JP2009055767A - Switching power supply unit - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To realize zero-bolt switching at low cost without requiring a resonance circuit like resonance inductance. <P>SOLUTION: A half-bridge converter is provided with first and second switching elements Q1, Q2, first and second voltage dividing capacitors C3, C4, an output transformer T that induces a predetermined voltage to the secondary side by alternately switching on and off the first and second switching elements, and first and second rectifier diodes D1, D2, smoothing chalk coil L2 and capacitor C2 that rectify and smoothen the voltage induced on the secondary side. The half-bridge converter shuts off the connection between the midpoint and the capacitor C2 of a secondary coil by a third switching element Q3 and discharges parasitic capacity by letting the first reflux current flow to the second switching element to make the voltage between the source and the drain of the second switching element zero so that the first reflux current does not leak to the secondary side right after the first switching element turns off. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a switching power supply device such as a half-bridge converter that converts a DC voltage into a predetermined voltage, for example.

  FIG. 3 is a circuit configuration diagram showing a schematic configuration inside a basic half-bridge converter.

  A half-bridge converter 100 shown in FIG. 3 includes a capacitor C1 connected between one end and the other end of the DC power supply E, and a first switching element Q1 and a second switching element Q2 connected between one end and the other end of the DC power supply E. A series circuit, a series circuit of a first voltage dividing capacitor C3 and a second voltage dividing capacitor C4 connected between one end and the other end of the DC power supply E, a primary winding T1, and a center tap type secondary winding T1 and a first voltage dividing capacitor C3 and a second voltage dividing capacitor C4 with a midpoint of interconnection A1 between the first switching element Q1 and the second switching element Q2 at one end of the primary winding T1. And an output transformer T that connects the interconnection midpoint A2 to the other end of the primary winding T1, a first rectifier diode D1 that connects to one end and the other end of the secondary winding T2, respectively. The second rectifier diode D2, the smoothing choke coil L2 connected to the cathode side of the first rectifier diode D1 and the second rectifier diode D2, and one end of the smooth choke coil L2 and the middle point A3 of the secondary winding T2 are connected. The capacitor C2 and the drive control circuit 101 that alternately turns ON / OFF the first switching element Q1 and the second switching element Q2 are provided.

  The output transformer T alternately turns ON / OFF the first switching element Q1 and the second switching element Q2, so that the secondary winding T2 corresponds to the exciting current IL1 flowing in the exciting inductance L1 on the primary winding T1 side. To induce an alternating current component of a predetermined voltage.

  The first switching element Q1 is composed of a field effect transistor (FET) and includes a parasitic diode DQ1 and a parasitic capacitor CQ1, and the second switching element Q2 similarly includes a parasitic diode DQ2 and a parasitic capacitor CQ2. And

  Next, the basic operation of the basic half-bridge converter 100 will be described. FIG. 4 is a timing chart briefly showing the basic operation of the half bridge 100.

  When the first switching element Q1 is driven ON while the second switching element Q2 is OFF, the drive control circuit 101 direct current power supply E → first switching element Q1 → interconnecting midpoint A1 → excitation inductance L1 and primary winding T1 → Current flows through the path of the interconnection midpoint A2 → second voltage dividing capacitor C4 → DC power supply E.

  As a result, as shown in FIG. 4, the drain-source voltage Q1Vds of the first switching element Q1 is 0 (V), and the drain-source voltage Q2Vds of the second switching element Q2 is equivalent to Vin (V) of the DC power supply E. Therefore, the excitation current IL1 flowing through the excitation inductance L1 gradually increases in the positive direction.

  In the secondary winding T2 of the output transformer T, an induced voltage is generated in response to an increase in the exciting current IL1 of the exciting inductance L1, and the induced voltage of this AC component is rectified by the first rectifier diode D1, and this rectified induced voltage is rectified. Is smoothed by the smoothing choke coil L2, and the first DC current Id1 is output as the output current, and the capacitor C2 is charged. At this time, the second DC current Id2 is zero.

  Next, when the first switching element Q1 is turned from ON to OFF, the drive control circuit 101 also turns off the second switching element Q2. Therefore, the drain-source voltage Q1Vds of the first switching element Q1 is also Vin / 2 ( V), since the drain-source voltage Q2Vds of the second switching element Q2 is also Vin / 2 (V), the first return current IL1 is generated in response to the release of the excitation energy accumulated in the excitation inductance L1.

  Further, in the smooth choke coil L2, when the first switching element Q1 and the second switching element Q2 are turned OFF, the second return current IL2 is generated in response to the release of the excitation energy accumulated in the smooth choke coil L2, and the smooth choke coil L2 → capacitor C2 → secondary winding T2 middle point A3 → secondary winding T2 → first rectifier diode D1 → smooth choke coil L2 path and smooth choke coil L2 → capacitor C2 → secondary winding T2 The second return current IL2 flows through the path of point A3 → secondary winding T2 → second rectifier diode D2 → smoothing choke coil L2.

