Power supply circuit

Abstract

To provide a power supply circuit capable of appropriately suppressing inrush current.SOLUTION: A power supply circuit (1) includes an inrush resistance element (3) and a switching element (4) parallel with each other and connected between a negative-side second input line (L2) and a negative-side second output terminal (T4), and an inrush control circuit (10) that turns off the switching element when the difference between a peak value of an input voltage (Vp1) and an output voltage (V2), i.e., Vp1-V2, is equal to or greater than a threshold value, and turns on the switching element when Vp1-V2 is less than the threshold value.SELECTED DRAWING: Figure 1

Description

[Technical Field]

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

[0002] Patent Document 1 discloses an inrush current suppression circuit, which switches a changeover switching element connected in parallel to a first resistor in accordance with a terminal voltage detected by a voltage detection circuit. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 2019-122158 Summary of the Invention [Problem to be solved by the invention]

[0004] However, when the input voltage fluctuates, switching the circuit based solely on the output voltage can result in large inrush currents.

[0005] An object of one embodiment of the present invention is to provide a power supply circuit that can appropriately suppress inrush current. [Means for solving the problem]

[0006] A power supply circuit according to a first aspect of the present invention comprises a first positive output terminal and a second negative output terminal, a first positive input wiring and a second negative input wiring, a resistive element connected between the second input wiring and the second output terminal, a switching element connected in parallel to the resistive element, and a control circuit that turns off the switching element if Vp1-V2, which is the difference between the peak value Vp1 of the input voltage and the output voltage V2, is equal to or greater than a threshold value, and turns on the switching element if Vp1-V2 is less than the threshold value.

[0007] According to the above configuration, when the difference between the input voltage and the output voltage is large, the switching element is turned off, and when the difference becomes small, the switching element is turned on, thereby making it possible to appropriately suppress inrush current.

[0008] A power supply circuit according to a second aspect of the present invention may be configured such that, in the above-mentioned first aspect, the control circuit includes a first subtraction circuit that outputs, as V2, a first voltage corresponding to the difference between the potential of the first output terminal and the potential of the second output terminal when the potential of the second input wiring is used as a reference, a second subtraction circuit that outputs, as Vp1-V2, a second voltage corresponding to the difference between the peak potential of the first input wiring and the potential of the second input wiring, and a third voltage corresponding to the difference from the first voltage, and a judgment circuit that judges whether Vp1-V2 is greater than or equal to the threshold value based on the third voltage.

[0009] According to the above configuration, the inrush current can be suppressed by an analog circuit using a subtraction circuit that operates in response to the input voltage and the output voltage, which eliminates the need for an increased circuit size.

[0010] A power supply circuit according to a third aspect of the present invention may be configured such that, in the second aspect described above, the control circuit includes a first buffer circuit that outputs a fourth voltage corresponding to the difference between the potential of the first output terminal and the potential of the second input wiring, and a second buffer circuit that outputs a fifth voltage corresponding to the difference between the potential of the second output terminal and the potential of the second input wiring, and the first subtraction circuit outputs the difference between the fourth voltage and the fifth voltage as the first voltage.

[0011] A power supply circuit according to a fourth aspect of the present invention may be configured in the second or third aspect above, wherein the control circuit includes a third buffer circuit that outputs the second voltage to the second subtraction circuit.

[0012] A power supply circuit according to a fifth aspect of the present invention may be configured in the above-mentioned first aspect, wherein the control circuit comprises a third subtraction circuit that outputs a sixth voltage corresponding to the difference between the peak potential of the first input wiring and the potential of the first output terminal when the potential of the second input wiring is used as a reference, an adder circuit that outputs a third voltage corresponding to the sum of a fifth voltage corresponding to the difference between the potential of the second output terminal and the potential of the second input wiring and the sixth voltage, and a judgment circuit that judges whether Vp1-V2 is greater than or equal to the threshold value based on the third voltage.

