Semiconductor device and switching power supply device

Abstract

To provide a semiconductor device that can be quickly started when switching from a standby state to a normal operation state.SOLUTION: A semiconductor device 100 includes a control circuit that switches a switching power supply device 10 between an operating state including a normal operating state and a standby state, and a stop state, in accordance with a value of a power supply voltage acquired from an auxiliary winding Ta of a transformer T. The semiconductor device 100 also includes a start-up circuit that supplies a current to a power supply terminal VCC according to an input voltage supplied from an input terminal ST, and that switches ON / OFF of current supply to the power supply terminal VCC. The control circuit sets the switching power supply device 10 to the operating state when the power supply voltage exceeds an operation start power supply voltage, and sets the switching power supply device 10 to the stop state when the power supply voltage falls below an operation stop power supply voltage. The control circuit switches ON / OFF of current supply of the start-up circuit according to a start-up threshold value, whose value differs between the standby state and the normal operating state, and the power supply voltage.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present disclosure relates to a semiconductor device and a switching power supply device.

Background Art

[0002] Conventionally, in a switching power supply that controls a switching element and obtains an output voltage from a winding of a transformer, a technique (start-up circuit) for securing a voltage for driving the switching element from an input voltage during a period until a voltage is obtained from the winding of the transformer has been proposed. Patent Document 1 discloses a switching power supply device including a transformer, a switching element, and a control circuit including a start-up circuit. The switching power supply device disclosed in Patent Document 1 controls the power supply lower limit voltage (minimum operation guarantee voltage) to be different between normal operation (heavy load) and light load, thereby preventing the operation at light load from being unintentionally stopped.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] In a control circuit for driving a motor used in an electric vehicle, it is common to supply power from a low-voltage power supply via an isolation transformer. However, in some vehicles, the demand for an auxiliary power supply that supplies power from a high-voltage battery to the control circuit is also increasing. When a switching power supply is used as an auxiliary power supply, it does not always operate during the operation of the entire device. Therefore, in order to reduce power consumption, there are cases where the normal operation state and the standby state are switched (when a standby function is provided). Therefore, the demand for a control device equipped with both a start-up circuit and a standby function is increasing.

[0005] The present disclosure has been made in view of the problems of such prior art. The object of the present disclosure is to provide a semiconductor device that can be quickly activated when switching from a standby state to a normal operating state.

Means for Solving the Problems

[0006] A semiconductor device according to an aspect of the present disclosure is a semiconductor device that controls a switching power supply device that obtains a predetermined output voltage from a secondary winding of a transformer by driving a switching element connected to a primary winding of the transformer, and includes an input terminal for inputting an input voltage from a battery power supply, an enable terminal for inputting an enable signal for switching the switching power supply device between a normal operating state and a standby state, a power supply terminal connected to an auxiliary winding of the transformer for obtaining a power supply voltage from the auxiliary winding, an output terminal connected to the switching element for outputting a voltage for driving the switching element, and a control circuit connected to the enable terminal, the power supply terminal, the output terminal, and a startup switching signal line for switching the switching power supply device between an operating state including the normal operating state and the standby state and a stop state according to the value of the power supply voltage, and a circuit for supplying a current to the power supply terminal according to the input voltage supplied from the input terminal, the circuit including a startup circuit for switching on and off the current supply to the power supply terminal under the control of the control circuit via the startup switching signal line. The control circuit sets the switching power supply device to the operating state when the power supply voltage exceeds the operating start power supply voltage, and sets the switching power supply device to the stop state when the power supply voltage drops below the operating stop power supply voltage. The control circuit switches on and off the current supply of the startup circuit according to the value of the power supply voltage and a startup threshold value, and the startup threshold value has different values in the standby state and the normal operating state.

Advantages of the Invention

[0007] According to the present disclosure, it is possible to provide a semiconductor device that can be quickly activated when switching from a standby state to a normal operating state.

Brief Description of the Drawings

[0008]

Figure 1

Figure 2

Figure 3

Figure 4

Embodiments for Carrying Out the Invention

[0009] Hereinafter, the semiconductor device 100 according to some embodiments of the present disclosure will be described in detail with reference to the drawings. The same or corresponding parts in the drawings of the drive circuit according to each embodiment are denoted by the same reference numerals, and the description thereof will be omitted.

