Surge protection circuit

Abstract

To provide a surge protection circuit excellent in manufacturability.SOLUTION: A surge protection circuit A1 includes: a load circuit 90 to which power is supplied from a power source B mounted in a vehicle C; a surge detection circuit 3 that detects that a surge is input from the power source B; and switch means 20 including an N-channel MOSFET that connects a drain to a load ground C_GND that is a negative electrode of the load circuit 90, a source to a power source negative electrode B_GND that is a negative electrode of the power source B, and a gate to the surge detection circuit 3. The surge detection circuit 3 turns off the switch means 20 when the surge is input from the power source B.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a surge protection circuit for supplying stable power to a load circuit that constitutes a vehicle display device. [Background technology]

[0002] Conventionally, a vehicle display device that displays vehicle information such as vehicle speed and cumulative mileage is disclosed, for example, in Patent Document 1. These vehicle display devices are connected to a battery that can supply a stable power supply, and display various vehicle information using this power supply. Also, various sensors mounted on the vehicle operate based on the power supply from the battery. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2016-152765 Summary of the Invention [Problem to be solved by the invention]

[0004] In a surge protection circuit used in a conventional vehicle display device described in Patent Document 1, a switching means made of a P-channel MOSFET is used. However, P-channel MOSFETs are relatively difficult to obtain, and there is room for improvement in manufacturability.

[0005] Therefore, an object of the present disclosure is to address the above-mentioned problems and to provide a surge protection circuit that is easy to manufacture. [Means for solving the problem]

[0006] The surge protection circuit of the present disclosure comprises: A surge protection circuit mounted on a vehicle, a load circuit supplied with power from a power source mounted on the vehicle; a surge detection circuit for detecting a surge from the power supply; a switch means consisting of an N-channel MOSFET, the drain of which is connected to a load ground that is the negative electrode of the load circuit, the source of which is connected to a power supply negative electrode that is the negative electrode of the power supply, and the gate of which is connected to the surge detection circuit; Equipped with The surge detection circuit turns off the N-channel MOSFET when the surge is input. [Brief explanation of the drawings]

[0007] [Figure 1] FIG. 1 is a diagram showing a circuit configuration according to a first embodiment of the present disclosure. [Figure 2] FIG. 10 is a diagram showing a circuit configuration according to a second embodiment of the present disclosure. DETAILED DESCRIPTION OF THE INVENTION

[0008] Hereinafter, a vehicle display device equipped with a surge protection circuit according to the present disclosure will be described in the following order with reference to the accompanying drawings. [First embodiment] [Second embodiment]

[0009] [First embodiment] FIG. 1 is a diagram showing the circuit configuration of a surge protection circuit A1 (within the rough dashed line) of a vehicle display device 1 (to the right of the two-dot chain line in the drawing), and shows the configuration up to the point where power is supplied from a power source B, which is a battery or generator of a vehicle C, to a load circuit 90 within the vehicle display device 1. The load circuit 90 includes a display unit 93 that displays vehicle information, a control unit 92 that controls the display unit 93, and a regulator 91. The load circuit 90 performs a predetermined operation based on the power supplied from the power source B and electrical signals input in connection with information communication.

[0010] The vehicle display device 1 includes a load circuit 90, and a surge protection circuit A1 is mounted on a circuit board for driving the load circuit 90. The display unit 93 includes a digital display unit using a liquid crystal display element and a backlight, and a pointer display unit that indicates measurement values ​​with a pointer that rotates using a motor as a drive source, and is controlled by a control unit 92. The regulator 91 is a circuit that reduces the power supply from a power source B to a predetermined voltage (e.g., 5 V) and supplies drive power to the control unit 92 and other components. The circuit board is provided inside the housing of the vehicle display device 1.

[0011] The control unit 92 can be a microcomputer driven by power from the regulator 91, and controls electronic components such as the liquid crystal display element, backlight, motor, etc. of the display unit 93 based on vehicle information input via a cable (not shown).

[0012] An alternator that uses the rotation of the engine, which is the vehicle's driving source, can be applied to the generator, which is an example of power source B. The battery is charged using the AC component from the generator, and also serves to provide a stable output from power source B. The battery can also output power even when the generator (engine) is not operating.

[0013] The vehicle display device 1 is connected to a power source B, and supplies power to a load circuit 90 including a regulator 91 and the like via a surge protection circuit A1.

[0014] The switch means 20 can be an N-channel MOSFET (field effect transistor), and switches between supplying and stopping power from the power supply B to the load circuit 90. To this end, the switch means 20 connects its gate to the surge detection circuit 3, its source to the negative pole of the power supply B (power supply negative pole B_GND), and its drain to the negative pole of the load circuit 90 (load ground C_GND). The switch means 20 is in the OFF state (no current flows from the load circuit 90 to the power supply B) when the gate-source voltage is less than a threshold, and is in the ON state (current flows from the load circuit 90 to the power supply B) when the gate-source voltage is equal to or greater than the threshold. In other words, these ON / OFF states are controlled by the surge detection circuit 3, which will be described later.