[0013] According to the above configuration, inrush current can be suppressed by an analog circuit using a subtraction circuit and an addition circuit that operate in response to the input voltage and the output voltage, so there is no need to increase the circuit size.

[0014] A power supply circuit according to a sixth aspect of the present invention may be configured in any of the first to fifth aspects above, wherein the switching element is an n-type field effect transistor.

[0015] According to the above configuration, the n-type field effect transistor with a small on-resistance is connected to the second negative output terminal, which reduces loss during normal operation.

[0016] A power supply circuit according to a seventh aspect of the present invention may be configured in any of the first to sixth aspects above, such that the control circuit obtains a smoothed DC input voltage as the peak value Vp1 of the input voltage.

[0017] According to the above configuration, the peak value Vp1 of the input voltage, which is a pulsating current, can be appropriately acquired, and the switching element can be appropriately switched in accordance with the peak value Vp1 of the input voltage and the output voltage V2. [Effects of the Invention]

[0018] According to one aspect of the present invention, it is possible to appropriately suppress inrush current. [Brief explanation of the drawings]

[0019] [Figure 1] 1 is a circuit diagram showing a configuration of a power supply circuit according to an embodiment of the present invention; [Figure 2] FIG. 2 is a circuit diagram of the power supply circuit, showing a detailed example of an inrush control circuit. [Figure 3] FIG. 2 is a circuit diagram of the power supply circuit, showing an example of a more detailed circuit configuration of an inrush control circuit. [Figure 4] 1 is a circuit diagram showing a configuration of a power supply circuit according to an embodiment of the present invention; DETAILED DESCRIPTION OF THE INVENTION

[0020] [Embodiment 1] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment according to one aspect of the present invention (hereinafter also referred to as "the present embodiment") will be described below with reference to the drawings.

[0021] §1 Application Examples FIG. 1 is a circuit diagram showing the configuration of a power supply circuit 1 according to this embodiment. The power supply circuit 1 receives AC voltage from an input side, converts the AC voltage to DC, and outputs the DC voltage from an output side to a load 90. The power supply circuit 1 includes a first input terminal T1, a second input terminal T2, a first positive-side output terminal T3, a second negative-side output terminal T4, a rectifier circuit 2, a first positive-side input wiring L1, a second negative-side input wiring L2, an inrush resistance element 3, and a switching element 4. The inrush resistance element 3 is connected between the second negative-side input wiring L2 and the second negative-side output terminal T4. The switching element 4 is connected in parallel with the inrush resistance element 3. The inrush resistance element 3 and the switching element 4 are used to suppress inrush current.

[0022] Immediately after the input voltage is applied, the switching element 4 is off. The current flows through the inrush resistance element 3, so the inrush current is suppressed. The output voltage V2 between the first output terminal T3 and the second output terminal T4 gradually increases and approaches the input voltage V1. When V1 - V2 becomes sufficiently small, the switching element 4 is switched from off to on, suppressing the inrush current and stabilizing the power supply.

[0023] However, because the second negative output terminal T4 and the rectifier circuit 2 are connected via the inrush resistor 3, a potential difference occurs across the inrush resistor 3. In a situation where the input voltage is unknown, this potential difference cannot be determined from the output voltage V2 alone. Therefore, if the switching element 4 is switched from off to on based only on the output voltage V2, V1 - V2 may still be large, and a large inrush current may flow.

[0024] Therefore, the power supply circuit 1 of this embodiment switches on the switching element 4 when the difference Vp1-V2 between the peak value Vp1 of the input voltage V1 and the output voltage V2 is less than a predetermined threshold value, thereby allowing the power supply circuit 1 to appropriately suppress the inrush current.

[0025] §2 Configuration example The configuration of the power supply circuit 1 will be described in more detail with reference to Fig. 1. The power supply circuit 1 includes a first input terminal T1, a second input terminal T2, a first positive output terminal T3, a second negative output terminal T4, a rectifier circuit 2, a first positive input wiring L1, a second negative input wiring L2, an inrush resistance element 3, a switching element 4, a smoothing capacitor 5, a coil 6, a first diode 7, a second diode 8, a PFC transistor 9, an inrush control circuit 10, and a PFC control circuit 30.

