Switching power supply and power supply system

Abstract

A switching power supply device according to one embodiment of the present invention includes: a pair of input terminals; a pair of output terminals; a transformer; an inverter circuit configured by including first and second switching elements, first and second rectifying elements as voltage clamp elements, a resonance inductor, and a resonance capacitor; a rectifying and smoothing circuit: a current detection unit for detecting whether a current is flowing in at least one rectifying element of the first and second rectifying elements; and a drive unit for performing switching drive. The resonance capacitor is disposed between a second connection point and one of a pair of connection lines. When the current detection unit detects a current flowing in the at least one rectifying device, the drive unit performs switching drive to set both of the first and second switching elements to off-state.

Description

[Technical field]

[0001] The present invention relates to a switching power supply device that performs voltage conversion using a switching element, and to a power supply system including such a switching power supply device. [Background technology]

[0002] As an example of a switching power supply device, various DC-DC converters have been proposed and put into practical use (for example, see Patent Document 1). This type of DC-DC converter generally includes an inverter circuit including a switching element, a power conversion transformer, and a rectifying and smoothing circuit. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent No. 5394213 Summary of the Invention

[0004] However, in switching power supply devices such as DC-DC converters, it is generally required to reduce power loss and improve reliability. It is desirable to provide a switching power supply device that can reduce power loss while improving reliability, and a power supply system including such a switching power supply device.

[0005] A switching power supply device according to one embodiment of the present invention includes an input terminal pair to which an input voltage is input, an output terminal pair to which an output voltage is output, a transformer having a primary winding and a secondary winding, an inverter circuit disposed between the input terminal pair and the primary winding and including first and second switching elements, first and second rectifying elements as voltage clamp elements, a resonant inductor, and a resonant capacitor, a rectifying and smoothing circuit disposed between the output terminal pair and the secondary winding and including a rectifier circuit having a plurality of rectifying elements and a smoothing circuit having a smoothing capacitor, and in at least one of the first and second rectifying elements: It does not flow during normal operation, but only during an overcurrent condition. The current 、 The inverter circuit includes a current detection unit that detects whether a current is flowing or not, and a drive unit that performs switching drive to control the operation of the first and second switching elements in the inverter circuit. The first and second switching elements are connected in series to each other between a pair of connection lines that are individually connected to the input terminal pair. The first and second rectifying elements are connected in series to each other between the pair of connection lines. The resonant inductor and the primary winding are connected in series to each other in no particular order between a first connection point that is a connection point between the first and second switching elements, and a second connection point that is a connection point between the first and second rectifying elements. The resonant capacitor is disposed between the second connection point and one of the pair of connection lines. When the current detection unit detects that a current is flowing in at least one of the rectifying elements, the drive unit performs switching drive so that both the first and second switching elements are set to an off state.

[0006] A power supply system according to an embodiment of the present invention includes the switching power supply device according to the embodiment of the present invention described above, and a power supply that supplies the input voltage to the input terminal pair.

[0007] According to the switching power supply device and power supply system according to an embodiment of the present invention, it is possible to improve reliability while suppressing power loss. [Brief description of the drawings]

[0008] [Figure 1] 1 is a circuit diagram illustrating a schematic configuration example of a switching power supply device according to an embodiment of the present invention. [Diagram 2] 1 is a circuit diagram illustrating a schematic configuration example of a switching power supply device according to a comparative example. [Diagram 3] FIG. 11 is a timing waveform diagram illustrating an example of operation in an overcurrent state in the comparative example. [Figure 4] 4 is a circuit diagram illustrating an example of operation in an overcurrent state according to the present embodiment. FIG. [Diagram 5] 1 is a circuit diagram illustrating a schematic configuration example of a switching power supply device according to a first modification. [Figure 6] FIG. 11 is a circuit diagram illustrating a schematic configuration example of a switching power supply device according to Modification 2. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0009] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. The description will be given in the following order. 1. Embodiment (Example of a case where a center-tapped rectifier circuit is used) 2. Variations Modification 1 (Example of a case where overcurrent detection is performed using another method) Modification 2 (Example of a case where a synchronous rectification circuit is used in the embodiment) 3. Other Modifications

[0010] <1. Preferred embodiment> [composition] FIG. 1 is a circuit diagram showing an example of a schematic configuration of a switching power supply device (switching power supply device 1) according to an embodiment of the present invention. This switching power supply device 1 functions as a DC-DC converter that converts a DC input voltage Vin supplied from a DC input power source 10 (e.g., a battery) into a DC output voltage Vout and supplies power to a load 9. Note that examples of this load 9 include electronic devices and batteries. Also, as described below, this switching power supply device 1 is a so-called "(isolated half-bridge) LLC resonant type" DC-DC converter. Note that the mode of voltage conversion in the switching power supply device 1 may be either up-conversion (boosting) or down-conversion (stepping down).

