JP2019041561A - Interleaved flyback converter - Google Patents

Abstract

To obtain an interleaved flyback converter in which power loss due to surge absorption is improved.SOLUTION: An interleaved flyback converter is configured such that: a DC power supply 1 is connected in parallel with a series circuit consisting of a first capacitor 2 and a second capacitor 3, a series circuit consisting of a first switch element 4 and a first diode 5, and a series circuit consisting of a second diode 6 and a second switch element 7, respectively; a series circuit consisting of the primary winding 81 of a first transformer 8 and the primary winding 91 of a second transformer 9 is connected between the first diode 5 terminal side of the first switch element 4 and the second switch element 7 side terminal of the second diode 6; the junction point of the first and second capacitors 2, 3 and the junction point of the primary winding 81 of the first transformer 8 and the primary winding 91 of the second transformer 9 are connected by wiring; and a rectification filter circuit is connected with the secondary windings of the first and second transformers 8, 9, respectively.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a switching power supply, and more particularly to an interleave type flyback converter.

  Interleaved converters have the effect of suppressing input / output ripple currents, and the use of a plurality of switching elements reduces the current per one, thereby expanding its application. Although there are many examples applied to the power factor correction circuit, the basic circuit is shown in FIG. In FIG. 8, an oscillation control circuit 114 turns on and off the switch elements 109 and 110 while maintaining a 180 ° phase angle. Two ripple currents flow through the capacitor 106 in one cycle. The peak value of the ripple current flowing through the capacitor 106 is halved, thereby reducing the effective value of the ripple current.

  The step-up type used for the power factor correction circuit in the topology of the switching power supply has a disadvantage that the output ripple current becomes large. Therefore, the application of the interleave type is effective in compensating for the disadvantage. In addition, since the inverting type, which is another topology, has a disadvantage that the output ripple current becomes large, the disadvantage can be compensated by applying the interleave type.

  FIG. 9 shows a basic circuit in which an interleave type is applied to a flyback converter in which an inversion type is applied to an isolation converter.

  In FIG. 9, an oscillation control circuit 209 turns on and off the switch elements 202 and 203 while maintaining a predetermined phase angle. The current waveform flowing through the secondary-side smoothing capacitor 208 is as shown in FIG. 10, and its effective value ICRMS is 0.58 times the output current. Since the effective value of the ripple current of the secondary side smoothing capacitor of the flyback converter of one switch element is 1.3 times the output current, the effect of interleaving is great.

  An array in which interleaving is applied to the flyback converter is disclosed in Patent Document 1.

JP 2009-89593 A

  The basic circuit of the interleaved flyback converter shown in FIG. 9 and the circuit shown in Patent Document 1 both turn on and off the flyback converter having the same configuration at a predetermined phase angle. As a result, the ripple current flowing in the secondary side smoothing capacitor can be reduced.

  The disadvantage of the flyback converter that the peak value of the current flowing through the switch element when operating with one switch element is large increases the ripple current of the secondary-side smoothing capacitor. This also increases the surge voltage applied to the switch element when the is turned off. The circuit that absorbs the surge voltage causes power loss and lowers the efficiency. In addition, the surge absorbing circuit is a factor that increases the cost.

  The surge voltage is a harmful voltage generated by the leakage component of the transformer, and increases as the peak current increases. The surge voltage is applied to both ends of the switch element and may be destroyed. A conventional flyback converter uses a clamper circuit or a damper circuit to suppress a surge voltage. These circuits suppress voltage by changing surge energy into thermal energy, and involve power loss.

