JP2010088259A - Switching power supply and control method thereof - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a synchronous rectification type switching power supply capable of suppressing degradation of efficiency due to increasing power loss. <P>SOLUTION: The synchronous rectification type switching power supply 1 includes a switching circuit 80 for changing gate voltage of switching elements 141 and 142. The switching circuit 80 includes capacitors 81 and 82 which charge/discharge according to respective voltages of the third secondary winding 101d and the fourth secondary winding 101e, a switching element 184 whose gate is connected to the capacitor 81, and a switching element 183 whose gate is connected to the capacitor 82. The capacitor 81 discharges to the gate of the switching element 184 as the voltage of the third secondary winding 101d drops. If the electric charges discharged from the capacitor 81 come to be a predetermined quantity when the voltage of the third secondary winding 101d drops down to VG1, the switching element 184 comes to be on-state for discharging electric charges of the gate of the switching element 141. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a switching power supply device, and more particularly, to a synchronous rectification switching power supply device and a control method for the synchronous rectification switching power supply device.

  Conventionally, a synchronous rectification switching power supply is known as a switching power supply.

  FIG. 8 is a circuit diagram of a synchronous rectification switching power supply apparatus 100 according to a conventional example. The synchronous rectification switching power supply apparatus 100 supplies a DC voltage to a load 102, and is provided on a transformer 101, a full bridge circuit 120 provided on the primary side of the transformer 101, and a secondary side of the transformer 101. Rectifier circuit 140, smoothing circuit 160, and switching circuit 180.

  The full bridge circuit 120 includes a DC power supply 121 and four switching elements 122, 123, 124, and 125 made of MOSFETs. The positive electrode side of the DC power supply 121 is connected to the drain of the switching element 122 and the drain of the switching element 124, and the negative electrode side of the DC power supply 121 is connected to the source of the switching element 123, the source of the switching element 125, Is connected. The source of the switching element 122 is connected to the drain of the switching element 123 and one end of the primary winding 101a of the transformer 101. The source of the switching element 124 is connected to the drain of the switching element 125 and the primary winding. The other end side of the line 101a is connected. A control circuit (not shown) is connected to the gates of the switching elements 122 to 125.

  The control circuit (not shown) supplies control signals to the gates of the switching elements 122 to 125, respectively, and controls the on / off of the switching elements 122 to 125. Specifically, a procedure of applying a positive voltage to the gates of the switching elements 122 and 125 (hereinafter referred to as “first procedure”) and a procedure of applying a positive voltage to the gates of the switching elements 123 and 124 (hereinafter referred to as “the first procedure”). 2nd procedure "). In the first procedure, the switching elements 122 and 125 are turned on, and in the second procedure, the switching elements 123 and 124 are turned on.

  In the above-described full bridge circuit 120, the control circuit (not shown) alternately performs the first procedure and the second procedure described above at a predetermined cycle, so that the switching elements 122 and 125, the switching elements 123 and 124, Are alternately turned on at predetermined intervals. According to this, a rectangular wave voltage is applied to the primary winding 101a based on the DC voltage output from the DC power supply 121.

  In addition to the above-described primary winding 101a, the transformer 101 includes a first secondary winding 101b, a second secondary winding 101c, a third secondary winding 101d, and a fourth secondary winding. 101e. The first secondary winding 101b and the second secondary winding 101c are connected by the center tap A, and the third secondary winding 101d and the fourth secondary winding 101e are the center tap B. Connected by. Each of the first secondary winding 101b, the second secondary winding 101c, the third secondary winding 101d, and the fourth secondary winding 101e is applied to the primary winding 101a. Based on the obtained voltage, a voltage corresponding to the turn ratio with the primary winding 101a is generated. Here, the number of turns of each of the primary winding 101a, the first secondary winding 101b, the second secondary winding 101c, the third secondary winding 101d, and the fourth secondary winding 101e is , Shall be equal.

  Here, as described above, the voltage applied to the primary winding 101a is a rectangular wave voltage. Therefore, the voltage generated in each of the first secondary winding 101b, the second secondary winding 101c, the third secondary winding 101d, and the fourth secondary winding 101e is also a rectangular wave voltage. Become.

