JP2005333796A - Switching power supply circuit and semiconductor integrating the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a switching power supply circuit in which a negative-feedback operation is stabilized with a small capacitance that can be mounted to a semiconductor integrated circuit, and to provide its manufacturing cost can be reduced. <P>SOLUTION: A switching power supply circuit is provided with a switched capacitor circuit 19 between a power supply output terminal 12 for delivering DC output voltages and the input of an error-magnifying circuit 16. Comparison is made, between the output signals and reference signals from the error magnifying circuit 16 for amplifying errors between DC output voltage and the reference voltage in a pulse width modulation circuit 15, and a voltage transforming portion 12 performs on/off operations continuously, in response to input voltages with a predetermined period by the output signals of the pulse width modulation circuit 15. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a switching power supply circuit, and more particularly to a switching power supply circuit that can be integrated in a semiconductor device.

  In recent years, there has been a demand for further reduction in size, weight, and cost of portable electronic devices such as mobile phones and digital still cameras. The power supply circuit of these portable electronic devices is constituted by a semiconductor integrated circuit. A switching power supply circuit is used. FIG. 7 is a block diagram showing a configuration of a conventional switching power supply circuit.

A conventional switching power supply circuit will be described below with reference to the drawings.
In the conventional switching power supply circuit shown in FIG. 7, the voltage conversion unit 3 includes a power supply input terminal 1 to which a DC voltage is input and an output terminal 2 that outputs a predetermined DC output voltage. Consists of a power transistor 53, a coil 54, a diode 55, and an output smoothing capacitor 56. The switching power supply circuit includes a pre-drive circuit 4, a pulse width modulation circuit 5, an error amplification circuit 6, a reference voltage circuit 7 that generates a reference voltage, a reference signal generation circuit 8 that generates a reference signal, and an output voltage setting. Resistors 50 and 51 are provided. A capacitor 52 is connected between the input and output of the error amplifier circuit 6. The conventional switching power supply circuit configured as described above outputs a stable DC output voltage from the output terminal 2 by the negative feedback operation.
Japanese Patent No. 3190914

  A negative feedback operation in the conventional switching power supply circuit configured as shown in FIG. 7 will be described with reference to FIG. FIG. 8 is a frequency characteristic diagram showing the relationship between gain and phase in the conventional switching power supply circuit configured as described above.

  In the conventional switching power supply circuit, the DC output voltage is divided by the output voltage setting resistors 50 and 51, and a detection voltage proportional to the DC output voltage is detected. The detected voltage and the reference voltage from the reference voltage circuit 7 are compared in the error amplifier circuit 6. When the detection voltage is higher than the reference voltage, the output voltage of the error amplification circuit 6 decreases. The lowered output voltage of the error amplifier circuit 6 is input to the pulse width modulation circuit 5 and compared with the reference signal of the reference signal generation circuit 8. In this case, since the output voltage of the error amplification circuit 6 becomes lower than the reference signal of the reference signal generation circuit 8, the pulse width modulation circuit 5 outputs a pulse signal that shortens the conduction time of the power transistor 53 of the voltage conversion unit 3, The voltage is output to the voltage converter 3 via the predrive circuit 4. As a result, the DC output voltage generated at the power output terminal 2 of the voltage conversion unit 3 decreases.

  On the other hand, when the detection voltage is lower than the reference voltage, the output voltage of the error amplifier circuit 6 rises. The increased output voltage of the error amplification circuit 6 is input to the pulse width modulation circuit 5 and compared with the reference signal of the reference signal generation circuit 8. In this case, since the output voltage of the error amplification circuit 6 becomes higher than the reference signal of the reference signal generation circuit 8, the pulse width modulation circuit 5 outputs a pulse signal that increases the conduction time of the power transistor 53. As a result, the DC output voltage generated at the output terminal 2 of the voltage converter 3 increases. As described above, the switching power supply circuit performs the negative feedback operation for level-controlling the DC output voltage so that the error between the detection voltage of the DC output voltage and the reference voltage becomes small, so that the DC output voltage becomes a predetermined value. To be stabilized.

