JP7705586B2 - Soft Switching Converter - Google Patents

Description

The present invention relates to a switching power supply device, and more particularly to soft switching.

In switching power supplies, capacitors are often connected in parallel across the switch element that turns the reactor current on and off. This capacitor is called a snubber capacitor, and its function is to convert the sudden change in current and voltage when turning off from the on state into a gradual change. This is because sudden changes in current are likely to generate noise, and sudden changes in voltage place a large stress on the switch element. However, this capacitor generates power loss when the switch element turns on from the off state.
The technology of slowing down the change in current and voltage when turning off and reducing power loss when turning on is called soft switching, and circuits have been devised as a means of achieving this.

As an example of conventional soft switching, Patent Document 1 provides a method used in a chopper type converter.

As another example, Patent Document 2 provides a method used in a half-bridge converter.

Patent Publication 2010-68619 Patent Publication 2013-188090

FIG. 1 of Patent Document 1 shows a diagram in which a soft switching circuit is applied to a boost chopper. In the diagram, 103 is a snubber capacitor, which makes the change in current and voltage applied to the switch element 101 a gradual change. Its function is described in detail in paragraphs [0018] to [0038], but can be summarized as follows. Before the switch element 101 turns on, the auxiliary switch element 104 is turned on to empty the charge of the snubber capacitor 103, and at that timing the auxiliary switch element 104 is turned off to turn on the switch element 101. That is, when the switch 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.

Figure 1 of Patent Document 2 shows a diagram in which a soft switching circuit is applied to a half-bridge converter. In the diagram, 3b and 4b are snubber capacitors. Diodes are connected in anti-parallel to the switch elements 3 to 6. Switch elements 3 and 4 are the main switch elements of the half-bridge converter, and 5 and 6 are auxiliary switches that distribute the current conduction direction for each half cycle. When it is 3's turn to turn on, 5 remains on for that half cycle even after 3 turns off, and when it is 4's turn to turn on, 6 remains on for that half cycle.

This is described in detail in paragraphs [0014] to [0030] of Patent Document 2, but can be summarized as follows: When the main switching element 3 is turned off, the excitation energy of the primary winding of the transformer 7 passes through diodes 4a and 6a and the auxiliary switch 5 to charge the capacitor 2b. At that time, the charge in 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 slowly in accordance with the discharge of 4b. Since the auxiliary switch conducts electricity in only one direction, there is no reverse flow even if the charge in 4b becomes empty. Therefore, when the main switching element 4 is turned on, no power loss occurs due to the discharge of 4b.

In both Patent Document 1 and Patent Document 2, the control signal for the auxiliary switch has a different timing from the control signal for the main switch element, and therefore separate signals must be prepared.

Many mass-produced ICs for switching power supplies are easy to obtain and inexpensive, but there is a drawback in that there is no control signal for the auxiliary switch, and the ICs to which the methods provided by the above two patent documents can be applied are specialized and expensive.

SUMMARY OF THE PRESENT EMBODIMENT An object of the present invention is to provide a simple and inexpensive method for achieving soft switching using a conventional switching power supply control IC.

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

The invention of claim 2 relates to an interleaved switching converter including a DC power supply, a series circuit including a first input capacitor and a second input capacitor connected in parallel to the DC power supply, a series circuit including a first switch element and a first transformer connected in parallel to the first input capacitor, a series circuit including a second switch element and a second transformer connected in parallel to the second input capacitor, and an oscillation control circuit which applies signals to control terminals of the first and second switch elements to alternately turn on and off the first and second switch elements, wherein a series circuit including a first diode and a first capacitor is connected in parallel to the first switch element, and a series circuit including 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 a terminal of the first reactor on the first reverse non-conducting switch element side and a connection point of the second input capacitor with the DC power supply, a fourth diode is connected between a terminal of the second reactor on the second reverse non-conducting switch element side and a connection point of the first input capacitor with the DC power supply, a signal synchronized with a 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 a 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.

The soft switching means in claim 1 is applied to a chopper type converter, but the means is also applied to an interleaved type converter in claim 2. The two claims have common technical features.