  Further, the excitation inductance L1 on the primary winding T1 side causes the first return current IL1 to flow to the second rectifier diode D2 side via the output transformer T in response to the release of the accumulated excitation energy, and the second rectifier diode D2 has the second One return current IL1 + second return current IL2 flows.

  Thereafter, when the second switching element Q2 is turned ON while the first switching element Q1 is OFF, the drive control circuit 101 direct current power supply E → first voltage dividing capacitor C3 → interconnecting midpoint A2 → excitation inductance L1 and A current flows through the path of the primary winding T1 → interconnection middle point A1 → second switching element Q2 → DC power supply E.

  As a result, as shown in FIG. 4, the drain-source voltage Q2Vds of the second switching element Q2 is 0 (V), and the drain-source voltage Q1Vds of the first switching element Q1 is equivalent to Vin (V) of the DC power supply E. Therefore, the excitation current IL1 flowing through the excitation inductance L1 gradually increases in the negative direction.

  In the secondary winding T2 of the output transformer T, an induced voltage is generated in response to a negative increase in the exciting current IL1 of the exciting inductance L1, and the induced voltage of the AC component is rectified by the second rectifier diode D2, and this rectification is performed. The AC component thus smoothed is smoothed by the smoothing choke coil L2, and the second DC current Id2 is output as the output current, and the capacitor C2 is charged. At this time, the first DC current Id1 is zero.

  Next, when the second switching element Q2 is turned off from the ON state, the drive control circuit 101 also turns off the first switching element Q1, so that the drain-source voltage Q2Vds of the second switching element Q2 is also Vin / 2 ( V) Since the drain-source voltage Q1Vds of the first switching element Q1 is also Vin / 2 (V), the first return current IL1 is generated according to the release of the excitation energy accumulated in the excitation inductance L1.

  Further, the smooth choke coil L2 generates the second return current IL2 in response to the release of the excitation energy accumulated in the smooth choke coil L2 when the first switching element Q1 and the second switching element Q2 are turned OFF, and the smooth choke coil L2 → capacitor C2 → secondary winding T2 middle point A3 → secondary winding T2 → first rectifier diode D1 → smooth choke coil L2 path and smooth choke coil L2 → capacitor C2 → secondary winding T2 The second return current IL2 flows through the path of point A3 → secondary winding T2 → second rectifier diode D2 → smoothing choke coil L2.

  Further, the excitation inductance L1 on the primary winding T1 side causes the first return current IL1 to flow into the first rectifier diode D1 via the output transformer T in response to the release of the accumulated excitation energy, and the first rectifier diode D1 has the first The return current IL1 + the second return current IL2 flows.

  Therefore, according to the conventional half-bridge converter 100, the first switching element Q1 and the second switching element Q2 are alternately turned ON / OFF, so that the secondary of the output transformer T1 corresponds to the exciting current IL1 of the exciting inductance L1. An AC component induced voltage is generated in the winding T2, and the induced voltage is rectified and smoothed to obtain the first DC current Id1 and the second DC current Id2 as desired output currents.

  However, according to such a conventional half-bridge converter 100, the first switching element Q1 and the second switching element Q2 are alternately turned ON / OFF, so that the output transformer T1 corresponds to the exciting current IL1 of the exciting inductance L1. An induced voltage of an alternating current component is generated in the secondary winding T2 and a desired direct current is obtained by rectifying and smoothing the induced voltage. For example, when the first switching element Q1 is turned on, Since the parasitic capacitance of the parasitic capacitor CQ1 is present, the drain-source voltage Q1Vds cannot maintain the zero volt state, resulting in a switching loss. Even when the second switching element Q2 is turned on, the drain-source voltage Q2Vds cannot be maintained at the zero volt state due to the parasitic capacitance of the parasitic capacitor CQ2, and switching loss occurs.

  Therefore, in order to reduce such switching loss, for example, when the first switching element Q1 is turned ON, the drain-source voltage Q1Vds of the first switching element Q1 is maintained in the zero volt state, and the first switching element Q1 A device that employs a zero volt switching method in which switching loss during ON driving is significantly reduced is widely known (for example, see Patent Document 1).