[0026] The first input terminal T1 and the second input terminal T2 are terminals to which an AC input voltage is input. The rectifier circuit 2 rectifies the AC to DC. Here, the rectifier circuit 2 is a bridge circuit including a plurality of diodes, but is not limited to this and may be a circuit including a plurality of switching elements. The rectifier circuit 2 has a first AC terminal 2a connected to the first input terminal T1, a second AC terminal 2b connected to the second input terminal T2, a positive terminal 2c, and a negative terminal 2d. The rectifier circuit 2 outputs a DC (pulsating) input voltage V1 from the positive terminal 2c and the negative terminal 2d.

[0027] The first input wiring L1 is a wiring connected to the positive terminal 2c of the rectifier circuit 2. The second input wiring L2 is a wiring connected to the negative terminal 2d of the rectifier circuit 2. The voltage between the first input wiring L1 and the second input wiring L2 is a DC (pulsating) input voltage V1. The second input wiring L2 is grounded.

[0028] One end of the inrush resistance element 3 is connected to the negative-side second input wiring L2, and the other end of the inrush resistance element 3 is connected to the second output terminal T4. The inrush resistance element 3 may be, for example, a thermistor whose resistance decreases as the temperature increases.

[0029] The switching element 4 is connected in parallel to the inrush resistance element 3. The switching element 4 is, for example, a transistor. The switching element 4 is preferably an n-type field effect transistor. The n-type field effect transistor has a small on-resistance, which makes it possible to reduce loss. Because the n-type field effect transistor is controlled by a positive gate voltage, it is more convenient to provide the switching element 4 on the low side (between the negative side terminal 2d and the second output terminal T4) rather than on the high side (between the positive side terminal 2c and the first output terminal T3).

[0030] The smoothing capacitor 5 is connected between the first output terminal T3 and the second output terminal T4.

[0031] The coil 6 is connected to the first positive input wiring L1. The anode of the first diode 7 is connected to the coil 6, and the cathode is connected to the first output terminal T3. The second diode 8 is connected in parallel to the coil 6 and the first diode 7. The cathode of the second diode 8 is connected to the first output terminal T3.

[0032] One end of the PFC transistor 9 is connected to the node between the coil 6 and the first diode 7, and the other end of the PFC transistor 9 is connected to the second output terminal T4. The coil 6, the first diode 7, the second diode 8, and the PFC transistor 9 form a boost circuit. The PFC transistor 9 is driven by the PFC control circuit 30 and improves the power factor of the power supply circuit 1.

[0033] The PFC control circuit 30 detects the voltage across the switching element 4 and controls the PFC transistor 9 based on the detected voltage.

[0034] The first output terminal T3 is a positive output terminal. The second output terminal T4 is a negative output terminal. The voltage between the first output terminal T3 and the second output terminal T4 is a smoothed DC output voltage V2. The first output terminal T3 and the second output terminal T4 output the output voltage V2 to the load 90.

[0035] After AC input voltage is applied to the power supply circuit 1, the output voltage V2 gradually increases. During the period immediately after application, the peak value of the potential of the first input wiring L1 > the potential of the first output terminal T3 > the potential of the second output terminal T4 > the potential of the second input wiring L2 (ground). Because current flows through the inrush resistance element 3, the potential of the second output terminal T4, which is the negative side of the output, becomes higher than the potential of the second input wiring L2, which is ground. Therefore, Vp1 > V2.

[0036] The inrush control circuit 10 determines Vp1-V2, which is the difference between the peak value Vp1 of the input voltage V1 and the output voltage V2. The inrush control circuit 10 controls the switching element 4 based on Vp1-V2. For example, if Vp1-V2 is equal to or greater than a predetermined threshold, the inrush control circuit 10 turns off the switching element 4. If Vp1-V2 is less than the predetermined threshold, the inrush control circuit 10 turns on the switching element 4. Note that since the input voltage V1 is a pulsating current, the inrush control circuit 10 uses the peak value Vp1 of the input voltage for its judgment.