According to the present invention, soft switching can be achieved by applying a conventional switching power supply control IC, which makes it possible to utilize technological assets such as circuits and transformers, and greatly reduces development costs and mass production costs.

Since both efficiency and noise are improved, it becomes possible to make switching power supplies smaller and lighter.

1 is a circuit diagram showing an embodiment of the invention according to claim 1. FIG. 2 shows the state of the circuit of FIG. 1; 3A to 3C are diagrams showing current waveforms in each state of FIG. 2; FIG. 11 is a circuit diagram showing another embodiment of the invention according to claim 1. FIG. 11 is a circuit diagram showing another embodiment of the invention according to claim 1. FIG. 11 is a circuit diagram showing another embodiment of the invention according to claim 1. FIG. 4 is a circuit diagram showing an embodiment of the invention according to claim 2. FIG. 11 is a circuit diagram showing another embodiment of the invention according to claim 2 .

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 first aspect of the invention.
In the figure, 7 is a DC power supply, 101 is a reactor, 9 is a switch element, 10 is a diode, 6 is an output capacitor, and 8 is an oscillation control circuit, which are the basic components of a boost chopper converter. When the switch element 9 is turned off from an on state, a sudden rise in voltage occurring across the switch element 9 is suppressed by a first diode 1 and a first capacitor 2. While the switch element 9 is in the off state, the first capacitor 2 is charged with a voltage approximately equal to the output voltage.

In FIG. 1, the first reverse non-conducting switch element 4 is configured by connecting a diode 4b and a MOSFET 4a in series, but it may also be a circuit in which two identical MOSFETs are connected in series in the opposite directions.

When the switch element 9 is turned on from the off state, the first reverse non-conducting switch element 4 is also turned on, so that the charge in the first capacitor 2 is discharged through the first reactor 3. This state is state I shown in FIG.

When the charge in the first capacitor 2 disappears due to discharging, the first reactor 3 releases excitation energy and pushes current in the same direction, so that the current continues to flow through the first reverse non-conducting switch element 4, which is in the on state, the switch element 9, and the first diode 1. This state is state II shown in FIG.

The current in state II flows through a loop circuit formed by two diodes and two switch elements in the ON state, so the gradient of the current is very small and nearly constant, and therefore the decrease in the excitation energy of the first reactor 3 is small.

Furthermore, as shown in state II, currents flow in opposite directions through the switch element 9, which has the effect of reducing power loss due to the on-resistance of the switch element 9.

When the switch element 9 is turned off from the on state, the first reverse non-conducting switch element 4 is also turned off at the same time, so that the excitation energy remaining in the first reactor 3 flows through the loop circuit formed by the second diode 5, the first diode 1, and the conducting diode 10. This state is state III shown in FIG.

The current in state III flows through the two diodes and the diode 10 in a conducting state, so the gradient of the current is very small and nearly constant. Also, the current in the diode 10 is subtracted by plus and minus, so the loss is small, resulting in an effect of reducing power loss.

The current waveforms of the main components in Fig. 1 are shown in Fig. 3. In state I, the current in reactor 101 is the same as the current in switch element 9. In state II, the current in reactor 101 is the current in switch element 9 plus the current in first reverse non-conducting switch element 4. In state III, the current in reactor 101 is the current in diode 10 plus the current in second diode 5.

The current in the first reactor 3 changes slightly depending on the on/off state of the two switch elements, but always flows in one direction.

The first capacitor 2 absorbs the steep current and voltage changes caused by the switch element 9 and stores energy as electric charge. The stored energy is effectively utilized, so noise is suppressed and loss is also suppressed.

FIG. 4 is a circuit diagram showing another embodiment of the present invention.
The figure shows a step-down chopper converter, but the configuration and connection positions of the parts added for soft switching are as described in claim 1. Also, the state changes and current waveforms are basically the same.

FIG. 5 is a circuit diagram showing another embodiment of the present invention.
The figure shows an inverting chopper type converter, but the configuration and connection positions of the parts added for soft switching are as described in claim 1. Also, the state changes and current waveforms are basically the same.

