JP2016077073A - Switching power supply - Google Patents

Abstract

PROBLEM TO BE SOLVED: To achieve high power conversion efficiency while preventing a switching element from being destroyed by a spike current until reaching a stable current resonant state in a current resonant bridge system switching power supply.SOLUTION: In switch parts 13 and 14 of a half bridge connection, super junction structure MOSFET 131 and 141 with small ON resistance and IGBT 132 and 142 with high current resistance of body diodes are disposed in parallel. At a startup time, a control part 3 supplies a PWM signal the pulse width of which is gradually widened to the IGBT 132 and 142, thereby gradually increasing a switching current that flows to a primary coil 201 of a transformer 20. When a switching current waveform becomes sinusoidal after the lapse of a predetermined time, the control part 3 supplies a drive signal meeting a resonant frequency of a resonance circuit to the SJ-MOSFET 131 and 141 and performs switching in a resonance operation mode.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a switching power supply device used for a DC-DC converter, a DC-AC converter, and the like, and more specifically, an insulation type switching power supply device in which a primary side circuit and a secondary side circuit are electrically insulated by a transformer. About.

  A switching power supply device such as a DC-DC converter is characterized by being highly efficient while being small and light, and has recently been widely used as a power source for various electronic devices and devices. Such a switching power supply device generally has a configuration in which a primary side circuit and a secondary side circuit are electrically insulated using a transformer.

  In this type of switching power supply device, several systems are known as a circuit configuration for converting DC power into high-frequency AC power and converting it into DC power again. The simplest configuration is a single forward system in which a switching element is connected in series to a primary winding of a transformer, and the switching element is driven on and off to allow current to flow intermittently through the primary winding. This method has an advantage that not only the configuration is simple but also the control is stable, but there is a problem that the power conversion efficiency is low because the utilization efficiency of the transformer is low. On the other hand, the half-bridge method and the full-bridge method using a plurality of switching elements that are alternately turned on alternately flow current in both directions alternately to the primary winding of the transformer, so that the efficiency of use of the transformer is high. Therefore, there is an advantage that the power conversion efficiency is also high.

  In any method, since the current is supplied to the primary winding of the transformer through the element when the switching element provided in the primary circuit is on, the on-resistance of the switching element is large. As a result, the current loss at the resistor increases, and the power conversion efficiency decreases accordingly. Therefore, in order to suppress power loss, it is desirable that the on-resistance of the switching element provided in the primary circuit is as small as possible.

  A MOSFET having a special structure called a super junction structure (hereinafter, a commonly used abbreviation “SJ-MOSFET”) is known as a switching element having a particularly low on-resistance. In the SJ-MOSFET, a normal power MOSFET has a structure in which thin p-type layers and thin n-type layers are alternately arranged in a vertical direction in a drift layer which is an n-type semiconductor region, and a depletion layer is n It spreads over the entire interface between the mold layer and the p-type layer. In this case, the electric field formed by the voltage applied between the source and the drain exists not only in the direction from the source to the drain but also in the direction from each n-type layer to the adjacent p-type layer. Thereby, the electric field does not concentrate on a specific portion, and the withstand voltage can be increased while lowering the on-resistance.

  The use of such an SJ-MOSFET as a switching element of a primary circuit of a switching power supply device is disclosed in Patent Documents 1 and 2 and the like. The switching power supply devices described in these patent documents are all of the single forward system. As mentioned above, the half-bridge method and the full-bridge method are preferable to the single-forward method in terms of power conversion efficiency. It is conceivable to use an SJ-MOSFET for the switching element of the primary circuit, but unlike the single forward method, an attempt is made to use the SJ-MOSFET for the bridge type switching power supply device. If you do, there are the following problems.

  That is, in a single forward switching power supply, even if a current flows through the body diode of a switching element and the element temporarily becomes short during the reverse recovery period, In this case, the circuit is not completely short-circuited. Thereby, the switching element is prevented from being destroyed.

