JP2004357495A - Switching power circuit and control method used for switching power circuit - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To reduce switching loss in a switching power circuit. <P>SOLUTION: When a switching element 33 changes from an on-state to an off-state, a capacitor 35 is charged, and a rising of voltage becomes gentle as compared with the falling of a current passed through the switching element 33. As a result, the switching loss is reduced. When the switching element 33 changes from the off state to the on state, a diode 34 has been already in the on-state. Therefore, zero-voltage switching takes place, and the switching loss is reduced. When an auxiliary switching element 39 changes from the on-state to the off-state, an auxiliary capacitor 41 is charged, and a rising of voltage becomes gentle as compared with the falling of a current passed through the auxiliary switching element 39. As a result, the switching loss is reduced. When the auxiliary switching element 39 changes from the off-state to the on-state, an auxiliary diode 40 has been already in the on-state. Therefore, zero-voltage switching takes place, and the switching loss is reduced. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a switching power supply circuit and a control method used for the switching power supply circuit. For example, the present invention relates to a switching power supply suitable for use in an electronic device operated by a power supply voltage obtained by boosting a relatively low voltage such as a battery. The present invention relates to a power supply circuit and a control method used for the switching power supply circuit.

  In recent years, electronic devices have been miniaturized, and there has been a demand for miniaturization of a built-in power supply unit. A switching power supply circuit is often used as the power supply unit. When the switching power supply circuit is downsized, it is generally dealt with by increasing the switching frequency. If the switching frequency is increased, the switching loss in the switching element increases and the amount of heat generated increases. Therefore, it is necessary to increase the size of the radiator or the like, which is an obstacle to downsizing. For this reason, a reduction in switching loss is required. The switching power supply circuit is classified into a step-down type, a step-up type, and a step-up / step-down type. Among these, the step-up type includes a DC power supply unit such as a battery, a choke coil, a switching element, a rectifying diode, and It has a smoothing capacitor. When the switching element is on, the electromagnetic energy supplied from the DC power supply is stored in the choke coil, and when the switching element is off, the back electromotive force generated in the choke coil is the DC power supply. Is applied to the smoothing capacitor via the rectifying diode, and the output voltage of the DC power supply is boosted.

  Conventionally, this type of switching power supply circuit includes a battery 1, a choke coil 2, a switching element (n-channel MOSFET, hereinafter referred to as "nMOS") 3, a diode 4, as shown in FIG. It comprises a capacitor 5, a rectifier diode 6, a smoothing capacitor 7, and a control unit 8, and a load Z is connected to the smoothing capacitor 7 in parallel.

  In this switching power supply circuit, the electromagnetic energy supplied from the battery 1 is stored in the choke coil 2 when the switching element 3 is on, and the reverse energy generated in the choke coil 2 when the switching element 3 is off. The electromotive voltage is superimposed on the voltage E of the battery 1 and applied to the smoothing capacitor 7 via the rectifying diode 6. The output voltage E of the battery 1 is boosted and the output voltage N is supplied to the load Z. The output voltage N is monitored by the control unit 8, and the time width of the ON state of the switching element 3 is controlled by the control unit 8 so that the output voltage N is kept substantially at a set value.

However, this switching power supply circuit has the following problems.
That is, a loss occurs when the switching element 3 is turned on and off. For example, when the switching element 3 is turned on and immediately before the turn-on, the capacitor 5 is a parasitic capacitance of the switching element 3 and is charged with a voltage substantially equal to the output voltage N. Then, the charge of the capacitor 5 is discharged through the switching element 3 at the time of turn-on. At this time, the electromagnetic energy stored in the capacitor 5 is consumed by the switching element 3, and a power loss occurs. Immediately before the switching element 3 turns on, a load current flows in the rectifier diode 6 in the forward direction. When the switching element turns on in this state, a reverse voltage is applied to the rectifier diode 6 from the smoothing capacitor 7. You. For this reason, a recovery current flows through the rectifier diode 6 and there is nothing to limit the current, so that there is a problem that a great loss and noise are generated. When the rectifier diode 6 is constituted by a fast recovery diode, the recovery current decreases, but does not completely disappear.