Hereinafter, the stability of the negative feedback operation will be described with reference to FIGS. In FIG. 7, a capacitor 52 is connected between the input and output of the error amplifier circuit 6. The capacitor 52 functions as a feedback capacitor, and the error amplifier circuit 6 is an integral amplifier circuit. FIG. 8 shows two frequency characteristic curves when the feedback capacitance is different, and the gain / phase characteristic 1 is a characteristic diagram showing a case where the feedback capacitance is set larger than the gain / phase characteristic 2.
Hereinafter, the case where the feedback capacitance between the input and output of the error amplifier circuit 6 is small and the gain / phase characteristic 2 is indicated by a broken line in FIG. In this case, at a frequency equal to or lower than the cut-off frequency fc (pole P2), an amplification operation is performed with a bare gain (gain without negative feedback). On the other hand, at frequencies exceeding the cut-off frequency fc (pole P2), the gain decreases at a rate of -6 dB / octave as the frequency increases. Assuming that the frequency at which the gain of the error amplifying circuit 6 becomes 0 dB (1 degree of amplification) is the zero cross frequency fz0, the impedance 1 / (2π × fz0 ×) of the capacitor 52 having the capacitance C2 (feedback capacitance) at the zero cross frequency fz0. The value of the input resistance Zi connected to the input of the error amplifying circuit 6 is equal to C2). When the frequency is higher than the zero cross frequency fz0, the error amplifying circuit 6 functions as an attenuator. Here, since the input resistance Zi connected to the input of the error amplifier circuit 6 can be considered as a parallel resistance with the resistors 50 and 51, the zero cross frequency fz0 in the case of the gain / phase characteristic 2 is expressed by the following formula (1). be able to.

  fz0 = 1 / (2π × Zi × C2) (1)

  On the other hand, a second-order LC filter is generated at the resonance frequency fL determined by the coil 54 having the inductance L1 and the output smoothing capacitor 56 having the capacitance C1 in the voltage converter 3. The resonance frequency fL is shown in the following formula (2).

  fL = 1 / (2π × √ (L1 × C1)) (2)

This gain characteristic and phase characteristic are the gain / phase characteristic 2 shown by the broken line in FIG. In FIG. 8, the frequency at which the gain becomes zero dB is displayed as the zero cross frequency fz0.
The phase characteristic starts to advance when the frequency is greater than 1/10 of the cutoff frequency fc (pole P2), and reaches a leading phase of 45 ° at the cutoff frequency fc, which is 10 times the cutoff frequency fc (pole P2). At double frequency, the lead phase is approximately 90 °.
When the gain / phase characteristic 2 has the characteristics as described above and the resonance frequency fL is smaller than the zero cross frequency fz0, the following problems occur.
The pulse width modulation circuit 5 generates a PWM signal for controlling the pulse width in accordance with a comparison error obtained by comparing the output signal of the reference signal generation circuit 8 and the output signal of the error amplification circuit 6. The power transistor 53 is chopped by the predrive circuit 4 that predrives the PWM signal. The chopping signal generated at this time is converted into a DC output voltage smoothed by the coil 54 and the capacitor 56 constituting the voltage converter 3. When the chopping operation is performed, a ringing phenomenon occurs at the resonance frequency fL. The ringing signal generated by this ringing phenomenon is further amplified in the error amplification circuit 6. The pulse width modulation circuit 5 compares the amplified ringing signal with the reference signal to generate a chopping signal. Therefore, if the ringing phenomenon occurs every time the chopping operation is performed, a phenomenon similar to the oscillation phenomenon occurs, and the operation of the entire circuit becomes unstable.

  In order to solve this problem, the capacitance C2 of the capacitor 52 is set large, the zero cross frequency is changed from fz0 to fz1, and the phase shown by the solid line in FIG. 8 is established so that fz1 <fL is established. • Set as gain characteristic 1. If the phase / gain characteristic 1 is as shown in FIG. 8, the error amplification circuit 6 has a gain of 0 dB or less at the resonance frequency fL, that is, functions as an attenuator. For this reason, the circuit operation of the negative feedback path is stabilized. For the purpose of stabilizing the negative feedback operation, for example, Japanese Patent No. 3190914 includes an integration type error amplification circuit in which a phase correction circuit is provided between the input and output of the error amplification circuit in FIG. It is disclosed.

  However, semiconductor integrated circuits used in portable devices such as mobile phones and digital still cameras are required to be smaller and lighter, and at the same time be faster to enable high-speed information processing. It has been. Therefore, switching power supply circuits are also required to be reduced in size, weight, speed, and cost. In a switching power supply circuit, the inductance L1 of the coil 54 is generally 47 μH or less and the capacitance C1 of the output smoothing capacitor 56 is 47 μF or less because of restrictions on output load current and component mounting space. Thereby, the resonance frequency fL becomes about 4 KHz. Further, in order to stabilize the negative feedback operation of the conventional switching power supply circuit, the zero cross frequency fz1 in the integral type error amplifier circuit needs to have a relationship of fz1 <4 kHz.

