Switch driver and switching power supply using the same

Abstract

To suppress resonance noise generated when bidirectional on / off drive is stopped.SOLUTION: A switch drive device 130 comprises a controller 133 constituted to individually control a first switch element 110 and a second switch element 120 forming a bidirectional switch X. The controller 133 temporarily turns one of the first switch element 110 and the second switch element 120 on for predetermined ON time after turning both of the first switch element 110 and the second switch element 120 off when on / off drive of the bidirectional switch X is stopped.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The invention disclosed in this specification relates to a switch driver and a switching power supply using the same. [Background technology]

[0002] Conventionally, the applicant of the present application has proposed a switch driver capable of suppressing heat generation in a bidirectional switch by individually performing zero-voltage switching control (so-called ZVS [zero-volt switching] control) on a first switch element and a second switch element that form a bidirectional switch of a switching power supply (see Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent Publication No. 2021-13295 Summary of the Invention [Problem to be solved by the invention]

[0004] However, in the conventional switch drive device, there is room for improvement in suppressing the resonance noise that occurs when the on / off drive of the bidirectional switch is stopped.

[0005] In view of the above problems found by the inventors of the present application, the invention disclosed in this specification aims to provide a switch driver capable of suppressing resonance noise and a switching power supply using the same. [Means for solving the problem]

[0006] For example, the switch driving device disclosed in this specification has a controller configured to individually control a first switch element and a second switch element that form a bidirectional switch, and when stopping the on / off driving of the bidirectional switch, the controller turns off both the first switch element and the second switch element, and then temporarily turns on either the first switch element or the second switch element for a predetermined on-time.

[0007] However, other features, elements, steps, advantages, and characteristics will become more apparent from the detailed description that follows and the accompanying drawings related thereto. Effect of the Invention

[0008] According to the invention disclosed in this specification, it is possible to provide a switch driver capable of suppressing resonance noise, and a switching power supply using the same. [Brief description of the drawings]

[0009] [Figure 1] FIG. 1 is a diagram showing a first embodiment of a switching power supply. [Diagram 2] FIG. 2 is a diagram showing an equivalent circuit of a transformer. [Diagram 3] FIG. 3 is a diagram showing an equivalent circuit of a rectifier diode. [Figure 4] FIG. 4 is a diagram illustrating a first example of individual ZVS control. [Diagram 5] FIG. 5 is a diagram illustrating a second example of individual ZVS control. [Figure 6] FIG. 6 is a diagram illustrating a third example of individual ZVS control. [Figure 7] FIG. 7 is a diagram illustrating a fourth example of individual ZVS control. [Figure 8] FIG. 8 is a diagram showing a second embodiment of the switching power supply. [Figure 9] FIG. 9 is a diagram showing a third embodiment of a switching power supply. [Figure 10] FIG. 10 is a diagram showing a fourth embodiment of the switching power supply. [Figure 11] FIG. 11 is a diagram illustrating a fifth example of individual ZVS control. [Figure 12] FIG. 12 is a diagram showing a fifth embodiment of the switching power supply. [Figure 13] FIG. 13 is a diagram showing a sixth embodiment of the switching power supply. [Figure 14] FIG. 14 is a diagram showing a seventh embodiment of the switching power supply. [Figure 15] FIG. 15 is a diagram showing an eighth embodiment of the switching power supply. [Figure 16] FIG. 16 is a diagram showing a ninth embodiment of the switching power supply. [Figure 17] FIG. 17 is a diagram showing the decrease in efficiency due to the clamping operation. [Figure 18] FIG. 18 is a diagram illustrating an example of a configuration of a main part of a controller. [Figure 19] FIG. 19 is a diagram illustrating an example of internal control of the controller. [Figure 20] FIG. 20 is a diagram showing a tenth embodiment of the switching power supply. [Figure 21] FIG. 21 is a diagram showing a first operation example (V1>V2) of the individual ZVS control in the tenth embodiment. [Figure 22] FIG. 22 is a diagram showing a current path in the first phase of the first operation example. [Figure 23] FIG. 23 is a diagram showing a current path in the second phase of the first operation example. [Figure 24] FIG. 24 is a diagram showing a current path in the third phase of the first operation example. [Diagram 25] FIG. 25 is a diagram showing a current path in the fourth phase of the first operation example. [Figure 26] FIG. 26 is a diagram showing a current path in the fifth phase of the first operation example. [Figure 27] FIG. 27 is a diagram showing a current path in the sixth phase of the first operation example. [Figure 28] Figure 28 is a diagram showing a current path in the seventh phase of the first operation example. [Figure 29] Figure 29 is a diagram showing a second operation example (V1 < V2) of individual ZVS control in the tenth embodiment. [Diagram 30] Figure 30 is a diagram showing a current path in the first phase of the second operation example. [Diagram 31] Figure 31 is a diagram showing a current path in the second phase of the second operation example. [Diagram 32] Figure 32 is a diagram showing a current path in the third phase of the second operation example. [Diagram 33] Figure 33 is a diagram showing a current path in the fourth phase of the second operation example. [Diagram 34] Figure 34 is a diagram showing a current path in the fifth phase of the second operation example. [Diagram 35] Figure 35 is a diagram showing a current path in the sixth phase of the second operation example. [Diagram 36] Figure 36 is a diagram showing a current path in the seventh phase of the second operation example. [Figure 37] Figure 37 is a diagram showing the state when the on / off drive of the bidirectional switch is stopped at the polarity inversion timing of the AC input voltage. [Figure 38] Figure 38 is an enlarged view of region α in Figure 37. [Figure 39] Figure 39 is a diagram showing a first example of the drive stop process. [Diagram 40] Figure 40 is a diagram showing a second example of the drive stop process.

Embodiments for Carrying Out the Invention

[0010] <First Embodiment> 1 is a diagram showing a first embodiment of a switching power supply. The switching power supply 100 of this embodiment is an isolated AC / DC converter that directly converts an AC input voltage Vin (=V2-V1, for example, V1=GND) supplied from an AC power supply P into a DC output voltage Vout and supplies it to a load Z while electrically insulating a primary circuit system from a secondary circuit system, and includes switch elements 110 and 120, a switch driver 130, a transformer 140, capacitors 151 to 154, diodes 161 and 162, and a snubber circuit 170.

[0011] The switch elements 110 and 120 are connected in reverse in series between a second node (= an application end of the voltage V2) of the AC power supply P and a second input tap (= a winding start end of the primary winding 141) of the transformer 140. The switch elements 110 and 120 connected in this manner form a bidirectional switch X connected in series to the primary winding 141 of the transformer 140.

[0012] For example, when the switch elements 110 and 120 are Si-based or SiC-based NMOSFETs [N-channel type metal oxide semiconductor field effect transistors], the sources S of the switch elements 110 and 120 are common, the drain D of the switch element 110 is connected to a second node of the AC power supply P, and the drain D of the switch element 120 (= an application terminal of the switch voltage Vsw) is connected to a second input tap of the transformer 140. Note that, as the switch elements 110 and 120, GaN devices or IGBTs [insulated gate bipolar transistors] or the like may be used.

[0013] Moreover, the switch elements 110 and 120 include intrinsic diodes 112 and 122 and intrinsic capacitances 113 and 123, in addition to switch function units 111 and 121 (transistor bodies), respectively. In the case of this figure, the cathode of the intrinsic diode 112 and a first end of the intrinsic capacitance 113 are connected to the drain D of the switch function unit 111. Also, the anode of the intrinsic diode 112 and a second end of the intrinsic capacitance 113 are connected to the source S of the switch function unit 111. On the other hand, the cathode of the intrinsic diode 122 and a first end of the intrinsic capacitance 123 are connected to the drain D of the switch function unit 121. Also, the anode of the intrinsic diode 122 and a second end of the intrinsic capacitance 123 are connected to the source S of the switch function unit 121.

[0014] The switch driver 130 includes drivers 131 and 132 that generate drive signals (gate signals) for the switch elements 110 and 120, respectively, and a controller 133 that controls these, and turns on / off the switch elements 110 and 120 individually.

[0015] For example, the switch driver 130 has a function (output feedback control function) of turning on / off the bidirectional switch X so that the DC output voltage Vout coincides with a desired target value. By providing such a function, it becomes possible to stably supply a constant DC output voltage Vout to the load Z.

[0016] In addition, the switch driver 130 has a function (power factor correction function) of turning on / off the bidirectional switch X so as to bring the power factor of the switching power supply 100 closer to 1. By providing such a function, a separate power factor correction circuit becomes unnecessary, and it becomes possible to realize a one-converter type switching power supply 100.

[0017] Furthermore, the switch driver 130 also has a function of individually performing zero-voltage switching control on the switch elements 110 and 120 (=individual ZVS function). By providing such a function, it is possible to reduce the switching loss of the bidirectional switch X, thereby suppressing heat generation in the bidirectional switch X and increasing the conversion efficiency of the switching power supply 100. The individual ZVS function will be described in detail later.

[0018] The transformer 140 includes a primary winding 141 provided in a primary circuit system, and secondary windings 142a and 142b provided in a secondary circuit system and magnetically coupled to the primary winding 141. A first input tap (=winding end of the primary winding 141) of the transformer 140 is connected to a first node (=application end of voltage V1) of the AC power source P. A second input tap (=winding start end of the primary winding 141) of the transformer 140 is connected to a second node (=application end of voltage V2) of the AC power source P via a bidirectional switch X. A first output tap (=winding start end of the secondary winding 142a) of the transformer 140 is connected to the anode of the diode 161. A second output tap (=winding end of the secondary winding 142b) of the transformer 140 is connected to the anode of the diode 162. A third output tap of the transformer 140 (=the winding end of the secondary winding 142a and the winding start of the secondary winding 142b) is connected to the low potential end of the load Z as the ground of the secondary circuit system.

[0019] As the transformer 140, a flyback converter circuit may be configured using a transformer with a high degree of coupling, a voltage resonant circuit may be configured using a leakage transformer (resonant transformer) having leakage inductance, or a voltage resonant circuit may be configured by connecting a coil to a leakage transformer. In addition, the transformer 140 is accompanied by stray capacitances C1 to C4 as shown in FIG. 2.

[0020] The capacitor 151 is connected in parallel to the AC power supply P, and functions as an input filter capacitor that removes noise components from the AC input voltage Vin.

[0021] The capacitor 152 is connected in parallel to the bidirectional switch X, and functions as a resonant capacitor that forms a resonant circuit together with the primary winding 141 and leakage inductance (not shown) of the transformer 140. Therefore, even if surplus energy that is not supplied from the primary winding 141 to the secondary windings 142a and 142b occurs due to the use of a leakage transformer or a resonant transformer as the transformer 140, this can be regenerated and utilized, so that the conversion efficiency of the switching power supply 100 is not reduced. Note that since the switch elements 110 and 120 have their own internal capacitances 113 and 123, respectively, the capacitor 152 may not be necessary in some cases.

