Switching power supply device, and electric equipment having the same

Abstract

To provide a switching power supply device capable of preventing an output voltage that is not a feedback target from becoming too small when switching to a power saving mode in an isolation type flyback switching power supply device, and electric equipment having the same.SOLUTION: A switching power supply device is configured to be capable of supplying / receiving power while isolating between a power supply circuit and a second output circuit and a first output circuit. The power supply circuit includes a switching element switched on the basis of a feedback value in the first output circuit. The first output circuit includes a capacitor that generates a first output voltage, and a first output voltage setting circuit connected in parallel to the capacitor to set a target value of the first output voltage. The first output voltage setting circuit is capable of switching the first output voltage between either one of a first voltage and a second voltage. The first output circuit includes a discharge circuit connected in parallel to the capacitor to discharge electric charges stored in the capacitor.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present invention relates to a switching power supply device and an electric device equipped with the same. [Background technology]

[0002] Some switching power supplies used in electrical equipment can switch to a power saving mode to reduce power consumption. At this time, the output voltage of the switching power supply becomes a second voltage that is lower than the first voltage in the normal mode.

[0003] An isolated flyback converter may be used for the switching power supply device (see, for example, Patent Document 1 below). In the isolated flyback converter, power is transferred from a first winding on the primary side of a transformer to a second winding on the secondary side. The output voltage in the secondary output circuit connected to the second winding is fed back to the primary power supply circuit connected to the first winding. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Patent No. 6013810 Summary of the Invention [Problem to be solved by the invention]

[0005] In such a transformer of an isolated flyback switching power supply device, a configuration may be adopted in which a third winding is added in addition to the first winding on the primary side and the second winding on the secondary side to extract a second output voltage different from the first output voltage obtained from the second winding. In this case, the value of either the first output voltage or the second output voltage is fed back to the primary side power supply circuit. For example, the first output voltage obtained from the second winding is fed back to the primary side power supply circuit, while the second output voltage obtained from the third winding is not fed back to the primary side power supply circuit.

[0006] In such a configuration, when the first output voltage obtained from the second winding is dropped from the first voltage to the second voltage when switching to the power saving mode, the second output voltage that is not the subject of feedback may become lower than the minimum operating voltage of the electrical load that operates at that second output voltage, which may cause the load to stop operating or be reset. This is because the target value of the first output voltage is changed to the second voltage, and switching in the primary-side power supply circuit stops until the first output voltage drops to the second voltage, so that the power supply from the power supply circuit to the output circuit that generates the second output voltage is also stopped.

[0007] The above-mentioned Patent Document 1 discloses a configuration for suppressing a decrease in the first output voltage caused by the stopping of switching on the power supply circuit side when the output load decreases, but this cannot be applied to the above-mentioned configuration in which it is necessary to decrease the first output voltage.

[0008] The present invention has been made to solve the above-mentioned problems, and has an object to provide an isolated flyback type switching power supply device that can prevent an output voltage that is not subject to feedback from becoming excessively small when switching to a power saving mode, and an electrical device equipped with the same. [Means for solving the problem]

[0009] A switching power supply device according to one aspect of the present invention includes a power supply circuit that introduces power from a power supply unit, a first output circuit that generates a first output voltage, a second output circuit that generates a second output voltage, a first winding connected to the power supply circuit, a second winding connected to the first output circuit, and a third winding connected to the second output circuit, a transformer configured to be able to exchange power between the power supply circuit and the second output circuit and to insulate the first output circuit from the second output circuit, a feedback circuit that detects the first output voltage in the first output circuit and feeds back a feedback value corresponding to the first output voltage to the power supply circuit, and a first controller connected to the first output circuit, the power supply circuit including a switch element connected to the first winding and switched on the basis of the feedback value, the first output circuit includes a diode connected to the second winding for rectifying a current flowing through the second winding, a capacitor connected to the diode for generating the first output voltage, and a first output voltage setting circuit connected in parallel to the capacitor for setting a target value of the first output voltage, the first output voltage setting circuit being configured to be able to switch the first output voltage between a first voltage and a second voltage lower than the first voltage in accordance with a control signal from the first controller, the second output circuit supplies the second output voltage generated from the power received from the first winding to a predetermined electric load, and the first output circuit further includes a discharge circuit connected in parallel to the capacitor for discharging an electric charge stored in the capacitor.

[0010] According to the above configuration, when the target value of the first output voltage that is the subject of feedback is switched from the first voltage to the lower second voltage, the first output voltage is fed back to the power supply circuit and the switch element is turned off, thereby stopping the power supply from the power supply circuit to the first output circuit. Here, the first output circuit is connected in parallel to a capacitor that generates the first output voltage, and a discharge circuit for discharging the charge stored in the capacitor is connected to the first output circuit. Therefore, when the power supply from the power supply circuit to the first output circuit is stopped, the charge stored in the capacitor is quickly discharged by the discharge circuit. Therefore, the first output voltage is quickly switched from the first voltage to the second voltage, and the period during which the switch element in the power supply circuit is turned off is shortened. As a result, it is possible to suppress the influence of a voltage drop caused by the switch element being turned off in the second output voltage that is not the subject of feedback. Therefore, in an isolated flyback switching power supply device, it is possible to suppress the output voltage that is not the subject of feedback from becoming too small when switching to the power saving mode.

