JP6637754B2 - Power supply circuit and electronic device including the same - Google Patents

Description

  The present invention relates to a power supply circuit and an electronic device including the same.

  Conventionally, a power supply circuit including a voltage conversion circuit that steps down or boosts an input voltage from a DC power supply has been known. An overvoltage (for example, a surge voltage) may be input to such a power supply circuit. Therefore, an overvoltage protection circuit that protects the voltage conversion circuit from overvoltage is provided at a stage preceding the voltage conversion circuit.

  For example, Patent Document 1 discloses that a clamp circuit including an N-channel MOSFET and a Zener diode is provided as an overvoltage protection circuit. In such a clamp circuit, even if an overvoltage is input, the gate voltage of the N-channel MOSFET is maintained at the Zener voltage, so that the source of the N-channel MOSFET is suppressed to a voltage lower than the Zener voltage. Thereby, the voltage conversion circuit connected to the source side of the N-channel MOSFET is protected.

JP 2007-193458 A

  However, the overvoltage protection circuit described in Patent Document 1 has a problem from the viewpoint of power loss due to the N-channel MOSFET, because when an overvoltage is input, the source voltage of the N-channel MOSFET is greatly reduced with respect to the drain voltage. Was.

  The present invention has been made in view of the above, and an object of the present invention is to provide a power supply circuit capable of performing overvoltage protection while reducing power loss, and an electronic device including the same.

  In order to solve the above problems and achieve the object, a power supply circuit according to the present invention includes a voltage conversion circuit and an overvoltage protection circuit disposed at a stage preceding the voltage conversion circuit. The overvoltage protection circuit includes: an N-channel MOSFET having a drain connected to an input side and a source connected to the voltage conversion circuit side; a Zener diode provided between a gate of the N-channel MOSFET and a reference potential; A voltage application unit for applying a voltage higher than the voltage on the input side to the gate of the N-channel MOSFET.

  According to the present invention, it is possible to provide a power supply circuit capable of performing overvoltage protection while reducing power loss, and an electronic device including the same.

FIG. 1 is a diagram illustrating a configuration of a power supply circuit according to an embodiment of the present invention. FIG. 2 is a diagram illustrating a configuration example of the vehicle-mounted device according to the embodiment of the present invention. FIG. 3 is a diagram illustrating an example of a specific configuration of a power supply circuit included in the vehicle-mounted device illustrated in FIG. 2. FIG. 4 is a diagram showing a state change of the voltage at the time of startup. FIG. 5 is a diagram illustrating a voltage state change when a surge voltage is input.

  Hereinafter, embodiments of a power supply circuit and an electronic device including the same according to the present invention will be described in detail with reference to the drawings. Note that the present invention is not limited by the embodiments.

[1. Power supply circuit]
FIG. 1 is a diagram illustrating a configuration of a power supply circuit according to an embodiment of the present invention. As shown in FIG. 1, the power supply circuit 1 includes an input terminal T1, a voltage conversion circuit 10, and an overvoltage protection circuit 11.

  The voltage conversion circuit 10 is a circuit that converts a DC voltage input from the DC power supply 2 into DC voltages of different magnitudes, and is, for example, a DC / DC converter or a step-down regulator. The overvoltage protection circuit 11 is disposed at a stage before the voltage conversion circuit 10 and protects the voltage conversion circuit 10 from overvoltage.

  The overvoltage protection circuit 11 includes an N-channel MOSFET 20 (hereinafter sometimes simply referred to as an NMOSFET 20), a Zener diode 21, a resistor 23, and a voltage application unit 28. The drain of the NMOSFET 20 is connected to the input terminal T1 (an example of the input side), and the source of the NMOSFET 20 is connected to the input side of the voltage conversion circuit 10.

The gate of the NMOSFET 20 is connected to a ground potential GND (an example of a reference potential) via a Zener diode 21. Therefore, when a positive voltage surge overvoltage is input to the input terminal T1, the gate voltage V _G of the NMOSFET 20, is clamped by the Zener voltage Vz, the voltage input to the voltage conversion circuit 10 is limited to less than the Zener voltage Vz .