[0015] The surge detection circuit 3 is connected between a power supply positive terminal, which is the positive terminal of the power supply B, and a power supply negative terminal B_GND (also referred to as power supply ground), which is the negative terminal of the power supply B. The surge detection circuit 3 is also capable of adjusting the potential of the gate of the switch means 20, and switches the switch means 20 between on and off states. Under normal conditions, the surge detection circuit 3 maintains the switch means 20 in an on state. However, when the power supplied from the power supply B contains a surge (a voltage that momentarily exceeds the steady state), the surge detection circuit 3 switches the switch means 20 to an off state.

[0016] This prevents current from flowing from the load circuit 90 (load ground C_GND) to the power supply B (power supply negative electrode B_GND), thereby stopping the power supply from the power supply B and preventing an abnormal voltage from being excessively applied to the load circuit 90 due to a surge.

[0017] (1) The surge protection circuit A1 of the present disclosure includes: a load circuit 90 supplied with power from a power source B mounted on a vehicle C; a surge detection circuit 3 that detects a surge input from power supply B; a switch means 20 consisting of an N-channel MOSFET, the drain of which is connected to a load ground C_GND, which is the negative electrode of the load circuit 90, the source of which is connected to a power supply negative electrode B_GND, which is the negative electrode of the power supply B, and the gate of which is connected to the surge detection circuit 3; Equipped with When a surge is input from the power supply B, the surge detection circuit 3 turns off the switch means 20.

[0018] This configuration improves manufacturability by using N-channel MOSFETs, which have a higher supply than P-channel MOSFETs. Furthermore, N-channel MOSFETs have a higher rated current than P-channel MOSFETs, and therefore can better withstand surges. Furthermore, connecting the power supply negative terminal B_GND and the load ground C_GND via the N-channel MOSFET reduces the dark current that flows from the load ground C_GND to the power supply negative terminal B_GND when the switch means 20 is in the off state. Furthermore, compared to P-channel MOSFETs, N-channel MOSFETs generally have more types (models) in circulation and many types with higher current ratings, making it easier to realize surge protection circuits with higher rated currents, and therefore easier to manufacture.

[0019] [Second embodiment] The vehicle display device 10 according to the second embodiment will be described, focusing on the configuration that differs from the first embodiment.

[0020] 2, the vehicle display device 10 (to the right of the two-dot chain line in the drawing) includes a surge protection circuit A2 (inside the rough dashed line) and a load circuit 90. The vehicle display device 10 is electrically connected to the vehicle C via three wirings: an ignition line IGN, a power supply line BAT, and a power supply negative electrode B_GND.

[0021] The surge protection circuit A2 has a switch means 20, a surge detection circuit 30 (inside the thin dashed line), an ignition detection circuit 40 (inside the thin dashed line), diodes 71 and 72, an indeterminacy prevention circuit 81 (inside the thin dashed line), and a capacitor 82 (inside the thin dashed line).

[0022] Diodes 71 and 72 are protection circuits that prevent current from flowing in the opposite direction to normal at each input end of surge protection circuit A2, such as by reversing the connection of the terminals of power supply B, and connect the wiring from power supply B to the anode.

[0023] The ignition detection circuit 40 switches the switch means 20 between an on state and an off state depending on whether an ignition switch SW, which is a start switch of the vehicle C, is in an on state or an off state.

[0024] Specifically, the ignition detection circuit 40 is located between the ignition switch SW and the gate of the switch means 20, and when the ignition switch SW is in the on state, the ignition detection circuit 40 applies to the gate a voltage obtained by lowering the output voltage of the power supply B using a voltage dividing resistor or the like. When the ignition switch SW is in the off state, the ignition detection circuit 40 is in a high impedance state.

[0025] The surge detection circuit 30 includes Zener diodes 31a and 31b, resistors 32a and 32b, a transistor 33, and a Zener diode .

[0026] Similar to the surge detection circuit 3, when a surge is detected, the surge detection circuit 30 turns off the switch means 20. The threshold voltage that the surge detection circuit 30 regards as a surge is determined to a predetermined value by the Zener voltages of the Zener diodes 31a and 31b.

[0027] Resistors 32a and 32b form a voltage divider and are provided to reduce the voltage and current generated by the surge to a level that the base of transistor 33 can tolerate.