[0011] The first output circuit may include a switch element connected in series to the discharge circuit, and the first controller may control the switch element to be turned on for a predetermined period to energize the discharge circuit when switching the target value of the first output voltage from the first voltage to the second voltage. By energizing the discharge circuit only for a period during which discharging is required, unnecessary power consumption can be suppressed.

[0012] The first controller may turn on the switch element for the predetermined period from when the target value of the first output voltage is switched from the first voltage to the second voltage. By starting discharging from the timing when the target value of the first output voltage is switched from the first voltage to the second voltage, the period during which discharging is performed can be shortened.

[0013] The discharge circuit may be a resistor element, which allows the discharge circuit to be realized with a simple configuration.

[0014] When the first controller switches the target value of the first output voltage from the first voltage to the second voltage, the first controller generates a control signal for the first output voltage setting circuit, which repeats a first signal level corresponding to the first voltage and a second signal level corresponding to the second voltage for a predetermined period, and the control signal may be a signal in which the ratio of the period in which the second signal level is the first signal level to the period in which the first signal level is the first signal level gradually increases. According to this, the ratio of the period in which the second voltage is the first voltage to the period in which the first output voltage is the second voltage gradually increases, so that the first output voltage gradually decreases. Moreover, since the period in which the target value of the first output voltage is the first voltage and the period in which the second voltage is the second voltage alternately occur, a timing occurs in which a switch element of a power supply circuit is turned on, and thereby power is also supplied to the second output circuit. Therefore, the decrease in the second output voltage is gradual. Therefore, it is possible to suppress the output voltage that is not the subject of feedback from becoming too small.

[0015] According to another aspect of the present invention, an electric device includes the switching power supply device having the above configuration, the electric device being a range hood including a fan, and the electric load being a second controller that controls the driving of the fan or a sensor that detects the open / closed state of the cover of the fan. With the above configuration, when the switching power supply device transitions to a power saving mode, it is possible to prevent the second output voltage of the second output circuit from dropping to a voltage at which the electric load connected to the second output circuit cannot operate. As a result, even if the second controller that drives the fan or the sensor that detects the open / closed state of the cover of the fan is connected to the second output circuit as an electric load, the range hood can continue to operate the electric load that is important for safety. Effect of the Invention

[0016] According to one aspect, in an isolated flyback switching power supply device, when switching to a power saving mode, it is possible to suppress an output voltage that is not the subject of feedback from becoming too small. [Brief description of the drawings]

[0017] [Figure 1] FIG. 1 is a block diagram showing a schematic configuration of an electric device equipped with a switching power supply device according to an embodiment of the present invention. [Diagram 2] FIG. 2 is a diagram showing a schematic circuit configuration of a switching power supply device in the electric device shown in FIG. [Diagram 3] FIG. 3 is a timing chart of the switching power supply device shown in FIG. [Figure 4] FIG. 4 is a timing chart of a switching power supply device according to a modified example. [Diagram 5] FIG. 5 is a diagram showing a schematic circuit configuration of a switching power supply device according to a reference example. [Figure 6] FIG. 6 is a timing chart of the switching power supply device in the reference example. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0018] Hereinafter, embodiments of the present invention will be described with reference to the drawings. In the following, the same or corresponding elements are denoted by the same reference numerals throughout the drawings, and duplicated descriptions thereof will be omitted.

[0019] [One embodiment] 1 is a block diagram showing a schematic configuration of an electric device including a switching power supply device according to an embodiment of the present invention. The electric device 100 in this embodiment is a range hood including a fan 101, an operation panel 102, and a switching power supply device 1. The fan 101 and the operation panel 102 are insulated from each other. The electric device 100 includes a first controller 8 that controls the operation panel 102, and a second controller 10 that controls the driving of the fan 101. The first controller 8 and the second controller 10 are capable of communicating with each other.

[0020] In addition, an openable / closable cover 103 is attached to the fan 101. The fan 101 can be accessed by opening the cover 103 during maintenance or the like. For safety reasons, the cover 103 must be closed when the fan 101 is in operation. Therefore, the electrical device 100 includes a sensor 104 that detects whether the cover 103 is open or closed. For example, the sensor 104 outputs an open state detection signal to the second controller 10 when the cover 103 is open.

[0021] The switching power supply device 1 supplies power supplied from a power supply unit 3 such as a commercial power supply to an electrical load included in an electrical device 100. A first controller 8, a second controller 10, and a power supply controller 11 described below are each composed of a processing circuit including an integrated circuit, a microcontroller, etc.

