JP2008005575A - Dc/ac inverter - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a high efficiency low noise DC/AC inverter by assuring a resonance current even when the input voltage is high. <P>SOLUTION: The DC/AC inverter comprises a first converter having a switching circuit where switching elements Q1 and Q2 are connected in series across a DC power supply Vdc1, and a series circuit of a capacitor C6 connected across the Q1 and the primary winding P of a transformer Tb, a second converter having a switching circuit where Q3 and Q4 are connected in series across the Vdc1, and a series circuit of a capacitor C5 connected across the Q4 and the primary winding P of the Ta, low pass filters L2 and C0 connected across the series circuit of the secondary winding S of the Ta and the secondary winding S of the Tb, a control circuit 10 for regulating the phase between the first and second converters by turning one and the other switch elements each of the first and second converters on/off alternately and regulating the output voltage, and a reactor Lf connected across the series circuit of the tertiary winding Th of the Ta and the tertiary winding Th of the Tb. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a DC / AC inverter that converts a DC voltage into a high-frequency AC voltage and lights a discharge lamp such as a cold cathode fluorescent lamp (CCFL), an external electrode fluorescent lamp, or a fluorescent lamp by the AC voltage.

  Conventionally, a DC / AC inverter that turns on a CCFL for a backlight of a liquid crystal television is generally connected to a direct current output of a switching power supply or a direct current power supply rectified from a commercial power supply, and through an inverter using a switch element. AC voltage is output to one or more CCFLs. In particular, when a DC power supply obtained by rectifying a commercial power supply is used, the DC voltage is high, so that the switching loss of the switch element increases. For this reason, a conventional DC / AC inverter as shown in FIG. 7 has been used (Patent Document 1).

  The DC / AC inverter shown in FIG. 7 is composed of a phase shift type bridge inverter, and four switch elements Q1 to Q4 are bridge-connected, and the arms of the switch elements Q1 and Q2 and the switch elements Q3 and Q4 have the same duty. The switching loss is reduced by turning on / off alternately and adjusting the phase between the arms to adjust the output voltage and performing the resonance operation.

  Details of the DC / AC inverter shown in FIG. 7 will be described. At both ends of the DC power supply Vdc1, a series circuit of a switch element Q1 made of MOSFET and a switch element Q2 made of MOSFET and a series circuit of a switch element Q3 made of MOSFET and a switch element Q4 made of MOSFET are respectively parallel. It is connected.

  The drain of the switch element Q1 and the drain of the switch element Q3 are connected to the positive electrode of the DC power supply Vdc1, and the source of the switch element Q2 and the source of the switch element Q4 are connected to the negative electrode of the DC power supply Vdc1.

  Between the connection point A1 between the source of the switch element Q1 and the drain of the switch element Q2 and the connection point A2 between the source of the switch element Q3 and the drain of the switch element Q4, the primary winding of the capacitor C5 and the transformer T A series circuit with P (turn number np) is connected.

  A diode D1 and a voltage resonance capacitor C1 are connected in parallel between the drain and source of the switch element Q1, and a diode D2 and a voltage resonance capacitor C2 are connected in parallel between the drain and source of the switch element Q2. Has been. A diode D3 and a voltage resonance capacitor C3 are connected in parallel between the drain and source of the switch element Q3, and a diode D4 and a voltage resonance capacitor C4 are connected in parallel between the drain and source of the switch element Q4. Has been.

  A series circuit of a reactor L2 and a capacitor C0 is connected to both ends of the secondary winding S (number of turns ns) of the transformer T, and a CCFL14 and a current detection circuit for detecting a current flowing through the CCFL14 are connected to both ends of the capacitor C0. 12 is connected in series.

  The control circuit 10a alternately turns on / off the switch elements Q1 and Q2 at the same duty with a dead time as a period for turning off both, and sandwiches the dead time as a period for turning off both the switch elements Q3 and Q4. Are alternately turned on / off at the same duty. Further, the voltage applied to the primary winding P of the transformer T is changed by shifting the voltage phase of the connection point A2 with respect to the voltage phase of the connection point A1 based on the current detected by the current detection circuit 12. Control to adjust the output voltage V0 (the voltage across the capacitor C0).

  Next, the operation of the conventional DC / AC inverter configured as described above will be described in detail with reference to the timing charts shown in FIGS. FIG. 8 is a timing chart of signals at various parts when the input voltage of the conventional DC / AC inverter is low. FIG. 9 is a timing chart of signals at various parts when the input voltage of the conventional DC / AC inverter is high.