Conventionally, as a half-bridge converter adopting such a zero volt switching method, a series circuit of a first switching element and a second switching element connected between one end and the other end of a DC power supply and between one end and the other end of the DC power supply The first voltage dividing capacitor and the second voltage dividing capacitor connected in series to a series circuit, a primary winding and a secondary winding, and the interconnection midpoint between the first switching element and the second switching element is the primary An output transformer that connects the interconnection midpoint between the first voltage dividing capacitor and the second voltage dividing capacitor to the other end of the primary winding at one end of the winding, and a rectifier circuit that is connected to both ends of the secondary winding A smoothing choke coil connected to the rectifier circuit, a smoothing capacitor connected to one end of the smoothing choke coil and one end of the rectifier circuit, a first switch A switching power supply device such as a half-bridge converter having an element and a drive control circuit for alternately turning ON / OFF the second switching element, wherein the first voltage dividing capacitor and the second voltage dividing capacitor are being interconnected A parallel resonance circuit composed of a resonance inductance and a resonance capacitor connected between the point and the primary winding is arranged, and for example, the first switching element (second switching element) During ON driving, a reverse resonance current is passed through the parasitic capacitance of the first switching element (second switching element), the source-drain voltage of the first switching element (second switching element) is set to zero volts, and the first switching element ( Zero volts eliminates power loss that occurs when the second switching element is turned on. It realizes the etching.
JP 2000-125560 A (see paragraph numbers “0002” to “0005” and FIG. 5)

  However, according to the switching power supply device such as the half-bridge converter of Patent Document 1 described above, zero volt switching is realized using the resonance operation of the parallel resonance circuit of the resonance capacitor and the resonance inductance. In order for the resonance current to flow in the direction of regenerating parasitic capacitance when the switching element (second switching element) is turned on, it is necessary to ensure a predetermined inductance value of the resonance inductance, but the inductance value varies and is inexpensive. The resonance inductance cannot be used, and it is necessary to secure a high-precision and expensive resonance inductance that can stably obtain a predetermined inductance value.

  Furthermore, according to the switching power supply device of Patent Document 1, zero volt switching is realized by using the resonance operation of a parallel resonance circuit of a resonance capacitor and a resonance inductance. Therefore, the resonance current flowing through the resonance inductance is smaller than that of the capacitor, and it is necessary to provide an external inductance separately in order to increase the inductance value.

  Therefore, the present invention has been made in view of the above points, and an object of the present invention is to provide a switching power supply device that reliably realizes zero-volt switching at low cost without requiring a resonance circuit such as a resonance inductance. There is to do.

  In order to achieve the above object, a switching power supply of the present invention includes a first switching element and a second switching element connected between one end and the other end of a power supply, and a first voltage connected between one end and the other end of the power supply. A dividing capacitor and a second voltage dividing capacitor, an interconnection midpoint between the first switching element and the second switching element, and an interconnection midpoint between the first voltage dividing capacitor and the second voltage dividing capacitor And the first switching element and the second switching element are alternately turned ON / OFF, so that the secondary winding of the center tap method on the secondary side according to the exciting current of the primary winding of the primary side. A switch having an output transformer that induces an alternating current of a predetermined voltage on the wire, and a rectifier circuit that rectifies the alternating current of the predetermined voltage induced in the secondary winding and outputs the direct current. And a switch means for cutting off the connection between the midpoint of the secondary winding and the rectifier circuit, and the switch means for cutting off the connection between the midpoint of the secondary winding and the rectifier circuit. A primary current generated immediately after one of the first switching element and the second switching element is turned off. In order to prevent the primary-side return current generated on the side from leaking to the secondary winding, the switch means interrupts the connection between the middle point of the secondary winding and the rectifier circuit, and the primary-side return current is By supplying to the other switching element, the parasitic capacitance of the switching element is discharged, and the voltage between the terminals of the switching element is set to zero volts.

  In the switching power supply device of the present invention, in the configuration of the switching power supply device of the present invention, a primary-side return current generated immediately after one of the first switching element and the second switching element is turned off is In order not to leak into the secondary winding, the switch means cuts off the connection between the middle point of the secondary winding and the rectifier circuit, and supplies the primary-side return current to the other switching element. The parasitic capacitance of the switching element was discharged to set the voltage between the terminals of the switching element to zero volts, and then the switching element was turned on.

  In the switching power supply device of the present invention, the charge amount of the primary-side return current is larger than the parasitic capacitance of the switching element in the configuration of the switching power supply device of the present invention.

  The switching power supply of the present invention is the above-described configuration of the switching power supply of the present invention, wherein the first switching element and the second switching element are composed of field effect transistors, and the inter-terminal voltage is between the source and drain. It was made to correspond to the voltage between terminals.