For example, if the value of the input resistance Zi of the error amplifier circuit 6 is about 100 kΩ, the capacitance C2 of the capacitor 52 is about 400 pF from equation (1), and a very large feedback capacitance is required. The capacitance that can be mounted on the semiconductor integrated circuit is generally at most 50 pF. In the case of a larger capacity, a configuration for connecting to the outside of the package is adopted. Therefore, such a large feedback capacity has a problem that an external component is increased in a semiconductor integrated circuit in which a switching power supply circuit is integrated.
In addition, in order to stably operate the entire circuit, it is necessary to lower the gain characteristics in a high frequency region, which causes a problem that transient response in a high frequency region is deteriorated.
Furthermore, since the output load current and the component space are different for each portable electronic device, and the inductance L1 of the coil 54 and the capacitance C1 of the output smoothing capacitor 56 are changed for each electronic device, the resonance frequency fL is different for each electronic device. Yes. Accordingly, since it is necessary to optimize the feedback capacity for each electronic device, the time for developing the optimized semiconductor integrated circuit has been a factor for delaying the development period of the electronic device.
In order to solve the problems in the above-described conventional switching power supply circuit, the present invention can stabilize the negative feedback operation with a small capacitance that can be mounted on a semiconductor integrated circuit, and can reduce the manufacturing cost. An object is to provide a switching power supply circuit.

In order to achieve the above object, a switching power supply circuit according to a first aspect of the present invention includes:
A switching power supply circuit for storing energy in a coil and performing a chopping operation for discharging the stored energy from the coil to output a predetermined DC output voltage;
An error amplifying circuit for amplifying an error between the DC output voltage and a reference voltage;
A first capacitor connected between an input terminal and an output terminal of the error amplifier circuit;
A pulse width modulation circuit that outputs a PWM signal by comparing a reference signal having an inclined waveform with an output signal of the error amplification circuit;
A voltage converter that includes at least the coil and a second capacitor that smoothes energy released from the coil, performs the chopping operation according to the PWM signal, and outputs the predetermined DC output voltage to a power supply output terminal When,
A switched capacitor circuit provided between the power supply output terminal and the input terminal of the error amplifier circuit. In the switching power supply circuit of the present invention configured as described above, since the switched capacitor circuit functions as an input resistor having a large value, the zero cross frequency which is a transfer characteristic of the negative feedback loop can be sufficiently lowered, and the switching power supply circuit is small. The negative feedback operation can be stabilized by the feedback capacitance. Therefore, it is possible to integrate a switching power supply circuit including a feedback capacitor.

In the switching power supply circuit according to the second aspect of the present invention, a third capacitor may be provided between the input and output terminals of the switched capacitor circuit according to the first aspect. The switching power supply circuit of the present invention configured as described above can stabilize the negative feedback operation and improve the transient response of the high frequency.
The switching power supply circuit according to the third aspect of the present invention may be a triangular wave signal or a sawtooth wave signal generated by a reference signal generation circuit, wherein the reference signal according to the first aspect or the second aspect described above is generated. Good.

The switching power supply circuit according to the fourth aspect of the present invention may be configured such that the sampling frequency of the switched capacitor circuit according to the first aspect or the second aspect described above is linked with the reference signal. The switching power supply circuit of the present invention configured as described above can freely set the zero-cross frequency by changing the frequency of the reference signal.
Furthermore, the switching power supply circuit according to the fifth aspect of the present invention further includes a frequency divider circuit that divides the reference signal according to the first aspect or the second aspect, and an output signal of the frequency divider circuit. The switched capacitor circuit may be configured to perform a sampling operation. The switching power supply circuit of the present invention configured as described above can reduce the sampling frequency of the switched capacitor circuit at the ratio of the dividing ratio of the frequency dividing circuit without reducing the frequency of the reference signal. It is possible to easily take measures against oscillation of the negative feedback operation without sacrificing responsiveness to load fluctuations.

In order to achieve the above object, a semiconductor device according to a sixth aspect of the present invention includes:
A semiconductor device that integrates a switching power supply circuit that accumulates energy in a coil and performs a chopping operation for discharging the accumulated energy from the coil to output a predetermined DC output voltage,
An error amplifying circuit for amplifying an error between the DC output voltage and a reference voltage;
A first capacitor connected between an input terminal and an output terminal of the error amplifier circuit;
A pulse width modulation circuit that outputs a PWM signal by comparing a reference signal having an inclined waveform with an output signal of the error amplification circuit;
A voltage converter that includes at least the coil and a second capacitor that smoothes energy released from the coil, performs the chopping operation according to the PWM signal, and outputs the predetermined DC output voltage to a power supply output terminal When,
A switched capacitor circuit provided between the power supply output terminal and the input terminal of the error amplifier circuit;
At least the error amplifier circuit, the first capacitor, the pulse width modulation circuit, and the switched capacitor circuit are formed in one semiconductor substrate. Since the switching power supply circuit in the semiconductor device of the present invention configured as described above has good matching between the capacitor configured in the switched capacitor circuit and the first capacitor, the frequency characteristic of the negative feedback loop is manufactured. It can be set without being affected by variations. On the other hand, the switched capacitor circuit functions as an input resistor having a large value, the negative feedback operation can be stabilized with a small feedback capacitance, and a switching power supply circuit with uniform characteristics can be manufactured. Therefore, the semiconductor device for the switching power supply has less manufacturing variation and can reduce the manufacturing cost.
Further, according to the semiconductor device of the present invention, by integrating the above-described switching power supply circuit of the present invention, a switching power supply circuit having uniform characteristics can be provided, and the function of the switched capacitor circuit can be provided. The input resistance of the error amplifier circuit can be made very large, the zero cross frequency can be shifted to the low frequency side, and the negative feedback operation for stabilizing the DC output voltage can be stabilized. it can. In the present invention, the low frequency is a relatively low frequency and means a frequency of 1 kHz or less as a guide.
Furthermore, the semiconductor device according to the present invention may include a frequency dividing circuit that divides the reference signal, and may be configured to perform the sampling operation of the switched capacitor circuit using the output signal of the frequency dividing circuit. The semiconductor device of the present invention configured as described above can reduce the sampling frequency of the switched capacitor circuit at the ratio of the dividing ratio of the frequency dividing circuit without reducing the frequency of the reference signal. It is possible to easily take measures against oscillation of negative feedback operation without sacrificing responsiveness to fluctuations.