In addition to the above-described switching power supply circuit, conventionally, as this kind of technology, there has been one described in the following literature, for example.
As shown in FIG. 7, the boost chopper type switching power supply described in Patent Literature 1 includes a battery 1, a choke coil 2, a main switching element 3, a diode 4, a capacitor 5, a rectifying diode 6, It comprises a smoothing capacitor 7, a controller 8A, a choke coil 9, diodes 10, 11, an auxiliary switching element 12, and a diode 13, and a load Z is connected to the smoothing capacitor 7 in parallel.

  In this switching power supply, as shown in FIG. 8, the auxiliary switching element 12 is turned on immediately before the main switching element 3 is turned on, and the auxiliary switching element 12 is turned on immediately after the main switching element 3 is turned on. It turns off. First, when the auxiliary switching element 12 is turned on, the current flowing through the auxiliary switching element 12 is gradually changed by the choke coil 9 so that the auxiliary switching element 12 transitions from the off state to the on state. The switching loss at the time is reduced. Next, when the current flowing through the choke coil 9 rises and becomes equal to the current of the choke coil 2, the charge of the capacitor 5 is extracted by resonance between the choke coil 9 and the capacitor 5, and when the discharge of the capacitor 5 is completed. , The diode 4 is turned on. Since the main switching element 3 is turned on while the diode 4 is in the on state, the main switching element 3 performs zero-voltage switching, and the switching loss is reduced.

  Next, when the auxiliary switching element 12 transitions from the on state to the off state, the voltage across the auxiliary switching element 12 rises rapidly due to the electromagnetic energy accumulated in the choke coil 9, and the auxiliary switching element 12 performs switching. Loss occurs. Next, the electromagnetic energy stored in the choke coil 9 is emitted through the current path of the main switching element 3, the choke coil 9, and the diode 10. As described above, this switching power supply has a problem that a switching loss occurs when the auxiliary switching element 12 is turned off. In this case, if a capacitor is connected in parallel to the auxiliary switching element 12, the rise of the voltage at both ends of the auxiliary switching element 12 can be moderated. However, when the auxiliary switching element 12 is turned on, Is discharged, which causes a problem that switching loss occurs.

  As shown in FIG. 9, the switching power supply device described in Patent Document 2 includes a battery 1, a choke coil 2, a main switching element 3, a diode 4, a capacitor 5, a rectifying diode 6, It comprises a smoothing capacitor 7, a transformer 21, an auxiliary switching element 22, a diode 23, a capacitor 24, and a capacitor 25.

  In this switching power supply device, as shown in FIG. 10, when main switching element 3 is turned on at time t0, voltage E of battery 1 is applied to a series circuit of choke coil 2 and primary winding n1 of transformer 21. Is done. At this time, since the auxiliary switching element 22 is off, no current flows through the secondary winding n2 of the transformer 21. Therefore, the transformer 21 is equivalent to its exciting inductance, and performs the same operation as the switching power supply circuit of FIG. At time t1, when the main switching element 3 is turned off, a flyback voltage is generated in the transformer 21, and the capacitor 25 is charged through the diode 23. The voltage of the secondary winding n2 of the transformer 21 is clamped by the voltage of the capacitor 25, and its current decreases linearly. At this time, the current of the choke coil 2 is supplied to the load through the diode 6.

  At time t2, the current of the transformer 21 becomes zero. At this time, since the auxiliary switching element 22 is in the off state, no current flows through the secondary winding n2 of the transformer 21. Therefore, the transformer 21 becomes equivalent to the exciting inductance again, and starts to resonate with the capacitors 5 and 24. At this time, the resonance current flows through the loop of the capacitor 5, the diode 6, and the capacitor 7, and the loop of the capacitor 24, the transformer 21, and the capacitor 25. At time t3, the auxiliary switching element 22 is turned on, the voltage of the capacitor 25 is applied to the secondary winding n2 of the transformer 21, and the current increases linearly.

