JP2008079425A - Switching power supply - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a compact low loss switching power supply. <P>SOLUTION: In an AC/DC conversion circuit, a DC voltage VD1 is created by rectifying and smoothing an AC voltage VA, the voltage VD1 between the terminals of a capacitor 8 is transmitted to a capacitor 11 by turning transistors 9, 10 and 12, 13 on alternately, and the voltage VD2 between the terminals of the capacitor 11 is transmitted to a capacitor 16 using a diode element 14 and an inductor 15. Consequently, the power supply side and the load side can be insulated and a transformer is not required. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a switching power supply device, and more particularly to a switching power supply device such as an AC / DC conversion circuit.

  FIG. 2 is a circuit diagram showing a configuration of a conventional AC / DC conversion circuit. In FIG. 2, this AC / DC conversion circuit includes input terminals 31 and 32 that receive a commercial AC voltage VA and four diode elements 33 to 36 that are bridge-connected. It includes a full-wave rectifier circuit 37 that converts to a flowing voltage and a capacitor 38 that smoothes the pulsating voltage and generates a DC voltage VD1.

  Between the terminals of the capacitor 38, the primary winding 39a of the transformer 39 and the transistor 40 as a switching element are connected in series. A diode element 41, an inductor 43 and a capacitor 44 are connected in series between one terminal and the other terminal of the secondary winding 39b of the transformer 39. A diode element 42 is connected between the other terminal of the secondary winding 39 b and the cathode of the diode element 41.

When the transistor 40 is turned on / off at a predetermined switching frequency, an AC voltage is generated in the secondary winding 39b of the transformer 39. When the anode of the diode element 41 is set to a positive voltage, a charging current is supplied to the capacitor 44 via the diode element 41 and the inductor 43, and when the anode of the diode element 41 is set to a negative voltage, the diode element A charging current is supplied to the capacitor 44 through the inductor 42 and the inductor 43. In this way, the capacitor 44 is charged to a predetermined DC voltage VD2 lower than the DC voltage VD1, and the DC voltage VD2 is applied to the load circuit 47 via the output terminals 45 and 46 (see, for example, Non-Patent Document 1).
Practical power circuit design handbook, 148 pages, CQ publisher

  In such an AC / DC conversion circuit, a silicon transistor 40 has been used as a switching element, but the switching speed of a transistor that can withstand commercial AC voltage is 50 nS to 100 nS or more. Therefore, when switching at a high frequency, loss in the transistor increases, so switching at a low frequency of about 300 kHz or less is generally present. For this reason, there is a problem that the inductor 43 and the capacitor 44 become large and the circuit becomes large.

  However, recently, SiC transistors, GaN transistors, and the like have attracted attention as switching elements that replace silicon transistors, and according to these new transistors, high-speed switching of about several nS is possible. Therefore, by using these new transistors, high-speed switching of 300 kHz or more is possible, and the inductor 43 and the capacitor 44 can be downsized. In addition, these new transistors have smaller on-resistance values than silicon transistors, and power loss in the switching elements can be reduced.

  On the other hand, when the circuit of FIG. 2 is configured using SiC transistors or GaN transistors and the switching frequency is increased, the loss in the transformer 39 increases.

  Therefore, a main object of the present invention is to provide a small-sized and low-loss switching power supply device.

  The switching power supply device according to the present invention includes a pair of first switching elements, a first capacitor, a pair of second switching elements, and a voltage generation circuit. The pair of first switching elements receives a first DC voltage between their first electrodes. The first capacitor is connected between the second electrodes of the pair of first switching elements. The pair of second switching elements receives the voltage across the terminals of the first capacitor between their first electrodes and is turned on alternately with the pair of first switching elements. The voltage generation circuit is connected between the second electrodes of the pair of second switching elements, generates a second DC voltage lower than the first DC voltage, and applies the second DC voltage to the load circuit.

  Preferably, the voltage generation circuit includes a diode element, an inductor, and a second capacitor. The cathode of the diode element is connected to the second electrode of one second switching element of the pair of second switching elements, and the anode thereof is connected to the second electrode of the other second switching element. The One terminal of the inductor is connected to the cathode of the diode element. The second capacitor is connected between the other terminal of the inductor and the anode of the diode element and charged to the second DC voltage.

