Power circuit

Abstract

A first circuit (10) includes an input positive electrode terminal (P12) and an input negative electrode terminal (N12) that are configured so as to be able to receive a voltage from a first power source (1), and a first switch (18) that switches the application of an input voltage to a first winding (N1) on and off. A second circuit (20) includes a second control circuit (502) that switches whether a voltage from a second power source (2) is received and power is induced in a second winding (N2), or power that was induced in the second winding (N2) in accordance with the voltage applied to the first winding (N1) is outputted to an external load. A third circuit (30) includes an output positive electrode terminal (P31) and an output negative electrode terminal (N31) that output power which was induced in a third winding (N3) in accordance with the voltage applied to the first winding (N1) or the second winding (N2).

Description

[Technical field]

[0001] The present disclosure relates to a power supply circuit. [Background technology]

[0002] A power supply circuit is a circuit that generates a constant voltage for a certain input voltage range. However, for example, when generating 5V from an input voltage of AC85V to 264V and when generating 5V from an input voltage of DC24V, the difference between the input voltage ranges is large, so it is common to use separate power supplies.

[0003] Non-isolated power supplies (system power supplies) are primarily used as power sources for input voltages of AC 85V to 264V, while isolated power supplies are primarily used as power sources for input voltages of DC 24V. The reference potentials (grounds) of these power supplies are different. Therefore, when inputting multiple input voltages into a single electrical device to perform the same operation, multiple power supplies and switching transformers must be prepared.

[0004] In order to solve such problems, as described in Patent Document 1, a method is disclosed in which a single transformer is provided with a plurality of input windings. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Publication No. 9-098544 Summary of the Invention [Problem to be solved by the invention]

[0006] However, the power supply circuit described in Patent Document 1 requires two windings: one for generating an output voltage and one for applying an input voltage. Furthermore, the power supply circuit described in Patent Document 1 requires that the output voltage terminal and the input voltage terminal be electrically separated.

[0007] Therefore, an object of the present disclosure is to provide a power supply circuit that can be driven by multiple different ground input voltages and can generate multiple output voltages, with at least one of the multiple output voltage terminals being electrically common to the input voltage terminal. [Means for solving the problem]

[0008] The power supply circuit of the present disclosure includes a switching transformer having a first winding, a second winding, and a third winding, a first circuit, a second circuit, and a third circuit. The first circuit includes an input positive terminal and an input negative terminal configured to be able to receive the voltage of a first power source, a first switch that switches application of the input voltage to the first winding on or off, and a first control circuit that controls the first switch. The second circuit includes a second control circuit that switches whether to induce power in the second winding by receiving the voltage of the second power source, or to output the power induced in the second winding to an external load according to the voltage applied to the first winding. The third circuit includes an output positive terminal and an output negative terminal that output the power induced in the third winding according to the voltage applied to the first winding or the second winding, and a feedback circuit that feeds back to the first control circuit and the second control circuit a feedback signal that changes according to the output voltage generated between the output positive terminal and the output negative terminal. Effect of the Invention

[0009] The power supply circuit disclosed herein can be driven by multiple different ground input voltages and can generate multiple output voltages, and at least one of the multiple output voltage terminals can be electrically common to the input voltage terminal. [Brief description of the drawings]

[0010] [Figure 1] 1 is a diagram showing a configuration of a power supply circuit 100 according to a first embodiment. [Diagram 2] 1 is a diagram showing waveforms of voltage and current in the power supply circuit 100 in the first embodiment when the input voltage Vin1 is input to the first circuit 10 and the input voltage Vin2 is not input to the second circuit 20. FIG. [Diagram 3] 1 is a diagram showing waveforms of voltage and current in the power supply circuit 100 in the first embodiment when the input voltage Vin2 is input to the second circuit 20 and the input voltage Vin1 is not input to the first circuit 10. FIG. [Figure 4] FIG. 2 is a diagram illustrating a configuration of a power supply circuit of a reference example. [Diagram 5] FIG. 1 is a diagram showing a configuration of a power supply circuit 200 according to a second embodiment. [Figure 6] FIG. 11 is a diagram illustrating waveforms of voltage and current in the power supply circuit 200 in the second embodiment when the input voltage Vin1 is input to the first circuit 10A and the input voltage Vin2 is not input to the second circuit 20A. [Figure 7] FIG. 11 is a diagram showing waveforms of voltage and current in the power supply circuit 200 in the second embodiment when the input voltage Vin2 is input to the second circuit 20A and the input voltage Vin1 is not input to the first circuit 10A. [Figure 8] FIG. 13 is a diagram showing a configuration of a power supply circuit 200A according to a modified example of the second embodiment. [Figure 9] FIG. 11 is a diagram showing a configuration of a power supply circuit 300 according to a third embodiment. [Figure 10] FIG. 11 is a diagram showing waveforms of voltage and current in the power supply circuit 300 in the third embodiment when the input voltage Vin2 is input to the second circuit 20B and the input voltage Vin1 is not input to the first circuit 10A. [Figure 11] FIG. 11 is a diagram showing a configuration of a power supply circuit 400 according to a fourth embodiment. [Figure 12] FIG. 13 is a diagram showing waveforms of voltage and current in the power supply circuit 400 in the fourth embodiment when the input voltage Vin2 is input to the second circuit 20D and the input voltage Vin1 is not input to the first circuit 10A. [Figure 13] FIG. 13 is a diagram showing a configuration of a power supply circuit 400A according to a modification of the fourth embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0011] Hereinafter, the embodiments will be described in detail with reference to the drawings. In the drawings, the same or corresponding parts are denoted by the same reference characters, and the description thereof will not be repeated. Each of the embodiments or modifications described below may be appropriately and selectively combined.

[0012] Embodiment 1 <Configuration> FIG. 1 is a diagram showing a configuration of a power supply circuit 100 according to the first embodiment.

[0013] The power supply circuit 100 includes a switching transformer 3, a first circuit 10, a second circuit 20, and a third circuit 30.

[0014] The switching transformer 3 includes a first winding N1, a second winding N2, and a third winding N3. The winding directions of the first winding N1, the second winding N2, and the third winding N3 are the same. A first end of the first winding N1 without a polarity point faces a second end of the third winding N3 with a polarity point. A second end of the first winding N1 with a polarity point faces a first end of the third winding N3 without a polarity point. Similarly, a first end of the first winding N1 without a polarity point faces a second end of the second winding N2 with a polarity point. A second end of the first winding N1 with a polarity point faces a first end of the second winding N2 without a polarity point. Here, the polarity point means a point at which the winding of the winding starts.

[0015] The first circuit 10 is configured to be connectable to a first power supply 1. The first circuit 10 is configured to be able to input an input voltage Vin1 from the first power supply 1. The second circuit 20 is configured to be connectable to a second power supply 2. The second circuit 20 is configured to be able to input an input voltage Vin2 from the second power supply 2, and is configured to be able to output an output voltage Vout1 to a load (not shown). The third circuit 30 is configured to be able to output an output voltage Vout2 to a load (not shown).

[0016] The first circuit 10 includes an input positive terminal P12 and an input negative terminal N12, a capacitor (first capacitor) 12, a resistor (first resistor) 13, a capacitor (second capacitor) 14, a diode (first diode) 11, a diode (second diode) 15, a switch (first switch) 17, and a first control circuit 501.