[0022] The capacitor 153 is connected between the first output tap (the winding start end of the secondary winding 142a) and the second output tap (the winding end end of the secondary winding 142b) of the transformer 140, and functions as a rectifying capacitor.

[0023] The capacitor 154 is connected in parallel to the load Z, and functions as a smoothing capacitor for smoothing the output of the full-wave rectifier circuit (=diodes 161 and 162) to generate the DC output voltage Vout.

[0024] The anode of the diode 161 is connected to a first output tap of the transformer 140. The anode of the diode 162 is connected to a second output tap of the transformer 140. The cathodes of the diodes 161 and 162 are connected to a high potential end of the load Z as an output end of the DC output voltage Vout. The diodes 161 and 162 connected in this manner function as a full-wave rectifier circuit that full-wave rectifies the induced voltage (=flyback voltage or forward voltage) generated in the secondary windings 142a and 142b. Note that the diodes 161 and 162 are accompanied by an internal capacitance C5 as shown in FIG. 3.

[0025] The snubber circuit 170 is connected across the primary winding 141 and serves to absorb excessive surges. However, if the energy fluctuation of the transformer 140 when the bidirectional switch X is off is sufficiently gentle due to the action of the capacitor 152, it is possible to omit the snubber circuit 170.

[0026] The operation mode of the switching power supply 100 having the above configuration is either a first operation mode in which the flyback system is used alone or a second operation mode in which the flyback system and the forward system are used in combination, depending on the periodic AC fluctuation of the AC input voltage Vin.

[0027] In this way, the switching power supply 100 that uses both the flyback and forward types can extract both the forward and flyback voltages appearing in the secondary windings 142a and 142b as outputs. This eliminates the drawback of the flyback type, that the peak value of the secondary current is large, and makes it possible to directly convert the AC input voltage Vin to the DC output voltage Vout with high efficiency even when medium to high power is used.

[0028] <Individual ZVS control> Next, the individual ZVS control by the switch driver 130 will be described in detail with reference to the drawings.

[0029] FIG. 4 is a diagram showing a first example of individual ZVS control (where Vin<0 (V1>V2) and |Vin| is relatively small), and depicts, from the top, the switch voltage Vsw and the on / off states of each of the switch elements 110 and 120.

[0030] Before time t11, both switch elements 110 and 120 are on. At this time, a primary current flows through a current path from a first node (= application terminal of voltage V1) of the AC power supply P via the primary winding 141 and the bidirectional switch X to a second node (= application terminal of voltage V2) of the AC power supply P, and energy is stored in the primary winding 141. At this time, the switch voltage Vsw coincides with the voltage V2.

[0031] At time t11, when a predetermined amount of energy is accumulated in the primary winding 141, the switch driver 130 switches the bidirectional switch X from ON to OFF. The OFF timing of the bidirectional switch X may be detected by detecting that a predetermined time has elapsed since the ON timing of the bidirectional switch X, or by detecting that the integral value of the primary current has reached a predetermined threshold value.

[0032] At this time, the switch driver 130 does not turn off both the switch elements 110 and 120 at the same time, but keeps on the switch element 110 (= an element to which a forward voltage is applied) whose intrinsic diode 112 is forward biased, and turns off the switch element 120 (= an element to which a reverse voltage is applied) whose intrinsic diode 122 is reverse biased.

[0033] Specifically, the switch driver 130 continues to output an ON signal from the controller 133 via the driver 131 to the control end of the switch element 110, while outputting an OFF signal from the controller 133 via the driver 132 to the control end of the switch element 120.

[0034] Thereafter, as the switch voltage Vsw rises, the drain-source voltage (=Vsw-V2) of the switch element 120 gradually rises while storing energy in the internal capacitance 123 of the switch element 120, the stray capacitances C1 to C4 of the transformer 140, and the internal capacitance C5 of each of the diodes 161 and 162. The switch voltage Vsw rises until its absolute value matches the DC output voltage Vout.

[0035] At this time, the voltage across secondary winding 142a, which is magnetically coupled to primary winding 141 of transformer 140, also gradually increases. Then, when the voltage across secondary winding 142a becomes higher than the total voltage of the voltage across capacitor 154 and the forward drop voltage of diode 161, a current flows from secondary winding 142a through diode 161 to capacitor 154, and capacitor 154 is charged.

[0036] When the energy stored in the transformer 140 is completely discharged to the capacitor 154, the switch voltage Vsw starts to decrease due to the internal capacitance 123 of the switch element 120, the stray capacitances C1 to C4 of the transformer 140, and the internal capacitance C5 of the diodes 161 and 162, and the drain-source voltage of the switch element 120 starts to decrease gradually.

[0037] Then, at time t12, when the switch voltage Vsw drops to match the voltage V2 and the drain-source voltage of the switch element 120 becomes 0 V, the switch driver 130 waits for this timing to turn on the switch element 120 and simultaneously turn off the switch element 110.

[0038] Specifically, the switch driver 130 outputs an OFF signal from the controller 133 via the driver 131 to the control end of the switch element 110 , and outputs an ON signal from the controller 133 via the driver 132 to the control end of the switch element 120 .

[0039] At this time, the energy stored in the transformer 140 causes the switch voltage Vsw to drop to a potential lower than the voltage V2, so that the drain-source voltage (=V2-Vsw) of the switch element 110 rises, and a reverse voltage is applied to the switch element 110 (i.e., the internal diode 112 of the switch element 110 is reverse-biased).

[0040] However, when the energy stored in the transformer 140 runs out, the switch voltage Vsw starts to increase due to the internal capacitance 113 of the switch element 110 and other capacitances, and the drain-source voltage of the switch element 110 starts to gradually decrease.

[0041] Then, at time t13, when the switch voltage Vsw rises to match the voltage V2 and the drain-source voltage of the switch element 110 becomes 0 V, the switch driver 130 waits for this timing to turn on the switch element 110 while keeping the switch element 120 on.

[0042] Specifically, the switch driver 130 continues to output an ON signal from the controller 133 via the driver 132 to the control end of the switch element 120 , while outputting an ON signal from the controller 133 via the driver 131 to the control end of the switch element 110 .

[0043] In this way, in the first example of individual ZVS control shown in the figure, when the switch driver 130 switches the bidirectional switch X from off to on, it performs a first ZVS control to turn on the switch element 120, which was off until then, at a timing when the voltage across the switch element 120 becomes 0 V, and subsequently performs a second ZVS control to turn off the switch element 110 at a timing when the switch element 120 is turned on, and to turn on the switch element 110 at a timing when the voltage across the switch element 110 becomes 0 V.

[0044] By repeating the above switching control, when the bidirectional switch X turns on, the switch elements 110 and 120 can be individually turned on at a timing when no charge is stored in the internal capacitances 113 and 123 of the switch elements 110 and 120. Therefore, the switching loss of each of the switch elements 110 and 120 can be made as close to zero as possible, so that heat generation of the bidirectional switch X can be suppressed.

[0045] In this figure, the resonance energy of the primary winding 141 is released in a short time. This makes it possible to suppress the decrease in switching frequency at the time of low input voltage. Furthermore, if the decrease in switching frequency is suppressed, the switching current is suppressed, so that it is possible to suppress the decrease in efficiency. Furthermore, since the transformer 140 can be made smaller, it is possible to realize a switching power supply 100 that is smaller and more efficient.

[0046] FIG. 5 is a diagram showing a second example of individual ZVS control (where Vin>0 (V1<V2) and |Vin| is relatively small), and in order from the top, the switch voltage Vsw and the on / off states of the switch elements 110 and 120 are depicted.

[0047] Before time t21, both switch elements 110 and 120 are turned on. At this time, a primary current flows through a current path from the second node of the AC power supply P (= the applied end of voltage V2) to the first node of the AC power supply P (= the applied end of voltage V1) via the bidirectional switch X and the primary winding 141, and energy is stored in the primary winding 141. At this point, the switch voltage Vsw is equal to the voltage V2.

[0048] At time t21, when a predetermined amount of energy is stored in the primary winding 141, the switch driving device 130 switches the bidirectional switch X from on to off. As described above, for the off timing of the bidirectional switch X, it may be detected that a predetermined time has elapsed since the on timing of the bidirectional switch X, or it may be detected that the integrated value of the primary current has reached a predetermined threshold.

[0049] At this time, the switch driving device 130 does not turn off both switch elements 110 and 120 simultaneously. Instead, while keeping the switch element 120 (= the element to which the forward voltage is applied) with the internal diode 122 forward-biased turned on, the switch element 110 (= the element to which the reverse voltage is applied) with the internal diode 112 reverse-biased is turned off.

[0050] Specifically, the switch driving device 130 continues to output an on signal to the control terminal of the switch element 120 via the driver 132 from the controller 133, while outputting an off signal to the control terminal of the switch element 110 via the driver 131 from the controller 133.

[0051] Thereafter, as the switch voltage Vsw decreases, the drain-source voltage (=V2-Vsw) of the switch element 110 gradually increases while storing energy in the internal capacitance 113 of the switch element 110, the stray capacitances C1 to C4 of the transformer 140, and the internal capacitance C5 of each of the diodes 161 and 162. The switch voltage Vsw decreases until its absolute value matches the DC output voltage Vout.

[0052] At this time, the voltage across secondary winding 142b, which is magnetically coupled to primary winding 141 of transformer 140, also gradually increases. Then, when the voltage across secondary winding 142b becomes higher than the total voltage of the voltage across capacitor 154 and the forward drop voltage of diode 162, a current flows from secondary winding 142b through diode 162 to capacitor 154, and capacitor 154 is charged.

[0053] When the energy stored in the transformer 140 is completely discharged to the capacitor 154, the switch voltage Vsw begins to increase due to the internal capacitance 113 of the switch element 110, the stray capacitances C1 to C4 of the transformer 140, and the internal capacitance C5 of the diodes 161 and 162, and the drain-source voltage of the switch element 110 starts to gradually decrease.

[0054] Then, at time t22, when the switch voltage Vsw rises to match the voltage V2 and the drain-source voltage of the switch element 110 becomes 0 V, the switch driver 130 waits for this timing to turn on the switch element 110 and simultaneously turn off the switch element 120.

[0055] Specifically, the switch driver 130 outputs an ON signal from the controller 133 via the driver 131 to the control end of the switch element 110 , and outputs an OFF signal from the controller 133 via the driver 132 to the control end of the switch element 120 .