[0011] Here, the DC input voltage Vin corresponds to a specific example of the "input voltage" in the present invention, and the DC output voltage Vout corresponds to a specific example of the "output voltage" in the present invention. Moreover, the DC input power supply 10 corresponds to a specific example of the "power supply" in the present invention, and a system including this DC input power supply 10 and the switching power supply device 1 corresponds to a specific example of the "power supply system" in the present invention.

[0012] The switching power supply device 1 includes two input terminals T1, T2, two output terminals T3, T4, an inverter circuit 2, a transformer 3, a rectifying and smoothing circuit 4, a drive circuit 5, and a current detection unit 6. A DC input voltage Vin is input between the input terminals T1, T2, and a DC output voltage Vout is output between the output terminals T3, T4.

[0013] Here, the input terminals T1, T2 correspond to a specific example of an "input terminal pair" in the present invention, and the output terminals T3, T4 correspond to a specific example of an "output terminal pair" in the present invention.

[0014] For example, an input smoothing capacitor may be arranged between the primary high-voltage line L1H connected to the input terminal T1 and the primary low-voltage line L1L connected to the input terminal T2. Specifically, at a position between the inverter circuit 2 described later and the input terminals T1 and T2, a first end (one end) of the input smoothing capacitor may be connected to the primary high-voltage line L1H and a second end (the other end) of the input smoothing capacitor may be connected to the primary low-voltage line L1L. Such an input smoothing capacitor is a capacitor for smoothing the DC input voltage Vin input from the input terminals T1 and T2.

[0015] (Inverter circuit 2) The inverter circuit 2 is disposed between input terminals T1, T2 and a primary winding 31 of a transformer 3, which will be described later. The inverter circuit 2 has two switching elements S1, S2, rectifier diodes D1, D2, a resonant inductor Lr, and a resonant capacitor Cr, and is a so-called "half-bridge type" inverter circuit. Note that the resonant inductor Lr may be formed by a leakage inductance in the transformer 3, which will be described later, or may be provided separately from such a leakage inductance.

[0016] Here, the primary high-voltage line L1H and the primary low-voltage line L1L each correspond to a specific example of a "pair of connection lines" in the present invention. Also, the switching element S1 corresponds to a specific example of a "first switching element" in the present invention, and the switching element S2 corresponds to a specific example of a "second switching element" in the present invention. Also, the rectifier diode D1 corresponds to a specific example of a "first rectifier element" in the present invention, and the rectifier diode D2 corresponds to a specific example of a "second rectifier element" in the present invention.

[0017] As the switching elements S1 and S2, for example, switching elements such as a metal oxide semiconductor-field effect transistor (MOS-FET) or an insulated gate bipolar transistor (IGBT) are used. In the example shown in Fig. 1, the switching elements S1 and S2 are each composed of a MOS-FET. In this way, when a MOS-FET is used as the switching elements S1 and S2, the capacitors and diodes (not shown in Fig. 1) connected in parallel to each switching element S1 and S2 can be composed of the parasitic capacitance or parasitic diode of the MOS-FET.

[0018] In this inverter circuit 2, two switching elements S1, S2 are connected in series to each other in this order between the input terminals T1, T2 (between the primary high-voltage line L1H and the primary low-voltage line L1L). Specifically, the switching element S1 is arranged between the primary high-voltage line L1H and the connection point P1, and the switching element S2 is arranged between the connection point P1 and the primary low-voltage line L1L. In addition, two rectifier diodes D2, D1 as voltage clamp elements (clamp diodes) are connected in series to each other in this order between the primary high-voltage line L1H and the primary low-voltage line L1L. Specifically, the rectifier diode D2 has an anode connected to the connection point P2 and a cathode connected to the primary high-voltage line L1H. The rectifier diode D1 has an anode connected to the primary low-voltage line L1L and a cathode connected to the connection point P2.

[0019] Furthermore, in the inverter circuit 2, a resonant capacitor Cr is disposed between the connection point P2 and the primary low-voltage line L1L. That is, the resonant capacitor Cr is disposed in parallel with the above-mentioned rectifier diode D1 between the connection point P2 and the primary low-voltage line L1L.