[0010] (Outline and Configuration of Switching Power Supply Device 10) FIG. 1 is a diagram showing the configuration of a switching power supply device 10 to which the semiconductor device 100 according to the present embodiment is applied. For example, the switching power supply device 10 is used as an auxiliary power supply circuit that supplies power from a high-voltage battery to a control circuit. The switching power supply device 10, which is an auxiliary power supply circuit, converts the battery voltage (Battery) of an electric vehicle into a voltage (VOUT1) that can be used by an electronic device via a transformer T.

[0011] The switching power supply device 10 includes a transformer T, a switching element Q connected to the primary winding of the transformer T, and a semiconductor device 100. The switching power supply device 10 obtains a predetermined output voltage from the secondary winding of the transformer T by driving the switching element Q connected to the primary winding of the transformer T. This switching element Q is driven under the control from the semiconductor device 100.

[0012] The power supply voltage of the semiconductor device 100 is supplied by the voltage generated in the auxiliary winding Ta (hereinafter referred to as the auxiliary winding voltage Va). However, before the switching power supply device 10 is started, since the auxiliary winding voltage Va is not generated in the auxiliary winding Ta, no voltage is supplied to the semiconductor device 100, and the semiconductor device 100 cannot operate.

[0013] Therefore, the semiconductor device 100 includes a startup circuit 300 (see FIG. 2). The startup circuit 300 generates a startup current using the voltage of a battery at startup in order to start the semiconductor device 100, and accumulates the generated charge in the capacitor C. When the voltage accumulated in the capacitor C reaches the startup voltage of the semiconductor device 100, the semiconductor device 100 starts the operation of the switching power supply device 10, and when the power supply voltage can be supplied by the auxiliary winding voltage Va from the auxiliary winding Ta, the operation of the startup circuit 300 is stopped.

[0014] Therefore, during normal operation, the startup circuit 300 is stopped, but when a situation such as an overload occurs, for safety reasons, the semiconductor device 100 may stop operating. In this case, the auxiliary winding Ta cannot generate a voltage, and the auxiliary winding voltage Va (power supply voltage) supplied to the semiconductor device 100 decreases.

[0015] If this state continues, the power supply voltage drops below the value of the operation stop power supply voltage, which is the drive stop voltage of the semiconductor device 100, and all operations of the semiconductor device 100 stop. In order to prevent this stop of all operations, a threshold value is set to a voltage slightly higher than the operation stop power supply voltage, and when this voltage is reached, a temporary current is supplied by the startup circuit 300 so that the operation of the semiconductor device 100 does not stop.

[0016] On the other hand, in the case of an auxiliary power supply mounted in a vehicle, power supply operation is not required for all times of vehicle operation. During times when operation is not required, the semiconductor device 100 has a function of putting itself into a standby state in order to suppress the power consumption of the semiconductor device 100. The switching between this standby state and the normal operation state is performed, for example, by an enable signal from the outside.

[0017] In an auxiliary power supply having a standby state, when the threshold value of the startup circuit 300 does not change when changing from the normal operation state to the standby state, it may enter the stopped state immediately after returning from the standby state. Therefore, there is a concern that a time lag may occur between the timing of the enable signal and the product operation specifications.

[0018] Therefore, in the present embodiment, the threshold values of the startup circuit 300 are made different between the normal operation state and the standby state. As a result, when a switching signal from the standby state to the normal operation state is input to the semiconductor device 100 according to the present embodiment via the enable signal, the semiconductor device 100 can be quickly started up. Note that the switching power supply device 10 shown in FIG. 1 shows the configuration of a general switching power supply, and elements not described in this specification are assumed to have the same functions as the elements provided in a known switching power supply.

[0019] (Configuration and Function of Semiconductor Device 100) FIG. 2 is a block diagram showing the configuration of the semiconductor device 100 according to the present embodiment. The semiconductor device 100 according to the present embodiment controls a switching power supply device 10 that obtains a predetermined output voltage from the secondary winding of the transformer T by driving a switching element Q connected to the primary winding of the transformer T shown in FIG. 1.