  8 and 9, Q1v is the drain-source voltage of the switch element Q1, Q1i is the drain current of the switch element Q1, Q3v is the drain-source voltage of the switch element Q3, Q3i is the drain current of the switch element Q3, and Tnpi. Is the current of the primary winding P of the transformer T, Vo is the output voltage.

  First, at time t10, when the switch element Q4 is turned on, the switch elements Q2 and Q3 are turned off, and the switch element Q1 is turned on, a positive voltage is applied to the primary winding P of the transformer T, and Vdc1 → Q1 → P A resonance current flows through a path of C5 → Q4 → Vdc1. This resonance current (current Tnpi) flows in a sine wave shape in the positive direction. A voltage is generated in the secondary winding S of the transformer T, a high frequency component is removed by the reactor L2 and the capacitor C0, and a sine-wave high voltage is generated at both ends of the capacitor C0. The CCFL 14 is lit by this high voltage.

  Next, at time t11, when the switch element Q1 is turned on, the switch elements Q2 and Q3 are turned off, and the switch element Q4 is turned off, the current Tnpi continues to flow due to the energy stored in the exciting inductance of the transformer T, and the capacitor C3 Is discharged, and the capacitor C4 is charged. When the discharge of the capacitor C3 is completed, the diode D3 becomes conductive, and a current Tnpi flows through a path of P → C5 → D3 → Q1 → P. At this time, when the switch element Q3 is turned on, the switch element Q3 performs a zero voltage switching (ZVS) operation.

  Next, when the switch element Q3 is turned on, the switch elements Q2 and Q4 are turned off, and the switch element Q1 is turned off at time t12, the capacitor C1 is charged by the current Tnpi and the capacitor C2 is discharged. When the discharge of the capacitor C2 is completed, the diode D2 becomes conductive, and a current Tnpi flows through a path of P → C5 → Q3 (D3) → Vdc1 → D2 → P. At this time, when the switch element Q2 is turned on, the switch element Q2 performs a ZVS operation. Further, a negative voltage is applied to the primary winding P of the transformer T, and a resonance current flows through a path of Vdc1 → Q3 → C5 → P → Q2 → Vdc1. This resonance current (current Tnpi) flows in a sine wave shape in the negative direction.

  Next, at time t13, when the switch element Q2 is turned on, the switch elements Q1 and Q4 are turned off, and the switch element Q3 is turned off, the current Tnpi continues to flow due to the energy stored in the exciting inductance of the transformer T, and the capacitor C4 Is discharged and the capacitor C3 is charged. When the discharge of the capacitor C4 is completed, the diode D4 becomes conductive, and the current Tnpi flows through the path of P → Q2 → D4 → C5 → P. At this time, when the switch element Q4 is turned on, the switch element Q4 performs a ZVS operation.

Next, at time t14, when the switch element Q4 is turned on, the switch elements Q1 and Q3 are turned off, and the switch element Q2 is turned off, the capacitor C2 is charged by the current Tnpi and the capacitor C1 is discharged. When the discharge of the capacitor C1 is completed, the diode D1 becomes conductive, and a current Tnpi flows through a path of P → D1 → Vdc1 → Q4 (D4) → C5 → P. At this time, when the switch element Q1 is turned on, the switch element Q1 performs a ZVS operation. When switch element Q1 is turned on, the operation after time t10 is repeated.
JP 2003-259634 A

  However, as shown in the timing chart of FIG. 9, when the input voltage (the voltage of the DC power supply Vdc1) fluctuates and becomes high, the period from time t10 to time t11 (time t12 to time t13) is shortened. The period from time t11 to time t12 (time t13 to time t14) becomes longer. For this reason, the phase of the output current advances with respect to the voltage of the switch element, and the current Tnpi becomes substantially zero at time t14 (t10), for example. As a result, since the zero voltage switching (ZVS) operation of the switch element Q1 cannot be performed, the switching loss increases. It can be seen that a spike current flows in the current Q1i when the switch element Q1 is on.

  That is, in the period in which power is not supplied to the secondary side of the transformer T (time t13 to t14), the switching elements Q2 and Q4 are turned on to short-circuit the primary side of the transformer T. Since no voltage is applied to the primary winding P and the exciting current of the exciting inductance of the transformer T does not increase, the resonance current cannot be secured. Similarly, in the period (time t11 to t12), the primary side of the transformer T is short-circuited.