  FIG. 11 shows a clamper circuit that suppresses the surge voltage of the flyback converter. The secondary winding, the rectifying / smoothing circuit, and the load are omitted. In the figure, 301 is a DC power supply, 302 is a MOSFET, 303 is a primary winding, 303L is a leakage component of the primary winding, and 303M is a component excluding the leakage component. 304 to 306 are called clamper circuits and absorb a surge voltage caused by a leakage component. When the MOSFET 302 is turned off, a voltage whose polarity is reversed is generated in the primary winding 303. Of the voltages generated in the primary winding 303, the voltage generated in 303M shows a value proportional to the output voltage, but the voltage generated in 303L shows a surge characteristic with no theoretical upper limit. The capacitor 305 constituting the clamper circuit is charged with a voltage generated in both 303M and 303L. However, since the MOSFET 302 is discharged through the resistor 306 while the MOSFET 302 is in the ON state, the capacitor 305 is balanced at a certain voltage and a surge generated in the 303L. The voltage is also limited.

  In order to prevent the surge voltage from becoming high, the voltage of the capacitor 305 must be lowered by discharging by the resistor 306, which causes power loss.

  Since the conventional interleave type flyback converter employs a wiring configuration in which two flyback converters with one switch element are arranged and one terminal of the switch element is shared, a conventional surge absorption circuit with power loss Is required.

  An object of the present invention is to provide a simple circuit that prevents power loss by regenerating a surge voltage by changing the wiring configuration of a conventional interleaved flyback converter.

  In order to achieve the above object, the invention according to claim 1 is directed to a DC power supply, a first capacitor whose one terminal is a positive electrode of the DC power supply, the other terminal of the first capacitor and a negative electrode of the DC power supply. A second capacitor connected between the first switch element, one terminal connected to the positive electrode of the DC power supply, and the other terminal of the first switch element connected to the negative electrode of the DC power supply. A first diode; a second diode having one terminal connected to the positive electrode of the DC power supply; and a second switch element connected between the other terminal of the second diode and the negative electrode of the DC power supply. The primary winding of the first transformer and the 1 of the second transformer connected between the connection point of the first switch element and the first diode, and the connection point of the second diode and the second switch element. A series circuit consisting of a secondary winding and a first condenser Electromagnetically coupled to the connection point of the first and second capacitors, the wiring connecting the connection point of the primary winding of the first transformer and the primary winding of the second transformer, and the primary winding of the first transformer A secondary winding, a first rectifying and smoothing circuit for converting a voltage generated in the secondary winding into a DC voltage, a secondary winding electromagnetically coupled to the primary winding of the second transformer, A second rectifying / smoothing circuit for converting a voltage generated in the secondary winding into a DC voltage, and oscillation control for alternately turning on and off the first switch element and the second switch element at a predetermined phase angle. It is characterized by.

In the interleaved flyback converter according to claim 1, when the first switch element is in the ON state, the charge energy stored in the first capacitor flows as the current of the primary winding of the first transformer. The first transformer is excited. When the first switch element is turned off, the excitation energy of the first transformer is released as current from both the primary winding and the secondary winding of the first transformer. The current flowing through the line flows through the first diode and the wiring connecting the connection point between the first capacitor and the second capacitor, the connection point between the primary winding of the first transformer and the primary winding of the second transformer. To charge the second capacitor. The current flowing through the secondary winding of the first transformer generates a DC voltage via the first rectifying and smoothing circuit.
When the second switch element is on, the charge energy stored in the second capacitor becomes the current of the primary winding of the second transformer, and excites the second transformer. When the second switch element is turned off, the excitation energy of the second transformer is released as current from both the primary winding and the secondary winding of the second transformer, but the primary winding of the second transformer. The current flowing through the line flows through the second diode and the wiring connecting the connection point between the first capacitor and the second capacitor, the connection point between the primary winding of the first transformer and the primary winding of the second transformer. To charge the first capacitor. The current flowing through the secondary winding of the second transformer generates a DC voltage via the second rectifying and smoothing circuit.
The charge energy of the first capacitor consumed in the ON period of the first switch element is mainly supplied from the DC power supply, but a part of the charge energy is generated when the second switch element changes from the ON state to the OFF state. It is also supplemented by the current generated by the release of the excitation energy of the two transformers. Similarly, the second capacitor is also replenished with a current generated by releasing the excitation energy of the first transformer when the first switch element changes from the on state to the off state.