[0017] The input positive terminal P12 and the input negative terminal N12 are respectively connected to the first power supply positive terminal P11 and the first power supply negative terminal N11 of the first power supply 1. The input positive terminal P12 and the input negative terminal N12 are configured to be able to input the input voltage Vin1 from the first power supply 1.

[0018] The capacitor 12 is connected between the input positive terminal P12 and the input negative terminal N12, and receives the voltage of the first power supply 1 as an input voltage Vin1.

[0019] The cathode of the diode 11 is connected to the first end of the first winding N1. The anode of the diode 15 is connected to the second end of the first winding N1.

[0020] The resistor 13 is connected between the input positive terminal P12 and the anode of the diode 11, and the cathode of the diode 15. The capacitor 14 is connected between the input positive terminal P12 and the anode of the diode 11, and the cathode of the diode 15.

[0021] A first end of the resistor 13, a first end of the capacitor 14, and the anode of the diode 11 are connected to the input positive terminal P12. A second end of the resistor 13 and a second end of the capacitor 14 are connected to the cathode of the diode 15.

[0022] A resistor 13, a capacitor 14 and a diode 15 form an RCD snubber circuit.

[0023] A first terminal of the switch 17 is connected to a second terminal of the first winding N1 and the anode of the diode 15. A second terminal of the switch 17 is connected to the input negative terminal N12. The switch 17 switches the application of the input voltage to the first winding N1 on or off.

[0024] The first control circuit 501, for example by monitoring the voltage of the input positive terminal P12, transmits a detection signal DT indicating that the voltage of the first power source 1 is being input to the first circuit 10 to the second control circuit 502 in the second circuit 20 when the voltage of the first power source 1 is being input to the first circuit 10. The first control circuit 501 controls the switch 17 based on a feedback signal FB from the third circuit 30.

[0025] In order for the first control circuit 501 to transmit the detection signal DT to the second control circuit 502, an insulating element such as a photocoupler can be used. The control signal CT1 output from the first control circuit 501 to the switch 17 is, for example, a PWM (Pulse Width Modulation) signal. The first control circuit 501 is configured to be drivable by power from the first power source 1.

[0026] The second circuit 20 includes an input / output positive terminal P22 and an input / output negative terminal N22, a load resistor (fourth resistor) 23, a capacitor (third capacitor) 22, a switch (second switch) 24, a switch (third switch) 25, a diode (third diode) 21, and a second control circuit 502.

[0027] The input / output positive terminal P22 and the input / output negative terminal N22 are respectively connected to the second power supply positive terminal P21 and the second power supply negative terminal N21 of the second power supply 2. The input / output positive terminal P22 and the input / output negative terminal N22 are capable of receiving the voltage of the second power supply 2, and are configured to be capable of outputting power induced in the second winding N2 in response to the voltage applied to the first winding N1 to an external load (not shown).

[0028] The capacitor 22 and the load resistor 23 are connected between the input / output positive terminal P22 and the input / output negative terminal N22. The capacitor 22 and the load resistor 23 output the output voltage Vout1 or receive the input voltage Vin2.

[0029] The switch 24 is configured to switch between outputting the power induced in the second winding N2 to the input / output positive terminal P22 and the input / output negative terminal N22, and inputting the power from the second power supply 2 to the second winding N2.

[0030] The switch 24 has an output state terminal C1 and an input state terminal C2. The input state terminal C2 is connected to a first end of the second winding N2 and to the cathode of the diode 21. The output state terminal C1 is connected to a second end of the second winding N2 and to a first end of the switch 25.

[0031] The switch 24 switches, in response to a control signal CT3 from the second control circuit 502, whether to connect the input / output positive terminal P22 to the output state terminal C1 or to the input state terminal C2.

[0032] A second end of the switch 25 and the anode of the diode 21 are connected to the input / output negative terminal N22. The switch 25 switches on and off the application of the input voltage to the second winding N2.

[0033] The input negative terminal N12 and the input / output negative terminal N22 are insulated by, for example, reinforced insulation, so that these terminals have different potentials.

[0034] The second control circuit 502 switches between inducing power in the second winding N2 by receiving the voltage of the second power supply 2, or outputting the power induced in the second winding N2 to an external load in accordance with the voltage applied to the first winding N1.

[0035] The second control circuit 502 controls the switch 24 by a control signal CT3 based on the detection signal DT from the first control circuit 501 of the first circuit 10. The second control circuit 502 controls the switch 25 by a control signal CT2 based on the feedback signal FB from the third circuit 30.

[0036] The control signal CT2 output by the second control circuit 502 to the switch 25 is, for example, a PWM signal. The second control circuit 502 is configured to be capable of being driven by power from the second power supply 2 or by power (output voltage Vout1) induced in the second winding N2 in response to the voltage applied to the first winding N1.

[0037] The third circuit 30 includes a positive output terminal P31 and a negative output terminal N31, a capacitor 32, a load resistor 33, a diode 31, and a feedback circuit 503.

[0038] The positive output terminal P31 and the negative output terminal N31 output power induced in the third winding N3 to an external load (not shown) in accordance with the voltage applied to the first winding N1 or the second winding N2.

[0039] The capacitor 32 and the load resistor 33 are connected between the output positive terminal P31 and the output negative terminal N31. The capacitor 32 and the load resistor 33 can output an output voltage Vout2.

[0040] A first end of the capacitor 32 and a first end of the load resistor 33 are connected to the output positive terminal P31 and the cathode of the diode 31. A second end of the capacitor 32 and a second end of the load resistor 33 are connected to the output negative terminal N31 and a first end of the third winding N3.

[0041] A first end of the third winding N3 is connected to the output negative terminal N31. A second end of the third winding N3 is connected to the anode of a diode 31. A cathode of the diode 31 is connected to the output positive terminal P31.

[0042] The feedback circuit 503 transmits a feedback signal FB, which changes according to the output voltage Vout2 generated between the output positive terminal P31 and the output negative terminal N31, to the first control circuit 501 of the first circuit 10 and the second control circuit 502 of the second circuit 20. In order for the feedback circuit 503 to transmit the feedback signal FB to the first control circuit 501 or the second control circuit 502, an insulating element such as a photocoupler can be used.

[0043] <Operation 1> The operation of the power supply circuit 100 according to the first embodiment will be described with reference to Figures 2 and 3. In Figures 2 and 3, the voltage across the switch 17 is set to 0 on the side of the input negative terminal N12.

[0044] The current of the first winding N1, the current of the second winding N2, and the current of the third winding N3 (hereinafter simply referred to as the N1 current, the N2 current, and the N3 current, respectively) is positive when it flows from the first terminal to the second terminal. In the following, for simplicity, the forward voltage of each diode is ignored.

[0045] FIG. 2 is a diagram showing waveforms of voltage and current in the power supply circuit 100 in the first embodiment when the input voltage Vin1 is input to the first circuit 10 and the input voltage Vin2 is not input to the second circuit 20. In FIG.

[0046] That is, the first power supply positive terminal P11 is connected to the input positive terminal P12, and the first power supply negative terminal N11 is connected to the input negative terminal N12. At least one of the connections between the second power supply positive terminal P21 and the input / output positive terminal P22 and between the second power supply negative terminal N21 and the input negative terminal N22 is not connected. The first control circuit 501 and the second control circuit 502 control the switch 24 to connect the input / output positive terminal P22 to the output status terminal C1.