  An object of the present invention is to provide a DC / AC inverter that can secure a resonance current even when an input voltage is high, and achieve high efficiency and low noise.

  In order to solve the above problems, the present invention employs the following means. According to a first aspect of the present invention, there is provided a first switching circuit in which a first switch element and a second switch element are connected in series at both ends of a DC power source, a first capacitor and a first switch at both ends of the first or second switch element. A first converter having a first series circuit in which a primary winding of one transformer is connected in series, and a second switch in which a third switch element and a fourth switch element are connected in series at both ends of the DC power supply. A second converter having a switching circuit and a second series circuit in which a second capacitor and a primary winding of a second transformer are connected in series to both ends of the third or fourth switch element; and the first transformer A low-pass filter connected to both ends of a series circuit of the secondary winding of the second transformer and the secondary winding of the second transformer, and one switch element and the other switch element alternately for each of the first and second converters On / A control circuit for adjusting the output voltage to the load connected to the output terminal of the low-pass filter by adjusting the phase between the first and second converters, and the tertiary winding of the first transformer; And a first reactor connected to both ends of a series circuit in which a tertiary winding of the second transformer is connected in series.

  According to a second aspect of the present invention, in the DC / AC converter according to the first aspect, a voltage resonance capacitor and a diode are connected to both ends of the first, second, third and fourth switch elements, and the first The first, second, third, and fourth switch elements are caused to perform zero voltage switching operation by delaying the phase of the output current by the current of the reactor and the exciting inductance current of the first and second transformers. To do.

  According to a third aspect of the present invention, in the DC / AC inverter according to the first or second aspect of the present invention, the DC / AC inverter has a core composed of a first leg to a third leg in which a closed magnetic circuit is formed. The primary and secondary windings of the first transformer are wound, and the primary and secondary windings of the second transformer are wound on the second leg of the core. A gap is formed on the tripod.

  According to a fourth aspect of the present invention, in the DC / AC inverter according to any one of the first to third aspects, the low-pass filter includes a reactor and a capacitor, and the reactor includes the first and second reactors. The low-pass filter includes a leakage inductance between a primary winding and a secondary winding of a transformer, and the output voltage is made sinusoidal by the leakage inductance and the capacitor.

  A fifth aspect of the present invention is the DC / AC inverter according to any one of the first to fourth aspects, wherein the load is connected in series to a plurality of cold cathode tubes and the plurality of cold cathode tubes. And a balancer circuit for balancing the currents of the plurality of cold-cathode tubes.

  According to the present invention, the secondary winding of the first transformer and the secondary winding of the second transformer are connected in series, and the control circuit has one switch element and the other switch for each of the first and second converters. Since the output voltage is adjusted by adjusting the phase between the first and second converters by alternately turning on and off the elements, even during a period in which power is not supplied from the secondary winding of each transformer to the output A voltage is applied to the primary windings of the transformers of the first and second converters. For this reason, a lag current flows through the primary winding of each transformer. That is, the input voltage rises due to the tertiary winding of each transformer and the first reactor, and even if the phase of the output current advances with respect to the voltage of the switch element, the delay current of the first reactor causes the transformer to A delay current flows through the primary winding, and a resonance current when the switch element is OFF can be secured.

  For this reason, the zero voltage switching operation of the switch element can be performed, and the spike current component is not generated from the current flowing through the switch element. Therefore, the switching loss can be reduced, the efficiency can be improved and the noise can be reduced.

  Further, by integrating the transformer and the reactor, the number of parts can be reduced and further miniaturization can be achieved.

  Hereinafter, embodiments of the DC / AC inverter of the present invention will be described in detail with reference to the drawings.

  The DC / AC inverter according to the first embodiment includes two sets of half-bridge converters, and the secondary winding of a transformer that is an output winding is connected in series to adjust the phase between these converters. Adjust the AC power. When the input voltage is high by connecting the tertiary winding and reactor of each transformer in a closed loop and applying voltage to the reactor only during the period when power is not supplied from the secondary winding of each transformer to the output. As the reactor current increases, the resonance current is ensured even when the phase shift is large when the input voltage is high, and the switch element is operated in the ZVS mode. Thereby, even when the input voltage is high, high efficiency and low noise can be achieved. Further, by integrating the transformer and the reactor, a single transformer can be obtained, and further miniaturization can be achieved.