[0056] At this time, the energy stored in the transformer 140 causes the switch voltage Vsw to rise to a potential higher than the voltage V2, so that the drain-source voltage (=Vsw-V2) of the switch element 120 rises and a reverse voltage is applied to the switch element 120 (i.e., the internal diode 122 of the switch element 120 is reverse-biased).

[0057] However, when the energy stored in the transformer 140 runs out, the switch voltage Vsw starts to decrease due to the internal capacitance 123 of the switch element 120 and other capacitances, and the drain-source voltage of the switch element 120 starts to decrease gradually.

[0058] Then, at time t23, when the switch voltage Vsw drops to match the voltage V2 and the drain-source voltage of the switch element 120 becomes 0 V, the switch driver 130 waits for this timing to turn on the switch element 120 while keeping the switch element 110 on.

[0059] Specifically, the switch driver 130 continues to output an ON signal from the controller 133 via the driver 131 to the control end of the switch element 110 , while outputting an ON signal from the controller 133 via the driver 132 to the control end of the switch element 120 .

[0060] In this way, in the second example of individual ZVS control shown in the figure, when the switch driver 130 switches the bidirectional switch X from off to on, it performs a first ZVS control to turn on the switch element 110, which was off until then, at a timing when the voltage across the switch element 110 becomes 0 V, and subsequently performs a second ZVS control to turn off the switch element 120 at the timing when the switch element 110 is turned on, and to turn on the switch element 120 at a timing when the voltage across the switch element 120 becomes 0 V.

[0061] By repeating the above switching control, when the bidirectional switch X makes an on-transition, each of the switch elements 110 and 120 can be individually turned on at a timing when no charge is accumulated in the internal capacitances 113 and 123 of the switch elements 110 and 120, respectively. Therefore, since the switching losses of the switch elements 110 and 120 can be made to approach zero as much as possible, it is possible to suppress heat generation of the bidirectional switch X.

[0062] Note that in the switching power supply 100, a forward voltage and a reverse voltage can be applied to each of the switch elements 110 and 120 along with the resonance operation. Therefore, in order to realize a highly efficient switching power supply 100, it is effective to perform the individual ZVS control described above.

[0063] Also, the above individual ZVS control switches to either the first example (FIG. 4) or the second example (FIG. 5) every time the positive and negative polarities of the AC input voltage Vin are inverted. However, the above individual ZVS control can be applied without any problem even when the input voltage of the switching power supply 100 is fixed to positive or negative. For example, when the input voltage of the switching power supply 100 is fixed to negative (V1 > V2), the individual ZVS control of the first example (FIG. 4) is always performed. Conversely, when the input voltage of the switching power supply 100 is fixed to positive (V1 < V2), the individual ZVS control of the second example (FIG. 5) is always performed.

[0064] FIG. 6 is a diagram showing a third example of the individual ZVS control (Vin < 0 (V1 > V2) and |Vin| is relatively large), and in order from the top, the switch voltage Vsw and the on / off states of the switch elements 110 and 120 are depicted.

[0065] The individual ZVS control of the third example is basically the same as the above-described first example (FIG. 4), and thus its operation itself can be understood by replacing "time t11", "time t12", and "time t13" in the previous description with "time t31", "time t32", and "time t33", respectively.

[0066] However, when |Vin| is relatively large, as shown at times t32 to t33, the reverse voltage application time to the switching element 110 becomes very short. Therefore, it should be noted that the timing control from when the switching element 110 is turned off to when it is turned on again becomes severe.

[0067] In this figure, the case where Vin < 0 (V1 > V2) is illustrated. Needless to say, the same applies to the case where Vin > 0 (V1 < V2).

[0068] FIG. 7 is a diagram showing a fourth example of individual ZVS control (when the second ZVS control is not performed in the previous third example). In order from the top, the switch voltage Vsw and the on / off states of the switching elements 110 and 120 are depicted.

[0069] The individual ZVS control of the fourth example is characterized in that the second ZVS control (= ZVS control of the switching element 110) is not performed in view of the points noted in the previous third example (FIG. 6). Below, a series of operation descriptions will be given, including parts that overlap with the previous first example (FIG. 4).

[0070] Before time t41, both the switching elements 110 and 120 are turned on. At this time, a primary current flows through the current path from the first node of the AC power supply P (= the applied end of the voltage V1), through the primary winding 141 and the bidirectional switch X, to the second node of the AC power supply P (= the applied end of the voltage V2), and energy is stored in the primary winding 141. At this point, the switch voltage Vsw coincides with the voltage V2.

[0071] At time t41, when a predetermined amount of energy is stored in the primary winding 141, the switch drive device 130 switches the bidirectional switch X from on to off. As described above, for the off timing of the bidirectional switch X, it may be detected that a predetermined time has elapsed since the on timing of the bidirectional switch X, or it may be detected that the integrated value of the primary current has reached a predetermined threshold value.

[0072] At this time, the switch driver 130 does not turn off both the switch elements 110 and 120 at the same time, but keeps on the switch element 110 (= an element to which a forward voltage is applied) whose intrinsic diode 112 is forward biased, and turns off the switch element 120 (= an element to which a reverse voltage is applied) whose intrinsic diode 122 is reverse biased.

[0073] Specifically, the switch driver 130 continues to output an ON signal from the controller 133 via the driver 131 to the control end of the switch element 110, while outputting an OFF signal from the controller 133 via the driver 132 to the control end of the switch element 120.

[0074] Thereafter, as the switch voltage Vsw rises, the drain-source voltage (=Vsw-V2) of the switch element 120 gradually rises while storing energy in the internal capacitance 123 of the switch element 120, the stray capacitances C1 to C4 of the transformer 140, and the internal capacitance C5 of each of the diodes 161 and 162. The switch voltage Vsw rises until its absolute value matches the DC output voltage Vout.

[0075] At this time, the voltage across secondary winding 142a, which is magnetically coupled to primary winding 141 of transformer 140, also gradually increases. Then, when the voltage across secondary winding 142a becomes higher than the total voltage of the voltage across capacitor 154 and the forward drop voltage of diode 161, a current flows from secondary winding 142a through diode 161 to capacitor 154, and capacitor 154 is charged.

[0076] When the energy stored in the transformer 140 is completely discharged to the capacitor 154, the switch voltage Vsw starts to decrease due to the internal capacitance 123 of the switch element 120, the stray capacitances C1 to C4 of the transformer 140, and the internal capacitance C5 of the diodes 161 and 162, and the drain-source voltage of the switch element 120 starts to decrease gradually.

[0077] Then, at time t42, until the switch voltage Vsw drops to match the voltage V2 and the drain-source voltage of the switch element 120 becomes 0V, the switch drive device 130 turns on the switch element 120 while keeping the switch element 110 on, taking this timing into account.

[0078] Specifically, the switch drive device 130 continues to output an on signal to the control terminal of the switch element 110 from the controller 133 via the driver 131, and outputs an on signal to the control terminal of the switch element 120 from the controller 133 via the driver 132.

[0079] At this time, the energy stored in the transformer 140 is regenerated to the AC power supply P. When all the energy of the transformer 140 is gone, the transformer 140 starts to accumulate energy again.

[0080] As described above, in the individual ZVS control of the fourth example, the ZVS control (= the second ZVS control) of the switch element 110 is omitted, and only the high-frequency switching (= the first ZVS control) of the switch element 120 is performed while keeping the switch element 110 always on.

[0081] Therefore, even when |Vin| is relatively large and the reverse voltage application time to the switch element 110 becomes very short, it is possible to suppress the heat generation of the bidirectional switch X without requiring strict timing control.

[0082] Although not shown again, when Vin > 0 (V1 < V2), only the high-frequency switching (= the first ZVS control) of the switch element 110 is performed while keeping the switch element 120 always on.

[0083] In addition, the switch driver 130 may have a function of switching whether to perform the second ZVS control (i.e., whether to perform the individual ZVS control of the first to third examples (FIGS. 4 to 6) or the individual ZVS control of the fourth example (FIG. 7)) depending on the AC input voltage Vin or a predetermined condition.

[0084] <Second embodiment> Fig. 8 is a diagram showing a second embodiment of a switching power supply. A switching power supply 200 of this embodiment is based on the first embodiment (Fig. 1), but has switch elements 210 and 220 and a capacitor 230 instead of switch elements 110 and 120 and capacitor 152. The following description will focus on this change.

[0085] The switch element 210 is connected between a second node (=application end of voltage V2) of the AC power supply P and a second input tap (=winding start end of primary winding 141) of the transformer 140. On the other hand, the switch element 220 is connected between a first node (=application end of voltage V1) of the AC power supply P and a first input tap (=winding end end of primary winding 141) of the transformer 140. In other words, the primary winding 141 is connected between the switch element 210 and the switch element 220.

[0086] In addition, the switch elements 210 and 220 include intrinsic diodes 212 and 222 and intrinsic capacitances 213 and 223, respectively, in addition to switch function units 211 and 221 (transistor bodies). In the case of this figure, the cathode of the intrinsic diode 212 and a first end of the intrinsic capacitance 213 are connected to the drain D of the switch function unit 211. Also, the anode of the intrinsic diode 212 and a second end of the intrinsic capacitance 213 are connected to the source S of the switch function unit 211. On the other hand, the cathode of the intrinsic diode 222 and a first end of the intrinsic capacitance 223 are connected to the drain D of the switch function unit 221. Also, the anode of the intrinsic diode 222 and a second end of the intrinsic capacitance 223 are connected to the source S of the switch function unit 221.

[0087] In this manner, the switch elements 210 and 220 forming the bidirectional switch X are arranged separately to sandwich the primary winding 141 therebetween.

[0088] Moreover, unlike the above-mentioned capacitor 152, the capacitor 230 is connected in series to the bidirectional switch X (=connected in parallel to the primary winding 141).

[0089] In the switching power supply 200 of this embodiment, by implementing the individual ZVS control (any of the first to fourth examples) described above when driving the bidirectional switch X on and off, it is possible to obtain the same effects as those described above.

[0090] <Third embodiment> Fig. 9 is a diagram showing a third embodiment of a switching power supply. A switching power supply 300 of this embodiment is based on the first embodiment (Fig. 1), but instead of the secondary windings 142a and 142b, the capacitors 153 and 154, and the diodes 161 and 162, it has a secondary winding 142, capacitors 311 and 312, diodes 321 to 323, an auxiliary winding 330, and a current limiting element 340. The following will focus on these changes.

[0091] A first output tap (=winding end of secondary winding 142) of transformer 140 is connected to a high potential end of load Z as an output end of DC output voltage Vout. A low potential end of load Z is connected to a first input tap (=winding end of primary winding 141) of transformer 140. A second output tap (=winding start end of secondary winding 142) of transformer 140 is connected to a first end of auxiliary winding 330.