[0028] A PNP transistor can be used as the transistor 33, which switches the on and off states of the switch means 20 in response to the occurrence of a surge. The transistor 33 is in the off state during normal times when no surge is occurring, and is in the on state when a surge occurs. When the transistor 33 is in the on state, the collector and emitter of the transistor 33 are short-circuited, and the gate of the switch means 20 has the same potential as the negative power supply B_GND, so that the switch means 20 is in the off state.

[0029] The Zener diode 34 has an anode connected to the gate of the switch means 20 and a cathode connected to the source of the switch means 20. The Zener diode 34 plays a role in clamping the gate-source voltage (Vgs) of the switch means 20, which is an N-channel MOSFET, to a voltage that does not exceed the absolute maximum rating when an overvoltage or static electricity is applied.

[0030] An electrolytic capacitor connected between the power supply line BAT and the load ground C_GND can be used as the capacitor 82. The capacitor 82 is used to maintain power when the power supply is cut off, and can supply power to a load circuit 90 such as a regulator while the power supply B is stopped by the switch means 20. The capacitor 82 can have an optimum capacity based on the expected magnitude of the inrush current and the holding time required to supply sufficient power to the load circuit 90. The capacitor 82 may be a plurality of electrolytic capacitors connected in parallel, or a ceramic capacitor may be used.

[0031] The instability prevention circuit 81 prevents the potential of the load ground C_GND from becoming unstable when the switch means 20 is in the off state. The instability prevention circuit 81 is connected between the output terminal of the surge protection circuit A2 and the load ground C_GND. The instability prevention circuit 81 is configured by connecting an instability prevention resistor and a normally closed element (NC element, such as a contactless relay or FET) in series. The instability prevention circuit 81 is controlled by the downstream load circuit 90 (particularly the control unit 92, etc.) to be in a closed state when the power supply line BAT, the power supply negative electrode B_GND, and the load ground C_GND are in an open state.

[0032] (2) The surge protection circuit A2 of the present disclosure includes: The vehicle C further includes an ignition detection circuit 40 for detecting whether an ignition switch SW of the vehicle C is in an on state or an off state. The switch means 20 is in an ON state when no surge is detected and the ignition switch SW is in an ON state.

[0033] According to this configuration, when the ignition switch SW of the vehicle C is turned on, the switch means 20 can short-circuit the load ground C_GND and the power supply negative electrode B_GND.

[0034] (3) The surge protection circuit A2 of the present disclosure includes: The power supply further includes an instability prevention circuit 81 that prevents the potential of the load ground C_GND from becoming instability when the switch means 20 is in the off state.

[0035] According to this configuration, even if the power supply line BAT and the power supply negative electrode B_GND are open, it is possible to prevent the potential of the load ground C_GND from becoming unstable.

[0036] (Variation) Although the present invention has been described using the above-described embodiment as an example, the present invention is not limited to this, and it goes without saying that various improvements and design changes are possible in other configurations as long as they do not deviate from the gist of the present invention.

[0037] Vehicle display devices are mounted on vehicles such as automobiles, motorcycles, agricultural machinery, and construction machinery, and the surge protection circuit can be applied to these types of vehicle display devices.

[0038] Furthermore, the surge protection circuit is not limited to being installed in a vehicle display device, but may be installed between a power supply and a load device installed in the vehicle. For example, the load device may be a power device, a power unit, a display device, a communication device, etc., but is not limited to these, and may be any electrical device that operates based on electric power. [Explanation of symbols]

[0039] C vehicle B Power supply 1. Vehicle display device A1, A2 surge protection circuit 20 MOSFET (an example of a switching means) 3,30 Surge detection circuit 31a, 31b Zener diode 32a,32b resistance 33 Transistor 34 Zener diode 40 Ignition detection circuit 71,72 Diodes 81 Undefined prevention circuit 82 Capacitor 90 Load circuit 91 Regulator 92 Control Unit 93 Display section C_GND Load ground B_GND Power supply negative pole IGN Ignition line BAT power line

Claims

1. A surge protection circuit mounted on a vehicle, a load circuit supplied with power from a power source mounted on the vehicle; a surge detection circuit for detecting a surge from the power supply; a switch means consisting of an N-channel MOSFET, the drain of which is connected to a load ground that is the negative electrode of the load circuit, the source of which is connected to a power supply negative electrode that is the negative electrode of the power supply, and the gate of which is connected to the surge detection circuit; Equipped with The surge detection circuit turns off the N-channel MOSFET when the surge is input. Surge protection circuit.

2. an ignition detection circuit for detecting whether an ignition switch of the vehicle is in an on state or an off state; The switch means is turned on when the surge is not detected and the ignition switch is on.

2. The surge protection circuit of claim 1.

3. The load ground potential is prevented from becoming unstable when the switch means is in an OFF state.

2. The surge protection circuit of claim 1.

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