JP3761558B2 - Switching power supply circuit and control method used for the switching power supply circuit - Google Patents

Description

  The present invention relates to a switching power supply circuit and a control method used in the switching power supply circuit. For example, the switching power supply suitable for use in an electronic device that operates with 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 the built-in power supply unit is also required to be miniaturized. A switching power supply circuit is often used as the power supply unit. When the switching power supply circuit is miniaturized, generally, the switching frequency is increased to cope with it. When the switching frequency is increased, the switching loss in the switching element is increased and the amount of heat generation is increased. Therefore, it is necessary to increase the size of the radiator and the like, which becomes an obstacle to downsizing. For this reason, reduction of 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. Of 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 A smoothing capacitor is provided. The electromagnetic energy supplied from the DC power supply when the switching element is on is stored in the choke coil, and the back electromotive voltage generated in the choke coil when the switching element is off is the DC power supply. Is applied to the smoothing capacitor via a rectifying diode, and the output voltage of the DC power supply is boosted.

  Conventionally, this type of switching power supply circuit has 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. The capacitor 5 is composed of a rectifying diode 6, a smoothing capacitor 7, and a control unit 8, and a load Z is connected in parallel to the smoothing capacitor 7.

  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 in the on state, and the reverse generated in the choke coil 2 when the switching element 3 is in the off state. 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 maintained substantially at the 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, 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. The charged charge of the capacitor 5 is discharged through the switching element 3 when turned on. At this time, the electromagnetic energy accumulated in the capacitor 5 is consumed by the switching element 3 and a power loss occurs. Immediately before the switching element 3 is turned on, a load current flows through the rectifying diode 6 in the forward direction. When the switching element is turned on in this state, a reverse voltage is applied to the rectifying diode 6 from the smoothing capacitor 7. The For this reason, a recovery current flows through the rectifying diode 6 and there is nothing to limit the current, so that there is a problem that a great loss and noise occur. Further, when the rectifying diode 6 is composed of a fast recovery diode, the recovery current is reduced, but it is not completely eliminated.

In addition to the above-described switching power supply circuit, conventionally, this type of technology has been described in, for example, the following documents.
As shown in FIG. 7, the step-up chopper type switching power supply described in Patent Document 1 includes a battery 1, a choke coil 2, a main switching element 3, a diode 4, a capacitor 5, a rectifying diode 6, The smoothing capacitor 7, the control unit 8 </ b> A, the choke coil 9, the diodes 10 and 11, the auxiliary switching element 12, and the diode 13 are configured, 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. Turns off. First, when the auxiliary switching element 12 is turned on, the current flowing through the auxiliary switching element 12 rises gradually by the choke coil 9, so that the auxiliary switching element 12 changes from the off state to the on state. Switching loss 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 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 on, the main switching element 3 performs zero voltage switching, and 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 rapidly rises due to the electromagnetic energy accumulated in the choke coil 9, so that switching is performed by the auxiliary switching element 12. Loss occurs. Next, the electromagnetic energy accumulated in the choke coil 9 is released 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 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 voltage rise at both ends of the auxiliary switching element 12 can be moderated. However, when the auxiliary switching element 12 is turned on, the capacitor Has a problem in that switching loss occurs.

  Further, 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, The smoothing capacitor 7, the transformer 21, the auxiliary switching element 22, a diode 23, a capacitor 24, and a capacitor 25 are included.

  In this switching power supply device, as shown in FIG. 10, when the main switching element 3 is turned on at time t0, the voltage E of the battery 1 is applied to the series circuit of the choke coil 2 and the primary winding n1 of the transformer 21. Is done. 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. Accordingly, the transformer 21 is equivalent to its exciting inductance, and the same operation as the switching power supply circuit of FIG. 7 is performed. When the main switching element 3 is turned off at time t1, 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 the 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, the auxiliary switching element 22 is in an off state, so that no current flows through the secondary winding n2 of the transformer 21. Therefore, the transformer 21 becomes equivalent to the excitation 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 increased. Reduced. At this time, the current ID1 of the diode 6 approaches zero as shown in FIG. 10 (f), so that the recovery noise generated when the main switching element 3 is turned on next time is reduced.
Japanese Patent Laid-Open No. 06-311738 (first page, FIG. 1 and FIG. 2) Japanese Unexamined Patent Publication No. 07-203673 (first page, 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 an off state, the auxiliary switching element 22 is in an on state, and zero voltage switching is not performed, which causes a switching loss. Moreover, in the said patent document 2, the effect | action of the diode 4 in FIG. 9 is not described clearly.