  On the other hand, the situation is different in a bridge-type switching power supply device in which a current alternately flows bidirectionally in the primary winding of the transformer. That is, for example, in a half-bridge type switching power supply device, when one switching element is in an ON state, if the other switching element that is originally in an OFF state is turned on for some reason, the DC positive power supply line And the negative power supply line are short-circuited through a very small on-resistance of the switching element. Thus, depending on the application, a kiloampere current may flow through the switching element in microseconds, causing the element to break down.

  As is well known, in a bridge-type switching power supply device, energy stored in the primary winding (reactor) of the transformer is used when a plurality of switching elements are all off during the dead time period. The derived current tends to flow through the body diode of the switching element. When an SJ-MOSFET is used as a switching element in such a circuit, a plurality of SJ-MOSFETs are substantially short-circuited during a reverse recovery period when a current is passed through the body diode, for example, an excessive recovery current flows through the body diode. As a result, the device may be destroyed. Such a phenomenon can occur in the MOSFET, but in the SJ-MOSFET, the charge is likely to move particularly in the parasitic transistor due to the structure.

  In the current resonance type bridge type switch power supply device, when the circuit configuration and the element constant are appropriately selected, a mode in which no current flows through the body diode of the switching element at the time of the current resonance operation can be realized. In this state, a problem peculiar to the SJ-MOSFET as described above does not occur, and the SJ-MOSFET functions as a switching element having an extremely low on-resistance. This state has no relation to the increase or decrease of the load or the power supply voltage, and it has been confirmed by simulation and experiment that stable operation is maintained in the range from no load to about three times the rated load.

However, it is necessary to gradually increase the output voltage by applying a pulse width modulation (PWM) signal to the gate of the switching element during the period from when the switching power supply device is started until stable current resonance operation is performed. During such PWM control, a zero current switching operation is not performed, so that a large current flows through the body diode of the switching element.
That is, in the current resonance type bridge type switch power supply device, when the current resonance operation is performed, the SJ-MOSFET can be used as a switching element without any problem as in the above-described single forward type switching power supply device. Although possible, an excessive current may flow through the body diode of the switching element during the period from when the device is started to when the current resonance operation is performed, and the element may be destroyed. Therefore, in such a switching power supply device, an SJ-MOSFET cannot be used as a switching element.

JP 2000-156978 A JP 2011-55679 A

  The present invention has been made to solve the above-mentioned problems, and its object is to avoid problems such as breakage of the switching element in the period until the transition to the resonance operation mode in the bridge type switching power supply device. However, an object of the present invention is to provide a switching power supply device capable of realizing efficient power conversion using an SJ-MOSFET.

The first aspect of the present invention, which has been made to solve the above-mentioned problems, supplies a current that switches a DC current supplied from a DC power source and alternately inverts the primary winding of the transformer. In a switching power supply device that induces AC power in the secondary winding of the transformer by current flowing in the secondary winding,
a) a switch circuit provided between the DC power supply and the primary winding of the transformer, each of which includes a plurality of switch units each including at least one switching element, and a half bridge connection or a full bridge connection;
b) a resonance capacitor disposed in a closed circuit including a switch unit in the switch circuit, the DC power supply, and a primary winding of the transformer;
c) a control unit that turns on / off each of the switching elements included in the plurality of switch units in the switch circuit, and
Each of the switch parts includes a super junction MOSFET (SJ-MOSFET) and an insulated gate bipolar transistor (IGBT) connected in parallel as switching elements,
The control unit maintains the SJ-MOSFET in an off state until a predetermined time elapses from the start point or until the output voltage reaches a predetermined value, while increasing the target voltage. A PWM control operation for changing a pulse width of a drive signal supplied to the IGBT is performed, and after the start-up period, the IGBT is kept in an OFF state, while a resonance including a primary winding of the transformer and the capacitor. The operation mode is switched so as to perform the resonance operation for switching the SJ-MOSFET in accordance with the resonance frequency of the circuit.