  Thereby, for example, an increase in the withstand voltage of the voltage conversion circuit 10 can be avoided. Therefore, for example, it is easy to reduce the on-resistance of the switching element used in the voltage conversion circuit 10 and to achieve high-speed switching. be able to.

  When a positive surge voltage (an example of an overvoltage) is input to the power supply circuit 1, the DC voltage Vidc1 input to the voltage conversion circuit 10 is changed to a Zener voltage while the voltage supply from the NMOSFET 20 to the voltage conversion circuit 10 is continued. It can be limited to less than Vz.

  Here, a case where the voltage applying unit 28 is not provided will be considered. A resistor 23 is connected between the drain and the gate of the NMOSFET 20. Therefore, a DC voltage Vdc (hereinafter, referred to as an input voltage Vidc or a DC voltage Vidc) input from the DC power supply 2 is applied to the gate of the NMOSFET 20 via the resistor 23.

When the input voltage Vidc (an example of the voltage on the input side) is input to the gate of the NMOSFET 20, the voltage V _GS between the gate and the source of the NMOSFET 20 becomes a voltage corresponding to the threshold voltage Vth1 of the NMOSFET 20. Therefore, the voltage V _DS between the drain and the source of the NMOSFET 20 (hereinafter, referred to as a drain-source voltage V _DS ) becomes a voltage corresponding to the threshold voltage Vth1, and the power loss due to the channel resistance of the NMOSFET 20 is large.

On the other hand, the power supply circuit 1 according to the embodiment includes the voltage application unit 28. The voltage application unit 28 boosts the DC voltage Vodc output from the voltage conversion circuit 10 and applies a voltage Vudc higher than the input voltage Vidc (hereinafter, referred to as an applied voltage Vudc) to the gate of the NMOSFET 20. Therefore, the gate - voltage _{V DS} between the source is smaller than the threshold voltage Vth1, compared with the case without the voltage application unit 28, it is possible to suppress power loss due to the channel resistance of the NMOSFET 20.

  For example, by setting Vudc ≧ Vidc + Vth1, it is possible to operate the NMOSFET 20 in a sufficiently saturated state, whereby power loss due to the channel resistance of the NMOSFET 20 can be further reduced.

  Note that the applied voltage Vudc is set lower than the Zener voltage Vz of the Zener diode 21. Thus, the current flowing from the voltage applying unit 28 to the Zener diode 21 can be suppressed, and the power consumption of the power supply circuit 1 can be suppressed.

  Further, since the voltage application unit 28 can generate a voltage to be applied to the gate of the NMOSFET 20 based on the voltage at the subsequent stage (output side) of the overvoltage protection circuit 11, it is possible to avoid a high withstand voltage of the voltage application unit 28.

  As described above, the power supply circuit 1 can limit the voltage input to the voltage conversion circuit 10 to less than the zener voltage Vz while suppressing power loss in the NMOSFET 20. Hereinafter, the configuration of the power supply circuit 1 will be described in more detail.

[2. Electronic device including power supply circuit 1]
Next, an electronic device having the power supply circuit 1 according to the embodiment will be described. Hereinafter, an example will be described in which the power supply circuit 1 is incorporated in a vehicle-mounted device (an example of an electronic device) and a DC voltage is supplied from the DC power supply 2 to the vehicle-mounted device.

  FIG. 2 is a diagram illustrating a configuration example of the vehicle-mounted device 100. As shown in FIG. 2, the in-vehicle device 100 includes a power supply circuit 1, a microcomputer 101 (hereinafter, referred to as a microcomputer 101), a flash memory 102, a drive motor 103, an amplifier 104, and the like. The in-vehicle device 100 is, for example, a car navigation device.

