between the output terminal and the inverting input terminal of the operational amplifier and which is made up of a parallel circuit of a capacitor and a resistor,
a drive pulse generating circuit that, when the second control signal falls, changes a time ratio between high and low levels of the drive pulse in a direction that reduces an on-time ratio of the switching element, and, when the second control signal rises, changes a time ratio between high and low levels of the drive pulse in a direction that increases an on-time ratio of the switching element. a rectifying and smoothing circuit which rectifies and smoothes a commercial AC voltage to output an intermediate voltage, a DC-DC converter which converts the intermediate voltage into a predetermined output voltage, and a switching control circuit which controls on/off of a switching element of the DC-DC converter so that an output voltage signal which is a voltage signal obtained by detecting the output voltage approaches a reference voltage,
The switching control circuit includes:
an error amplifier circuit that generates a first control signal, which is a voltage signal obtained by inverting and amplifying a voltage obtained by subtracting the reference voltage from the output voltage signal;
a pulsating component signal injection circuit that detects a pulsating component of a frequency corresponding to a commercial frequency included in the intermediate voltage, and generates a second control signal in which a voltage signal obtained by inverting and amplifying the pulsating component is added to the first control signal or a voltage signal obtained by non-inverting and amplifying the first control signal;
a drive pulse generating circuit that generates a drive pulse for the switching element by pulse-width modulating the second control signal;
The pulsating flow component signal injection circuit comprises: a voltage dividing circuit which generates a stepped-down voltage by resistively dividing the intermediate voltage; an AD converter which converts the stepped-down voltage into a stepped-down voltage signal which is a digital signal; a digital signal processing section which generates a proportional voltage signal which is a digital signal corresponding to the stepped-down voltage based on the stepped-down voltage signal; a DA converter which converts the proportional voltage signal into a proportional voltage which is an analog voltage; an operational amplifier which receives the first control signal at a non-inverting input terminal and outputs the second control signal from an output terminal; an input circuit which is connected between the inverting input terminal of the operational amplifier and the output terminal of the DA converter and is made up of a series circuit of a capacitor and a resistor; and a feedback circuit which is connected between the output terminal and the inverting input terminal of the operational amplifier and is made up of a parallel circuit of a capacitor and a resistor.
a drive pulse generating circuit that, when the second control signal falls, changes a time ratio between high and low levels of the drive pulse in a direction that reduces an on-time ratio of the switching element, and, when the second control signal rises, changes a time ratio between high and low levels of the drive pulse in a direction that increases an on-time ratio of the switching element.

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