[0037] As a result, even if the peak value of the input AC voltage fluctuates, the inrush control circuit 10 can switch on the switching element 4 when the difference between the peak value Vp1 of the input voltage V1 and the output voltage V2 becomes sufficiently small, thereby enabling the power supply circuit 1 to appropriately suppress inrush current.

[0038] (Configuration example of inrush control circuit 10) 2 is a circuit diagram of the power supply circuit 1 showing a detailed example of the inrush control circuit 10. The inrush control circuit 10 includes a first subtraction circuit 11, a second subtraction circuit 12, and a determination circuit 13. The first subtraction circuit 11 generates a first voltage corresponding to the difference (V2) between the potential of the first output terminal T3 and the potential of the second output terminal T4, with the potential (ground) of the second input wiring L2 as the reference. The first subtraction circuit 11 outputs the first voltage, with the potential (ground) of the second input wiring L2 as the reference, to the second subtraction circuit 12.

[0039] However, if a subtraction circuit were to simply subtract the potentials of the first output terminal T3 and the second output terminal T4 as inputs to obtain V2, the output (V2) of the subtraction circuit would be a voltage based on the potential of the second output terminal T4. The potential of this output, as viewed from ground (the potential of the second input wiring L2), would change with fluctuations in the potential of the second output terminal T4. Therefore, Vp1-V2 cannot be obtained appropriately using this output.

[0040] In this embodiment, the first subtraction circuit 11 receives as input the potentials of the first output terminal T3 and the second output terminal T4, relative to the potential (ground) of the second input wiring L2. That is, the first subtraction circuit 11 receives as input the voltage difference between the potential of the first output terminal T3 and the potential (ground) of the second input wiring L2, and the voltage difference between the potential of the second output terminal T4 and the potential (ground) of the second input wiring L2. The first subtraction circuit 11 then generates a first voltage corresponding to the difference (V2) between these potentials. As a result, the first voltage becomes a voltage corresponding to the output voltage V2, relative to the potential (ground) of the second input wiring L2.

[0041] The first subtraction circuit 11 may receive as its input a voltage obtained by dividing the difference between the potential of the first output terminal T3 and the potential (ground) of the second input wiring L2 at a predetermined voltage division ratio. Similarly, the first subtraction circuit 11 may receive as its input a voltage obtained by dividing the difference between the potential of the second output terminal T4 and the potential (ground) of the second input wiring L2 at a predetermined voltage division ratio. The output (first voltage) obtained as a result of the subtraction by the first subtraction circuit 11 is also a voltage (a voltage equivalent to V2) obtained by dividing the difference (V2) between the potential of the first output terminal T3 and the potential of the second output terminal T4 at a predetermined voltage division ratio.

[0042] The second subtraction circuit 12 receives as input the potential of the first input wiring L1 and the first voltage when the potential (ground) of the second input wiring L2 is used as a reference. That is, the second subtraction circuit 12 receives as input the first voltage and a second voltage, which is the difference between the peak potential of the first input wiring L1 and the potential (ground) of the second input wiring L2. Since both the first voltage and the second voltage are voltages when the potential (ground) of the second input wiring L2 is used as a reference, they can be subtracted by the subtraction circuit. The second subtraction circuit 12 then generates a third voltage corresponding to the difference between the second voltage and the first voltage. As a result, the third voltage corresponds to Vp1-V2 when the potential (ground) of the second input wiring L2 is used as a reference. The second subtraction circuit 12 outputs the third voltage to the determination circuit 13.

[0043] The determination circuit 13 determines whether Vp1-V2 is equal to or greater than a predetermined threshold based on a third voltage equivalent to Vp1-V2. If Vp1-V2 is equal to or greater than the predetermined threshold, the determination circuit 13 turns off the switching element 4, and if Vp1-V2 is less than the predetermined threshold, the determination circuit 13 turns on the switching element 4. The comparison with the threshold by the determination circuit 13 may be performed using a comparator or a combination of a Zener diode and a transistor.