The second aspect of the present invention, which has been made to solve the above-mentioned problems, switches a DC current supplied from a DC power supply and supplies a current that is alternately inverted to the primary winding of the transformer. In a switching power supply apparatus that induces AC power in the secondary winding of the transformer by a current flowing in the primary winding,
a) a switch circuit provided between the DC power supply and the primary winding of the transformer, each of which includes a plurality of switch units each including at least one switching element, and a half bridge connection or a full bridge connection;
b) a resonant capacitor disposed in a closed circuit including the secondary winding of the transformer;
c) a control unit that turns on / off each of the switching elements included in the plurality of switch units in the switch circuit, and
Each of the switch parts includes a super junction MOSFET (SJ-MOSFET) and an insulated gate bipolar transistor (IGBT) connected in parallel as switching elements,
The control unit maintains the SJ-MOSFET in an off state until a predetermined time elapses from the start point or until the output voltage reaches a predetermined value, while increasing the target voltage. A PWM control operation for changing the pulse width of the drive signal supplied to the IGBT is performed, and after the start-up period, the IGBT is kept in an off state, while the resonance including the secondary winding of the transformer and the capacitor The operation mode is switched so as to perform the resonance operation for switching the SJ-MOSFET in accordance with the resonance frequency of the circuit.

  The switching power supply according to the first aspect of the present invention is provided with a resonance circuit on the primary winding side of the transformer, and the switching power supply according to the second aspect of the present invention resonates on the secondary winding side of the transformer. Although there is a difference that the circuit is provided, the switching element is driven in accordance with the resonance frequency of the resonance circuit, and zero current switching can be realized in any case.

  In any case, in the switching power supply device according to the present invention, each switch unit included in the switch circuit has a small on-resistance but a low current resistance of the body diode and a large on-resistance compared to the SJ-MOSFET. However, an IGBT with high current resistance of the body diode is connected in parallel.

In the start-up period from when the present apparatus is activated until the output voltage settles near the target voltage, it is necessary to perform PWM control in order to gradually increase the output voltage. At that time, the control unit does not supply an effective drive signal to the SJ-MOSFET of each switch unit, and supplies a drive signal for PWM control only to the IGBT. Thereby, a current is supplied to the primary winding of the transformer by the on / off operation of the IGBT. Therefore, at this time, although the loss in each switch part (that is, IGBT) is relatively large, even if a large current flows through the body diode of the IGBT during the dead time period when all the switch parts are in the OFF state, the IGBT is damaged. It will not reach.
At this time, a current also flows through the body diode of the SJ-MOSFET connected in parallel to the IGBT. However, the SJ-MOSFET is completely turned off during the PWM control operation period, and the current is interrupted by the SJ-MOSFET. Regardless of the gate, it is performed by IGBTs connected in parallel. Therefore, the problem caused by the reverse recovery time of the body diode of the SJ-MOSFET described above does not occur, and the current can be safely interrupted.

  For example, when a predetermined time elapses from the starting time and the output voltage settles near the target voltage, the control unit stops supplying the drive signal to the IGBT of each switch unit, and instead, the primary of the transformer A drive signal in accordance with the resonance frequency of the resonance circuit on the winding side or the secondary winding side is supplied to the gate of the SJ-MOSFET. As a result, the switching operation is performed at a frequency close to the resonance frequency of the resonance circuit. Therefore, the on / off operation is performed when almost no current flows through the switch unit, and the zero current switching operation is achieved. Therefore, a small amount of current flows through the body diode of the SJ-MOSFET driven on / off, and even if the current resistance of the SJ-MOSFET is low, it can be avoided that the device is damaged. Further, since the on-resistance of the SJ-MOSFET is small, the loss at the switch unit is small and efficient power conversion is performed.

  Note that if the switching of the operation mode from the PWM operation to the resonance operation is performed in a state where a large current flows through the IGBT, a large current may flow through the body diode of the SJ-MOSFET immediately after the switching. Therefore, in order to avoid such a situation, in the switching power supply according to the present invention, the control unit operates from the PWM operation to the resonance operation in synchronization with the change of the drive signal supplied to the IGBT when the PWM operation is executed. It is preferable that the mode is switched.