[0047] In this state, power is supplied from the first circuit 10 to the second circuit 20 and the third circuit 30 by the switch 17 and the switching transformer 3 driven by the first control circuit 501.

[0048] 2, when the switch 17 is on, the voltage across the switch 17 is zero, and a triangular wave current flows through the first winding N1 according to the inductance L1 of the first winding N1 and the input voltage Vin1. The peak current Ip of the N1 current is expressed by the following equation using the flow time ton1.

[0049] Ip = Vin1 x ton1 / L1…(A1) Energy is stored in the switching transformer 3 by a triangular wave current flowing through the first winding N1.

[0050] When the switch 17 is turned off, the stored energy causes a triangular wave current to flow through the second winding N2 and the third winding N3. The N2 current flows through a circuit loop formed by the second winding N2, the output state terminal C1, the capacitor 22, and the diode 21, and generates an output voltage Vout1 at the input / output positive terminal P22. The N3 current flows through a circuit loop formed by the third winding N3, the diode 31, and the capacitor 32, and generates an output voltage Vout2 at the output positive terminal P31. The N1 current flows through a circuit loop formed by the first winding N1, the diode 15, the capacitor 14, and the diode 11, and generates a snubber voltage across the resistor 13 and the capacitor 14.

[0051] The feedback circuit 503 included in the third circuit 30 transmits a feedback signal FB that changes according to the output voltage Vout2 generated between the output positive terminal P31 and the output negative terminal N31 to the first control circuit 501. The first control circuit 501 stabilizes the output voltage Vout2 by changing the flow time ton1 based on the feedback signal FB.

[0052] The voltage ratio of the output voltage Vout1 to the output voltage Vout2 is generally equal to the square root of the ratio of the inductance L2 of the second winding N2 and the inductance L3 of the third winding N3, as shown below.

[0053]

number

[0054] When no external load is connected to the I / O positive terminal P22 and the I / O negative terminal N22, the average current of the N2 current becomes equal to the average current flowing through the load resistor 23.

[0055] Similarly, when no external load is connected to the positive output terminal P31 and the negative output terminal N31, the average current of the N3 current becomes equal to the average current flowing through the load resistor P31.

[0056] The voltage V17 across the switch 17 after the switch 17 is turned off can be expressed by the following equation using the output voltage Vout2 of the third circuit 30 including the feedback circuit 503, the square root of the ratio between the inductance L1 of the first winding N1 and the inductance L3 of the third winding N3, and the input voltage Vin1.

[0057]

number

[0058] Furthermore, when the flow of the N3 current ends and the N3 current becomes 0, the voltage applied to each winding of the switching transformer 3 becomes 0, and the voltage across the switch 17 becomes Vin1. After that, the switch 17 turns on again.

[0059] <Extensibility of Operation 1> Although not shown in FIG. 1, external loads can be connected to the input / output positive terminal P22 and the input / output negative terminal N22, the output positive terminal P31 and the output negative terminal N31, respectively, so that output voltages Vout1 and Vout2 can be provided to the outside, thereby making it possible to supply power to the outside.

[0060] In this case, the average value of the N2 current is equal to the sum of the average values ​​of the currents flowing through the load resistor 23 and the external load. Similarly, the average value of the N3 current is equal to the sum of the average values ​​of the currents flowing through the load resistor 33 and the external load.

[0061] <Operation 2> FIG. 3 is a diagram showing waveforms of voltage and current in the power supply circuit 100 in the first embodiment when the input voltage Vin2 is input to the second circuit 20 and the input voltage Vin1 is not input to the first circuit 10.

[0062] That is, the second power supply positive terminal P21 is connected to the input / output positive terminal P22, and the second power supply negative terminal N21 is connected to the input negative terminal N22. At least one of the connections between the first power supply positive terminal P11 and the input / output positive terminal P12 and between the first power supply negative terminal N11 and the input negative terminal N12 is not connected.

[0063] When the detection signal DT is not sent from the first control circuit 501, the second control circuit 502 drives the switch 24 by a control signal CT3 to connect the input / output positive terminal P22 to the input status terminal C2.

[0064] In this state, power is supplied from the second circuit 20 to the first circuit 10 and the third circuit 30 by the switch 25 and the switching transformer 3 driven by the second control circuit 502.

[0065] When the switch 25 is on, the voltage across the switch 25 is 0. A triangular wave current according to the inductance L2 of the secondary winding N2 and the input voltage Vin2 flows through a circuit loop formed by the capacitor 22, the input state terminal C2, the secondary winding N2, and the switch 25. The peak current Ip2 of the N2 current is expressed by the following equation using the flow time ton2.

[0066] Ip2 = Vin2 × ton2 / L2 … (B1) Energy is stored in the switching transformer 3 by a triangular wave current flowing through the second winding N2.

[0067] When switch 25 is turned off, the stored energy causes a triangular wave current to flow through primary winding N1 and tertiary winding N3. The N1 current flows through a circuit loop formed by primary winding N1, diode 11, capacitor 14, and diode 15, generating a voltage across resistor 13 and capacitor 14. The N3 current flows through a circuit loop formed by tertiary winding N3, diode 31, and capacitor 32, generating an output voltage Vout2 at output positive terminal P31.

[0068] The feedback circuit 503 included in the third circuit 30 transmits a feedback signal FB that changes according to the output voltage Vout2 generated between the output positive terminal P31 and the output negative terminal N31 to the second control circuit 502. The second control circuit 502 stabilizes the output voltage Vout2 by changing the flow time ton2 based on the feedback signal FB.

[0069] When no external load is connected to the positive output terminal P31 and the negative output terminal N31, the average current of the N3 current becomes equal to the average current flowing through the load resistor 33.

[0070] The voltage V25 across the switch 25 after the switch 25 is turned off can be expressed by the following equation using the output voltage Vout2 of the third circuit including the feedback circuit 503, the square root of the ratio of the inductance L2 of the second winding N2 to the inductance L3 of the third winding N3, and the input voltage Vin2.

[0071]

number

[0072] Furthermore, when the flow of the N3 current ends and the N3 current becomes 0, the voltage applied to each winding of the switching transformer 3 becomes 0, and the voltage across the switch 25 becomes Vin2. After that, the switch 25 turns on again.

[0073] <Extensibility of Operation 2> Although not shown in Fig. 1, an external load can be connected to the output positive terminal P31 and the output negative terminal N31, so that the output voltage Vout2 can be provided to the outside and power can be supplied to the outside. In this case, the average value of the N3 current is equal to the sum of the average values ​​of the currents flowing through the load resistor 33 and the external load.

[0074] <Common Extensibility> In the above, the case where either one of the input voltage Vin1 and the input voltage Vin2 is input has been described, but the present invention is not limited to this. The input voltage Vin1 and the input voltage Vin2 may be input simultaneously. In this case, the switch 24 is controlled by the first control circuit 501 and the second control circuit 502 so that the input / output positive terminal P22 is connected to the output state terminal C1. Power is supplied from the first circuit 10 to the second circuit 20 and the third circuit 30 by the switch 17 driven by the first control circuit 501 and the switching transformer 3. At this time, power is supplied to the load resistor 23 from the higher voltage of the input voltage Vin2 and the output voltage Vout2 generated by the second circuit 20.