  Although the voltage generated when the switch element of the flyback converter changes from the on state to the off state is harmful, the interleave type flyback converter according to claim 1 is regenerated by the first capacitor and the second capacitor. So it will not be harmful.

  Even if there is no consumption of DC energy supplied by the first or second rectifying / smoothing circuit, that is, no load is applied, the voltage generated in the primary winding of the first or second transformer is the first or second voltage. The DC voltage converted from the secondary winding of the first or second transformer through the first or second rectifying / smoothing circuit is also the voltage of the first or second capacitor. Is proportional to That is, the interleave type flyback converter according to claim 1 is a DC voltage converted by each of the first and second rectifying and smoothing circuits without controlling the ON period of each of the first and second switch elements. Can be stabilized with coarse accuracy.

  According to a second aspect of the present invention, in the interleaved flyback converter according to the first aspect, the connection point of the first capacitor and the second capacitor, the primary winding of the first transformer, and the primary of the second transformer. A third capacitor is inserted in series with the wiring connecting the connection points of the windings.

  If the voltage of each of the first capacitor and the second capacitor is kept equal, there is an interleaving effect, but if the voltage is biased to one, the effect diminishes. The third capacitor functions to prevent the forward and reverse currents from being biased to either one.

  According to a third aspect of the present invention, in the interleaved flyback converter according to the first aspect, the connection point between the first capacitor and the second capacitor, the primary winding of the first transformer, and the primary of the second transformer. A current detection circuit is inserted in series with the wiring connecting the connection points of the windings to control the oscillation of the oscillation control circuit so that the current does not become excessive.

  According to a fourth aspect of the present invention, in the interleaved flyback converter according to the first to third aspects, a DC voltage converted by each of the first rectifying and smoothing circuit and the second rectifying and smoothing circuit is connected in series to the load. It is characterized by supplying.

  According to a fifth aspect of the present invention, in the interleaved flyback converter according to the first to third aspects, a DC voltage converted by each of the first rectifying and smoothing circuit and the second rectifying and smoothing circuit is connected in parallel to the load. It is characterized by supplying.

  According to a sixth aspect of the present invention, in the interleaved flyback converter according to the fourth to fifth aspects of the present invention, a function for controlling the on period is added to the oscillation control circuit in order to make the DC voltage supplied to the load constant. Features.

  The interleaved flyback converter according to claim 6 is capable of performing higher accuracy stabilization while the interleaved flyback converter according to claims 2 to 3 supplies a stable DC voltage to the load with coarse accuracy. Can do.

  According to the present invention, the disadvantage that the ripple current of the flyback converter is large and the disadvantage that the surge voltage is large can be improved at the same time. An improvement in ripple current leads to a reduction in the size of the smoothing capacitor, and an improvement in surge voltage leads to a reduction in the breakdown voltage of the switch element and the rectifier diode, both of which ultimately lead to a reduction in cost and an increase in efficiency. Therefore, it can be expected to be widely used for switch power supplies.

  The best mode for carrying out the present invention will be described with reference to the drawings.

FIG. 1 is a circuit diagram showing an embodiment of the present invention.
In the figure, 1 is a DC power source, 2 is a first capacitor, 3 is a second capacitor, 4 is a first switch element, 5 is a first diode, 6 is a second diode, and 7 is a second switch. The element, 8 is a first transformer, and 9 is a second transformer. Although 4 and 7 are represented by MOSFET symbols, bipolar transistors and IGBTs can also be applied. Although not labeled, a connection point between the capacitor 2 and the capacitor 3 and a connection point between the primary winding 81 of the transformer 8 and the primary winding 91 of the transformer 9 are connected by wiring.
The voltage of the DC power source 1 is divided by the capacitors 2 and 3. When the MOSFET 4 is turned on, the voltage of the capacitor 2 is applied to the primary winding 81 of the transformer 8 to excite the transformer 8. When the MOSFET 4 is turned off, the excitation energy of the transformer 8 is released through the winding 81 and the winding 82. The energy released through the winding 81 passes through the diode 5 and charges the capacitor 3. Since the diode 5 becomes conductive, the source side voltage of the MOSFET 4 becomes a value obtained by subtracting the forward drop voltage of the diode 5 from the potential on the negative side of the DC power supply 1. Since the drain side voltage of the MOSFET 4 is at the same potential as the positive side of the DC power source 1, the voltage applied between the drain and source of the MOSFET 4 is a voltage obtained by adding the forward drop voltage of the diode 5 to the voltage of the DC power source 1. Since the forward drop voltage of the diode 5 is smaller than the voltage of the DC power supply 1, the MOSFET 4 may have a withstand voltage obtained by adding a design margin to the voltage of the DC power supply 1 in normal use. The current due to the discharge of the excitation energy of the transformer 8 becomes a current for charging the capacitor 3, and the voltage of the capacitor 3 rises. However, since the rise by one switching is small, no surge voltage is generated.