At time t4, when the auxiliary switching element 22 is turned off and no current flows through the secondary winding n2 of the transformer 21, the transformer 21 becomes equivalent to its exciting inductance and starts to resonate with the capacitor 5. At this time, the resonance current flows through the loop of the capacitor 5, the transformer 21, the diode 6, and the capacitor 7, and the capacitor 5 is discharged. By turning on the main switching element 3 when the voltage of the capacitor 5 reaches zero or reaches the minimum point, the main switching element 3 becomes zero voltage switching or soft switching, and the switching loss is greatly reduced. Reduced. Further, at this time, the current ID1 of the diode 6 approaches zero as shown in FIG. 10F, so that the recovery noise generated when the main switching element 3 is turned on next time decreases.
Japanese Patent Application Laid-Open No. 06-311738 (page 1, FIG. 1, FIG. 2) Japanese Patent Application Laid-Open No. 07-203693 (page 1, FIG. 1, FIG. 3)

However, the switching power supply circuit of FIG. 9 has the following problems.
That is, after the auxiliary switch current ISW2 reaches zero at time t2, the auxiliary switching element 22 is turned on at time t3. For this reason, when the diode 23 connected in parallel to the auxiliary switching element 22 is in the off state, the auxiliary switching element 22 is in the on state, and there is a problem that a switching loss occurs because zero voltage switching is not performed. Further, in Patent Document 2, the function of the diode 4 in FIG. 9 is not clearly described.

  Also, instead of the battery 1 in FIG. 7 or FIG. 9, a commercial AC power supply and a rectifier circuit for rectifying an input voltage obtained from the commercial AC power supply to generate a pulsating voltage are provided, and the input current is substantially equal to the input voltage. Even when a power factor improvement circuit that controls so as to have a sine waveform of the same phase is configured, there is a problem that a similar switching loss occurs.

  The present invention has been made in view of the above circumstances, and has as its object to provide a switching power supply circuit with reduced switching loss and higher efficiency, and a control method used in the switching power supply circuit.

  In order to solve the above problem, the invention according to claim 1 stores electromagnetic energy supplied from a DC power supply unit in an inductance element when the switching element is in an on state, and stores the electromagnetic energy in the inductance element when the switching element is in an off state. A switching power supply circuit that boosts the output voltage of the DC power supply unit by superimposing the back electromotive voltage generated in the inductance element on the output voltage of the DC power supply unit and applying the superimposed voltage to the smoothing unit via rectifying means. A rectifying element interposed at both ends of the switching element in such a manner that a direction opposite to a direction of a current flowing through the switching element is a forward direction, a capacitance element interposed at both ends of the switching element, Before the switching element transitions from the off state to the on state, a forward current flows through the rectifier to turn the rectifier on. Discharging the capacitance element, charging the capacitance element when the switching element transitions from the on state to the off state, turning off the rectifying element, and turning on the switching element from the off state. And a control circuit for limiting a recovery current flowing into the switching element from the smoothing unit via the rectifying unit when the state transitions.

  According to a second aspect of the present invention, in the switching power supply circuit according to the first aspect, the control circuit causes a current flowing through the switching element to flow through a primary winding, and converts the electromagnetic energy stored in the primary winding into a secondary winding. Between the transformer that transfers current to the secondary winding and transfers electromagnetic energy stored in the secondary winding to the primary winding, and the secondary winding of the transformer. And a storage means for storing the electromagnetic energy supplied from the secondary winding, and an auxiliary switching element for flowing a current from the storage means to the secondary winding of the transformer when turned on. An auxiliary rectifying element interposed at both ends of the auxiliary switching element in such a manner that a direction opposite to a direction of a current flowing through the auxiliary switching element becomes a forward direction, and an auxiliary rectifying element inserted into the auxiliary switching element. And the capacitance element, the switching element and the auxiliary switching element and alternately turned on / off control, and is characterized in that it is composed of a control unit for setting a dead time period when both turned off.

  The invention according to claim 3 relates to the switching power supply circuit according to claim 1 or 2, wherein the switching element is configured by a MOS transistor, the rectifying element is configured by a parasitic diode of the MOS transistor, and The capacitive element is characterized by being constituted by the parasitic capacitance of the MOS transistor.

  According to a fourth aspect of the present invention, in the switching power supply circuit according to the second aspect, the auxiliary switching element includes a MOS transistor, the auxiliary rectifying element includes a parasitic diode of the MOS transistor, The capacitance element is characterized by being constituted by the parasitic capacitance of the MOS transistor.

