Switching Power Supply Unit

Abstract

To provide a switching power supply device with a simple structure, which can easily reduce low frequency ripple components of output voltage.SOLUTION: A switching power supply device comprises: an error amplification circuit 18 configured to generate a first control signal Ver1 obtained by inverting and amplifying voltage obtained by subtracting reference voltage Vref from an output voltage signal Vo1; a ripple component signal injection circuit 36 configured to detect a ripple component Vrip of a frequency Fr corresponding to a commercial frequency Fac included in intermediate voltage Vc, and generate a second control signal Ver2 added with the first control signal Ver1 and a voltage signal obtained by inverting and amplifying the ripple component Vrip; and a drive pulse generation circuit 20 configured to pulse-width-modulate the second control signal Ver2 to generate a drive pulse Vg of a switching element 14a. The drive pulse generation circuit 20 changes each time ratio of a high level and a low level of the drive pulse Vg toward a direction in which an ON-time ratio of the switching element 14a becomes small when the second control signal Ver2 decreases.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] 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 predetermined output voltage by a DC-DC converter. [Background technology]

[0002] Conventionally, 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 of the power conversion circuit so that an output voltage signal, which is a voltage signal obtained by detecting 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 Fig. 8.

[0003] The switching power supply device 10 is composed of a rectifier smoothing circuit 12 that rectifies and smoothes a commercial AC voltage Vi (commercial frequency Fac) and outputs an intermediate voltage Vc, a DC-DC converter 14 that converts the intermediate voltage Vc into 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.

[0004] The inverter type of DC-DC converter 14 is not particularly limited, but in order to ensure safety with respect to the commercial AC power supply (for example, to prevent electric shock accidents), an input / output isolated type converter is often selected.

[0005] 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 a 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.

[0006] The error amplifier circuit 18 is a so-called inverting amplifier circuit, and is configured to output a first control signal Ver1 obtained by inverting and amplifying a voltage obtained by subtracting a reference voltage Vref from the output voltage signal Vo1, through an insulating means 18a.

[0007] 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.

[0008] 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 at 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 at a low level to turn off the switching element 14a.

[0009] 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 on-time ratio of the switching element 14a, 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 on-time ratio of the switching element 14a.

[0010] Next, the operation of the feedback control of the switching power supply device 10 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 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 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 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 on-time ratio of the switching element 14a, so that the output voltage Vo rises and returns to the target value.

[0011] In this switching power supply device 10, the intermediate voltage Vc is not a completely DC voltage, but a voltage in which a pulsating component Vrip of a frequency Fr corresponding to the commercial frequency Fac is superimposed on a DC component Vdc, so that there is a problem in 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.

[0012] First, the pulsating component Vrip and the 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 improving the power factor, a pulsating component Vrip with a frequency Fr=2·Fac is generated in the intermediate voltage Vc.

[0013] Furthermore, 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 above-mentioned smoothing section 28. In this case, a pulsating component Vrip of frequency Fr=3·Fac is generated in the intermediate voltage Vc, as shown in FIG. 10(b).

[0014] 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, a large number of large-capacity capacitors are required, which results in problems such as an increase in the size and cost of the device.

[0015] Even if the ripple component Vrip occurs, the low-frequency ripple component Vor can be reduced in principle 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 reality, 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 tries to suppress the low-frequency ripple component Vor) corresponding to the ripple 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.

[0016] Another possible method for reducing the low-frequency ripple component Vor is to modify the switching power supply 10 into a switching power supply 10x shown in FIG. 12. 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. [Prior art documents] [Patent documents]

[0017] [Patent Document 1] JP 2014-128110 A [Patent Document 2] JP 2010-124524 A Summary of the Invention [Problem to be solved by the invention]

[0018] 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.

[0019] The conventional switching power supply device 10x performs feedforward control using the slope of the reference triangular wave Vosc, and therefore, in principle, 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 pulsating component Vrip of the intermediate voltage Vc. In addition, as explained in Patent Document 2, the 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 contents of the measures, there are problems 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.