[0044] (Example of circuit configuration of inrush control circuit 10) 3 is a circuit diagram of the power supply circuit 1 showing an example of a more detailed circuit configuration of the inrush control circuit 10. The inrush control circuit 10 is configured as an analog circuit. The inrush control circuit 10 includes a first subtraction circuit 11, a second subtraction circuit 12, a determination circuit 13, a first buffer circuit 16, a second buffer circuit 17, a third buffer circuit 18, resistive elements R1 to R6, a third diode 21, and an input capacitor 22.

[0045] The resistor element R1 and the resistor element R2 are connected in series between the first output terminal T3 and the second input wiring L2, and form a first voltage dividing circuit.

[0046] The input terminal of the first buffer circuit 16 is connected to the node between the resistor element R1 and the resistor element R2.

[0047] The resistor element R3 and the resistor element R4 are connected in series between the second output terminal T4 and the second input wiring L2, and form a second voltage dividing circuit.

[0048] The input terminal of the second buffer circuit 17 is connected to the node between the resistor element R3 and the resistor element R4.

[0049] The anode of the third diode 21 is connected to the first input wiring L1. The input capacitor 22 is connected between the cathode of the third diode 21 and the second input wiring L2.

[0050] Resistor element R5 and resistor element R6 are connected in series to each other and form a third voltage divider circuit. One end of resistor element R5 is connected to the cathode of third diode 21. The other end of resistor element R5 is connected to one end of resistor element R6. The other end of resistor element R6 is connected to second input wiring L2.

[0051] The input terminal of the third buffer circuit 18 is connected to the node between the resistor element R5 and the resistor element R6.

[0052] The first subtraction circuit 11 includes a first operational amplifier 11a and resistors R11 to R14. The non-inverting input terminal of the first operational amplifier 11a is connected to the output terminal of the first buffer circuit 16 via a resistor R13. The non-inverting input terminal of the first operational amplifier 11a is connected to the second input wiring L2 via a resistor R14. The inverting input terminal of the first operational amplifier 11a is connected to the output terminal of the second buffer circuit 17 via a resistor R11. The inverting input terminal of the first operational amplifier 11a is connected to the output terminal of the first operational amplifier 11a via a resistor R12. The output of the first operational amplifier 11a becomes the output of the first subtraction circuit 11.

[0053] The second subtraction circuit 12 includes a second operational amplifier 12a and resistors R21 to R24. The inverting input terminal of the second operational amplifier 12a is connected to the output terminal of the first operational amplifier 11a via the resistor R21. The inverting input terminal of the second operational amplifier 12a is connected to the output terminal of the second operational amplifier 12a via the resistor R22. The non-inverting input terminal of the second operational amplifier 12a is connected to the output terminal of the third buffer circuit 18 via the resistor R23. The non-inverting input terminal of the second operational amplifier 12a is connected to the second input wiring L2 via the resistor R24. The output of the second operational amplifier 12a becomes the output of the second subtraction circuit 12.

[0054] The decision circuit 13 includes a comparator 13a. The inverting input terminal of the comparator 13a is connected to the output terminal of the second operational amplifier 12a. The output terminal of the comparator 13a is connected to the control terminal (gate) of the switching element 4.

[0055] (Operation of inrush control circuit 10) The voltage division ratio of the first voltage dividing circuit (resistance elements R1 and R2), the voltage division ratio of the second voltage dividing circuit (resistance elements R3 and R4), and the voltage division ratio of the third voltage dividing circuit (resistance elements R5 and R6) are all the same predetermined voltage division ratio.

[0056] The inrush control circuit 10 obtains the smoothed DC input voltage V1 as the peak value Vp1 of the input voltage V1. Specifically, the input voltage V1 is smoothed by the third diode 21 and the input capacitor 22. Therefore, the potential at the node between the third diode 21 and the input capacitor 22 becomes the peak value Vp1 of the input voltage V1.