  The in-vehicle device 100 is supplied with an input voltage Vidc from a DC power supply 2 as a battery via a fuse 3. The power supply circuit 1 converts the input voltage Vidc into DC voltages Vodc1 and Vodc2 having different magnitudes. The DC voltage Vodc1 is supplied to the microcomputer 101, the flash memory 102, and the like, and the DC voltage Vodc2 is supplied to the drive motor 103, the amplifier 104, and the like.

  FIG. 3 is a diagram illustrating an example of a specific configuration of the power supply circuit 1 included in the vehicle-mounted device 100 illustrated in FIG. The power supply circuit 1 shown in FIG. 3 is an example of a specific configuration when the power supply circuit 1 shown in FIG. 1 is incorporated in the vehicle-mounted device 100, and is not limited to such a configuration. The power supply circuit 1 shown in FIG. 3 includes a voltage conversion circuit 10 and an overvoltage protection circuit 11.

[2.1. Voltage conversion circuit 10]
The voltage conversion circuit 10 includes a filter 30 and DC / DC converters 31 and 32 (an example of a plurality of voltage conversion units). The filter 30 includes a coil 40 and a capacitor 41, and removes a noise component included in the DC voltage Vidc1 output from the overvoltage protection circuit 11. Note that the filter 30 is not limited to the LC filter shown in FIG.

  The DC / DC converter 31 reduces the DC voltage Vidc1 input through the filter 30 to generate and output a DC voltage Vodc1 (hereinafter sometimes referred to as an output voltage Vodc1). The DC / DC converter 31 includes MOSFETs 51 and 52 (for example, N-channel MOSFETs), a coil 53, a capacitor 54, and a control unit 55.

  The control unit 55 turns on / off the MOSFET 51 and the MOSFET 52 alternately. When the MOSFET 51 is turned on, energy is stored in the coil 53, and when the MOSFET 52 is turned on, the energy stored in the coil 53 is output to the capacitor 54. The control unit 55 adjusts the on / off time of the MOSFETs 51 and 52 so that the output voltage Vodc1 becomes a set value.

  The DC / DC converter 32 generates a DC voltage Vodc2 (hereinafter sometimes referred to as an output voltage Vodc2) by stepping down the DC voltage Vidc1 input through the filter 30, and outputs the generated DC voltage Vodc2. The DC / DC converter 32 includes MOSFETs 61 and 62, a coil 63, a capacitor 64, and a control unit 65. In the DC / DC converter 32, as in the case of the DC / DC converter 31, the control unit 65 adjusts the on / off time of the MOSFETs 61 and 62 so that the output voltage Vodc2 becomes a set value.

[2.2. Overvoltage protection circuit 11]
The overvoltage protection circuit 11 includes an NMOSFET 20, a Zener diode 21, a switching diode 22, resistors 23 and 24, a capacitor 25, a rectifying diode 26, a transistor 27, and a voltage applying unit 28.

[2.2.1. NMOSFET 20 and Zener diode 21]
The drain of the NMOSFET 20 is connected to the input terminal T1, and the source of the NMOSFET 20 is connected to the input side of the voltage conversion circuit 10. A series connection circuit of a Zener diode 21 and a resistor 24 (an example of an abnormality detection resistor) is arranged between the gate of the NMOSFET 20 and the ground potential GND.

  In the example shown in FIG. 3, the cathode of the Zener diode 21 is connected to the gate of the NMOSFET 20. Further, the anode of the Zener diode 21 is connected to one end of the resistor 24, and the other end of the resistor 24 is connected to the ground potential GND.

[2.2.2. Switching diode 22 and resistor 23]
The switching diode 22 and the resistor 23 are connected in series, and are connected between the drain and the gate of the NMOSFET 20. Thus, when the voltage conversion circuit 10 is not operating, the input voltage Vidc can be applied to the gate of the NMOSFET 20 via the switching diode 22 and the resistor 23.

  Therefore, the DC voltage Vidc1 can be supplied to the voltage conversion circuit 10 via the NMOSFET 20. When the voltage drop of the resistor 23 is ignored, the voltage applied to the gate of the NMOSFET 20 is lower than the input voltage Vidc by the forward voltage Vf1 of the switching diode 22.