[0020] As shown in FIG. 2, the semiconductor device 100 includes an input terminal ST, an enable terminal RT, a power supply terminal VCC, and an output terminal OUT. The input terminal ST inputs an input voltage from a battery power supply. The enable terminal RT inputs an enable signal (see FIG. 1) for switching the switching power supply device 10 between a normal operation state and a standby state. Specifically, the semiconductor device 100 switches between the operation state and the standby state by turning on and off a switch SW (see FIG. 1) connected to the enable terminal RT by an enable signal input from the outside.

[0021] The power supply terminal VCC is connected to the auxiliary winding Ta of the transformer T and obtains the power supply voltage from the auxiliary winding Ta. The output terminal OUT is connected to the switching element Q and outputs a voltage for driving the switching element Q.

[0022] Further, the semiconductor device 100 includes a control circuit 200 and a startup circuit 300.

[0023] The control circuit 200 is connected to an enable terminal RT, a power supply terminal VCC, an output terminal OUT, and a startup switching signal line 230. Further, the control circuit 200 switches the switching power supply device 10 between an operating state including a normal operating state and a standby state and a stop state according to the value of the power supply voltage.

[0024] Further, when the power supply voltage exceeds the operation start power supply voltage, the control circuit 200 sets the switching power supply device 10 to the operating state, and when the power supply voltage drops below the operation stop power supply voltage, the control circuit 200 sets the switching power supply device 10 to the stop state. In this embodiment, the operation start power supply voltage and the operation stop power supply voltage correspond to the voltage at which the operation stop is determined by the under voltage lock out (UVLO) function.

[0025] The control circuit 200 switches the on / off of the current supply of the startup circuit 300 according to the value of the power supply voltage and the startup threshold value. The startup threshold value according to this embodiment has different values in the standby state and the normal operating state. For example, the startup threshold value is realized by two different values, a first threshold value (see FIG. 4) in the standby state and a second threshold value (see FIG. 4) in the normal operating state, according to the on / off of the enable signal.

[0026] The startup circuit 300 supplies current to the power supply terminal VCC according to the input voltage supplied from the input terminal ST. Further, the startup circuit 300 switches the on / off of the current supply to the power supply terminal VCC under the control from the control circuit 200 via the startup switching signal line 230.

[0027] FIG. 3 is a block diagram showing the configuration of the startup circuit 300 in the semiconductor device 100 according to the present embodiment. The startup circuit 300 includes a bias unit 310 connected to the control circuit 200 via a startup switching signal line 230. The startup circuit 300 also includes an input terminal ST, and a current supply unit 320 connected to a power supply terminal VCC.

[0028] The bias unit 310 controls the current supply unit 320 according to the control from the startup switching signal line 230, and switches the on / off of the current supply to the power supply terminal VCC. The current supply unit 320 includes a field effect transistor 321. The bias unit 310 includes at least one semiconductor element 311 and a resistance element 312.

[0029] In the example shown in FIG. 3, the voltage supplied from the input terminal ST is supplied to the bias unit 310 via the current supply unit 330. For example, when the startup switching signal line 230 is at a low level, the semiconductor element 311 is turned off, and the voltage supplied to the bias unit 310 is stepped down to a predetermined value in the resistance element 312, turning on the field effect transistor 321 of the current supply unit 320. As a result, current is supplied from the current supply unit 320 to the power supply terminal VCC.

[0030] On the other hand, when the startup switching signal line 230 is at a high level, the semiconductor element 311 is turned on, and the voltage supplied to the bias unit 310 is stepped down to a predetermined value in the resistance element 312, turning off the field effect transistor 321 of the current supply unit 320. As a result, no current is supplied from the current supply unit 320 to the power supply terminal VCC.

[0031] Thereby, in the control of the current supply of the startup circuit 300, the semiconductor device 100 according to the present embodiment can perform high-speed and power consumption-suppressed control by using the field effect transistor 321, the semiconductor element 311, and the resistance element 312.

[0032] FIG. 4 is a timing chart for explaining the processing of the semiconductor device 100 according to the present embodiment.

[0033] At time T1, the supply of the input voltage from the battery voltage to the input terminal ST is turned on, and the power supply voltage of the power supply terminal VCC rises. Thereafter, at time T2, when the power supply voltage reaches the operation start power supply voltage, the switching power supply device 10 becomes operable. Also, at time T3, when the power supply voltage reaches the first threshold value, the startup circuit 300 is turned off. On the other hand, after time T3, when the power supply voltage of the power supply terminal VCC falls below the first threshold value, the startup circuit 300 is turned on. That is, when the power supply voltage of the power supply terminal VCC crosses the first threshold value, the startup circuit 300 performs an oscillation operation of repeating on and off.