[0020] Furthermore, the resonant inductor Lr in the inverter circuit 2 and a primary winding 31 in the transformer 3, which will be described later, are connected in series with each other between the connection points P1 and P2. Specifically, in the example of Fig. 1, a first end (one end) of the resonant inductor Lr is connected to the connection point P1, a second end (the other end) of the resonant inductor Lr is connected to one end of the primary winding 31, and the other end of the primary winding 31 is connected to the connection point P2.

[0021] The above-mentioned connection point P1 corresponds to a specific example of a "first connection point" in the present invention, and the above-mentioned connection point P2 corresponds to a specific example of a "second connection point" in the present invention.

[0022] In the inverter circuit 2 configured as described above, the switching elements S1 and S2 perform switching operations (on / off operations) in accordance with drive signals SG1 and SG2 supplied from a drive circuit 5, which will be described later, so that the inverter circuit 2 operates as follows: That is, the DC input voltage Vin applied between the input terminals T1 and T2 is converted into an AC voltage and output to the transformer 3 (primary winding 31).

[0023] (Trans 3) The transformer 3 has one primary winding 31 and two secondary windings 321 and 322.

[0024] In the primary winding 31, a first end (one end) of the primary winding 31 is connected to the second end (other end) of the above-mentioned resonant inductor Lr, and a second end (other end) of the primary winding 31 is connected to the above-mentioned connection point P2.

[0025] In the secondary winding 321, a first end of the secondary winding 321 is connected to a cathode of a rectifier diode 41 (to be described later) via a connection line L21 (to be described later), and a second end of the secondary winding 321 is connected to a center tap P6 in a rectifier smoothing circuit 4 (to be described later). In the secondary winding 322, a first end of the secondary winding 322 is connected to a cathode of a rectifier diode 42 (to be described later) via a connection line L22 (to be described later), and a second end of the secondary winding 322 is connected to the center tap P6. In other words, the second ends of the secondary windings 321 and 322 are commonly connected to the center tap P6.

[0026] The transformer 3 converts the voltage generated by the inverter circuit 2 (a rectangular pulse wave voltage input to the primary winding 31 of the transformer 3) and outputs an AC voltage from each end of the secondary windings 321, 322. In this case, the degree of voltage conversion of the DC output voltage Vout relative to the DC input voltage Vin is determined by the turn ratio between the primary winding 31 and the secondary windings 321, 322, and a switching period Tsw (switching frequency fsw=1 / Tsw) described later.

[0027] (Rectifier smoothing circuit 4) The rectifying smoothing circuit 4 has two rectifying diodes 41 and 42, and one output smoothing capacitor Cout. Specifically, the rectifying smoothing circuit 4 includes a rectifying circuit having the rectifying diodes 41 and 42, and a smoothing circuit having the output smoothing capacitor Cout.

[0028] The two rectifier diodes 41 and 42 correspond to a specific example of "a plurality of rectifier elements" in the present invention. The output smoothing capacitor Cout corresponds to a specific example of "smoothing capacitor" in the present invention.

[0029] The above-mentioned rectifier circuit is a so-called "center tap type" rectifier circuit. That is, the anodes of the rectifier diodes 41 and 42 are connected to the ground line LG, the cathode of the rectifier diode 41 is connected to the first end of the secondary winding 321 via the connection line L21, and the cathode of the rectifier diode 42 is connected to the first end of the secondary winding 322 via the connection line L22. As described above, the second ends of the secondary windings 321 and 322 are commonly connected to the center tap P6, and the center tap P6 is connected to the output terminal T3 via the output line LO. The above-mentioned ground line LG is connected to the output terminal T4.

[0030] In the above-mentioned smoothing circuit, an output smoothing capacitor Cout is connected between the above-mentioned output line LO and ground line LG (between the output terminals T3 and T4). That is, a first terminal of the output smoothing capacitor Cout is connected to the output line LO, and a second terminal of the output smoothing capacitor Cout is connected to the ground line LG.

[0031] In the rectifier smoothing circuit 4 configured as above, the rectifier circuit including the rectifier diodes 41 and 42 rectifies and outputs the AC voltage output from the transformer 3. In addition, in the smoothing circuit including the output smoothing capacitor Cout, the voltage rectified by the rectifier circuit is smoothed to generate a DC output voltage Vout. Note that the DC output current Iout (load current) flows to the load 9 described above due to the DC output voltage Vout generated in this manner, and power is supplied to the load 9 from the output terminals T3 and T4.