  The invention according to claim 5 is directed to the switching power supply circuit according to claim 1, wherein the DC power supply unit is configured by a rectification circuit that rectifies an input voltage obtained from a commercial AC power supply to generate a pulsation voltage, and Current detection means for detecting an input current obtained from the commercial AC power supply is provided, and the control unit converts the input current to a sine waveform having substantially the same phase as the input voltage based on the pulsating voltage, the output voltage, and the input current. And a power factor improvement control means for controlling the ON time of the switching element and the auxiliary switching element such that

  The invention according to claim 6 relates to a control method, wherein the electromagnetic energy supplied from the DC power supply unit is stored in the inductance element when the switching element is on, and the inductance is stored when the switching element is off. A switching power supply circuit that boosts the output voltage of the DC power supply by superimposing a back electromotive voltage generated on the element on the output voltage of the DC power supply and applying the output voltage to the smoothing means via a rectifier; A rectifying element interposed at both ends of the switching element and a capacitance element interposed at both ends of the switching element are provided in such a manner that the direction opposite to the direction of the current flowing through the element is the forward direction. Before the switching element transitions from the off state to the on state, a forward current flows through the rectifier to turn the rectifier on. And discharging the capacitance element, charging the capacitance element when the switching element transitions from the on state to the off state, turning off the rectifying element, and turning off the switching element. The recovery current flowing from the smoothing means to the switching element via the rectifying means when the state changes from ON to ON state is limited.

  According to a seventh aspect of the present invention, in the control method according to the sixth aspect, a current flowing through the switching element is caused to flow through a primary winding, and electromagnetic energy stored in the primary winding is transferred to a secondary winding. A current flows through the secondary winding, a resonance current flows between a transformer that transfers the electromagnetic energy stored in the secondary winding to the primary winding, and a secondary winding of the transformer, A storage means for storing electromagnetic energy supplied from the secondary winding, an auxiliary switching element for flowing a current from the storage means to the secondary winding of the transformer when turned on, and a flow for the auxiliary switching element An auxiliary rectifying element interposed at both ends of the auxiliary switching element in such a manner that a direction opposite to the direction of the current becomes a forward direction; an auxiliary capacitance element interposed in the auxiliary switching element; And a control unit for alternately turning on / off the element and the auxiliary switching element and setting a dead time period in which the element and the auxiliary switching element are simultaneously turned off, before the auxiliary switching element transitions from the off state to the on state. The auxiliary rectifying element is turned on, the auxiliary capacitance element is discharged, and the auxiliary switching element is charged when the auxiliary switching element transitions from the on state to the off state, and the auxiliary rectifying element is charged. Is turned off.

  According to the configuration of the present invention, when the switching element transitions from the on state to the off state, the interposed capacitance element is charged, so that the rise of the voltage is lower than the fall of the current flowing through the switching element. Becomes moderate, so that switching loss can be reduced. Further, before the switching element transitions from the off state to the on state, the interposed rectifying element is turned on, so that zero voltage switching is performed, and the switching loss can be reduced. Similarly, when the auxiliary switching element transitions from the on state to the off state, the inserted auxiliary capacitance element is charged, so that the voltage rises more slowly than the current flowing through the auxiliary switching element. Therefore, the switching loss can be reduced. Further, before the auxiliary switching element transitions from the off state to the on state, the inserted auxiliary rectifying element is turned on, so that zero voltage switching is performed, and the switching loss can be reduced. Further, when the switching element transitions from the off state to the on state, the recovery current flowing from the smoothing means to the switching element via the rectifying means via the rectifying means is limited by the control circuit, so that the switching loss can be reduced. Further, since the on-time of the switching element and the auxiliary switching element is controlled by the power factor improvement control means, and the input current has a sine waveform having substantially the same phase as the input voltage, the power factor can be improved.

  A rectifying element is interposed at both ends of the switching element in such a manner that a direction opposite to a direction of a current flowing to the switching element such as a MOS transistor is a forward direction, and a capacitance element is interposed at both ends of the switching element. Before the switching element transitions from the off state to the on state, a forward current flows through the rectifying element to turn on the rectifying element and discharge the capacitance element, and the switching element is turned off from the on state. When the state transitions, the capacitance element is charged and the rectification element is turned off, and when the switching element transitions from the off state to the on state, the switching element is switched from the smoothing unit to the rectification unit through the rectification unit. A switching power supply circuit configured to limit a recovery current flowing into the switching power supply.

