JP2007330085A - Power supply unit - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a power supply to supply a large electric power to a primary side of a transformer as well as to prevent the transformer from heating. <P>SOLUTION: An LC resonance circuit is connected to an inverter, a primary side of a transformer is connected to the LC resonance circuit, and a power supply unit drives loads connected to a secondary side of the transformer. A primary side input of a transformer is connected parallel to the inductor of the LC resonance circuit, so that voltages at both ends of the inductor are applied to the primary side input of the transformer. The impedance of the LC resonance circuit is set at adequately smaller value compared with the impedance at the primary side of the transformer, so that reactive power of resonant power generated at the LC resonance circuit is consumed not at the primary side of the transformer, but at the inductor side. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a power supply apparatus for supplying AC power to a primary side of a transformer connected to a load such as a cold cathode fluorescent lamp (CCFL) or an external electrode fluorescent lamp (EEFL) on a secondary side.

Conventionally, as shown in FIG. 3, a switching circuit is formed by semiconductor switching elements F1, F2, F3, and F4 forming a full bridge circuit, and a capacitor C and a primary winding of a winding transformer T are formed in the switching circuit. There is known a power supply device in which a series resonance circuit including an inductor L is connected, the switching circuit is on / off controlled at high speed by a control circuit, and resonance power is generated in the series resonance circuit (for example, a patent) References 1 and 2). In this power supply device, the secondary side of the transformer T is connected to a discharge lamp 2 such as a cold cathode fluorescent lamp (CCFL) via a ballast capacitor 4, and the discharge lamp is generated by the output power of the transformer T. Light.
JP 2003-309997 A JP 2003-309981 A

In a conventional series resonance type power supply device, in order to transmit power efficiently from the primary side of the transformer to the secondary side, the primary side must have sufficient power corresponding to the power required by the secondary side. Don't be. A configuration in which a series resonance circuit is provided on the primary side of the transformer is suitable for generating a large resonance power on the primary side of the transformer, but the reactive power of the resonance power is consumed as heat on the primary side of the transformer. And the transformer generates heat. When the transformer is of a winding type, it is sufficient to make the primary winding thicker and lower its resistance value, but in that case, the transformer becomes larger, which is not preferable.
It is an object of the present invention to provide a self-excited or separately-excited oscillation circuit with a resonance circuit, and to suppress heat generation of the transformer in a power supply apparatus that supplies large resonance energy of the resonance circuit to the primary side of the transformer. Is.

To achieve the above object, the present invention provides a switching circuit comprising a plurality of semiconductor switching elements connected to a DC power supply, an LC resonance circuit comprising a capacitor and an inductance connected to the switching circuit, and on / off control of the switching circuit. A power supply apparatus for connecting a primary side of the transformer to the LC resonance circuit and driving a load connected to the secondary side of the transformer, the control circuit comprising: a primary side of the transformer An input unit is connected in parallel to the inductor of the LC resonance circuit, and the impedance of the LC resonance circuit is changed to suppress the primary side heat generation of the transformer due to the reactive power of the resonance power generated in the LC resonance circuit. It is characterized by being sufficiently smaller than the impedance on the primary side of the vessel.
Moreover, the present invention is characterized in that a plurality of the transformers are provided, and these are connected in parallel to the inductor.
According to the present invention, the inductor is a choke coil, and the transformer is a wire-wound transformer.
In the invention, the LC resonance circuit is a series resonance circuit.

  By configuring the present invention as described above, large energy can be supplied to the primary side of the transformer, and the heat generation can be suppressed or prevented.

Embodiments of the present invention will be described below in detail with reference to the accompanying drawings.
FIG. 1 shows a power supply apparatus for lighting a discharge lamp according to the present invention. An inverter board (not shown) has a high frequency inverter control IC (integrated circuit) 6 made of LSI, and switching elements F1, F2, made of MOSFET. A control circuit including a bridge output circuit including F3 and F4, a series resonance circuit including a capacitor C and an inductor Lo, and a plurality of winding type transformers T1, T2, T3, and T4 are attached.

The inductor Lo is composed of a choke coil, and primary windings 8 of a plurality of transformers T1, T2, T3, and T4 are connected in parallel to both ends of the inductor Lo. Discharge lamps 12, 14, 16, 18 such as cold cathode fluorescent lamps are connected to the secondary winding 10 of each transformer T1, T2, T3, T4, and from each transformer T1, T2, T3, T4. It is comprised so that it may light by the output voltage of.

The inductance of the inductor Lo is set to be considerably smaller than the inductance of each primary winding 8 of each transformer T1, T2, T3, T4 connected in parallel thereto. In the present embodiment, the inductance of the inductor Lo is set to an appropriate value between several microH and several tens of microH, for example, 10 to 30 microH. The inductance of each primary winding 8 of each transformer T1, T2, T3, T4 is several times to several tens of times that of the inductor Lo, for example, an appropriate value between 50 microH and several hundred microH is adopted. Yes. The transformers T1, T2, T3, and T4 have the same configuration. The discharge lamps 12, 14, 16, and 18 are connected to the transformer T1, so that opposite phase voltages are applied to both ends of a pair of discharge lamps 12, 14, and 16, 18 connected in series. It is connected to the secondary side of T2, T3, T4.

Each gate of the switching elements F1, F2, F3, and F4 is connected to gate control terminals 44, 46, 48, and 50 connected to a gate control circuit built in the high frequency inverter control IC 6. The phase detection terminal 52 of the high frequency inverter control IC 6 is connected to a phase detection circuit built in the high frequency inverter control IC 6. The phase detection terminal 52 is connected to the midpoint P of the series resonance circuit via a lead wire.