[0034] Also, in the example shown in FIG. 4, after time T2, the case where the switching power supply device 10 is in an operating state and the voltage of the enable terminal RT is at a high level and the enable is in an off state is shown. This state is a standby state in the operating state, and the switching element Q does not perform a switching operation.

[0035] Also, in the example shown in FIG. 4, after time T4, the case where the signal of the enable terminal RT becomes a low level and the enable is in an on state is shown. This state is the normal operating state in the operating state. In this case, the startup threshold value of the startup circuit 300 is set to a value between the operation start power supply voltage and the operation stop power supply voltage (second threshold value).

[0036] In the example shown in FIG. 4, an example is shown in which the switching operation stops due to a protection function or the like after time T5. In this case, the power supply voltage of the power supply terminal VCC drops, and the startup circuit 300 turns on at the timing (time T6) when it falls below the second threshold value. Thereafter, when the power supply voltage of the power supply terminal VCC crosses the second threshold value, the startup circuit 300 performs an oscillation operation of repeating on and off.

[0037] Also, as shown in FIG. 4, the operating start power supply voltage is higher in value than the operating stop power supply voltage. Thereby, the semiconductor device 100 according to the present embodiment can operate the switching power supply device 10 after sufficient charge is accumulated in the capacitor C by the current supplied from the startup circuit 300 at startup.

[0038] Furthermore, the startup threshold of the startup circuit 300 is set to a value equal to or higher than the operating start power supply voltage when the switching power supply device 10 is in a stopped state or a standby state (first threshold). Furthermore, the startup threshold of the startup circuit 300 is set to a value between the operating start power supply voltage and the operating stop power supply voltage when the switching power supply device 10 is in a normal operating state (second threshold). Thereby, when switching from the standby state to the normal operating state, the semiconductor device 100 according to the present embodiment does not enter a stopped state and can quickly transition to the normal operating state, enabling the startup of the semiconductor device 100 without a time lag.

[0039] In the example shown in FIG. 4, the startup threshold, when the switching power supply device 10 is in a normal operating state (second threshold), is a value between the operating start power supply voltage and the operating stop power supply voltage and is set to a value close to the operating stop power supply voltage. Thereby, the semiconductor device 100 according to the present embodiment further suppresses the transition to the stopped state during the switching from the standby state to the normal operating state, enabling the startup of the semiconductor device 100 more quickly.

[0040] As described above, the semiconductor device 100 according to the present embodiment is a semiconductor device 100 that controls a switching power supply device 10 that obtains a predetermined output voltage from a secondary winding of a transformer T by driving a switching element Q connected to a primary winding of the transformer T. The semiconductor device 100 includes an input terminal ST for inputting an input voltage from a battery power supply, and an enable terminal RT for inputting an enable signal for switching the switching power supply device 10 between a normal operation state and a standby state. Further, the semiconductor device 100 includes a power supply terminal VCC connected to an auxiliary winding Ta of the transformer T and obtaining a power supply voltage from the auxiliary winding Ta, and an output terminal OUT connected to the switching element Q and outputting a voltage for driving the switching element Q. Further, the semiconductor device 100 includes a control circuit 200 and a startup circuit 300. The control circuit 200 is connected to the enable terminal RT, the power supply terminal VCC, the output terminal OUT, and a startup switching signal line 230, and switches the switching power supply device 10 between an operation state including a normal operation state and a standby state and a stop state according to the value of the power supply voltage. The startup circuit 300 is a circuit that supplies a current to the power supply terminal VCC according to an input voltage supplied from the input terminal ST, and switches on and off the current supply to the power supply terminal VCC under the control of the control circuit 200 via the startup switching signal line 230. The control circuit 200 sets the switching power supply device 10 to an operation state when the power supply voltage exceeds the operation start power supply voltage, and sets the switching power supply device 10 to a stop state when the power supply voltage drops below the operation stop power supply voltage. Further, the control circuit 200 switches on and off the current supply of the startup circuit 300 according to the value of the power supply voltage and the startup threshold value. The startup threshold value has different values in the standby state and the normal operation state.