[0020] The present invention has been made in view of the above-mentioned background art, and has an object to provide a switching power supply device with a simple configuration that can easily reduce the low-frequency ripple component of the output voltage. [Means for solving the problem]

[0021] 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 to reduce 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 to increase the on-time ratio of the switching element when the second control signal rises.

[0022] The pulsating flow component signal injection circuit can be composed of an operational amplifier having a non-inverting input terminal to which the first control signal is input and an output terminal to which the second control signal is output, 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 end of the rectifying 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.

[0023] especiallyIn 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.

[0024] Alternatively, in the switching power supply device of the present invention, The pulsating flow component signal injection circuit includes a voltage divider circuit that generates a step-down voltage by resistively dividing the intermediate 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 made up 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 made up of a parallel circuit of a capacitor and a resistor. do .

[0025] Others, for example 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 that is a voltage signal of 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 non-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 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 that pulse-width modulates the second control signal to generate a drive pulse for the switching element; a drive pulse generating circuit that changes a time ratio between high and low levels of the drive pulse in a direction to reduce an on-time ratio of the switching element when the second control signal rises, and changes a time ratio between high and low levels of the drive pulse in a direction to increase an on-time ratio of the switching element when the second control signal falls. but be. Effect of the Invention

[0026] The switching power supply of the present invention is provided with a pulsating component signal injection circuit with a unique configuration, which performs feedforward control in which the on-time ratio of the main switching element is reduced when the pulsating component of the intermediate voltage oscillates in the upward direction, and the on-time ratio of the main switching element is reduced when the pulsating component oscillates in the downward direction. This makes it possible to easily solve the problem of low-frequency ripple components being generated in the output voltage due to the pulsating component of the intermediate voltage, without significantly affecting the feedback control system.

[0027] 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 a drive pulse (the input end of the drive pulse generation circuit), so that the operation of the main switching element can be changed extremely quickly in response to changes in the ripple component, which is extremely effective. [Brief description of the drawings]

[0028] [Figure 1]1 is a circuit diagram showing one embodiment of a switching power supply device. [Diagram 2] 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. [Diagram 3] 2 is a time chart showing operational waveforms of each part of the switching power supply device of FIG. 1. [Figure 4] 1 is a circuit diagram showing a switching power supply device according to a first embodiment of the present invention; [Diagram 5] 4 is a time chart showing operational waveforms of each part of the switching power supply device of the first embodiment; [Figure 6] FIG. 11 is a circuit diagram showing another embodiment of a switching power supply device. [Figure 7] 7 is a time chart showing operational waveforms of each part of the switching power supply device of FIG. 6. [Figure 8] FIG. 1 is a circuit diagram showing an example of a conventional switching power supply device. [Figure 9] 1A and 1B are circuit diagrams showing an example of a general rectifying and smoothing circuit, and FIG. 1C is a time chart showing the waveform of an intermediate voltage. [Figure 10] 1A is a circuit diagram showing an example of a general rectifying and smoothing circuit, and FIG. 1B is a time chart showing the waveform of an intermediate voltage. [Figure 11] 9 is a time chart showing operational waveforms of each part of the switching power supply device of FIG. 8. [Figure 12] FIG. 11 is a circuit diagram showing another example of a conventional switching power supply device. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0029] < A form of switching power supply > The following is a description of the switching power supply a form This will be described with reference to Figures 1 to 3. Here, the same components as those in the conventional switching power supply device 10 are given the same reference numerals and the description thereof will be omitted.

[0030] This formAs shown in the circuit diagram of FIG. 1, the switching power supply 34 generally has many things in common with the switching power supply 10, but a major difference is that a pulsating current component signal injection circuit 36 ​​is added to the switching control circuit 16.

[0031] 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 generating circuit 20.

[0032] 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 by 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.