[0022] Fig. 2 is a diagram showing a schematic circuit configuration of a switching power supply device in the electric device shown in Fig. 1. As shown in Fig. 2, the switching power supply device 1 in this embodiment includes a power supply circuit 4 that introduces power from a power supply unit 3, a first output circuit 5 that generates a first output voltage V1, a second output circuit 6 that generates a second output voltage V2, a transformer 7 that is configured to be able to exchange power between the power supply circuit 4 and the second output circuit 6 and the first output circuit 5 while providing insulation between the power supply circuit 4 and the second output circuit 6, and a first controller 8 that is connected to the first output circuit 5. The switching power supply device 1 forms an isolated flyback converter.

[0023] The transformer 7 includes a first winding 7a connected to the power supply circuit 4, a second winding 7b connected to the first output circuit 5, and a third winding 7c connected to the second output circuit 6. The second winding 7b is disposed opposite to the first winding 7a so as to have a different polarity. Hereinafter, the first winding 7a side may be referred to as the primary side, and the second winding 7b side may be referred to as the secondary side. The third winding 7c is disposed on the primary side so as to have a different polarity from the first winding 7a.

[0024] The first output circuit 5 includes a diode 51, a capacitor 52, and a first output voltage setting circuit 53. The diode 51 is connected to the second winding 7b and rectifies the current flowing through the second winding 7b. The capacitor 52 is connected to the diode 51 and generates the first output voltage V1. The second winding 7b is connected to the anode of the diode 51, and the capacitor 52 is connected to the cathode of the diode 51.

[0025] The first output voltage setting circuit 53 is connected in parallel to the capacitor 52 and sets a target value of the first output voltage V1. The first output voltage setting circuit 53 includes a first resistor 54 and a second resistor 55 that are connected in parallel to the capacitor 52 and configure voltage dividing resistors, a third resistor 56 that is connected in parallel to the second resistor 55 that is on the lower voltage side of the first resistor 54 and the second resistor 55, and a voltage switching element 57 that is connected in parallel to the second resistor 55 and in series to the third resistor 56. The voltage switching element 57 is composed of a transistor. The transistor used for the voltage switching switch element 57 may be a bipolar transistor or a field effect transistor.

[0026] The voltage switching element 57 is switched on / off based on a control signal from the first controller 8. When the voltage switching element 57 is turned on, the third resistor 56 is connected to the voltage dividing resistors 54, 55, and the target value of the first output voltage V1 is set to the first voltage. When the voltage switching element 57 is turned off, the third resistor 56 is disconnected from the voltage dividing resistors 54, 55, and the target value of the first output voltage V1 is set to the second voltage lower than the first voltage. In this way, the first output voltage setting circuit 53 is configured to be able to switch the first output voltage V1 to either the first voltage or the second voltage lower than the first voltage in accordance with the control signal from the first controller 8.

[0027] The first output voltage V1 is supplied as a power source for the operation panel 102 and the first controller 8. The first controller 8 and the like are connected via a regulator 58 to an output terminal of the first output circuit 5 that outputs the first output voltage V1.

[0028] The switching power supply device 1 further includes a feedback circuit 9. The feedback circuit 9 detects the first output voltage V1 in the first output circuit 5, and feeds back a feedback value corresponding to the first output voltage V1 to the power supply circuit 4. The feedback circuit 9 includes an error amplifier 91 connected in parallel to the first resistor 54, and a photocoupler 92 that transmits the output of the error amplifier 91 to the power supply circuit 4. The error amplifier 91 outputs an error between the first output voltage V1 and a target value of the first output voltage V1 set by the first output voltage setting circuit 53 as a feedback value. A light-emitting element that constitutes the photocoupler 92 is connected to an output terminal of the error amplifier 91, and transmits the feedback value to a light-receiving element that constitutes the photocoupler 92.

[0029] The switching power supply device 1 further includes a power supply controller 11 that controls the power supply circuit 4. The light receiving element of the photocoupler 92 is connected to the power supply controller 11 on the primary side. The power supply circuit 4 includes a switch element (power supply circuit switch element) 41 that is connected to the first winding 7a and is switched on and off based on a feedback value. The power supply circuit switch element 41 is configured with a transistor. The transistor used for the power supply circuit switch element 41 may be a bipolar transistor or a field effect transistor. When the power supply circuit switch element 41 is turned on, the power supply circuit 4 is closed, a current flows through the first winding 7a, and energy is stored in the transformer 7. When the power supply circuit switch element 41 is turned off, the energy stored in the first winding 7a is transferred to the second winding 7b, and an electric charge is stored in the capacitor 52 of the first output circuit 5. When the power supply circuit switch element 41 is turned on again, a current flows through the first winding 7a again, energy is stored, and the electric charge of the capacitor 52 is discharged.