  FIG. 1 is a circuit configuration diagram of a DC / AC inverter according to a first embodiment of the present invention. In the DC / AC inverter shown in FIG. 1, a DC power source Vdc1 has both ends of a series circuit (corresponding to the first switching circuit of the present invention) of a switch element Q1 made of MOSFET and a switch element Q2 made of MOSFET, and a MOSFET. A switch element Q3 and a series circuit (corresponding to the second switching circuit of the present invention) of a switch element Q4 made of MOSFET are connected in parallel.

  A series circuit of a capacitor C6, a reactor L6, and a primary winding P (number of turns np) of a transformer Tb is connected between the drain and source of the switch element Q1. A series circuit of a capacitor C5, a reactor L5, and a primary winding P (number of turns np) of a transformer Ta is connected between the drain and source of the switch element Q4. The switch element Q1, the switch element Q2, the capacitor C6, the reactor L6, and the transformer Tb form one half-bridge converter (corresponding to the first converter of the present invention), and the switch element Q3, the switch element Q4, the capacitor C5, and the reactor. One half bridge converter (corresponding to the second converter of the present invention) is formed by L5 and the transformer Ta. Each half-bridge converter receives power from the DC power supply Vdc1, and the switch elements in each half-bridge converter are alternately turned on / off at the same frequency.

  The drain of the switch element Q1 and the drain of the switch element Q3 are connected to the positive electrode of the DC power supply Vdc1, and the source of the switch element Q2 and the source of the switch element Q4 are connected to the negative electrode of the DC power supply Vdc1.

  A diode D1 and a voltage resonance capacitor C1 are connected in parallel between the drain and source of the switch element Q1, and a diode D2 and a voltage resonance capacitor C2 are connected in parallel between the drain and source of the switch element Q2. A diode D3 and a voltage resonance capacitor C3 are connected in parallel between the drain and source of the switch element Q3, and a diode D4 and a voltage resonance capacitor C4 are connected in parallel between the drain and source of the switch element Q4. It is connected to the.

  The capacitors C1 to C4 may be internal capacitances between the drains and the sources of the switching elements Q1 to Q4, and the diodes D1 to D4 may be internal diodes between the drains and the sources of the switching elements Q1 to Q4. good. The winding start of the transformers Ta and Tb is indicated by a dot (●).

  The secondary winding S (number of turns ns) of the transformer Ta and the secondary winding S (number of turns ns) of the transformer Tb are connected in series, and the reactor L2 (the second reactor of the present invention) is connected to both ends of the series circuit. And a series circuit (corresponding to the low-pass filter of the present invention) of the capacitor C0 is connected. A series circuit of a CCFL 14 and a current detection circuit 12 that detects a current flowing through the CCFL 14 is connected to both ends of the capacitor C0.

  Each transformer Ta, Tb is provided with a tertiary winding Th (number of turns nf). One tertiary winding Th, the other tertiary winding Th, and the reactor Lf (corresponding to the first reactor of the present invention) are connected in a closed loop shape. The side with no dot (●) of one secondary winding S is connected to the side with the dot (●) of the other secondary winding S, and the side with the dot (●) of one tertiary winding Th The other side of the tertiary winding Th is connected to the side with a dot (●). Therefore, output is generated at both ends of the two tertiary windings Th connected in series during a period in which output is not generated at the ends of the two secondary windings S connected in series. .

  The control circuit 10 alternately turns on / off the switch elements Q1 and Q2 at the same duty with a dead time as a period for turning off both, and sandwiches the dead time as a period for turning off both the switch elements Q3 and Q4. Are alternately turned on / off at the same duty. Further, the secondary winding S of the transformer Ta and the secondary winding of the transformer Tb are shifted by shifting the voltage phase of the connection point B2 with respect to the voltage phase of the connection point B1 based on the current detected by the current detection circuit 12. The voltage generated at both ends of the series circuit with the winding S is controlled to adjust the output voltage V0 (the voltage across the capacitor C0).

  Next, the operation of the thus configured DC / AC inverter according to the first embodiment will be described in detail with reference to timing charts shown in FIGS. FIG. 2 is a timing chart of signals at various parts when the input voltage of the DC / AC inverter according to the first embodiment of the present invention is low. FIG. 3 is a timing chart of signals at various parts when the input voltage of the DC / AC inverter according to the first embodiment of the present invention is high.

  2 and 3, Q1v is the drain-source voltage of the switch element Q1, Q1i is the drain current of the switch element Q1, Q3v is the drain-source voltage of the switch element Q3, Q3i is the drain current of the switch element Q3, and Lfi. Is the current of the reactor Lf, and Vo is the output voltage.