[0032] (Drive circuit 5) The drive circuit 5 is a circuit that performs switching drive and controls the operations of the switching elements S1 and S2 in the inverter circuit 2. Specifically, the drive circuit 5 controls the switching operation (on / off operation) of each of the switching elements S1 and S2 by individually supplying drive signals SG1 and SG2 to the switching elements S1 and S2, respectively.

[0033] Here, the drive circuit 5 performs switching frequency control when controlling the switching operation of each of the switching elements S1 and S2 (performing switching drive), i.e., performs PFM (Pulse Frequency Modulation) control on the drive signals SG1 and SG2.

[0034] The drive circuit 5 performs the above-mentioned switching drive so that the switching elements S1 and S2 each perform a switching operation at a fixed duty ratio and the switching frequency fsw operates variably. Incidentally, when the on-periods of the switching elements S1 and S2 are expressed as Ton1 and Ton2, respectively, the duty ratios of the above-mentioned switching elements S1 and S2 are expressed as (Ton1 / Tsw) and (Ton2 / Tsw) using the switching cycle Tsw (=1 / fsw). Moreover, both of these (Ton1 / Tsw) and (Ton2 / Tsw) are less than 50%, and a dead time is provided between the on-periods Ton1 and Ton2 to prevent short-circuit damage due to simultaneous on-periods.

[0035] Furthermore, the drive circuit 5 performs the above-mentioned switching drive in response to a detection result Rd output from a current detection unit 6, which will be described below. Details of the switching drive in response to such a detection result Rd will be described later (FIG. 4).

[0036] (Current detection section 6) In the example shown in FIG. 1, the current detection unit 6 is a circuit that detects whether or not a current ID1 is flowing in the rectifying diode D1 as the aforementioned clamp diode. Although details will be described later, such a current ID1 does not flow during the normal operation of the switching power supply device 1, but flows only when there is a load short circuit (short circuit of the load 9) in the switching power supply device 1 or the like.

[0037] Also, in the example shown in FIG. 1, such a current detection unit 6 detects that a current ID1 is flowing through the rectifying diode D1 as follows (and outputs a detection result Rd indicating that the current ID1 is flowing to the drive circuit 5). That is, when a voltage value VD1 (positive value) corresponding to the forward voltage drop (voltage drop from the anode side to the cathode side) in the rectifying diode D1 becomes equal to or higher than a threshold voltage Vth1 (VD1 ≧ Vth1), the current detection unit 6 outputs a detection result Rd indicating that the current ID1 is flowing. On the other hand, when such a voltage value VD1 is less than the threshold voltage Vth1 (VD1 < Vth1), the current detection unit 6 outputs a detection result Rd indicating that no current ID1 is flowing through the rectifying diode D1.

[0038] Note that such a threshold voltage Vth1 is, for example, a voltage value corresponding to the forward voltage Vf (= about 0.7 [V]) of the rectifying diode D1, and corresponds to a specific example of the "first threshold" in the present invention.

[0039] [Operation, Action, and Effect] (A. Basic Operation) In this switching power supply device 1, in the inverter circuit 2, a DC input voltage Vin supplied from the DC input power supply 10 via the input terminals T1 and T2 is switched by the switching elements S1 and S2, thereby generating a voltage that has been converted into a rectangular pulse wave. This voltage that has been converted into a rectangular pulse wave is supplied to the primary winding 31 in the transformer 3, and is transformed in this transformer 3, so that a transformed AC voltage is output from the secondary windings 321 and 322.

[0040] In the rectifying and smoothing circuit 4, the AC voltage output from the transformer 3 (the above-mentioned transformed AC voltage) is rectified by the rectifying diodes 41 and 42 in the rectifying circuit, and then smoothed by the output smoothing capacitor Cout in the smoothing circuit. As a result, a DC output voltage Vout is output from the output terminals T3 and T4. Then, this DC output voltage Vout causes a DC output current Iout to flow to the load 9, and power is supplied to the load 9.

[0041] In addition, in the switching power supply device 1 of this embodiment, the rectifier diodes D1 and D2 are provided as the clamp diodes in the inverter circuit 2, so that the voltage across the resonant capacitor Cr is limited. Specifically, the voltage across the resonant capacitor Cr is clamped within a predetermined range (above the ground voltage and below the DC input voltage Vin). This suppresses the current (overcurrent) flowing through the transformer 3 and elements such as the switching elements S1 and S2 (MOS-FET) when, for example, the load 9 is short-circuited (load short-circuited).