  According to the switching power supply device according to the present invention, an SJ-MOSFET having a small on-resistance can be used as a switching element in a half-bridge method or a full-bridge method with high power conversion efficiency. Thereby, loss in the switch unit can be suppressed and high power conversion efficiency can be realized. In addition, since switching using the IGBT instead of the SJ-MOSFET is performed at the time of starting the device that starts supplying power to the load, damage to the SJ-MOSFET can be avoided even if a large current flows through the body diode at the time of starting. .

BRIEF DESCRIPTION OF THE DRAWINGS The schematic block diagram of the switching power supply device which is 1st Example of this invention. The figure which shows the change of the target voltage of PWM control in the switching power supply device of 1st Example. The timing diagram of the principal part in the control part of the switching power supply device of 1st Example. The signal waveform figure of the principal part in the switching power supply device of 1st Example. The block diagram of a part of switching power supply which is a modification of 1st Example. The block diagram of a part of switching power supply which is a modification of 1st Example. The block diagram of a part of switching power supply which is a modification of 1st Example. The schematic block diagram of the switching power supply device which is 2nd Example of this invention. The block diagram of a part of switching power supply device which is a modification of 2nd Example. The block diagram of a part of switching power supply device which is a modification of 2nd Example.

[First embodiment]
A switching power supply device according to a first embodiment of the present invention will be described with reference to the accompanying drawings.
FIG. 1 is a schematic configuration diagram of a switching power supply device according to the present embodiment. The switching power supply of this embodiment is a current resonance type half-bridge switching power supply in which a resonance circuit is provided on the primary side of a transformer, and is a DC-DC converter whose output voltage is direct current.

  In the switching power supply device of the first embodiment, the primary side circuit 1 and the secondary side circuit 2 are insulated by the transformer 20 having the primary winding 201 and the secondary winding 202. In the primary side circuit 1, a first switch unit 13 and a second switch unit 14 are provided between a positive power supply line 11 and a negative power supply line 12 connected to the positive electrode and the negative electrode of the DC power supply 10. A series circuit connected in series is provided. A series circuit in which a resonance first capacitor 15 and a second capacitor 16 are connected in series is also provided between the positive power line 11 and the negative power line 12. The capacitances of the first and second capacitors 15 and 16 are equal. The primary winding 201 of the transformer 20 is connected between the connection point A of the two switch units 13 and 14 and the connection point B of the two capacitors 15 and 16.

  The first switch unit 13 includes a first SJ-MOSFET 131, a first IGBT 132, and a first diode 133 connected in the reverse direction, connected in parallel. Similarly, the second switch unit 14 includes a second SJ-MOSFET 141, a second IGBT 142, and a second diode 143 connected in the opposite direction, connected in parallel. Although the SJ-MOSFETs 131 and 141 have lower on-resistance than the IGBTs 132 and 142, the current resistance of the body diode is low, so that a large current cannot flow through the body diode.

  The secondary circuit 2 includes a full-wave rectifier circuit 21 in which four diodes are connected in a bridge configuration and a smoothing capacitor 22, and a load that is an object for supplying DC power to both ends of the capacitor 22. 23 is connected. As will be described later, the configuration of the secondary circuit 2 is not limited to this.

  The control unit 3 supplies drive signals to the SJ-MOSFETs 131 and 141 and the IGBTs 132 and 142 included in the switch units 13 and 14 via the drive circuit 4. The control unit 3 includes a soft start control unit 30, a PWM control unit 31, a counter unit 32, and a drive signal switching unit 33 as functional blocks. These can be configured by a hardware circuit, but at least some of the functions may be realized by a microcomputer including a CPU, a ROM, a RAM, a timer, and the like.