  First, at time t0, when the switch element Q3 is turned on, the switch elements Q1 and Q4 are turned off, and the switch element Q2 is turned on, a positive voltage is applied to the primary winding P of the transformer Tb, and Vdc1 → C6 → L6. A resonance current flows along a path of P → Q2 → Vdc1. A positive voltage is generated in the dot (●) direction in the secondary winding S and the tertiary winding Th of the transformer Tb. Similarly, a positive voltage is applied to the primary winding P of the transformer Ta, and a resonance current flows through a path of Vdc1 → Q3 → C5 → L5 → P → Vdc1. A positive voltage is generated in the dot (●) direction in the secondary winding S and the tertiary winding Th of the transformer Ta. Accordingly, since the secondary winding S of the transformer Ta and the secondary winding S of the transformer Tb are connected in series, the number of turns of the secondary winding S of the transformers Ta and Tb is equal at both ends of the series circuit. Then, a positive voltage approximately twice the voltage generated in the secondary winding S of the transformers Ta and Tb is generated, and the high frequency component is removed by the reactor L2 and the capacitor C0. High voltage is generated. The CCFL 14 is lit by this high voltage.

  Since the tertiary winding Th of the transformer Ta and the tertiary winding Th of the transformer Tb are connected in series, the number of turns of the tertiary winding Th of the transformers Ta and Tb is equal at both ends of the series circuit. Then, zero voltage is generated. Accordingly, no voltage is applied to the reactor Lf.

  Next, when the switch element Q2 is turned on, the switch elements Q1 and Q4 are turned off, and the switch element Q3 is turned off at the time t1 after the period T1 has elapsed from the time t0, it is stored in the exciting inductance of the transformer Ta. A current flows through the primary winding P due to the energy, the capacitor C4 is discharged, and the capacitor C3 is charged. When the discharge of the capacitor C4 is completed, the diode D4 becomes conductive, and a current flows through a path of P → D4 → C5 → L5 → P. At this time, when the switch element Q4 is turned on, the switch element Q4 performs a ZVS operation. Further, a negative voltage is applied to the primary winding P of the transformer Ta, and a negative voltage is generated in the dot (●) direction in the secondary winding S and the tertiary winding Th of the transformer Ta. Accordingly, zero voltage is generated at both ends of the series circuit of the secondary winding S of the transformer Ta and the secondary winding S of the transformer Tb.

  In addition, a voltage approximately twice the voltage generated in the tertiary winding Th of the transformers Ta and Tb is generated at both ends of the series circuit of the tertiary winding Th of the transformer Ta and the tertiary winding Th of the transformer Tb. To do. This voltage is applied to the reactor Lf, and a current flows linearly.

  Next, when the switch element Q4 is turned on, the switch elements Q1 and Q3 are turned off, and the switch element Q2 is turned off at the time t2 after the period T2 has elapsed from the time t1, the energy stored in the reactor Lf is 1 A current flows through the next winding P, the capacitor C1 is discharged, and the capacitor C2 is charged. That is, it is considered that the energy stored in the exciting inductance of the transformer Tb is increased by applying a voltage to the reactor Lf.

  When the discharge of the capacitor C1 is completed, the diode D1 becomes conductive, and a current flows through a path of P → D1 → C6 → L6 → P. At this time, when the switch element Q1 is turned on, the switch element Q1 performs a ZVS operation. Further, a negative voltage is applied to the primary winding P of the transformer Tb, and a negative voltage is generated in the dot (●) direction in the secondary winding S and the tertiary winding Th of the transformer Tb. Accordingly, a negative voltage approximately twice as large is generated at both ends of the series circuit of the secondary winding S of the transformer Ta and the secondary winding S of the transformer Tb.

  A zero voltage is generated at both ends of the series circuit of the tertiary winding Th of the transformer Ta and the tertiary winding Th of the transformer Tb. Accordingly, no voltage is applied to the reactor Lf.

  Next, when the switch element Q1 is turned on, the switch elements Q2 and Q3 are turned off, and the switch element Q4 is turned off at the time t3 after the period T3 has elapsed from the time t2, the switch element Q4 is stored in the exciting inductance of the transformer Ta. A current flows through the primary winding P due to the energy, the capacitor C3 is discharged, and the capacitor C4 is charged. When the discharge of the capacitor C3 is completed, the diode D3 becomes conductive, and a current flows through a path of P → L5 → C5 → D3 → Vdc1 → P. At this time, when the switch element Q3 is turned on, the switch element Q3 performs a ZVS operation. Further, a positive voltage is applied to the primary winding P of the transformer Ta, and a positive voltage is generated in the dot (●) direction in the secondary winding S and the tertiary winding Th of the transformer Ta. Accordingly, zero voltage is generated at both ends of the series circuit of the secondary winding S of the transformer Ta and the secondary winding S of the transformer Tb.