[0041] With this configuration, the semiconductor device 100 according to the present embodiment has different threshold values of the startup circuit 300 between the normal operation state and the standby state. Thereby, when a switching signal from the standby state to the normal operation state is input to the semiconductor device 100 via the enable signal, the semiconductor device 100 can be quickly started up.

[0042] (Other embodiments) Although the embodiments have been described in detail with reference to the drawings, the present embodiments are not limited to the contents described in the above embodiments. Further, the constituent elements described above include those that can be easily assumed by those skilled in the art and those that are substantially the same. Furthermore, the configurations described above can be combined as appropriate. Also, various omissions, substitutions, or changes in the configuration can be made without departing from the gist of the embodiments.

[0043] The features of the semiconductor device 100 will be described below.

[0044] The semiconductor device 100 according to the first aspect is a semiconductor device 100 that controls a switching power supply device 10 which obtains a predetermined output voltage from a secondary winding of a transformer T by driving a switching element Q connected to a primary winding of the transformer T. The semiconductor device 100 includes an input terminal ST for inputting an input voltage from a battery power supply, and an enable terminal RT for inputting an enable signal for switching the switching power supply device 10 between a normal operation state and a standby state. Further, the semiconductor device 100 includes a power supply terminal VCC connected to an auxiliary winding Ta of the transformer T and obtaining a power supply voltage from the auxiliary winding Ta, and an output terminal OUT connected to the switching element Q and outputting a voltage for driving the switching element Q. Further, the semiconductor device 100 includes a control circuit 200 and a startup circuit 300. The control circuit 200 is connected to the enable terminal RT, the power supply terminal VCC, the output terminal OUT, and a startup switching signal line 230, and switches the switching power supply device 10 between an operation state including a normal operation state and a standby state and a stop state according to the value of the power supply voltage. The startup circuit 300 is a circuit that supplies a current to the power supply terminal VCC according to the input voltage supplied from the input terminal ST, and switches the on / off of the current supply to the power supply terminal VCC under the control of the control circuit 200 via the startup switching signal line 230. The control circuit 200 sets the switching power supply device 10 to an operation state when the power supply voltage exceeds the operation start power supply voltage, and sets the switching power supply device 10 to a stop state when the power supply voltage drops below the operation stop power supply voltage. Further, the control circuit 200 switches the on / off of the current supply of the startup circuit 300 according to the value of the power supply voltage and the startup threshold value. The startup threshold value has different values in the standby state and the normal operation state.

[0045] With this configuration, the semiconductor device 100 has different threshold values of the startup circuit 300 between the normal operation state and the standby state. Thereby, when a switching signal from the standby state to the normal operation state is input to the semiconductor device 100 via the enable signal, the semiconductor device 100 can be quickly started up.

[0046] The startup circuit 300 of the semiconductor device 100 according to the second aspect may further include an input terminal ST, a current supply unit 320 connected to a power supply terminal VCC, and a bias unit 310 connected to the control circuit 200 via a startup switching signal line 230. The bias unit 310 may control the current supply unit 320 according to the control from the control circuit 200 via the startup switching signal line 230, and switch the on / off of the current supply to the power supply terminal VCC.

[0047] With this configuration, the semiconductor device 100 switches the on / off of the current supply according to the control from the control circuit 200 via the startup switching signal line 230. As a result, in the control of the current supply of the startup circuit 300, the control from the control circuit 200 is more appropriately reflected in the semiconductor device 100, and the on / off of the current supply to the power supply terminal VCC can be switched more accurately.

[0048] The current supply unit 320 of the semiconductor device 100 according to the third aspect may be configured to include a field effect transistor 321. Further, the bias unit 310 may be configured to include at least one semiconductor element 311 and a resistance element 312.

[0049] With this configuration, in the control of the current supply of the startup circuit 300, the semiconductor device 100 can perform high-speed and power consumption-suppressed control by using the field effect transistor 321, the semiconductor element 311, and the resistance element 312.

[0050] The operation start power supply voltage of the semiconductor device 100 according to the fourth aspect may be higher in value than the operation stop power supply voltage.

[0051] With this configuration, the semiconductor device 100 can operate the switching power supply device 10 after sufficient charge is accumulated in the capacitor C by the current supplied from the startup circuit 300 at startup.