  Next, the operation of the switching power supply device according to the first embodiment will be described with reference to FIGS. 2 to 4 in addition to FIG. FIG. 2 is a diagram showing changes in the target voltage of PWM control, FIG. 3 is a timing diagram of the main part in the control unit, and FIG. 4 is a signal waveform diagram of the main part.

  When the switching power supply device of the first embodiment is activated, an activation signal is input to the soft start control unit 30 and the counter unit 32 in the control unit 3. Here, “startup” means the start of an operation for starting to supply power to the load 23 in the present apparatus. When receiving the start signal, the soft start control unit 30 outputs a target voltage that changes with time to the PWM control unit 31 as shown in FIG.

  The PWM control unit 31 has a built-in frequency-adjustable oscillator, and the oscillation frequency is adjusted so as to coincide with the resonance frequency when the primary side circuit 1 resonates. That is, as will be described later, the first switch unit 13 and the second switch unit 14 are driven so as to be alternately turned on with an appropriate dead time interposed therebetween, so that the first switch unit 13 is turned on. In operation, the closed circuit including the DC power supply 10, the first switch unit 13, the primary winding 201 of the transformer 20, and the second capacitor 16 is a resonance circuit. When the second switch unit 14 is turned on, the closed circuit including the DC power source 10, the first capacitor 15, the primary winding 201 of the transformer 20, and the second switch unit 14 is a resonance circuit. .

  The PWM control unit 31 synchronizes with a clock signal CLK (see FIG. 3C) having a predetermined frequency generated by the oscillator, and outputs a PWM signal having a pulse width corresponding to the target voltage supplied from the soft start control unit 30. Generate. As shown in FIGS. 3A and 3B, the PWM signals are two systems of signals PWM1 and PWM2 in which pulses appear alternately for each clock signal CLK. The two PWM signals PWM1 and PWM2 are input to the drive signal switching unit 33. On the other hand, the counter unit 32 serves as a timer for measuring the elapse of a predetermined time from the activation point, is reset by the activation signal, and then counts the clock signal CLK. When the count value reaches a predetermined value, the output Q changes from “L” (= logic level O) to “H” (= logic level 1). That is, as shown in FIG. 3D, the output Q of the counter unit 32 is “L” until a predetermined time elapses from the start of activation, and “H” after the predetermined time elapses. "

  The drive signal switching unit 33 includes a plurality of gate circuits that receive two systems of PWM signals PWM1 and PWM2 and a counter output Q, and two systems of PWM signals IG-PWM1, IG-PWM2, and SJ-MOSFET for IGBT. Two systems of PWM signals SJ-PWM1 and SJ-PWM2 are output. Specifically, as shown in FIGS. 3E and 3F, the two PWM signals IG-PWM1 and IG-PWM2 for IGBT are obtained by inverting counter output Q and two PWM signals PWM1 and PWM2. AND (logical product) output. Further, as shown in FIGS. 3G and 3H, the two PWM signals SJ-PWM1 and SJ-PWM2 for the SJ-MOSFET are ANDed with the counter output Q and the two PWM signals PWM1 and PWM2. (Logical product) output. That is, a PWM signal is input only to the IGBTs 132 and 142 during a period until a predetermined time elapses from the starting time, and a PWM signal is input only to the SJ-MOSFETs 131 and 141 during a period after the predetermined time elapses. Entered.

  As described above, when a PWM signal is supplied from the control unit 3 to the switch units 13 and 14 through the drive circuit 4, immediately after startup, the SJ-MOSFETs 131 and 141 remain off, and the IGBTs 132 and 142 are appropriately dead. It turns on alternately with time. When the first IGBT 132 is turned on, a current flows upward in FIG. 1 in the primary winding 201 of the transformer 20, and when the second IGBT 142 is turned on, the current is passed through the primary winding 201 of the transformer 20. In 1, current flows downward. A waveform of the switching current flowing through the primary winding 201 at this time is shown in FIG.

