JP2009207272A - Dc booster circuit - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a DC booster circuit having a compact output capacitor without increasing ripple of the output voltage. <P>SOLUTION: In a booster circuit 10, a switching element 15 is connected between a ground GND and a series circuit 14 of a coil 13 and a primary winding 12a of a transformer 12 through which a current supplied from an input terminal 11 connected with a DC power supply E flows, and an anode of a diode 16 is connected to the contact between the series circuit 14 and the switching element 15. An output capacitor 17 is connected between a cathode of the diode 16 and the ground GND. A secondary winding 12b of the transformer 12 is connected between the cathode of the diode 16 and an output terminal 18. Polarity of the secondary winding 12b is set such that the potential on the output terminal 18 side increases as an exciting current increases in the direction from the input terminal 11 side of the primary winding 12a. A second capacitor 19 is connected between the ground and the contact between the secondary winding 12b and the output terminal 18. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a DC boost circuit, and more particularly to a DC boost circuit provided with an output capacitor.

  As a basic DC booster circuit, there is a booster circuit shown in FIG. 6 (see, for example, Patent Document 1). This booster circuit is controlled on and off by a coil 31 having one end connected to an input terminal 30 to which a DC power supply is input, a diode 32 having an anode connected to the other end of the coil 31, and a DC voltage. And a switching element 33 for boosting the voltage. The booster circuit includes a noise filter capacitor 34 and an output capacitor (smoothing capacitor) 35. When the switching element 33 is turned on at a predetermined cycle, energy is stored in the coil 31. When the switching element 33 is turned off, a voltage is generated in the coil 31, and the voltage is superimposed on the voltage of the DC power supply so that a current flows through the output terminal 36. At this time, the output capacitor 35 is charged. When the switching element 33 is on, power is supplied to the output terminal 36 by the discharge of the output capacitor 35, so that the output voltage decreases with time. As a result, when the capacitance of the output capacitor 35 is small, the ripple of the output voltage increases.

Further, as shown in FIG. 7, as a booster circuit for reducing the ripple of the output voltage, coils 31a and 31b, switching elements 33a and 33b, and diodes 32a and 32b are provided between the input terminal 30 and the output terminal 36. There is a booster circuit in which circuits are connected in parallel. In this booster circuit, both switching elements 33a and 33b are alternately controlled on and off.
Japanese Patent Laid-Open No. 2005-223989

  In the booster circuit of FIG. 6, it is necessary to increase the capacitance of the output capacitor 35 in order to reduce the output voltage ripple. On the other hand, in the booster circuit of FIG. 7, the output capacitor 35 can be made smaller without changing the ripple as compared with the booster circuit of FIG. However, the number of coils 31a and 31b, switching elements 33a and 33b, and diodes 32a and 32b increases. Further, in the high-power booster circuit, the configuration shown in FIG. 7 requires a plurality of large coils, resulting in an increase in size as a whole.

  The present invention has been made in view of the above problems, and an object of the present invention is to provide a DC booster circuit capable of downsizing an output capacitor without increasing the output voltage ripple.

  In order to achieve the above object, an invention according to claim 1 is directed to an input terminal connected to a DC power supply, a transformer primary winding and a series circuit of a coil through which a current supplied from the input terminal flows, and A switching element connected between the series circuit and the ground, and a rectifying element connected to a connection point between the series circuit and the switching element and blocking a current in the direction of the connection point. In addition, a first output capacitor connected between the rectifier element and the ground, and a capacitor connected between the rectifier element and the output terminal, and flowing from the input terminal side of the primary winding. The secondary winding of the transformer whose polarity is set so that the potential on the output terminal side becomes higher when the excitation current increases, and the connection point between the secondary winding and the output terminal and the ground. And a connected second capacitor.

  In the present invention, the output current is supplied from the first capacitor and the second capacitor while the switching element is in the ON state. At the same time, since the primary winding of the transformer is excited, the output voltage is the sum of the voltage across the first capacitor and the voltage appearing on the secondary side of the transformer. On the other hand, while the switching element is off, the first capacitor is charged by the energy stored in the coil and the voltage at both ends rises, but a voltage is generated on the secondary side of the transformer in a direction to reduce the output voltage. To do. Therefore, the ripple of the output voltage is reduced without increasing the capacities of the first capacitor and the second capacitor. In other words, the output capacitor can be reduced in size without increasing the output voltage ripple.