FIG. 1 is a circuit diagram showing an electrical configuration of a switching power supply circuit according to a first embodiment of the present invention.
As shown in the figure, the switching power supply circuit of this example includes a battery 31, a choke coil 32, a switching element 33 composed of an nMOS, a diode 34, a capacitor 35, a rectifying diode 36, a smoothing capacitor 37, a transformer 38, an auxiliary switching element 39 formed of an nMOS, an auxiliary diode 40, an auxiliary capacitor 41, a storage capacitor 42, and a control unit 43. They are connected in parallel. The diode 34 is formed of a parasitic diode of the switching element 33, and is connected in parallel to both ends of the switching element 33 such that the direction opposite to the direction of the current flowing through the switching element 33 is the forward direction. The capacitor 35 is constituted by the parasitic capacitance of the switching element 33, and is connected in parallel to both ends of the switching element 33.

  The transformer 38 includes a primary winding n1 connected in series to the switching element 33, a current flowing through the switching element 33 flowing through the same primary winding n1, and a secondary winding n2 storing the electromagnetic energy stored in the same primary winding n1. While the current is flowing through the secondary winding n2, the electromagnetic energy stored in the secondary winding n2 is transferred to the same secondary winding n1. The auxiliary switching element 39 allows current to flow from the storage capacitor 42 to the secondary winding n2 of the transformer 38 when turned on. The auxiliary diode 40 is formed of a parasitic diode of the auxiliary switching element 39, and is connected in parallel to both ends of the auxiliary switching element 39 such that the direction opposite to the direction of the current flowing through the auxiliary switching element 39 is the forward direction. . The auxiliary capacitor 41 is configured by the parasitic capacitance of the auxiliary switching element 39 and is connected to the auxiliary switching element 39 in parallel.

  The storage capacitor 42 allows a resonance current to flow between itself and the secondary winding n2 of the transformer 38, and stores the electromagnetic energy supplied from the secondary winding n2. The control unit 43 monitors the output voltage N and controls the ON time of the switching element 33 and the auxiliary switching element 39 so that the output voltage N becomes substantially constant. In particular, in this embodiment, the control unit 43 alternately controls on / off of the switching element 33 and the auxiliary switching element 39, and sets a dead time at which the switching element 33 and the auxiliary switching element 39 are simultaneously turned off. The transformer 38, the auxiliary switching element 39, the auxiliary diode 40, the auxiliary capacitor 41, the storage capacitor 42, and the control unit 43 constitute a control circuit.

  This control circuit turns on the diode 34 when the switching element 33 changes from the off state to the on state by flowing a forward current through the diode 34, discharges the capacitor 35, and turns on the switching element 33. When the capacitor 35 is charged when the state transitions to the off state, the diode 34 is turned off after the switching element 33 transitions to the off state, and when the switching element 33 transitions from the off state to the on state. The recovery current flowing from the smoothing capacitor 37 to the switching element 33 via the rectifying diode 36 is limited by the inductance of the primary winding of the transformer 38.

FIG. 2 is a time chart for explaining the operation of the switching power supply circuit of FIG. 1, in which the vertical axis represents voltage or current and the horizontal axis represents time.
With reference to this figure, a control method used for the switching power supply circuit of this example will be described.
In this switching power supply circuit, the electromagnetic energy supplied from the battery 31 is stored in the choke coil 32 when the switching element 33 is on, and the reverse energy generated in the choke coil 32 when the switching element 33 is off. The electromotive voltage is superimposed on the output voltage E of the battery 31, applied to the smoothing capacitor 37 via the rectifying diode 36, and the output voltage E is boosted to generate the output voltage N.

  In this case, as shown in FIG. 2, the switching elements 33 and the auxiliary switching elements 39 are alternately turned on / off, and dead times Td1 and Td2 at which both are simultaneously turned off are set. Then, at time t1, when the switching element 33 is in the off state, the auxiliary switching element 39 changes from the on state to the off state. Thereafter, at the dead time Td1, the electric charge of the capacitor 35 is instantaneously discharged by the electromagnetic energy of the inductance of the primary winding n1 of the transformer 38, and further, the exciting current flows through the diode 34 to the transformer 38, the diode 36, and the smoothing capacitor 37. Flows, and the diode 34 is turned on. At time t2, when the switching element 33 is turned on, the diode 34 connected in parallel is already in the on state, so that zero voltage switching is performed, and the switching loss is reduced.