[0042] (B. Operation during load short circuit, etc.) Next, with reference to FIG. 1 as well as FIG. 2 to FIG. 4, the detailed operation of the switching power supply device 1 (the detailed operation when the load 9 is short-circuited as described above) will be described in detail in comparison with a comparative example.

[0043] (B-1. Comparative example) 2 is a circuit diagram showing a schematic configuration example of a switching power supply device (switching power supply device 101) according to a comparative example. The switching power supply device 101 of this comparative example corresponds to the switching power supply device 1 of the present embodiment shown in FIG. 1, except that the current detection unit 6 described above is not provided and a drive circuit 105 is provided instead of the drive circuit 5.

[0044] The drive circuit 105 controls the switching operation of each of the switching elements S1 and S2 (performs switching drive) in the same manner as the drive circuit 5. However, since the switching power supply device 101 is not provided with a current detection unit 6, the drive circuit 105, unlike the drive circuit 5, does not perform switching drive according to the detection result Rd in the current detection unit 6.

[0045] Fig. 3 is a timing waveform diagram showing an example of operation in an overcurrent state (when an overcurrent flows due to the above-mentioned load short circuit, etc.) in such a comparative example. Specifically, Fig. 3(A) to Fig. 3(D) respectively show examples of timing waveforms for the DC output voltage Vout, the voltage Vcr across the resonant capacitor Cr, the current I31 flowing through the primary winding 31, and the currents ID1 and ID2 flowing through the rectifier diodes D1 and D2 shown in Fig. 2. In Fig. 3, the horizontal axis indicates time t.

[0046] 3, at timing t1, an overcurrent state occurs due to a short circuit in the load 9. Specifically, due to the short circuit in the load 9, the DC output voltage Vout becomes 0 V, and the currents I31, ID1, ID2 and the voltage Vcr all increase.

[0047] Here, since the switching power supply device 101 of this comparative example is not provided with the current detection unit 6 as described above, there is a risk that the following will occur. That is, when an overcurrent occurs during a load short circuit as described above, the detection of such an overcurrent may be delayed, and the countermeasure (stopping the operation of the switching power supply device 101) may also be delayed. If such a countermeasure is delayed, an excessive current may continue to flow, causing damage to each element in the switching power supply device 101 (components such as the transformer 3 and switching elements S1 and S2), and the reliability of the switching power supply device 101 may decrease.

[0048] In addition, in this comparative example, a method of detecting an overcurrent during a load short circuit or the like by constantly detecting, for example, the DC output current Iout or the current flowing through the winding of the transformer 3 (such as the current I31 flowing through the primary winding 31), etc., is also conceivable, but this method has the following problem: That is, even during normal operation of the switching power supply device 101, the above-mentioned current is constantly detected, and therefore unnecessary power loss occurs (power loss increases) during such current detection.

[0049] Thus, in the switching power supply device 101 of this comparative example, there is a risk that the reliability will decrease and the power loss will increase.

[0050] (B-2. This embodiment) In contrast, in the switching power supply device 1 of this embodiment, when the load 9 is short-circuited (in an overcurrent state) as described above, the following operation is performed. Fig. 4 is a schematic circuit diagram showing an example of operation in an overcurrent state in this embodiment.

[0051] First, as described above, in this embodiment, the voltage across the resonant capacitor Cr is clamped within a predetermined range by the rectifier diodes D1 and D2 serving as clamp diodes. In this embodiment, the current detector 6 detects whether or not a current ID1 flows through the rectifier diode D1. When the current detector 6 detects that a current ID1 flows through the rectifier diode D1, the drive circuit 5 performs the above-described switching drive so that both switching elements S1 and S2 are set to the OFF state (see FIG. 4).

[0052] In this manner, in this embodiment, when it is detected that a current ID1 (an overcurrent due to a load short circuit or the like) is flowing, the switching elements S1 and S2 are set to the OFF state to (promptly) stop the operation of the switching power supply device 1. As a result, in this embodiment, unlike the above-mentioned comparative example, the risk of an excessive current continuing to flow during a load short circuit or the like and damaging each element (components such as the transformer 3 and the switching elements S1 and S2) is avoided.

[0053] As described above, such a current ID1 (current flowing through the rectifier diode D1 serving as a clamp diode) does not flow during normal operation of the switching power supply device 1, but flows only when the load is short-circuited or the like (when an overcurrent state occurs). In other words, in this embodiment, unlike the method described above (a method of detecting an overcurrent when a load is short-circuited or the like by constantly detecting the DC output current Iout, current I31, or the like), overcurrent detection is performed only when an overcurrent state occurs, such as when a load is short-circuited. As a result, in this embodiment, unnecessary power loss during normal operation of the switching power supply device 1 is avoided, and overcurrent detection can be performed with almost no loss.