[0030] By repeating such on-off operation of the power circuit switch element 41, the first output voltage V1 is supplied to the electric load connected to the capacitor 52. Furthermore, when the first output voltage V1 becomes higher than the target value, the power supply controller 11 shortens the on-period of the power circuit switch element 41. This reduces the energy transmitted to the second winding 7b, and the charge stored in the capacitor 52 decreases. As a result, the first output voltage V1 decreases. Conversely, when the first output voltage V1 becomes lower than the target value, the power supply controller 11 lengthens the on-period of the power circuit switch element 41. This increases the energy transmitted to the second winding 7b, and the charge stored in the capacitor 52 increases. As a result, the first output voltage V1 increases.

[0031] The second output circuit 6 includes a diode 61 and a capacitor 62. The diode 61 is connected to the tertiary winding 7c and rectifies the current flowing through the tertiary winding 7c. The capacitor 62 is connected to the diode 61 and generates a second output voltage V2. The tertiary winding 7c is connected to the anode of the diode 61, and the capacitor 62 is connected to the cathode of the diode 61.

[0032] The second output circuit 6 supplies a second output voltage V2 generated from power received from the power supply circuit 4 via a transformer 7 to a predetermined electric load as a power source. In this embodiment, the electric loads connected to the second output circuit 6 are the second controller 10 and the sensor 104. The second controller 10 and the like are connected via a regulator 63 to an output terminal of the second output circuit 6 that outputs the second output voltage V2.

[0033] Here, in this embodiment, the first output circuit 5 includes a discharge circuit 80 that is connected in parallel to the capacitor 52 and discharges the charge stored in the capacitor 52. In this embodiment, the discharge circuit 80 is a resistive element 81. Furthermore, the first output circuit 5 includes a switch element (discharge switch element) 82 that is connected in series to the discharge circuit 80. The discharge switch element 82 is configured by a transistor. The transistor used for the discharge switch element 82 may be a bipolar transistor or a field effect transistor.

[0034] The operation of the discharge circuit 80 will be described below. Fig. 3 is a timing chart of the switching power supply device shown in Fig. 2. Fig. 3 shows a timing chart of the voltage switching switch element 57, the discharge switch element 82, the first output voltage V1, and the second output voltage V2. In Fig. 3, the voltage switching switch element 57 is represented as Q1, and the discharge switch element 82 is represented as Q2.

[0035] In the normal operation mode of the electric device 100 (the period up to time t1 in FIG. 3), the voltage switching element 57 (Q1) is in an ON state, whereby the third resistor 56 is connected and the target value of the first output voltage V1 is set to the first voltage V1H. At time t1, for example, the first controller 8 switches from the normal operation mode to the power saving mode because a predetermined period of time has elapsed without any operation input to the operation panel 102. At this time, the voltage switching element 57 is switched from ON to OFF by a control signal from the first controller 8.

[0036] When the voltage switching element 57 is turned off based on a control signal from the first controller 8, the third resistor 56 is disconnected, and the target value of the first output voltage V1 is set to the second voltage V1L lower than the first voltage V1H.

[0037] As a result, the feedback value in the feedback circuit 9 becomes a value indicating a state higher than the second voltage V1L, which is the target value of the first output voltage V1, until the first output voltage V1 drops to the second voltage V1L. As a result, the power supply controller 11, which has received the feedback value, controls the power supply circuit switch element 41 to be turned off for a predetermined period. This causes a period in which the capacitor 52 of the first output voltage V1 is discharged without being charged. As a result, the first output voltage V1 drops.

[0038] While the first output voltage V1 is decreasing, the power supply circuit switch element 41 is maintained in the off state, and therefore not only the power supply from the first winding 7a to the second winding 7b but also the power supply from the first winding 7a to the third winding 7c is stopped. As a result, like the first output voltage V1 in the first output circuit 5, the capacitor 62 in the second output circuit 6 is also discharged, and the second output voltage V2 decreases.

[0039] If the discharge circuit 80 is not connected (a conventional configuration without the discharge circuit 80), the first output voltage V1 gradually decreases from time t1, as shown by the two-dot chain line in the time chart of the first output voltage V1 in FIG. 3, and reaches the second voltage V1L at time t3. During this period, the second output voltage V2 also continues to decrease, as shown by the two-dot chain line in the time chart of the second output voltage V2 in FIG. 3. This may cause the second output voltage V2 to decrease to a level below the minimum operating voltage V2m required for the operation of the second controller 10 or the sensor 104. Since the second output voltage V2 is not fed back to the power supply circuit 4, the power supply circuit 4 cannot detect whether the second output voltage V2 is equal to or higher than the minimum operating voltage V2m.

[0040] When the second output voltage V2 falls below the minimum operating voltage V2m, the second controller 10 or the sensor 104 cannot operate. If the second controller 10 cannot operate, for example, mutual communication with the first controller 8 cannot be performed, and the first controller 8 unintentionally issues a communication error. Furthermore, if the sensor 104 cannot operate, it cannot detect whether the cover 103 of the fan 101 is open, which may cause a safety problem.