[0033] The values ​​of R1, C1, R2, and C2 that determine the impedances Z1 and Z2 are individually adjusted according to the circumstances of the power supply device, but at the frequency Fr [frequency corresponding to the commercial frequency] of the ripple component Vrip, R1>>(ωC1) -1 , R2<<(ωC2) -1 It is preferable to adjust the resistors so that almost no phase delay occurs, as shown in equation [3]. Furthermore, by adjusting the resistors so that R1>>R2 is satisfied, the setting is as shown in the following equation [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].

[0034] 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 to the voltage signal, and outputs the second control signal Ver2 to the drive pulse generation circuit 20 in the downstream stage.

[0035] 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 feedback control operation 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 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 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 generating 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 on-time ratio of the switching element 14a, so that the output voltage Vo rises and returns to the target value. The above operation is basically the same as in the case of the conventional switching power supply device 10.

[0036] The actual operation of the switching power supply device 34, that is, the operation when a large ripple component Vrip (frequency Fr) occurs in the intermediate voltage Vc, is shown in Fig. 3. Since the gain of the error amplifier circuit 18 in the low frequency band including the frequency Fr is kept low, almost no oscillation component of the frequency Fr (component that tries to suppress the low frequency ripple component Vor) corresponding to the ripple component Vrip occurs in the waveform of the first control signal Ver1.

[0037] The pulsating current component signal injection circuit 36 ​​receives the intermediate voltage Vc and the first control signal Ver1, and generates a second control signal Ver2 by adding a voltage signal -(R2 / R1)·Vrip, which is obtained by inverting and amplifying the pulsating current component Vrip, to the first control signal Ver1. Therefore, the waveform of the second control signal Ver2 sometimes oscillates in the downward direction when the pulsating current component Vrip oscillates in the upward direction, and sometimes oscillates in the downward direction when the pulsating current component Vrip oscillates in the upward direction.

[0038] When the second control signal Ver2 oscillates downward (when the pulsating component Vrip oscillates upward), the driving pulse generating circuit 20 changes the time ratio of the high level and low level of the driving 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 held at a substantially constant value. On the other hand, 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 driving 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 held at a substantially constant value. Therefore, the low-frequency ripple component Vor is hardly generated.

[0039] Note that 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 current component Vrip, to an appropriate value; however, this can be easily optimized by adjusting the values ​​of resistors R1 and R2.

[0040] As described above, the switching power supply device 34 has the following features: PrescribedBy providing the pulsating component signal injection circuit 36, feedforward control is performed 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.

[0041] Furthermore, the ripple component signal injection circuit 36 ​​injects the ripple component signal -(R2 / R1)·Vrip at a position (the input end of the drive pulse generating circuit 20) immediately before the drive pulse Vg is generated by performing pulse width control in the feedback control system. This is extremely effective in that it can change the operation of the main switching element extremely quickly in response to changes in the ripple voltage Vrip.

[0042] < The switching power supply device of the present invention One embodiment> Next, the switching power supply device of the present invention One embodiment 4 and 5. Here, the same components as those in the above-described switching power supply device 34 are given the same reference numerals and the description thereof will be omitted.

[0043] As shown in the circuit diagram of FIG. 4, a switching power supply 44 of this embodiment has much in common with the switching power supply 34 as a whole, 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.

[0044] The pulsating voltage injection circuit 46 includes a voltage dividing circuit 48, a pulse width modulation section 50, and a smoothing circuit 52. The pulse width modulation section 50 is a block that performs digital signal processing, and is provided within a digital processor that operates at a low voltage.

[0045] 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.

[0046] In addition, the pulsating voltage injection circuit 46 includes an amplifier circuit configured with the operational amplifier 38, the input circuit 40, and the 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.

[0047] 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 here, it is preferable to adjust the values ​​of R1 and R2 so that R1>>R2 is not satisfied, and set equation [3].

[0048] In this way, the pulsating current signal injection circuit 46 detects the pulsating current component Vrip of 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 current component Vrip to the voltage signal (1+R2 / R1)·Ver1 obtained by non-inverting and amplifying the first control signal Ver1, and outputs the second control signal Ver2 to the drive pulse generation circuit 20 in the downstream stage.

