JP4608519B2 - Switching power supply - Google Patents

Description

  The present invention relates to a switching power supply device in which a frequency control type DC-DC conversion circuit is connected to a subsequent stage of a power factor correction booster circuit, and more particularly, a power supply device that suppresses fluctuations in the switching frequency of the DC-DC conversion circuit. It is related with the technique of aiming at high efficiency.

  As this type of switching power supply device, for example, a power supply device is known in which a current resonance type DC-DC conversion circuit is connected to the subsequent stage of the power factor correction booster circuit. In general, in a current resonance type DC-DC conversion circuit, the resonance frequency is set so that the efficiency becomes maximum at the maximum load. For this reason, when the load fluctuates, the switching frequency of the power supply device deviates from the resonance frequency, so that the efficiency is deteriorated. Therefore, a power supply device that can maintain high efficiency regardless of the size of the load has been proposed (see, for example, Patent Document 1).

In this power supply device, the DC voltage output from the power factor correction booster circuit is generally a constant voltage based on the AC input voltage of the power factor correction booster circuit and the load current of the DC-DC converter circuit. By varying the output voltage of the rate improving booster circuit (that is, the input voltage of the DC-DC converter circuit), fluctuations in the switching frequency of the DC-DC converter circuit are suppressed, and the efficiency of the power supply device is increased. is there. Specifically, the DC-DC converter circuit is designed to increase the switching frequency in order to avoid an increase in the output voltage at light loads. By reducing the output voltage of the power factor correction booster circuit, the DC-DC converter circuit Decreases the output voltage, thereby suppressing the fluctuation (increase) in the switching frequency of the DC-DC converter circuit.
Japanese Patent Laying-Open No. 2005-65395 (paragraphs “0020” to “0026”, FIG. 1)

However, the conventional example having such a configuration has the following problems.
That is, the conventional power supply apparatus detects the output voltage of the DC-DC converter circuit and returns the detection signal to the control unit for frequency control of the switching element provided in the DC-DC converter circuit. And a second feedback system for detecting the output current of the DC-DC conversion circuit and returning the detection signal to the control unit for the pulse width control of the switching element provided in the power factor correction booster circuit. Since the feedback system is provided, there is a problem that the device configuration becomes complicated.

  The present invention has been made in view of such circumstances, and an object of the present invention is to realize a highly efficient switching power supply device with a relatively simple configuration.

In order to achieve such an object, the present invention has the following configuration.
In other words, the switching power supply according to the first aspect of the present invention is a power factor correction booster circuit body that switches and boosts an input voltage by a first switching element and rectifies and smoothes it to convert it to a first DC voltage. And a pulse width control unit that varies the first DC voltage by controlling the conduction pulse width of the first switching element based on the first feedback signal;
Connected to the latter stage of the power factor boosting circuit, the first DC voltage is switched by the second switching element and applied to the primary winding of the transformer, and the voltage induced in the secondary winding of the transformer is rectified and smoothed. A DC-DC conversion circuit main body that converts the second DC voltage into a second DC voltage, and a frequency control unit that varies the second DC voltage by controlling the switching frequency of the second switching element based on the second feedback signal; A DC-DC conversion circuit including:
A feedback circuit that detects the second DC voltage and returns the detection signal to the frequency control unit and the pulse width control unit;
The frequency control unit takes in the detection signal of the second DC voltage returned via the feedback circuit as a second feedback signal, and the switching frequency of the second switching element so that the second DC voltage becomes a predetermined voltage. Control
The pulse width control unit takes in the first DC voltage detection signal and the second DC voltage detection signal returned through the feedback circuit as a first feedback signal, and uses the first DC voltage as a predetermined voltage. To the direction of suppressing the fluctuation of the switching frequency of the second switching element.