[0075] In the above, the power supply circuit 100 has been described as including one first circuit 10, one second circuit 20, and one third circuit 30, but is not limited to this. The power supply circuit 100 may include a plurality of first circuits 10, a plurality of second circuits 20, and a plurality of third circuits 30. In this case, the power supply circuit 100 becomes a multi-input / output power supply circuit. Even in this case, it is only necessary to increase the fourth winding and thereafter in the switching transformer 3, and it is not necessary to provide a plurality of switching transformers as in the conventional configuration shown in FIG. 4 below.

[0076] <Effects> As described above, in this embodiment, as long as at least one of the input voltages Vin1 and Vin2 is input to the power supply circuit 100, it can output the output voltage Vout1 and the output voltage Vout2. In addition, since a voltage is applied from the first end of the second winding N2, which has no polarity point, and the second end of the second winding N2, which has a polarity point, is switched, a boost operation is possible, and even if the value of the input voltage Vin2 is small, it is possible to output an output voltage Vout2 that is greater than the value obtained by multiplying the square root of the ratio of the inductance L2 of the second winding N2 and the inductance L3 of the third winding N3 by the input voltage Vin2.

[0077] Furthermore, the input / output positive terminal P22 and the input / output negative terminal N22 function as both an input terminal for inputting the input voltage Vin2 and an output terminal for outputting the output voltage Vout1. Conventionally, it was necessary to provide separate windings for the input switching transformer and windings for the output switching transformer, but in this embodiment, the number of windings of the switching transformer 3 can be reduced, allowing the switching transformer 3 to be made smaller.

[0078] Furthermore, in this embodiment, the input terminals and the output terminals can be made common, so that the number of terminals can be reduced. As a result, the power supply circuit can be made smaller. Furthermore, according to this embodiment, it is possible to tolerate mistakes in wiring the input / output terminals by the user, and safety is improved.

[0079] <Reference example> FIG. 4 is a diagram showing a configuration of a power supply circuit of a reference example.

[0080] The first circuit 40A, the third circuit 50A, and the switching transformer 3A are used to generate an output voltage Vout1, which is output from the second power supply positive terminal P21 and the second power supply negative terminal N21. The second power supply positive terminal P21 and the second power supply negative terminal N21 are connected to the input / output positive terminal P22 and the input / output negative terminal N22, respectively.

[0081] The output voltage Vout2 is generated using the first circuit 40B, the third circuit 50B, and the switching transformer 3B, and is output from the output positive terminal P31 and the output negative terminal N31.

[0082] For example, if the power conversion efficiency of one power supply (first circuit 40A, switching transformer 3A, and third circuit 50A) is 80% and the power conversion efficiency of the other power supply (first circuit 40B, switching transformer 3B, and third circuit 50B) is 80%, the overall power conversion efficiency is 64%. Therefore, the power conversion efficiency of the power supply circuit of the reference example is poor. The power supply circuit of the reference example has a problem of generating a lot of heat. The power supply circuit of the reference example requires two switching transformers and two feedback circuits, which causes a problem of being large in size.

[0083] In contrast, according to the present embodiment, since there is no need to use a two-stage power supply, it is possible to provide a power supply circuit that is small in size and has good power conversion efficiency.

[0084] Furthermore, if a multiple-output power supply circuit is created by adding windings to the switching transformer 3 as described above, the start-up sequence (start-up order) of each output voltage will be the same even if the input voltage is switched, making the design easier.

[0085] Embodiment 2 <Configuration> FIG. 5 is a diagram showing a configuration of a power supply circuit 200 according to the second embodiment.

[0086] Power supply circuit 200 includes a first circuit 10A, a second circuit 20A, a third circuit 30, and a switching transformer 3. Third circuit 30 and switching transformer 3 are similar to third circuit 30 and switching transformer 3 included in power supply circuit 100 of the first embodiment, and therefore description thereof will not be repeated.

[0087] The first circuit 10A differs from the first circuit 10 of the first embodiment in that the first circuit 10A includes an n-channel Metal-Oxide-Semiconductor Field-Effect Transistor (MOSFET) 47 instead of the switch 17 as a first switch.

[0088] The drain of the n-channel MOSFET 55 is connected to the second end of the first winding N1 and to the anode of the diode 15. The source of the n-channel MOSFET 55 is connected to the input negative terminal N12.

[0089] The second circuit 20A differs from the second circuit 20 of the first embodiment in that the second circuit 20A includes a relay 54 as a second switch instead of the switch 24, and includes an n-channel MOSFET (first transistor) 55 as a third switch instead of the switch 25. The second circuit 20A further includes a Zener diode 56 connected in parallel with the n-channel MOSFET (first transistor) 55.

[0090] The drain of the n-channel MOSFET 55 and the cathode of the Zener diode 56 are connected to the second terminal of the second winding N2 and to the output status terminal C1.

[0091] The source of the n-channel MOSFET 55 and the anode of the Zener diode 56 are connected to the anode of the diode 21, the second end of the load resistor 23, the second end of the capacitor 22, and the I / O negative terminal N22.

[0092] The Zener voltage Vz of the Zener diode 56 is selected to be equal to or lower than the rated drain-source voltage of the n-channel MOSFET 55 .

[0093] The first control circuit 501 operates on an input voltage Vin1. The second control circuit 502 operates on an input voltage Vin2.

[0094] The relay 54 has a c-contact. Even if the power supply circuit 200 is in a non-energized state, the input / output positive terminal P22 is connected to the output state terminal C1. As a result, even if the input voltage Vin2 is not supplied to the second control circuit 502 and the second control circuit 502 is not operating, a loop circuit is formed and the output voltage Vout1 can be output. That is, it is possible to start the power supply circuit 200 only by the input voltage Vin1.

[0095] When the input voltage Vin2 is connected to the second circuit 20A, the second control circuit 502 receives the input voltage Vin2 and starts up. When the second control circuit 502 detects that the detection signal DT is not sent from the first control circuit 501, that is, that the input voltage Vin1 is not connected, the second control circuit 502 drives the relay 54 by the control signal CT3 to connect the input / output positive terminal P22 to the input status terminal C2. This starts driving the n-channel MOSFET 55.

[0096] When the second control circuit 502 receives the detection signal DT from the first control circuit 501, it does not drive the relay 54 and maintains the state in which the input / output positive terminal P22 is connected to the output state terminal C1. This makes it possible to allow the input voltages Vin1 and Vin2 to be input simultaneously.

[0097] <Operation 1> FIG. 6 is a diagram showing waveforms of voltage and current in the power supply circuit 200 in the second embodiment when the input voltage Vin1 is input to the first circuit 10A and the input voltage Vin2 is not input to the second circuit 20A.

[0098] In FIG. 6, the drain-source voltage of the n-channel MOSFET 47 is shown instead of the voltage across the switch 17 shown in FIG. 2. In the first embodiment, the operation of an ideal switch and transformer is shown. However, in an actual circuit, the switching transformer 3 has leakage inductance in each winding. Immediately after the n-channel MOSFET 47 is turned off, a surge voltage exceeding the voltage V17 of the above-mentioned formula (A3) is generated. This surge voltage is suppressed to the drain-source rated voltage of the n-channel MOSFET 47 or less by the resistor 13, the capacitor 14, and the diode 15, which are an RCD snubber circuit.