  The rectifier circuit 140 includes two switching elements 141 and 142 made of MOSFETs. One end of the first secondary winding 101b is connected to the drain of the switching element 141. One end side of the second secondary winding 101c is connected to the other end side of the first secondary winding 101b via the center tap A, and the second secondary winding is connected to the drain of the switching element 142. The other end of 101c is connected. A source of a switching element 184 described later is connected to the gate of the switching element 141, and a source of a switching element 183 described later is connected to the gate of the switching element 142. A center tap B and one end side of a smoothing inductor 161 described later are connected to the source of the switching element 141 and the source of the switching element 142.

  The switching circuit 180 includes diodes 181 and 182 and two switching elements 183 and 184 formed of MOSFETs. The gate of the switching element 183 is connected to the anode of the diode 181 and one end side of the third secondary winding 101d. The other end side of the third secondary winding 101d is connected to one end side of the fourth secondary winding 101e via the center tap B. The gate of the switching element 184 is connected to the anode of the diode 182 and the second end of the third secondary winding 101d. 4 is connected to the other end of the secondary winding 101e. The source of the switching element 183 is connected to the cathode of the diode 181 and the gate of the switching element 142. The source of the switching element 184 is connected to the cathode of the diode 182 and the gate of the switching element 141. A center tap B is connected to the drain of the switching element 183 and the drain of the switching element 184.

  Here, as described above, the voltage generated in the third secondary winding 101d and the fourth secondary winding 101e is a rectangular wave voltage. For this reason, a period in which a positive voltage is applied to the gate of the switching element 183 and a period in which a positive voltage is applied to the gate of the switching element 184 alternately occur at a predetermined cycle. According to this, the switching element 183 and the switching element 184 are alternately turned on at a predetermined cycle.

  When the switching element 183 is turned on, the switching element 142 whose gate is connected to the source of the switching element 183 is turned on. On the other hand, when the switching element 184 is turned on, the switching element 141 whose gate is connected to the source of the switching element 184 is turned on. For this reason, the switching element 141 and the switching element 142 are alternately turned on at a predetermined cycle.

  As a result, as described above, the voltages generated in the first secondary winding 101b and the second secondary winding 101c are rectangular wave voltages, but these rectangular wave voltages are rectified by the rectifier circuit 140 and pulsed. The current is supplied to the smoothing circuit 160 as a current voltage.

  The smoothing circuit 160 includes a smoothing inductor 161 and a smoothing capacitor 162. The source of the switching element 141, the source of the switching element 142, and the center tap B are connected to one end side of the smoothing inductor 161. The other end side of the smoothing inductor 161 is connected to an electrode on one end side of the smoothing capacitor 162 and one end side of the load 102. The other end side of the load 102 and the center tap A are connected to the electrode on the other end side of the smoothing capacitor 162.

  The pulsating voltage supplied from the rectifier circuit 140 is smoothed by the smoothing capacitor 162 and ripples are removed by the smoothing inductor 161. As a result, a DC voltage is supplied to the load 102.

  FIG. 9 is a timing chart of the synchronous rectification switching power supply apparatus 100 according to the conventional example. Vgs 141 represents a gate-source voltage of the switching element 141, and Vgs 142 represents a gate-source voltage of the switching element 142. The switching element 141 is on when the voltage Vgs 141 is a positive voltage VGH, and is off when the voltage Vgs 141 is VGL. Similarly to the switching element 141, the switching element 142 is on when the voltage Vgs 142 is a positive voltage, and is off when the voltage Vgs 142 is VGL. Id 141 represents the drain current of the switching element 141.

  From time t1 to t2, the voltage Vgs 141 changes from VGL to VGH, and the voltage Vgs 142 changes from VGH to VGL. For this reason, the switching element 141 transitions from the off state to the on state, and the switching element 142 transitions from the on state to the off state.