[0054] As a result, in this embodiment, it is possible to reduce power loss in the switching power supply device 1 and improve reliability, compared to the comparative example and the like.

[0055] Furthermore, as described above, since damage to each element due to overcurrent can be avoided, elements with a low rated current can be used, which makes it possible to reduce the size and cost of the switching power supply device 1.

[0056] In this embodiment, when the voltage value VD1 corresponding to the forward voltage drop in the rectifier diode D1 becomes equal to or greater than the threshold voltage Vth1 (VD1≧Vth1), the current detection unit 6 outputs a detection result Rd indicating that the current ID1 is flowing (see FIG. 4). This makes it possible to easily detect an overcurrent when the load is short-circuited, etc.

[0057] Furthermore, in this embodiment, as described above, the switching elements S1 and S2 each perform switching operation at a fixed duty ratio, and the switching frequency fsw is variable, so that the following is true. That is, soft switching in each of the switching elements S1 and S2 is facilitated, so that switching loss is reduced, and as a result, members such as heat dissipation components can be made smaller. Therefore, in this embodiment, it is possible to make the switching power supply device 1 smaller.

[0058] In addition, in this embodiment, when the resonant inductor Lr in the inverter circuit 2 is configured by the leakage inductance in the transformer 3, it is not necessary to separately provide the resonant inductor Lr, and therefore the number of components can be reduced. As a result, it is possible to further reduce the size and cost of the switching power supply device 1.

[0059] Furthermore, in this embodiment, since the switching elements S1, S2 in the inverter circuit 2 are each configured with a MOS-FET, the switching frequency fsw can be increased, and the components can be made smaller.

[0060] Furthermore, in this embodiment, the rectifier circuit in the rectifying and smoothing circuit 4 is a so-called "center tap type" rectifier circuit, which has the following advantages compared to a so-called "bridge type" rectifier circuit: The number of rectifier elements is reduced to two (rectifier diodes 41 and 42), which allows the rectifier circuit to be made smaller, with lower loss and lower cost.

[0061] <2. Modifications> Next, modified examples (modifications 1 and 2) of the above embodiment will be described. Note that, in the following, the same components as those in the embodiment will be given the same reference numerals, and the description will be omitted as appropriate.

[0062] [Variation 1] (composition) FIG. 5 is a circuit diagram showing an example of the schematic configuration of a switching power supply device (switching power supply device 1A) according to the first modification.

[0063] As in the embodiment, a system including the DC input power supply 10 and this switching power supply device 1A corresponds to one specific example of the "power supply system" of the present invention.

[0064] The switching power supply 1A of this variant example 1 corresponds to the switching power supply 1 of the embodiment in which an inverter circuit 2A and a current detection unit 6A are provided instead of the inverter circuit 2 and the current detection unit 6, but the other configurations are similar.

[0065] The inverter circuit 2A is configured similarly to the inverter circuit 2, except that a resistive element R1 is further provided that is connected in series to the rectifier diode D1. Specifically, as shown in Fig. 5, the resistive element R1 is disposed between the anode of the rectifier diode D1 and the primary low-voltage line L1L.

[0066] The current detection unit 6A is a circuit that detects whether or not the current ID1 flows through the rectifier diode D1, similar to the above-mentioned current detection unit 6. However, unlike the current detection unit 6, this current detection unit 6A detects whether the current ID1 flows through the rectifier diode D1 (outputs a detection result Rd indicating that the current ID1 flows to the drive circuit 5) in the following manner.

[0067] That is, when the voltage value VR1 (absolute value, positive value) between both ends of the above-described resistor element R1 becomes equal to or higher than the threshold voltage Vth2 (VR1 ≥ Vth2), the current detection unit 6A outputs a detection result Rd indicating that the current ID1 is flowing (see FIG. 5). In other words, when the current value flowing through the resistor element R1 becomes equal to or higher than (threshold voltage Vth2 / resistance value of the resistor element R1), the current detection unit 6A outputs a detection result Rd indicating that the current ID1 is flowing. On the other hand, when such a voltage value VR1 is less than the threshold voltage Vth2 (VR1 < Vth2), the current detection unit 6A outputs a detection result Rd indicating that no current ID1 is flowing through the rectifying diode D1. In other words, when the current value flowing through the resistor element R1 is less than (threshold voltage Vth2 / resistance value of the resistor element R1), the current detection unit 6A outputs a detection result Rd indicating that no current ID1 is flowing.