[0099] After the N3 current becomes zero, the drain-source voltage of the n-channel MOSFET 47 oscillates due to the parasitic capacitance between the drain and source of the n-channel MOSFET 47, the parasitic capacitance of the diode 11, and the inductance L1 of the primary winding N1.

[0100] <Operation 2> FIG. 7 is a diagram showing waveforms of voltage and current in the power supply circuit 200 in the second embodiment when the input voltage Vin2 is input to the second circuit 20A and the input voltage Vin1 is not input to the first circuit 10A.

[0101] In Fig. 7, the drain-source voltage of n-channel MOSFET 55 is shown instead of the voltage across switch 25 shown in Fig. 3. Immediately after n-channel MOSFET 55 is turned off, a surge voltage exceeding voltage V25 of the above-mentioned equation (B3) is generated.

[0102] Here, the Zener voltage Vz of the Zener diode 56 is selected to be equal to or lower than the rated drain-source voltage of the n-channel MOSFET 55. Therefore, as shown in FIG. 7, the surge voltage is clamped at Vz, and the n-channel MOSFET 55 can be protected with a simple configuration.

[0103] <Unique Effects of the Second Embodiment> The Zener diode 56 allows the power supply circuit 200 to operate stably without causing a circuit breakdown, and suppresses generated noise, even when the power supply circuit 200 is driven by the input voltage Vin2.

[0104] <Modification of the second embodiment> FIG. 8 is a diagram showing a configuration of a power supply circuit 200A according to a modification of the second embodiment.

[0105] Power supply circuit 200A includes a first circuit 10A, a second circuit 20C, a third circuit 30, and a switching transformer 3. The third circuit 30 and the switching transformer 3 are similar to the third circuit 30 and the switching transformer 3 included in power supply circuit 100 of the first embodiment, and therefore will not be described repeatedly. The first circuit 10A is similar to the first circuit 10A included in power supply circuit 200 of the second embodiment, and therefore will not be described repeatedly.

[0106] The second circuit 20C differs from the second circuit 20A of the second embodiment in that the second circuit 20C includes an RCD snubber circuit 89 connected across the second winding N2 instead of the Zener diode 56.

[0107] The RCD snubber circuit 89 includes a resistor 81 , a capacitor 82 , and a diode 83 .

[0108] The anode of the diode 83 is connected to the second end of the second winding N2 and to the output state terminal C1. The cathode of the diode 83 is connected to the first end of the resistor 81 and to the first end of the capacitor 82.

[0109] A second end of the resistor 81 and a second end of the capacitor 82 are connected to a first end of the second winding N2, the cathode of the diode 21, and the input state terminal C2.

[0110] In this modification, as in the case of the Zener diode 56 in the second embodiment, the effect of suppressing the drain-source voltage of the n-channel MOSFET 55 can be obtained.

[0111] Embodiment 3 <Configuration> FIG. 9 is a diagram showing a configuration of a power supply circuit 300 according to the third embodiment.

[0112] Power supply circuit 300 includes a first circuit 10A, a second circuit 20B, a third circuit 30, and a switching transformer 3. Third circuit 30 and switching transformer 3 are similar to third circuit 30 and switching transformer 3 included in power supply circuit 100 of embodiment 1, and therefore description thereof will not be repeated. First circuit 10A is similar to first circuit 10A included in power supply circuit 200 of embodiment 2, and therefore description thereof will not be repeated.

[0113] The second circuit 20B differs from the second circuit 20A of the second embodiment in that the second circuit 20B includes, instead of the relay 54, a diode (fourth diode) 61, a diode (fifth diode) 62, a p-channel MOSFET (second transistor) 63, an n-channel MOSFET (third transistor) 64, a resistor (second resistor) 65, and a resistor (third resistor) 66.

[0114] The second circuit 20B does not include the Zener diode 56. In the second embodiment, the Zener diode 56 is provided to suppress a surge voltage generated across the n-channel MOSFET 55 when the n-channel MOSFET 55 is turned off. In the third embodiment, when the n-channel MOSFET 55 is turned off, the current flowing through the second winding N2 is regenerated to the input voltage Vin2 by making the diode 62 conductive, and the voltage across the n-channel MOSFET 55 is maintained at Vin2. Therefore, in the third embodiment, a circuit for suppressing a surge voltage is not necessary, and therefore the Zener diode 56 is not provided.

[0115] An anode of the diode 62 is connected to a second end of the second winding N2 and a drain (first electrode) of the n-channel MOSFET 55. A cathode of the diode 62 is connected to a source (first electrode) of the p-channel MOSFET 63, a first end of the resistor 65, a first end of the capacitor 22, a first end of the load resistor 23, and the input / output positive terminal P22.

[0116] A drain (second electrode) of the p-channel MOSFET 63 is connected to an anode of the diode 61. A cathode of the diode 61 is connected to a first end of the second winding N2 and to the cathode of the diode 21.

[0117] A gate (control electrode) of the p-channel MOSFET 63 is connected to a second end of the resistor 65 and a first end of the resistor 66. A second end of the resistor 66 is connected to a drain (first electrode) of the n-channel MOSFET 64. A source (second electrode) of the n-channel MOSFET 64 is connected to the anode of the diode 21, the source (second electrode) of the n-channel MOSFET 55, the second end of the capacitor 22, the second end of the load resistor 23, and the input / output negative terminal N22.

[0118] A control signal CT4 from a second control circuit 502 is input to the gate (control electrode) of the n-channel MOSFET 64 and the gate (control electrode) of the n-channel MOSFET 55.

[0119] The first control circuit 501 operates on an input voltage Vin1. The second control circuit 502 operates on an input voltage Vin2.

[0120] <Operation 1> The operation of the power supply circuit 300 when the input voltage Vin1 is input to the first circuit 10A and the input voltage Vin2 is not input to the second circuit 20B is the same as in the second embodiment, and is therefore not shown in the figures.

[0121] When the input voltage Vin1 is input, the first control circuit 501 controls the n-channel MOSFET 47 .

[0122] When the n-channel MOSFET 47 is off, the N2 current flows through the circuit loop formed by the secondary winding N2, the diode 62, the capacitor 22, and the diode 21, and generates the output voltage Vout1 at the I / O positive terminal P22.

[0123] As a result, even when power is not supplied to the second control circuit 502 and the second control circuit 502 is not operating, a circuit is formed and the output voltage Vout1 can be output. In other words, the power supply circuit 300 can be started up by only the input voltage Vin1.

[0124] On the other hand, when the n-channel MOSFET 47 is on, a circuit loop cannot be formed by the diodes 21 and 61, and the N2 current cannot flow and becomes 0. Therefore, the power supply circuit 300 can be operated in the same manner as the power supply circuit 200 shown in the second embodiment.

[0125] <Operation 2> FIG. 10 is a diagram showing waveforms of voltage and current in the power supply circuit 300 in the third embodiment when the input voltage Vin2 is input to the second circuit 20B and the input voltage Vin1 is not input to the first circuit 10A.

[0126] When the input voltage Vin2 is input, the second control circuit 502 receives the input voltage Vin2 and starts up. When the second control circuit 502 detects that the detection signal DT is not sent from the first control circuit 501, that is, that the input voltage Vin1 is not connected, the second control circuit 502 starts driving the n-channel MOSFET 55 and the n-channel MOSFET 64 by the control signal CT4.