  The voltage of the capacitor 3 is applied to the primary winding 91 of the transformer 9 when the MOSFET 7 is turned on to excite the transformer 9. When the MOSFET 7 is turned off, the excitation energy of the transformer 9 is released through the winding 91 and the winding 92. The energy released through the winding 91 passes through the diode 6 and charges the capacitor 2. Since the diode 6 becomes conductive, the drain side voltage of the MOSFET 7 is a value obtained by adding the forward drop voltage of the diode 6 to the positive side potential of the DC power supply 1. Since the source side voltage of the MOSFET 7 has the same potential as the negative side of the DC power supply 1, the voltage applied between the drain and source of the MOSFET 7 is a voltage obtained by adding the forward drop voltage of the diode 6 to the voltage of the DC power supply 1. Since the forward drop voltage of the diode 6 is smaller than the voltage of the DC power source 1, the MOSFET 7 may have a withstand voltage obtained by adding a design margin to the voltage of the DC power source 1 in a normal usage. The current due to the discharge of the excitation energy of the transformer 9 becomes a current for charging the capacitor 2, and the voltage of the capacitor 2 rises, but since the increase due to one switching is small, no surge voltage is generated.

  The voltage of the capacitor 3 is increased by the current for charging the capacitor 3 through the winding 81 with the excitation energy of the transformer 8 and the voltage of the capacitor 2 is decreased accordingly. However, the excitation energy of the transformer 9 is passed through the winding 91 to the capacitor 2. The voltage of the capacitor 2 is increased by the current charged, and the voltage of the capacitor 3 is decreased accordingly. The increase / decrease in the voltage of the capacitor 2 and the capacitor 3 occurs every time the MOSFET 4 or the MOSFET 7 is turned on / off.

  The energy released through the winding 82 and the winding 92 is converted into a DC voltage through each rectifying / smoothing circuit. Since the voltage of the winding 82 is proportional to the voltage of the winding 81, the converted DC voltage is proportional to the voltage of the capacitor 3. Since the voltage of the winding 92 is proportional to the voltage of the winding 91, the converted DC voltage is proportional to the voltage of the capacitor 2.

FIG. 2 is a circuit diagram showing an embodiment of the invention as set forth in claim 4.
In the figure, a DC voltage converted by a rectifying / smoothing circuit constituted by a winding 82, a winding 92, and 11 to 14 is connected in series and supplied to one load 18.

FIG. 3 is a circuit diagram showing an embodiment of the invention as set forth in claim 5.
In the figure, 10 is a third capacitor. A DC voltage converted by a rectifying / smoothing circuit composed of the winding 82 and the winding 92 and 11 to 13 is supplied to the load 18. The voltages generated in the winding 82 and the winding 92 are equal to each other. The capacitor 13 is charged by a current that alternately flows through the winding 82 and the winding 92. If the conduction angle of each current is 180 °, the current flowing through the capacitor 13 has the waveform shown in FIG. 10 and the ripple current becomes small.

FIG. 4 is a circuit diagram showing an embodiment of the invention as set forth in claim 6.
In the figure, the oscillation control circuit 17 detects the voltage of a load 18 and controls the pulse width for driving the gates of the MOSFET 4 and the MOSFET 7.