The logic circuit built in the high-frequency inverter control IC 6 generates signals for turning on / off the switching elements F1, F2, F3, and F4 based on the resonance phase signal from the phase detection terminal 52, and gate control terminals 44, 46, and 48. , 50.

  In the above configuration, when the power switch is turned on, the gate control terminals 44, 50 and 46, 48 alternately output on / off signals. As a result, a current flows through the series resonance circuit in the forward and reverse directions, the series resonance circuit resonates, and a resonance voltage is generated in the inductor Lo. The frequency signal of the resonance voltage of the inductor Lo is supplied to the phase detection circuit in the high frequency inverter control IC 6 through a lead wire.

The logic circuit and the PWM control circuit in the high frequency inverter control IC 6 drive the gate control circuit based on the phase signal from the phase detection circuit, and control the switching elements F1, F2, F3, and F4 at high speed, and the capacitor C And self-oscillation at the resonance frequency of the inductor Lo. When the power supply circuit self-oscillates and the series resonance circuit resonates, the resonance power flows mainly through the inductor Lo having a small impedance. The energy required by the secondary side of the transformers T1, T2, T3, T4 from the energy of the inductor Lo is as much as necessary via the primary winding 8 of the transformers T1, T2, T3, T4. Is transmitted.

The energy remaining in the inductor Lo is consumed in the inductor Lo. However, since the winding of the inductor Lo is thick and has a small resistance value, the amount of heat generation can be suppressed small. The inductor Lo used in the present embodiment has a small number of turns and employs a thick conducting wire to reduce the resistance and inductance of the conducting wire. Alternatively, a wire suitable for high-frequency switching in which a large number of thin wires such as litz wires are bundled in parallel to lower the resistance value and the surface area through which current flows can be increased. By adjusting the inductance, it is possible to easily adjust the resonance frequency of the resonance circuit. Further, since the inductance of each primary winding 8 of each transformer T1, T2, T3, T4 connected in parallel to the inductor Lo is sufficiently larger than the inductance of the inductor Lo, the transformer includes the inductor Lo and the capacitor C. The basic resonance frequency of the series resonance circuit is not significantly affected.

Therefore, by setting the inductance value of the primary side winding 8 of the transformers T1, T2, T3, and T4 to a predetermined large value, the inductance of the primary side windings of the transformers T1, T2, T3, and T4 can be reduced. In addition, a configuration not related to the basic resonance operation of the series resonance circuit including the capacitor C and the inductor Lo can be adopted.

  In the above embodiment, a plurality of transformers are used. However, the present invention is not particularly limited to a single transformer, and as shown in FIG. 2, a 1-input 4-output type wound transformer. T5 may be used. In FIG. 2, the primary winding 8 of the transformer T5 is connected in parallel to an inductor Lo made of a choke coil that constitutes an LC resonance circuit. The discharge lamps 20 and 24 are connected in series, and one electrode of the discharge lamp 20 is connected to the high-voltage terminal 28 of the secondary winding 30 of the transformer T5 through a ballast capacitor. The electrode is connected to the high voltage terminal 38 of the secondary winding 36 of the transformer T5 through a ballast capacitor.

The discharge lamps 22 and 26 are connected in series, and one electrode of the discharge lamp 22 is connected to the high-voltage terminal 40 of the secondary winding 34 of the transformer T5 through a ballast capacitor. The electrode is connected to the high voltage terminal 42 of the secondary winding 32 of the transformer T5 through a ballast capacitor. The high-voltage terminals 28 and 38, 40 and 42 are in opposite phases to each other. The other configuration of the embodiment shown in FIG. 2 is the same as that of the embodiment shown in FIG. 1, and the inductance value of the inductor Lo is set to be considerably smaller than the inductance of the primary winding of the transformer T5. .

It is an electronic circuit diagram which shows schematic structure of the power supply device which concerns on this invention. It is an electronic circuit diagram which shows other embodiment of this invention. It is an electronic circuit diagram which shows a prior art.

Explanation of symbols

2 Discharge lamp
4 Ballast capacitor 6 High frequency inverter control IC
8 Primary winding 10 Secondary winding 12 Discharge lamp 14 Discharge lamp 16 Discharge lamp 18 Discharge lamp 20 Discharge lamp 22 Discharge lamp 24 Discharge lamp 26 Discharge lamp 28 High voltage terminal 30 Secondary winding 32 Secondary winding 34 Secondary winding 36 Secondary winding 38 High voltage terminal 40 High voltage terminal 42 High voltage terminal 44 Gate control terminal 46 Gate control terminal 48 Gate control terminal 50 Gate control terminal 52 Phase detection terminal

Claims (4)

A switching circuit comprising a plurality of semiconductor switching elements connected to a DC power supply; an LC resonance circuit comprising a capacitor and an inductance connected to the switching circuit; and a control circuit for controlling on / off of the switching circuit, the LC resonance A power supply device for connecting a primary side of a transformer to a circuit and driving a load connected to the secondary side of the transformer, wherein the primary side input portion of the transformer is an inductor of the LC resonance circuit In order to suppress heat generation on the primary side of the transformer due to reactive power generated in the LC resonance circuit in parallel, the impedance of the LC resonance circuit is compared with the impedance on the primary side of the transformer. A power supply device characterized by being sufficiently small. The power supply device according to claim 1, wherein a plurality of the transformers are provided, and these are connected in parallel to the inductor. The power supply device according to claim 1, wherein the inductor is a choke coil, and the transformer is a winding type transformer. The power supply apparatus according to claim 1, wherein the LC resonance circuit is a series resonance circuit.

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