  On the other hand, when the auxiliary switching element 39 shifts to the off state at the time t1, the auxiliary capacitor 41 connected in parallel is charged at the dead time Td1. For this reason, since the rise of the voltage becomes slower than the fall of the current flowing through the auxiliary switching element 39, the product of the voltage and the current becomes small, and the switching loss in the auxiliary switching element 39 is reduced. At this time, the auxiliary diode 40 is turned off.

  At time t3, the auxiliary diode 40 is turned on and the auxiliary capacitor 41 is discharged by the exciting current of the transformer 38. At time t4, when the auxiliary switching element 39 is in the off state, the switching element 33 transitions from the on state to the off state. Thereafter, at the dead time Td2, the capacitor 35 connected in parallel is charged. Since the rise of the voltage becomes slower than the fall of the current flowing through the switching element 33, the product of the voltage and the current is reduced, and the switching loss in the switching element 33 is reduced. At this time, the diode 34 is turned off. At time t5, when the auxiliary switching element 39 transitions from the off state to the on state, the exciting current of the transformer 38 flows through the auxiliary diode 40 connected in parallel, and the auxiliary diode 40 is in the on state. , The auxiliary switching element 39 performs zero voltage switching, and the switching loss in the auxiliary switching element 39 is reduced.

  As described above, in the first embodiment, when the switching element 33 transitions from the on state to the off state, the capacitor 35 connected in parallel is charged. Since the rise of the voltage becomes gentler, the switching loss is reduced. Further, before the switching element 33 transitions from the off state to the on state, the diode 34 connected in parallel is turned on, so that zero voltage switching is performed, and the switching loss is reduced. Similarly, when the auxiliary switching element 39 transitions from the on state to the off state, the auxiliary capacitor 41 connected in parallel is charged, so that the rise of the voltage is slower than the fall of the current flowing through the auxiliary switching element 39. , The switching loss is reduced. Further, since the auxiliary diode 40 connected in parallel is turned on before the auxiliary switching element 39 transitions from the off state to the on state, zero voltage switching is performed, and switching loss is reduced. Further, since the recovery current flowing into the switching element 33 from the smoothing capacitor 37 via the rectifying diode 36 when the switching element 33 transitions from the off state to the on state is limited by the inductance of the primary winding of the transformer 38, Switching loss is reduced.

FIG. 3 is a circuit diagram showing an electrical configuration of a switching power supply circuit according to a second embodiment of the present invention. In FIG. 3, components common to those in FIG. Is attached.
In the switching power supply circuit of this example, a commercial AC power supply 51, a rectifier circuit 52, and a power factor improvement control unit 43A are provided instead of the battery 31 and the control unit 43 in FIG. Further, a current detection resistor 44 is connected in parallel between the source electrode of the switching element 33 and the rectifier circuit 52. Rectifier circuit 52 rectifies input voltage W obtained from commercial AC power supply 51 to generate pulsating voltage M. The current detection resistor 44 indirectly detects the input current obtained from the commercial AC power supply 51 by detecting the pulsating current i output from the rectifier circuit 52. The power factor improvement control unit 43A is configured by, for example, an integrated circuit and performs switching so that the input current has a sine waveform having substantially the same phase as the input voltage W based on the pulsating voltage M, the output voltage N, and the pulsating current i. The on-time of the element 33 and the auxiliary switching element 39 is controlled. Other configurations are the same as those in FIG.

  In this switching power supply circuit, after an input voltage W of, for example, AC100V to AC240V is applied from the commercial AC power supply 51, the same operation as in the first embodiment is performed. Then, an output voltage N of about 360 V DC is output. Further, the ON times of the switching element 33 and the auxiliary switching element 39 are controlled by the power factor improvement control unit 43A, and the input current obtained from the commercial AC power supply 51 has a sine waveform having substantially the same phase as the input voltage W, and the power factor is reduced. Be improved.

  As described above, in the second embodiment, the ON times of the switching element 33 and the auxiliary switching element 39 are controlled by the power factor improvement control unit 43A, and the input current becomes a sine waveform having substantially the same phase as the input voltage W. Therefore, in addition to the advantages of the first embodiment, the power factor is improved.