[0127] The n-channel MOSFET 64 is provided to drive the gate of the p-channel MOSFET 63. When the n-channel MOSFET 64 is off, the gate-source voltage of the p-channel MOSFET 63 is 0, and the p-channel MOSFET 63 is off. On the other hand, when the n-channel MOSFET 64 is on, the gate-source voltage of the p-channel MOSFET 63 is a value obtained by dividing Vin2 by resistors 65 and 66, and the p-channel MOSFET 63 is on. However, if the allowable value of the gate-source voltage of the p-channel MOSFET 63 is higher than the input voltage Vin2, the resistor 66 is not necessary and can be shorted. That is, the second end of the resistor 65 and the drain of the N-channel MOSFET 64 may be connected.

[0128] Therefore, in this embodiment, the n-channel MOSFET 55, the n-channel MOSFET 64, and the p-channel MOSFET 63 can be driven simultaneously.

[0129] 10, when n-channel MOSFET 55, n-channel MOSFET 64, and p-channel MOSFET 63 are all on, the drain-source voltage of n-channel MOSFET 55 is 0. In this case, a triangular wave current according to inductance L2 and input voltage Vin2 flows through a circuit loop formed by capacitor 22, p-channel MOSFET 63, diode 61, second winding N2, and n-channel MOSFET 55. A peak current Ip3 of the N2 current is expressed by the following equation using a flow time ton2, as in the power supply circuit 100 of the first embodiment and the power supply circuit 200 of the second embodiment.

[0130] Ip3 = Vin2 × ton2 / L2 … (C1) This causes energy to be stored in the switching transformer 3.

[0131] When the n-channel MOSFET 55, the n-channel MOSFET 64, and the p-channel MOSFET 63 are turned off, the stored energy flows as a triangular wave current through the first winding N1 and the third winding N3.

[0132] On the other hand, in the power supply circuit 300 of the third embodiment, in a section where the n-channel MOSFET 55, the n-channel MOSFET 64, and the p-channel MOSFET 63 are all off (hereinafter, the off section), the drain-source voltage of the n-channel MOSFET 55 is equal to the input voltage Vin2. This is because, in the off section, the leakage inductance of the second winding N2 causes the diodes 62 and 21 to be conductive, and the voltage applied to the second winding N2 is clamped to the input voltage Vin2.

[0133] When the flow of the N3 current ends and the N3 current becomes zero, the drain-source voltage of the n-channel MOSFET 55 oscillates due to the parasitic capacitance between the drain and source of the n-channel MOSFET 55, the parasitic capacitance between the drain and source of the p-channel MOSFET 63, the parasitic capacitance of the diode 61, the parasitic capacitance of the diode 62, and the inductance L2 of the second winding N2.

[0134] In addition, when the second control circuit 502 receives the detection signal DT from the first control circuit 501, the n-channel MOSFET 55 and the n-channel MOSFET 64 are not driven, thereby allowing the input voltages Vin1 and Vin2 to be input simultaneously.

[0135] <Unique Effects of the Third Embodiment> When the input voltage Vin2 is input to the power supply circuit 300, the current flowing through the leakage inductance of the second winding N2 is regenerated to the second power supply 2. Therefore, the power supply circuit 300 of the third embodiment is a more efficient power supply circuit than the power supply circuit 200 of the second embodiment in which energy is consumed by the Zener diode 56.

[0136] Furthermore, in the operation when the input voltage Vin2 is input, the voltage applied to the second winding N2 is clamped to the input voltage Vin2 during the off section, which means that, in principle, an upper limit is placed on the output voltage Vout2 generated by the third circuit 30. The limit value LM is expressed by the following equation.

[0137]

number

[0138] This eliminates the need for an overvoltage protection circuit for the output voltage Vout2, making it possible to reduce the size of the circuit.

[0139] Compared with the power supply circuit 200 of the second embodiment, in the power supply circuit 300 of the third embodiment, when the input voltage Vin2 is input, the power supply circuit 300 can be started up quickly because it is not necessary to drive the relay 54. In the power supply circuit 300 of the third embodiment, since it is not necessary to drive the relay 54, the second control circuit 502 can be made smaller.

[0140] <Scalability and effectiveness> Although each component is specifically described in the above second and third embodiments, the same effect can be obtained even if these components are replaced with other components having a function of switching the circuit.

[0141] For example, although the relay 54 has been described as being configured by a relay having a contact c, the present invention is not limited to this. The relay 54 may be configured by combining a relay having an a contact and a relay having a b contact. The relay 54 may be, for example, (a) a semiconductor analog switch, (b) a photoMOS relay, (c) a photovoltaic output photocoupler and MOSFET, (d) a photothyristor, or the like.

[0142] Also, bipolar transistors can be used instead of MOSFETs. In this case, the n-channel MOSFET can be an NPN transistor, and the p-channel MOSFET can be a PNP transistor. This allows resistor 65 to be eliminated.

[0143] Embodiment 4 <Configuration> FIG. 11 is a diagram showing a configuration of a power supply circuit 400 according to the fourth embodiment.

[0144] Power supply circuit 400 includes a first circuit 10A, a second circuit 20D, a third circuit 30, and a switching transformer 3. The third circuit 30 and the switching transformer 3 are similar to the third circuit 30 and the switching transformer 3 included in power supply circuit 100 of the first embodiment, and therefore will not be described repeatedly. The first circuit 10A is similar to the first circuit 10A included in power supply circuit 200 of the second embodiment, and therefore will not be described repeatedly.

[0145] The second circuit 20D differs from the second circuit 20A of the second embodiment in that the second circuit 20D includes an inductor 74 instead of the relay 54, and includes an n-channel MOSFET 71 and an inverter 73 instead of the diode 21.

[0146] A first end without a polarity point of the inductor 74 is connected to a first end of the capacitor 22, a first end of the load resistor 23, and the input / output positive terminal P22. A second end with a polarity point of the inductor 74 is connected to a second end with a polarity point of the second winding N2 and the drain of the n-channel MOSFET 55. The inductance of the inductor 74 is represented as L74.

[0147] A drain of the n-channel MOSFET 71 is connected to a first end without a polarity point of the second winding N2. A source of the n-channel MOSFET 71 is connected to a source of the n-channel MOSFET 55, a second end of the capacitor 22, a second end of the load resistor 23, and the input / output positive terminal P22. A gate of the n-channel MOSFET 71 is connected to an output of the inverter 73, and an input of the inverter 73 is connected to the gate of the n-channel MOSFET 55.

[0148] The n-channel MOSFET 55 is arranged between a first node ND1 between the second end of the second winding N2, where the polarity point is located, and the inductor 74, and a second node ND2 between the input / output negative terminal N22 and the n-channel MOSFET 71.

[0149] A control signal CT5 from a second control circuit 502 is input to the gate (control electrode) of the n-channel MOSFET 55 and the input of the inverter 73.

[0150] The first control circuit 501 operates on an input voltage Vin1. The second control circuit 502 operates on an input voltage Vin2.

[0151] <Operation 1> The operation of the power supply circuit 400 when the input voltage Vin1 is input to the first circuit 10A and the input voltage Vin2 is not input to the second circuit 20D is the same as in the second embodiment, and is therefore not shown in the figures.

[0152] When the input voltage Vin1 is input, the first control circuit 501 controls the n-channel MOSFET 47 .