  The pulse width is controlled so that the voltage of the load 18 becomes constant, but the controlled voltage value is set lower than the voltage value applied to the load 18 when not controlled. In theory, the voltages generated in the winding 81 and the winding 91 are lower than the voltages charged in the capacitor 3 and the capacitor 2, respectively. Even if the MOSFET 4 or the MOSFET 7 is turned off, these capacitors Current due to the release of the excitation energy does not flow, and all flows through the secondary winding. However, since leakage inductance actually exists, a part of the excitation energy flows to the capacitor 3 and the capacitor 2.

  FIG. 6 is a diagram including leakage conductances of the winding 81 and the winding 82, and is a circuit diagram in which only components on the current path when the excitation energy of the transformer 8 is released is extracted.

  In the figure, at the moment when the MOSFET 4 is turned off, a voltage that is not limited by the turns ratio is generated in the leakage component 81L of the winding 81, and a voltage proportional to the number of turns is generated in a component 81M obtained by subtracting the leakage component. Therefore, the voltage across the winding 81 is a voltage obtained by adding the forward drop voltage of the diode 5 to the voltage of the capacitor 3 until the current of the leakage component 81L disappears.

FIG. 7 is a diagram showing a voltage-current waveform when the MOSFET 4 of FIG. 6 is in an OFF state, where (a) is the voltage across the winding 81, (b) is the current of the leakage component 81L, and (c) is the winding 82. Current.
In the figure, V2 is a voltage of the leakage component 81L, and V1 is a voltage of 81M. T2 is a period during which the excitation energy of the leakage component 81L is released, and T1 is a period during which the excitation energy of the entire transformer 8 is released. The value obtained by adding V2 to V1 is equal to the value obtained by adding the forward drop voltage of the diode 5 to the voltage of the capacitor 3.

  When the current flowing through the load 18 increases, the ON period of the MOSFET 4 increases and the excitation energy of the transformer 8 also increases. As a result, T2 and T1 are also lengthened. Conversely, when the current flowing through the load 18 is reduced, the ON period of the MOSFET 4 is shortened, and as a result, T2 and T1 are also shortened.

FIG. 5 is a circuit diagram showing another embodiment of the sixth aspect of the present invention.
In the figure, the current flowing through the primary winding of the transformer is converted into a voltage by the resistor 5 and sent to the oscillation control circuit 17. The oscillation control circuit 17 limits the pulse width for driving the MOSFET 4 and the MOSFET 7 when the voltage across the resistor 5 exceeds a predetermined value. In FIG. 5, the current detection circuit is configured by a resistor, but a current sensor using a current transformer or a Hall element may be used instead of the resistor.

  The third capacitor according to claim 2 is inserted in FIGS. 3 to 4, but is not essential. If there is no bias in the forward and reverse currents flowing through this circuit, the third capacitor is omitted and directly connected. Also good.

  Although the current detection circuit according to claim 3 is inserted in FIG. 5, it is not essential and may be directly omitted if the current flowing through this circuit does not become excessive.

Industrial applicability

  The flyback converter has a large output ripple current when one switch element is used, and is difficult to apply to a large power supply. However, the adoption of the interleave type has improved the difficulty. Further, the flyback converter has a large surge voltage applied to the switch element, and it has been difficult to increase the efficiency by a snubber circuit that absorbs the surge voltage, but the flyback converter has been improved by the present invention.

  Since the two difficulties in applying flyback converters to high-power power supplies have been improved, the application of flyback converters, which are said to be inexpensive in the topology of power supply circuits, to high-power power supplies has expanded, and industrial use The possibility is high.