  According to a second aspect of the present invention, in the first aspect of the present invention, the inductance of the coil is set larger than the inductance of the primary winding of the transformer. In this invention, the ripple voltage can be effectively suppressed without impairing the boosting action.

  According to a third aspect of the present invention, in the first or second aspect of the present invention, the coil is wound around the same core as the primary winding of the transformer. In the present invention, the number of parts is reduced.

  According to the present invention, it is possible to provide a DC booster circuit that can reduce the size of an output capacitor without increasing the output voltage ripple.

Hereinafter, an embodiment embodying the present invention will be described with reference to FIGS. 1 and 2.
As shown in FIG. 1, in the booster circuit 10, a primary circuit 12 a of a transformer 12 and a series circuit 14 of a booster coil 13 are connected to an input terminal 11 connected to a positive electrode of a DC power source E. The inductance of the coil 13 is set larger than the inductance of the primary winding 12a of the transformer 12. A switching element 15 is connected between the series circuit 14 and the ground GND. An N-channel MOSFET is used for the switching element 15.

  The connection point between the series circuit 14 and the switching element 15 is connected to the anode of a diode 16 as a rectifying element that blocks current in the direction of the connection point, and the output is connected between the cathode of the diode 16 and the ground GND. An output capacitor 17 as a first capacitor is connected. A secondary winding 12 b of the transformer 12 is connected between the cathode of the diode 16 and the output terminal 18. The secondary winding 12b is connected to the output terminal 18 side (black circle in FIG. 1) when the excitation current increases in the direction of flowing from the input terminal 11 side (side with the black circle in FIG. 1) of the primary winding 12a. The polarity is set so that the potential on the side marked with is increased. A second capacitor 19 is connected between the connection point between the secondary winding 12b and the output terminal 18 and the ground GND. A noise filter capacitor 20 is connected between a connection point between the input terminal 11 and the primary winding 12a and the ground GND.

Next, the operation of the booster circuit 10 configured as described above will be described.
The booster circuit 10 is used with the input terminal 11 connected to the positive electrode of the DC power supply E. When there is a request for power supply from a load (not shown) connected to the output terminal 18, the switching element 15 is controlled to be switched by a command from a control device (not shown).

  When the switching element 15 is turned on, as shown in FIG. 2A, the current Ia flows from the input terminal 11 to the ground GND through the primary winding 12a of the transformer 12, the coil 13, and the switching element 15. At this time, energy is stored in the coil 13. On the other hand, a current Ib flows from the output capacitor 17 and the second capacitor 19 to the load. At this time, since the exciting current increases in the direction in which the primary winding 12a flows from the input terminal 11 side, the potential on the output terminal 18 side of the secondary winding 12b becomes higher than the potential on the output capacitor 17 side. As a result, the output voltage is the sum of the voltage across the output capacitor 17 and the voltage appearing on the secondary side of the transformer 12, that is, the secondary winding 12b. Therefore, as compared with the conventional booster circuit shown in FIG. 6, the rate at which the output voltage decreases with the passage of time is small while the switching element 15 is on.

  On the other hand, when the switching element 15 is turned off, as shown in FIG. 2B, the current Ic flows from the output terminal 18 to the load through the primary winding 12a, the coil 13, the diode 16, and the secondary winding 12b. At this time, the second capacitor 19 is charged. Further, the output capacitor 17 is charged by the energy stored in the coil 13, and the voltage at both ends thereof rises. However, a voltage is generated on the secondary side of the transformer 12, that is, the secondary winding 12b in a direction to reduce the output voltage. Therefore, as compared with the conventional booster circuit shown in FIG. 6, the rate of increase of the output voltage with the passage of time is small while the switching element 15 is turned off. As a result, output voltage ripple accompanying switching of the switching element 15 is reduced. That is, if the ripple is the same, the output capacitor 17 and the second capacitor 19 can be made smaller, and if the output capacitor 17 has the same size, a large output voltage can be handled.

  The output voltage ripples of the booster circuit (comparative example) shown in FIG. 6 and the booster circuit 10 (example) shown in FIG. 1 were compared by simulation. The simulation conditions were an output voltage of 42 V, a coil inductance of 13 μH, and a switching frequency of 30 kHz. The capacitance of the output capacitor in the circuit of FIG.

  When the input voltage is 14 V and the output current is 35 A, the values of the respective elements are determined so that the output voltage ripples of the booster circuit of FIG. 6 and the booster circuit 10 of FIG. The turn ratio 1: 2, the capacity of the output capacitor 17 and the capacity of the second capacitor 19 were both 160 μH.