  [Operation / Effect] According to the invention described in claim 1, the frequency controller of the DC-DC converter circuit uses the second DC voltage detection signal returned through the feedback control circuit as the second feedback signal. And the switching frequency of the second switching element is controlled so that the second DC voltage becomes a predetermined voltage. For example, in the case of a current resonance type DC-DC conversion circuit in which the resonance condition is determined so that the efficiency is maximized at the maximum load, the second DC voltage rises above a predetermined voltage when the load is lightened. Become a trend. At this time, the frequency control unit suppresses the second DC voltage from attempting to rise above the predetermined voltage by increasing the switching frequency of the second switching element. However, when the switching frequency of the second switching element increases, the loss of the DC-DC converter circuit increases, so it is necessary to prevent the switching frequency of the second switching element from increasing too much. Therefore, the pulse width controller of the power factor correction booster circuit changes the first DC voltage, which is the input voltage of the DC-DC converter circuit, so as to suppress fluctuations in the switching frequency of the second switching element. Usually, the pulse width control unit of the power factor correction booster circuit maintains the first DC voltage at a predetermined voltage based on the detection signal of the first DC voltage. Therefore, even if the input voltage of the power factor correction booster circuit fluctuates, the first DC voltage is maintained at a predetermined voltage. On the other hand, when the second DC voltage of the DC-DC converter circuit fluctuates, the first feedback signal changes according to the detection signal of the second DC voltage returned through the feedback circuit. Based on this, the pulse width control unit changes the first DC voltage from a predetermined voltage in a direction to suppress the fluctuation of the switching frequency of the second switching element. That is, when the second DC voltage of the DC-DC converter circuit tends to increase and the switching frequency of the second switching element increases, the input voltage (that is, the first DC voltage) of the DC-DC converter circuit decreases. By lowering the second DC voltage of the DC-DC converter circuit, an increase in the switching frequency of the second switching element is suppressed.

  As described above, according to the present invention, when the load fluctuates, the switching frequency of the second switching element of the DC-DC converter circuit is controlled, and the first DC voltage of the power factor correction booster circuit is changed. Thus, since the fluctuation of the switching frequency of the second switching element is suppressed, high efficiency can be maintained. In addition, the second DC voltage is detected, and the detection signal is returned to both the frequency control unit of the DC-DC conversion circuit and the pulse width control unit of the power factor correction booster circuit by a common feedback circuit. The circuit configuration can be simplified as compared with the case where the detection signal is returned to the control unit via an individual feedback circuit.

  In the present invention, the DC-DC converter circuit is, for example, a current resonance type DC-DC converter circuit (the invention according to claim 2). Further, in the present invention, the feedback circuit preferably returns the detection signal of the second DC voltage to the frequency control unit and the pulse width control unit via the photocoupler (the invention according to claim 3).

  ADVANTAGE OF THE INVENTION According to this invention, while suppressing the fluctuation | variation of the switching frequency of the 2nd switching element with which a DC-DC converter circuit is equipped, high efficiency can be maintained and a switching power supply device with a simple circuit configuration is realized. Can do.

Hereinafter, a switching power supply according to an embodiment of the present invention will be described with reference to the drawings.
FIG. 1 is a circuit diagram illustrating a configuration of a switching power supply apparatus according to an embodiment.

  The switching power supply according to the embodiment includes a noise filter 10 connected to an AC power supply AC, a rectifier circuit 20 connected to the subsequent stage of the noise filter 10, and a power factor correction booster connected to the subsequent stage of the rectifier circuit 20. A circuit 30, a current resonance type DC-DC conversion circuit 40 connected to a subsequent stage of the power factor correction booster circuit 30, and an output voltage (second DC voltage in the present invention) of the DC-DC conversion circuit 40. And a feedback circuit 60 that detects and returns the detection signal to the frequency control unit 42 of the DC-DC conversion circuit 40 and the pulse width control unit 32 of the power factor correction booster circuit 30.

  Hereinafter, the configuration of each unit will be described in detail. The noise filter 10 includes a common mode choke coil 11 and capacitors 12 and 13 connected to input / output terminals of the choke coil 11, respectively. The rectifier circuit 20 is a well-known diode bridge.