[0153] The second control circuit 502 turns off the n-channel MOSFET 55 and turns on the n-channel MOSFET 71 .

[0154] When the n-channel MOSFET 47 is off, the N2 current flows through a circuit loop formed by the secondary winding N2, the inductor 74, the capacitor 22, and the n-channel MOSFET 71, and generates an output voltage Vout1 at the I / O positive terminal P22.

[0155] As a result, even when power is not supplied to the second control circuit 502 and the second control circuit 502 is not operating, a circuit is formed and the output voltage Vout1 can be output. In other words, the power supply circuit 300 can be started up by only the input voltage Vin1.

[0156] On the other hand, when the n-channel MOSFET 47 is on, the n-channel MOSFET 71 prevents a circuit loop from being formed, and the N2 current cannot flow and becomes 0. Therefore, the power supply circuit 300 can be operated in the same manner as the power supply circuit 200 shown in the second embodiment.

[0157] <Operation 2> FIG. 12 is a diagram showing waveforms of voltage and current in the power supply circuit 300 in the fourth embodiment when the input voltage Vin2 is input to the second circuit 20D and the input voltage Vin1 is not input to the first circuit 10A.

[0158] When the input voltage Vin2 is input, the second control circuit 502 receives the input voltage Vin2 and starts up. When the second control circuit 502 detects that the detection signal DT is not sent from the first control circuit 501, that is, that the input voltage Vin1 is not connected, the second control circuit 502 starts driving the n-channel MOSFET 55 and the n-channel MOSFET 71 by the control signal CT5.

[0159] By the inverter 73, the level of the gate signal of the n-channel MOSFET 71 is inverted from the level of the gate signal of the n-channel MOSFET 55. Therefore, in this embodiment, the n-channel MOSFET 55 and the n-channel MOSFET 71 can be driven alternately.

[0160] 12, when the n-channel MOSFET 55 is on and the n-channel MOSFET 71 is off, the drain-source voltage of the n-channel MOSFET 55 is 0. In this case, a triangular wave current according to the inductance L74 and the input voltage Vin2 flows through the circuit loop formed by the capacitor 22, the inductor 74, and the n-channel MOSFET 55. As a result, energy is stored in the inductor 74.

[0161] When the n-channel MOSFET 55 is turned off and the n-channel MOSFET 71 is turned on, a voltage obtained by adding together the input voltage Vin2 and the back electromotive force RV generated in the inductor 74 is applied to the second winding N2, and a triangular wave current flows through the first winding N1 and the third winding N3. At this time, the voltage applied between the drain and source of the n-channel MOSFET 55 is the product of the output voltage Vout2 and the square root of the ratio of the inductance L2 of the second winding N2 to the inductance L3 of the third winding N3. This product is equal to the voltage obtained by adding together the input voltage Vin2 and the back electromotive force RV generated in the inductor 74.

[0162] When the flow of the N3 current ends and the N3 current becomes zero, the drain-source voltage of the n-channel MOSFET 55 oscillates due to the parasitic capacitance between the drain and source of the n-channel MOSFET 55 and the inductance L74. Also, during this time, if the n-channel MOSFET 71 is on, the inductance L74 and the inductance L2 of the secondary winding N2 are excited by the input voltage Vin2, the current of the inductor 74 increases, and the current of the secondary winding N2 decreases. After that, the n-channel MOSFET 55 turns on again in the next period.

[0163] In addition, when the second control circuit 502 receives the detection signal DT from the first control circuit 501, the n-channel MOSFET 55 and the n-channel MOSFET 71 are not driven, thereby allowing the input voltages Vin1 and Vin2 to be input simultaneously.

[0164] <Unique Effects of the Fourth Embodiment> When a voltage is applied from the second end of the second winding N2, which has a polarity point, and the first end of the second winding N2, which has no polarity point, is switched, only an output voltage Vou2 with an upper limit of the square root of the ratio of the inductance L2 of the second winding N2 to the inductance L3 of the third winding N3 multiplied by the input voltage Vin2 can be output. In other words, the power supply is vulnerable to a drop in the input voltage Vin2. However, since the power supply circuit 400 has the inductor 74, it is capable of a boost operation, and even if the value of the input voltage Vin2 is small, it is possible to output an output voltage Vout2 larger than the square root of the ratio of the inductance L2 of the second winding N2 to the inductance L3 of the third winding N3 multiplied by the input voltage Vin2.

[0165] <Scalability and effectiveness> In the above description, the polarity of the inductor 74 is shown, but the same effect can be obtained even if the polarity is reversed.

[0166] Also, for simplicity, inverter 73 has been used in the description, but an appropriate dead time may be provided for the gate signal of n-channel MOSFET 55 and the gate signal of n-channel MOSFET 71, or they may be controlled separately by second control circuit 502. When the gate signal of n-channel MOSFET 71 is controlled separately, the surge voltage applied to the drain-source of n-channel MOSFET 71 is reduced by making the on-time of the gate signal shorter than the value obtained by subtracting ton3 from T shown in FIG.

[0167] <Modification of the fourth embodiment> FIG. 13 is a diagram showing a configuration of a power supply circuit 400A according to a modification of the fourth embodiment.

[0168] Power supply circuit 400A includes a first circuit 10A, a second circuit 20E, a third circuit 30, and a switching transformer 3. The third circuit 30 and the switching transformer 3 are similar to the third circuit 30 and the switching transformer 3 included in power supply circuit 200 of the first embodiment, and therefore will not be described repeatedly. The first circuit 10A is similar to the first circuit 10A included in power supply circuit 200 of the second embodiment, and therefore will not be described repeatedly.

[0169] The second circuit 20E differs from the second circuit 20D of the fourth embodiment in that the second circuit 20E includes a rectifier circuit 77 connected across the second winding N2.

[0170] The rectifier circuit 77 includes a capacitor 76 and an n-channel MOSFET 72. The capacitor 76 and the n-channel MOSFET 72 are connected in series between a first node ND1 and a second node ND2.

[0171] A first end of the capacitor 76 is connected to the second end of the second winding N2, the second end of the inductor 74, and the drain of the n-channel MOSFET 55. A second end of the capacitor 76 is connected to the drain of the n-channel MOSFET 72.

[0172] The source of the n-channel MOSFET 72 is connected to the source of the n-channel MOSFET 71, the source of the n-channel MOSFET 55, the second end of the capacitor 22, the second end of the load resistor 23, and the I / O positive terminal P22.

[0173] A control signal CT6 from the second control circuit 502 is input to the gate (control electrode) of the n-channel MOSFET 72.

[0174] The second control circuit 502 controls the n-channel MOSFET 72 by a control signal CT6 based on the detection signal DT from the first control circuit 501 of the first circuit 10.

[0175] When the input voltage Vin1 is input, the second control circuit 502 receives the output voltage Vout1 and starts up. When the second control circuit 502 detects that the detection signal DT is sent from the first control circuit 501, that is, that the input voltage Vin1 is connected, the second control circuit 502 turns on the n-channel MOSFET 72 by turning on the control signal CT6.

[0176] As a result, when the input voltage Vin1 is connected, the N2 current flows through a circuit loop formed by the second winding N2, the capacitor 76, and the n-channel MOSFET 72. As a result, in the power supply circuit 400A, the influence of the inductor 74, which is a parasitic component for the inductance L2 of the second winding N2, can be suppressed, and a decrease in the output voltage Vout1 can be prevented.