[0092] The capacitor 311 is connected in parallel to the load Z. The capacitor 312 is connected between the second input tap of the transformer 140 (=the winding start end of the primary winding 141) and the second end of the auxiliary winding 330.

[0093] The anode of diode 321 is connected to the first input tap of transformer 140. The cathode of diode 321 is connected to the second end of the auxiliary winding 330. The anode of diode 322 is connected to the second input tap of transformer 140. The cathode of diode 322 is connected to the first output tap of transformer 140. The anode of diode 323 is connected to the second end (= the voltage V2 applied end) of the AC power supply P via the current limiting element 340. The cathode of diode 323 is connected to the first output tap of transformer 140.

[0094] The basic operation of the switching power supply 300 will be described. For example, when the AC input voltage Vin is positive (V1 < V2), a limited current flows through the current path from the second node of the AC power supply P (= the voltage V2 applied end), via the current limiting element 340, diode 323, secondary winding 142, and auxiliary winding 330 to capacitor 312, and capacitor 312 is charged.

[0095] When the bidirectional switch X is turned on, a primary current flows through the primary winding 141 of the transformer 140 and energy is stored. When a predetermined amount of energy is stored, the bidirectional switch X is turned off. At this time, the second input tap (= the start end of the primary winding 141) and the second output tap (= the start end of the secondary winding 142) of the transformer 140 gradually decrease at almost the same voltage drop rate. Therefore, no short-circuit current flows through capacitor 312.

[0096] When the voltage applied to the second input tap of the transformer 140 becomes lower than the sum of the voltage across capacitor 312 and the forward voltage drop of diode 321, current flows into capacitor 312 through diode 321 and capacitor 312 is charged. Furthermore, the energy stored in capacitor 312 is used to charge capacitor 311 via the auxiliary winding 330 and the secondary winding 142. After that, when all the energy of the transformer 140 is discharged to capacitor 312, the bidirectional switch X is turned on again at an appropriate timing.

[0097] Next, when the capacitors 311 and 312 are already charged and the AC input voltage Vin is negative (V1>V2), when the bidirectional switch X is turned on, a primary current flows through the primary winding 141 of the transformer 140 and energy is stored. When a certain amount of energy is stored, the bidirectional switch X is turned off. At this time, the second input tap (= the winding start end of the primary winding 141) and the second output tap (= the winding start end of the secondary winding 142) of the transformer 140 gradually become higher at approximately the same voltage rise rate. Therefore, no short-circuit current flows through the capacitor 312.

[0098] When the voltage applied to the second input tap of the transformer 140 becomes higher than the sum of the voltage across the capacitor 311 and the forward drop voltage of the diode 322, a current flows into the capacitor 311 via the diode 322, charging the capacitor 311. After that, when the energy of the transformer 140 is completely discharged into the capacitor 311, the bidirectional switch X is turned on again at an appropriate timing.

[0099] In the switching power supply 300 of this embodiment, by implementing the individual ZVS control (any of the first to fourth examples) described above when driving the bidirectional switch X on and off, it is possible to obtain the same effects as those described above.

[0100] <Fourth embodiment> 10 is a diagram showing a fourth embodiment of a switching power supply. A switching power supply 400 of this embodiment is based on the first embodiment (FIG. 1) and has a differentiation circuit 410 as means for detecting zero-cross timing required for the individual ZVS control described above.

[0101] The differential circuit 410 includes a resistor 411 and a capacitor 412, and differentiates the switch voltage Vsw that appears at one end of the bidirectional switch X to generate a differential voltage Vd. The first end of the resistor 411 is connected to the first input tap of the transformer 140 (= the winding end of the primary winding 141). The second end of the resistor 411 and the first end of the capacitor 412 are both connected to the output end of the differential voltage Vd. The second end of the capacitor 412 is connected to the second input tap of the transformer 140 (= the winding start of the primary winding 141).

[0102] Based on the differential voltage Vd described above, the switch driving device 130 performs individual ZVS control of the switch elements 110 and 120. For example, the switch driving device 130 determines the on / off timing of the switch elements 110 and 120 based on the comparison result between the differential voltage Vd and predetermined threshold voltages VH and VL (where VL < 0 < VH). Hereinafter, a detailed description will be given with reference to the drawings.

[0103] FIG. 11 is a diagram showing a fifth example of individual ZVS control (ZVS control based on the differential voltage Vd), and depicts, in order from the top, the switch voltage Vsw, the differential voltage Vd, and the on / off states of the switch elements 110 and 120 respectively. Hereinafter, a series of operations will be described while paying particular attention to the differential voltage Vd, including parts overlapping with the first example (FIG. 4) described above.

[0104] Before time t51, both the switch elements 110 and 120 are on. At this time, a primary current flows through the current path from the first node of the AC power supply P (= the applied end of the voltage V1), through the primary winding 141 and the bidirectional switch X, to the second node of the AC power supply P (= the applied end of the voltage V2), and energy is stored in the primary winding 141. At this point, the switch voltage Vsw is equal to the voltage V2. Also, the differential voltage Vd is 0V.

[0105] At time t51, when a predetermined amount of energy is accumulated in the primary winding 141, the switch driver 130 switches the bidirectional switch X from ON to OFF. As described above, the OFF timing of the bidirectional switch X may be detected by detecting that a predetermined time has elapsed since the ON timing of the bidirectional switch X, or by detecting that the integral value of the primary current has reached a predetermined threshold value.

[0106] At this time, the switch driver 130 does not turn off both the switch elements 110 and 120 at the same time, but keeps on the switch element 110 (= an element to which a forward voltage is applied) whose intrinsic diode 112 is forward biased, and turns off the switch element 120 (= an element to which a reverse voltage is applied) whose intrinsic diode 122 is reverse biased.

[0107] Specifically, the switch driver 130 continues to output an ON signal from the controller 133 via the driver 131 to the control end of the switch element 110, while outputting an OFF signal from the controller 133 via the driver 132 to the control end of the switch element 120.

[0108] Thereafter, as the switch voltage Vsw rises, the drain-source voltage (=Vsw-V2) of the switch element 120 gradually rises while storing energy in the internal capacitance 123 of the switch element 120, the stray capacitances C1 to C4 of the transformer 140, and the internal capacitance C5 of each of the diodes 161 and 162. The switch voltage Vsw rises until its absolute value matches the DC output voltage Vout. At this time, the differential voltage Vd once exceeds the threshold voltage VH, and then falls below the threshold voltage VH again.

[0109] At this time, the voltage across secondary winding 142a coupled to primary winding 141 of transformer 140 also gradually increases. Then, when the voltage across secondary winding 142a becomes higher than the total voltage of the voltage across capacitor 154 and the forward drop voltage of diode 161, a current flows from secondary winding 142a through diode 161 to capacitor 154, and capacitor 154 is charged.

[0110] At time t52, when all the energy stored in the transformer 140 is discharged to the capacitor 154, due to the internal capacitance 123 of the switching element 120, the parasitic capacitances C1 to C4 of the transformer 140, and the internal capacitance C5 of each of the diodes 161 and 162, the switching voltage Vsw starts to decrease, and the drain-source voltage of the switching element 120 gradually starts to decrease. At this time, the differential voltage Vd is lower than the threshold voltage VL.

[0111] Then, at time t53, when the switching voltage Vsw decreases until it matches the voltage V2 and the drain-source voltage of the switching element 120 becomes 0V, the switch driving device 130, taking this timing into account, turns on the switching element 120 and at the same time turns off the switching element 110.

[0112] Specifically, the switch driving device 130 outputs an off signal to the control terminal of the switching element 110 from the controller 133 via the driver 131, while outputting an on signal to the control terminal of the switching element 120 from the controller 133 via the driver 132.

[0113] Note that at time t53, since the switching voltage Vsw is clamped to a voltage lower than the voltage V2 by the forward voltage drop of the internal diode 122, the differential voltage Vd rises steeply from a negative value (<VL) to 0V. Therefore, in the switch driving device 130, it is advisable to turn on the switching element 120 and at the same time turn off the switching element 110 at the timing when the differential voltage Vd exceeds the threshold voltage VL. Also, although there are timings other than time t53 when the differential voltage Vd exceeds the threshold voltage VL, they should all be ignored or masked.

[0114] At this time, due to the energy stored in the transformer 140, the switch voltage Vsw drops to a potential lower than the voltage V2. Therefore, the drain-source voltage (=V2 - Vsw) of the switch element 110 increases, and a reverse voltage is applied to the switch element 110 (that is, the internal diode 112 of the switch element 110 is in a reverse-biased state). Accordingly, the differential voltage Vd falls below the threshold voltage VL again.

[0115] However, when the energy stored in the transformer 140 runs out at time t54, the switch voltage Vsw starts to rise due to the internal capacitance 113 of the switch element 110 and other capacitances, and the drain-source voltage of the switch element 110 gradually starts to decrease. At this time, the differential voltage Vd rises from a negative value (<VL) through 0V to a positive value (>VH).

[0116] Then, at time t55, when the switch voltage Vsw rises to match the voltage V2 and the drain-source voltage of the switch element 110 becomes 0V, the switch driving device 130 turns on the switch element 110 while keeping the switch element 120 on, taking this timing into account.

[0117] Specifically, the switch driving device 130 continuously outputs an on signal to the control terminal of the switch element 120 from the controller 133 via the driver 132, and at the same time, outputs an on signal to the control terminal of the switch element 110 from the controller 133 via the driver 131.

[0118] Note that at time t55, since the switch voltage Vsw is clamped to a voltage higher than the voltage V2 by the forward voltage drop of the internal diode 112, the differential voltage Vd rapidly decreases from a positive value (>VH) to 0V. Therefore, in the switch driving device 130, it is advisable to turn on the switch element 110 at the timing when the differential voltage Vd falls below the threshold voltage VH. Also, although there are timings other than time t55 when the differential voltage Vd falls below the threshold voltage VH, they should all be ignored or masked.

[0119] In this way, when switching the bidirectional switch X from off to on, the switch driver 130 performs a first ZVS control to turn on the switch element 120, which was off until then, at a timing when the voltage across the switch element 120 becomes 0 V, and subsequently performs a second ZVS control to turn off the switch element 110 at a timing when the switch element 120 is turned on, and to turn on the switch element 110 at a timing when the voltage across the switch element 110 becomes 0 V.

[0120] By repeating the above switching control, when the bidirectional switch X turns on, the switch elements 110 and 120 can be individually turned on at a timing when no charge is stored in the internal capacitances 113 and 123 of the switch elements 110 and 120. Therefore, it is possible to reduce the switching loss of each of the switch elements 110 and 120 and suppress heat generation in the bidirectional switch X.