In the switching power supply circuit according to the present invention, the capacitor connected in parallel to the switched capacitor circuit can reduce the input impedance of the error amplifier circuit at a high frequency and improve the transient response at the high frequency. can do. The high frequency is a relatively high frequency and means a frequency of 100 kHz or more as a guide.
In the switching power supply circuit according to the present invention, since the sampling frequency of the switched capacitor circuit is linked to the reference signal, the zero-cross frequency can be freely set by changing the frequency of the reference signal.

According to the switching power supply circuit of the present invention, it is possible to perform a stable negative feedback operation with a small capacity that can be mounted on a semiconductor integrated circuit, and to improve a good transient response at a high frequency and to reduce a manufacturing cost. be able to.
According to the present invention, it is possible to provide a switching power supply circuit that is small and light and highly reliable.
According to the switching power supply circuit of the present invention, the switched capacitor circuit can make the input resistance of the error amplifier circuit very large, and the feedback connected between the input terminal and the output terminal of the error amplifier circuit. Even if the capacitance value is reduced, the zero cross frequency can be set to a low frequency, and the switching power supply circuit including the feedback capacitance can be integrated in the semiconductor device.

In the switching power supply circuit according to the present invention, the capacitor connected in parallel with the switched capacitor circuit can reduce the input impedance at the high frequency and improve the transient response at the high frequency. In addition, since the sampling frequency of the switched capacitor circuit is linked to the reference signal, the zero cross frequency can be freely set by changing the frequency of the reference signal.
Furthermore, according to the semiconductor device of the present invention, since the switching power supply circuit having the above-mentioned effects is integrated, a small and lightweight switching power supply circuit that has a small manufacturing variation during mass production and operates stably is provided. It becomes possible.
The novel features of the invention are nonetheless specifically set forth in the appended claims, but the invention, both in terms of structure and content, should be read in conjunction with the drawings and in the detailed description that follows. Will be better understood and appreciated.

  Preferred embodiments of a switching power supply circuit according to the present invention will be described below in detail with reference to the accompanying drawings.

Embodiment 1
FIG. 1 is a block diagram showing a configuration of a switching power supply circuit according to a first embodiment of the present invention. FIG. 2 is a frequency characteristic diagram showing gain / phase characteristics of the switching power supply circuit according to the first embodiment of the present invention.

  As shown in FIG. 1, the switching power supply circuit of Embodiment 1 is provided with a power supply input terminal 11 to which a DC voltage is input and a power supply output terminal 12 that outputs a DC output voltage stabilized to a predetermined value. The power input terminal 11 and the power output terminal 12 are provided in the voltage conversion unit 13 including a power transistor 66, a coil 67, a diode 68, and an output smoothing capacitor 69. In addition, the switching power supply circuit is provided with a drive signal control unit 10 that turns on / off (chopping) the power transistor 66 with a pulse whose width is modulated. The drive signal control unit 10 includes a pre-drive circuit 14, a pulse width modulation circuit 15, an error amplification circuit 16, a reference voltage circuit 17 that generates a reference voltage, a reference signal generation circuit 18 that generates a reference signal, an output voltage setting resistor 60, 61 and a switched capacitor circuit 19.

As shown in FIG. 1, a capacitor 65 having a capacitance C <b> 2 is provided between the input and output of the error amplifier circuit 16. The reference signal generated by the reference signal generation circuit 18 is a signal having an inclined waveform such as a triangular wave or a sawtooth wave, and is repeated at a predetermined frequency.
The switched capacitor circuit 19 is provided between the connection point of the output voltage setting resistors 60 and 61 and one inverting input terminal of the error amplifying circuit 16, and is turned on / off in synchronization with the sampling frequency fs. It is composed of switches 62 and 63 and a capacitor 64 having a capacitance C3. Here, the sampling frequency fs is linked to the operating frequency of the reference signal output from the reference signal generation circuit 18.