  Here, the voltage Vgs 142 changes from VGH to VGL in the period from the time t1 to the time t2. The voltage on one end side of the third secondary winding 101d is lowered, and one end of the third secondary winding 101d is reduced. This is because the switching element 183 whose gate is connected to the side transitions from the on state to the off state. However, the voltage at one end of the third secondary winding 101d becomes dull when it falls due to the influence of the exciting current of the transformer 101 and the parasitic capacitance. For this reason, the timing at which the switching element 183 transitions from the on state to the off state is delayed, the timing at which the voltage Vgs 142 changes from VGH to VGL is delayed, and as a result, the timing at which the switching element 142 transitions from the on state to the off state is delayed. It will be. Therefore, a period in which both switching element 141 and switching element 142 are both on is generated, a through current flows through switching elements 141 and 142, and current Id 141 temporarily rises to ID3.

  On the other hand, from time t3 to t4, the voltage Vgs141 changes from VGH to VGL, and the voltage Vgs142 changes from VGL to VGH. For this reason, the switching element 141 changes from the on state to the off state, and the switching element 142 changes from the off state to the on state.

  Here, the voltage Vgs 141 changes from VGH to VGL in the period from the time t3 to the time t4 because the voltage on the other end side of the fourth secondary winding 101e is lowered and the voltage of the fourth secondary winding 101e is reduced. This is because the switching element 184 whose gate is connected to the other end side transitions from the on state to the off state. However, the voltage at the other end of the fourth secondary winding 101e becomes dull due to the influence of the exciting current of the transformer 101 and parasitic capacitance. For this reason, the timing at which the switching element 184 transitions from the on state to the off state is delayed, the timing at which the voltage Vgs 141 changes from VGH to VGL is delayed, and as a result, the timing at which the switching element 141 transitions from the on state to the off state is delayed. It will be. Therefore, a period in which both the switching element 141 and the switching element 142 are turned on occurs, a through current flows through the switching elements 141 and 142, and the current Id141 temporarily decreases to ID0.

  As described above, when a through current flows through the switching elements 141 and 142, power loss may increase or the switching elements 141 and 142 may be damaged.

Thus, a synchronous rectification switching power supply device has been proposed in which such two switching elements are alternately turned on with a predetermined dead time period interposed therebetween (see, for example, Patent Document 1). According to this synchronous rectification type switching power supply device, it is possible to suppress the occurrence of a period in which both of the two switching elements are in the ON state, and to suppress a through current from flowing through the switching element.
JP 2002-354799 A

  FIG. 10 shows an example of a synchronous rectification switching power supply apparatus 100 according to a conventional example, in which switching elements 141 and 142 are alternately arranged with a dead time period (for example, a period from time t2a to t1 or a period from time t4 to t3a). It is a timing chart in the case of setting to an ON state. LOSS 141 indicates power loss caused by a parasitic diode between the drain and source of the switching element 141.

  Here, when a load current flows through the load 102 during the dead time period, a parasitic diode between the drain and source of the switching element 141 and between the drain and source of the switching element 142 even if the switching elements 141 and 142 are in the OFF state. In this parasitic diode, a switching current corresponding to the load current flows, and power loss occurs. For this reason, as shown in FIG. 10, the power loss LOSS 141 is large in the dead time period.

  As described above, in the conventional synchronous rectification switching power supply device, when the load current increases in the dead time period, the power loss generated in the parasitic diode between the drain and the source of the switching element may increase, and the efficiency may decrease. there were.

  In view of the above-described problems, an object of the present invention is to provide a synchronous rectification switching power supply device that can suppress an increase in power loss and a decrease in efficiency.

The present invention proposes the following items in order to solve the above-described problems.
(1) The present invention rectifies the voltage generated in the first secondary winding of the transformer by the switching operation of the transformer, the voltage supply circuit for supplying the rectangular wave voltage to the primary winding of the transformer, and the switching element. A synchronous rectification type switching power supply device comprising: a rectifying circuit for switching; and a switching circuit for changing a voltage of a control terminal of the switching element, wherein the switching circuit is a voltage generated in a second secondary winding of the transformer And a switching unit connected to the charging / discharging unit, the charging / discharging unit charging as the voltage generated in the second secondary winding decreases. The switching unit discharges the charged electric charge to the switching unit, and the switching unit reduces the voltage generated in the second secondary winding to a predetermined value and discharges the electric charge discharged from the charging / discharging unit. There becomes a predetermined amount, it proposed a synchronous rectification type switching power supply device, characterized in that to discharge the control terminals of the switching element.