[0121] In this embodiment, an example in which individual ZVS control is performed based on the differential voltage Vd has been given, but the differentiation process is merely one example of how to process the switch voltage Vsw, and various modifications are possible. That is, the differentiation circuit 410 is a specific example of a voltage detection circuit that detects the switch voltage Vsw, and as long as individual ZVS control can be performed based on the switch voltage Vsw, the method of processing the switch voltage Vsw is not important.

[0122] Of course, the method of detecting the zero cross timing is not limited to the above. In the following, other zero cross detection methods will be proposed using the fifth embodiment (FIG. 12) and the sixth embodiment (FIG. 13) as examples.

[0123] <Fifth embodiment> 12 is a diagram showing a fifth embodiment of a switching power supply. A switching power supply 500 of this embodiment is based on the first embodiment (FIG. 1) and has a zero voltage detection circuit 510 as a means for detecting zero cross timing required for the individual ZVS control described above.

[0124] The zero voltage detection circuit 510 detects when the drain-source voltage (or divided voltage) of each of the switch elements 110 and 120 becomes 0V, and outputs the detection result to the controller 133. This makes it possible to realize the individual ZVS described above. In particular, if the zero voltage detection circuit 510 is implemented as an IC, it can be said that it can be easily configured.

[0125] Sixth Embodiment 13 is a diagram showing a sixth embodiment of a switching power supply. A switching power supply 600 of this embodiment is based on the first embodiment (FIG. 1) and has an auxiliary winding 610 and a zero voltage detection circuit 620 as means for detecting the zero cross timing required for the individual ZVS control described above.

[0126] The auxiliary winding 610 is magnetically coupled to the primary winding 141 and the secondary winding 142. The zero voltage detection circuit 620 detects an induced voltage generated across the auxiliary winding 610 and outputs the detection result to the controller 133. This makes it possible to realize the above-mentioned individual ZVS.

[0127] Moreover, the above-described fourth embodiment (FIG. 10), fifth embodiment (FIG. 12), and sixth embodiment (FIG. 13) can be combined and implemented within a range in which no contradiction occurs.

[0128] Seventh embodiment Fig. 14 is a diagram showing a seventh embodiment of a switching power supply. A switching power supply 700 of this embodiment is based on the first embodiment (Fig. 1) and further includes a start-up circuit 710. The start-up circuit 710 is connected between both ends of the primary winding 141, and pre-charges the capacitor 154 when the switching power supply 700 is started. According to this embodiment, it is possible to stably and reliably start up the switching power supply 700.

[0129] Eighth embodiment Fig. 15 is a diagram showing an eighth embodiment of a switching power supply. A switching power supply 800 of this embodiment is based on the first embodiment (Fig. 1) and further includes a start-up circuit 810. The start-up circuit 810 is directly connected to the capacitor 154 of the secondary circuit system, and pre-charges the capacitor 154 when the switching power supply 800 is started. According to this embodiment, it is possible to start the switching power supply 800 stably and reliably.

[0130] <Ninth embodiment> Fig. 16 is a diagram showing a ninth embodiment of a switching power supply. The switching power supply 900 of this embodiment is based on the above-mentioned fourth embodiment (Fig. 10), and has a function of monitoring the magnitude of the AC input voltage Vin (=V2-V1) together with the differential voltage Vd by the switch driver 130 (particularly the controller 133) and controlling the drive of the bidirectional switch X based on the monitoring result. The technical significance of such an additional function will be described in detail below.

[0131] Fig. 17 is a diagram for explaining the decrease in efficiency caused by the clamp operation at the zero cross timing. This diagram is basically the same as Fig. 11, but the clamp period Tc (=time t53 to t53x) at the zero cross timing is clearly shown, and the ideal waveform of the switch voltage Vsw (i.e., the waveform when Tc=0) is depicted by a dashed line.

[0132] As described above in FIG. 11, the switch driver 130 (particularly the controller 133) determines the on / off timing of each of the switch elements 110 and 120 depending on the result of comparing the differential voltage Vd with the threshold voltages VH and VL (see times t53 and t55).

[0133] Incidentally, the clamp period Tc (= time t53 to t53x) in this figure corresponds to the period during which the switch voltage Vsw is clamped to a voltage lower than the voltage V2 by only the forward voltage drop of the internal diode 122. During such a clamp period Tc, energy returns to the input side. As a result, the amount of undershoot Vsw* of the switch voltage Vsw (= the difference between the lower peak value (< V2) of the switch voltage Vsw and the voltage V2) becomes smaller than the ideal waveform, and the amount of energy that can be fed into the output side decreases accordingly, resulting in a decrease in efficiency.

[0134] In this figure, the case where Vin < 0 (V1 > V2) is illustrated. However, for the case where Vin > 0 (V1 < V2), basically for the same reasons as above, a decrease in efficiency due to the clamp operation may occur.

[0135] Therefore, in order to shorten the above clamp period Tc, the switching power supply 900 of this embodiment has a function of monitoring the magnitude (= positive / negative and absolute value) of the AC input voltage Vin (= V2 - V1) together with the differential voltage Vd by the switch driving device 130 (particularly the controller 133), and performing drive control of the bidirectional switch X (including the adjustment process of the threshold voltages VH and VL) based on the monitoring result.

[0136] FIG. 18 is a diagram showing an example of the main configuration of the controller 133. The controller 133 of this configuration example includes a voltage dividing section 133a, a comparison section 133b, and a control section 133c.

[0137] The voltage dividing section 133a includes resistors R1 and R2 connected in series between the applied end of the voltage V2 and the applied end of the voltage V1 (= GND), and outputs a divided voltage Vx corresponding to the AC input voltage Vin from the connection node therebetween.

[0138] The comparison unit 133b compares the divided voltage Vx with predetermined threshold voltages (±a, ±b, ±c, ±d, and ±e in this figure, where 0<|a|<|b|<|c|<|d|<|e|) and outputs multiple comparison signals SC. Note that the number (types) of threshold voltages compared with the divided voltage Vx are not limited to this. Also, instead of the comparison unit 133b (comparator), an amplifier that generates an error signal ERR corresponding to the difference between the divided voltage Vx and a predetermined reference voltage Vref (=Vref-Vx) may be used.

[0139] The control unit 133c performs drive control of each of the drivers 131 and 132 in response to the comparison signal SC. For example, the control unit 133c determines the magnitude (=positive / negative and absolute value) of the AC input voltage Vin from the logical combination of the multiple comparison signals SC, and executes various internal controls (such as adjustment processing of threshold voltages VH and VL, switching stop processing of the bidirectional switch X, and enable processing of the second ZVS control, which will be described in detail later) based on the determination result.

[0140] 19 is a diagram showing an example of internal control of the controller 133, which illustrates, from the top, the operation mode of the bidirectional switch X and the threshold voltages VH and VL. The horizontal axis of this diagram indicates the magnitude of the divided voltage Vx (and thus the AC input voltage Vin).

[0141] In addition, in the following explanation, the possible voltage values ​​VH1 to VH5 of the positive threshold voltage VH (>0) are set as |VH1|<|VH2|<|VH3|<|VH4|<|VH5|, and the possible voltage values ​​VL1 to VL5 of the negative threshold voltage VL (<0) are set as |VL1|<|VL2|<|VL3|<|VL4|<|VL5|.

[0142] It is also possible to set |VH1|=|VL1|, |VH2|=|VL2|, |VH3|=|VL3|, |VH4|=|VL4|, and |VH5|=|VL5|.

[0143] Also, it is preferable that the voltage values VH1 to VH5 that the positive-side threshold voltage VH can take and the voltage values VL1 to VL5 that the negative-side threshold voltage VL can take can be arbitrarily set by the user.

[0144] When Vx < -e, for example, the threshold voltage VH is set to the voltage value VH1 and the threshold voltage VL is set to the voltage value VL1.

[0145] When -e < Vx < -d, for example, the threshold voltage VH is set to the voltage value VH2 and the threshold voltage VL is set to the voltage value VL2.

[0146] When -d < Vx < -c, for example, the threshold voltage VH is set to the voltage value VH3 and the threshold voltage VL is set to the voltage value VL3.

[0147] When -c < Vx < -b, for example, the threshold voltage VH is set to the voltage value VH4 and the threshold voltage VL is set to the voltage value VL4.

[0148] When -b < Vx < +b, for example, the threshold voltage VH is set to the voltage value VH5 and the threshold voltage VL is set to the voltage value VL5. However, when -a < Vx < +a, the bidirectional switch X enters the stop mode STOP (details will be described later), so the voltage values of the threshold voltages VH and VL are irrelevant.

[0149] When +b < Vx < +c, for example, the threshold voltage VH is set to the voltage value VH4 and the threshold voltage VL is set to the voltage value VL4.

[0150] When +c < Vx < +d, for example, the threshold voltage VH is set to the voltage value VH3 and the threshold voltage VL is set to the voltage value VL3.

[0151] When +d < Vx < +e, for example, the threshold voltage VH is set to the voltage value VH2 and the threshold voltage VL is set to the voltage value VL2.

[0152] When +d < Vx, for example, the threshold voltage VH is set to the voltage value VH1, and the threshold voltage VL is set to the voltage value VL1.

[0153] In this way, the switch driving device 130 (especially the controller 133) adjusts the threshold voltages VH and VL according to the magnitude (= positive / negative and absolute value) of the AC input voltage Vin.

[0154] More specifically, the switch driving device 130 (especially the controller 133) increases the absolute values of the threshold voltages VH and VL so as to advance the crossing timing between the differential voltage Vd and the threshold voltages VH and VL as the absolute value of the AC input voltage Vin becomes smaller.

[0155] For example, while referring to the above-mentioned FIG. 17, the adjustment operation of the threshold voltage VL will be described by taking the case where Vin < 0 (V1 > V2) as an example. In this case, as the absolute value of the AC input voltage Vin becomes larger, the penetration amount Vsw* of the switch voltage Vsw becomes smaller, and consequently, the change amount of the differential voltage Vd (= the lower peak value of the differential voltage Vd) also becomes smaller.

[0156] Therefore, unless the absolute value of the threshold voltage VL is set to be sufficiently small, there is a risk of failing to detect the change timing of the differential voltage Vd (= the timing when the differential voltage Vd that has fallen below the threshold voltage VL rises above the threshold voltage VL again) because the differential voltage Vd does not fall below the threshold voltage VL.

[0157] On the other hand, as the absolute value of the AC input voltage Vin becomes smaller, the penetration amount Vsw* of the switch voltage Vsw becomes larger, and consequently, the change amount of the differential voltage Vd (= the lower peak of the differential voltage Vd) also becomes larger. Therefore, within the range where the change timing of the differential voltage Vd can be detected, by setting the absolute value of the threshold voltage VL to be larger, the crossing timing between the differential voltage Vd and the threshold voltage VL can be advanced, and the clamp period Tc can be shortened.