  Further, the switching diode 22 suppresses a current from flowing to the input terminal T1 side via the resistor 23 due to the voltage applied from the voltage application unit 28. Therefore, when a voltage is applied to the cathode of the Zener diode 21 from the voltage application unit 28, power consumption in the resistor 23 can be reduced. Note that, as shown in FIG. 1, a configuration in which the switching diode 22 is not provided may be employed.

[2.2.3. Capacitor 25]
Capacitor 25 is arranged between the gate of NMOSFET 20 and ground potential GND. With such a capacitor 25, it is possible to stabilize the gate voltage _{V G} of the NMOSFET 20.

[2.2.4. Rectifier diode 26]
The rectifying diode 26 is a protection element against a negative voltage surge, and can prevent the voltage conversion circuit 10 from breaking down even when the negative voltage surge is applied to the input terminal T1.

[2.2.5. Transistor 27]
The transistor 27 is turned on when the voltage across the resistor 24 becomes equal to or higher than the threshold voltage of the transistor 27. Therefore, for example, by adjusting the value of the resistor 24 so that the transistor 27 is turned on by the current flowing through the Zener diode 21 when a positive voltage surge occurs, the occurrence of the positive voltage surge can be easily detected. .

  For example, when the input voltage Vidc is a voltage higher than the voltage Ve (= Vz + Vf1), a current corresponding to a difference voltage between the input voltage Vidc and the voltage Ve flows through the resistors 23 and 24. Therefore, for example, by appropriately adjusting the ratio between the resistor 23 and the resistor 24, the occurrence of the positive voltage surge can be appropriately detected.

  Thus, the resistor 24 and the transistor 27 function as an overvoltage detection circuit. With such an overvoltage detection circuit, the occurrence of an overvoltage (for example, a positive voltage surge) can be easily notified to a control unit (for example, the microcomputer 101 shown in FIG. 2) of the vehicle-mounted device 100 having the power supply circuit 1.

  When notified of the occurrence of overvoltage from the overvoltage detection circuit, the control unit of the in-vehicle device 100 stops, for example, power supply to a display unit (not shown) or partially stops the operation of the display unit. Thereby, consumption of the power output from the power supply circuit 1 can be suppressed. Further, the control unit of the in-vehicle device 100 can also suppress the consumption of the power output from the power supply circuit 1 by stopping the DC / DC converter 32, for example.

Thus, when an overvoltage occurs, the drain of the NMOSFET 20 - even when the source voltage _{V DS} is increased to suppress the current flowing through the NMOSFET 20, it is possible to reduce power loss in the NMOSFET 20.

  Note that the overvoltage detection circuit is not limited to the one configured by the resistor 24 and the transistor 27. For example, the overvoltage detection circuit may use a magnetoelectric conversion element or a current transformer for detecting a current flowing through the Zener diode 21. The magnetoelectric conversion element is, for example, a Hall element. In addition, by configuring the overvoltage detection circuit with the resistor 24 and the transistor 27, the overvoltage detection circuit can be configured at low cost and easily as compared with the case where the voltage detection circuit is configured by a magnetoelectric conversion element or a current transformer.

[2.2.6. Voltage application unit 28]
The voltage application unit 28 includes switching diodes 71, 73, 75, 77, capacitors 72, 76, and resistors 74, 78.

  The switching diode 71 and the capacitor 72 function as a booster circuit (hereinafter, sometimes referred to as a first booster circuit) using the switching action of the DC / DC converter 31. The switching diode 75 and the capacitor 76 function as a booster circuit (hereinafter, sometimes referred to as a second booster circuit) by using the switching action of the DC / DC converter 32.

  The voltage Vudc1 boosted by the first boosting circuit (hereinafter referred to as boosted voltage Vudc1) is applied to the gate of the NMOSFET 20 via the switching diode 73 and the resistor 74. As a result, a voltage higher than the input voltage Vidc is applied to the gate of the NMOSFET 20.