  More preferably, it further comprises a rectifier circuit for rectifying the AC voltage, and a third capacitor for smoothing the output voltage of the rectifier circuit to generate the first DC voltage, and the capacitance value of the third capacitor is the first value. It is larger than the capacitance value of the capacitor.

  Further preferably, a control circuit is further provided for controlling the switching frequency of the first and second switching elements so that the second DC voltage becomes a predetermined voltage.

  Preferably, the switching frequency of the first and second switching elements is 300 KHz or more.

  Preferably, each of the first and second switching elements is a transistor formed of SiC or GaN.

  In the switching power supply device according to the present invention, a pair of first switching elements, a first capacitor, a pair of second switching elements, and a voltage generation circuit are provided, and the pair of first switching elements are those Receiving a first DC voltage between the first electrodes of the first and second electrodes, the first capacitor being connected between the second electrodes of the pair of first switching elements, the pair of second switching elements being their second The voltage between the terminals of the first capacitor is received between the electrodes of the first capacitor and alternately turned on with the pair of first switching elements, and the voltage generating circuit is connected between the second electrodes of the pair of second switching elements. A second DC voltage that is connected and lower than the first DC voltage is generated and applied to the load circuit. Accordingly, since the first and second switching elements are alternately turned on, the power supply side and the load side can be insulated. Further, the ratio between the first DC voltage and the second DC voltage can be adjusted by adjusting the switching frequency or the like. Therefore, the transformer can be eliminated, and the switching power supply device can be reduced in loss and size.

  FIG. 1 is a circuit block diagram showing a configuration of an AC / DC conversion circuit according to an embodiment of the present invention. In FIG. 1, this AC / DC conversion circuit includes input terminals 1 and 2 that receive a commercial AC voltage VA and four diode elements 3 to 6 that are bridge-connected. It includes a full-wave rectifier circuit 7 for converting to a flowing voltage and a capacitor 8 for smoothing the pulsating voltage to generate a DC voltage VD1.

  A first electrode (drain or source) of a pair of transistors 9 and 10 is connected to one terminal and the other terminal of the capacitor 8, respectively. Between the second electrodes (source or drain) of the transistors 9 and 10, The capacitor 11 is connected, and the first electrodes (drain or source) of the transistors 12 and 13 are connected to the second electrodes of the transistors 9 and 10. The gates of the transistors 9 and 10 receive the switching signal S1, and the gates of the transistors 12 and 13 receive the switching signal S2. The transistors 9, 10, 12, and 13 are made of SiC or GaN, and power loss is small even when switching is performed at a frequency of 300 KHz or higher.

  The cathode of the diode element 14 is connected to the second electrode (source or drain) of the transistor 12, and the anode of the diode element 14 is connected to the second electrode (source or drain) of the transistor 13. An inductor 15 and a capacitor 16 are connected in series between the second electrodes of the transistors 12 and 13. The inter-terminal voltage VD3 of the capacitor 16 is supplied to the load circuit 20 via the output terminals 17 and 18 and also to the control circuit 19.

  The control circuit 19 alternately activates the transistors 9 and 10 and the transistors 12 and 13 by alternately switching the switching signals S1 and S2 at a switching frequency of 300 KHz or more so that the DC voltage VD3 becomes a predetermined voltage. In addition, the switching frequency of the transistors 9, 10, 12, and 13 is controlled. Since switching is performed at a frequency of 300 KHz or more, the inductor 15 and the capacitor 16 can be small.

  Next, the operation of this AC / DC conversion circuit will be described. Commercial AC voltage VA is full-wave rectified by full-wave rectifier circuit 7, smoothed by capacitor 8, and converted to DC voltage VD1. When the transistors 9 and 10 are turned on and the transistors 12 and 13 are turned off, the capacitors 8 and 11 are coupled via the transistors 9 and 10, and the capacitor 11 is charged to the DC voltage VD2 (VD2 ≦ VD1). At this time, if the capacitance value C11 of the capacitor 11 is greater than or equal to the capacitance value C8 of the capacitor 8, the inter-terminal voltage VD1 of the capacitor 8 is greatly reduced, and it becomes difficult to keep the output voltage VD3 constant, so that C8> C11 Need to be.