[0158] If the clamp period Tc is shortened, the energy that returns to the input side decreases. As a result, the amount of undershoot Vsw* of the switch voltage Vsw approaches the ideal waveform, and the energy that can be fed into the output side increases accordingly, making it possible to improve the efficiency.

[0159] Note that although the clamp period Tc is originally very short, the delay of several tens of ns here significantly affects the amount of undershoot Vsw* of the switch voltage Vsw (and thus the efficiency). The improvement in efficiency is from several tenths of a percent to 0.2%, and at first glance, the improvement effect may seem small. However, the efficiency of today's switching power supplies has already reached the high 99% range, and further efficiency improvement is required. In view of this, it can be seen that an improvement of several tenths of a percent has a very large impact.

[0160] Also, if the topology of the circuit proposed in this embodiment is adopted, it is possible to easily configure a high-efficiency AC / DC converter and an isolated power supply with a component configuration that is available everywhere.

[0161] In addition, due to the shortening of the clamp period Tc, even when the AC input voltage Vin is large, the amount of undershoot Vsw* of the switch voltage Vsw increases. Therefore, the range of the AC input voltage Vin in which the change timing of the differential voltage Vd can be correctly detected expands.

[0162] As is clear from the above description, when Vin < 0 (V1 > V2), since the adjustment process of the threshold voltage VL contributes to the shortening of the clamp period Tc, the threshold voltage VH may be set to a fixed value (for example, the voltage value VH1).

[0163] Also, although not shown again, when Vin > 0 (V1 < V2), conversely, since the adjustment process of the threshold voltage VH contributes to the shortening of the clamp period Tc, the threshold voltage VL may be set to a fixed value (for example, the voltage value VL1).

[0164] Furthermore, the threshold voltages VH and VL may be adjusted stepwise using a comparator as shown in the figure, or may be adjusted continuously using an amplifier.

[0165] In addition, in the above, an example was given in which the threshold voltages VH and VL are adjusted according to the magnitude of the AC input voltage Vin. However, as another example, it is also possible to adjust the threshold voltages VH and VL according to the waveform (degree of dullness) of the differential voltage Vd.

[0166] For example, the switch driver 130 (particularly the controller 133) may increase the absolute values ​​of the threshold voltages VH and VL so as to advance the timing at which the differential voltage Vd crosses the threshold voltages VH and VL as the waveform of the differential voltage Vd becomes duller.

[0167] As information on the waveform (dullness) of the differential voltage Vd, for example, the peak value of the differential voltage Vd, or the time from zero to the peak value, or the slope at the start of the change in the differential voltage Vd may be detected.

[0168] In particular, in an actual device, it is advisable to adjust the threshold voltages VH and VL taking into consideration both the magnitude of the AC input voltage Vin and the waveform (dullness) of the differential voltage Vd. For example, when the AC input voltage Vin is large, the absolute values ​​of the threshold voltages VH and VL should be reduced, but if the waveform of the differential voltage Vd is significantly dull, the absolute values ​​of the threshold voltages VH and VL should not be reduced. Therefore, it is necessary to adjust the threshold voltages VH and VL taking into consideration the balance between the two.

[0169] In any case, in order to shorten the clamp period Tc, it is important to appropriately adjust the threshold voltages VH and VL in accordance with at least one of the magnitude of the AC input voltage Vin and the waveform of the differential voltage Vd, rather than setting the threshold voltages VH and VL to fixed values.

[0170] Next, the operation modes of the bidirectional switch X shown in the upper part of this figure will be described. First, in the first input voltage range (-e < Vin < -a and +a < Vin < +e), an operation mode [ZVS1 + ZVS2] is adopted in which both the first ZVS control and the second ZVS control described above are performed (see FIGS. 4, 5, 6, etc.).

[0171] On the other hand, in the second input voltage range (Vin < -e and +e < Vin), an operation mode [ZVS1] is adopted in which only the first ZVS control is performed (see FIG. 7, etc.). That is, when the absolute value of the AC input voltage Vin is greater than a predetermined upper limit value (e in this figure), the switch driving device 130 (particularly the controller 133) switches to an operation mode [ZVS1] in which one of the switch elements 110 and 120 is kept on and the other is turned on / off. Thereby, as described above, it is possible to suppress the heat generation of the bidirectional switch X without requiring strict timing control.

[0172] Also, in the third input voltage range (-a < Vin < +a), a stop mode [STOP] is adopted in which the driving of the bidirectional switch X is stopped. That is, when the absolute value of the AC input voltage Vin is smaller than a predetermined lower limit value (a in this figure), the switch driving device 130 (particularly the controller 133) switches to a stop mode [STOP] in which both the switch elements 110 and 120 are turned off. In this way, in an input voltage range where sufficient excitation cannot be expected even when the bidirectional switch X is driven, by stopping the driving of the bidirectional switch X, it is possible to reduce the switching losses of the switch elements 110 and 120 respectively and improve the efficiency.

[0173] <Tenth Embodiment> FIG. 20 is a diagram showing a tenth embodiment of the switching power supply. The switching power supply 1000 of this embodiment is based on the third embodiment (FIG. 9) with some modifications. Specifically, in this figure, a filter FLT is provided between the AC power supply P and the bidirectional switch X. The filter FLT may include the capacitor 151 described above.

[0174] Moreover, the switching power supply 1000 of this embodiment has a resistor Ri connected in series with the primary winding 141, and a current detection signal Is is drawn from one end of the resistor Ri. The switch driver 130 receives the input of this current detection signal Is, and has a function of stopping the on / off driving of the bidirectional switch X when the primary current flowing through the primary winding 141 is larger than an upper limit value, that is, a so-called overcurrent protection function.

[0175] The switch driver 130 also receives an input of an output feedback signal corresponding to the DC output voltage Vout, and has a function of stopping the on / off driving of the bidirectional switch X when the DC output voltage Vout is higher than an upper limit value, i.e., a so-called overvoltage prevention function.

[0176] Furthermore, in the switching power supply 1000 of this embodiment, the capacitor 152 and the current limiting element 340 in FIG. 9 are not explicitly shown, but it is up to the discretion of the user whether or not to omit them.

[0177] Next, the above-mentioned individual ZVS control in the switching power supply 1000 of this embodiment will be explained again with reference to the current path in each phase.

[0178] Fig. 21 is a diagram showing a first operation example (V1>V2) of the individual ZVS control in the tenth embodiment, depicting the switch voltage Vsw appearing at one end (=the drain of the switch element 120) of the bidirectional switch X, and the on / off states of the switch elements 110 and 120. Figs. 22 to 28 are diagrams showing current paths in each phase of the first operation example.

[0179] Before time t61, both switch elements 110 and 120 are on. At this time, as shown in Fig. 22, a primary current flows through a current path from a first node (= application end of voltage V1) of the AC power supply P via resistor Ri, primary winding 141, and bidirectional switch X to a second node (= application end of voltage V2) of the AC power supply P, and energy is stored in the primary winding 141. At this time, the switch voltage Vsw coincides with the voltage V2.

[0180] At time t61, when a predetermined amount of energy is accumulated in the primary winding 141, the switch driver 130 switches the bidirectional switch X from ON to OFF. The OFF timing of the bidirectional switch X may be detected by detecting that a predetermined time has elapsed since the ON timing of the bidirectional switch X, or may be detected by detecting that the integral value of the primary current has reached a predetermined threshold value.

[0181] At this time, the switch driver 130 does not turn off both the switch elements 110 and 120 at the same time, but keeps on the switch element 110 (= an element to which a forward voltage is applied) whose intrinsic diode 112 is forward biased, and turns off the switch element 120 (= an element to which a reverse voltage is applied) whose intrinsic diode 122 is reverse biased, as shown in FIG. 23.

[0182] Thereafter, as the switch voltage Vsw rises, the drain-source voltage (=Vsw-V2) of the switch element 120 gradually rises while storing energy mainly in the internal capacitance 123 of the switch element 120. The switch voltage Vsw rises until its absolute value matches the DC output voltage Vout.

[0183] Furthermore, when the switch voltage Vsw becomes higher than the sum of the voltage across the capacitor 311 and the forward drop voltage of the diode 322, as shown in FIG. 23, a current flows into the capacitor 311 via the diode 322, and the capacitor 311 is charged.

[0184] At time t62, when the energy stored in the transformer 140 is completely discharged to the capacitor 311, the internal capacitance 123 of the switch element 120 and other capacitances start to regenerate a primary current from the bidirectional switch X to the primary winding 141, as shown in Fig. 24. As a result, the switch voltage Vsw starts to decrease, and the drain-source voltage of the switch element 120 starts to decrease gradually.

[0185] 25, at time t63, a primary current is regenerated in a current path from the second node (=application end of voltage V2) of the AC power supply P through the switch function unit 111 of the switch element 110 and the internal diode 122 of the switch element 120 to the primary winding 141. In this state, the switch voltage Vsw is clamped to a voltage lower than the voltage V2 by the forward drop voltage of the internal diode 122.

[0186] The switch driver 130, at the appropriate timing, turns on the switch element 120 and turns off the switch element 110 at the same time, as shown in Fig. 26. By this switching control, the clamp on the switch voltage Vsw is released.

[0187] As a result, the resonant operation continues due to the energy stored in the transformer 140, and the switch voltage Vsw drops to a potential lower than the voltage V2. Therefore, the drain-source voltage (=V2-Vsw) of the switch element 110 rises, and a reverse voltage is applied to the switch element 110 (i.e., the internal diode 112 of the switch element 110 is reverse-biased).

[0188] 27, when the energy stored in the transformer 140 is exhausted, the regeneration of the primary current ends and the primary current starts to flow again from the primary winding 141 toward the bidirectional switch X. The direction of this primary current is the same as before time t61, and energy is stored in the primary winding 141. As a result, the switch voltage Vsw starts to increase due to the internal capacitance 113 of the switch element 110 and other capacitances, and the drain-source voltage of the switch element 110 starts to gradually decrease.

[0189] 28, at time t65, a state is reached in which a primary current flows in a current path from the primary winding 141 to the second node (=application end of voltage V2) of the AC power supply P via the switch function unit 121 of the switch element 120 and the internal diode 112 of the switch element 110. In this state, the switch voltage Vsw is clamped to a voltage higher than the voltage V2 by the forward drop voltage of the internal diode 112.

[0190] The switch driver 130 waits for the above timing to turn on the switch element 110 while keeping on the switch element 120. By such switching control, the switching power supply 1000 returns to the same state (FIG. 22) as before time t61.

