JP2007318931A - Switching power supply circuit and its control method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a switching power supply suppressing, with a simple structure, a harmonic current which flows at the AC power supply side and, having small external size, and improved transient response characteristics, and to provide its control method. <P>SOLUTION: This switching power supply circuit is provided with a first rectifier circuit 22, a switching circuit 24, a transformer 25, a second rectifier circuit 26, a secondary smoothing capacitor 27, and a control circuit 28. This control circuit 28 is provided with an insulation 28b that outputs a signal S2 of a result of comparing an output DC voltage with a reference voltage, a multiplier 28c that outputs a signal S4 obtained by multiplying the signal S2 by a signal S3 proportional to a first pulsating voltage, a comparator 28d that compares the signal S4 with a signal S5 proportional to a current value flowing in the switching circuit 24 to output a resultant signal S6, a current detection circuit that detects a current (O) of the transformer 5 to output a signal S7, and a flip-flop circuit 28e that turns on and off the switching circuit 24 using the signals S6 and S7 as reset and set signals, respectively. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a switching power supply circuit used for an AC power supply such as a commercial power supply, and more particularly to a switching power supply circuit that suppresses a harmonic current and has a reduced outer shape and a control method thereof.

  In a switching power supply that generates direct current from an alternating current power supply such as a commercial power supply, the mainstream circuit system is currently a capacitor input type switching power supply. Capacitor-input type switching power supplies rectify and smooth the AC voltage, which is the output of an AC power supply such as a commercial power supply, and convert it to the required DC voltage with a DC-DC converter. The output voltage is held constant by negative feedback control with respect to load fluctuations.

  An example of the circuit configuration of such a conventional switching power supply circuit is shown in FIG. In FIG. 2, the noise filter 1, the first rectifier circuit 2, the primary side smoothing capacitor 3, the switching circuit 4, the transformer 5, the second rectifier circuit 6, and the secondary side smoothing capacitor 7 in order from the input side of the AC power supply. And a control circuit 8 are provided. The first rectifier circuit 2 outputs a first pulsation voltage by full-wave rectifying an AC voltage of a commercial power source or the like. The primary side smoothing capacitor 3 is usually composed of an aluminum electrolytic capacitor, and smoothes the first pulsating voltage to output a DC voltage V2. The switching circuit 4 performs on / off control of the DC voltage V2 at a predetermined frequency (for example, 20 kHz to 500 kHz) based on a given control signal, and generates a high frequency AC voltage V4 on the secondary side of the transformer 5. The second rectifier circuit 6 full-wave rectifies the AC voltage V4 and outputs a second pulsating voltage V5. The pulsating voltage V5 is smoothed by the secondary side smoothing capacitor 7 to obtain a DC voltage V6, and an output load To be applied. The DC voltage V6 is compared with the reference voltage in the control circuit 8, and the result is fed back to the control voltage of the switching circuit 4 to stabilize the output.

  However, in such a capacitor-input type switching power supply circuit, the charging current flows only when the first pulsation voltage exceeds the terminal voltage of the primary side smoothing capacitor 3, so that the input AC voltage waveform (sine wave) A large pulse current flows instantaneously near the peak, and this current includes harmonic components of the input AC voltage waveform. The noise filter 1 is provided in order to remove the influence of the harmonic current on the AC power supply. However, the noise filter 1 is normally not sufficiently removed by itself, and the AC power supply is contaminated, and other electronic devices connected to the AC power supply are used. There arises a problem that a failure occurs and transmission loss increases. Further, in this switching power supply circuit, since the primary side smoothing capacitor 3 and the secondary side smoothing capacitor 7 are composed of relatively large aluminum electrolytic capacitors, there is a problem that the switching power supply circuit itself cannot be reduced in size. There is also.

  In order to solve such problems of the capacitor input type switching power supply circuit, a switching power supply circuit is proposed in which a harmonic countermeasure is taken with a unique circuit configuration. As an example of such a switching power supply circuit, for example, a circuit configuration shown in Patent Document 1 is shown in FIG. The switching power supply circuit includes a noise filter 31, a first rectifier circuit 32, a switching circuit 34, a transformer 35, a second rectifier circuit 36, a secondary smoothing capacitor 37, and a control circuit 38, as shown in FIG. Is provided. The individual components such as the noise filter 31 and the first rectifier circuit 32 are all the same in configuration and function as the noise filter 1 and the first rectifier circuit 2 which are components of the conventional switching power supply circuit of FIG. . However, the primary side smoothing capacitor is not installed in the circuit of FIG.