  Next, when the transistors 9 and 10 are turned off and the transistors 12 and 13 are turned on, current flows from the capacitor 11 through the path of the transistor 12, the inductor 15, the capacitor 16, and the transistor 13, and the capacitor 16 is charged. . At this time, the current flowing through the inductor 15 gradually increases, and electromagnetic energy is stored in the inductor 15.

  Next, when the transistors 12 and 13 are turned off and the transistors 9 and 10 are turned on, a current flows through the path of the inductor 15, the capacitor 16, and the diode element 14, and the capacitor 16 is charged. At this time, the current flowing through the inductor 15 gradually decreases, and the electromagnetic energy stored in the inductor 15 is released. At this time, the capacitor 11 is charged again.

  The control circuit 19 increases the switching frequency of the transistors 9, 10, 12, and 13 when the inter-terminal voltage VD3 of the capacitor 16 is lower than the target voltage, and when the inter-terminal voltage VD3 of the capacitor 16 is higher than the target voltage. The switching frequency of the transistors 9, 10, 12, and 13 is lowered. In this way, the inter-terminal voltage VD3 of the capacitor 16 is maintained at a desired voltage. However, VD3 <VD2 ≦ VD1.

  In this embodiment, since the transistors 9 and 10 and the transistors 12 and 13 are turned on alternately, the power supply side and the load side can be insulated. Further, the ratio between VD1 and VD3 can be adjusted by adjusting the capacitance values of the capacitors 8, 11 and 16, the switching frequency, the inductance of the inductor 15, and the like. Therefore, the transformer 39 of FIG. 2 can be eliminated.

  Further, since the SiC transistor or the GaN transistor is used as the switching element, switching can be performed with a low loss at a high frequency of 300 KHz or more, and the inductor 15 and the capacitor 16 can be downsized. Therefore, it is possible to realize a reduction in circuit loss and a reduction in size.

  The embodiment disclosed this time should be considered as illustrative in all points and not restrictive. The scope of the present invention is defined by the terms of the claims, rather than the description above, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.

1 is a circuit block diagram showing a configuration of an AC / DC conversion circuit according to an embodiment of the present invention. It is a circuit diagram which shows the structure of the conventional AC / DC conversion circuit.

Explanation of symbols

  1, 2, 31, 32 Input terminal, 3-6, 14, 33-36, 41, 42 Diode element, 7, 37 Full wave rectifier circuit, 8, 11, 16, 38, 44 Capacitor, 9, 10, 12 , 13 Transistor, 15, 43 Inductor, 17, 18, 45, 46 Output terminal, 19 Control circuit, 20, 47 Load circuit, 39 Transformer, 39a Primary winding, 39b Secondary winding.

Claims (6)

A pair of first switching elements, a first capacitor, a pair of second switching elements, and a voltage generation circuit;
The pair of first switching elements receive a first DC voltage between their first electrodes;
The first capacitor is connected between second electrodes of the pair of first switching elements;
The pair of second switching elements receive the voltage across the terminals of the first capacitor between their first electrodes, and are alternately turned on with the pair of first switching elements,
The voltage generation circuit is connected between the second electrodes of the pair of second switching elements, generates a second DC voltage lower than the first DC voltage, and supplies the second DC voltage to the load circuit. apparatus. The voltage generation circuit includes a diode element, an inductor, and a second capacitor,
The cathode of the diode element is connected to the second electrode of one second switching element of the pair of second switching elements, and the anode thereof is connected to the second electrode of the other second switching element. Connected,
One terminal of the inductor is connected to the cathode of the diode element;
2. The switching power supply device according to claim 1, wherein the second capacitor is connected between the other terminal of the inductor and an anode of the diode element and is charged to the second DC voltage. Furthermore, a rectifier circuit that rectifies the AC voltage;
A third capacitor for smoothing the output voltage of the rectifier circuit and generating the first DC voltage;
The switching power supply according to claim 1 or 2, wherein a capacitance value of the third capacitor is larger than a capacitance value of the first capacitor.   The control circuit according to any one of claims 1 to 3, further comprising a control circuit that controls a switching frequency of the first and second switching elements so that the second DC voltage becomes a predetermined voltage. Switching power supply.   The switching power supply device according to any one of claims 1 to 4, wherein a switching frequency of the first and second switching elements is 300 KHz or more.   6. The switching power supply device according to claim 1, wherein each of the first and second switching elements is a transistor formed of SiC or GaN.

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