[0191] Thus, in the first operation example (V1>V2) in the figure, when the switch driver 130 switches the bidirectional switch X from off to on, it performs a first ZVS control to turn on the switch element 120, which was off until then, at a timing when the voltage across the switch element 120 becomes 0 V, and subsequently performs a second ZVS control to turn off the switch element 110 at a timing when the switch element 120 is turned on, and to turn on the switch element 110 at a timing when the voltage across the switch element 110 becomes 0 V.

[0192] By repeating the above switching control, when the bidirectional switch X makes an on-transition, the switch elements 110 and 120 can be individually turned on at a timing when no charge is accumulated in the inherent capacitances 113 and 123 of the switch elements 110 and 120, respectively. Also, the primary winding 141 is performing excitation for the next energy transport substantially from time t64, and effectively utilizes a part of the resonance energy without regenerating it. Therefore, it is possible to reduce the switching losses of the switch elements 110 and 120 respectively, and suppress the heat generation of the bidirectional switch X.

[0193] FIG. 29 is a diagram showing a second operation example (V1 <V2) of the individual ZVS control in the tenth embodiment, depicting the switch voltage Vsw appearing at one end of the bidirectional switch X (= the drain of the switch element 120), and the on / off states of the switch elements 110 and 120 respectively. Also, FIGS. 30 to 36 are diagrams showing the current paths in each phase of the second operation example respectively.

[0194] Before time t71, both the switch elements 110 and 120 are turned on. At this time, as shown in FIG. 30, a primary current flows through the current path from the second node of the AC power supply P (= the applied end of the voltage V2) to the first node of the AC power supply P (= the applied end of the voltage V1) via the bidirectional switch X, the primary winding 141, and the resistor Ri, and energy is accumulated in the primary winding 141. At this point, the switch voltage Vsw coincides with the voltage V2.

[0195] At time t71, when a predetermined amount of energy is accumulated in the primary winding 141, the switch drive device 130 switches the bidirectional switch X from on to off. Regarding the off-timing of the bidirectional switch X, it may be detected that a predetermined time has elapsed from the on-timing of the bidirectional switch X, or it may be detected that the integrated value of the primary current has reached a predetermined threshold value.

[0196] At this time, the switch driver 130 does not turn off both the switch elements 110 and 120 at the same time, but turns off the switch element 110 (= element to which a reverse voltage is applied) whose internal diode 112 is reverse biased, while keeping on the switch element 120 (= element to which a forward voltage is applied) whose internal diode 122 is forward biased, as shown in FIG. 31 .

[0197] Thereafter, as the switch voltage Vsw decreases, the drain-source voltage (=V2-Vsw) of the switch element 110 gradually increases while storing energy mainly in the internal capacitance 113 of the switch element 110. The switch voltage Vsw decreases until its absolute value matches the DC output voltage Vout.

[0198] 31, a current flows into the capacitor 312 via the diode 321, and the capacitor 312 is charged. Furthermore, the energy stored in the capacitor 312 is used to charge the capacitor 311 via the auxiliary winding 330 and the secondary winding 142.

[0199] At time t72, when the energy stored in the transformer 140 is completely discharged to the capacitor 311, a primary current starts to be regenerated from the primary winding 141 toward the bidirectional switch X, as shown in Fig. 32. As a result, the switch voltage Vsw starts to increase due to the internal capacitance 113 of the switch element 110 and other capacitances, and the drain-source voltage of the switch element 110 starts to gradually decrease.

[0200] 33, a state is reached in which a primary current is regenerated in a current path from the primary winding 141 to the second node (=application end of voltage V2) of the AC power supply P via the switch function unit 121 of the switch element 120 and the internal diode 112 of the switch element 110. In this state, the switch voltage Vsw is clamped to a voltage higher than the voltage V2 by the forward drop voltage of the internal diode 112.

[0201] The switch driver 130, at the appropriate timing, turns on the switch element 110 and turns off the switch element 120 at the same time, as shown in Fig. 34. By this switching control, the clamp on the switch voltage Vsw is released.

[0202] As a result, the resonant operation continues due to the energy stored in the transformer 140, and the switch voltage Vsw rises to a potential higher than the voltage V2. Therefore, the drain-source voltage (=Vsw-V2) of the switch element 120 rises, and a reverse voltage is applied to the switch element 120 (i.e., the internal diode 122 of the switch element 120 is reverse-biased).

[0203] 35, when the energy stored in the transformer 140 is exhausted, the regeneration of the primary current ends and the primary current starts to flow again from the bidirectional switch X to the primary winding 141. The direction of this primary current is the same as before time t71, and energy is stored in the primary winding 141. As a result, the switch voltage Vsw starts to decrease due to the internal capacitance 123 of the switch element 120 and other capacitances, and the drain-source voltage of the switch element 120 starts to decrease gradually.

[0204] 36, a state is reached where a primary current flows through a current path from the second node (=application end of voltage V2) of the AC power supply P to the primary winding 141 via the switch function unit 111 of the switch element 110 and the intrinsic diode 122 of the switch element 120. In this state, the switch voltage Vsw is clamped to a voltage lower than the voltage V2 by the forward drop voltage of the intrinsic diode 122.

[0205] The switch driver 130 waits for the above timing to turn on the switch element 120 while keeping on the switch element 110. By such switching control, the switching power supply 1000 returns to the same state (FIG. 30) as before time t71.

[0206] Thus, in the second operation example (V1 < V2) of this figure, when the switch driving device 130 switches the bidirectional switch X from off to on, the switch element 110 that has been off is turned on at the timing when the voltage between its both ends becomes 0V, and the first ZVS control is performed. Subsequently, at the timing when the switch element 110 is turned on, the switch element 120 is turned off, and the second ZVS control is performed so that the switch element 120 is turned on at the timing when the voltage between its both ends becomes 0V.

[0207] By repeating the above switching control, at the timing when the charge is not accumulated in the internal capacitances 113 and 123 of the switch elements 110 and 120 respectively during the on-transition of the bidirectional switch X, the switch elements 110 and 120 can be individually turned on. Therefore, it is possible to reduce the switching losses of the switch elements 110 and 120 respectively and suppress the heat generation of the bidirectional switch X.

[0208] <Consideration Regarding the Stop of On / Off Driving> By the way, in the switching power supply 1000 of the present embodiment (the same applies to the switching power supplies 100 to 900 of other embodiments), in response to a predetermined stop trigger STOP, the on / off driving of the bidirectional switch X may be forcibly stopped.

[0209] For example, at the timing when the polarity of the AC input voltage Vin is reversed (for example, -12V < Vin < +12V), sufficient excitation cannot be expected even if the bidirectional switch X is driven. Therefore, by stopping the on / off driving of the bidirectional switch X, it is possible to reduce the switching losses of the switch elements 110 and 120 respectively and improve the efficiency.

[0210] Also, when the primary current flowing through the primary winding 141 becomes larger than the upper limit value and the overcurrent prevention function is activated, or when the DC output voltage Vout becomes higher than the upper limit value and the overvoltage prevention function is activated, the on / off driving of the bidirectional switch X can also be stopped.

[0211] Fig. 37 is a diagram showing a state when the on / off driving of the bidirectional switch X is stopped at the polarity reversal timing of the AC input voltage Vin, and depicts the switch voltage Vsw and the AC input voltage Vin. Fig. 38 is an enlarged view of the region α in Fig. 37.

[0212] As shown in this figure, when the AC input voltage Vin switches from negative to positive polarity, the on / off driving of the bidirectional switch X is stopped when Vin>-Vx (e.g., -12 V), and then the on / off driving of the bidirectional switch X is resumed when Vin>+Vy (e.g., +36 V).

[0213] In addition, when the AC input voltage Vin switches from positive to negative polarity, the on / off driving of the bidirectional switch X is stopped at the timing when Vin<+Vx (e.g., +12 V), and then, the on / off driving of the bidirectional switch X is resumed at the timing when Vin<-Vy (e.g., -36 V).

[0214] In this way, when the on / off driving of the bidirectional switch X is stopped, both the switch elements 110 and 120 are turned off. At this time, the bidirectional switch X is not necessarily ZVS controlled. Therefore, depending on the excitation state and the resonance state immediately before the bidirectional switch X is turned off, energy may be stored in the primary winding 141 or the internal capacitances 113 and 123, and LC resonance may occur due to the energy that has nowhere to go.

[0215] The above-mentioned LC resonance can be a source of noise. If the LC resonance continues until the on / off drive is restarted, it can have a negative effect on the circuit operation. Therefore, in the following, we propose a drive stop process that can suppress the LC resonance.

[0216] <Drive stop processing> 39 is a diagram showing a first example (V1>V2) of the drive stop processing by the switch driver 130 (particularly the controller 133), depicting the switch voltage Vsw and the on / off states of the switch elements 110 and 120. Note that for the switch voltage Vsw, the solid line indicates the behavior in a new drive stop processing, and the dashed line indicates the behavior when the switch elements 110 and 120 are simply turned off.

[0217] Before time t81, the bidirectional switch X is turned on, so that a primary current flows through the primary winding 141 and energy is stored. At this point in time, the switch voltage Vsw coincides with the voltage V2.

[0218] At time t81, when a predetermined amount of energy is accumulated in the primary winding 141, the bidirectional switch X is switched from on to off. More specifically, the switch element 120 is turned off while the switch element 110 remains on. As a result, the switch voltage Vsw rises until its absolute value matches the DC output voltage Vout.

[0219] At time t82, when some stop trigger STOP (such as polarity reversal of the AC input voltage Vin, overcurrent protection, or overvoltage protection) is activated, the on / off driving of the bidirectional switch X is stopped. That is, both switch elements 110 and 120 are turned off. At this time, energy has been accumulated in the primary winding 141, and LC resonance occurs due to the energy that has nowhere to go.

[0220] After both switch elements 110 and 120 are turned off as described above, switch element 110 is temporarily turned on for a predetermined on-time T1 from time t83 to time t84. That is, switch element 110 is turned on at time t83 and turned off again at time t84.

[0221] Here, the switch element 110 that is temporarily turned on is, of the switch elements 110 and 120, the switch element in which the internal diode 112 is reverse-biased when a primary current is regenerated from the bidirectional switch X toward the primary winding 141 (see FIG. 25 above).

[0222] According to such a drive stop process, the resonance energy (= the energy stored in the primary winding 141 or the internal capacitances 113 and 123) can be regenerated to the AC power supply P, so that the LC resonance can be suppressed.

[0223] The on-time T1 of the switch element 110 should be set to a length equal to or longer than the resonance period T0. The resonance period T0 basically has a length according to the inductance of the primary winding 141 and the built-in capacitance of the bidirectional switch X (=either one of the built-in capacitances 113 and 123).