  In FIG. 2, the zero cross frequency fz1 is determined by the sampling frequency fs of the sampling signal of the switched capacitor circuit 19 shown in FIG. 1, the capacitance C3 of the capacitor 64, and the capacitance C2 (feedback capacitance) of the capacitor 65. Is the frequency. Further, fL is a resonance frequency determined by the inductance L1 of the coil 67 of the voltage conversion unit 13 and the capacitance C1 of the output smoothing capacitor 69. In FIG. 2, the zero cross frequency fz1 needs to be set in a frequency region lower than the resonance frequency fL (fz1 <fL).

The operation of the switching power supply circuit according to the first embodiment configured as described above will be described.
The equivalent resistance R of the switched capacitor circuit 19 determined by the sampling frequency fs of the switched capacitor circuit 19 and the capacitance C3 of the capacitor 64 can be expressed by the following equation (3).

  R = 1 / (fs × C3) (3)

Therefore, if the capacitance C3 of the capacitor 64 is set to a small value, it is possible to set Zi << R. The zero cross frequency fz1 can be determined by the equivalent resistance R of the switched capacitor circuit 19 and the feedback capacitance of the error amplifier circuit 16. At the zero cross frequency fz1 at which the gain of the error amplifier circuit 16 becomes 0 dB, the impedance 1 / (2π × fz1 × C2) of the capacitor 65 and the equivalent resistance R are equal. Therefore, the zero cross frequency fz1 can be expressed by the following formula (4) based on the formula (3).

  fz1 = (1 / 2π) × (C3 / C2) × fs (4)

  If the capacitance ratio of the capacitance C3 of the capacitor 64 of the switched capacitor circuit 19 and the capacitance C2 of the capacitor 65, which is the feedback capacitance of the error amplifier circuit 16, is set small, the zero cross frequency fz1 is set to the inductance L1 of the coil 67 and the output smoothing capacitor 69. It is possible to easily set a frequency region lower than the resonance frequency fL determined by the capacitance C1. As shown in FIG. 2, at the resonance frequency fL, the gain of the error amplifier circuit 16 is 0 dB or less, and the ringing phenomenon that occurs in the voltage converter 13 can be attenuated. It becomes possible to operate.

  In the switching power supply circuit of the first embodiment, the capacitance C3 of the capacitor 64 of the switched capacitor circuit 19 and the feedback capacitance of the error amplifier circuit 16 can be designed with small values. Since a capacitor having a small capacitance has a small planar shape when formed on a semiconductor substrate, it can be easily mounted on a semiconductor integrated circuit, and the switching power supply circuit of Embodiment 1 has excellent economic efficiency and stability. .

  In the switching power supply circuit according to the first embodiment, at least the drive signal control unit 10 is integrated in the semiconductor device, and the power transistor 66 and the diode 68 are integrated in the semiconductor device according to the specifications of the output load. . For this reason, a small and light semiconductor device with high reliability can be provided.

  As the switching power supply circuit of the first embodiment, the step-down switching power supply circuit that steps down the DC output voltage from the input voltage has been described. However, the present invention is not limited to such a configuration. A step-up switching power supply circuit that boosts the DC output voltage from the input voltage or a DC output voltage (negative DC The present invention can also be applied to a polarity inversion switching power supply circuit that outputs an output voltage.

  FIG. 3 is a block diagram showing a configuration of a step-up switching power supply circuit to which the configuration of the switching power supply circuit of the first embodiment is applied. FIG. 4 is a block diagram showing a configuration of a polarity inversion switching power supply circuit to which the configuration of the switching power supply circuit of the first embodiment is applied. 3 and 4, the drive signal control unit 10 has the same configuration as the step-down switching power supply circuit shown in FIG. In the voltage converter 13A of the step-up switching power supply circuit shown in FIG. 3, the power transistor Tr1 performs a chopping operation in accordance with the output signal of the drive signal controller 10. When the power transistor Tr1 is turned on, energy is stored in the coil L1, and when the power transistor Tr1 is turned off, the diode D1 rectifies the energy stored in the coil L1, and the boosted DC output voltage is supplied to the power supply output terminal 12. Is output.

  In the voltage converter 13B of the polarity inversion switching power supply circuit shown in FIG. 4, the power transistor Tr1 performs a chopping operation in accordance with the output signal of the drive signal controller 10. Then, when the power transistor Tr1 is turned on, energy is stored in the coil L1, and when the power transistor Tr1 is turned off, the diode D1 rectifies the energy stored in the coil L1, and a negative DC output voltage is supplied to the power output terminal 12. Is output.

<< Embodiment 2 >>
FIG. 5 is a block diagram showing the configuration of the switching power supply circuit according to the second embodiment of the present invention.