  In addition, a voltage approximately doubled is generated at both ends of the series circuit of the tertiary winding Th of the transformer Ta and the tertiary winding Th of the transformer Tb. This voltage is applied to the reactor Lf, and a current flows linearly.

  Next, when the switch element Q3 is turned on, the switch elements Q2 and Q4 are turned off, and the switch element Q1 is turned off at the time t4 after the period T4 has elapsed from the time t3, the energy stored in the reactor Lf is 1 A current flows through the next winding P, the capacitor C2 is discharged, and the capacitor C1 is charged. When the discharge of the capacitor C2 is completed, the diode D2 becomes conductive, and a current flows through a path of P → L6 → C6 → Vdc1 → D2 → P. At this time, when the switch element Q2 is turned on, the switch element Q2 performs a ZVS operation. When switch element Q2 is turned on, the operation after time t0 is repeated.

  The output voltage Vo generates an AC voltage that is twice the secondary output of the transformer Ta (or Tb) in the periods T1 and T3 and becomes zero in the periods T2 and T4.

  Here, if the phase between both converters is adjusted by the control circuit 10 performing on / off timing control of the switch elements Q1 to Q4, the time ratio between the periods T1 and T3 and the periods T2 and T4 is adjusted. The output voltage Vo can be adjusted. FIG. 2 shows a case where the input voltage is low. The periods T1 and T3 are long and the periods T2 and T4 are short. FIG. 3 shows a case where the input voltage is high, the periods T1 and T3 are short, the periods T2. It can be seen that the output voltage Vo is adjusted by increasing T4.

  When the input voltage is high, in the case of the conventional method, as shown in FIG. 9, the phase of the output current advances at time t14 (t10) and becomes substantially zero. Accordingly, the current Tnpi of the primary winding P of the transformer T is also zero at this time, and even when the switch element Q2 is turned off, no current flows and the voltages of the capacitors C1 and C2 do not change. For this reason, the ZVS operation of the switch element Q1 cannot be performed, and a hard switch is formed as shown in FIG. 8 to generate a spike current. As a result, switching loss increases and noise also increases.

  On the other hand, in Example 1, the current Lfi flows through the reactor Lf during the periods T2 and T4 when the sum of the voltages of the secondary windings S becomes zero. Further, when the input voltage is high, the phase is controlled and the periods T2 and T4 are lengthened, so that the current Lfi of the reactor Lf further increases.

  When the input voltage is high, a large amount of energy is required to charge (discharge) the capacitors C1 to C4 of the switching elements Q1 to Q4, and therefore the current of the reactor Lf needs to be large.

  According to the first embodiment, when the input voltage is low, the current Lfi of the reactor Lf is low, and when the input voltage is high, the current Lfi of the reactor Lf is high. Therefore, the current Lfi of the reactor Lf is higher than the input voltage. Can be optimized. For this reason, even when the input voltage rises and the phase of the output current advances with respect to the voltage of the switch element, the resonance current of the switch elements Q1 to Q4 can be optimized by the delay current of the reactor Lf.

  As shown in FIG. 3, even when the input voltage is high, current flows at times t2 and t4, and the ZVS operation of the switch elements Q1 and Q2 can be performed. Accordingly, since a spike current component is not generated from the current flowing through the switch elements Q1 and Q2, switching loss can be reduced, efficiency can be improved, and noise can be reduced.

  In the above embodiment, the configuration in which the series circuit of the capacitor C6, the reactor L6, and the primary winding P of the transformer Tb is connected in parallel to the switch element Q1 is shown. However, this series circuit is parallel to the switch element Q2. The structure connected to may be sufficient. In addition, the configuration in which the series circuit of the capacitor C5, the reactor L5, and the primary winding P of the transformer Ta is connected in parallel to the switch element Q4 is shown, but this series circuit is connected in parallel to the switch element Q3. It may be.

(Example of a magnetic circuit integrating a transformer and a reactor)
FIG. 4 is a diagram illustrating a magnetic circuit in which the transformer and the reactor of the DC / AC inverter according to the first embodiment are integrated. FIG. 4 shows a method for integrating the transformer and the reactor.