[0224] In addition, in this figure, after both switch elements 110 and 120 are turned off, switch element 110 is turned on after a waiting time T2 has elapsed, but this waiting time T2 can be adjusted as desired.

[0225] For example, if suppression of LC resonance is to be prioritized, the waiting time T2 may be set to zero (or nearly zero), and only the switch element 110 may be turned on again immediately after both the switch elements 110 and 120 are turned off. On the other hand, if safety is to be prioritized in the event that a stop trigger STOP is activated due to activation of the abnormality protection function, the waiting time T2 may be set to a longer value.

[0226] In addition, the standby time T2 may be set individually depending on the type of the stop trigger STOP. For example, it is possible to set the standby time T2 longer to prioritize safety when an overcurrent is detected, whereas it is possible to set the standby time T2 shorter to prioritize suppression of LC resonance when an overvoltage is detected.

[0227] Also, when the polarity of the AC input voltage Vin is reversed, since little energy is accumulated in the primary winding 141 in the first place, the amplitude of the LC resonance does not increase so much. In view of this, when the polarity of the AC input voltage Vin is reversed, after turning off both the switch elements 110 and 120, it is also possible to keep both the switch elements 110 and 120 off without temporarily turning on the switch element 110.

[0228] In this figure, the case where the stop trigger STOP is applied when the switch element 110 is on and the switch element 120 is off is illustrated. However, the stop trigger STOP may be applied during the period when the switch element 110 is off and the switch element 120 is on (for example, at times t63 to t65 in FIG. 21). In that case, turning on the switch element 120 temporarily rather than the switch element 110 can lead to faster convergence of the LC resonance.

[0229] Thus, if the state of the LC resonance can be fully grasped, it is possible to suppress the LC resonance by temporarily turning on the more appropriate one of the switch elements 110 and 120 for the on-time T1. In this case, the on-time T1 only needs to be set to a length of at least half of the resonance period T0 or more.

[0230] FIG. 40 is a diagram showing a second example (V1 < V2) of the drive stop process by the switch drive device 130 (particularly the controller 133). Similar to the previous FIG. 39, the switch voltage Vsw and the on / off states of the switch elements 110 and 120 are depicted. Regarding the switch voltage Vsw, the solid line indicates the behavior in the new drive stop process, and the dashed line indicates the behavior when the switch elements 110 and 120 are simply turned off.

[0231] Before time t91, since the bidirectional switch X is on, a primary current flows through the primary winding 141 and energy is accumulated. At this point, the switch voltage Vsw coincides with the voltage V2.

[0232] At time t91, when a predetermined amount of energy is accumulated in the primary winding 141, the bidirectional switch X is switched from on to off. More specifically, the switch element 110 is switched off while the switch element 120 remains on. As a result, the switch voltage Vsw drops until its absolute value matches the DC output voltage Vout.

[0233] At time t92, when some stop trigger STOP (such as polarity reversal of the AC input voltage Vin, overcurrent protection, or overvoltage protection) is activated, the on / off driving of the bidirectional switch X is stopped. That is, both switch elements 110 and 120 are turned off. At this time, energy has been accumulated in the primary winding 141, and LC resonance occurs due to the energy that has nowhere to go.

[0234] After both switch elements 110 and 120 are turned off as described above, switch element 120 is temporarily turned on for a predetermined on-time T1 from time t93 to t94. That is, switch element 120 is turned on at time t93 and turned off again at time t94.

[0235] Here, the switch element 120 that is temporarily turned on is, of the switch elements 110 and 120, the switch element in which the internal diode 122 is reverse-biased when a primary current is regenerated from the primary winding 141 toward the bidirectional switch X (see FIG. 33 above).

[0236] According to such a drive stop process, as in the first operation example (FIG. 39) described above, the resonance energy (= the energy stored in the primary winding 141 or the internal capacitances 113 and 123) can be regenerated to the AC power supply P, so that it is possible to suppress the LC resonance. Moreover, since other points are also similar to the first operation example, a duplicated description will be omitted.

[0237] <Summary> The following provides an overview of the various embodiments described herein.

[0238] For example, the switch driving device disclosed in this specification has a controller configured to individually control a first switch element and a second switch element that form a bidirectional switch, and the controller is configured (first configuration) to turn off both the first switch element and the second switch element when stopping the on / off driving of the bidirectional switch, and then temporarily turn on either the first switch element or the second switch element for a predetermined on-time.

[0239] In the switch driving device according to the first configuration, the switch element that is temporarily turned on may be configured (second configuration) to be a switch element whose internal diode is reverse-biased during current regeneration.

[0240] In the switch driver according to the first or second configuration, the on-time may be set to a length equal to or longer than the resonance period (third configuration).

[0241] Furthermore, in the switch driving device according to any one of the first to third configurations, the controller may be configured (fourth configuration) to keep one of the first switch element and the second switch element on and turn the other switch element off when switching the bidirectional switch from on to off.

[0242] In addition, in the switch driving device according to the fourth configuration, the controller may be configured to perform a first zero voltage switching control (fifth configuration) so that, when switching the bidirectional switch from off to on, the other switch element is turned on at a timing when the voltage between both ends of the other switch element becomes 0 V.

[0243] Furthermore, in the switch driving device according to the fifth configuration, the controller may be configured (sixth configuration) to perform, when switching the bidirectional switch from off to on, second zero voltage switching control subsequent to the first zero voltage switching control, so as to turn off the one switch element at a timing to turn on the other switch element and to turn on the one switch element at a timing when the voltage between both ends of the one switch element becomes 0 V.

[0244] Also, for example, a switching power supply disclosed in this specification has a primary winding configured to receive an AC input voltage, a secondary winding configured to be coupled to the primary winding, a bidirectional switch configured to be connected in series to the primary winding, a full-wave rectifier circuit configured to full-wave rectify an induced voltage generated in the secondary winding, a smoothing capacitor configured to smooth the output of the full-wave rectifier circuit, and a switch driver that drives the bidirectional switch by any one of the first to sixth configurations above, and is configured to extract a flyback voltage or both a forward voltage and a flyback voltage from the secondary winding to directly convert the AC input voltage into a DC output voltage (seventh configuration).

[0245] In the switching power supply according to the seventh configuration, the switch driver may be configured (eighth configuration) to stop on / off driving of the bidirectional switch when the absolute value of the AC input voltage is smaller than a lower limit value.

[0246] In addition, in the switching power supply according to the seventh or eighth configuration, the switch driver may be configured (ninth configuration) to stop on / off driving of the bidirectional switch when the DC output voltage is higher than an upper limit value.

[0247] In addition, in the switching power supply according to any one of the seventh to ninth configurations, the switch driver may be configured (tenth configuration) to stop on / off driving of the bidirectional switch when the primary current flowing through the primary winding is larger than an upper limit value.

[0248] <Other Modifications> In addition to the above-mentioned embodiment, various technical features disclosed in this specification can be modified in various ways without departing from the spirit of the technical creation. In other words, the above-mentioned embodiment should be considered to be illustrative and not restrictive in all respects, and the technical scope of the present invention should not be limited to the above-mentioned embodiment, but should be understood to include all modifications that fall within the meaning and scope equivalent to the scope of the claims. [Explanation of symbols]

[0249] 100, 200, 300, 400, 500, 600, 700, 800, 900, 1000 Switching Power Supply 110, 120 Switch element 111, 121 Switch function part 112, 122 Intrinsic diode 113, 123 intrinsic capacity 130 Switch drive device 131, 132 Driver 133 Controller 133a Voltage divider 133b Comparison section 133c Control section 140 Transformer 141 Primary Winding 142, 142a, 142b Secondary winding 151, 152, 153, 154 Capacitors 161, 162 Diodes 170 Snubber Circuit 210, 220 Switch element 211, 221 Switch function part 212, 222 Intrinsic diode 213, 223 intrinsic capacity 230 Capacitor 311, 312 Capacitor 321, 322, 323 Diodes 330 Auxiliary Winding 340 Current limiting element 410 Differential circuit 411 Resistance 412 Capacitor 510 Zero voltage detection circuit 610 Auxiliary Winding 620 Zero voltage detection circuit 710 Starter Circuit 810 Starter Circuit C1~C4 Floating capacitance C5 intrinsic capacity FLT Filter P AC power supply R1, R2, Rin resistance X Two-way switch Z load

Claims

1. a controller configured to individually control a first switch element and a second switch element that form a bidirectional switch; the controller, when stopping the on / off driving of the bidirectional switch, turns off both the first switch element and the second switch element, and then temporarily turns on either the first switch element or the second switch element for a predetermined on-time.

2. 2. The switch driver according to claim 1, wherein the switch element that is temporarily turned on is a switch element whose internal diode is reverse-biased during current regeneration.

3. 3. The switch driver according to claim 1, wherein the on-time is set to a length equal to or longer than a resonance period.

4. 4. The switch drive device according to claim 1, wherein when the bidirectional switch is switched from on to off, the controller turns off one of the first switch element and the second switch element while keeping the other switch element on.

5. 5. The switch drive device according to claim 4, wherein the controller performs a first zero voltage switching control when switching the bidirectional switch from off to on so that the other switch element is turned on at a timing when a voltage between both ends of the other switch element becomes 0 V.

6. 6. The switch drive device according to claim 5, wherein, when switching the bidirectional switch from off to on, the controller performs, following the first zero voltage switching control, a second zero voltage switching control so as to turn off the one switch element at a timing at which the other switch element is turned on and to turn on the one switch element at a timing at which a voltage between both ends of the one switch element becomes 0 V.

7. a primary winding configured to receive an AC input voltage; a secondary winding configured to be coupled to the primary winding; a bidirectional switch configured to be connected in series with the primary winding; a full-wave rectifier circuit configured to full-wave rectify an induced voltage generated in the secondary winding; a smoothing capacitor configured to smooth the output of the full-wave rectifier circuit; A switch driving device according to any one of claims 1 to 6 that drives the bidirectional switch; having A switching power supply that derives a flyback voltage, or both a forward voltage and a flyback voltage, from the secondary winding to directly convert the AC input voltage into a DC output voltage.

8. 8. The switching power supply according to claim 7, wherein the switch driver stops on / off driving of the bidirectional switch when the absolute value of the AC input voltage is smaller than a lower limit value.

9. 9. The switching power supply according to claim 7, wherein the switch driver stops on / off driving of the bidirectional switch when the DC output voltage is higher than an upper limit value.

10. 10. The switching power supply according to claim 7, wherein the switch driver stops on / off driving of the bidirectional switch when a primary current flowing through the primary winding is greater than an upper limit value.

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