JP2012178952A - Switching power supply circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a high-efficiency switching power supply circuit capable of achieving zero-voltage switching without exceeding a switching element withstanding voltage by voltage rise of a capacitor.SOLUTION: A switching power supply circuit has: a second reactor Lr connected in series to a first reactor in which a first coil L1-1 and a second coil L1-2 magnetically coupled to the first coil are connected in series; a series circuit connected between one end and the other end of a DC power supply Vin and in which the first reactor, the second reactor, a first diode D1, and a first capacitor C1 are connected in series; a switching element Q1 connected between a connection point between the first coil and the second coil, and the one end of the DC power supply; a series circuit having one end connected to the connection point between the first coil and the second coil and the other end connected to a connection point between the first diode and the first capacitor or a connection point between the second reactor and the first diode, and to which a switching element Q2 and a second capacitor C2 are connected in series; and a control circuit 10 on-off controlling the switching element Q2 so that turn-on of the switching element Q1 becomes zero-voltage switching.

Description

  The present invention relates to a switching power supply circuit that can reduce switching loss of a switching element.

  Conventionally, a step-up switching power supply circuit is known. FIG. 9 shows an example of a conventional step-up switching power supply circuit. In FIG. 9, a series circuit of a reactor L10, a switching element Q1 composed of a MOSFET, and a current detection resistor R1 is connected to both ends of the DC power supply Vin.

 A parallel circuit of a diode Da and a capacitor Ca is connected between the drain and source of the switching element Q1. The diode Da may be a parasitic diode of the switching element Q1, and the capacitor Ca may be a parasitic capacitor of the switching element Q1.

 A series circuit of a reactor L20, a diode D1, and a capacitor C1 is connected to both ends of a series circuit of the switching element Q1 and the current detection resistor R1. A series circuit of a switching element Q2 made of a MOSFET and a capacitor C2 is connected to both ends of the reactor L20. Switching element Q2 and capacitor C2 constitute an active clamp circuit.

 A parallel circuit of a diode Db and a capacitor Cb is connected between the drain and source of the switching element Q2. The diode Db may be a parasitic diode of the switching element Q2, and the capacitor Cb may be a parasitic diode of the switching element Q2.

 The control circuit 100 alternately turns on / off the switching element Q1 and the switching element Q2 based on the voltage from the capacitor C1 and the voltage from the current detection resistor R1, and is higher than the input voltage (voltage of the DC power supply Vin). Control is performed to output a constant output voltage Vo.

  Next, the operation of the conventional step-up switching power supply circuit shown in FIG. 9 will be described. First, when the switching element Q1 is switched from on to off, energy energized by the reactor L10 during the on period of the switching element Q1 is turned off along with the switching element Q1, the capacitor C2 and the diode D1 along the path. It is divided into a first path for releasing energy to C1, and a second path for the reactor L20 and the diode D1. In the second path, the energy of the reactor L10 is released, and the reactor L20 is excited.

  In the first path, the capacitor C2 is charged and the voltage of the capacitor C2 rises. When the switching element Q2 is turned on after the capacitor Cb is discharged and the diode Db is turned on, the polarity of the current flowing through the switching element Q2 and the capacitor C2 is reversed by the resonance operation. When the switching element Q2 is turned off, the energy excited in the reactor L20 is released, and the charge of the capacitor Ca is drawn out through the path of the reactor L20, the diode D1, the capacitor C1, the current detection resistor R1, and the capacitor Ca. After turning on, the switching element Q1 is turned on to realize zero voltage switching (ZVS) of the switching element Q1.

JP 2004-201373 A

  However, in the conventional switching power supply circuit described in Patent Document 1, the switching element Q1 and the switching element Q2 are alternately turned on / off, the energy of the reactor L20 is regenerated in the capacitor C2, and the polarity current is inverted. However, since the charging voltage of the capacitor C2 is added to the output voltage (the voltage of the capacitor C1), the drain-source voltage of the switching elements Q1 and Q2 is the voltage of the capacitor C1. And may exceed the breakdown voltage of the switching elements Q1 and Q2.

  An object of the present invention is to provide a highly efficient switching power supply circuit that suppresses a voltage increase of a capacitor of an active clamp circuit so as not to exceed a withstand voltage of a switching element and realizes zero voltage switching.

In order to solve the above-described problems, a switching power supply circuit according to the present invention includes a first reactor in which a first winding and a second winding that is magnetically coupled to the first winding are connected in series, and the first reactor. A reactor composed of a second reactor connected in series and a DC power source connected between one end and the other end, and the first reactor, the second reactor, the first diode, and the first capacitor are connected in series. A first switching element connected between a connection point of the first winding and the second winding and one end of the DC power source, and one end of the first winding and the first winding. The second switching is connected to the connection point of the second winding and the other end is connected to the connection point of the first diode and the first capacitor or the connection point of the second reactor and the first diode. The element and the second capacitor Are connected in series, and a control circuit that controls on / off of the second switching element so that the first switching element is turned on in zero voltage switching.