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

  The present invention has been made in view of the above-described circumstances, and an object thereof is to provide a switching power supply circuit with higher efficiency and a control method used in the switching power supply circuit that reduces switching loss.

In order to solve the above-described problem, the invention according to claim 1 stores the electromagnetic energy supplied from the DC power supply unit in the inductance element when the switching element is in the on state, and when the switching element is in the off state. The present invention relates to a switching power supply circuit that boosts the output voltage of the DC power supply unit by applying a counter electromotive voltage generated in the inductance element to the smoothing unit via a rectifying unit superimposed on the output voltage of the DC power supply unit, A rectifying element inserted at both ends of the switching element in a manner in which the direction opposite to the direction of the current flowing through the switching element is a forward direction, a capacitance element inserted at both ends of the switching element, and the switching Before the element transitions from the off state to the on state, a forward current is passed through the rectifying element to turn the rectifying element on. Both discharge the capacitance element, charge the capacitance element when the switching element transitions from the on state to the off state, turn the rectifier element off, and turn the switching element on from the off state. And a control circuit that limits a recovery current that flows from the smoothing means to the switching element via the rectifying means when the state transitions, and the control circuit performs a primary winding of the current flowing through the switching element. The electromagnetic energy stored in the primary winding is transferred to the secondary winding, while the current is passed through the secondary winding, and the electromagnetic energy stored in the secondary winding is transferred to the primary winding. Storage means for storing electromagnetic energy supplied from the secondary winding through which a resonant current flows between the transformer transferred to the secondary winding and the secondary winding of the transformer; An auxiliary switching element that causes a current to flow from the storage means to the secondary winding of the transformer when in a state, and a direction opposite to the direction of the current that flows to the auxiliary switching element is a forward direction. Auxiliary rectifying element inserted at both ends of the auxiliary switching element, an auxiliary capacitance element inserted in the auxiliary switching element, the switching element and the auxiliary switching element are alternately turned on / off, and simultaneously turned off. The dead time period when the switching element transitions from the on-state to the off-state, compared to the fall of the current flowing through the switching element. The rise of the voltage is set to be gentle, while the auxiliary switching element is turned off from the on state. In the dead time period when transitioning to a state, the rising of the voltage is set to be slower than the falling of the current flowing through the auxiliary switching element .

According to a second aspect of the invention relates to a switching power supply circuit according to claim 1, wherein the switching element is a MOS transistor, the rectifier element is constituted by a parasitic diode of the MOS transistor, the capacitive element Is constituted by the parasitic capacitance of the MOS transistor.

Further, an invention according to claim 3, relates to a switching power supply circuit according to claim 1, wherein the auxiliary switching element is composed of a MOS transistor, the auxiliary rectifier element is composed of a parasitic diode of the MOS transistor, wherein The auxiliary capacitance element is characterized by being composed of a parasitic capacitance of the MOS transistor.

  According to a fourth aspect of the present invention, in the switching power supply circuit according to the first aspect, the DC power supply unit is configured by a rectifier circuit that rectifies an input voltage obtained from a commercial AC power supply to generate a pulsating voltage, and Current detecting means for detecting an input current obtained from the commercial AC power source is provided, and the control unit converts the input current to a sign having substantially the same phase as the input voltage based on the pulsating voltage, the output voltage, and the input current. It is characterized by comprising power factor correction control means for controlling the ON time of the switching element and the auxiliary switching element so as to have a waveform.

According to a fifth aspect of the present invention, the electromagnetic energy supplied from the DC power supply unit is stored in the inductance element when the switching element is on, and is generated in the inductance element when the switching element is off. The counter electromotive voltage is superimposed on the output voltage of the DC power supply unit and applied to the smoothing unit via the rectifying unit, thereby being used in a switching power supply circuit that boosts the output voltage of the DC power supply unit and flows to the switching element. A rectifying element inserted at both ends of the switching element and a capacitance element inserted at both ends of the switching element in a manner in which the direction opposite to the current direction is the forward direction, and the switching When a forward current is passed through the rectifier element before the element transitions from the off state to the on state, the rectifier element is turned on. When the switching element transitions from an on state to an off state, the capacitance element is charged, the rectifier element is turned off, and the switching element is turned on from the off state. The present invention relates to a control method characterized by limiting a recovery current flowing from the smoothing means to the switching element through the rectifying means when transitioning to a state, and passing a current flowing through the switching element through a primary winding, A transformer for transferring the electromagnetic energy stored in the primary winding to the secondary winding, while passing a current through the secondary winding and transferring the electromagnetic energy stored in the secondary winding to the primary winding; A resonance current flows between the secondary winding of the transformer and the storage means for storing electromagnetic energy supplied from the secondary winding; Auxiliary switching element for passing current from the product means to the secondary winding of the transformer, and inserted in both ends of the auxiliary switching element in such a manner that the direction opposite to the direction of the current flowing through the auxiliary switching element is the forward direction. The auxiliary rectifying element, the auxiliary capacitance element inserted in the auxiliary switching element, the switching element and the auxiliary switching element are alternately turned on / off, and a dead time period in which the off state is simultaneously set is set. A control unit configured to turn on the auxiliary rectifying element and discharge the auxiliary capacitance element before the auxiliary switching element transitions from the off state to the on state, and the auxiliary switching element is turned on. Charging the auxiliary capacitance element at the time of transition from the state to the off state and turning off the auxiliary rectifier element; and In the dead time period when the switching element transitions from the on state to the off state, the voltage rising is set to be gentler than the falling of the current flowing through the switching element, while the auxiliary switching element A control method characterized in that, during the dead time period when the transition from the on state to the off state, the rise of the voltage is set slower than the fall of the current flowing through the auxiliary switching element .