  According to this invention, as the voltage generated in the second secondary winding decreases by the charging / discharging unit, the charged charge is discharged to the switching unit. When the voltage generated in the second secondary winding is lowered to a predetermined value by the switching unit and the electric charge discharged from the charging / discharging unit reaches a predetermined amount, the electric charge at the control terminal of the switching element is discharged.

  For this reason, when the voltage generated in the second secondary winding decreases to a predetermined value, the switching circuit can turn off the switching element and prevent the timing at which the switching element transitions from the on state to the off state from being delayed. . Therefore, it is possible to shorten the dead time period while suppressing the through current from flowing through the switching element, and it is possible to suppress power loss that occurs during the dead time period and to suppress a decrease in efficiency.

  (2) The present invention relates to the synchronous rectification switching power supply device according to (1), wherein the first secondary winding includes two unit secondary windings connected by a center tap, and the rectifier circuit includes: The present invention proposes a synchronous rectification type switching power supply device that rectifies a voltage generated at both ends of the first secondary winding.

  According to the present invention, the first secondary winding includes the two unit secondary windings connected by the center tap, and the voltage generated at both ends of the first secondary winding is rectified by the rectifier circuit. can do.

  (3) The present invention proposes a synchronous rectification type switching power supply apparatus according to (1), wherein the rectification circuit is a double current rectification circuit.

  According to the present invention, a double current rectifier circuit can be used as the rectifier circuit.

  (4) The present invention rectifies the voltage generated in the first secondary winding of the transformer by the switching operation of the transformer, the voltage supply circuit for supplying the rectangular wave voltage to the primary winding of the transformer, and the switching element. And a switching circuit for changing a voltage at a control terminal of the switching element, wherein the switching circuit includes a second secondary winding of the transformer. The charging / discharging part which charges / discharges according to the voltage which arises in this and the switching part connected to the said charging / discharging part are provided, The voltage which arises in a said 2nd secondary winding falls by the said charging / discharging part. In accordance with the first step of discharging the charged charge to the switching unit, the voltage generated in the second secondary winding is reduced to a predetermined value by the switching unit. And a second step of discharging the charge of the control terminal of the switching element when the charge discharged from the charging / discharging unit reaches a predetermined amount. Proposed method.

  According to this invention, as the voltage generated in the second secondary winding decreases by the charging / discharging unit, the charged charge is discharged to the switching unit. When the voltage generated in the second secondary winding is lowered to a predetermined value by the switching unit and the electric charge discharged from the charging / discharging unit reaches a predetermined amount, the electric charge at the control terminal of the switching element is discharged.

  For this reason, when the voltage generated in the second secondary winding decreases to a predetermined value, the switching circuit can turn off the switching element and prevent the timing at which the switching element transitions from the on state to the off state from being delayed. . Therefore, it is possible to shorten the dead time period while suppressing the through current from flowing through the switching element, and it is possible to suppress power loss that occurs during the dead time period and to suppress a decrease in efficiency.

  According to the present invention, when the voltage generated in the second secondary winding decreases to a predetermined value, the switching circuit turns off the switching element, and the timing at which the switching element transitions from the on state to the off state is delayed. Can be prevented. Therefore, it is possible to shorten the dead time period while suppressing the through current from flowing through the switching element, and it is possible to suppress power loss that occurs during the dead time period and to suppress a decrease in efficiency.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. Note that the constituent elements in the present embodiment can be appropriately replaced with existing constituent elements and the like, and various variations including combinations with other existing constituent elements are possible. Therefore, the description of the present embodiment does not limit the contents of the invention described in the claims. In the following description of the embodiments, the same constituent elements are denoted by the same reference numerals, and the description thereof is omitted or simplified.

<First Embodiment>
FIG. 1 is a circuit diagram of a synchronous rectification switching power supply device 1 according to a first embodiment of the present invention. The synchronous rectification switching power supply device 1 is different in the configuration of the switching circuit from the synchronous rectification switching power supply device 100 according to the conventional example shown in FIG. In the synchronous rectification switching power supply device 1, the same components as those of the synchronous rectification switching power supply device 100 are denoted by the same reference numerals, and the description thereof is omitted.