  According to the switching power supply device of the present invention configured as described above, the switching means for cutting off the connection between the midpoint of the secondary winding and the rectifier circuit, And a current return means for returning a secondary return current generated inside the rectifier circuit when the connection between the point and the rectifier circuit is cut off, and switching between one of the first switching element and the second switching element In order not to leak the primary return current generated on the primary side immediately after the element is turned off to the secondary winding, the connection between the middle point of the secondary winding and the rectifier circuit is interrupted by the switch means, By supplying the primary-side return current to the other switching element, the parasitic capacitance of the switching element is discharged so that the voltage between the terminals of the switching element becomes zero volts. Without using a resonance circuit composed of the resonance inductance, it is possible to realize a stable zero volt switching at low cost.

  Further, according to the switching power supply device of the present invention, the primary-side return current generated immediately after one of the first switching element and the second switching element is turned off does not leak to the secondary winding. The switching means cuts off the connection between the middle point of the secondary winding and the rectifier circuit, and supplies the primary return current to the other switching element, thereby discharging the parasitic capacitance of the switching element. Since the switching element is turned on after the inter-terminal voltage of the switching element is set to zero volts, the switching loss of the switching element can be greatly reduced.

  Further, according to the switching power supply device of the present invention, since the charge amount of the primary side return current is made larger than the parasitic capacitance of the switching element, stable zero volt switching can be realized.

  According to the switching power supply device of the present invention, the first switching element and the second switching element are configured by field effect transistors, and the terminal voltage corresponds to the terminal voltage between the source and the drain. Therefore, stable zero volt switching can be realized.

  Hereinafter, a half-bridge converter showing an embodiment related to a switching power supply device of the present invention will be described based on the drawings. FIG. 1 is a block diagram showing a schematic configuration inside the half bridge converter according to the present embodiment. In addition, the same code | symbol shall be attached | subjected about the structure same as the half-bridge converter 100 shown in FIG.

  The half-bridge converter 1 shown in FIG. 1 includes a capacitor C1 connected between one end and the other end of a DC power supply E, and a first switching element Q1 and a second switching element Q2 connected between one end and the other end of the DC power supply E. A series circuit, a series circuit of a first voltage dividing capacitor C3 and a second voltage dividing capacitor C4 connected between one end and the other end of the DC power supply E, a primary winding T1, and a center tap type secondary winding T1 and a first voltage dividing capacitor C3 and a second voltage dividing capacitor C4 with a midpoint of interconnection A1 between the first switching element Q1 and the second switching element Q2 at one end of the primary winding T1. An output transformer T that connects the interconnection midpoint A2 to the other end of the primary winding T1, a first rectifier diode D1 that connects to one end and the other end of the secondary winding T2, and A rectifying diode D2, a smoothing choke coil L2 connected to the cathode side of the first rectifying diode D1 and the second rectifying diode D2, and a capacitor C2 connected to one end of the smoothing choke coil L2 and a midpoint A3 of the secondary winding T2. A third switching element Q3 that cuts off the connection between the middle point A3 of the secondary winding T2 and the capacitor C2, and between the middle point A3 of the secondary winding T2 and the capacitor C2 at the third switching element Q3. When the connection is cut off, the freewheeling diode D3 that recirculates the second return current IL2 corresponding to the excitation energy of the smoothing choke coil L2 to the smoothing choke coil L2, the first switching element Q1, the second switching element Q2, and the third switching element Q3. And a drive control circuit 11 for driving ON / OFF.

  The first switching element Q1 is composed of an FET and includes a parasitic capacitor CQ1 and a parasitic diode DQ1. Similarly, the second switching element Q2 includes a parasitic capacitor CQ2 and a parasitic diode DQ2.

  The output transformer T alternately turns ON / OFF the first switching element Q1 and the second switching element Q2, so that the secondary winding T2 corresponds to the exciting current IL1 flowing in the exciting inductance L1 on the primary winding T1 side. To induce an alternating current component of a predetermined voltage.

  In addition, the drive control circuit 11 is configured such that, for example, the first return current IL1 generated by the exciting inductance IL1 on the primary winding T1 side immediately after the second switching element Q2 is turned off from the second time when the first switching element Q1 is off is the secondary. The third switching element Q3 is driven from ON to OFF so as not to leak into the winding T2, the connection between the middle point A3 of the secondary winding T2 and the capacitor C2 is cut off, and the second return generated in the smooth choke coil L2 The current flows through the current path of the smooth choke coil L2, the capacitor C2, the freewheeling diode D3, and the smooth choke coil L2. As a result, it is possible to cope with a situation in which the energy stored in the capacitor C2 is reduced due to the second return current returning through the current path.