[0049] Next, a description will be given of 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 no pulsating voltage Vrip is generated in the intermediate voltage Vc) is similar to that of the switching power supply device 34, and therefore a description thereof will be omitted.

[0050] The actual operation of the switching power supply device 34, that is, the operation when a large ripple component Vrip (frequency Fr) occurs in the intermediate voltage Vc, is shown in Fig. 5. Since the gain of the error amplifier circuit 18 in the low frequency band including the frequency Fr is kept low, almost no oscillation component of the frequency Fr (component that tries to suppress the low frequency ripple component Vor) corresponding to the ripple component Vrip occurs in the waveform of the first control signal Ver1.

[0051] The pulsating current 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 a pulsating current voltage signal -(R2 / R1)·k·Vrip obtained by inverting and amplifying the pulsating current component Vrip and a 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 current component Vrip oscillates upward, and sometimes oscillates downward when the pulsating current component Vrip oscillates upward.

[0052] When the second control signal Ver2 oscillates downward (when the pulsating component Vrip oscillates upward), the driving pulse generating circuit 20 changes the time ratio of the high level and low level of the driving 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 held at a substantially constant value. On the other hand, 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 driving 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 held at a substantially constant value. Therefore, the low-frequency ripple component Vor is hardly generated.

[0053] Note that in order to achieve Vor ≈ 0, the voltage signal -(R2 / R1) · k1 · k2 · Vrip, which corresponds to the ripple current component Vrip, must be set to an appropriate magnitude; however, this can be easily optimized by adjusting the values ​​of resistors R1, R2 and coefficients k1, k2.

[0054] As described above, according to the switching power supply device 44, As mentioned above It is possible to obtain the same effects as those of the switching power supply device 34. Furthermore, since the pulsating flow component signal injection circuit 46 is provided with a pulse width modulation section 50 and a smoothing circuit 52, which work together to generate the analog smoothed voltage Vc2, Even better results Obtained.

[0055] The pulse width modulation unit 50 is a block 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 and to detect the intermediate voltage Vc with high accuracy without using an expensive high-speed digital processor.

[0056] In addition, 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 an operation for injecting 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, so that highly intelligent and advanced control can be performed.

[0057] < Other forms of switching power supplies > next, Switching power supply Other forms 6 and 7. Here, the same components as those in the above-described switching power supply device 34 are given the same reference numerals and the description thereof will be omitted.

[0058] This form As shown in the circuit diagram of FIG. 6, the switching power supply 54 is obtained by replacing the error amplifier circuit 18, the ripple component signal injection circuit 36 ​​and the drive pulse generating circuit 20 of the switching power supply 34 with a new error amplifier circuit 56, a ripple component signal injection circuit 58 and a drive pulse generating circuit 60, respectively.

[0059] 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 is that the difference voltage (Vo1-Vref) is not inverted but amplified.

[0060] 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 non-inverted and amplified.

[0061] 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, and when the second control signal Ver2 drops, it 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, and when the second control signal Ver2 rises, it changes the time ratio of the high level and low level of the drive pulse Vg 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 drops / rises, it does not increase / decrease the on-time ratio of the switching element 14a, but decreases / increases it.

[0062] 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 feedback control operation 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 then 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 maintained 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 generating circuit 60. The drive pulse generating circuit 60 then changes the time ratio of the high level and low level of the drive pulse Vg in the direction increasing the time ratio of the switching element 14a that is on, so that the output voltage Vo rises and returns to the target value.

[0063] The actual operation of the switching power supply device 34, that is, the operation when a large ripple component Vrip (frequency Fr) occurs in the intermediate voltage Vc, is shown in Fig. 7. Since the gain of the error amplifier circuit 56 in the low frequency band including the frequency Fr is kept low, almost no oscillation component of the frequency Fr (component that tries to suppress the low frequency ripple component Vor) corresponding to the ripple component Vrip occurs in the waveform of the first control signal Ver1.