[0041] As a method for solving such a problem, it is conceivable to increase the capacitance of the capacitor 62 of the second output circuit 6 or to increase the number of turns of the third winding 7c of the transformer 7 to increase the voltage applied to the capacitor 62, thereby preventing the second output voltage V2 from falling below the minimum operating voltage V2m during the period when the power supply to the capacitor 62 is stopped. However, this would lead to an increase in the size of the capacitor 62 and / or the transformer 7, which would increase the cost of the components and also increase the area occupied by these components on the wiring board of the switching power supply device 1.

[0042] Therefore, in this embodiment, a discharge circuit 80 with relatively low component cost and small component occupation area is used. When switching the target value of the first output voltage V1 from the first voltage V1H to the second voltage V1L, the first controller 8 controls the discharge switch element 82 (Q2) to be on for a predetermined period to pass current through the discharge circuit 80. The first controller 8 turns on the discharge switch element 82 for a predetermined on-period T from when the target value of the first output voltage V1 is switched from the first voltage V1H to the second voltage V1L (time t1).

[0043] In this embodiment, the period during which the first output voltage V1 changes from the first voltage V1H to the second voltage V1L while the discharge switch element 82 is on is set to the on-period T of the discharge switch element 82. In other words, the resistance value of the resistive element 81 is set to a resistance value during which the first output voltage V1 changes from the first voltage V1H to the second voltage V1L during the on-period T. In addition, the on-period T is set to a period during which the second output voltage V2 becomes a voltage higher than the minimum operating voltage V2m at the end of the on-period T when the second output voltage V2 drops from the normal value V2H.

[0044] When the discharge switch element 82 is turned on, the discharge circuit 80 is connected in parallel to the capacitor 52 of the first output circuit 5. Therefore, the charge stored in the capacitor 52 is discharged through the resistance element 81 of the discharge circuit 80, and the amount of charge discharged per unit time in the capacitor 52 becomes larger than when the discharge circuit 80 is not connected. In the example of FIG. 3, the first output voltage V1 reaches the second voltage V1L at time t2 before time t3. After the first output voltage V1 reaches the second voltage V1L, the feedback value is fed back to the power supply controller 11 so that the first output voltage V1 is maintained at the second voltage V1L, and the switching of the power supply circuit switch element 41 is resumed.

[0045] As a result, after time t2, power supply to the second output circuit 6 is also resumed, so the amount of decrease in the second output voltage V2 is smaller than when the power circuit switch element 41 is stopped until time t3. Note that, since the second output circuit 6 receives power supply in accordance with the feedback control of the first output voltage V1 as described above, even if power supply to the second output circuit 6 is resumed, the second output voltage V2 is maintained at a voltage V2L that is lower than the value V2H before the target value of the first output voltage V1 was switched from the first voltage V1H to the second voltage V1L and higher than the minimum operating voltage V2m.

[0046] As described above, according to this embodiment, when the target value of the first output voltage V1 that is the subject of feedback switches from the first voltage V1H to the lower second voltage V1L, the first output voltage V1 is fed back to the power supply circuit 4 and the power supply circuit switch element 41 is turned off, thereby stopping the power supply from the power supply circuit 4 to the first output circuit 5.

[0047] Here, in the first output circuit 5, a discharge circuit 80 for discharging the charge stored in the capacitor 52 that generates the first output voltage V1 is connected in parallel to the capacitor 52. Therefore, when the power supply from the power supply circuit 4 to the first output circuit 5 is stopped, the charge stored in the capacitor 52 is quickly discharged by the discharge circuit 80. Therefore, the first output voltage V1 is quickly switched from the first voltage V1H to the second voltage V1L, and the period during which the power supply circuit switch element 41 is off is shortened. As a result, the effect of a voltage drop caused by the power supply circuit switch element 41 being turned off in the second output voltage V2 that is not the subject of feedback can be suppressed. Therefore, in the switching power supply device 1 of the isolated flyback type, when switching to the power saving mode, it is possible to suppress the second output voltage V2 that is not the subject of feedback from becoming too small.

[0048] Such a configuration of the switching power supply device 1 makes it possible to prevent the second output voltage V2 in the second output circuit 6 from dropping to a voltage at which the electrical load (the second controller 10 or the sensor 104) connected to the second output circuit 6 cannot operate (below the minimum operating voltage V2m) when the switching power supply device 1 transitions to the power saving mode. As a result, even if the second controller 10 that drives the fan 101 or the sensor 104 that detects the open / closed state of the cover 103 of the fan 101 are connected as electrical loads to the second output circuit 6 that is not feedback controlled, it is possible to continue operating the electrical load that is important for safety in the range hood.