  According to the present invention, when the first switching element is turned off, the excitation energy of the first reactor is discharged from the first winding to the first capacitor via the second switching element and the second capacitor, and the second capacitor is charged. At the same time, energy is released from the second winding, and the second winding, the second reactor, the first diode, the second capacitor, the path of the second switching element or the second winding, the second reactor, the second Since the second capacitor is discharged through the path of the two capacitors and the second switching element, the charging voltage of the second capacitor is suppressed to a low level and does not exceed the withstand voltage of the first and second switching elements. Zero voltage switching can be realized, and a highly efficient switching power supply circuit can be provided.

It is a block diagram of the switching power supply circuit of Example 1 of this invention. It is a wave form diagram which shows operation | movement of each part of the switching power supply circuit of Example 1 of this invention. It is a wave form diagram which shows operation | movement of each part of the switching power supply circuit of Example 1 of this invention. It is the figure which showed the electric current path | route when each part of the switching power supply circuit of Example 1 of this invention operate | moves for every period with the thick line. It is the figure which showed the electric current path | route when each part of the switching power supply circuit of Example 1 of this invention operate | moves for every period with the thick line. It is a block diagram of the switching power supply circuit of Example 2 of this invention. It is a block diagram of the switching power supply circuit of Example 3 of this invention. It is a block diagram of the switching power supply circuit of Example 4 of this invention. It is a figure which shows an example of the conventional step-up type switching power supply circuit.

  Hereinafter, a switching power supply circuit according to an embodiment of the present invention will be described in detail with reference to the drawings.

  1 is a configuration diagram of a switching power supply circuit according to a first embodiment of the present invention. The switching power supply circuit according to the first embodiment shown in FIG. 1 is a continuous current mode step-up chopper circuit in which a current flowing through the reactor L1 continuously flows, and is the first in comparison with the configuration of the conventional switching power supply circuit shown in FIG. A reactor L1 including a first reactor having a winding L1-1 and a second winding L1-2 that is magnetically coupled to the first winding L1-1 and a second reactor Lr is provided. .

  1 is replaced with the reactor L1 instead of the reactors L10 and L20 of FIG. Since other configurations are the same as those in FIG. 9, the same reference numerals are given to the same portions.

  The second reactor Lr is composed of a leakage inductance caused by a leakage magnetic flux between the first winding L1-1 and the second winding L1-2 of the first reactor. The second reactor Lr may be provided individually instead of the leakage inductance. The turn ratio between the first winding L1-1 and the second winding L1-2 may be about 10: 1.

  The control circuit 10 generates a gate signal Q1g based on the voltage from the capacitor C1 and the voltage from the current detection resistor R1, and outputs the gate signal Q1g to the gate of the switching element Q1 to turn on / off the switching element Q1 (first switching element).

  The control circuit 10 generates a gate signal Q2g obtained by inverting the gate signal Q1g for turning on / off the switching element Q1, and outputs the gate signal Q2g to the gate of the switching element Q2 (second switching element) to turn on / off the switching element Q2.

  Further, the control circuit 10 controls on / off of the switching element Q2 so that the turn-on of the switching element Q1 is zero voltage switching.

  The voltage applied to switching elements Q1, Q2 is the sum of the voltage across capacitor C1 and the voltage across capacitor C2.

 2 and 3 are waveform diagrams showing the operation of each part of the switching power supply circuit according to the first embodiment of the present invention. 4 and 5 are bold lines showing current paths when each part of the switching power supply circuit according to the first embodiment of the present invention operates for each period.

 4 and 5, the voltage C2v of the capacitor C2 is defined such that the drain side potential of the switching element Q2 is positive and the + Vo side potential is 0 volts.

  Next, the operation of each part of the switching power supply circuit according to the first embodiment will be described with reference to FIGS. The switching element Q1 and the switching element Q2 have a predetermined dead time td and are turned on / off alternately. FIG. 4A shows an initial state.

 First, in the period t3 in FIG. 4B, the drain of the switching element Q1 is taken along the negative path L1-1 → Q1 (Ca) → R1 → Vin by the energy of the reactor L1 excited by the voltage of the DC power supply Vin. -The capacitor Ca between the sources is charged. For this reason, the voltage Q1v between the drain and source of the switching element Q1 rises.

 At the same time, the energy of the reactor L1 also flows in the negative path of L1-1 → Q2 (Cb) → C2 → C1 → Vin, so that the drain-source voltage Q2v of the switching element Q2 also starts to decrease. The voltage change rate dv / dt of the capacitors Ca and Cb changes with an inclination formed by the time constant between the first winding L1-1 and the capacitors Ca and Cb.