  Therefore, in this switching power supply circuit, since there is no smoothing capacitor in the subsequent stage of the first rectifier circuit 32, the input current waveform to the switching circuit 34 becomes a full-wave rectified sine wave waveform, which appears in the circuit of FIG. No pulsating current is generated. Therefore, no harmonic current that affects the AC power supply side flows. Further, the primary side smoothing capacitor is unnecessary, and the secondary side smoothing capacitor 37 can use an electric double layer capacitor having a smaller volume per unit capacitance than the aluminum electrolytic capacitor, so that the switching power supply circuit itself can be made compact. There is a merit that can be.

  The control circuit 38 generates a control signal for performing negative feedback control of the pulse width of the control voltage of the switching circuit 34 based on the level of the output DC voltage. A reference voltage comparison unit 38a, an insulation unit 38b, and an LPF 38c are provided. The reference voltage comparison unit 38a compares the output DC voltage with a reference voltage corresponding to the set value, and outputs a comparison result signal. The insulation unit 38b is configured by, for example, a photocoupler, and the comparison result signal is electrically converted. Is transmitted in an electrically insulated state. The LPF 38c, which is a low-pass frequency filter, passes and outputs only the frequency component lower than the ripple frequency included in the output DC voltage from the signal of the comparison result. For example, when the frequency of the AC power supply is 50 Hz and the first rectifier circuit 32 is a full-wave rectifier circuit, the frequency of the ripple included in the output DC voltage is 100 Hz, so the cutoff frequency of the LPF 38c is a frequency lower than 100 Hz. (For example, about 10 Hz).

Japanese Patent No. 3506649

  As described above, the switching power supply circuit of FIG. 3 does not generate a pulsed current and has an advantage that the switching power supply circuit itself can be downsized. However, since the control circuit 38 requires the LPF 38c, the transient response is poor, it is difficult to follow a steep fluctuation of the load, and the output voltage is not sufficiently stabilized. Accordingly, an object of the present invention is to provide a switching power supply circuit that can suppress harmonic current flowing to the AC power supply side with a simple circuit configuration, can be reduced in size, and has improved transient response characteristics, and a control method therefor. is there.

  In order to solve the above-described problem, a switching power supply circuit according to the present invention includes a first rectifier circuit that generates a first pulsation voltage by full-wave rectifying an input first AC voltage, and a frequency of the AC voltage. A switching circuit for generating a first high-frequency AC voltage by controlling on / off of the first pulsating voltage at a high frequency, a transformer having a primary winding connected in series to the switching circuit, and the transformer A second rectifying circuit for generating a second pulsating voltage by rectifying a second high-frequency AC voltage generated on the secondary winding side of the first winding, and a smoothing for smoothing the second pulsating voltage to generate a DC voltage A switching power supply circuit comprising: a circuit; and a control circuit for detecting the difference between the DC voltage and a preset reference voltage to control the switching circuit, the control circuit including the DC voltage and the base A reference voltage comparison unit that compares the voltage and outputs a signal of the first comparison result, and transmits the signal of the first comparison result in an electrically insulated state and outputs a signal of the second comparison result An insulating section that performs multiplication, a signal that is multiplied by the signal of the second comparison result and a signal that is proportional to the first pulsation voltage, an output signal from the multiplier, and a current value that flows through the switching circuit A comparator that compares the proportional signal and outputs the result, a current detection circuit that outputs a signal when the current of the secondary winding of the transformer becomes zero, and an output signal from the comparator And a flip-flop circuit that turns on and off the switching circuit using the output of the current detection circuit as a reset signal and a set signal.

  The smoothing circuit is preferably composed of a capacitor having a larger capacitance per unit volume than an aluminum electrolytic capacitor.

  For this reason, the smoothing circuit may be composed of a tantalum capacitor, a niobium capacitor, an electric double layer capacitor, or a capacitor that combines them, which has a larger capacitance per unit volume than an aluminum electrolytic capacitor.