[0049] Furthermore, in this embodiment, the discharge switch element 82 energizes the discharge circuit 80 only during the period when discharging is required. This prevents the capacitor 52 from discharging more than necessary in the normal operation mode, thereby reducing unnecessary power consumption. Also, by starting discharging from the timing (time t2) when the target value of the first output voltage V1 switches from the first voltage V1H to the second voltage V1L, the period during which discharging is performed can be shortened.

[0050] In addition, in this embodiment, since the resistive element 81 is used as the discharge circuit 80, the discharge circuit 80 can be realized with a simple configuration. Furthermore, adding the discharge circuit 80 increases costs and space less than increasing the size of the transformer 7 and / or the capacitor 62. Therefore, it is possible to suppress an increase in size and cost of the switching power supply device 1.

[0051] [Variations] A modification of the above embodiment will be described below. The configuration of the electric device 100, including the switching power supply device 1, is similar to that of the above embodiment (FIGS. 1 and 2).

[0052] Fig. 4 is a timing chart of a switching power supply device in a modified example. Like Fig. 3, Fig. 4 shows a timing chart of the voltage changeover switch element 57 (Q1), the discharge switch element 82 (Q2), the first output voltage V1, and the second output voltage V2.

[0053] In this modification, when switching the target value of the first output voltage V1 from the first voltage V1H to the second voltage V1L, the first controller 8 generates a control signal for the first output voltage setting circuit 53 such that a first signal level corresponding to the first voltage V1H and a second signal level corresponding to the second voltage V1L are repeated for a predetermined period. Furthermore, the first controller 8 generates the control signal as a signal such that the ratio of the period at which the signal is at the second signal level to the period at which the signal is at the first signal level gradually increases.

[0054] In this modification, switching from the normal operation mode to the power saving mode starts at time t1, as in the example of Fig. 3. However, the control signal transmitted from the first controller 8 is a signal in which the first signal level and the second signal level are repeated, as described above. Based on this, the voltage switching element 57 is switched off at time t1, and then turns on again when the first off period TL1 has elapsed, and turns off when the first on period TH1 has elapsed since being switched on. In the voltage switching element 57, such on and off are repeated for a predetermined period.

[0055] Here, the first off-period TL1, the second off-period TL2, the third off-period TL3, … are set to longer periods in order (TL1 < TL2 < TL3 < …). On the other hand, the first on-period TH1, the second on-period TH2, the third on-period TH3, … are set to the same period (TH1 = TH2 = TH3 = …). As a result, the ratio of the second on-period TH2 to the second off-period TL2 is smaller than the ratio of the first on-period TH1 to the first off-period TL1, and the ratio of the third on-period TH3 to the third off-period TL3 is smaller than the ratio of the second on-period TH2 to the second off-period TL2.

[0056] According to this modification example, at the target value of the first output voltage V1, the ratio of the period during which the second voltage V1L is present to the period during which the first voltage V1H is present gradually increases, so the first output voltage V1 gradually decreases. Moreover, since the on-periods TH1, TH2, … during which the target value of the first output voltage V1 becomes the first voltage V1H and the off-periods TL1, TL2, … during which it becomes the second voltage V1L occur alternately, the timing at which the power supply circuit switch element 41 is turned on occurs, and thereby power is also supplied to the second output circuit 6. For this reason, the decrease in the second output voltage V2 becomes gentle. Therefore, it is possible to suppress the second output voltage V2, which is not the target of feedback, from becoming too small.

[0057] According to this modification example, compared to the case where the voltage switching switch element 57 is simply switched from on to off at time t1 (the example in FIG. 3), the time until the first output voltage V1 reaches the second voltage V1L (the period between time t1 and time t2) becomes longer. On the other hand, according to this modification example, the drop width of the second output voltage V2 becomes smaller compared to the example in FIG. 3. For this reason, this is particularly effective when, due to size constraints of the switching power supply device 1 or the like, a sufficiently large resistor cannot be employed as the resistor element 81 in the discharge circuit 80 such that the first output voltage V1 reaches the second voltage V1L before the second output voltage V2 becomes equal to or lower than the minimum operating voltage V2m.

[0058] In this modification, an example has been shown in which the control signal is a signal in which the off periods TL1, TL2, TL3, ... gradually become longer and the on periods TH1, TH2, TH3, ... are constant, in order to make the control signal a signal in which the ratio of the period in which the second signal level is present to the period in which the first signal level is present gradually increases. Alternatively, the control signal may be a signal in which the off periods TL1, TL2, TL3, ... gradually become longer and the on periods TH1, TH2, TH3, ... gradually become shorter. Alternatively, the control signal may be a signal in which the off periods TL1, TL2, TL3, ... are constant and the on periods TH1, TH2, TH3, ... gradually become shorter.

[0059] Although the embodiment of the present invention has been described above, the present invention is not limited to the above embodiment, and various improvements, changes, and modifications are possible without departing from the spirit of the present invention.

