Soft-switching converter

Abstract

To achieve soft switching with a conventional oscillation control circuit.SOLUTION: A series circuit consisting of a first diode and a first capacitor is connected in parallel to a switching element, a series circuit consisting of a first reactor and a first reverse non-conducting switching element is connected in parallel to the first capacitor, and a second diode is connected between the terminal of the first reactor on the side of the first reverse non-conducting switching element and the output capacitor.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a switching power supply device, and particularly to soft switching.

Background Art

[0002] In a switching power supply device, it is common to connect a capacitor in parallel across both ends of a switch element that turns the current of a reactor on and off. This capacitor is called a snubber capacitor and functions to change a rapid change in current and voltage when turning off from an on state into a gentle change. This is because a rapid change in current is likely to generate noise, and a rapid change in voltage applies a large stress to the switch element. However, this capacitor generates power loss when the switch element turns on from an off state. A technique for reducing the change in current and voltage during turn-off and reducing power loss during turn-on is called soft switching, and circuits have been conventionally devised as means therefor.

[0003] As an example of conventional soft switching, Patent Document 1 provides a method used for a chopper type converter.

[0004] Also, as another example, Patent Document 2 provides a method used for a half bridge converter.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Patent Document 2

Disclosure of the Invention

Problems to be Solved by the Invention

[0006] FIG. 1 of Patent Document 1 shows a diagram in which a soft switching circuit is applied to a boost chopper. In the figure, 103 is a snubber capacitor, which softens the change in the current and voltage applied to the switching element 101. Its operation is described in detail in paragraphs

[0018] to

[0038] , but can be summarized as follows. Before the switching element 101 turns on, the auxiliary switching element 104 is turned on to empty the charge of the snubber capacitor 103, and at that timing, the auxiliary switching element 104 is turned off and the switching element 101 is turned on. That is, when the switching element 101 turns on, the voltage of the snubber capacitor 103 is zero, so no power loss occurs. The charge of the snubber capacitor 103 becomes the excitation energy of the reactor 108b and is output via the diode 109.

[0007] FIG. 1 of Patent Document 2 shows a diagram in which a soft switching circuit is applied to a half-bridge converter. In the figure, 3b and 4b are snubber capacitors. Diodes are connected in anti-parallel to the switching elements 3 to 6. The switching elements 3 and 4 are the main switching elements of the half-bridge converter, and 5 and 6 are auxiliary switches that distribute the conduction direction of the current by half a cycle. When 3 turns on, in that half cycle, 5 remains on even after 3 turns off, and when 4 turns on, in that half cycle, 6 remains on.

[0008] Although it is described in detail in paragraphs

[0014] to

[0030] of Patent Document 2, it can be summarized as follows. When the main switching element 3 turns off, the excitation energy of the primary winding of the transformer 7 charges the capacitor 2b through the diodes 4a and 6a and the auxiliary switch 5. At that time, the charge of the snubber capacitor 4b of the main switching element 4 is also discharged. The voltage of the snubber capacitor 3b of the main switching element 3 rises in a gentle change in accordance with the discharge of 4b. Since the auxiliary switch conducts only in one direction, the charge of 4b does not flow back even when it becomes empty. Therefore, when the main switching element 4 turns on, no power loss due to the discharge of 4b occurs.

[0009] Since the control signals of the auxiliary switches in both Patent Document 1 and Patent Document 2 have different timings from the control signal of the main switch element, separate signals must be prepared.

[0010] Most of the mass-produced ICs for switching power supplies are easily available and inexpensive, but there is no control signal for the auxiliary switch, and the ICs to which the methods provided in the above two patent documents can be applied are special and expensive.

[0011] An object of the present invention is to provide a simple and inexpensive method capable of realizing soft switching using a conventional control IC for a switching power supply.

Means for Solving the Problems

[0012] In order to achieve the above object, the invention according to claim 1 is a chopper-type switching converter including a DC power supply, a switch element, a diode, an output capacitor, and an oscillation control circuit that applies a signal to a control terminal of the switch element to turn it on and off. A series circuit composed of a first diode and a first capacitor is connected in parallel to the switch element, a series circuit composed of a first reactor and a first reverse non-conducting switch element is connected in parallel to the first capacitor, and a second diode is connected between a terminal on the first reverse non-conducting switch element side of the first reactor and a connection point between the diode and the output capacitor, and a signal synchronized with the signal applied to the control terminal of the switch element is applied to the control terminal of the first reverse non-conducting switch element.