[0052] The startup threshold of the semiconductor device 100 according to the fifth aspect is set to a value equal to or higher than the operation start power supply voltage when the switching power supply device 10 is in a stopped state or a standby state, and may be set to a value between the operation start power supply voltage and the operation stop power supply voltage when in a normal operation state.

[0053] With this configuration, when the semiconductor device 100 switches from the standby state to the normal operation state, it does not enter a stopped state, but quickly transitions to the normal operation state, enabling the startup of the semiconductor device 100 without a time lag.

[0054] The startup threshold of the semiconductor device 100 according to the sixth aspect may be set to a value between the operation start power supply voltage and the operation stop power supply voltage, and a value close to the operation stop power supply voltage, when the switching power supply device 10 is in a normal operation state.

[0055] With this configuration, the semiconductor device 100 further suppresses the transition to the stopped state when switching from the standby state to the normal operation state, enabling the startup of the semiconductor device 100 more quickly.

[0056] The switching power supply device 10 according to the seventh aspect includes a transformer T, a switching element Q connected to the primary winding of the transformer T, and the semiconductor device 100 described in any of the above.

[0057] With this configuration, the switching power supply device 10 has different thresholds for the startup circuit 300 provided in the semiconductor device 100 between the normal operation state and the standby state. As a result, the switching power supply device 10 according to the present embodiment enables the semiconductor device 100 to start up quickly when a switching signal from the standby state to the normal operation state is input via an enable signal.

Description of Reference Numerals

[0058] Q Switching element T Transformer Ta Auxiliary winding Va Auxiliary winding voltage 10 Switching power supply device 100 Semiconductor device 200 Control circuit 230 Start switching signal line 300 Start circuit 310 Bias section 311 Semiconductor element 312 Resistance element 320, 330 Current supply section 321 Field effect transistor

Claims

1. A semiconductor device that controls a switching power supply device that obtains a predetermined output voltage from a secondary winding of a transformer by driving a switching element connected to a primary winding of the transformer, an input terminal for inputting an input voltage from a battery power supply, an enable terminal for inputting an enable signal for switching the switching power supply device between a normal operation state and a standby state, a power supply terminal connected to an auxiliary winding of the transformer for obtaining a power supply voltage from the auxiliary winding, an output terminal connected to the switching element for outputting a voltage for driving the switching element, a control circuit connected to the enable terminal, the power supply terminal, the output terminal, and a startup switching signal line, and switching the switching power supply device between an operation state including the normal operation state and the standby state and a stop state according to the value of the power supply voltage, a circuit for supplying a current to the power supply terminal according to the input voltage supplied from the input terminal, and including a startup circuit that switches on / off the current supply to the power supply terminal under the control of the control circuit via the startup switching signal line, when the power supply voltage exceeds an operation start power supply voltage, the control circuit sets the switching power supply device to the operation state, and when the power supply voltage drops below an operation stop power supply voltage, the control circuit sets the switching power supply device to the stop state, the control circuit switches on / off the current supply of the startup circuit according to the value of the power supply voltage and a startup threshold value, the startup threshold value has different values in the standby state and the normal operation state, a semiconductor device.

2. The startup circuit is, a current supply unit connected to the input terminal and the power supply terminal, further including a bias unit connected to the control circuit via the startup switching signal line, the semiconductor device according to claim 1, wherein the bias unit controls the current supply unit according to the control from the control circuit via the startup switching signal line and switches on / off the current supply to the power supply terminal.

3. The current supply unit is configured to include a field effect transistor, the semiconductor device according to claim 2, wherein the bias unit is configured to include at least one semiconductor element and a resistance element.

4. The semiconductor device according to claim 1, wherein the operation start power supply voltage is higher in value than the operation stop power supply voltage.

5. The start threshold value is set to a value equal to or higher than the operation start power supply voltage when the switching power supply device is in the stopped state or the standby state, and is set to a value between the operation start power supply voltage and the operation stop power supply voltage when the switching power supply device is in the normal operation state. The semiconductor device according to claim 1.

6. The start threshold value is a value between the operation start power supply voltage and the operation stop power supply voltage and is set to a value close to the operation stop power supply voltage when the switching power supply device is in the normal operation state. The semiconductor device according to claim 5.

7. A transformer and, A switching element connected to the primary winding of the transformer, A switching power supply device including the semiconductor device according to any one of claims 1 to 6.

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