  Further, the drive control circuit 11 drives the third switching element Q3 from ON to OFF, and when the connection between the middle point A3 of the secondary winding T2 and the capacitor C2 is cut off, the first return current generated in the excitation inductance L1 IL1 does not leak into the secondary winding T2, and the first return current IL1 discharges the parasitic capacitance on the parasitic capacitor CQ1 side of the first switching element Q1 to make the drain-source voltage Q1Vds of the first switching element Q1 zero volts. Thereafter, the first switching element Q1 is driven from OFF to ON. When the charge amount QL1 of the first return current IL1 = IL1 * T (time second) and the parasitic capacitance (charge amount) Q10 = Vin / 2 * CQ1 of the first switching element Q1, the condition of QL1> Q10 is satisfied. Shall.

  In addition, when the first switching element Q1 and the third switching element Q3 are turned ON, the drive control circuit 11 direct current power supply E → first switching element Q1 → interconnection middle point A1 → excitation inductance L1 and primary winding T1 → A current path of the interconnection midpoint A2 → second voltage dividing capacitor C4 → DC power supply E is formed, and an AC component is applied to the first rectifier diode D1 side on the secondary winding T2 side according to the excitation current IL1 of the excitation inductance L1. The induced voltage is generated.

  When an induced voltage of an AC component is generated on the first rectifier diode D1 side on the secondary winding T2 side, the first rectifier diode D1, the smoothing choke coil L2, the capacitor C2, the third switching element Q3, the secondary winding T2, and the like. The first DC current Id1 flows through the current path of the first rectifier diode D1, and the first DC current Id1 is charged as an output current to the capacitor C2 via the first rectifier diode D1 and the smoothing choke coil L2.

  In addition, the drive control circuit 11 causes the first return current IL1 generated by the primary side excitation inductance L1 to be applied to the secondary winding T2 immediately after the first switching element Q1 is turned off after the second switching element Q2 is turned off. To prevent leakage, the third switching element Q3 is driven from ON to OFF, the connection between the middle point A3 of the secondary winding T2 and the capacitor C2 is cut off, and the second return current generated by the smoothing choke coil L2 is smoothed into the choke. The current path of the coil L2 → capacitor C2 → reflux diode D3 → smoothing choke coil L2 is passed. As a result, it is possible to cope with a situation in which the energy stored in the capacitor C2 is reduced due to the second return current returning through the current path.

  Further, the drive control circuit 11 drives the third switching element Q3 from ON to OFF, and when the connection between the middle point A3 of the secondary winding T2 and the capacitor C2 is cut off, the first return current generated in the excitation inductance L1 IL1 does not leak into the secondary winding T2, and the first return current IL1 discharges the parasitic capacitance on the parasitic capacitor CQ2 side of the second switching element Q2 to make the drain-source voltage Q2Vds of the second switching element Q2 zero volts. Thereafter, the second switching element Q2 is driven from OFF to ON. When the charge amount QL1 of the first return current IL1 = IL1 * T (time second) and the parasitic capacitance (charge amount) Q20 = Vin / 2 * CQ2 of the second switching element Q2, the condition of QL1> Q20 is satisfied. Shall.

  Further, when the second switching element Q2 and the third switching element Q3 are ON-driven, the drive control circuit 11 is connected to the DC power source E → the first voltage dividing capacitor C3 → the interconnection midpoint A2 → the exciting inductance L1 and the primary winding. A current path of T1 → interconnecting midpoint A1 → second switching element Q2 → DC power supply E is formed, and an AC component is applied to the second rectifier diode D2 side of the secondary winding T2 in accordance with the exciting current IL1 of the exciting inductance L1. The induced voltage is generated.

  When an induced voltage of an AC component is generated on the second rectifier diode D2 side on the secondary winding T2, the second rectifier diode D2, the smoothing choke coil L2, the capacitor C2, the third switching element Q3, the secondary winding T2, and the like. The second DC current Id2 flows through the current path of the second rectifier diode D2, and the second DC current Id2 is charged as an output current to the capacitor C2 via the second rectifier diode D2 and the smoothing choke coil L2.

  The drive control circuit 11 also turns the third switching element Q3 from ON to OFF immediately after the first switching element Q1 is turned off, for example, and immediately before the next second switching element is turned from OFF to ON. The third switching element Q3 is turned ON at the timing when the first switching element Q1 is turned ON, and immediately before the next first switching element Q1 is turned ON from OFF, the third switching element Q3 is turned OFF from ON, and the first switching element Q1 is turned ON. A predetermined cycle for driving the third switching element Q3 to ON is set in advance at the timing to turn on / off the first switching element Q1, the second switching element Q2, and the third switching element Q3 based on the set predetermined period. It controls the OFF timing.