  The voltage Vudc2 boosted by the second booster circuit (hereinafter, referred to as boosted voltage Vudc2) is applied to the gate of the NMOSFET 20 via the switching diode 77 and the resistor 78. As a result, a voltage higher than the input voltage Vidc is applied to the gate of the NMOSFET 20.

  In the example shown in FIG. 3, a boosted voltage Vudc1 (an example of the applied voltage Vudc) of the first booster circuit and a boosted voltage Vudc2 (an example of the applied voltage Vudc) of the second booster circuit are both connected via a switching diode and a resistor to a Zener diode. 21 is applied to the cathode. Therefore, for example, even when one of the DC / DC converters 31 and 32 is not operated, a voltage higher than the input voltage Vidc can be applied to the gate of the NMOSFET 20.

  When both the first booster circuit and the second booster circuit perform the boosting operation, the higher one of the boosted voltage Vudc1 and the boosted voltage Vudc2 is applied to the cathode of the Zener diode 21.

  Here, the operation of the first booster circuit will be described. Note that the operation of the second booster circuit is the same as the operation of the first booster circuit, and a description thereof will be omitted. In the following, it is assumed that the boosted voltage Vudc1 of the first booster circuit is lower than the boosted voltage Vudc2 of the second booster circuit, and that the ON voltages of the MOSFETs 51 and 52 are negligible.

  When the MOSFET 51 is off and the MOSFET 52 is on, one end of the capacitor 72 is connected to the ground potential GND, and the voltage Vc1 at the one end of the capacitor 72 becomes 0 V (ground potential). On the other hand, the output voltage Vodc1 is applied to the other end of the capacitor 72 via the switching diode 71. Therefore, the other end voltage Vc2 of the capacitor 72 becomes the same voltage as the difference voltage Vdif1 (= Vodc1−Vf2) between the output voltage Vodc1 and the forward voltage Vf2 of the switching diode 71. Therefore, the voltage Vc across the capacitor 72 becomes the same voltage as the difference voltage Vdif1.

  Thereafter, when the MOSFET 51 is turned on and the MOSFET 52 is turned off, the DC voltage Vidc1 is applied to one end of the capacitor 72 via the MOSFET 51, so that the voltage Vc1 at one end of the capacitor 72 becomes the same voltage as the DC voltage Vidc1. Since the voltage Vc across the capacitor 72 is the same voltage as the difference voltage Vdif1, when the voltage Vc1 at one end of the capacitor 72 becomes the DC voltage Vidc1, the voltage Vc2 at the other end of the capacitor 72 can be expressed as Vc2 = Vidc1 + Vodc1-Vf2.

  Since the MOSFETs 51 and 52 are repeatedly turned on / off at a predetermined switching cycle TA, the voltage Vc2 at the other end of the capacitor 72 is between the voltage VA (= Vodc1−Vf2) and the voltage VB (= Vidc1 + Vodc1−Vf2). Is changed alternately. Therefore, the voltage Va (= VA−Vf3) and the voltage Vb (= VB−Vf3) are alternately applied to the cathode of the Zener diode 21 in the ON / OFF cycle of the MOSFETs 51 and 52. Vf3 is a forward voltage of the switching diode 73.

  A capacitor 25 is connected to the cathode of the Zener diode 21. When the voltage Va and the voltage Vb are lower than the Zener voltage Vz, the current flowing through the Zener diode 21 is small. Therefore, the voltage on the cathode side of the Zener diode 21 becomes substantially equal to the voltage Vb (= Vidc1 + Vodc1-Vf2-Vf3) by the capacitor 25, and a voltage higher than the input voltage Vidc can be applied to the gate of the NMOSFET 20. It is assumed that Vidc <(Vidc1 + Vodc1-Vf2-Vf3).

  As described above, by applying a voltage higher than the input voltage Vidc to the gate of the NMOSFET 20, the NMOSFET 20 can be brought into a saturation state, and the loss of the NMOSFET 20 can be reduced.