[0060] [Other embodiments] For example, in the above embodiment, the discharge circuit 80 is configured with the resistive element 81, but this is not limiting. For example, the discharge circuit 80 may be configured with a constant current circuit.

[0061] In the above embodiment, the timing at which the discharge switch element 82 is turned on coincides with the timing (time t1) at which the voltage switching switch element 57 is turned off, i.e., the target value of the first output voltage V1 is switched from the first voltage V1H to the second voltage V1L and the discharge circuit 80 is connected, but this is not limiting. For example, the connection timing of the discharge circuit 80 may be before or after the timing at which the target value of the first output voltage V1 is switched from the first voltage V1H to the second voltage V1L. In addition, the connection timing of the discharge circuit 80 may be the same as, before, or after the timing at which the first output voltage V1 reaches the second voltage V1L (time t2).

[0062] In the above embodiment, the discharge circuit 80 is switched between connection and disconnection by the discharge switch element 82, but the present invention is not limited to this. For example, the discharge circuit 80 may be constantly connected in parallel to the capacitor 52.

[0063] In the above embodiment, the second controller 10 and the sensor 104 are exemplified as the electric load to which the second output voltage V2 is supplied, but the electric load may be only one of them, or may be another electric load different from them. In the above embodiment, the range hood is exemplified as the electric device 100, but the switching power supply device of the present invention can be applied to electric devices other than the range hood. In particular, the operation of an electric device that needs to be connected to an electric load that needs to be constantly operated using the second output voltage V2 as a power source can be stabilized.

[0064] [Reference example] The control modes shown in the above modified examples can also be employed in switching power supply devices that do not include a discharge circuit 80. Fig. 5 is a diagram showing a schematic circuit configuration of a switching power supply device in a reference example. In Fig. 5, the same components as those in Fig. 2 are given the same reference numerals, and descriptions thereof will be omitted. The switching power supply device X shown in Fig. 5 differs from the switching power supply device 1 shown in Fig. 2 in that the switching power supply device X does not include a discharge circuit 80 and a discharge switch element 82.

[0065] 6 is a timing chart of a switching power supply device in a reference example. In this reference example, as in the above modification, when the first controller 8 switches the target value of the first output voltage V1 from the first voltage V1H to the second voltage V1L, the first controller 8 generates a control signal for the first output voltage setting circuit 53 such that a first signal level corresponding to the first voltage V1H and a second signal level corresponding to the second voltage V1L are repeated for a predetermined period. Furthermore, the first controller 8 generates the control signal as a signal such that the ratio of the period at which the signal is at the second signal level to the period at which the signal is at the first signal level gradually increases.

[0066] As in the above modification, the control signal may be configured as a signal in which the off period is constant and the on period is gradually shortened, a signal in which the on period is constant and the off period is gradually lengthened, or a signal in which the on period is gradually shortened and the off period is gradually lengthened.

[0067] According to this reference example, the ratio of the period during which the first output voltage V1 is the second voltage V1L to the period during which the first output voltage V1H is gradually increased in the target value of the first output voltage V1, so that the first output voltage V1 gradually decreases. Moreover, since the on-periods TH1, TH2, ... during which the target value of the first output voltage V1 is the first voltage V1H and the off-periods TL1, TL2, ... during which the target value of the first output voltage V1 is the second voltage V1L occur alternately, there occurs a timing at which the power supply circuit switch element 41 is turned on, and thus power is also supplied to the second output circuit 6. Therefore, the decrease in the second output voltage V2 becomes gradual. Therefore, it is possible to prevent the second output voltage V2, which is not the subject of feedback, from becoming too small.

[0068] [Summary of this disclosure] Each of the following sections discloses a preferred embodiment of the present disclosure.

[0069] [Item 1] a power supply circuit for introducing power from a power supply unit, a first output circuit for generating a first output voltage, a second output circuit for generating a second output voltage, a transformer including a first winding connected to the power supply circuit, a second winding connected to the first output circuit, and a third winding connected to the second output circuit, the transformer being configured to be able to exchange power between the power supply circuit and the second output circuit and the first output circuit while providing insulation between the power supply circuit and the second output circuit, a feedback circuit for detecting the first output voltage in the first output circuit and feeding back a feedback value according to the first output voltage to the power supply circuit, and a first controller connected to the first output circuit, the power supply circuit including a switch element connected to the first winding and switched on based on the feedback value, the second winding having a polarity opposite to that of the first winding, the first output circuit includes a diode connected to the second winding and rectifying a current flowing through the second winding, a capacitor connected to the diode and generating the first output voltage, and a first output voltage setting circuit connected in parallel to the capacitor and setting a target value of the first output voltage, the first output voltage setting circuit being configured to be able to switch the first output voltage between a first voltage and a second voltage lower than the first voltage in accordance with a control signal from the first controller, the second output circuit supplies the second output voltage generated from power received from the first winding to a predetermined electric load, and the first output circuit further includes a discharge circuit connected in parallel to the capacitor and discharging charge stored in the capacitor.

