JP5424327B2 - Switching power supply - Google Patents

Description

  The present invention relates to a switching power supply apparatus that converts an externally input AC voltage into a predetermined DC voltage to be supplied to a load and outputs the same.

  In recent years, switching power supply devices that drive semiconductor integrated circuits such as microprocessors are required to have low output voltage, high output current, and high efficiency. As a conventional switching power supply device studied to satisfy these requirements, for example, there is one described in Non-Patent Document 1 (see FIG. 5).

  In addition, a switching power supply device 1 ′ shown in FIG. 5 in which a PFC circuit is further added for power factor improvement and harmonic countermeasures has been conventionally known.

As shown in FIG. 6, a conventional switching power supply 1 ″ includes a rectifying / smoothing unit 2 for rectifying and smoothing a commercial AC voltage, a power factor improving unit 3 (PFC circuit) provided on the output side thereof, and an output thereof. Is a step-down DC / DC converter unit 4 ′ that converts DC voltage to a predetermined DC voltage V ₂ , a switching unit 5 that switches DC voltage V ₂ to generate a switching voltage, a primary winding T _1, and a secondary winding A transformer T having T ₂ and a switching voltage supplied to the primary winding T ₁ , and a secondary output voltage V _O obtained by rectifying and smoothing the induced voltage of the secondary winding T ₂ And a secondary output unit 6.

Further, the switching power supply device 1 ″ further includes a feedback unit 7 ′ that feeds back the secondary output voltage V _O to the switching control unit 4a of the DC / DC converter unit 4 ′. Maintains the secondary output voltage V _O at the required voltage of the load.

As shown in FIG. 7, the voltage V ₁ output from the power factor correction unit 3 fluctuates under the influence of a commercial ripple voltage or an instantaneous power failure. For this reason, the DC / DC converter unit 4 ′ stabilizes the DC voltage V ₂ supplied to the switching unit 5 and the transformer T by stepping down the voltage V ₁ to a voltage lower than the lower limit of the fluctuation. Yes.

Ninomiya Tamotsu, Abe Seiya, Electronic Technology April issue “Low-Voltage and High-Current Converter Circuit Technology”, published by Nikkan Kogyo Shimbun, April 1, 2002, page 10 (particularly, FIG. 10)

However, in this conventional switching power supply device 1 ″, all of the current I _DC directed to the switching unit 5 and the transformer T flows through the switching element Q ₃ and the choke coil L of the DC / DC converter unit 4 ′. The loss due to the conduction loss of Q ₃ and the impedance of the choke coil L cannot be avoided.

  Therefore, an object of the present invention is to provide a switching power supply device that can reduce loss in a DC / DC converter section and can significantly improve efficiency compared to the conventional one.

In order to solve the above-described problems, a switching power supply according to the present invention includes a rectifying / smoothing unit that rectifies and smoothes an AC voltage input from the outside, and an output side of the rectifying / smoothing unit, and improves a power factor. A power factor improving unit, a DC / DC converter unit that converts an output of the power factor improving unit into a predetermined DC voltage, a switching unit that generates a switching voltage by switching the predetermined DC voltage, and a primary winding A transformer having a wire and a secondary winding, to which the switching voltage is supplied to the primary winding, and a secondary output voltage obtained by rectifying and smoothing the induced voltage induced in the secondary winding. A switching power supply device including a secondary output unit for outputting,
The power factor improvement unit is feedback controlled based on a DC component of the secondary output voltage, and the DC / DC converter unit is a bidirectional DC / DC converter capable of both step-down and step-up operations, The feedback control is performed based on the AC component of the secondary output voltage.

  According to this configuration, when a deviation occurs between the required voltage of the load and the secondary output voltage, the power factor improving unit that is responsible for stabilizing the DC component and the DC that is responsible for stabilizing the AC component By cooperating with the / DC converter unit, the secondary output voltage can be maintained at the required voltage of the load. Further, according to this configuration, since there is no need to stabilize the DC component in the DC / DC converter unit, each element (such as a choke coil that is indispensable for the step-up / step-down operation) constituting the DC / DC converter unit. In this case, only a ripple current flows. Therefore, the loss in the DC / DC converter unit can be greatly reduced.