  As shown in FIG. 4A, the transformer Ta in the / AC inverter of the first embodiment includes a primary winding P and a secondary winding S on a first leg 21a of a core made of a magnetic material in which a closed magnetic circuit is formed. Are wound in a loosely coupled manner, and the third winding Th is tightly coupled with the primary winding P around the second leg 21b of the core. The transformer Tb is wound by loosely coupling the primary winding P and the secondary winding S to the first leg 22b of the core in which a closed magnetic circuit is formed, and the tertiary winding Th is wound on the second leg 22a of the core. The primary winding P is tightly coupled and wound.

  The reactor Lf is configured by winding a winding W around a first leg 23a of a core in which a gap (gap) is formed. A gap 24 is formed in the second leg 23b of the core.

  The transformer Ta, the transformer Tb, and the reactor Lf are connected as shown in FIG. Thereby, even if the cores of the transformer Ta, the transformer Tb, and the reactor Lf shown in FIG.

  In the magnetic circuit shown in FIG. 4C, the primary winding P and the secondary winding S of the transformer Ta are wound around the first leg 30a of the core 30 in which the closed magnetic circuit is formed, and the transformer Ta is wound around the second leg 30b. The third winding 30 is wound, the winding W is wound on the third leg 30c, the primary winding P and the secondary winding S of the transformer Tb are wound on the fourth leg 30d, and the fifth leg 30e is wound. A tertiary winding Th of the transformer Tb is wound, and a gap 34 is formed in the sixth leg 30f. The magnetic flux passing through the tertiary winding Th of the transformer Ta is Φ1, the magnetic flux passing through the winding W of the reactor Lf is Φ2, and the magnetic flux passing through the tertiary winding Th of the transformer Tb is Φ3.

  Here, since the tertiary winding Th of the transformer Ta, the tertiary winding Th of the transformer Tb, and the reactor Lf are connected in a ring shape (closed loop shape), the voltage of the tertiary winding Th of the transformer Ta is Assuming that V1, the voltage of the winding W of the reactor Lf is V2, and the voltage of the tertiary winding Th of the transformer Tb is V3, the sum of the voltages generated in the windings Th, W, Th is V1 + V2 + V3 = 0. .

  When the number of turns of each winding Th, W, Th is equal and the number of turns is N, the magnetic flux Φ of the core around which the winding is wound is dΦ / dt = V. Since zero is zero, the total magnetic flux change of the core is also zero. Therefore, even if the magnetic circuit shown in FIG. 4A is replaced with the magnetic circuit shown in FIG. 4C, the total magnetic flux is Φ1 + Φ2 + Φ3 = 0, so that the operation is not affected.

  Further, since Φ1 + Φ2 + Φ3 = 0, all three legs of the leg 30b through which the magnetic flux Φ1 passes, the leg 30c through which the magnetic flux Φ2 passes, and the leg 30e through which the magnetic flux Φ3 passes are removed, and the magnetic circuit as shown in FIG. Does not affect the operation. In the magnetic circuit shown in FIG. 4D, the primary winding P and the secondary winding S of the transformer Ta are wound around the first leg 40a of the core 40 in which the closed magnetic circuit is formed, and the transformer Tb is wound around the second leg 40b. The primary winding P and the secondary winding S are wound, and a gap 44 is formed in the third leg 40c. That is, the magnetic circuit can be reduced in size.

  In this way, by using the core consisting of three legs, the two transformers and the reactor can be simplified, and the circuit configuration can be simplified.

  FIG. 5 is an example of a transformer in the DC / AC inverter according to the first embodiment of the present invention. The transformer shown in FIG. 5 shows the transformer shown in FIG. 4 (d) in more detail. The transformer shown in FIG. 5 has a sun-shaped core 20, and a gap between the core portion 20a that is the center leg of the core 20 21 is formed.

  A primary winding P and a secondary winding S are wound in close proximity to each of the side leg 20b and the side leg 20c of the core 20. The secondary winding S is divided into a winding Sa, a winding Sb, a winding Sc, and a winding Sd. Accordingly, a leakage inductance is provided between the primary winding P and the secondary winding S, and this leakage inductance is used as the reactor L2.