As shown in FIG. 5, the switching power supply circuit according to the second embodiment has a configuration in which a capacitor 90 is provided in parallel with the switched capacitor circuit 29 in the configuration of the switching power supply circuit according to the first embodiment.
The switching power supply circuit according to the second embodiment includes an input terminal 21 to which a DC voltage is input and an output terminal 22 that outputs a predetermined DC output voltage. These input terminal 21 and output terminal 22 are the power transistor 76. , A coil 77, a diode 78, and an output smoothing capacitor 79. In addition, the switching power supply circuit is provided with a drive signal control unit 20 that turns on / off (chopping) the power transistor 76 with a pulse whose width is modulated. The drive signal control unit 20 includes a pre-drive circuit 24, a pulse width modulation circuit 25, an error amplification circuit 26, a reference voltage circuit 27 that generates a reference voltage, a reference signal generation circuit 28 that generates a reference signal, an output voltage setting resistor 70, 71, a switched capacitor circuit 29, and a capacitor 90 having a capacitance C4 connected between the input and output of the switched capacitor circuit 29.

As shown in FIG. 5, a capacitor 75 having a capacitance C2 (feedback capacitance) is provided so as to connect the input / output terminals of the error amplifier circuit 26, that is, in parallel with the error amplifier circuit 26. The reference signal generated by the reference signal generation circuit 28 is a waveform signal having a slope like a triangular wave or a sawtooth wave, and is repeated at a predetermined frequency.
The switched capacitor circuit 29 is provided between the connection point of the output voltage setting resistors 70 and 71 and one inverting input terminal of the error amplifier circuit 26, and is turned on / off in synchronization with the sampling frequency fs. It consists of switches 72 and 73 and a capacitor 74 having a capacitance C3.

As described in the switched capacitor circuit 19 in the first embodiment, the switched capacitor circuit 29 in the second embodiment functions like a resistor having an equivalent impedance between input and output. doing. For this reason, the error amplifying circuit 26 functioning as an integrating amplifying circuit has poor responsiveness at high frequencies. However, by connecting the capacitor 90 in parallel between the input and output of the switched capacitor circuit 29, the responsiveness particularly to a high frequency is improved. Therefore, the switching power supply circuit according to the second embodiment stabilizes the negative feedback operation for stabilizing the DC output voltage, and realizes excellent characteristics against a transient response at a high frequency.
In addition, the switching power supply circuit according to the second embodiment can be easily mounted on a semiconductor integrated circuit, and enables excellent economic efficiency, stability, and transient response.

<< Embodiment 3 >>
In the first embodiment described above, the switched capacitor circuit 19 functions as a resistor, and the equivalent resistance R having a large resistance value is obtained by reducing the capacitance C3 of the capacitor 64. This reduces the gain at a high frequency (particularly the resonance frequency fL), eliminates the influence of the ringing phenomenon, and stabilizes the negative feedback operation of the switching power supply circuit. However, there is a limit to reducing the capacitance of the capacitor 64. When the capacitance is 0.2 pF or less, the switched capacitor circuit 19 does not perform its function originally due to the influence of the wiring capacitance associated with the wiring material. As a result, the frequency characteristic cannot be determined only by the switched capacitor circuit 19 and the feedback capacitance, and there is a disadvantage that oscillation occurs due to manufacturing variations during mass production. A switching power supply circuit according to the third embodiment for solving such a problem will be described below.
FIG. 6 is a block diagram showing the configuration of the switching power supply circuit according to Embodiment 3 of the present invention.

As shown in FIG. 6, the switching power supply circuit of the third embodiment controls the switched capacitor circuit by inputting the reference signal from the reference signal generating circuit to the configuration of the switching power supply circuit of the first embodiment. A frequency divider circuit 40 is provided.
The switching power supply circuit of Embodiment 3 is provided with an input terminal 31 to which a DC voltage is input and an output terminal 32 that outputs a predetermined DC output voltage. These input terminal 31 and output terminal 32 are connected to a power transistor 86. , A coil 87, a diode 88, and an output smoothing capacitor 89. Further, the switching power supply circuit is provided with a drive signal control unit 30 for turning on / off (chopping) the power transistor 86 with a pulse whose width is modulated. The drive signal control unit 30 includes a pre-drive circuit 34, a pulse width modulation circuit 35, an error amplification circuit 36, a reference voltage circuit 37 that generates a reference voltage, a reference signal generation circuit 38 that generates a reference signal, an output voltage setting resistor 80, 81, a switched capacitor circuit 39 and a frequency dividing circuit 40.

  In the third embodiment shown in FIG. 6, the switched capacitor circuit 39 performs a sampling operation by the output signal of the frequency dividing circuit 40. Since the other points in the third embodiment are the same as those in the first embodiment shown in FIG. 1, it can be easily understood that the third embodiment can take countermeasures against oscillation as in the first embodiment. Will. Therefore, the sampling operation will be described.