  Here, the DC / DC converter unit in the switching power supply device includes, for example, a first switching element having a drain connected to a high potential line, a drain connected to a source of the first switching element, A second switching element connected to a low potential line; a choke coil having one end connected to a connection point of the first switching element and the second switching element; the other end of the choke coil; and the low potential line A second capacitor connected between the high-potential line and the low-potential line on the output side of the first switching element and the second switching element; Based on the AC component of the secondary output voltage, the first switching element and the second switch It can be composed of a switching control unit for controlling the switching element.

  When the AC component fed back to the DC / DC converter unit is positive, the first switching element switches under the control of the switching control unit, and the second switching unit When the alternating current component fed back to the DC / DC converter section is negative, it operates as a step-down DC / DC converter that charges the first capacitor with the accumulated charge of the capacitor. It is configured to operate as a step-up DC / DC converter that switches under the control of the control unit and charges the second capacitor with the accumulated charge of the first capacitor, so that the bidirectional DC / DC can be operated relatively easily. A DC converter can be realized.

  ADVANTAGE OF THE INVENTION According to this invention, the switching power supply device which can improve efficiency significantly conventionally can be provided.

1 is a circuit diagram of a switching power supply device according to the present invention. 2A and 2B are equivalent circuit diagrams of a DC / DC converter unit, where FIG. 1A is an equivalent circuit diagram when operating as a step-down DC / DC converter, and FIG. 2B is an equivalent circuit diagram when operating as a step-up DC / DC converter. It is. It is a voltage waveform of the switching power supply concerning the present invention. It is a figure for demonstrating the loss of a switching power supply device, Comprising: (A) is a partial block diagram of the switching power supply device which concerns on this invention, (B) is a partial block diagram of the conventional switching power supply device. It is a circuit diagram of the conventional switching power supply device. It is a circuit diagram of the conventional switching power supply device provided with the PFC circuit. It is a voltage waveform of the conventional switching power supply device shown in FIG.

  Hereinafter, preferred embodiments of a switching power supply according to the present invention will be described with reference to the accompanying drawings.

FIG. 1 shows a switching power supply device according to the present invention. The switching power supply device 1 includes a rectifying / smoothing unit 2 that rectifies and smoothes an AC voltage (for example, a commercial AC voltage), a power factor improvement unit 3 including a PFC circuit provided on the output side thereof, and outputs the predetermined DC. It includes a DC / DC converter 4 for converting the voltage V _2, a switching unit 5 for generating a switching voltage by switching a DC voltage V _2, the. These are all provided on the primary side of the switching power supply device 1.

The switching power supply unit 1, the switching voltage is supplied to the primary winding T _1, a transformer T which AC voltage is induced in the secondary winding T _2, rectifying the induced voltage in the secondary winding T ₂ And a secondary side output unit 6 that outputs the secondary side output voltage V _O obtained by smoothing to the load. In the embodiment shown in FIG. 1, the switching unit 5, the transformer T, and the secondary output unit 6 constitute a resonant half-bridge circuit, but a half-bridge circuit and a full bridge that use the magnetic flux of the transformer in both directions. The circuit and the push-pull circuit can be changed as appropriate.

The switching power supply device 1 further includes a feedback unit 7 that feeds back the secondary output voltage V _O to the PFC circuit 3 and the switching control units 3 a and 4 a of the DC / DC converter unit 4. As a result, the switching power supply device 1 maintains the secondary output voltage V _O at the required voltage of the load.

The feedback unit 7 has a function of separating the secondary output voltage V _O into a DC component and an AC component, and only the DC component of the secondary output voltage V _O is fed back to the switching control unit 3a. Further, only the AC component of the secondary output voltage V _O is fed back to the switching control unit 4a.

  The DC / DC converter unit 4 is a bidirectional DC / DC converter that operates as a step-up DC / DC converter or a step-down DC / DC converter under the control of the switching control unit 4a. The DC / DC converter unit 4 can realize a bidirectional DC / DC converter relatively easily by adopting the following configuration, for example.

That is, the DC / DC converter unit 4 includes a first switching element Q ₁ having a drain connected to the high potential line 8H, a drain connected to the source of the _first switching element Q _{1, and} a source connected to the low potential line 8L. The second switching element Q ₂ connected to the choke coil L, the choke coil L having one end connected to the connection point of the first and second switching elements Q ₁ and Q ₂ , the other end of the choke coil L, and the low potential line A first capacitor C ₁ connected between 8L, a second capacitor C ₂ connected between the high potential line 8H and the low potential line 8L, and the first and second switching elements Q ₁ , Q _And a switching control unit 4a for controlling ₂ .