  In the power supply circuit 1 shown in FIG. 3, since the first and second booster circuits are configured using the switching action of the DC / DC converter 31, the number of components and the cost can be reduced. Note that an example in which the voltage application unit 28 is formed by sharing a part of the voltage conversion circuit 10 is not limited to the configuration illustrated in FIG. 3 and may have another configuration. Also in this case, the number of parts and cost can be reduced.

  For example, the anodes of the switching diodes 71 and 75 may be connected to the output side (DC voltage Vidc1) of the overvoltage protection circuit 11, or may be connected between the filter 30 and the DC / DC converters 31 and 32. Also in this case, since the voltage application unit 28 can generate a voltage to be applied to the gate of the NMOSFET 20 based on the voltage at the subsequent stage of the overvoltage protection circuit 11, it is possible to avoid a high withstand voltage of the voltage application unit 28.

  Further, the first and second booster circuits are not limited to the configuration shown in FIG. That is, the first and second boosting circuits may be configured to generate a voltage higher than the input voltage Vidc.

  For example, a circuit for boosting the output voltage Vodc1 of the DC / DC converter 31 (for example, a boost chopper circuit or a boost DC / DC converter) is provided separately as a first booster circuit without sharing a part of the voltage conversion circuit 10. Is good. Further, a circuit for boosting the output voltage Vodc2 of the DC / DC converter 32 (for example, a boost chopper circuit or a boost DC / DC converter) may be provided as the second booster circuit without sharing a part of the voltage conversion circuit 10. Good.

  Further, a circuit (for example, a step-up chopper circuit or a step-up DC / DC converter) for boosting the DC voltage Vidc1 output from the overvoltage protection circuit 11 without sharing a part of the voltage conversion circuit 10 is provided by the first and second boosters. It may be provided as a circuit.

  In the above-described example, the DC / DC converters 31 and 32 are described as step-down voltage converters. However, the DC / DC converters 31 and 32 may be step-up voltage converters. In this case, if the output voltages Vodc1 and Vodc2 are higher than the input voltage Vidc by, for example, the forward voltage Vf3 or more, the switching diodes 71 and 75 and the capacitors 72 and 76 need not be provided.

  In this case, for example, in the voltage application unit 28, the output of the DC / DC converter 31 can be directly connected to the switching diode 73, and the output of the DC / DC converter 32 can be directly connected to the switching diode 77. The voltage conversion circuit 10 may be provided with three voltage conversion units that generate three or more types of output voltages, or may be configured to generate one output voltage.

[3. Operation of power supply circuit 1]
Next, the operation of the power supply circuit 1 will be described. Figure 4 is a diagram showing the gate voltage _{V G} of NMOSFET20 at startup, the state change of the DC voltage Vidc1 and output voltage Vodc1. It is assumed that Vidc = 24V, Vodc1 = 5V, Vf1 = Vf2 = Vf3 = 0.7V, and Vth1 = 3V, and that the DC / DC converter 32 is not operating. Further, for example, the on-voltage of the MOSFET 51 and the MOSFET 52 and the voltage drop of the resistors 23, 24, 74 and 78 are neglected.

As shown in FIG. 4, the input of the input voltage Vidc starts from the DC power supply 2, the gate voltage _{V G} of NMOSFET20 a forward voltage Vf1 only low voltage of the switching diode 22 than the input voltage Vidc _(V G = (Vidc-Vf1 = 23.3 V).

  Therefore, the DC voltage Vidc1 output from the overvoltage protection circuit 11 becomes lower than the input voltage Vidc by the forward voltage Vf1 and the threshold voltage Vth1 (Vidc1 = Vidc−Vf1−Vth1 = 20.3V).

  The DC / DC converter 31 starts the voltage conversion operation a predetermined period after the DC voltage Vidc1 output from the overvoltage protection circuit 11 becomes equal to or higher than a predetermined value, so that the output voltage Vodc1 becomes the set value V1 (= 5V). , The output voltage Vodc1 is increased.