Since the frequency dividing circuit 40 divides the output signal of the reference signal generating circuit 38 by a predetermined frequency dividing ratio, the sampling frequency fs is proportional to the reference signal from the reference signal generating circuit 38 (fs∝f). And a sampling signal having a frequency lower than the operating frequency f of the reference signal can be generated. Thereby, as can be seen from the equation (3) shown in the first embodiment, the equivalent resistance R can be increased in inverse proportion to the decrease in the sampling frequency fs. Therefore, even if the capacitance C3 of the capacitor 84 of the switched capacitor circuit 39 is relatively large, a large equivalent resistance R can be obtained. As a result, the equivalent resistance R can be set without being affected by the wiring capacity of the wiring material, and stable circuit operation is possible even if this switching power supply circuit is configured on a printed circuit board or integrated in a semiconductor integrated circuit. Can be realized.
In addition, as a switching power supply circuit, load responsiveness that stabilizes the DC output voltage in response to fluctuations in the DC output voltage due to load fluctuations is important. As for the load responsiveness, if the repetition frequency for PWM control, that is, the frequency of the reference signal is increased, it responds quickly to the load fluctuation, and if the frequency is lowered, it becomes difficult to follow the load fluctuation.
In the switching power supply circuit according to the third embodiment, the sampling frequency of the switched capacitor circuit can be reduced at the ratio of the frequency division ratio without reducing the frequency of the reference signal. It is possible to easily take oscillation countermeasures for negative feedback operation without sacrificing responsiveness.

A modification to which the configuration of the third embodiment is applied will be described below with specific numerical values.
For example, when the frequency dividing circuit 40 that divides the frequency by 1/8 is used as the first modification, the sampling operation is performed at the sampling frequency fs that is 1/8 of the operating frequency f of the reference signal. For this reason, even if the capacitance C3 having the same value as that of the first embodiment is used, an equivalent resistance R that is eight times larger can be obtained, and the zero-cross frequency fz1 can be shifted to a frequency of 1/8. As a result, the switching power supply circuit of Modification 1 can easily take measures against oscillation.
When the operation is performed using the reference signal having the same frequency as that of the first embodiment, the equivalent resistance R having the same resistance value as that of the first embodiment is obtained even in the second modification using the capacitance C3 having a capacity eight times that of the first embodiment. Can do. In the case of the second modification, when a circuit is formed on a printed circuit board or a semiconductor substrate, the wiring capacity hardly affects the circuit operation, and it is possible to mass-produce with a uniform quality hardly affected by manufacturing variations. .

Further, when the frequency dividing circuit 40 that performs 1/8 frequency division is used as the third modification and the capacitance C3 that is four times that of the first embodiment is used, the equivalent resistance R is calculated by the above-described equation (3). The zero cross frequency fz1 can be shifted to a half frequency. In this case, the zero cross frequency fz can be shifted to the low frequency side even if a capacitance value four times larger than that in the first embodiment is used. In the switching power supply circuit according to the third modification, the above-described first and second modifications in which the oscillation phenomenon is less likely to occur and the stability of the circuit operation is less affected by the wiring capacity than the first embodiment. An excellent circuit design having both effects can be realized.
The same effect can be obtained if the frequency dividing ratio of the frequency dividing circuit 40 of the third embodiment is 1/2 or higher. However, when the sampling frequency fs of the switched capacitor circuit 39 is reduced, When the load current flowing through the load connected to the output terminal 32 fluctuates, the responsiveness for stabilizing the DC output voltage is deteriorated. For this reason, in consideration of responsiveness to load fluctuations, it is preferable to employ a frequency dividing circuit having a frequency dividing ratio in a range from 1/2 frequency division to 1/16 frequency division.

  In each of the first to third embodiments described above, an example using an in-phase type switched capacitor circuit (19, 29, 39) that switches the input side switch and the output side switch in the same phase will be described. However, even if a switched capacitor circuit that performs switching operation in reverse phase is used, the same operation can be obtained and the same effect can be obtained. Further, the switching power supply circuit of the present invention is not limited to the switched capacitor circuit as described above. In addition, a switched capacitor circuit that suppresses switching noise by adding an extra switch is used. May be. In each of the first to third embodiments described above, the rectifying diodes (68, 78, 88 and D1) have been described as silicon diodes or Schottky diodes. However, the rectifying diodes are replaced with MOS transistors. If the MOS transistor is turned on / off in the opposite phase to the chopping operation of the power transistor that is the main switch, the rectification operation by the MOS transistor can be performed, and the same effect as that of the rectification diode can be obtained. Is obtained. The present invention basically has the same effect as that of the configuration of the above-described embodiment, and may be appropriately adopted according to the required design specifications.