  The switching power supply circuit control method according to the present invention includes a first rectifier circuit that generates a first pulsation voltage by full-wave rectification of an input AC voltage, and a frequency higher than the frequency of the AC voltage. A switching circuit that generates a first high-frequency AC voltage by controlling on / off of the first pulsation voltage, a transformer having a primary winding connected in series to the switching circuit, and a secondary winding of the transformer A second rectifier circuit for generating a second pulsating voltage by rectifying a second high-frequency AC voltage generated on the side, a smoothing circuit for generating a DC voltage by smoothing the second pulsating voltage, and the DC A control method of a switching power supply circuit comprising a control circuit for detecting a difference between a voltage and a preset reference voltage and controlling the switching circuit, and comparing the DC voltage with the reference voltage The first comparison result signal is output, the first comparison result signal is transmitted in an electrically insulated state, the second comparison result signal is output, and the second comparison result signal is output. And the signal proportional to the first pulsation voltage are multiplied to output the multiplication result, the multiplication result signal is compared with the signal proportional to the current value flowing through the switching circuit, and the comparison result is output. A signal is output when the current of the secondary winding of the transformer becomes 0, the signal of the comparison result is a reset signal, and the signal when the current of the secondary winding is 0 is a set signal. A flip-flop process for turning on / off the switching circuit is performed.

  The present invention improves the drawbacks by applying a control method used in a power factor correction circuit (PFC) or the like to the control of a flyback type switching power supply circuit as shown in FIG. With the above switching power supply circuit configuration and its control method, the harmonic current flowing to the AC power supply side can be suppressed with a simple circuit configuration, and the outer shape can be reduced with the simple circuit configuration, and the switching of FIG. It is possible to improve the transient response characteristic that was a drawback of the power supply circuit.

  Embodiments of the present invention will be described below with reference to the drawings.

  FIG. 1 is an explanatory diagram of a switching power supply circuit according to an embodiment of the present invention, FIG. 1 (a) is a block diagram showing the overall configuration of the present embodiment, and FIG. 1 (b) is a control circuit. FIG. FIG. 1C and FIG. 1D are diagrams illustrating an example of a relationship between signals generated from each component of the switching power supply circuit and used in the control circuit.

  The switching power supply circuit according to the embodiment of the present invention includes a first rectifier circuit 22 that generates a first pulsation voltage by full-wave rectifying an input AC voltage in, as shown in FIG. A switching circuit 24 that generates a first high-frequency AC voltage by ON / OFF control of the first pulsation voltage at a frequency higher than the frequency of the AC voltage in, and a primary winding connected in series to the switching circuit 24 The transformer 25, the second rectification circuit 26 that rectifies the second high-frequency AC voltage generated on the secondary winding side of the transformer 25 to generate the second pulsation voltage, and the second pulsation voltage. A secondary-side smoothing capacitor 27 that is a smoothing circuit that generates an output DC voltage by smoothing, and a control circuit 28 that controls the switching circuit 24 by detecting a difference between the output DC voltage and a preset reference voltage. Preparation . In the present embodiment, the noise filter 21 is inserted on the input side of the first rectifier circuit 22.

  Here, the noise filter 21 is an LC filter composed of a choke coil, a capacitor, and the like, and suppresses switching noise generated in the switching circuit 24. The switching circuit 24 is configured by a switching element such as a MOSFET, and the first pulsating voltage is turned on / off at a predetermined frequency (for example, 20 kHz to 500 kHz) under the control of the control circuit 28, so that the first high frequency AC voltage is supplied. It is to convert to. The transformer 25 transforms the first high-frequency AC voltage to generate a predetermined second high-frequency AC voltage. The secondary-side smoothing capacitor 27 is composed of an electric double layer capacitor having a predetermined capacitance value and a volume per unit capacity smaller than that of an aluminum electrolytic capacitor, and smoothes the second pulsating voltage to generate an output DC voltage. It supplies to the load which is not illustrated. This electric double layer capacitor has a characteristic capable of sufficiently smoothing the second pulsation voltage at a frequency of 100 Hz or 120 Hz. For example, in the case of a switching power supply that outputs 16 V and 2.5 A, when the ripple component included in the output DC voltage is suppressed to within 10%, the capacitance of the smoothing capacitor needs to be 5000 μF or more.

  FIG. 1B is an internal block diagram of the control circuit 28 of FIG. The control circuit 28 compares the output DC voltage S1 with the reference voltage and outputs a first comparison result signal, and transmits the first comparison result signal in an electrically insulated state. And an insulator 28b for outputting the second comparison result signal S2, and a multiplier 28c for multiplying and outputting the second comparison result signal S2 and the signal S3 proportional to the first pulsation voltage; The comparator 28d that compares the signal S4 output from the multiplier 28c with the signal S5 proportional to the current value flowing through the switching circuit 24 and outputs the result, and the current of the secondary winding of the transformer 5 becomes zero. A current detection circuit (not shown) that sometimes outputs the signal S7, and the switching circuit using the signal S6 output from the comparator 28d as a reset signal and the signal S7 output from the current detection circuit as a set signal. And a flip-flop circuit 28e for turning on / off. Here, the current detection circuit detects an output from the auxiliary winding provided in a part of the transformer 25.