  The switching power supply device according to the present invention is the half-bridge converter 1, the power supply is the DC power supply E, the first switching element is the first switching element Q1, the second switching element is the second switching element Q2, and the first voltage dividing capacitor is The first voltage dividing capacitor C3, the second voltage dividing capacitor is the second voltage dividing capacitor C4, the primary winding is the primary winding T1, the secondary winding is the secondary winding T2, the output transformer is the output transformer T, The rectifier circuit corresponds to the first rectifier diode D1 and the second rectifier diode D2, the switch means corresponds to the third switching element Q3, and the current return means corresponds to the return diode D3.

  Next, the operation of the half bridge converter 1 showing the present embodiment will be described. FIG. 2 is a timing chart briefly showing the operation of the half-bridge converter 1 showing the present embodiment.

  When the second switching element Q2 is OFF and the third switching element Q3 is ON, the drive control circuit 11 turns on the first switching element Q1, and the DC power supply E → the first switching element Q1 → the interconnection midpoint A1. → Current flows through the path of exciting inductance L1 and primary winding T1 → interconnection middle point A2 → second voltage dividing capacitor C4 → DC power supply E.

  As a result, as shown in FIG. 2, the drain-source voltage Q1Vds of the first switching element Q1 is 0 (V), and the drain-source voltage Q2Vds of the second switching element Q2 is equivalent to Vin (V) of the DC power supply E. Therefore, the drain-source current Q1Ids of the first switching element Q1 flows, and the exciting current IL1 flowing in the exciting inductance L1 gradually increases in the positive direction.

  In the secondary winding T2 of the output transformer T, an induced voltage is generated in response to an increase in the exciting current IL1 of the exciting inductance L1, and the AC component of the induced voltage is rectified by the first rectifier diode D1, and this rectified AC component is rectified. Is smoothed by the smoothing choke coil L2, and the first DC current Id1 is output as the output current, and the capacitor C2 is charged. At this time, the second DC current Id2 and the third DC current Id3 are zero.

  Thereafter, when the first switching element Q1 is driven from ON to OFF, the drive control circuit 11 has the drain / source of the first switching element Q1 because the second switching element Q2 is OFF and the third switching element Q3 is ON. Since the inter-voltage Q1Vds is also Vin / 2 (V) and the drain-source voltage Q2Vds of the second switching element Q2 is also Vin / 2 (V), the source-drain between the first switching element Q1 and the second switching element Q2 The currents Q1Ids and Q2Ids stop flowing, and the first return current IL1 is generated in response to the release of the excitation energy accumulated in the excitation inductance L1.

  Further, the secondary smoothing choke coil L2 generates the second return current IL2 in response to the release of the excitation energy accumulated in the smoothing choke coil L2 when the first switching element Q1 and the second switching element Q2 are turned off. Smooth choke coil L2 → capacitor C2 → third switching element Q3 → middle point A3 of secondary winding T2 → secondary winding T2 → first rectifier diode D1 → first current path of smooth choke coil L2 and smooth choke Coil L2 → capacitor C2 → third switching element Q3 → secondary winding T2 midpoint A3 → secondary winding T2 → second rectifier diode D2 → second choke coil L2 second current path and smooth choke coil L2 → The second return current IL2 flows through the capacitor C2, the return diode D3, and the third current path of the smoothing choke coil L2. . Note that the first return current IL1 of the primary side excitation inductance L1 leaks into the second current path, and the sum of the first return current IL1 and the second return current IL2 flows.

  At this time, when the third switching element Q3 is driven from ON to OFF while the first switching element Q1 and the second switching element Q2 are OFF, the connection between the midpoint A3 of the secondary winding T2 and the capacitor C2 is cut off. The second return current IL2 generated in the smooth choke coil L2 flows through the current path of the smooth choke coil L2, the capacitor C2, the return diode D3, and the smooth choke coil L2, and the first return current from the primary side to the secondary side. There is no leakage of IL1.

  As a result, the first return current IL1 is blocked from flowing into the secondary side, so that the second voltage dividing capacitor C4 is charged and flows in the direction from the source to the drain of the second switching element Q2. The parasitic capacitance of the parasitic capacitor CQ2 of the switching element Q2 is discharged, and the drain-source voltage Q2Vds of the second switching element Q2 gradually becomes zero volts from Vin / 2 (V).

  Thereafter, when the drain-source voltage Q2Vds of the second switching element Q2 becomes zero volts, the drive control circuit 11 drives the second switching element Q2 and the third switching element Q3 from OFF to DC power supply E → first voltage. A current flows through the path of the dividing capacitor C3 → interconnecting midpoint A2 → excitation inductance L1 and primary winding T1 → interconnecting midpoint A1 → second switching element Q2 → DC power supply E.