  According to the configuration of the present invention, when the switching element transitions from the on state to the off state, the inserted electrostatic capacitance element is charged, so that the voltage rise compared to the fall of the current flowing through the switching element. Since it becomes gentle, switching loss can be reduced. Further, since the inserted rectifier element is turned on before the switching element transitions from the off state to the on state, zero voltage switching is performed, and 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 fall of the current flowing through the auxiliary switching element. Therefore, switching loss can be reduced. In addition, since the inserted auxiliary rectifier element is turned on before the auxiliary switching element transitions from the off state to the on state, zero voltage switching is performed, and switching loss can be reduced. Further, since the recovery current that flows from the smoothing means to the switching element via the rectifying means when the switching element changes from the OFF state to the ON state is limited by the control circuit, switching loss can be reduced. Further, the ON time of the switching element and the auxiliary switching element is controlled by the power factor correction control means, and the input current becomes a sine waveform having substantially the same phase as the input voltage, so the power factor can be improved.

  A rectifying element is inserted at both ends of the switching element in a manner in which the direction opposite to the direction of the current flowing through the switching element such as a MOS transistor is a forward direction, and a capacitance element is inserted at both ends of the switching element, Before the switching element transitions from the off-state to the on-state, a forward current is supplied to 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. The capacitance element is charged at the time of transition to the state, the rectifier element is turned off, and the switching element is switched from the smoothing means through the rectifier means when the switching element transitions from the off state to the on state. Provided is a switching power supply circuit configured to limit a recovery current flowing into the 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.
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, and a smoothing capacitor, as shown in FIG. 37, a transformer 38, an auxiliary switching element 39 composed of an nMOS, an auxiliary diode 40, an auxiliary capacitor 41, a storage capacitor 42, and a control unit 43. A load Z is applied to the smoothing capacitor 37. Connected in parallel. The diode 34 is composed of a parasitic diode of the switching element 33, and is connected in parallel to both ends of the switching element 33 in such a manner that the direction opposite to the direction of the current flowing through the switching element 33 is the forward direction. The capacitor 35 is composed of a parasitic capacitance of the switching element 33 and is connected in parallel to both ends of the switching element 33.

  In the transformer 38, the primary winding n1 is connected in series to the switching element 33, the current flowing through the switching element 33 is passed through the primary winding n1, and the electromagnetic energy stored in the primary winding n1 is transferred to the secondary winding n2. On the other hand, a current is passed through the secondary winding n2, and the electromagnetic energy stored in the secondary winding n2 is transferred to the primary winding n1. When the auxiliary switching element 39 is turned on, a current flows from the storage capacitor 42 to the secondary winding n2 of the transformer 38. The auxiliary diode 40 is composed of a parasitic diode of the auxiliary switching element 39, and is connected in parallel to both ends of the auxiliary switching element 39 in such a manner 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 composed of a parasitic capacitance of the auxiliary switching element 39 and is connected in parallel to the auxiliary switching element 39.

  The storage capacitor 42 stores a resonance current between the secondary winding n2 of the transformer 38 and stores 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 performs on / off control of the switching element 33 and the auxiliary switching element 39 and sets a dead time during which the switching element 33 is turned off at the same time. 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 the diode 34 on by discharging a forward current through the diode 34 when the switching element 33 transitions from the off state to the on state, and discharges the capacitor 35. When the capacitor 35 is charged when transitioning from the state 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 that flows 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, with the vertical axis representing voltage or current and the horizontal axis representing time.
With reference to this figure, the control method used for the switching power supply circuit of this example is demonstrated.
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 in the on state, and the reverse generated in the choke coil 32 when the switching element 33 is in the off state. The electromotive voltage is superimposed on the output voltage E of the battery 31 and 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 are set in which both are turned off simultaneously. 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 is passed 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 has already been turned on, so that zero voltage switching is performed and the switching loss is reduced.