[0013] The invention according to claim 2 is an interleaved switching converter comprising a DC power supply, a series circuit consisting of a first input capacitor and a second input capacitor connected in parallel to the DC power supply, a series circuit consisting of a first switch element and a first transformer connected in parallel to the first input capacitor, a series circuit consisting of a second switch element and a second transformer connected in parallel to the second input capacitor, and an oscillation control circuit for alternately turning on and off the first and second switch elements by applying a signal to the control terminals of each of the first and second switch elements. In this converter, a series circuit consisting of a first diode and a first capacitor is connected in parallel to the first switch element, a series circuit consisting of a third diode and a second capacitor is connected in parallel to the second switch element, a series circuit consisting of a first reactor and a first reverse non-conducting switch element is connected in parallel to the first capacitor, a series circuit consisting of a second reactor and a second reverse non-conducting switch element is connected in parallel to the second capacitor, a second diode is connected between the terminal of the first reactor on the side of the first reverse non-conducting switch element and the connection point of the second input capacitor to the DC power supply, a fourth diode is connected between the terminal of the second reactor on the side of the second reverse non-conducting switch element and the connection point of the first input capacitor to the DC power supply, a signal synchronized with the signal applied to the control terminal of the first switch element is applied to the control terminal of the first reverse non-conducting switch element, and a signal synchronized with the signal applied to the control terminal of the second switch element is applied to the control terminal of the second reverse non-conducting switch element.

[0014] The soft-switching means according to claim 1 is applied to a chopper-type converter, and this means can also be applied to the interleaved converter according to claim 2 It is applied. The two claims have common technical features.

Advantages of the Invention

[0015] According to the present invention, soft switching can be realized by applying a conventional control IC for a switching power supply, so that the technical assets of circuits and transformers can be utilized, and the development cost and mass production cost can be significantly reduced.

[0016] Since both efficiency and noise are improved, miniaturization and weight reduction of the switching power supply become possible.

Brief Description of the Drawings

[0017]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Best Mode for Carrying Out the Invention

[0018] The best mode for carrying out the present invention will be described with reference to the drawings.

Embodiment 1

[0019] In FIG. 1, the first reverse non-conducting switch element 4 is composed of a series connection of a diode 4b and a MOSFET 4a, but a circuit in which two identical MOSFETs are connected in series in opposite directions may also be used.

[0020] When the switch element 9 turns on from the off state, the first reverse non-conducting switch element 4 also turns on. Therefore, the charge of the first capacitor 2 discharges through the first reactor 3. This state is state I shown in FIG. 2.

[0021] When the charge of the first capacitor 2 disappears due to discharge, the first reactor 3 releases the excitation energy and drives the current in the same direction. Therefore, the current continues to flow through the first reverse non-conducting switch element 4, the switch element 9, and the first diode 1 in the on state. This state is state II shown in FIG. 2.

[0022] Since the current in state II flows through a loop circuit composed of two diodes and two switch elements in the on state, the slope of the current is very small and almost constant. Therefore, the decrease in the excitation energy of the first reactor 3 is small.

[0023] Also, as shown in state II, since currents flowing in opposite directions flow through the switch element 9, it has the effect of reducing the power loss due to the on-resistance of the switch element 9.

[0024] When the switch element 9 turns off from the on state, the first reverse non-conducting switch element 4 also turns off simultaneously. Therefore, the excitation energy remaining in the first reactor 3 flows through a loop circuit formed by the second diode 5, the first diode 1, and the diode 10 in the conducting state. This state is state III shown in FIG. 2.

[0025] Since the current in state III flows through two diodes and the diode 10 in the conducting state, the slope of the current is very small and almost constant. Also, since the currents of the diode 10 are subtracted from each other, the loss is reduced, resulting in the effect of reducing the power loss.