  As a result, as shown in FIG. 2, the drain-source voltage Q2Vds of the second switching element Q2 is 0 (V), and the drain-source voltage Q2Vds of the first switching element Q1 is equivalent to Vin (V) of the DC power supply E. Therefore, the drain-source current Q2Ids of the second switching element Q2 flows, and the exciting current IL1 flowing through the exciting inductance L1 gradually increases in the negative direction.

  In the secondary winding T2 of the output transformer T, an induced voltage is generated in response to a negative increase in the exciting current IL1 of the exciting inductance L1, and the AC component of this induced voltage is rectified by the second rectifier diode D2, and this rectification is performed. The AC component thus smoothed is smoothed by the smoothing choke coil L2, and the second DC current Id2 is output to charge the capacitor C2. At this time, the first DC current Id1 and the third DC current Id3 are zero.

  Thereafter, when the second switching element Q2 is driven from ON to OFF, the drive control circuit 11 has the drain / source of the second switching element Q2 because the first switching element Q1 is OFF and the third switching element Q3 is ON. Since the inter-voltage Q2Vds is also Vin / 2 (V), the drain-source currents Q1Ids and Q2Ids of the first switching element Q1 and the second switching element Q2 do not flow, and according to the release of the excitation energy accumulated in the excitation inductance L2. Thus, the first return current IL1 is generated.

  Further, the secondary smoothing choke coil L2 generates the second return current IL2 in response to the release of the excitation energy accumulated in the smoothing choke coil L2 when the first switching element Q1 and the second switching element Q2 are turned off. Smooth choke coil L2 → capacitor C2 → third switching element Q3 → middle point A3 of secondary winding T2 → secondary winding T2 → first rectifier diode D1 → first current path of smooth choke coil L2 and smooth choke Coil L2 → capacitor C2 → third switching element Q3 → secondary winding T2 midpoint A3 → secondary winding T2 → second rectifier diode D2 → second choke coil L2 second current path and smooth choke coil L2 → The second return current IL2 flows through the capacitor C2, the return diode D3, and the third current path of the smoothing choke coil L2. . Note that the first return current IL1 of the primary side excitation inductance L1 leaks into the first current path, and the sum of the first return current IL1 and the second return current IL2 flows.

  At this time, when the third switching element O3 is driven from ON to OFF while the first switching element Q1 and the second switching element Q2 are OFF, the drive control circuit 11 is between the middle point A3 of the secondary winding T2 and the capacitor C2. And the second return current IL2 generated in the smooth choke coil L2 is returned in the current path of the smooth choke coil L2, the capacitor C2, the return diode D3, and the smooth choke coil L2, and the secondary side from the primary side. There is no leakage of the first return current IL1.

  As a result, the first return current IL1 flows in the direction from the source to the drain of the first switching element Q3 by blocking the current flow to the secondary side, and the parasitic capacitance of the parasitic capacitor CQ1 of the first switching element Q1 is reduced. As a result, the drain-source voltage Q1Vds of the first switching element Q1 gradually becomes zero volts from Vin / 2 (V).

  Thereafter, at the timing when the drain-source voltage Q1Vds of the first switching element Q1 becomes zero volts, the drive control circuit 11 drives the first switching element Q1 and the third switching element Q3 from OFF to DC power supply E → second The current flows through the path of 1 switching element Q1 → interconnecting midpoint A1 → excitation inductance L1 and primary winding T1 → interconnecting midpoint A2 → second voltage dividing capacitor C4 → DC power supply E.

  As a result, as shown in FIG. 2, the drain-source voltage Q1Vds of the first switching element Q1 is 0 (V), and the drain-source voltage Q2Vds of the second switching element Q2 is equivalent to Vin (V) of the DC power supply E. Therefore, the drain-source current Q1Ids of the first switching element Q1 flows, and the exciting current IL1 flowing in the exciting inductance L1 gradually increases in the positive direction.

  According to the present embodiment, the third switching element Q3 that cuts off the connection between the midpoint A3 of the secondary winding T2 and the capacitor C2, and the midpoint A3 of the secondary winding T2 at the third switching element Q3 and A free-wheeling diode D3 that recirculates the second free-wheeling current IL2 generated inside the smoothing choke coil L2 when the connection between the capacitors C2 is interrupted, and one of the first switching element Q1 and the second switching element Q2 is the switching element Q1 In order to prevent the first return current IL1 generated in the primary side excitation inductance L1 from leaking to the secondary winding T2 immediately after turning off (Q2), the third switching element Q3 causes the middle point A3 of the secondary winding T2 and By disconnecting the connection between the capacitors C2 and passing the first return current IL1 from the source to the drain of the other switching element Q2 (Q1), the switch The parasitic capacitance of the switching element Q2 (Q1) is discharged so that the drain-source voltage Q2Vds (Q1Vds) of the switching element Q2 (Q1) is set to zero volts. Stable zero volt switching can be realized at low cost without using a circuit.