  The switching circuit 80 included in the synchronous rectification switching power supply device 1 includes a capacitor 81 as a charging / discharging unit that performs charging / discharging according to voltages of the third secondary winding 101d and the fourth secondary winding 101e, 82, switching elements 183 and 184 as switching units having gates connected to capacitors 81 and 82, diodes 83, 84, 181, and 182 and resistors 85 and 86, respectively.

  One end of the third secondary winding 101d and the anode of the diode 181 are connected to the electrode on one end of the capacitor 81, and the cathode of the diode 83 is connected to the electrode on the other end of the capacitor 81. The gate of the switching element 184 and one end side of the resistor 86 are connected. The center tap B, the source of the switching element 183, and the other end side of the resistor 85 are connected to the anode of the diode 83.

  The electrode on one end side of the capacitor 82 is connected to the other end side of the fourth secondary winding 101 e and the anode of the diode 182. The electrode on the other end side of the capacitor 82 is connected to the cathode of the diode 84. The gate of the switching element 183 and one end side of the resistor 85 are connected. The center tap B, the source of the switching element 184, and the other end side of the resistor 86 are connected to the anode of the diode 84.

  The switching circuit 80 described above makes the fall of the voltage between the gate and the source of the switching element 141 and the voltage between the gate and the source of the switching element 142 steep.

  2 and 3 are timing charts of the synchronous rectification switching power supply device 1. 4, 5, and 6 are equivalent circuits of the switching circuit 80 of the synchronous rectification switching power supply device 1. In FIG. 3, Vgs 184 indicates a gate-source voltage of the switching element 184.

  From time t13 to t14, the voltage Vgs 141 changes from VGL to VGH as shown in FIG. This is because the voltage at the other end of the fourth secondary winding 101e rises from VGL by the full bridge circuit 120, and at time t14, the voltage at the other end of the fourth secondary winding 101e becomes VGH. Because it becomes.

  Here, as shown in FIG. 4, the voltage on the other end side of the fourth secondary winding 101e from time t13 to t14 is Vx (provided that Vx satisfies VGL <Vx ≦ VGH). To do. During this period, the switching element 141 is turned on, so that the current Ix1 flows from the other end side of the fourth secondary winding 101e via the diode 182 and the switching element 141.

  Also, from time t13 to t14, the voltage Vgs 142 changes from VGH to VGL as shown in FIG. This is because the voltage at one end of the third secondary winding 101d drops from VGH by the full bridge circuit 120, and the voltage at one end of the third secondary winding 101d becomes VGL at time t14. It is.

  Here, as shown in FIG. 4, since the switching element 142 is turned off from time t13 to time t14, the current Ix2 is supplied to the capacitor 81 from the other end side of the third secondary winding 101d via the diode 83. The capacitor 81 is charged. Then, as shown in FIG. 5, when the voltage of the electrode on the other end of the capacitor 81 becomes equal to the voltage on the other end of the third secondary winding 101d, that is, VGH, the charging of the capacitor 81 is finished. To do.

  Here, from time t <b> 13 to t <b> 15, the voltage Vx on the other end side of the third secondary winding 101 d is supplied to the gate of the switching element 184 via the diode 83. However, as shown in FIGS. 4 and 5, if the contact point between the cathode of the diode 83 and the electrode on the other end side of the capacitor 81 is a contact point C, the voltage at the contact point C and the voltage at the center tap B are substantially equal. . For this reason, the voltage of the gate of the switching element 184 connected to the contact C is substantially equal to the voltage of the source of the switching element 184 connected to the center tap B. Therefore, from time t13 to t15, the switching element 184 is turned off.

  From time t15 to t16, the voltage Vgs 141 decreases from VGH to VG1, as shown in FIG. This is because the voltage at the other end of the fourth secondary winding 101e decreases from VGH by the full bridge circuit 120, and the voltage at the other end of the fourth secondary winding 101e becomes VG1 at time t16. Because it becomes.