[0064] The pulsating current component signal injection circuit 58 receives the intermediate voltage Vc and the first control signal Ver1, and generates a second control signal Ver2 obtained by adding the pulsating current voltage signal +A·Vrip obtained by non-inverting and amplifying the pulsating current 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). Therefore, the waveform of the second control signal Ver2 oscillates upward when the pulsating current component Vrip oscillates upward, and oscillates downward when the pulsating current component Vrip oscillates downward.

[0065] When the second control signal Ver2 oscillates in the upward direction (when the pulsating component Vrip oscillates in the upward direction), the driving pulse generating circuit 60 changes the time ratio of the high level and the low level of the driving 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 held at a substantially constant value. On the other hand, 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 the low level of the driving 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 held at a substantially constant value. Therefore, the low-frequency ripple component Vor is hardly generated.

[0066] Note that achieving Vor ≈ 0 requires that the voltage signal +A·Vrip, which corresponds to the ripple current component Vrip, be set to an appropriate magnitude; however, this can be easily optimized by adjusting the value of the amplification factor A.

[0067] As described above, in the switching power supply device 54, the above The same effects as those of the switching power supply device 34 can be obtained.

[0068] The switching power supply device of the present invention is not limited to the above embodiment. It's not something like that.

[0069] In order to enable highly intelligent control, the switching power supply device 44 shown in Fig. 4 is configured to include a voltage dividing circuit 48, a pulse width modulation section 50, and a smoothing circuit 52 in the pulsating flow component signal injection circuit 46, and inputs the output voltage Vc2 of the smoothing circuit 52 to the input circuit 40, but this portion may be changed to a voltage dividing circuit 48, an AD converter, a digital signal processing section, 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 performs a process of converting the step-down voltage Vc1 generated by the voltage dividing circuit 48 into a step-down voltage signal that is a digital signal, the digital signal processing section performs a process of generating 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 performs a process of converting the proportional voltage signal into the proportional voltage Vc2 that is an analog voltage.

[0070] When generating the voltage Vc2 using a DA converter, it becomes necessary to improve the resolution of the voltage Vc2. However, by applying the dithering technology described in Japanese Patent No. 6368696 by the applicant of the present application, the resolution of the voltage Vc2 can be easily improved, and the intermediate voltage Vc can be detected with high accuracy without using an expensive high-speed digital processor.

[0071] In addition, the pulsating flow component signal injection circuit 58 has the following features: Switching Power Supply 54 This is an example of a pulsating flow component signal injection circuit, and although a preferred concrete example is not shown, it can be freely configured by appropriately combining known circuits. [Explanation of symbols]

[0072] 10,34,44,54 Switching power supply 12 Rectifier smoothing circuit 14 DC-DC converter 14a Switching element 16 Switching control circuit 18, 56 Error Amplifier Circuit 20,60 Drive pulse generating circuit 36,46,58 Pulsating flow component signal injection circuit 38 Operational Amplifiers 40 Input circuit (capacitor C1, resistor R1) 42 Feedback circuit (capacitor C2, resistor R2) 48 Voltage divider 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

1. 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 changes a time ratio of high level to low level of the drive pulse in a direction decreasing an on-time ratio of the switching element when the second control signal drops, and that changes a time ratio of high level to low level of the drive pulse in a direction increasing an on-time ratio of the switching element when the second control signal rises.

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 is composed of a voltage dividing circuit which generates a step-down voltage by resistively dividing the intermediate voltage, an AD converter which converts the step-down voltage into a step-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 step-down voltage based on the step-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 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, a drive pulse generating circuit that changes a time ratio of high level to low level of the drive pulse in a direction decreasing an on-time ratio of the switching element when the second control signal drops, and that changes a time ratio of high level to low level of the drive pulse in a direction increasing an on-time ratio of the switching element when the second control signal rises.

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