[0026] The current waveforms of the main components in FIG. 1 are shown in FIG. 3. The current of the reactor 101 in state I is the same as the current of the switch element 9. The current of the reactor 101 in state II is the sum of the current of the switch element 9 and the current of the first reverse non-conducting switch element 4. The current of the reactor 101 in state III is the sum of the current of the diode 10 and the current of the second diode 5.

[0027] The current of the first reactor 3 changes somewhat depending on the on / off states of the two switch elements, but always flows in only one direction.

[0028] The first capacitor 2 absorbs the steep current-voltage changes caused by the switch element 9 and accumulates energy as charge. Since the accumulated energy is effectively utilized, noise is suppressed and losses are also suppressed.

Embodiment 2

[0029] FIG. 4 is a circuit diagram showing another embodiment of the invention according to claim 1. The figure is a buck chopper type converter, but the configuration and connection positions of the components added for soft switching are as described in claim 1. Also, the state changes and current waveforms are basically the same.

Embodiment 3

[0030] FIG. 5 is a circuit diagram showing another embodiment of the invention according to claim 1. The figure is a flyback chopper type converter, but the configuration and connection positions of the components added for soft switching are as described in claim 1. Also, the state changes and current waveforms are basically the same.

[0031] In FIG. 1, since one of the control terminals of the switch element 9 and the first reverse non-conducting switch element 4 has the same potential, only one signal is required. However, in FIGS. 4 to 5, since the potentials of the control terminals are all different, the oscillation control circuit supplies each signal separately through separate windings of the transformer and insulated from each other. It is also possible to use a photocoupler for insulation instead of the transformer.

Embodiment 4

[0032] FIG. 6 is a circuit diagram showing another embodiment of the invention according to claim 1. The figure is obtained by changing the connection positions of the components in FIG. 1 with the boost chopper type converter made into soft switching. The positions of the first diode 1 and the first capacitor 2 are interchanged, and also the position of the first reverse non-conducting switch element 4 is interchanged, but the effect is the same. Also, similar changes are possible for the topologies of FIGS. 4 and 5.

Embodiment 5

[0033] FIG. 7 is a circuit diagram showing an embodiment of the invention according to claim 2. The same reference numerals are used for the components having the same names as those in FIG. 1.

[0034] In the figure, 22 and 23 are the first and second input capacitors connected in parallel to the DC power supply, 24 and 26 constitute a series circuit composed of the first switch element and the first transformer, and 25 and 27 constitute a series circuit of the second switch element and the second transformer. 26a and 26b are the primary winding and the secondary winding of the first transformer 26, 27a and 27b are the primary winding and the secondary winding of the second transformer 27, 29a, 29b and 29c are the rectifying and smoothing circuits, and 28 is the oscillation control circuit. These components constitute the circuit of the interleaved type isolated converter.

[0035] 2 and 1 are the first capacitor and the first diode, 3 and 4 are the first reactor and the first reverse non-conducting switch element, and 5 is the second diode. These components make the high-side switch element 24 into soft switching.

[0036] Similarly, reference numerals 11 to 15 make the low-side switch element 25 into soft switching.

[0037] The configuration and connection of the circuits that function as soft switching added to the high-side and the low-side are almost the same as the configuration and connection of the circuits that function as soft switching of the boost chopper shown in FIG. 1.

[0038] The operations of both the high side and the low side are the same as the state diagram shown in Fig. 2. The charges absorbed by capacitors 2 and 12 are converted into excitation energy by reactors 3 and 13 to become current, which flows reversely when switch elements 24 and 25 are conducting to reduce the on-loss, and further regenerated to the second and first input capacitors 23 and 22 connected in parallel to the DC power supply through diodes 5 and 15 respectively.

[0039] In the figure, although the rectifying and smoothing circuit is of the flyback type, it can also be changed to the forward type.

Embodiment 6

[0040] Fig. 8 is Claimed in claim 2 a circuit diagram showing an Another embodiment of the invention. The same reference numerals as those in Fig. 7 are used for the components related to soft switching.