FIG. 4 is a circuit diagram showing an electrical configuration of a switching power supply circuit according to a third embodiment of the present invention.
In the switching power supply circuit of this example, as shown in FIG. 4, one end of the secondary winding n2 of the transformer 38 in FIG. 1 is connected to the anode side of the rectifier diode 36, and the auxiliary switching element 39 and the auxiliary diode 40, the auxiliary capacitor 41, and the storage capacitor 42 are not connected to one end of the smoothing capacitor 37. Other configurations are the same as those in FIG.

  In this switching power supply circuit, the same operation as that of the first embodiment is performed, and there are similar advantages.

FIG. 5 is a circuit diagram showing an electrical configuration of a switching power supply circuit according to a fourth embodiment of the present invention.
In the switching power supply circuit of this example, as shown in FIG. 5, one end of the secondary winding n2 of the transformer 38 in FIG. 3 is connected to the anode side of the rectifier diode 36, and the auxiliary switching element 39 and the auxiliary diode 40, the auxiliary capacitor 41, and the storage capacitor 42 are not connected to one end of the smoothing capacitor 37. Other configurations are the same as those in FIG.

  In this switching power supply circuit, the same operation as in the second embodiment is performed, and there are similar advantages.

As described above, the embodiment of the present invention has been described in detail with reference to the drawings. However, the specific configuration is not limited to the embodiment, and even if there is a design change without departing from the gist of the present invention, the present invention is not limited thereto. Included in the invention.
For example, in each embodiment, the switching element 33 and the auxiliary switching element 39 are configured by nMOS, but may be, for example, a bipolar transistor or an IGBT (Insulated Gate Bipolar Transistor). In this case, a diode and a capacitor are connected between the emitter and the collector of each transistor. Further, in addition to the current detection resistor 44 for detecting the pulsating current i, a current sensor for indirectly detecting the pulsating current i by detecting a magnetic field generated around a wire through which the pulsating current i flows may be used. good.

  INDUSTRIAL APPLICABILITY The present invention is applicable to all switching power supply circuits for boosting a low voltage, and is applicable to all electronic devices using a boosting type switching power supply circuit.

FIG. 1 is a circuit diagram showing an electrical configuration of a switching power supply circuit according to a first embodiment of the present invention. 2 is a time chart for explaining the operation of the switching power supply circuit of FIG. FIG. 4 is a circuit diagram showing an electrical configuration of a switching power supply circuit according to a second embodiment of the present invention. FIG. 9 is a circuit diagram showing an electrical configuration of a switching power supply circuit according to a third embodiment of the present invention. FIG. 11 is a circuit diagram showing an electrical configuration of a switching power supply circuit according to a fourth embodiment of the present invention. FIG. 10 is a circuit diagram illustrating an electrical configuration of a conventional switching power supply circuit. FIG. 11 is a circuit diagram showing an electrical configuration of a boost chopper type switching power supply described in Patent Document 1. It is a time chart of FIG. FIG. 11 is a circuit diagram illustrating an electrical configuration of a switching power supply device described in Patent Document 2. It is a time chart of FIG.

Explanation of reference numerals

31 Battery (DC power supply)
32 Choke coil (inductance element)
33 switching element 34 diode (rectifying element)
35 Capacitor (capacitance element)
36 Rectifier diode (rectifier)
37 Smoothing capacitors (smoothing means)
38 Transformer (part of control circuit)
39 Auxiliary switching element (part of control circuit)
40 Auxiliary diode (part of control circuit)
41 Auxiliary capacitor (part of control circuit)
42 Storage capacitor (part of control circuit)
43 control unit (part of control circuit)
43A power factor improvement control unit (power factor improvement control means)
44 Current detection resistor (current detection means)
51 Commercial AC power supply 52 Rectifier circuit

Claims (7)