When the output voltage Vodc1 rises, continue to increase the gate voltage _{V G} of the NMOSFET 20, the gate voltage _{V G} of the NMOSFET 20, becomes higher than the input voltage Vidc (= 24V). Further, the gate voltage _{V G} of the NMOSFET 20, become approximately 27.6V above the threshold voltage Vth1 of the NMOSFET 20 than the input voltage Vidc, the drain of the NMOSFET 20 - source voltage _{V DS} becomes substantially 0V. Therefore, the power loss in the NMOSFET 20 can be significantly reduced as compared with the case where the voltage application unit 28 is not provided.

Figure 5 is a diagram showing an input voltage Vidc, state change of the gate voltage _{V G} of the DC voltage Vidc1 and NMOSFET20 when pulsed surge voltage is input to the power supply circuit 1.

As shown in FIG. 5, when a pulse-like surge voltage (150 V in the example shown in FIG. 5) occurs at time t1, a pulse-like input voltage Vidc is input to the power supply circuit 1. In this case, the gate voltage _{V G} of NMOSFET20 is clamped by the Zener voltage Vz of the Zener diode 21.

  Therefore, the DC voltage Vidc1 input to the voltage conversion circuit 10 becomes a voltage lower than the Zener voltage Vz by the threshold voltage Vth1. Thus, the voltage conversion circuit 10 can be protected from a surge voltage.

When the in-vehicle device 100 is mounted on a commercial vehicle, for example, a load dump surge of about 150 V is input as a surge voltage. Therefore, when the Zener voltage Vz of the Zener diode 21 is set to 36V, the breakdown voltage (V _DSS ) of the NMOSFET 20 can be suppressed to about 120V.

  Further, even when the surge voltage is input to the power supply circuit 1 as the input voltage Vidc, the voltage supply from the overvoltage protection circuit 11 to the voltage conversion circuit 10 is continued. Can be suppressed. Therefore, it is not necessary to design in consideration of the avalanche breakdown voltage.

  As described above, the power supply circuit 1 according to the embodiment includes the overvoltage protection circuit 11 including the NMOSFET 20, the zener diode 21, and the voltage application unit 28. The NMOSFET 20 has a drain connected to the input terminal T1 (an example of an input side) and a source connected to the voltage conversion circuit 10 side. The Zener diode 21 is provided between the gate of the NMOSFET 20 and a ground potential GND (an example of a reference potential). The voltage application unit 28 applies a voltage higher than the input voltage Vidc (an example of an input-side voltage) to the gate of the NMOSFET 20.

  Thus, the voltage input to the voltage conversion circuit 10 can be limited to less than the Zener voltage Vz while suppressing the power loss in the NMOSFET 20. Further, power consumption in the vehicle-mounted device 100 (an example of an electronic device) including the power supply circuit 1 can be suppressed. Further, by setting the voltage applied to the gate of the NMOSFET 20 by the voltage applying unit 28 to be lower than the Zener voltage Vz of the Zener diode 21, the current flowing from the voltage applying unit 28 to the Zener diode 21 can be suppressed. Therefore, power consumption of the power supply circuit 1 can be suppressed.

  Further, the voltage applying unit 28 boosts the DC voltage Vodc1 or Vodc2 output from the voltage conversion circuit 10 or the DC voltage Vidc1 output from the overvoltage protection circuit 11, and generates and generates a voltage higher than the input voltage Vidc. A voltage is applied to the gate of NMOSFET 20. Thus, a voltage to be applied to the gate of the NMOSFET 20 can be generated based on the voltage at the subsequent stage of the overvoltage protection circuit 11, so that a high breakdown voltage of the voltage generation circuit can be avoided.

  Further, the voltage application unit 28 is configured by sharing a part of the voltage conversion circuit 10. Thus, for example, the number of components can be reduced, and downsizing and cost reduction can be achieved.