[0041] In the figure, The primary winding 36a of the transformer 36 is the common winding of the primary winding of the first transformer and the primary winding of the second transformer as claimed in claim 2. A series circuit of the common winding and the switch element 34 is connected in parallel to the first input capacitor 32, and a series circuit of the common winding and the switch element 35 is connected in parallel to the second input capacitor 33. The windings 36b and 36c correspond to the secondary windings of the first transformer and the second transformer, respectively.

[0042] In the figure, when the first and second switch elements 34 and 35 alternately turn on and off, forward and reverse currents alternately flow through the primary winding 36a of the transformer 36.

[0043] By sharing the primary windings of the first transformer and the second transformer, current flows alternately in both directions through the winding, and the magnetic flux change in the core swings from minus to plus, thus improving the utilization efficiency of the transformer core.

[0044] Center-tap diodes 39a and 39b, a reactor 39c, and a capacitor 39d are connected to the secondary windings 36b and 36c, and the full-wave rectified current is converted into a flat DC voltage.

[0045] Capacitors 2 (12), diodes 1 (11) connected in parallel with the switch element 34 (35), reactors 3 (13) connected in parallel with the capacitors 2 (12), and reverse non-conducting switch elements 3 (13) function the same as the components with the same reference numerals in Fig. 7. The numbers in parentheses are the reference numerals on the low side, and the same applies hereinafter.

[0046] A part of the current of the diode 5(15) flows into the input capacitor, and the remainder flows through the transformer 36 to the capacitor 39d, which is the same regenerative current as the current of the diode 5(15) in FIG. 7.

[0047] 1 First diode 2 First capacitor 3 First reactor 4 First reverse non-conducting switch element 5 Second diode 6 Output capacitor 7, 21, 31 DC power supply 8, 28, 38 Oscillation control circuit 9, 24, 25, 34, 35 MOSFET 10, 29a, 29b, 39a, 39b Diode 11 Third diode 12 Second capacitor 13 Second reactor 14 Second reverse non-conducting switch element 15 Fourth diode 22, 23, 32, 33 Input capacitor 26, 27 Transformer 26a, 27a, 36a Primary winding 26b, 27b, 36b, 36c Secondary winding 29c, 39d Capacitor 101, 39c Reactor 102, 103 Resistor

Claims

1. In a chopper-type switching converter comprising a DC power supply, a switching element, a diode, an output capacitor, and an oscillation control circuit that applies a signal to a control terminal of the switching element to turn it on and off, a series circuit consisting of a first diode and a first capacitor is connected in parallel with the switching element, a series circuit consisting of a first reactor and a first reverse non-conducting switching element is connected in parallel with the first capacitor, a second diode is connected between a terminal of the first reactor on the first reverse non-conducting switching element side and a connection point between the diode and the output capacitor, and a signal synchronized with the signal applied to the control terminal of the switching element is applied to the control terminal of the first reverse non-conducting switching element. A soft-switching converter characterized by the above.

2. In an interleaved switching converter including a DC power supply, a series circuit composed of a first input capacitor and a second input capacitor connected in parallel to the DC power supply, a series circuit composed of a first switch element and a first transformer connected in parallel to the first input capacitor, a series circuit composed of a second switch element and a second transformer connected in parallel to the second input capacitor, and an oscillation control circuit for applying signals to control terminals of each of the first and second switch elements to alternately turn on and off the first and second switch elements, a series circuit composed of a first diode and a first capacitor is connected in parallel to the first switch element, a series circuit composed of a third diode and a second capacitor is connected in parallel to the second switch element, a series circuit composed of a first reactor and a first reverse non-conducting switch element is connected in parallel to the first capacitor, a series circuit composed of a second reactor and a second reverse non-conducting switch element is connected in parallel to the second capacitor, a second diode is connected between a terminal on the first reverse non-conducting switch element side of the first reactor and a connection point between the second input capacitor and the DC power supply, a fourth diode is connected between a terminal on the second reverse non-conducting switch element side of the second reactor and a connection point between the first input capacitor and the DC power supply, a signal synchronized with the signal applied to the control terminal of the first switch element is applied to the control terminal of the first reverse non-conducting switch element, and a signal synchronized with the signal applied to the control terminal of the second switch element is applied to the control terminal of the second reverse non-conducting switch element, characterized by a soft-switching converter.

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