  On the other hand, when the auxiliary switching element 39 transitions to the OFF state at time t1, the auxiliary capacitor 41 connected in parallel is charged at the dead time Td1. For this reason, since the rising of the voltage becomes gentler than the falling 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 t 3, 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, the capacitor 35 connected in parallel is charged at the dead time Td2, and therefore the switching element 33 is charged. Since the voltage rises more slowly than the current falling, the product of the voltage and 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 becomes 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, so that the current flowing through the switching element 33 falls. Since the voltage rises more slowly than that, switching loss is reduced. Further, since the diode 34 connected in parallel is turned on before the switching element 33 transitions from the off state to the on state, zero voltage switching is performed, and 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 voltage rises more slowly than the fall of the current flowing through the auxiliary switching element 39. Therefore, switching loss is reduced. In addition, 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 that flows from the smoothing capacitor 37 to the switching element 33 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. Elements common to those in FIG. 1 showing the first embodiment are denoted by common reference numerals. It 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 correction control unit 43A are provided in place of the battery 31 and the control unit 43 in FIG. A current detection resistor 44 is connected in parallel between the source electrode of the switching element 33 and the rectifier circuit 52. The rectifier circuit 52 rectifies the input voltage W obtained from the commercial AC power supply 51 to generate a 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 correction 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. The other configuration is the same as that shown in FIG.

  In this switching power supply circuit, after the input voltage W of, for example, AC 100V to AC240V is applied from the commercial AC power supply 51, the same operation as that of the first embodiment is performed. Then, an output voltage N of about 360 V DC is output. Further, the ON time of the switching element 33 and the auxiliary switching element 39 is controlled by the power factor correction control unit 43A, and the input current obtained from the commercial AC power source 51 becomes a sine waveform having substantially the same phase as the input voltage W, and the power factor is Improved.

  As described above, in the second embodiment, the ON time of the switching element 33 and the auxiliary switching element 39 is controlled by the power factor correction control unit 43A, and the input current has 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, auxiliary diode 40, the auxiliary capacitor 41, and the storage capacitor 42 are not connected to one end of the smoothing capacitor 37. The other configuration is the same as that shown in FIG.

  In this switching power supply circuit, the same operation as in 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, auxiliary diode 40, the auxiliary capacitor 41, and the storage capacitor 42 are not connected to one end of the smoothing capacitor 37. The other configuration is the same as in FIG.

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

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, Included in the invention.
For example, in each embodiment, the switching element 33 and the auxiliary switching element 39 are composed of 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 collector of each transistor. In addition to the current detection resistor 44 that detects the pulsating current i, a current sensor that indirectly detects the pulsating current i by detecting a magnetic field generated around the wire through which the pulsating current i flows may be used. good.

  The present invention can be applied to all switching power supply circuits for boosting a low voltage, and can be used for all electronic devices using a boosting switching power supply circuit.

1 is a circuit diagram showing an electrical configuration of a switching power supply circuit according to a first embodiment of the present invention. FIG. 2 is a time chart for explaining the operation of the switching power supply circuit of FIG. 1. It is a circuit diagram which shows the electrical constitution of the switching power supply circuit which is 2nd Example of this invention. It is a circuit diagram which shows the electrical constitution of the switching power supply circuit which is the 3rd Example of this invention. It is a circuit diagram which shows the electrical constitution of the switching power supply circuit which is the 4th Example of this invention. It is a circuit diagram which shows the electrical constitution of the conventional switching power supply circuit. 6 is a circuit diagram showing an electrical configuration of a step-up chopper type switching power supply described in Patent Document 1. FIG. It is a time chart of FIG. It is a circuit diagram which shows the electric constitution of the switching power supply device described in patent document 2. FIG. It is a time chart of FIG.