  As the target voltage increases with time, the pulse width of the PWM signal increases, so that the time during which current flows through the primary winding 201 gradually increases and the current value also increases. At this time, since the IGBTs 132 and 142 are turned off while the current is flowing through the primary winding 201, a spike-like current due to the energy accumulated in the primary winding 201 flows in the reverse direction immediately after the turn-off. This current flows through the body diodes of the IGBTs 132 and 142 that are in the off state. Although the current in the reverse direction also increases with time, the current resistance of the body diodes of the IGBTs 132 and 142 is large, so that even if a large current flows, the current does not break. However, since the on-resistances of the IGBTs 132 and 142 are relatively large, the loss when the switching current flows through the IGBTs 132 and 142 in the on state is large.

  When the target voltage reaches the final output voltage and the pulse width of the PWM signal becomes sufficiently wide, the waveform of the switching current flowing through the primary winding 201 becomes almost sinusoidal. That is, it becomes a state close to switching due to current resonance, and when the switching current is almost zero, the IGBTs 132 and 142 are turned off. After reaching such a state, the output Q from the counter section 32 changes from “L” to “H”, and as described above, the supply of the PWM signal to the IGBTs 132 and 142 is stopped, while the SJ-MOSFET 131. , 141 starts supplying PWM signals. Since the counter unit 32 counts the clock signal CLK serving as a reference for the PWM signal, the change in the counter output Q is also synchronized with the clock signal CLK. Therefore, in a state where the PWM signal is “L” as shown in FIG. 3, the supply of the PWM signal only to the IGBTs 132 and 142 is switched to the supply of the PWM signal only to the SJ-MOSFETs 131 and 141. That is, when the switching current is almost zero, the use of the IGBTs 132 and 142 is switched to the use of the SJ-MOSFETs 131 and 141, so that it is possible to prevent a large spike-like current from flowing due to the switching.

Then, the SJ-MOSFETs 131 and 141 are alternately turned on by a drive signal that matches the resonance frequency of the resonance circuit, thereby performing a zero current switching operation by current resonance, and a sinusoidal switching current is supplied to the primary of the transformer 20. Supply to winding 201. In response to this, a DC current obtained by rectifying the AC current appearing in the secondary winding 202 of the transformer 20 is supplied to the load 23.
Thus, in the switching power supply device of the present embodiment, in the PWM operation mode in which the PWM control is mainly performed until a predetermined time elapses from the starting time point, that is, until a stable current resonance state is reached, the body diode IGBTs 132 and 142 having high current resistance are used for switching. Further, in a period after a predetermined time has elapsed from the starting time point, that is, in a resonance operation mode after reaching a stable current resonance state, the SJ-MOSFETs 131 and 141 having a small on-resistance are used for switching. Thereby, power conversion can be performed efficiently by taking advantage of the respective advantages of the IGBT and the SJ-MOSFET.

  In the above embodiment, the operation mode is switched from the PWM operation mode to the resonance operation mode when a predetermined time elapses from the starting time. This is the time required to reach a stable current resonance state. This is because it can be experimentally grasped. Of course, instead of control based on time as described above, for example, the output voltage (voltage applied to the load 23) is monitored, and when this output voltage converges to the target value, the operation mode is switched from the PWM operation mode to the resonance operation mode. You may do it.

  The above embodiment is an example in which the present invention is applied to a half-bridge type switching power supply device. However, the current resonance type full-bridge type switching in which two switch units are combined and two sets of switch units are connected in a full bridge connection. It is obvious that the present invention can be applied to the power supply device.

In addition, since the resonance capacitor only needs to be disposed in the closed circuit formed when one of the two switch sections 13 and 14 is turned on, the circuit of the switching power supply device according to the first embodiment has a connection point. It can be modified to a configuration in which one resonance capacitor 18 is provided in series with the primary winding 201 between A and B. FIG. 5 is a partial configuration diagram of a switching power supply device according to such a modification.
In the modification of FIG. 5, two capacitors 171 and 712 provided between the positive power supply line 11 and the negative power supply line 12 are electrolytic capacitors for determining a midpoint potential, and the primary winding 201 is The resonance frequency of the included resonance circuit is determined by the capacitance of the resonance capacitor 18. Also in this configuration, the control of the switch units 13 and 14 is exactly the same as in the first embodiment, and the effects as described above can be obtained.