  The relationship between the input voltage and the output voltage ripple at this time is as shown in FIG. FIG. 3A shows the relationship between the input voltage and output voltage ripple of the embodiment (boost circuit 10), and FIG. 3B shows the input voltage and output voltage ripple of the comparative example (boost circuit shown in FIG. 6). It is a relationship. Further, the relationship between the load current and the output voltage ripple is as shown in FIG. FIG. 4A shows the relationship between the load current and output voltage ripple of the embodiment (boost circuit 10), and FIG. 4B shows the load current and output voltage ripple of the comparative example (boost circuit shown in FIG. 6). It is a relationship. 3A and 3B and FIGS. 4A and 4B show that the output voltage ripple can be reduced without increasing the capacitance of the output capacitor 17.

According to this embodiment, the following effects can be obtained.
(1) An input terminal 11 connected to the DC power source E, a primary circuit 12a of a transformer 12 through which a current supplied from the input terminal 11 flows, and a series circuit 14 of a boosting coil 13, a series circuit 14 and a ground GND And a switching element 15 connected between them. A diode 16 as a rectifying element that blocks current in the direction of the connection point is connected to the connection point between the series circuit 14 and the switching element 15 at the anode. The output capacitor 17 is connected between the cathode of the diode 16 and the ground GND, and is connected between the cathode of the diode 16 and the output terminal 18 and flows into the primary winding 12a from the input terminal 11 side. And a secondary winding 12b whose polarity is set so that the potential on the output terminal 18 side increases when the excitation current increases. Therefore, the output capacitor 17 can be reduced in size without increasing the output voltage ripple during the switching step-up operation of the switching element 15.

(2) A second capacitor 19 is connected between a connection point between the secondary winding 12b and the output terminal 18 and the ground GND. Therefore, the output voltage is stabilized.
(3) The output capacitor 17 can be downsized without increasing the ripple of the output voltage with a simple configuration in which the transformer 12 and the second capacitor 19 are added to a general booster circuit.

  (4) Since the diode 16 is used as the rectifying element, a transistor is used instead of the diode 16, and the transistor is turned off when the switching element 15 is turned on, and the transistor is turned on when the switching element 15 is turned off. Compared to a configuration that performs control, the configuration is simplified.

The embodiment is not limited to the above, and may be embodied as follows, for example.
Instead of the configuration in which the boosting coil 13 and the transformer 12 are provided independently, the boosting coil 13 and the transformer 12 may be integrated. For example, as shown in FIG. 5A, a magnetic core 25 having a shape in which E-type cores are joined face to face is used, and a primary winding 12a and a coil 13 are provided at a central portion 25a of the magnetic core 25. The primary winding 26a is also wound. Further, the secondary winding 26b is wound around the other portion 25b. And the low-permeability part 27 is provided between the center part 25a of the magnetic body core 25 and the other part 25b. The low magnetic permeability portion 27 is configured, for example, by providing a gap in the magnetic core 25 and inserting (filling) a polyester film or paper into the gap.

  When a current is passed through the primary winding 26a of the transformer having this configuration, a magnetic field is generated around the primary winding 26a, and a magnetic flux 28 is generated in the central portion 25a of the magnetic core 25 by the generated magnetic field. The generated magnetic flux 28 passes through a magnetic path constituted by the magnetic core 25. The magnetic core 25 does not have the same magnetic permeability as a whole, and a low magnetic permeability portion 27 is provided between a central portion 25a around which the primary winding 26a is wound and another portion 25b around which the secondary winding 26b is wound. Exists. As a result, the magnetic flux 28 generated from the primary winding 26a does not flow equally in two closed paths continuing from the central portion 25a to the central portion 25a of the magnetic core 25, but instead of the low magnetic permeability portion 27. A large amount flows in a path (the magnetic flux 28 is indicated by a solid arrow), and a small amount flows in a path where the low magnetic permeability portion 27 exists (a magnetic flux 28 is indicated by a two-dot chain arrow). As a result, the primary winding 26a has the same function as the combination of the coil portion through which the magnetic flux 28 not interlinked with the secondary winding 26b and the coil portion through which the magnetic flux 28 interlinked with the secondary winding 26b is coupled. Fulfill. That is, as shown in FIG. 5 (b), the primary winding 26a portion is equivalent to the coil 13 and the primary winding 12a connected in series, and the secondary winding 26b portion is the secondary winding. Equivalent to line 12b. By changing the magnetic permeability values of the magnetic core 25 and the low magnetic permeability portion 27 and the turns ratio of the primary winding 26a and the secondary winding 26b, the target coil 13, the primary winding 12a and the secondary winding 12b are changed. Equivalent to the combination of Therefore, the number of parts is reduced as compared with a configuration in which the coil and the transformer are independent.