  Further, according to the present embodiment, the first return current IL1 generated immediately after the switching element Q1 (Q2) of the first switching element Q1 and the second switching element Q2 is turned off is applied to the secondary winding T2. In order to prevent leakage, the connection between the middle point A3 of the secondary winding T2 and the capacitor C2 is cut off by the third switching element Q3, and the first return current IL1 is transferred from the source to the drain of the other switching element Q2 (Q1). Since the parasitic capacitance of the switching element is discharged and the drain-source voltage Q2Vds (Q1Vds) of the switching element Q2 (Q1) is set to zero volts, the switching element is driven ON. The switching loss of the element can be greatly reduced.

  In addition, according to the present embodiment, the charge amount QL1 of the first return current IL1 is larger than the parasitic capacitance Q10 (parasitic capacitance Q20) of the first switching element Q1 (second switching element Q2), and thus stable. Zero volt switching can be realized.

  According to the switching power supply device of the present invention, of the first switching element and the second switching element, the primary-side return current generated on the primary side immediately after one of the switching elements is turned off does not leak to the secondary winding. The connection between the middle point of the secondary winding and the rectifier circuit is interrupted by the switch means, and the primary side return current is supplied to the other switching element, so that the parasitic capacitance of the switching element is discharged. Since the voltage between terminals is set to zero volts, stable zero-volt switching can be realized at low cost without using a conventional resonant circuit composed of a resonant inductance. For example, a half-bridge converter It is useful for switching power supply devices such as.

It is a circuit block diagram which shows schematic structure inside the half bridge converter which shows embodiment in connection with the switching power supply device of this invention. It is a timing chart which shows the operation | movement inside the half bridge converter which shows this Embodiment. It is a circuit block diagram which shows schematic structure inside a general half bridge converter. It is a timing chart which shows the operation | movement inside a general half bridge converter.

Explanation of symbols

1 Half-bridge converter (switching power supply)
E DC power supply (power supply)
Q1 1st switching element Q2 2nd switching element Q3 3rd switching element (switch means)
C3 First voltage dividing capacitor C4 Second voltage dividing capacitor T Output transformer T1 Primary winding T2 Secondary winding L2 Smooth choke coil (rectifier circuit)
D1 First rectifier diode (rectifier circuit)
D2 Second rectifier diode (rectifier circuit)
D3 Reflux diode (current reflux means)

Claims (4)

A first switching element and a second switching element connected between one end and the other end of the power source; a first voltage dividing capacitor and a second voltage dividing capacitor connected between one end and the other end of the power source; The switching element and the second switching element are connected to an interconnection midpoint and to the interconnection midpoint between the first voltage dividing capacitor and the second voltage dividing capacitor, and the first switching element and the second switching element are connected. An output transformer that induces alternating current of a predetermined voltage in the secondary winding of the center tap type on the secondary side according to the exciting current of the primary winding on the primary side by alternately driving the elements ON / OFF; A switching power supply device having a rectifying circuit that rectifies and outputs a predetermined voltage alternating current induced in the next winding,
Switch means for cutting off the connection between the midpoint of the secondary winding and the rectifier circuit;
Current recirculation means for recirculating secondary return current generated inside the rectifier circuit when the connection between the middle point of the secondary winding and the rectifier circuit is cut off by the switch means;
Of the first switching element and the second switching element, the switch means prevents the primary-side return current generated on the primary side immediately after turning off one of the switching elements from leaking to the secondary winding. By disconnecting the connection between the midpoint of the secondary winding and the rectifier circuit and supplying the primary-side return current to the other switching element, the parasitic capacitance of the switching element is discharged, and the voltage across the terminals of the switching element A switching power supply characterized by setting zero to zero volts.   Of the first switching element and the second switching element, the secondary winding is switched by the switch means so that the primary-side return current generated immediately after turning off one of the switching elements does not leak to the secondary winding. The connection between the rectifier circuit and the rectifier circuit is cut off, and the primary side return current is supplied to the other switching element, thereby discharging the parasitic capacitance of the switching element and reducing the voltage across the switching element to zero volts. The switching power supply device according to claim 1, wherein the switching element is turned on. The charge amount of the primary reflux current is
The switching power supply device according to claim 2, wherein the switching power supply device is larger than a parasitic capacitance of the switching element. The said 1st switching element and a 2nd switching element are comprised with a field effect transistor, The said voltage between terminals is corresponded to the voltage between terminals between a source and a drain, The Claim 1, 2, or 3 characterized by the above-mentioned. Switching power supply.

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