[0057] The third voltage divider circuit generates a second voltage by dividing the peak value Vp1 of the input voltage at a predetermined voltage division ratio. The second voltage is a voltage divided at a predetermined voltage division ratio that corresponds to the difference between the peak potential of the first input line L1 and the potential of the second input line L2. The second voltage is input to the third buffer circuit 18. The third buffer circuit 18 outputs the input second voltage.

[0058] A fourth voltage divided by a predetermined voltage division ratio, which corresponds to the difference between the potential of the first output terminal T3 and the potential of the second input line L2, is input to the first buffer circuit 16. The first buffer circuit 16 outputs the input fourth voltage.

[0059] A fifth voltage divided by a predetermined voltage division ratio, which corresponds to the difference between the potential of the second output terminal T4 and the potential of the second input line L2, is input to the second buffer circuit 17. The second buffer circuit 17 outputs the input fifth voltage.

[0060] The first subtraction circuit 11 outputs the difference between the fourth voltage and the fifth voltage as the first voltage. If the resistance values ​​of the resistive elements R11 to R14 are r11 to r14, respectively, and r11=r13 and r12=r14, the following relationship holds: 1st voltage = (r12 / r11) (4th voltage - 5th voltage) The fourth voltage and the fifth voltage are both voltages relative to ground (the potential of the second input wiring L2). Therefore, the first voltage obtained as the subtraction result in the first subtraction circuit 11 is also a voltage relative to ground (the potential of the second input wiring L2).

[0061] The second subtraction circuit 12 outputs the difference between the second voltage and the first voltage as a third voltage. The third voltage is a voltage measured with respect to ground (the potential of the second input wiring L2). Both the first voltage and the second voltage are measured with respect to the same ground (the potential of the second input wiring L2). Therefore, the third voltage, which is the subtraction result of the second subtraction circuit 12, has a value corresponding to Vp1-V2.

[0062] If the third voltage is equal to or greater than a predetermined voltage, the determination circuit 13 determines that Vp1-V2 is equal to or greater than a predetermined threshold, and if the third voltage is less than the predetermined voltage, the determination circuit 13 determines that Vp1-V2 is less than the predetermined threshold. If the third voltage is equal to or greater than the predetermined voltage, the determination circuit 13 keeps the switching element 4 off. If the third voltage is less than the predetermined voltage, the determination circuit 13 turns on the switching element 4.

[0063] In this way, the inrush control circuit 10 acquires all voltages used in the calculation as voltages based on the potential of the second input wiring L2, thereby enabling it to appropriately evaluate the difference between the peak value Vp1 of input voltages with different negative potentials and the output voltage V2. Furthermore, because the inrush control circuit 10 performs these calculations using analog circuits, it is possible to make the circuit configuration compact.

[0064] (Variation) The voltage divider circuit can be omitted. For example, the resistor elements R1, R3, and R5 may be omitted, and the paths of the resistor elements R2, R4, and R6 may be cut off. The same result can be obtained if the resistor element R14 of the first subtraction circuit 11 and the resistor element R24 of the second subtraction circuit 12 are connected to the second input wiring L2.

[0065] The first buffer circuit 16, the second buffer circuit 17, and the third buffer circuit 18 can be omitted. However, it is preferable to provide the first buffer circuit 16, the second buffer circuit 17, and the third buffer circuit 18 so that the impedance of the subsequent stage does not affect the impedance of the input stage.

[0066] [Embodiment 2] Other embodiments of the present invention will be described below. For ease of explanation, the same reference numerals will be used to designate components having the same functions as those described in the above embodiment, and the description thereof will not be repeated.