As described above, the present invention is a switching power supply circuit used as a power supply circuit in an electronic device and is useful in a mobile phone, a portable electronic device, and the like because it is excellent in economy and stability.
Although the invention has been described in its preferred form with a certain degree of detail, the present disclosure of this preferred form should vary in the details of construction, and combinations of elements and changes in order may vary in the claimed invention. It can be realized without departing from the scope and spirit.

  The present invention relates to a switching power supply circuit that can be integrated in a semiconductor device and can reduce manufacturing costs, and is useful in a power supply circuit.

1 is a block diagram showing a configuration of a switching power supply circuit according to a first embodiment of the present invention. Frequency characteristic diagram showing gain / phase characteristics of the switching power supply circuit according to the first embodiment of the present invention 1 is a block diagram showing a configuration of a boost type switching power supply circuit to which the configuration of a switching power supply circuit according to a first embodiment of the present invention is applied. 1 is a block diagram showing a configuration of a polarity inversion switching power supply circuit to which the configuration of a switching power supply circuit according to a first embodiment of the present invention is applied. The block diagram which shows the structure of the switching power supply circuit of Embodiment 2 which concerns on this invention The block diagram which shows the structure of the switching power supply circuit of Embodiment 3 which concerns on this invention Block diagram showing the configuration of a conventional switching power supply circuit Frequency characteristics diagram showing gain and phase characteristics in a conventional switching power supply circuit

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Drive signal control part 11, 12 Power supply input terminal 13 Voltage conversion part 14 Predrive circuit 15 Pulse width modulation circuit 16 Error amplification circuit 17 Reference voltage circuit 18 Reference signal generation circuit 19 Switched capacitor circuit 60, 61 Output voltage setting resistance 62, 63 Switch 64, 65 Capacitor 66 Power transistor 67 Coil 68 Diode 69 Output smoothing capacitor

Claims (10)

A switching power supply circuit for storing energy in a coil and performing a chopping operation for discharging the stored energy from the coil to output a predetermined DC output voltage;
An error amplifying circuit for amplifying an error between the DC output voltage and a reference voltage;
A first capacitor connected between an input terminal and an output terminal of the error amplifier circuit;
A pulse width modulation circuit that outputs a PWM signal by comparing a reference signal having an inclined waveform with an output signal of the error amplification circuit;
A voltage converter that includes at least the coil and a second capacitor that smoothes energy released from the coil, performs the chopping operation according to the PWM signal, and outputs the predetermined DC output voltage to a power supply output terminal When,
A switched capacitor circuit provided between the power supply output terminal and the input terminal of the error amplifier circuit;
A switching power supply circuit comprising:   2. The switching power supply circuit according to claim 1, wherein a third capacitor is provided between the input and output terminals of the switched capacitor circuit.   3. The switching power supply circuit according to claim 1, wherein the reference signal is a triangular wave signal or a sawtooth wave signal generated by a reference signal generation circuit.   3. The switching power supply circuit according to claim 1, wherein a sampling signal of the switched capacitor circuit is configured to be interlocked with the reference signal.   3. The switching power supply circuit according to claim 1, further comprising a frequency dividing circuit that divides the reference signal, and configured to sample the switched capacitor circuit with an output signal of the frequency dividing circuit. . A semiconductor device that integrates a switching power supply circuit that accumulates energy in a coil and performs a chopping operation for discharging the accumulated energy from the coil to output a predetermined DC output voltage,
An error amplifying circuit for amplifying an error between the DC output voltage and a reference voltage;
A first capacitor connected between an input terminal and an output terminal of the error amplifier circuit;
A pulse width modulation circuit that outputs a PWM signal by comparing a reference signal having an inclined waveform with an output signal of the error amplification circuit;
A voltage converter that includes at least the coil and a second capacitor that smoothes energy released from the coil, performs the chopping operation according to the PWM signal, and outputs the predetermined DC output voltage to a power supply output terminal When,
A switched capacitor circuit provided between the power supply output terminal and the input terminal of the error amplifier circuit;
At least the error amplifier circuit, the first capacitor, the pulse width modulation circuit, and the switched capacitor circuit are formed in one semiconductor substrate.   7. The semiconductor device according to claim 6, wherein a third capacitor connected between input and output terminals of the switched capacitor circuit is formed in the semiconductor substrate.   8. The semiconductor device according to claim 6, wherein the reference signal is a triangular wave signal or a sawtooth wave signal generated by a reference signal generation circuit.   8. The semiconductor device according to claim 6, wherein the sampling signal of the switched capacitor circuit is configured to be interlocked with the reference signal. 8. The semiconductor device according to claim 6, further comprising a frequency dividing circuit that divides the reference signal, and configured to perform the sampling operation of the switched capacitor circuit with an output signal of the frequency dividing circuit.

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