  Here, the reference voltage comparison unit 28a compares the output DC voltage S1 with a preset reference value of the output DC voltage, and outputs a comparison result signal corresponding to the difference between them. The insulating unit 28b is composed of, for example, a photocoupler, and outputs the comparison result signal as an electrically insulated signal S2 and transmits it to the multiplier 28c side. The multiplier 28c multiplies the output of the first rectifier circuit 22, that is, the signal S3 proportional to the first pulsation voltage and the signal S2, and outputs a signal S4. Here, the waveform of the signal S4 is similar to the waveform of the first pulsating voltage because the signal S2 from the comparison result has a substantially constant value. The comparator 28d compares this signal S4 with a signal S5 proportional to the current value flowing through the switching circuit 24, and inputs the result as a signal S6 to the reset input (R) of the flip-flop 28e. Further, the flip-flop 28e inputs a signal S7 for detecting that the current of the transformer 25 has become 0 to the set input (S), and controls on / off of the switching circuit 24 by the output signal S8. An example of the relationship between the signals S2, S3, and S4 is shown in FIG. 1C, and an example of the relationship between the signals S4 and S5 is shown in FIG.

Next, operations of the switching power supply circuit and the control circuit 28 according to the present embodiment will be described. This control method is based on a control method used in a power factor correction circuit (PFC) or the like, and its switching operation is as follows.
(1) When the switching circuit 24 is turned on, the current flowing through the switching circuit 24 (same as the current of the primary winding of the transformer 25 and corresponding to S5) increases.
(2) The signal S5 corresponding to this current value is input to the comparator 28d. When the reference value determined by the signal S4 output from the multiplier 28c reaches the reference value as shown in FIG. The signal S6 is a reset signal (R) for resetting the flip-flop 28e, and the switching circuit 24 is turned OFF. Here, as shown in FIG. 1C, the signal S4 output from the multiplier 28c is the product of a difference signal S2 between the output DC voltage S1 and its reference voltage and a signal S3 proportional to the first pulsation voltage. Therefore, the current value is proportional to the first pulsation voltage.
(3) When the switching circuit 24 is turned off, a current is discharged from the secondary side winding of the transformer 25, and at the same time, a positive voltage is generated in a current detection circuit including an auxiliary winding provided in a part of the transformer 25.
(4) When the discharge of current from the secondary winding of the transformer 25 is finished, the voltage of the auxiliary winding of the transformer 25 also decreases.
(5) When the voltage of the auxiliary winding of the transformer 25 becomes 0, the current detection circuit detects it, and the output signal S7 is input as a set signal (S) for setting the flip-flop 28e. As a result, the switching circuit 24 is turned ON again and the next cycle is started.

  As shown in FIG. 1D, by performing such switching control, the current flowing through the primary winding of the transformer 25 becomes a sawtooth waveform like the signal S5, and its peak value corresponds to the signal S4. It is similar to the first pulsation voltage. Therefore, the average value is also a current value proportional to the first pulsating voltage, and the average value of the output current from the input AC power supply is also proportional to the input AC voltage, thereby suppressing the harmonic current.

  Thus, in this embodiment, since the harmonic current flowing to the AC power supply side is suppressed with a simple circuit configuration, video equipment and audio equipment are commonly connected to the AC power supply to which this switching power supply circuit is connected. In this case, the deterioration of the image quality of these video devices and the sound quality of the audio devices is avoided. In addition, since the primary side smoothing capacitor is not used and the secondary side smoothing capacitor 27 is composed of an electric double layer capacitor having a smaller shape per volume than the aluminum electrolytic capacitor, the outer shape of the switching power supply circuit Is miniaturized. Further, since the control circuit does not include a low-frequency pass filter (LPF) like the switching power supply of FIG. 3, the transient response characteristic is also improved.