FIG. 2 is a circuit diagram showing an embodiment of the invention as set forth in claim 1; It is a circuit diagram which shows the Example of invention of Claim 4. It is a circuit diagram which shows the Example of invention of Claim 5. It is a circuit diagram which shows the Example of invention of Claim 6. It is a circuit diagram which shows another Example of the invention of Claim 6. It is a circuit which shows the discharge | release path | route of the excitation energy of a transformer. It is a wave form diagram which shows the voltage current at the time of excitation energy discharge | release. It is a circuit diagram which shows the example of the interleave type power factor improvement circuit of a conventional system. It is a circuit diagram which shows the example of the interleave type | mold flyback converter of a conventional system. FIG. 10 is a waveform diagram showing a ripple current waveform of the capacitor 208 of FIG. 9. It is a circuit diagram explaining the mechanism of the surge generation | occurrence | production of a flyback converter.

1 DC power supply 2, 3 Capacitor 4, 7 MOSFET
5, 6 Diode 8, 9 Transformer 10 Capacitor 11, 12 Diode 13, 14 Capacitor 15, 16 Resistor 17 Oscillation control circuit 18 Resistor 81, 82 Transformer winding 91, 92 Transformer winding 81L, 82L Leakage component 81M, 82M Components excluding leakage components 101 AC power supply 102 Filter 103 Capacitor 104 Bridge rectifier 105, 106 Capacitor 107, 108 Reactor 109, 110 MOSFET
111, 112 Diode 113 Resistance 114 Oscillation control circuit 201 DC power supply 202, 203 MOSFET
204, 205 Transformer 206, 207 Diode 208 Capacitor 209 Oscillation control circuit 211 Resistor 301 DC power supply 302 MOSFET
303 Primary winding 303L Leakage component 303M Component excluding leakage component 304 Diode 305 Capacitor 306 Resistance

Claims (6)

  A DC capacitor, a first capacitor having one terminal connected to the positive electrode of the DC power source, a second capacitor connected between the other terminal of the first capacitor and the negative electrode of the DC power source, and one terminal Is connected to the positive electrode of the DC power supply, the other terminal of the first switch element, the first diode connected between the negative electrode of the DC power supply, and one terminal of the DC power supply. The second diode connected to the positive electrode of the first switch, the second switch element connected between the other terminal of the second diode and the negative electrode of the DC power supply, the first switch element, and the first diode A series circuit comprising a primary winding of a first transformer and a primary winding of a second transformer connected between a connection point of the first transformer and a connection point of the second diode and the second switch element; With the first capacitor The wiring connecting the connection point of the second capacitor, the primary winding of the first transformer and the connection point of the primary winding of the second transformer, and the primary winding of the first transformer are electromagnetically The first winding of the second transformer and the first winding of the second transformer are electromagnetically coupled to the first winding of the second transformer and the first winding for converting the voltage generated in the secondary winding of the first transformer to a DC voltage. A second rectifying / smoothing circuit that converts a voltage generated in the secondary winding and the secondary winding of the second transformer into a DC voltage, the first switch element, and the second switch element have a predetermined phase angle. The interleave type flyback converter is characterized by comprising an oscillation control circuit that alternately turns on and off.   A third capacitor is connected in series with a connection point between the connection point of the first capacitor and the second capacitor, and the connection point of the primary winding of the first transformer and the primary winding of the second transformer. The interleave type flyback converter according to claim 1, wherein the interleave type flyback converter is inserted.   A current detection circuit is inserted in series in the wiring connecting the connection point of the first capacitor and the second capacitor, and the connection point of the primary winding of the first transformer and the primary winding of the second transformer. 3. The interleave type flyback converter according to claim 1, wherein the oscillation of the oscillation control circuit is controlled so that the current does not become excessive.   4. The interleaved flyback converter according to claim 1, wherein a DC voltage converted by each of the first rectifying / smoothing circuit and the second rectifying / smoothing circuit is connected in series and supplied to a load.   4. The interleaved flyback converter according to claim 1, wherein a DC voltage converted by each of the first rectifying and smoothing circuit and the second rectifying and smoothing circuit is connected in parallel and supplied to a load.   The oscillation control circuit is further provided with a function of controlling an on period of each of the first switch element and the second switch element in order to make a DC voltage supplied to the load constant. The interleaved flyback converter according to any one of Items 4 to 5.

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