The switching control unit 4a determines the first and second switching elements Q ₁ and Q ₂ based on the polarity (positive / negative) and the absolute value of the AC component of the secondary output voltage V _O that has been fed back. Control. In the embodiment shown in FIG. 1, the first and second switching elements Q ₁ and Q ₂ are both FETs, but bipolar transistors and IGBTs can be used instead.

When the AC component fed back to the DC / DC converter unit 4 is “positive”, that is, when the secondary output voltage V _O is higher than the required voltage of the load, the switching control unit 4a reduces the DC voltage V ₂ . In order to achieve this, the DC / DC converter unit 4 is operated as a step-down DC / DC converter. In this case, the DC / DC converter unit 4, and the second capacitor C ₂ first input connection point of the switching element Q ₁ (high potential line 8H), a choke coil L and the first capacitor C ₁ Can be handled as an equivalent circuit having an output of the connection point (see FIG. 2A).

As shown in the figure, when operating as a step-down DC / DC converter, the first switching element Q ₁ is repeatedly turned ON / OFF under the control of the switching control unit 4a and stored in the second capacitor C ₂ . The charged charge is moved to the first capacitor C ₁ . As a result, the second capacitor C ₂ is discharged, and the voltage at both ends (= DC voltage V ₂ ) decreases. On the other hand, the first capacitor C ₁ is charged, and the voltage between both ends rises. The second switching element Q ₂ are kept OFF, the can be regarded as a diode for synchronous rectification.

When the AC component fed back to the DC / DC converter unit 4 is “negative”, that is, when the secondary output voltage V _O is lower than the required voltage of the load, the switching control unit 4a increases the DC voltage V ₁ . For this purpose, the DC / DC converter unit 4 is operated as a step-up DC / DC converter. In this case, the DC / DC converter unit 4 is inputted with a connection point between the choke coil L and the first capacitor C ₁ , and a connection point (high potential) between the _second capacitor C ₂ and the first switching element Q _1. It can be handled as an equivalent circuit having the output of line 8H) (see FIG. 2B).

As shown in the figure, when operating as a step-up DC / DC converter, the second switching element Q ₂ repeats ON / OFF under the control of the switching control unit 4a and accumulates in the first capacitor C ₁ . the once was charge moving second to the capacitor C _2. As a result, the first capacitor C ₁ is discharged, and the voltage at both ends decreases. On the other hand, the second capacitor C ₂ is charged, and the voltage at both ends (= DC voltage V ₂ ) increases. Note that the first switching element Q ₁ remains OFF and can be regarded as a diode for synchronous rectification.

On the other hand, as described above, the switching control unit 3a of the power factor improvement unit 3 is feedback-controlled based on the DC component of the secondary output voltage V _O. For this reason, as shown in FIG. 3, the voltage V ₁ output from the power factor improvement unit 3 fluctuates due to the effects of commercial ripple voltage and instantaneous power failure, but the DC component is applied to the switching unit 5 and the transformer T. It corresponds to the DC voltage V ₂ to be supplied. Accordingly, DC / DC converter unit 4, by stepping down or up the voltage V _1, may be removed only variations due to commercial ripple voltage and momentary power failure.

In other words, the switching power supply device 1 according to the present invention includes a power factor improving unit 3 that is responsible for stabilizing the DC component when a deviation occurs between the required load voltage and the secondary output voltage V _O. The secondary side output voltage V _O is maintained at the required voltage of the load by the cooperation of the DC / DC converter unit 4 in charge of stabilizing the AC component. Of course, the power factor correction unit 3 also performs waveform shaping for power factor improvement.

ここで、Ｉ_mは交流電流のピーク値である。 Next, the loss reduction effect of the switching power supply device 1 according to the present invention will be described with reference to FIG. In the figure, r ₁ is the input impedance of the power factor correction unit 3, r ₂ is the input impedance of the DC / DC converter units 4, 4 ′, I _DC is the DC value of the current, I _rms is the effective value of the current, I _r means a ripple current. I _DC , I _rms , and I _r can be expressed by the following equations, respectively.

Here, _Im is the peak value of the alternating current.