[0070] [Item 2] 2. The switching power supply device according to item 1, wherein the first output circuit includes a switch element connected in series to the discharge circuit, and the first controller controls the switch element to be turned on for a predetermined period to pass current through the discharge circuit when switching a target value of the first output voltage from the first voltage to the second voltage.

[0071] [Item 3] 3. The switching power supply device according to item 2, wherein the first controller turns on the switch element for the predetermined period from when the target value of the first output voltage is switched from the first voltage to the second voltage.

[0072] [Item 4] 4. The switching power supply device according to any one of items 1 to 3, wherein the discharge circuit is a resistive element.

[0073] [Item 5] 5. The switching power supply device according to any one of items 1 to 4, wherein, when switching the target value of the first output voltage from the first voltage to the second voltage, the first controller generates, as a control signal for the first output voltage setting circuit, a control signal that repeats a first signal level corresponding to the first voltage and a second signal level corresponding to the second voltage for a predetermined period, and the control signal is a signal such that a ratio of a period at the second signal level to a period at the first signal level gradually increases.

[0074] [Item 6] 6. An electrical device including the switching power supply device according to any one of items 1 to 5, wherein the electrical device is a range hood including a fan, and the electrical load is a second controller that controls driving of the fan or a sensor that detects whether a cover of the fan is open or closed. [Industrial Applicability]

[0075] INDUSTRIAL APPLICABILITY The present invention is useful for preventing an output voltage that is not the subject of feedback from becoming excessively small when switching to a power saving mode in an isolated flyback switching power supply device. [Explanation of symbols]

[0076] 1 Switching power supply device, 3 Power supply unit, 4 Power supply circuit, 5 First output circuit, 6 Second output circuit, 7 Transformer, 7a First winding, 7b Second winding, 7c Third winding, 9 Feedback circuit, 8 First controller, 10 Second controller, 41 Power supply circuit switch element (switch element of power supply circuit), 51 Diode, 52 Capacitor, 53 First output voltage setting circuit, 80 Discharge circuit, 81 Resistance element, 82 Discharge switch element (switch element of first output circuit), 100 Electrical equipment, 101 Fan, 104 Sensor

Claims

1. a power supply circuit for introducing power from a power supply unit; a first output circuit for generating a first output voltage; a second output circuit for generating a second output voltage; a transformer including a first winding connected to the power supply circuit, a second winding connected to the first output circuit, and a third winding connected to the second output circuit, the transformer being configured to be able to exchange electric power between the power supply circuit and the second output circuit and between the first output circuit and the second output circuit while being insulated from the first output circuit; a feedback circuit that detects the first output voltage in the first output circuit and feeds back a feedback value corresponding to the first output voltage to the power supply circuit; a first controller connected to the first output circuit; the power supply circuit includes a switch element connected to the first winding and switched on or off based on the feedback value; the second winding is disposed opposite to the first winding so that the polarities of the second winding are different from each other; The first output circuit is a diode connected to the second winding and rectifying a current flowing through the second winding; a capacitor coupled to the diode for generating the first output voltage; a first output voltage setting circuit connected in parallel to the capacitor and configured to set a target value of the first output voltage; the first output voltage setting circuit is configured to be able to switch the first output voltage between a first voltage and a second voltage lower than the first voltage in accordance with a control signal from the first controller; the second output circuit supplies the second output voltage generated from the power received from the first winding to a predetermined electric load; The first output circuit further includes a discharge circuit connected in parallel to the capacitor for discharging the charge stored in the capacitor.

2. the first output circuit includes a switch element connected in series to the discharge circuit, 2. The switching power supply device according to claim 1, wherein the first controller controls the switch element to be on for a predetermined period to pass current through the discharge circuit when switching the target value of the first output voltage from the first voltage to the second voltage.

3. 3. The switching power supply device according to claim 2, wherein the first controller keeps the switch element on for the predetermined period from when the target value of the first output voltage is switched from the first voltage to the second voltage.

4. 4. The switching power supply device according to claim 1, wherein the discharge circuit is a resistive element.

5. the first controller generates, when switching a target value of the first output voltage from the first voltage to the second voltage, a control signal for the first output voltage setting circuit such that a first signal level corresponding to the first voltage and a second signal level corresponding to the second voltage are repeated for a predetermined period; 4. The switching power supply device according to claim 1, wherein the control signal is a signal in which a ratio of a period during which the control signal is at the second signal level to a period during which the control signal is at the first signal level gradually increases.

6. An electric device including the switching power supply device according to any one of claims 1 to 3, The electrical appliance is a range hood including a fan, The electrical load is an electrical device that is a second controller that controls driving of the fan or a sensor that detects whether a cover of the fan is open or closed.

Images