The power factor correction booster circuit 30 includes a power factor correction booster circuit body 31 and a pulse width controller 32. The power factor correction booster circuit body 31 switches the input voltage supplied from the rectifier circuit 20 by a FET (field effect transistor) 33 which is a first switching element to boost and rectify and smooth the first DC voltage. It converted to V _0. Specifically, the power factor correction booster circuit body 31 includes a choke coil 34, a diode 35, and a capacitor 36 in addition to the FET 33. One end of the choke coil 34 is connected to the output end of the rectifier circuit 20, and the other end is connected to the anode of the diode 35. The drain of the FET 33 is connected to the anode side of the diode 35, and the source is connected to the ground line. An ON / OFF control signal is given from the pulse width control unit 32 to the gate of the FET 33. The capacitor 36 is connected between the cathode of the diode 35 and the ground line. The first DC voltage V ₀ is detected by being divided by resistors 37 and 38, and the detection signal is given to the input terminal V _S of the pulse width controller 32.

The pulse width control unit 32 generates a first feedback signal (specifically, a detection signal of the first DC voltage V ₀ and a second DC voltage returned via the feedback circuit 60) applied to the input terminal V _S. Based on the detection signal of V _OUT ), the first DC voltage V ₀ is varied by controlling the conduction pulse width of the FET 33. As will be apparent from the description of the operation to be described later, the pulse width controller 32 suppresses the fluctuation of the switching frequency of the second switching element provided in the DC-DC converter circuit 40 based on the first feedback signal. It changes the first DC voltage _{V 0.}

The DC-DC conversion circuit 40 includes a DC-DC conversion circuit main body 41 and a frequency variable control unit 42. The DC-DC conversion circuit main body 41 alternately switches the first DC voltage V ₀ given from the power factor correction booster circuit 30 by the FETs 43 and 44 that are the second switching elements to form the primary winding of the transformer 45. When applied, the voltage induced in the secondary winding of the transformer 45 is rectified and smoothed to be converted into a second DC voltage _VOUT . Specifically, in the DC-DC conversion circuit main body 41, a resonant capacitor 46 and a leakage inductance 47 of the transformer 45 are interposed in series between the drain of the FET 43 and one end of the primary winding of the transformer 45. The other end of the primary winding of the transformer 45 is connected to the source of the FET 43 and the drain of the FET 44, respectively. The source of the FET 44 is connected to the ground line via the resistor 48. An ON / OFF control signal is given to each gate of the FETs 43 and 44 from the frequency control unit 42. The anode of the diode 49 is connected to one end of the secondary winding of the transformer 45, the anode of the diode 50 is connected to the other end of the secondary winding, and the intermediate terminal of the secondary winding is connected to the ground line. Yes. The cathodes of both diodes 49 and 50 are connected, and a capacitor 51 is connected between the connection point and the ground line.

The detection signal of the second DC voltage _VOUT that is the output voltage of the DC-DC conversion circuit main body 41 is returned to the frequency control unit 42 via the feedback circuit 60. The frequency control unit 42 takes in the detection signal of the second DC voltage _{VOUT as} a second feedback signal, and controls the switching frequency of the FETs 43 and 44 so that the second DC voltage _VOUT becomes a predetermined voltage.

The configuration of the feedback circuit 60 will be described. The feedback circuit 60 returns the detection signal of the second DC voltage _VOUT to the frequency control unit 42 and the pulse width control unit 32 via the photocoupler 61. Specifically, the second DC voltage _VOUT is applied to the anode of the photodiode 62 of the photocoupler 61. The cathode of the photodiode 62 is connected to the cathode of a shunt regulator 64 as a constant voltage source. The anode of the shunt regulator 64 is connected to the ground line. Second DC voltage _{V OUT} which is divided by resistors 65 and 66 min is given to the reference voltage terminal _{V REF} of the shunt regulator 64. The collector of the phototransistor 63 of the photocoupler 61, the input terminal V _I of the frequency control unit 42, an emitter to the ground line are connected. The collector of the phototransistor 63 is further connected to one input terminal (+) of the error amplifier 69 via a forward diode 67 and a resistor 68. A reference voltage Va is applied to the other input terminal (−) of the error amplifier 69. The output terminal of the error amplifier 69 is connected to the input terminal (base of the transistor 70) of the amplifier circuit 74 composed of the transistors 70 and 71 and the resistors 72 and 73. The output terminal of the amplifier circuit 74 (emitter of the transistor 71) is connected to the input terminal V _S of the pulse width controller 32 (the connection point of the voltage dividing resistors 37 and 38) via the diode 75 and the resistor 76 connected in the forward direction. )It is connected to the.