Also, in FIG. 4 and the following description, for simplicity,
(A) The power factor of the DC / DC converter units 4 and 4 ′ is set to 1.
(B) No switching loss (considering only impedance)
(C) The input impedances of the DC / DC converter units 4 and 4 ′ are equal.
I am going to do that.

First, a conventional switching power supply device 1 ″ (see FIG. 6) will be described with reference to FIG. 4B. In the switching power supply device 1 ″, all of the direct current I _DC directed to the switching unit 5 and the transformer T is obtained. Since the current flows through the switching element Q ₃ and the choke coil L of the DC / DC converter unit 4 ′, a loss of r ₂ · I _DC ² (= P ′) occurs in the DC / DC converter unit 4 ′.

On the other hand, in the switching power supply device 1 according to the present invention, the first switching element Q ₁ , the second switching element Q _2, and the choke coil L of the DC / DC converter unit 4 are connected to the path through which the direct current I _DC flows. Connected in parallel. Therefore, the direct current I _DC does not flow through these elements, and only the ripple current I _r flowing between the first capacitor C ₁ and the second capacitor C ₂ when stabilizing the alternating current component. Flowing. As a result, in the DC / DC converter unit 4, a loss of r ₂ · I _r ² (= P) occurs as shown in FIG.

つまり、ＤＣ／ＤＣコンバータ部４の損失Ｐは、ＤＣ／ＤＣコンバータ部４’の損失Ｐ’の約１／４である。 When the loss P of the DC / DC converter unit 4 in the switching power supply device 1 according to the present invention is compared with the loss P ′ of the DC / DC converter unit 4 ′ in the conventional switching power supply device 1 ″, the following equation is obtained. .

That is, the loss P of the DC / DC converter unit 4 is about ¼ of the loss P ′ of the DC / DC converter unit 4 ′.

  As described above, according to the present invention, it is possible to significantly reduce the loss in the DC / DC converter unit as compared with the conventional case. Therefore, according to the present invention, it is possible to provide a switching power supply apparatus in which the efficiency is greatly improved as compared with the prior art.

  Note that the switching power supply according to the present invention is not limited to the specific configuration described above, and it is obvious that various modifications can be conceived by those skilled in the art.

1 Switching power supply device 2 Rectification smoothing unit 3 Power factor improvement unit (PFC circuit)
4 DC / DC converter section 5 switching section 6 secondary output section 7 feedback section C ₁ first capacitor C ₂ second capacitor Q ₁ first switching element Q ₂ second switching element L choke coil T transformer

Claims (3)

A rectifying / smoothing unit for rectifying and smoothing an AC voltage input from the outside, a power factor improving unit for improving a power factor provided on the output side of the rectifying / smoothing unit, and an output of the power factor improving unit are predetermined. A DC / DC converter unit for converting the DC voltage into a DC voltage, a switching unit for switching the predetermined DC voltage to generate a switching voltage, a primary winding and a secondary winding, and the switching on the primary winding A switching power supply device comprising: a transformer to which a voltage is supplied; and a secondary side output unit that outputs a secondary side output voltage obtained by rectifying and smoothing the induced voltage induced in the secondary winding. ,
The power factor improvement unit is feedback controlled based on a DC component of the secondary output voltage,
The DC / DC converter unit is a bidirectional DC / DC converter capable of both step-down and step-up operations, and is feedback-controlled based on an AC component of the secondary side output voltage.
The switching power supply device characterized by the above-mentioned. The DC / DC converter unit includes:
A first switching element having a drain connected to the high potential line;
A second switching element having a drain connected to a source of the first switching element and a source connected to a low potential line;
A choke coil having one end connected to a connection point of the first switching element and the second switching element;
A first capacitor connected between the other end of the choke coil and the low potential line;
A second capacitor connected between the high potential line and the low potential line on the output side of the first switching element and the second switching element;
A switching control unit for controlling the first switching element and the second switching element based on an AC component of the secondary output voltage;
The switching power supply device according to claim 1, further comprising: The DC / DC converter unit includes:
When the AC component fed back to the DC / DC converter unit is positive, the first switching element switches under the control of the switching control unit, and the first capacitor is stored by the charge stored in the second capacitor. Operates as a step-down DC / DC converter that charges
When the AC component fed back to the DC / DC converter unit is negative, the second switching element is switched under the control of the switching control unit, and the second capacitor is stored by the charge stored in the first capacitor. Operates as a step-up DC / DC converter that charges
The switching power supply device according to claim 2.

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