  The magnetic core 25 having the low-permeability portion 27 may be any material as long as it has two closed magnetic paths and can be provided with the low-permeability portion 27 in one of the closed magnetic paths. For example, a combination of an E-type core and an I-type core may be used.

  The values of the inductance of the coil 13 constituting the booster circuit 10, the capacitances of the output capacitor 17 and the second capacitor 19, the primary excitation inductance of the transformer 12, and the turns ratio are not limited to the values used in the embodiment. The maximum output voltage and the load current may be changed as appropriate. In that case, an appropriate value is obtained by simulation or test.

  The coil 13 may be configured to be connected between the input terminal 11 and the primary winding 12a of the transformer 12 instead of the configuration connected between the primary winding 12a of the transformer 12 and the switching element 15.

  A transistor is used instead of the diode 16 as the rectifying element, and the transistor is synchronized with the switching element 15 so that the transistor is turned off when the switching element 15 is turned on and the transistor is turned on when the switching element 15 is turned off. You may make it the structure controlled by a control apparatus. In such a circuit configuration, loss in the rectifying element can be reduced as compared with the case where the diode 16 is used as the rectifying element.

  The switching element 15 is not limited to MOSFET, but may be IGBT (Insulated Gate Bipolar Transistor) or other switching elements.

The noise filter capacitor 20 may be omitted.
The direct current power source E of the booster circuit 10 is not limited to a battery, and may be an AC / DC inverter that converts alternating current into direct current and outputs it.

The following technical idea (invention) can be understood from the embodiment.
(1) In the invention according to any one of claims 1 to 3, the rectifying element is a diode, an anode thereof is connected to the series circuit, and a cathode to the first capacitor for output. It is connected.

  (2) In the invention according to claim 3, the core includes two closed magnetic paths, a primary winding is wound around the center portion thereof, and a secondary winding is provided at one portion extending along the center portion. And a low magnetic permeability portion is formed between a portion where the primary winding is wound and a portion where the secondary winding is wound.

The circuit diagram of the booster circuit of one embodiment. (A) is a circuit diagram showing the flow of current when the switching element is on, (b) is a circuit diagram showing the flow of current when the switching element is off. (A) is a graph which shows the relationship between the input voltage and output voltage ripple of an Example, (b) is a graph which shows the relationship between the input voltage and output voltage ripple of a comparative example. (A) is a graph which shows the relationship between the load current of an Example, and an output voltage ripple, (b) is a graph which shows the relationship between the load current and output voltage ripple of a comparative example. (A) The schematic diagram which shows the trans | transformer of another embodiment, (b) is an equivalent circuit schematic. The circuit diagram of the booster circuit of a prior art. The circuit diagram of the booster circuit in another prior art.

Explanation of symbols

  E ... DC power supply, Ia, Ib, Ic ... current, GND ... ground, 11 ... input terminal, 12 ... transformer, 12a, 26a ... primary winding, 12b, 26b ... secondary winding, 13 ... coil, 14 ... series Circuit 15, switching element 16, diode as rectifier element 17, output capacitor as first capacitor 18, output terminal 19, second capacitor

Claims (3)

An input terminal connected to a DC power supply;
A transformer primary winding through which a current supplied from the input terminal flows, and a series circuit of coils;
A switching element connected between the series circuit and the ground;
A rectifying element that is connected to a connection point between the series circuit and the switching element and blocks a current in the direction of the connection point;
A first capacitor for output connected between the rectifying element and ground;
The polarity is set so that the potential on the output terminal side is increased when the excitation current increases in a direction that flows between the rectifying element and the output terminal and flows from the input terminal side of the primary winding. The transformer secondary winding,
A DC booster circuit comprising a second capacitor connected between a connection point between the secondary winding and the output terminal and a ground.   2. The DC booster circuit according to claim 1, wherein an inductance of the coil is set larger than an inductance of a primary winding of the transformer.   The DC booster circuit according to claim 1, wherein the coil is wound around the same core as the primary winding of the transformer.

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