Next, the operation of the switching power supply according to the embodiment configured as described above will be described.
An AC input voltage from the AC power supply AC is applied to the rectifier circuit 20 via the noise filter 10 and rectified. The rectified voltage output from the rectifier circuit 20 is supplied to the power factor correction booster circuit 30 and boosted with the improvement of the power factor. First DC as the first DC voltage V ₀ switching by and boosted pulse voltage is rectified and smoothed by a diode 35 and a capacitor 36 of FET33 as a switching element - provided to DC converter circuit 40.

The frequency control unit 42 switches the FETs 43 and 44 alternately so that the first DC voltage V ₀ is applied to the primary winding of the transformer 45. The pulse voltage induced in the secondary winding of the transformer 45 is rectified and smoothed by the diodes 49 and 50 and the capacitor 51, and is output as the second DC voltage _VOUT .

The detection signal of the second DC voltage _VOUT is returned to the frequency control unit 42 via the photocoupler 61 of the feedback circuit 60. The frequency control unit 42 is set in advance so that the switching frequency of the FETs 43 and 44 is a resonance frequency determined by the resonance capacitor 46 and the leakage inductance 47 in a state where the maximum load is connected to the DC-DC conversion circuit 40. ing. Further, in the state where the maximum load is connected to the DC-DC conversion circuit 40, the output voltage of the error amplifier 69 for comparing the detection signal of the second DC voltage _VOUT and the reference voltage Va is substantially “0”. In addition, a reference voltage Va is preset. At this time, the pulse width control unit 32 mainly inputs a detection signal of the first DC voltage V ₀ divided by the resistors 37 and 38 as the first feedback signal, and the first DC voltage V ₀ is The conduction pulse width of the FET 33 is controlled so as to be constant.

  Next, an operation when the load connected to the DC-DC conversion circuit 40 becomes lighter than the maximum load will be described.

When the load connected to the DC-DC conversion circuit 40 becomes lighter, the second DC voltage _VOUT tends to increase. As a result, the current flowing through the photodiode 62 of the photocoupler 61 increases and the collector current of the phototransistor 63 increases. In this way, the detection signal (second feedback signal) of the second DC voltage _VOUT is returned to the frequency control unit 42 as the collector current value of the phototransistor 63. When detecting that the load has become lighter due to the increase in the collector current, the frequency control unit 42 increases the switching frequency of the FETs 43 and 44, thereby suppressing the amount of power transmitted to the secondary side of the transformer 45. The DC voltage _VOUT is returned to a downward trend to try to suppress the increase of the second DC voltage. At this time, if the switching frequency of the FETs 43 and 44 is increased too much, the switching loss increases as the switching frequency increases, so the efficiency of the switching power supply device decreases.

Therefore, in the present embodiment, the detection signal (second feedback signal) of the second DC voltage V _OUT is further returned to the pulse width control unit 32 of the power factor correction booster circuit 30 to generate the first DC voltage V ₀ . By changing, the fluctuation of the switching frequency of the DC-DC conversion circuit 40 is suppressed. That is, when the second DC voltage _VOUT rises from the predetermined voltage at the maximum load, the error output voltage of the error amplifier 69 rises. Increase the output current of the amplifier circuit 74 by increasing the error output voltage, the connection point of the current I _S results flowing through the dividing resistor 38 of the power factor improving step-up circuit 30 to the ground line, dividing resistors 37 and 38 Increase the voltage. As a result, since the voltage at the V _S terminal of the pulse width control unit 32 increases, the pulse width control unit 32 changes the conduction pulse width of the FET 33 in the direction of decreasing the voltage at the V _S terminal. That is, the conduction pulse width of the FET 33 is narrowed, and the first DC voltage V ₀ of the power factor correction booster circuit 30 is lowered.