Explanation of symbols

31 Battery (DC power supply)
32 Choke coil (inductance element)
33 Switching element 34 Diode (rectifier element)
35 Capacitor (Capacitance element)
36 Rectifier diode (rectifier)
37 Smoothing capacitor (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 (5)

The electromagnetic energy supplied from the DC power supply when the switching element is on is stored in the inductance element, and the counter electromotive voltage generated in the inductance element when the switching element is turned off is output from the DC power supply. A switching power supply circuit that boosts the output voltage of the DC power supply unit by applying it to the smoothing means through the rectifying means in a superimposed manner with a voltage,
A rectifying element inserted at both ends of the switching element in a manner in which the direction opposite to the direction of the current flowing through the switching element is a forward direction;
A capacitive element inserted at both ends of the switching element;
Before the switching element transitions from the off state to the on state, a forward current is passed through the rectifying element to turn on the rectifying element and discharge the capacitive element, so that the switching element is turned off from the on state. The capacitance element is charged at the time of transition to the state, the rectifier element is turned off, and the switching from the smoothing means through the rectifier means when the switching element transitions from the off state to the on state. And a control circuit that limits a recovery current flowing into the element ,
The control circuit includes:
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 generated electromagnetic energy to the primary winding;
A storage means for storing a resonance current between the secondary winding of the transformer and storing electromagnetic energy supplied from the secondary winding;
An auxiliary switching element that causes a current to flow from the storage means to the secondary winding of the transformer when turned on;
An auxiliary rectifying element inserted at both ends of the auxiliary switching element in a mode in which a direction opposite to the direction of the current flowing through the auxiliary switching element is a forward direction;
An auxiliary capacitance element interposed in the auxiliary switching element;
The switching element and the auxiliary switching element are alternately turned on / off, and at the same time, a controller configured to set a dead time period to be turned off, and
In the dead time period when the switching element transitions from the on-state to the off-state, the voltage rise is set to be gentle compared to the fall of the current flowing through the switching element,
In the dead time period when the auxiliary switching element transitions from the on state to the off state, the voltage rise is set to be gentler than the fall of the current flowing through the auxiliary switching element. Switching power supply circuit. The switching element is composed of a MOS transistor,
The rectifying element is composed of a parasitic diode of the MOS transistor,
The switching power supply circuit according to claim 1 , wherein the electrostatic capacitance element includes a parasitic capacitance of the MOS transistor. The auxiliary switching element is composed of a MOS transistor,
The auxiliary rectifying element is composed of a parasitic diode of the MOS transistor,
The auxiliary capacitive element, a switching power supply circuit according to claim 1, characterized in that it is constituted by parasitic capacitance of the MOS transistor. The switching power supply circuit according to claim 1,
The DC power supply unit is
Consists of a rectifier circuit that rectifies an input voltage obtained from a commercial AC power source to generate a pulsating voltage,
And current detection means for detecting an input current obtained from the commercial AC power supply is provided,
The controller is
Based on the pulsating voltage, the output voltage, and the input current, power factor improvement control means for controlling the on-time of the switching element and the auxiliary switching element so that the input current has a sine waveform having substantially the same phase as the input voltage. The switching power supply circuit characterized by the above-mentioned. The electromagnetic energy supplied from the DC power supply when the switching element is on is stored in the inductance element, and the counter electromotive voltage generated in the inductance element when the switching element is turned off is output from the DC power supply. Used in a switching power supply circuit that boosts the output voltage of the DC power supply unit by applying it to the smoothing means through the rectifying means in a superimposed manner on the voltage,
Provided is a rectifier element inserted at both ends of the switching element and a capacitance element inserted 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 a forward direction. And
Before the switching element transitions from the off state to the on state, a forward current is passed through the rectifying element to turn on the rectifying element and discharge the capacitive element, so that the switching element is turned off from the on state. The capacitance element is charged at the time of transition to the state, the rectifier element is turned off, and the switching from the smoothing means through the rectifier means when the switching element transitions from the off state to the on state. A control method characterized by limiting a recovery current flowing into the element ,
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 generated electromagnetic energy to the primary winding;
A storage means for storing electromagnetic energy supplied from the secondary winding through which a resonance current flows between the transformer and the secondary winding;
An auxiliary switching element that causes a current to flow from the storage means to the secondary winding of the transformer when turned on;
An auxiliary rectifying element inserted at both ends of the auxiliary switching element in a mode in which a direction opposite to the direction of the current flowing through the auxiliary switching element is a forward direction;
An auxiliary capacitance element interposed in the auxiliary switching element;
A controller for alternately turning on and off the switching element and the auxiliary switching element and setting a dead time period in which the switching element is turned off at the same time;
When the auxiliary rectifying element is turned on and the auxiliary capacitance element is discharged before the auxiliary switching element transits from the off state to the on state, and the auxiliary switching element transits from the on state to the off state Charging the auxiliary capacitance element and turning off the auxiliary rectifying element; and
In the dead time period when the switching element transitions from the on-state to the off-state, the voltage rise is set to be gentle compared to the fall of the current flowing through the switching element,
In the dead time period when the auxiliary switching element transitions from the on state to the off state, the rising of the voltage is set to be gentler than the falling of the current flowing through the auxiliary switching element. Control method.

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