  As described above, the configuration of the secondary circuit 2 is not limited to that shown in FIG. 1. For example, when a DC voltage is output to the load 23, the secondary circuit 2 is configured as shown in FIG. 7. It may be. In this configuration, the center winding 203A is provided in the secondary winding 202A of the transformer 20A, and the center tap 203A is used as a negative DC voltage output, and the voltage rectified from both ends of the secondary winding 202A through the rectifier diode 24. To take out. Further, when an AC voltage is output to the load 23, the secondary circuit 2 may be configured as shown in FIG. In this case, this switching power supply is a DC-AC converter.

  In the switching power supply device of the first embodiment, the resonance circuit is provided on the primary side of the transformer 20, but when the current resonance is realized by the insulating switching power supply device, the resonance circuit is provided on the secondary side of the transformer. It can also be provided. When the leakage inductance is used for resonance by using a leakage flux type transformer, when the resonance circuit is provided on the primary side of the transformer, the leakage inductance becomes the inductance of the primary winding itself, and the secondary side of the transformer When a resonance circuit is provided, the leakage inductance is equivalent to the inductance when the primary winding and the secondary winding are connected in series. As described above, only the leakage inductance used in the resonance circuit is different, and the resonance circuit is equivalently provided regardless of whether the resonance circuit is provided on the primary side or the secondary side.

FIG. 8 is a schematic configuration diagram of a switching power supply device according to a second embodiment of the present invention in which a resonance circuit is provided on the secondary side.
In this example, a voltage doubler rectifier circuit 27 including two diodes 271 and 272 and two capacitors 273 and 274 is connected to both ends of the secondary winding 202 of the transformer 20, and the capacitors 273 and 274 and the transformer A resonant circuit is formed with 20 leakage inductances. It can be seen that in a certain half cycle of the AC voltage, the capacitor 273 and the leakage inductance of the transformer 20 are connected in series through the diode 271. It can also be seen that in the other half cycle of the AC voltage, the capacitor 274 and the leakage inductance of the transformer 20 are connected in series through the diode 272. Therefore, by appropriately determining the values of the capacitances of the capacitors 273 and 274 and the value of the leakage inductance of the transformer 20, current resonance can be realized every 1/2 cycle at a desired frequency. In order to turn the switching element on and off when the current is almost zero and to prevent the current from flowing through the body diode of the switching element, it is necessary to appropriately select the constant of the resonance circuit. This is the same as in the case of resonance. In other words, by appropriately setting such constants, zero current switching can be realized in the switching power supply device of the second embodiment, and the switch units 13 and 14 are exactly the same as in the first embodiment. By controlling in this way, the effects as described above can be obtained.

  Also in the switching power supply device of the second embodiment shown in FIG. 8, the configuration of the secondary circuit 2 can be modified as appropriate, similarly to the first embodiment. FIG. 10 shows an example in which a DC voltage is output to the load 23 and a diode-wave full-wave rectifier circuit 21 is used. In this case, the resonant capacitor 25 may be provided between the full-wave rectifier circuit 21 and the secondary winding 202 of the transformer 20. FIG. 9 shows a case where an AC voltage is output to the load 23. In this case, the resonance capacitor 25 may be provided in series with the secondary winding 202 of the transformer 20. In any case, it is the same as in the above example that the constant of the resonance circuit must be selected appropriately.

  Furthermore, since each of the above-described embodiments is merely an example of the present invention, it is a matter of course that modifications, corrections, and additions as appropriate within the scope of the present invention are included in the scope of the claims of the present application.