  Although one embodiment of the present invention has been described in detail above, the specific configuration for realizing the present invention is not limited to the above-described embodiment, and the design does not depart from the gist of the present invention. This change is included in the present invention. For example, the AC power source is not limited to a commercial power source, and may be an AC power source output from a private power generator, for example. The secondary side smoothing capacitor 27 is not limited to an electric double layer capacitor or the like, but may be replaced when a capacitor having a smaller volume per unit capacity than an aluminum electrolytic capacitor is developed. In FIG. 1, the noise filter 21 may be provided after the first rectifier circuit 22 or may be provided both before and after the first rectifier circuit 22.

1 is an explanatory diagram of a switching power supply circuit according to an embodiment of the present invention, FIG. 1A is a block diagram showing an overall configuration, FIG. 1B is an internal block diagram of a control circuit, FIG. (D) is a figure which shows an example of the relationship of the signal used for a control circuit. The figure which shows an example of the circuit structure of the conventional switching power supply circuit. The figure which shows the circuit structure of an example of the switching power supply circuit by which the conventional harmonic measure was taken.

Explanation of symbols

1, 21, 31 Noise filters 2, 22, 32 First rectifier circuit 3 Primary smoothing capacitors 4, 24, 34 Switching circuits 5, 25, 35 Transformers 6, 26, 36 Second rectifier circuits 7, 27, 37 Secondary-side smoothing capacitors 8, 28, 38 Control circuits 28a, 38a Reference voltage comparison units 28b, 38b Insulation unit 28c Multiplier 28d Comparator 28e Flip-flop circuit 38c LPF
S1 output DC voltage S2, S3, S4, S5, S6, S7, S8 signal

Claims (4)

  A first rectifier circuit that generates a first pulsation voltage by full-wave rectification of the input AC voltage, and ON / OFF control of the first pulsation voltage at a frequency higher than the frequency of the AC voltage. A switching circuit for generating a first high-frequency AC voltage, a transformer having a primary winding connected in series to the switching circuit, and a second high-frequency AC voltage generated on the secondary winding side of the transformer A second rectifier circuit that generates a second pulsating voltage, a smoothing circuit that smoothes the second pulsating voltage to generate a DC voltage, and a difference between the DC voltage and a preset reference voltage is detected. A control circuit for controlling the switching circuit, wherein the control circuit compares the DC voltage with the reference voltage and outputs a first comparison result signal. Part The first comparison result signal is transmitted in an electrically insulated state and outputs a second comparison result signal; the second comparison result signal and the first pulsation voltage; A multiplier that multiplies and outputs a proportional signal, a comparator that compares the output signal from the multiplier with a signal that is proportional to a current value flowing through the switching circuit, and outputs the result; and a secondary of the transformer A current detection circuit that outputs a signal when the winding current becomes zero, and the switching circuit is turned on / off using the output signal from the comparator as a reset signal and the output of the current detection circuit as a set signal A switching power supply circuit comprising a flip-flop circuit.   2. The switching power supply circuit according to claim 1, wherein the smoothing circuit comprises a capacitor having a larger capacitance per unit volume than an aluminum electrolytic capacitor.   3. The switching according to claim 2, wherein the smoothing circuit is composed of a tantalum capacitor, a niobium capacitor, an electric double layer capacitor, or a capacitor that combines them, which has a larger capacitance per unit volume than an aluminum electrolytic capacitor. Power supply circuit. A first rectifier circuit that generates a first pulsation voltage by full-wave rectification of the input AC voltage, and ON / OFF control of the first pulsation voltage at a frequency higher than the frequency of the AC voltage. A switching circuit for generating a first high-frequency AC voltage, a transformer having a primary winding connected in series to the switching circuit, and a second high-frequency AC voltage generated on the secondary winding side of the transformer A second rectifier circuit that generates a second pulsating voltage, a smoothing circuit that smoothes the second pulsating voltage to generate a DC voltage, and a difference between the DC voltage and a preset reference voltage is detected. A control method for a switching power supply circuit comprising a control circuit for controlling the switching circuit,
The DC voltage and the reference voltage are compared to output a first comparison result signal, the first comparison result signal is transmitted in an electrically insulated state, and a second comparison result signal is output. Output, multiply the signal of the second comparison result and the signal proportional to the first pulsation voltage, and output the multiplication result, and the signal proportional to the current value flowing through the multiplication result signal and the switching circuit And the comparison result is output, and a signal is output when the current of the secondary winding of the transformer becomes 0. The signal of the comparison result is used as a reset signal and the current of the secondary winding is 0. A control method for a switching power supply circuit, wherein flip-flop processing for turning on / off the switching circuit is performed using a signal at the time of becoming a set signal as a set signal.

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