  Further, the voltage conversion circuit 10 includes a plurality of DC / DC converters 31 and 32 (an example of a plurality of voltage conversion units). The voltage application unit converts the DC voltages Vodc1 and Vodc2 output from the plurality of DC / DC converters 31 and 32, respectively, to a voltage higher than the input voltage Vidc and applies the voltage to the gate of the NMOSFET 20. Thus, for example, even when some of the plurality of DC / DC converters 31 and 32 are stopped, power is input to the voltage conversion circuit 10 while suppressing power loss in the NMOSFET 20. Voltage can be limited to less than the zener voltage Vz.

  The power supply circuit 1 includes a switching diode 22 and a resistor 23 connected in series between the input terminal T1 (an example of an input side) and the gate of the NMOSFET 20. Thereby, when a voltage is applied to the cathode of the Zener diode 21 from the voltage application unit 28, power consumption in the resistor 23 can be reduced.

  In addition, the power supply circuit 1 includes an overvoltage detection circuit that detects occurrence of an overvoltage based on a current flowing through the Zener diode 21. Thereby, for example, the occurrence of overvoltage can be easily notified to the control unit of the vehicle-mounted device 100 having the power supply circuit 1.

  Further, as an overvoltage detection circuit, a resistor 24 (an example of an abnormality detection resistor) connected in series with the Zener diode 21 between the gate of the NMOSFET 20 and the ground potential GND, and an overvoltage is detected based on the voltage of the resistor 24. And a transistor 27. As a result, overvoltage can be detected while suppressing costs.

  Further effects and modifications can be easily derived by those skilled in the art. Thus, the broader aspects of the present invention are not limited to the specific details and representative embodiments shown and described above. Accordingly, various modifications may be made without departing from the spirit or scope of the general inventive concept as defined by the appended claims and equivalents thereof.

DESCRIPTION OF SYMBOLS 1 Power supply circuit 2 DC power supply 10 Voltage conversion circuit 11 Overvoltage protection circuit 20 N-channel MOSFET
Reference Signs List 21 Zener diode 22 Switching diode 23, 24 Resistance 28 Voltage application unit 27 Transistor 31, 32 DC / DC converter (an example of a voltage conversion unit)
32 DC / DC converter 100 In-vehicle device (one example of electronic device)

Claims (6)

A voltage conversion circuit;
An overvoltage protection circuit arranged at a stage preceding the voltage conversion circuit,
The overvoltage protection circuit,
An N-channel MOSFET having a drain connected to the input side and a source connected to the voltage conversion circuit side;
A Zener diode provided between the gate of the N-channel MOSFET and a reference potential;
A voltage application unit that applies a voltage higher than the voltage on the input side to the gate of the N-channel MOSFET ,
The voltage application unit,
Boosting the DC voltage output from the voltage conversion circuit to generate a voltage higher than the voltage on the input side, applying the generated voltage to the gate of the N-channel MOSFET,
A power supply circuit configured to share a part of the voltage conversion circuit and to function as a booster circuit by using a switching action of the voltage conversion circuit. The voltage conversion circuit includes a plurality of voltage conversion units,
The voltage application unit,
The power supply circuit according to claim 1 , wherein the DC voltage output from each of the plurality of voltage conversion units is converted into a voltage higher than the voltage on the input side and applied to the gate of the N-channel MOSFET. A power supply circuit according to claim 1 or 2, characterized in that it comprises a and a diode connected resistor and between the input side to the gate. The power supply circuit according to any one of claims 1 to 3 , further comprising: an overvoltage detection circuit that detects occurrence of an overvoltage based on a current flowing through the zener diode. The overvoltage detection circuit,
An abnormality detection resistor connected in series with the Zener diode between the gate of the N-channel MOSFET and the reference potential;
The power supply circuit according to claim 4 , further comprising: a transistor that detects the overvoltage based on a voltage of the abnormality detection resistor. Electronic device characterized in that it comprises a power supply circuit according to any one of claims 1-5.

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