 In the period t4 in FIG. 4C, the energy released from the first winding L1-1 begins to flow through the diode Db of the switching element Q2. The negative current Q2i shown in FIGS. 2 and 3 indicates that a current flows through the diode Db. By turning on the switching element Q2 by the gate signal Q2g during the period in which the negative current Q2i flows, zero voltage switching of the switching element Q2 can be realized.

 Also, the first path of the positive electrode of Vin → L1-1 → L1-2 → Lr → D1 → C1 → Vin and the second path of the negative electrode of Vin → L1-1 → Q2 → C2 → C1 → Vin negative. The energy is discharged to the capacitor C1 through the path.

 In a period t5 in FIG. 4D, the switching element Q1 is off and the switching element Q2 is on. At this time, the capacitor C2 is charged via the switching element Q2 by the energy of the reactor L1. At the same time, the energy of the second winding L1-2 starts to be released, and the capacitor C2 is discharged through a path of L1-2 → Lr → D1 → C2 → Q2 → L1-2.

 Since the second winding L1-2 and the second reactor Lr are connected to the diode D1, the energy released from the second winding L1-2 is output to the capacitor C1 while exciting the second reactor Lr. . Eventually, when the charging voltage C2v of the capacitor C2 rises, this time the capacitor C2 is discharged, and a current flows out through a path of C2, Q2, L1-2, Lr, D1, and C2. This can also be seen from the fact that the current Q2i of the switching element Q2 is positively inverted in polarity.

 In the period t6 in FIG. 5A, the switching element Q2 is turned off by the gate signal Q2g, and at the same time, the second reactor Lr starts to emit excitation energy. A current flows through a path of Lr → D1 → C2 → Q2 (Cb) → L1-2 → Lr, and the capacitor Cb is gradually charged with a slope dv / dt due to the time constant between the second reactor Lr and the capacitor Cb. The voltage of the capacitor Cb, that is, the voltage Q2v between the drain and source of the switching element Q2 increases.

 Further, the excitation energy of the second reactor Lr starts to be released through a route of Lr → D1 → C1 → R1 → Q1 (Ca) → L1-2 → Lr. At this time, the charge of the capacitor Ca of the switching element Q1 is extracted, and the voltage Q1v of the switching element Q1 decreases.

 In the period t7 in FIG. 5B, since the current flows through the same current path as that in the period t6, the emission energy of the second reactor Lr flows through the diode Da of the switching element Q1. The negative current Q1i shown in FIGS. 2 and 3 indicates that a current flows through the diode Da. By turning on the switching element Q1 with the gate signal Q1g during the period in which the negative current Q1i flows, zero voltage switching of the switching element Q1 can be realized.

 In the period t1 in FIG. 5C, the switching element Q1 is turned on, and the switching element Q1 has an exciting current flowing in the first winding L1-1 by the DC power source Vin and a current flowing due to the energy release of the second reactor Lr. The difference current flows.

 In the period t2 in FIG. 5D, the energy release of the second reactor Lr is completed, and the current Q1i of the switching element Q1 flows with the slope of the current excited by the DC power supply Vin.

  As the number of turns of the second winding L1-2 is increased, the voltage C2v of the capacitor C2 may become a negative voltage as shown in FIG. 3, and the voltages Q1v and Q2v of the switching elements Q1 and Q2 are reduced. It can be made lower than the output voltage (the voltage of the capacitor C1).

  Thus, according to the switching power supply circuit of the first embodiment, when the switching element Q1 is turned off, the exciting energy of the reactor L1 is first passed from the first winding L1-1 through the switching element Q2 and the capacitor C2. The capacitor C1 or the load is discharged, and the capacitor C2 is charged. At the same time, energy is released from the second winding L1-2, and the second winding L1-2, the second reactor Lr, the diode D1, the capacitor C2, The capacitor C2 is discharged through the path of the switching element Q2.

  Therefore, the charging voltage of the capacitor C2 is kept low, and the drain-source voltage Vds of the switching elements Q1, Q2 does not exceed the withstand voltage. That is, by providing the second winding L1-2, the capacitor C2 is positively discharged, so that the switching element withstand voltage due to the rise in the voltage of the capacitor C2 is not exceeded, and the zero voltage of the switching elements Q1, Q2 Switching can be realized and a highly efficient switching power supply circuit can be provided.

 FIG. 6 is a configuration diagram of the switching power supply circuit according to the second embodiment of the present invention. The second embodiment shown in FIG. 6 is characterized in that the second winding L1-2, the second reactor Lr, the capacitor C2, and the switching element Q2 are connected in a closed circuit.