  In addition, from time t15 to t16, the voltage on the other end side of the third secondary winding 101d also decreases in the same manner as the voltage on the other end side of the fourth secondary winding 101e. As the voltage at the other end of the winding 101d decreases, the voltage at the electrode at the other end of the capacitor 81 also decreases. Then, as shown in FIG. 6, the charge charged in the capacitor 81 moves to the gate of the switching element 184, and the current Iy2 flows from the electrode on the other end side of the capacitor 81 to the gate of the switching element 184 via the contact C. Will flow.

  Then, the gate-source voltage Vgs 184 of the switching element 184 rises, and at time t16, as shown in FIG. 3, the switching element 184 changes to Vth from the off state to the on state, and the switching element 184 is in the on state. Become. As a result, as shown in FIG. 6, a current Iy1 flows from the gate of the switching element 141 to the source of the switching element 141 via the switching element 184 in the on state, and the gate of the switching element 141 is discharged.

  Therefore, at time t16, the gate voltage of the switching element 141 rapidly decreases, and the voltage Vgs141 rapidly decreases from VG1 to VGL as shown in FIG.

  From time t16 to t17, it becomes a dead time period, and from time t17 to t18, the voltage Vgs142 changes from VGL to VGH.

  According to the synchronous rectification switching power supply device 1 described above, the switching element 141 is changed from the on state to the off state as follows. First, when the capacitor 81 is charged to switch the switching element 141 from the on state to the off state, the charge charged in the capacitor 81 is discharged to the gate of the switching element 184 to turn the switching element 184 on. . Then, the gate of the switching element 141 is discharged through the switching element 184 in the on state, and the gate-source voltage Vgs 141 of the switching element 141 is rapidly reduced.

  On the other hand, according to the above synchronous rectification switching power supply device 1, the switching element 142 is changed from the on state to the off state as follows. First, when the capacitor 82 is charged to switch the switching element 142 from the on state to the off state, the charge charged in the capacitor 82 is discharged to the gate of the switching element 183 to turn the switching element 183 on. . Then, the gate of the switching element 142 is discharged through the switching element 183 in the on state, and the gate-source voltage Vgs 142 of the switching element 142 is rapidly reduced.

  As described above, the dead time period can be shortened while suppressing the through current from flowing through the switching elements 141 and 142 at the same time. Therefore, it is possible to suppress power loss that occurs during the dead time period and to suppress a decrease in efficiency.

<Second Embodiment>
FIG. 7 is a circuit diagram of a synchronous rectification switching power supply apparatus 1A according to the second embodiment of the present invention. The synchronous rectification switching power supply device 1A is different from the synchronous rectification switching power supply device 1 in the configuration of the transformer and the configuration of the smoothing circuit.

  A transformer 101A included in the synchronous rectification switching power supply apparatus 1A is replaced with a first 2nd winding 101b and a second secondary winding 101c of the transformer 1 included in the synchronous rectification switching power supply apparatus 1 in the fifth 2 A next winding 101f is provided. The drain of the switching element 141 and one end side of a smoothing inductor 61 described later are connected to one end side of the fifth secondary winding 101f, and the other end side of the fifth secondary winding 101f is connected to the other end side of the fifth secondary winding 101f. The drain of the switching element 142 is connected to one end side of the smoothing inductor 62 described later. Note that the numbers of turns of the primary winding 101a, the third secondary winding 101d, the fourth secondary winding 101e, and the fifth secondary winding 101f are equal.

  A smoothing circuit 60A included in the synchronous rectification switching power supply device 1A includes smoothing inductors 61 and 62 and a smoothing capacitor 162. One end of the smoothing inductor 61 is connected to the drain of the switching element 141 and one end of the fifth secondary winding 101 f. The other end of the smoothing inductor 61 is connected to the smoothing capacitor 162. The electrode on one end side and the one end side of the load 102 are connected.

  The drain of the switching element 142 and the other end side of the fifth secondary winding 101f are connected to one end side of the smoothing inductor 62, and the smoothing capacitor 162 is connected to the other end side of the smoothing inductor 62. Are connected to one end side of the load 102 and one end side of the load 102.

  The other end side of the load 102, the source of the switching element 141, the source of the switching element 142, and the center tap B are connected to the electrode on the other end side of the smoothing capacitor 162.