[0068] Note that the above-described threshold voltage Vth1 corresponds to a specific example of the "first threshold value" in the present invention.

[0069] (Operation and Effect) Also in the switching power supply device 1A of the first modification having such a configuration, basically, the same effects can be obtained by the same operation as the switching power supply device 1 of the embodiment.

[0070] Further, particularly in this first modification, as described above, when the voltage value VR1 between both ends of the resistor element R1 connected in series to the rectifying diode D1 becomes equal to or higher than the threshold voltage Vth2 (VR1 ≥ Vth2), the current detection unit 6A outputs a detection result Rd indicating that the current ID1 is flowing (see FIG. 5). Thus, in this first modification, since the threshold value at the time of overcurrent detection can be finely adjusted using the resistor element R1, the convenience can be improved.

[0071] [Second Modification] The switching power supply device (switching power supply device 1B) according to the second modification is configured such that in the above-described embodiment, each of the rectifying circuits in the rectifying and smoothing circuit 4 is a so-called synchronous rectifying circuit as described below.

[0072] Specifically, FIG. 6 is a circuit diagram showing a schematic configuration example of a switching power supply device (switching power supply device 1B) according to Modification 2.

[0073] A switching power supply device 1B of this modified example 2 corresponds to one in which a rectifying and smoothing circuit 4B is provided instead of the rectifying and smoothing circuit 4 in the switching power supply device 1 of the embodiment, and other configurations are similar.

[0074] In the synchronous rectifier circuit of the second modification, as shown in Fig. 6, the rectifier diodes 41 and 42 described in the embodiment are each configured with a MOS-FET (MOS transistors M3 and M4) as a switching element. In this synchronous rectifier circuit, the MOS transistors M3 and M4 themselves are controlled to be turned on (perform synchronous rectification) in synchronization with the period during which the parasitic diodes of the MOS transistors M3 and M4 are conductive. Specifically, the drive circuit 5 of the second modification uses drive signals SG3 and SG4 to control the on / off operation of the MOS transistors M3 and M4 (see Fig. 6).

[0075] As in the embodiment and the first modification, a system including DC input power supply 10 and this switching power supply device 1B corresponds to one specific example of the "power supply system" of the present invention.

[0076] The switching power supply device 1B of the second modification thus configured basically operates in the same manner as the switching power supply device 1 of the embodiment, and thus can provide the same effects.

[0077] In particular, in this modification 2, each of the rectifier elements (rectifier diodes) in the rectifier circuit is configured with a switching element, and the rectifier circuit is configured as a synchronous rectifier circuit, as described below. That is, such a synchronous rectifier circuit reduces the conduction loss during rectification, making it possible to reduce the size and loss of the rectifier circuit. Incidentally, examples of such switching elements include, in addition to the above-mentioned MOS-FET, HEMT ((High Electron Mobility Transistor) = HFET (Heterostructure Field-Effect Transistor)), IGBT or bipolar transistor with a diode added in parallel, etc.

[0078] In addition, in this modification 2 as well, as in the above-described modification 1, an inverter circuit 2A and a current detection unit 6A may be provided instead of the inverter circuit 2 and the current detection unit 6. In other words, the configurations of modifications 1 and 2 may be combined with each other.

[0079] <3. Other Modifications> Although the present invention has been described above by way of the embodiment and modifications, the present invention is not limited to these embodiments and can be modified in various ways.

[0080] For example, in the above-mentioned embodiment, the configuration of the inverter circuit is specifically described, but the present invention is not limited to the above-mentioned embodiment, and may be configured in another way as the inverter circuit. Specifically, the arrangement of the resonant inductor Lr and the primary winding 31, which are connected in series with each other, is not limited to the arrangement described in the above-mentioned embodiment, and may be in random order (reverse arrangement). In the above-mentioned embodiment, the resonant capacitor Cr is arranged between the connection point P2 and the primary low-voltage line L1L, but the resonant capacitor Cr may be arranged between the connection point P2 and the primary high-voltage line L1H. In the above-mentioned embodiment, the current detectors 6 and 6A detect whether the current ID1 flows through the rectifier diode D1, but the present invention is not limited to this example. That is, for example, each of the current detection units 6 and 6A may detect whether or not the current ID2 flows through the rectifier diode D2, or may detect whether or not the currents ID1 and ID2 flow through both the rectifier diodes D1 and D2. When detecting whether or not the current ID2 flows through the rectifier diode D2, a resistor element R1 may be provided in series with the rectifier diode D2, and an overcurrent may be detected using a voltage value VR1 across the resistor element R1, as in the case of the first modification example described above.