In Fig. 1, one of the control terminals of the switch element 9 and the first reverse non-conducting switch element 4 is at the same potential, so one signal is sufficient, but in Fig. 4 and Fig. 5, the control terminals are all at different potentials, so the oscillation control circuit supplies each signal through a separate transformer winding and insulated from each other. It is also possible to provide isolation by using a photocoupler instead of a transformer.

FIG. 6 is a circuit diagram showing another embodiment of the present invention.
The figure shows a step-up chopper converter with soft switching, with the connection positions of the components in Fig. 1 changed. The positions of the first diode 1 and the first capacitor 2 are interchanged, and the position of the first reverse non-conducting switch element 4 is also interchanged, but the effect is the same. Similar changes are also possible for the topologies in Figs. 4 and 5.

7 is a circuit diagram showing an embodiment of the invention as set forth in claim 2. The same reference numerals are used for parts that are the same as those in FIG.

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

Reference numerals 2 and 1 denote a first capacitor and a first diode, reference numerals 3 and 4 denote a first reactor and a first reverse non-conducting switch element, and reference numeral 5 denotes a second diode. These components make the switch element 24 on the high side soft-switch.

Similarly, reference numerals 11 to 15 make the low-side switch element 25 soft-switch.

The configuration and connections of the circuits that perform soft switching and are added to the high side and low side are almost the same as the configuration and connections of the circuit that performs soft switching of the boost chopper shown in FIG.

The operation of both the high side and the low side is the same as the state diagram shown in FIG. 2, and the charge absorbed in capacitors 2 and 12 is converted into excitation energy by reactors 3 and 13 and becomes a current that flows in the reverse direction when switch elements 24 and 25 are conductive, reducing the on-loss, and further flows through diodes 5 and 15 and is regenerated in the second and first input capacitors 23 and 22 connected in parallel to the DC power supply.

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

8 is a circuit diagram showing another embodiment of the invention as set forth in claim 2. The same reference numerals as those in FIG. 7 are used for components relating to soft switching.

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

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

By sharing the primary winding of the first transformer and the second transformer, current flows alternately in both directions in the winding, and the magnetic flux change in the core swings from negative to positive, improving the utilization efficiency of the transformer core.

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

Capacitor 2 (12) connected in parallel to switch element 34 (35), diode 1 (11), reactor 3 (13) connected in parallel to capacitor 2 (12), and reverse non-conducting switch element 3 (13) function in the same way as the components with the same reference numerals in Figure 7. The numbers in parentheses indicate the reference numerals for the low side, and the same applies to the following.

A part of the current of the diode 5 (15) flows to the input capacitor, and the remainder flows to the capacitor 39d via the transformer 36, but this is the same regenerative current as the current of the diode 5 (15) in FIG.

REFERENCE SIGNS LIST 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 (2)

1. A chopper-type switching converter comprising a DC power supply, a switch element, a diode, an output capacitor, and an oscillation control circuit which applies a signal to a control terminal of the switch element to turn it on and off, wherein a series circuit consisting of a first diode and a first capacitor is connected in parallel to the 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 second diode is connected between a terminal of the first reactor on the first reverse non-conducting switch element side and a connection point of the diode to the output capacitor, and a signal synchronized with a signal applied to the control terminal of the switch element is applied to the control terminal of the first reverse non-conducting switch element. In an interleaved switching converter including a DC power supply, a series circuit including a first input capacitor and a second input capacitor connected in parallel to the DC power supply, a series circuit including a first switch element and a first transformer connected in parallel to the first input capacitor, a series circuit including a second switch element and a second transformer connected in parallel to the second input capacitor, and an oscillation control circuit that applies 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, the interleaved switching converter further includes a series circuit including a first diode and a first capacitor connected in parallel to the first switch element, a series circuit including a third diode and a second capacitor connected in parallel to the second switch element, and a first reactor connected in parallel to the first capacitor. and a first reverse non-conducting switch element, 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 a terminal of the first reactor on the first reverse non-conducting switch element side and a connection point of the second input capacitor with the DC power supply, a fourth diode is connected between a terminal of the second reactor on the second reverse non-conducting switch element side and a connection point of the first input capacitor with the DC power supply, and a signal synchronized with a signal applied to a 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 a 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.

Images