  For example, the above-described embodiment is directed to a DC-DC converter that converts a DC voltage into an AC voltage, converts the AC voltage into a DC voltage, and supplies the load to the load, or a DC-AC converter that supplies the AC voltage as it is to the load. The switching power supply device according to the above is applied. In this case, the DC power supply 10 may be a battery or the like, but it is obvious that the DC power supply 10 may be a DC power supply that rectifies and smoothes AC power from a commercial AC power supply.

DESCRIPTION OF SYMBOLS 1 ... Primary side circuit 10 ... DC power supply 11 ... Positive power supply line 12 ... Negative power supply line 13, 14 ... Switch part 131, 141 ... SJ-MOSFET
132, 142 ... IGBT
133, 143 ... Diode 15, 16 ... Capacitor 2 ... Secondary circuit 20 ... Transformer 201 ... Primary winding 202 ... Secondary winding 21 ... Full-wave rectifier circuit 22 ... Capacitor 23 ... Load 24 ... Rectifier diode 25 ... Resonance Capacitor 27 ... Voltage doubler rectifier circuit 271, 272 ... Diode 273, 274 ... Capacitor 3 ... Control unit 30 ... Soft start control unit 31 ... PWM control unit 32 ... Counter unit 33 ... Drive signal switching unit 4 ... Drive circuit

Claims (3)

A DC current supplied from a DC power source is switched to supply an alternating current to the primary winding of the transformer, and AC power is supplied to the secondary winding of the transformer by the current flowing through the primary winding of the transformer. Inducing switching power supply
a) a switch circuit provided between the DC power supply and the primary winding of the transformer, each of which includes a plurality of switch units each including at least one switching element, and a half bridge connection or a full bridge connection;
b) a resonance capacitor disposed in a closed circuit including a switch unit in the switch circuit, the DC power supply, and a primary winding of the transformer;
c) a control unit that turns on / off each of the switching elements included in the plurality of switch units in the switch circuit, and
Each of the switch parts includes a super junction MOSFET (SJ-MOSFET) and an insulated gate bipolar transistor (IGBT) connected in parallel as switching elements,
The control unit maintains the SJ-MOSFET in an off state until a predetermined time elapses from the start point or until the output voltage reaches a predetermined value, while increasing the target voltage. A PWM control operation for changing a pulse width of a drive signal supplied to the IGBT is performed, and after the start-up period, the IGBT is kept in an OFF state, while a resonance including a primary winding of the transformer and the capacitor. A switching power supply apparatus characterized by switching an operation mode so as to perform a resonance operation for switching the SJ-MOSFET in accordance with a resonance frequency of a circuit. A DC current supplied from a DC power source is switched to supply an alternating current to the primary winding of the transformer, and AC power is supplied to the secondary winding of the transformer by the current flowing through the primary winding of the transformer. Inducing switching power supply
a) a switch circuit provided between the DC power supply and the primary winding of the transformer, each of which includes a plurality of switch units each including at least one switching element, and a half bridge connection or a full bridge connection;
b) a resonant capacitor disposed in a closed circuit including the secondary winding of the transformer;
c) a control unit that turns on / off each of the switching elements included in the plurality of switch units in the switch circuit, and
Each of the switch parts includes a super junction MOSFET (SJ-MOSFET) and an insulated gate bipolar transistor (IGBT) connected in parallel as switching elements,
The control unit maintains the SJ-MOSFET in an off state until a predetermined time elapses from the start point or until the output voltage reaches a predetermined value, while increasing the target voltage. A PWM control operation for changing the pulse width of the drive signal supplied to the IGBT is performed, and after the start-up period, the IGBT is kept in an off state, while the resonance including the secondary winding of the transformer and the capacitor A switching power supply apparatus characterized by switching an operation mode so as to perform a resonance operation for switching the SJ-MOSFET in accordance with a resonance frequency of a circuit. The switching power supply device according to claim 1 or 2,
The control unit switches the operation mode from a PWM operation to a resonance operation in synchronization with a change in a drive signal supplied to the IGBT when the PWM operation is executed.

Images