Since the first DC voltage V ₀ of the power factor correction step-up circuit 30 is an input voltage of the DC-DC conversion circuit 41, when the first DC voltage V ₀ decreases, the DC-DC conversion circuit 41 is accompanied accordingly. The output voltage (second DC voltage) _VOUT of the output voltage V _OUT also decreases. As a result, the rising tendency of the second DC voltage _VOUT due to the light load described above is suppressed. As a result, the fluctuation of the second DC voltage _VOUT can be suppressed without increasing the switching frequency of the FETs 43 and 44 of the DC-DC conversion circuit 40 so high that the efficiency of the switching power supply device is maintained high. can do.

FIG. 2 is a characteristic diagram showing the relationship between the output power of the switching power supply device according to the present embodiment and the first DC voltage V ₀ of the power factor correction booster circuit 30. As can be seen from the figure, as the output power of the switching power supply device decreases (load decreases), the first DC voltage V ₀ of the power factor correction booster circuit 30 decreases.

In this embodiment, the detection signal of the second DC voltage _VOUT , which is the output voltage of the DC-DC conversion circuit 40, is connected to the frequency control unit 42 of the DC-DC conversion circuit 40 via the common feedback circuit 60. Since the power factor correction booster circuit 30 is returned to both of the pulse width control units 32, the circuit configuration is simplified compared to the case where the detection signals are returned to the control units 42 and 32 via individual feedback circuits. You can also.

  The present invention is not limited to the above-described embodiments, and can be modified as follows.

  (1) In the above-described embodiment, a current resonance type DC-DC conversion circuit is shown as an example of the DC-DC conversion circuit, but the present invention is not limited to this. The DC-DC conversion circuit of the present invention may be any circuit as long as it controls the switching frequency of the second switching element to vary the second DC voltage, and may be a ringing choke converter, for example.

1 is a circuit diagram of a switching power supply device according to an embodiment of the present invention. It is the characteristic view which showed the relationship between the output electric power of an Example apparatus, and the 1st DC voltage of a power factor improvement step-up circuit.

Explanation of symbols

DESCRIPTION OF SYMBOLS 30 ... Power factor improvement booster circuit 31 ... Power factor improvement booster circuit body 32 ... Pulse width control part 40 ... DC-DC conversion circuit 41 ... DC-DC conversion circuit body 42 ... Frequency control part 60 ... Feedback circuit

Claims (3)

Based on the first feedback signal, the power factor improving booster circuit body that switches the input voltage by the first switching element and boosts it, and rectifies and smoothes it to convert it to the first DC voltage. A power factor improving step-up circuit including a pulse width control unit that varies the first DC voltage by controlling the conduction pulse width;
Connected to the latter stage of the power factor boosting circuit, the first DC voltage is switched by the second switching element and applied to the primary winding of the transformer, and the voltage induced in the secondary winding of the transformer is rectified and smoothed. A DC-DC conversion circuit main body that converts the second DC voltage into a second DC voltage, and a frequency control unit that varies the second DC voltage by controlling the switching frequency of the second switching element based on the second feedback signal; A DC-DC conversion circuit including:
A feedback circuit that detects the second DC voltage and returns the detection signal to the frequency control unit and the pulse width control unit;
The frequency control unit takes in the detection signal of the second DC voltage returned via the feedback circuit as a second feedback signal, and the switching frequency of the second switching element so that the second DC voltage becomes a predetermined voltage. Control
The pulse width control unit takes in the first DC voltage detection signal and the second DC voltage detection signal returned through the feedback circuit as a first feedback signal, and uses the first DC voltage as a predetermined voltage. To change the switching frequency of the second switching element in a direction that suppresses fluctuations. The switching power supply device according to claim 1,
The DC-DC converter circuit is a switching power supply device that is a current resonance type DC-DC converter circuit. The switching power supply device according to claim 1,
The feedback circuit is a switching power supply device that returns a detection signal of the second DC voltage to the frequency control unit and the pulse width control unit via a photocoupler.

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