When the switching element is on, the electromagnetic energy supplied from the DC power supply is stored in the inductance element, and when the switching element is turned off, the back electromotive force generated in the inductance element is output from the DC power supply. A switching power supply circuit that boosts an output voltage of the DC power supply unit by applying the voltage to a smoothing unit via a rectifying unit in a manner superimposed on a voltage,
Rectifying elements interposed at both ends of the switching element in such a manner that the direction opposite to the direction of the current flowing through the switching element is the forward direction,
A capacitance element interposed at both ends of the switching element,
Before the switching element transitions from the off state to the on state, a forward current flows through the rectifying element to turn on the rectifying element and discharge the capacitance element, and the switching element is turned off from the on state. When the state transitions, the capacitance element is charged and the rectifying element is turned off, and when the switching element transitions from the off state to the on state, the switching operation is performed from the smoothing unit through the rectifying unit. And a control circuit for limiting a recovery current flowing into the element. The control circuit includes:
The current flowing through the switching element flows through the primary winding, and the electromagnetic energy stored in the primary winding is transferred to the secondary winding, while the current flows through the secondary winding and stored in the secondary winding. A transformer for transferring the received electromagnetic energy to the primary winding;
A storage means for allowing a resonance current to flow between the secondary winding of the transformer and the electromagnetic energy supplied from the secondary winding;
An auxiliary switching element that allows current to flow from the storage means to the secondary winding of the transformer when turned on;
An auxiliary rectifying element interposed at both ends of the auxiliary switching element in such a manner that a direction opposite to a direction of a current flowing through the auxiliary switching element is a forward direction,
An auxiliary capacitance element inserted in the auxiliary switching element,
2. The switching power supply according to claim 1, further comprising: a control unit that alternately turns on / off the switching element and the auxiliary switching element and sets a dead time period in which the switching element is turned off simultaneously. circuit. The switching element is configured by a MOS transistor,
The rectifying element is constituted by a parasitic diode of the MOS transistor,
3. The switching power supply circuit according to claim 1, wherein the capacitance element is configured by a parasitic capacitance of the MOS transistor. The auxiliary switching element includes a MOS transistor,
The auxiliary rectifying element is constituted by a parasitic diode of the MOS transistor.
3. The switching power supply circuit according to claim 2, wherein the auxiliary capacitance element is configured by a parasitic capacitance of the MOS transistor. The switching power supply circuit according to claim 1,
The DC power supply,
It is composed of a rectifier circuit that rectifies the input voltage obtained from the commercial AC power supply and generates a pulsating voltage,
And current detection means for detecting an input current obtained from the commercial AC power supply is provided,
The control unit includes:
Power factor improvement control means for controlling the on time of the switching element and the auxiliary switching element such that the input current has a sine waveform having substantially the same phase as the input voltage based on the pulsating voltage, the output voltage, and the input current. A switching power supply circuit characterized in that: When the switching element is on, the electromagnetic energy supplied from the DC power supply is stored in the inductance element, and when the switching element is turned off, the back electromotive force generated in the inductance element is output from the DC power supply. It is used in a switching power supply circuit that boosts the output voltage of the DC power supply unit by applying the voltage to the smoothing unit via the rectifying unit by superimposing on the voltage,
A rectifying element interposed at both ends of the switching element and a capacitance element interposed at both ends of the switching element are provided in such a manner that a direction opposite to a direction of a current flowing through the switching element is a forward direction. In addition,
Before the switching element transitions from the off state to the on state, a forward current flows through the rectifying element to turn on the rectifying element and discharge the capacitance element, and the switching element is turned off from the on state. When the state transitions, the capacitance element is charged and the rectifying element is turned off, and when the switching element transitions from the off state to the on state, the switching operation is performed from the smoothing unit through the rectifying unit. A control method characterized by limiting a recovery current flowing into an element. The control method according to claim 6,
The current flowing through the switching element is passed through the primary winding, and the electromagnetic energy stored in the primary winding is transferred to the secondary winding, while the current is passed through the secondary winding and stored in the secondary winding. A transformer for transferring the received electromagnetic energy to the primary winding;
Storage means for causing a resonance current to flow between the secondary winding of the transformer and electromagnetic energy supplied from the secondary winding;
An auxiliary switching element that allows current to flow from the storage means to the secondary winding of the transformer when turned on;
An auxiliary rectifying element interposed at both ends of the auxiliary switching element in such a manner that a direction opposite to a direction of a current flowing through the auxiliary switching element is a forward direction,
An auxiliary capacitance element inserted in the auxiliary switching element,
A control unit that alternately turns on / off the switching element and the auxiliary switching element and sets a dead time period in which the switching element and the auxiliary switching element are simultaneously turned off;
Before the auxiliary switching element transitions from the off state to the on state, the auxiliary switching element is turned on and the auxiliary capacitance element is discharged, and the auxiliary switching element transitions from the on state to the off state. A control method comprising: charging the auxiliary capacitance element and turning off the auxiliary rectifier element.

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