[0177] Furthermore, the inductor 74 and the capacitor 22 form an LC filter for the output voltage Vout1, which has the effect of reducing differential mode noise output to the output voltage Vout1.

[0178] When the input voltage Vin2 is input, the second control circuit 502 receives the input voltage Vin2 and starts up. When the second control circuit 502 detects that the detection signal DT is not sent from the first control circuit 501, that is, that the input voltage Vin1 is not connected, the second control circuit 502 turns off the control signal CT6 to turn off the n-channel MOSFET 72 and separate the capacitor 76 from the circuit.

[0179] The embodiments disclosed herein should be considered to be illustrative and not restrictive in all respects. The scope of the present disclosure is defined by the claims, not the above description, and is intended to include all modifications within the meaning and scope of the claims. [Explanation of symbols]

[0180] 1 first power supply, 2 second power supply, 3, 3A, 3B switching transformer, 10, 10A, 40A, 40B first circuit, 11, 15, 21, 31, 61, 62, 83 diode, 12, 14, 22, 32, 76, 82 capacitor, 13, 65, 66, 81 resistor, 17, 24, 25 switch, 20, 20A, 20B, 20C, 20D, 20E second circuit, 23, 33 load resistor, 30, 50A, 50B third circuit, 47, 55, 63, 64, 71, 72 MOSFET, 54 relay, 56 Zener diode, 89 snubber circuit, 100, 200, 200A, 300 power supply circuit, 501 first control circuit, 502 second control circuit, 503 feedback circuit, C1 output state terminal, C2 Input state terminal, N1 first winding, N2 second winding, N3 third winding, N11, N12, N21, N22, N31 negative terminals, P11, P12, P21, P22, P31 positive terminals, 73 inverter, 74 inductor, 77 rectifier circuit.

Claims

1. a switching transformer having a first winding, a second winding, and a third winding; A first circuit, a second circuit, and a third circuit, The first circuit is an input positive terminal and an input negative terminal configured to be able to receive a voltage of a first power supply; a first switch that switches application of an input voltage to the first winding on or off; a first control circuit that controls the first switch; the second circuit includes a second control circuit, and when the voltage of the first power supply is input to the first circuit, the first control circuit sends a detection signal representing that the voltage of the first power supply is being input to the second control circuit; the second control circuit receives a voltage of a second power supply, and switches, based on the detection signal, whether to induce power in the second winding, or to output the power induced in the second winding in response to the voltage applied to the first winding to an external load; The third circuit is a positive output terminal and a negative output terminal for outputting power induced in the third winding in response to a voltage applied to the first winding or the second winding; a feedback circuit that feeds back to the first control circuit and the second control circuit a feedback signal that varies depending on an output voltage generated between the output positive terminal and the output negative terminal.

2. The second circuit is an input / output positive terminal and an input / output negative terminal configured to receive a voltage of the second power supply and to output power induced in the second winding in response to a voltage applied to the first winding; a second switch configured to switch between outputting the power induced in the second winding to the input / output positive terminal and the input / output negative terminal, or inputting power from the second power source to the second winding; a third switch that switches on or off application of an input voltage to the second winding; The power supply circuit according to claim 1 , wherein the second control circuit controls the second switch and the third switch.

3. The first circuit further comprises: a first capacitor connected between the input positive terminal and the input negative terminal; a first diode having a cathode connected to a first end of the first winding; a second diode having an anode connected to the second end of the first winding; a first resistor connected between the input positive terminal and the anode of the first diode and the cathode of the second diode; a second capacitor connected between the input positive terminal and the anode of the first diode and the cathode of the second diode; 3. The power supply circuit of claim 2, wherein a first end of the first switch is connected to the second end of the first winding and the anode of the second diode, and a second end of the first switch is connected to the input negative terminal.

4. 3. The power supply circuit according to claim 2, wherein the first control circuit controls the first switch based on the feedback signal, and the second control circuit controls the third switch based on the feedback signal.

5. A power supply circuit as described in claim 2, wherein the second control circuit controls the second switch based on the detection signal from the first control circuit.

6. the first control circuit is driven by power from the first power source; The power supply circuit of claim 5 , wherein the second control circuit is powered by power from the second power supply.

7. The second circuit further comprises: a third diode; The second switch is an output state terminal and an input state terminal; the input state terminal is connected to a first end of the second winding and to a cathode of the third diode; the output state terminal is connected to a first end of the third switch and a second end of the second winding; a second end of the third switch is connected to the anode of the third diode and the input / output negative terminal; 7. The power supply circuit according to claim 6, wherein the second switch switches between connecting the I / O positive terminal and the output status terminal or connecting the I / O positive terminal and the input status terminal.

8. the second switch is constituted by a relay, 8. The power supply circuit according to claim 7, wherein the relay connects the input / output positive terminal to the output status terminal when the second control circuit is not in operation.

9. the third switch is constituted by a first transistor, 8. The power supply circuit according to claim 7, wherein said second circuit further includes a Zener diode connected in parallel with said first transistor.

10. the first transistor is an n-channel MOSFET; 10. The power supply circuit according to claim 9, wherein the Zener voltage of the Zener diode is equal to or lower than a rated drain-source voltage of the first transistor.

11. the third switch is constituted by a first transistor, The power supply circuit according to claim 7 , wherein the second circuit further comprises a snubber circuit connected across the second winding.

12. The second circuit further comprises: a third diode; the third switch is constituted by a first transistor, The second switch is a fourth diode, a fifth diode, a second transistor, a third transistor, a second resistor, and a third resistor; an anode of the fifth diode is connected to the second end of the second winding and to the first electrode of the first transistor, and a cathode of the fifth diode is connected to the first electrode of the second transistor, to the first end of the second resistor, and to the input / output positive terminal; a second electrode of the second transistor is connected to an anode of the fourth diode, a cathode of the fourth diode is connected to a first end of the second winding and to a cathode of the third diode; a control electrode of the second transistor is connected to a second end of the second resistor and a first end of the third resistor, a second end of the third resistor is connected to a first electrode of the third transistor, and a second electrode of the third transistor is connected to an anode of the third diode, a second electrode of the first transistor, and the input / output negative terminal; 7. The power supply circuit according to claim 6, wherein said second control circuit outputs a control signal to a control electrode of said first transistor and to a control electrode of said third transistor.

13. The second circuit is an input / output positive terminal and an input / output negative terminal configured to receive a voltage of the second power supply and to output power induced in the second winding in response to a voltage applied to the first winding; a fourth transistor disposed between the input / output negative terminal and a first end of the second winding; an inductor disposed between the input / output positive terminal and a second end of the second winding; a fifth transistor disposed between a first node between the second end of the second winding and the inductor and a second node between the input / output negative terminal and the fourth transistor; 2. The power supply circuit according to claim 1, wherein the second control circuit sets the fifth transistor off when the fourth transistor is set on, and sets the fifth transistor on when the fourth transistor is set off.

14. The second circuit further comprises:

14. The power supply circuit of claim 13 further comprising a third capacitor and a sixth transistor connected in series between said first node and said second node.

15. The second circuit further comprises: The power supply circuit according to any one of claims 7 to 14, further comprising a fourth capacitor and a fourth resistor connected in parallel between the input / output positive terminal and the input / output negative terminal.

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