[0067] 4 is a circuit diagram showing the configuration of a power supply circuit 1a of this embodiment. The power supply circuit 1a includes an inrush control circuit 10a instead of the inrush control circuit 10. The inrush control circuit 10a includes a third subtraction circuit 14, an adder circuit 15, and a determination circuit 13. The third subtraction circuit 14 generates a sixth voltage corresponding to the difference between the peak potential of the first input wiring L1 and the potential of the first output terminal T3, with the potential of the second input wiring L2 (ground) taken as the reference. The third subtraction circuit 14 outputs the sixth voltage, with the potential of the second input wiring L2 (ground) taken as the reference, to the adder circuit 15.

[0068] The adder circuit 15 receives the potential of the second output terminal T4 and the sixth voltage when the potential (ground) of the second input wiring L2 is used as a reference. That is, the adder circuit 15 receives the fifth voltage, which corresponds to the difference between the potential of the second output terminal T4 and the potential (ground) of the second input wiring L2, and the sixth voltage. Since both the fifth voltage and the sixth voltage are voltages when the potential (ground) of the second input wiring L2 is used as a reference, they can be added by the adder circuit. The adder circuit 15 then generates a third voltage, which corresponds to the sum of the fifth voltage and the sixth voltage. As a result, the third voltage becomes a voltage corresponding to Vp1-V2 when the potential (ground) of the second input wiring L2 is used as a reference. The adder circuit 15 outputs the third voltage to the determination circuit 13.

[0069] The specific configuration of the third subtraction circuit 14 can be the same as that of the above-described embodiment. The addition circuit 15 can also be a known addition circuit.

[0070] The determination circuit 13 determines whether or not Vp1-V2 is equal to or greater than a predetermined threshold value, based on a third voltage equivalent to Vp1-V2.

[0071] Even if the adder circuit 15 is used as in the power supply circuit 1a, the same results as those of the power supply circuit 1 of the first embodiment can be obtained.

[0072] As with the inrush control circuit 10 of the first embodiment, the inrush control circuit 10a may receive as input a voltage that has been divided at a predetermined voltage division ratio.

[0073] 〔summary〕 A power supply circuit according to a first aspect of the present invention comprises a first positive output terminal and a second negative output terminal, a first positive input wiring and a second negative input wiring, a resistive element connected between the second input wiring and the second output terminal, a switching element connected in parallel to the resistive element, and a control circuit that turns off the switching element if Vp1-V2, which is the difference between the peak value Vp1 of the input voltage and the output voltage V2, is equal to or greater than a threshold value, and turns on the switching element if Vp1-V2 is less than the threshold value.

[0074] A power supply circuit according to a second aspect of the present invention may be configured such that, in the above-mentioned first aspect, the control circuit includes a first subtraction circuit that outputs, as V2, a first voltage corresponding to the difference between the potential of the first output terminal and the potential of the second output terminal when the potential of the second input wiring is used as a reference, a second subtraction circuit that outputs, as Vp1-V2, a second voltage corresponding to the difference between the peak potential of the first input wiring and the potential of the second input wiring, and a third voltage corresponding to the difference from the first voltage, and a judgment circuit that judges whether Vp1-V2 is greater than or equal to the threshold value based on the third voltage.

[0075] A power supply circuit according to a third aspect of the present invention may be configured such that, in the second aspect described above, the control circuit includes a first buffer circuit that outputs a fourth voltage corresponding to the difference between the potential of the first output terminal and the potential of the second input wiring, and a second buffer circuit that outputs a fifth voltage corresponding to the difference between the potential of the second output terminal and the potential of the second input wiring, and the first subtraction circuit outputs the difference between the fourth voltage and the fifth voltage as the first voltage.

[0076] A power supply circuit according to a fourth aspect of the present invention may be configured in the second or third aspect above, wherein the control circuit includes a third buffer circuit that outputs the second voltage to the second subtraction circuit.