  Further, the magnetizing inductance is set to an appropriate value by inserting the gap 21. Further, when driving the CCFL 14, a high voltage of 1 KV or more is necessary, and therefore, by dividing the secondary winding S into the winding Sa, the winding Sb, the winding Sc, and the winding Sd, a stray capacitor is obtained. And withstand voltage are improved.

  FIG. 6 shows a CCFL driving unit using a balancer circuit in the DC / AC inverter according to the first embodiment of the present invention. In FIG. 6, it is for the backlight of a large-sized liquid crystal television, and is configured using a plurality of CCFLs 14-1 to 14-n. In this case, a series circuit of a plurality of CCFLs 14-1 to 14-n connected in parallel and the balancer circuit 16 (corresponding to the balancer circuit of the present invention) is connected to both ends of the capacitor C0. By correcting the impedance of the plurality of CCFLs 14-1 to 14-n by the balancer circuit 16, the currents of the plurality of CCFLs 14-1 to 14-n can be balanced and can be lit well.

  As described above, in the present invention, even when a plurality of CCFLs 14-1 to 14-n are turned on by two transformers Ta and Tb, the switching loss is small, so that a small-capacity switch element can be used, which is small and highly efficient. A simple discharge lamp lighting system.

It is a circuit block diagram of the DC / AC inverter of Example 1 of this invention. It is a timing chart of the signal of each part when the input voltage of the DC / AC inverter of Example 1 of this invention is low. It is a timing chart of the signal of each part in case the input voltage of the DC / AC inverter of Example 1 of this invention is high. It is a figure which shows the magnetic circuit which integrated the transformer and reactor of the DC / AC inverter of Example 1 of this invention. It is an example of the transformer in the DC / AC inverter of Example 1 of the present invention. It is a CCFL drive part using the balancer circuit in the DC / AC inverter of Example 1 of this invention. It is a circuit block diagram of the conventional DC / AC inverter. It is a timing chart of the signal of each part when the input voltage of the conventional DC / AC inverter is low. It is a timing chart of the signal of each part in case the input voltage of the conventional DC / AC inverter is high.

Explanation of symbols

Vdc1 DC power supplies L2, L5, L6, Lf Reactors Q1 to Q4 Switch elements T, Ta, Tb Transformer P Primary winding S Secondary windings D1 to D4 Diodes C0 to C6 Capacitors 10, 10a Control circuit 12 Current detection circuit 14 CCFL
16 Balancer circuit 20 Core 20a Core part 21 Gap

Claims (5)

A first switching circuit in which a first switch element and a second switch element are connected in series at both ends of a DC power supply, and a first capacitor and a primary winding of a first transformer at both ends of the first or second switch element. A first converter having a first series circuit connected to each other in series;
A second switching circuit in which a third switch element and a fourth switch element are connected in series at both ends of the DC power supply; a primary capacitor and a second transformer at both ends of the third or fourth switch element; A second converter having a second series circuit connected in series with the line;
A low pass filter connected to both ends of a series circuit of the secondary winding of the first transformer and the secondary winding of the second transformer;
For each of the first and second converters, one switch element and the other switch element are alternately turned on / off to adjust the phase between the first and second converters, thereby connecting to the output terminal of the low-pass filter. A control circuit for adjusting the output voltage to the connected load;
A first reactor connected to both ends of a series circuit in which the tertiary winding of the first transformer and the tertiary winding of the second transformer are connected in series;
A DC / AC inverter characterized by comprising:   A voltage resonance capacitor and a diode are connected to both ends of the first, second, third, and fourth switch elements, and output by the current of the first reactor and the current of the exciting inductance of the first and second transformers. 2. The DC / AC inverter according to claim 1, wherein the first, second, third, and fourth switching elements are subjected to zero voltage switching operation by delaying a phase of current.   A first leg to a third leg having a closed magnetic path formed thereon, and a primary winding and a secondary winding of the first transformer are wound around the first leg of the core; The primary winding and the secondary winding of the second transformer are wound around the second leg, and a gap is formed in the third leg of the core. DC / AC inverter.   The low-pass filter includes a reactor and a capacitor. The reactor includes a leakage inductance between a primary winding and a secondary winding of the first and second transformers. The low-pass filter includes the leakage inductance and the leakage inductance. The DC / AC inverter according to any one of claims 1 to 3, wherein the output voltage is made sinusoidal by the capacitor. The load includes a plurality of cold cathode tubes,
5. The DC according to claim 1, further comprising a balancer circuit connected in series to the plurality of cold cathode tubes and balancing currents of the plurality of cold cathode tubes. / AC inverter.

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