[0081] In addition, in the above embodiments, the configuration of the transformer (primary winding and secondary winding) has been specifically given and described, but the present invention is not limited to the examples of the above embodiments, and for example, a transformer (primary winding and secondary winding) with a different configuration may be used.

[0082] Furthermore, in the above embodiment etc., the configuration of the rectifying smoothing circuit (rectifying circuit and smoothing circuit) has been specifically given and described, but the present invention is not limited to the above embodiment etc., and for example, a rectifying smoothing circuit (rectifying circuit and smoothing circuit) with another configuration may be used. Specifically, in the above embodiment etc., the so-called "center tap type" rectifying circuit has been described as an example, but the present invention is not limited to this example, and for example, a so-called "bridge type" rectifying circuit may be used.

[0083] In addition, in the above embodiment, etc., a method of controlling the operation of each switching element by the drive circuit (switching drive) is specifically given and described, but the present invention is not limited to the above embodiment, etc., and other methods may be used as the switching drive method. Specifically, for example, the switching drive method when the load is short-circuited (in an overcurrent state) as described above is not limited to the method described in the above embodiment, etc., and other methods may be used. Also, in the above embodiment, etc., a method of detecting current by the current detection unit is specifically given and described, but the present invention is not limited to the above embodiment, etc., and other methods may be used to detect current.

[0084] In addition, in the above embodiment, a DC-DC converter has been described as an example of a switching power supply device according to the present invention, but the present invention can also be applied to other types of switching power supply devices, such as an AC-DC converter.

[0085] Furthermore, the configuration examples described so far may be applied in any combination.

Claims

1. an input terminal pair to which an input voltage is input; an output terminal pair for outputting an output voltage; a transformer having a primary winding and a secondary winding; an inverter circuit disposed between the input terminal pair and the primary winding, the inverter circuit including first and second switching elements, first and second rectifying elements, a resonant inductor, and a resonant capacitor; a rectifying and smoothing circuit disposed between the output terminal pair and the secondary winding, the rectifying circuit having a plurality of rectifying elements, and a smoothing circuit having a smoothing capacitor; a current detection unit that detects whether or not a current that does not flow during normal operation but flows only in an overcurrent state is flowing through at least one of the first and second rectifying elements; a drive unit that performs switching drive to control operations of the first and second switching elements in the inverter circuit; Equipped with the first and second switching elements are connected in series to each other between a pair of connection lines that are individually connected to the input terminal pair, the first and second rectifying elements are connected in series to each other between the pair of connection lines, the resonant inductor and the primary winding are connected in series in no particular order between a first connection point which is a connection point between the first and second switching elements and a second connection point which is a connection point between the first and second rectifying elements, the resonant capacitor is disposed between the second connection point and one of the pair of connection lines, The drive unit is When the current detection unit detects that the current flows in at least one of the rectifying elements, The switching drive is performed so that both the first and second switching elements are set to an off state. Switching power supply.

2. The current detection unit When a voltage value corresponding to a forward voltage drop in the at least one rectifying element becomes equal to or greater than a first threshold value, The detection result that the current is flowing is output.

2. The switching power supply device according to claim 1.

3. the inverter circuit further includes a resistive element connected in series to the at least one rectifying element, The current detection unit When the voltage value between both ends of the resistive element becomes equal to or greater than a second threshold value (when the current value flowing through the resistive element becomes equal to or greater than (the second threshold value / the resistance value of the resistive element)), outputting a detection result that the current is flowing; When the voltage value between the two ends becomes less than the second threshold value (when the current value becomes less than (the second threshold value / the resistance value)), The detection result that the current is not flowing is output.

2. The switching power supply device according to claim 1.

4. The drive section performs the switching drive so that the first and second switching elements each perform a switching operation at a fixed duty ratio and a switching frequency is variably operated.

4. The switching power supply device according to claim 1.

5. Each of the plurality of rectifier elements is configured by a switching element, and the rectifier circuit is a synchronous rectifier circuit.

5. The switching power supply device according to claim 1.

6. The resonant inductor is formed by a leakage inductance in the transformer.

6. The switching power supply device according to claim 1.

7. A switching power supply device according to any one of claims 1 to 6, a power supply for supplying the input voltage to the input terminal pair; A power supply system comprising:

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