 In FIG. 6, the connection of the capacitor C2 in FIG. 1 is changed. Since other configurations are the same as those in FIG. 1, the same reference numerals are given to the same portions.

 Even with such a configuration, operations and effects similar to those of the switching power supply circuit according to the first embodiment shown in FIG. 1 can be obtained.

 FIG. 7 is a configuration diagram of the switching power supply circuit according to the third embodiment of the present invention. The third embodiment shown in FIG. 7 is characterized in that a snubber circuit including diodes D2 and D3 and a capacitor C3 is provided.

 In FIG. 7, diodes D2 and D3 and a capacitor C3 are added to FIG. Since other configurations are the same as those in FIG. 1, the same reference numerals are given to the same portions.

 One end of a capacitor C3 is connected to the anode of the diode D1, and the anode of the diode D2 and the cathode of the diode D3 are connected to the other end of the capacitor C3. The anode of the diode D3 is connected to the negative electrode of the DC power supply Vin, one end of the capacitor C1, the output terminal (−Vo), and one end of the current detection resistor R1. The cathode of the diode D2 is connected to the other end of the capacitor C1, the cathode of the diode D1, and one end of the capacitor C2.

 According to the above configuration, when the switching element Q1 is turned on, the voltage of the direct current power source Vin is applied to the first winding L1-1, and the first winding L1-1 and the second winding L1-2 are magnetic. Since they are coupled, a voltage of Vin × (the number of turns of L1-2) / (the number of turns of L1-1) is generated in the second winding L1-2, and a voltage obtained by adding this voltage and the output voltage Vo. Is applied to the diode D1. At this time, a surge voltage may be generated in the diode D1 due to the charge accumulated in the diode D1 being extracted.

 At this time, the voltage generated in the second winding L1-2 charges the capacitor C1 via the capacitor C3 and the diode D2. The diode D3 is used when the voltage is negative. For this reason, the voltage applied to the diode D1 becomes low, and no surge voltage is generated in the diode D1. That is, since a lossless snubber circuit including the diodes D2 and D3 and the capacitor C3 is added, the withstand voltage of the diode D1 can be suppressed.

  The switching power supply circuit according to the fourth embodiment shown in FIG. 8 is a PFC circuit (power factor correction circuit) provided with an AC power supply Vac and a rectifier circuit RC1 instead of the DC power supply Vin of the switching power supply circuit shown in FIG. It is characterized by that.

  The AC power supply Vac supplies an AC voltage to the rectifier circuit RC1. The rectifier circuit RC1 rectifies the AC voltage from the AC power supply Vac.

 The control circuit 10a shown in FIG. 8 further inputs the voltage at the connection point between the resistor R2 and the resistor R3 connected in series to both ends of the output of the rectifier circuit RC1 to the control circuit 10 shown in FIG. The input AC voltage waveform at the connection point between R2 and resistor R3 is multiplied by the output error voltage of capacitor C1, and the input AC current waveform becomes an input AC voltage waveform based on the obtained multiplication output and the voltage of current detection resistor R1. It is characterized by improving the power factor by controlling to match.

  According to the switching power supply circuit of the fourth embodiment, the power factor is improved and the same operation as that of the switching power supply circuit of the first embodiment is performed, and the same effect is obtained.

  The present invention is applicable to a DC-DC converter, a power factor correction circuit, and an AC-DC converter.

Vin DC power source Vac AC power source L1 Reactor L1-1 First reactor first winding L1-2 First reactor second winding Lr Second reactor Q1, Q2 Switching element D1 Diode RC1 Rectifier circuit R1-R3 Resistance C1- C3 capacitor 10, 10a control circuit

Claims (4)

A reactor including a first reactor in which a first winding and a second winding magnetically coupled to the first winding are connected in series, and a second reactor connected in series to the first reactor;
A first series circuit connected between one end and the other end of the DC power source, wherein the first reactor, the second reactor, the first diode, and the first capacitor are connected in series;
A first switching element connected between a connection point between the first winding and the second winding and one end of the DC power supply;
One end is connected to a connection point between the first winding and the second winding, and the other end is a connection point between the first diode and the first capacitor or a connection between the second reactor and the first diode. A second series circuit connected to the point and having a second switching element and a second capacitor connected in series;
A control circuit for controlling on / off of the second switching element such that the turn-on of the first switching element is zero voltage switching;
A switching power supply circuit comprising:   The switching power supply circuit according to claim 1, wherein the second reactor is a leakage inductance between the first winding and the second winding of the first reactor.   The switching power supply circuit according to claim 1, wherein a snubber circuit is connected to the first diode. The switching power supply circuit according to any one of claims 1 to 3, wherein the DC power supply includes an AC power supply and a rectifier circuit, and the control circuit has control for improving a power factor.

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