[0077] A power supply circuit according to a fifth aspect of the present invention may be configured in the above-mentioned first aspect, wherein the control circuit comprises a third subtraction circuit that outputs a sixth voltage corresponding to the difference between the peak potential of the first input wiring and the potential of the first output terminal when the potential of the second input wiring is used as a reference, an adder circuit that outputs a third voltage corresponding to the sum of a fifth voltage corresponding to the difference between the potential of the second output terminal and the potential of the second input wiring and the sixth voltage, and a judgment circuit that judges whether Vp1-V2 is greater than or equal to the threshold value based on the third voltage.

[0078] A power supply circuit according to a sixth aspect of the present invention may be configured in any of the first to fifth aspects above, wherein the switching element is an n-type field effect transistor.

[0079] A power supply circuit according to a seventh aspect of the present invention may be configured in any of the first to sixth aspects above, such that the control circuit obtains a smoothed DC input voltage as the peak value Vp1 of the input voltage.

[0080] The present invention is not limited to the above-described embodiments, and various modifications are possible within the scope of the claims. Embodiments obtained by appropriately combining the technical means disclosed in different embodiments are also included in the technical scope of the present invention. [Explanation of symbols]

[0081] 1, 1a power circuit 2 Rectifier circuit 3 Inrush resistance element 4 Switching elements 5 smoothing capacitors 9 PFC transistor 10, 10a Inrush control circuit 11 First subtraction circuit 12 Second subtraction circuit 13 Judgment circuit 14 Third subtraction circuit 15 Addition circuit 16 First buffer circuit 17 Second buffer circuit 18 Third buffer circuit 21 Third diode 22 Input capacitor 30 PFC control circuit 90 load L1 First input wiring L2 Second input wiring T1 First input terminal T2 Second input terminal T3 1st output terminal T4 Second output terminal V1 input voltage V2 Output voltage

Claims

1. a first positive output terminal and a second negative output terminal; a first input wiring on the positive side and a second input wiring on the negative side; a resistive element connected between the second input wiring and the second output terminal; a switching element connected in parallel to the resistance element; a control circuit that turns off the switching element when Vp1-V2, which is the difference between a peak value Vp1 of an input voltage and an output voltage V2, is equal to or greater than a threshold value, and turns on the switching element when Vp1-V2 is less than the threshold value.

2. The control circuit a first subtraction circuit that outputs, as V2, a first voltage corresponding to a difference between a potential of the first output terminal and a potential of the second output terminal when the potential of the second input wiring is used as a reference; a second subtraction circuit that outputs, as Vp1-V2, a second voltage corresponding to the difference between the peak potential of the first input wiring and the potential of the second input wiring, and a third voltage corresponding to the difference between the first voltage and the second voltage; 2. The power supply circuit according to claim 1, further comprising: a determination circuit that determines whether or not Vp1-V2 is equal to or greater than the threshold value based on the third voltage.

3. The control circuit a first buffer circuit that outputs a fourth voltage corresponding to a difference between a potential of the first output terminal and a potential of the second input wiring; a second buffer circuit that outputs a fifth voltage corresponding to a difference between a potential of the second output terminal and a potential of the second input wiring; 3. The power supply circuit according to claim 2, wherein the first subtraction circuit outputs the difference between the fourth voltage and the fifth voltage as the first voltage.

4. The control circuit 3. The power supply circuit according to claim 2, further comprising a third buffer circuit that outputs the second voltage to the second subtraction circuit.

5. The control circuit a third subtraction circuit that outputs a sixth voltage corresponding to a difference between a peak potential of the first input wiring and a potential of the first output terminal when the potential of the second input wiring is used as a reference; an adder circuit that outputs a third voltage corresponding to the sum of a fifth voltage corresponding to a difference between a potential of the second output terminal and a potential of the second input wiring and the sixth voltage; 2. The power supply circuit according to claim 1, further comprising: a determination circuit that determines whether or not Vp1-V2 is equal to or greater than the threshold value based on the third voltage.

6. 2. The power supply circuit according to claim 1, wherein the switching element is an n-type field effect transistor.

7. The power supply circuit according to claim 1 , wherein the control circuit obtains the input voltage as a smoothed DC voltage as a peak value Vp1 of the input voltage.

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