  A synchronous rectification switching power supply device 1A including the above-described transformer 101A and smoothing circuit 60A has a so-called double current rectifier circuit. This synchronous rectification switching power supply device 1A can achieve the same effects as the synchronous rectification switching power supply device 1.

  In the above-described embodiment, the full bridge circuit 120 is provided on the primary side of the transformers 101 and 101A. However, the present invention is not limited to this. For example, instead of the full bridge circuit 120, a half bridge circuit or a push-pull circuit may be provided.

  The present invention is not limited to the above-described embodiments, and various modifications and applications can be made without departing from the gist of the present invention.

1 is a circuit diagram of a synchronous rectification switching power supply device according to a first embodiment of the present invention. 3 is a timing chart of the synchronous rectification switching power supply according to the first embodiment of the present invention. 3 is a timing chart of the synchronous rectification switching power supply according to the first embodiment of the present invention. It is an equivalent circuit of the switching circuit of the synchronous rectification type switching power supply device according to the first embodiment of the present invention. It is an equivalent circuit of the switching circuit of the synchronous rectification type switching power supply device according to the first embodiment of the present invention. It is an equivalent circuit of the switching circuit of the synchronous rectification type switching power supply device according to the first embodiment of the present invention. It is a circuit diagram of the synchronous rectification type | mold switching power supply device which concerns on the 2nd Embodiment of this invention. It is a circuit diagram of the synchronous rectification type switching power supply device which concerns on a prior art example. It is a timing chart of the synchronous rectification type switching power supply concerning a conventional example. It is a timing chart at the time of providing a dead time period in the synchronous rectification type switching power supply concerning a conventional example.

Explanation of symbols

1, 1A, 100; synchronous rectification type switching power supply device 60A, 160; smoothing circuit 80, 180; switching circuit 81, 82; capacitor 101, 101A; transformer 101a; primary winding 101b; Second secondary winding 101d; third secondary winding 101e; fourth secondary winding 101f; fifth secondary winding 102; load 120; full bridge circuit 121; DC power supply 122, 123 , 124, 125, 141, 142, 183, 184; switching element 140; rectifier circuit

Claims (4)

With a transformer,
A voltage supply circuit for supplying a rectangular wave voltage to the primary winding of the transformer;
A rectifier circuit for rectifying a voltage generated in the first secondary winding of the transformer by a switching operation of the switching element;
A switching circuit for changing a voltage of a control terminal of the switching element;
A synchronous rectification type switching power supply device comprising:
The switching circuit is
A charging / discharging unit that performs charging / discharging according to a voltage generated in the second secondary winding of the transformer;
A switching unit connected to the charge / discharge unit;
With
The charging / discharging unit discharges the charged charge to the switching unit as the voltage generated in the second secondary winding decreases,
The switching unit discharges the charge of the control terminal of the switching element when the voltage generated in the second secondary winding decreases to a predetermined value and the charge discharged from the charge / discharge unit reaches a predetermined amount. The synchronous rectification type switching power supply device characterized by the above. The first secondary winding includes two unit secondary windings connected by a center tap,
The synchronous rectification switching power supply device according to claim 1, wherein the rectifier circuit rectifies a voltage generated at both ends of the first secondary winding.   The synchronous rectification switching power supply device according to claim 1, wherein the rectifier circuit is a double current rectifier circuit. With a transformer,
A voltage supply circuit for supplying a rectangular wave voltage to the primary winding of the transformer;
A rectifier circuit for rectifying a voltage generated in the first secondary winding of the transformer by a switching operation of the switching element;
A switching circuit for changing a voltage of a control terminal of the switching element;
A control method for a synchronous rectification switching power supply device comprising:
The switching circuit is
A charging / discharging unit that performs charging / discharging according to a voltage generated in the second secondary winding of the transformer;
A switching unit connected to the charge / discharge unit;
With
A first step of discharging the charged charge to the switching unit as the voltage generated in the second secondary winding decreases by the charge / discharge unit;
When the voltage generated in the second secondary winding decreases to a predetermined value by the switching unit and the charge discharged from the charge / discharge unit reaches a predetermined amount, the charge of the control terminal of the switching element is discharged. A second step;
A control method for a synchronous rectification type switching power supply device comprising:

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