Surge protection circuit

Abstract

To provide a surge protection circuit with excellent manufacturability. [Solution] The surge protection circuit A of the present disclosure is a surge protection circuit A mounted on a vehicle C that prevents surges from being applied to a regulator 80 which is powered by a power supply B mounted on the vehicle C, and comprises a surge detection circuit D that detects surges from the power supply B, and a switching means S including a P-channel MOSFET 41 whose drain is connected to the input terminal which is the positive terminal of the regulator 80, whose source is connected to the power supply line BAT which is the positive terminal of the power supply B, and whose gate is connected to the surge detection circuit D.

Description

Technical Field

[0001] The present invention relates to a surge protection circuit.

Background Art

[0002] Conventionally, as a vehicle display device for displaying vehicle information such as vehicle speed and total mileage, there is, for example, a vehicle instrument disclosed in Patent Document 1. This vehicle display device is connected to a battery that can stably supply power, and uses this power to display various vehicle information. Further, the vehicle display device includes a vehicle power supply circuit and includes a feedback line (f) that connects a switching circuit (1) and a surge cut circuit (2).

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] In the conventional surge protection circuit used in the vehicle display device described in Patent Document 1, there is still room for improvement in improving the withstand voltage against the application of an abnormal voltage.

[0005] Therefore, an object of the present disclosure is to provide a surge protection circuit that focuses on the above problems and has improved withstand voltage against the application of an abnormal voltage.

Means for Solving the Problems

[0006] The surge protection circuit of the present disclosure is a surge protection circuit mounted on a vehicle for preventing a surge from being applied to a load circuit supplied with power from a power supply mounted on the vehicle, a surge detection circuit that detects a surge from the power supply, A switching means including a P-channel MOSFET, the drain of which is connected to the input terminal which is the positive terminal of the load circuit, the source of which is connected to the output terminal which is the positive terminal of the power supply, and the gate of which is connected to the surge detection circuit, Equipped with, The surge detection circuit described above is If no surge is input, the P-channel MOSFET is turned on. When the aforementioned surge is input, the P-channel MOSFET is turned off. The switching means further includes a parallel circuit connected in parallel with the P-channel MOSFET between the drain and the source. [Brief explanation of the drawing]

[0007] [Figure 1] A circuit diagram showing the electrical configuration of vehicle C according to the first embodiment of this disclosure. [Modes for carrying out the invention]

[0008] The vehicle display device equipped with the surge protection circuit of this disclosure will be described below with reference to the attached drawings.

[0009] [First Embodiment] Figure 1 is a circuit diagram showing some of the electrical components (electrical configuration) included in vehicle C. Vehicle C is a vehicle such as a four-wheeled automobile, motorcycle, or work vehicle (including agricultural and construction vehicles), but it may also be a mobile entity such as a ship or aircraft.

[0010] Vehicle C is equipped with a power supply B and a vehicle display device 10 (to the right of the dashed line in the drawing). Power supply B is composed of, for example, a battery or a generator, and in this disclosure is composed of, for example, a lead-acid battery, and supplies predetermined power to electrical components with a power supply voltage of 12.5V at its rated value. Power supply B is electrically connected to various electrical components installed in vehicle C and also supplies power to the vehicle display device 10, which is one of the electrical components.

[0011] The vehicle display device 10 includes a surge protection circuit A, a regulator 80, and a load circuit 90. The load circuit 90 includes a display unit 92 that displays vehicle information and a control unit 91 that controls the display of the display unit 92. The load circuit 90 performs predetermined operations, such as displaying vehicle status information and road environment information, based on power supplied from power supply B and electrical signals input from an information and communication system (not shown).

[0012] The display unit 92 includes a digital display unit using a liquid crystal display element and a backlight, and a pointer display unit that indicates the measured value by a pointer that rotates using a motor as power, and is controlled by the control unit 91. The regulator 80 is a circuit that supplies operating power to the control unit 91 and other components by stepping down the voltage to a predetermined voltage (for example, 5V) based on the power supply from the power supply B.

[0013] The control unit 91 can be a microcomputer powered by the regulator 80, and controls electronic components such as the liquid crystal display element, backlight, and motor of the display unit 92 based on vehicle information input via a cable (not shown).

[0014] Surge protection circuit A (within the roughly dashed frame) is electrically connected between power supply B and regulator 80 and load circuit 90, and transmits the power supplied by power supply B to regulator 80 and load circuit 90. Furthermore, surge protection circuit A, in the configuration described later, performs protective operation to prevent damage to regulator 80 and load circuit 90 when power supply B outputs an abnormal voltage (especially high voltage noise, surge). The protective operation by surge protection circuit A is basically realized by abnormal voltage detection operation by surge detection circuit D and cutoff operation by switch means D in response to the abnormal voltage detection operation.

[0015] The surge protection circuit A consists of printed wiring formed on a substrate and mounted electrical and electronic components. The surge protection circuit A may be formed on the same substrate as the regulator 80. The surge protection circuit A comprises a surge detection circuit D (within the dashed line frame) and a switching means S (within the dashed line frame).

[0016] The surge detection circuit D is connected between an input line Di connected to the power supply line BAT, an output line Do connected to the switch means S (particularly the gate of a P-channel MOSFET), a feedback line Df connected to the output line Lo of the surge protection circuit A, and the ground.

[0017] The abnormal voltage detection operation of the surge detection circuit D includes the following behavior. When the potential of the input line Di (power supply line BAT) is not within the normal range (for example, 15V or less), the surge detection circuit D outputs a cut-off signal (a signal that sets the gate-source voltage to the off potential in order to turn off the switch means (particularly the P-channel MOSFET 41)) via the output line Do.

[0018] When the potential of the input line Di (power supply line BAT) is within the normal range, the surge detection circuit D outputs a conduction signal (a signal that sets the gate-source voltage to the on potential in order to turn on the switch means S via the output line Do).

[0019] The surge detection circuit D performs the above-described detection operation by connecting the Zener diode 21, resistors 22, 23, and transistors 24, 25 as shown in the figure. However, this is merely an example, and the surge detection circuit may be realized by other electrical configurations that perform similar operations.

[0020] The switch means S switches the on and off of the power supply to the regulator 80 according to the cut-off signal and conduction signal output by the surge detection circuit D. When the cut-off signal is input, the switch means S stops the power supply to the regulator 80 by turning off the P-channel MOSFET as a cut-off operation.

[0021] The switch means S includes a P-channel MOSFET 41, resistors 42, 43, a transistor 44, a start switch 50, and a parallel path S1 (within the two-dot chain line frame).

[0022] The P-channel MOSFET 41 has its source connected to the power line BAT, its drain connected to the input terminal of the regulator 80, and its gate connected to the output line Do of the surge detection circuit D.

[0023] Transistor 44 is a switch element that turns surge protection circuit A on and off. The start switch 50 could be an ignition switch or the like, which triggers the starting and stopping of vehicle C.

[0024] However, the switching means S does not necessarily have to include the activation switch 50; it may suffice to have wiring connecting an external activation switch and transistor 44 so that the operation of the surge protection circuit A is switched on and off by transistor 44.

[0025] Furthermore, the transistor 44 is not necessarily required, and the surge protection circuit A may be configured to operate at all times by connecting the resistor 43 to ground without going through the transistor 44.

[0026] The parallel circuit S1 is connected in parallel to the source and drain of the P-channel MOSFET, and suppresses the surge current flowing through the P-channel MOSFET when a surge is applied from power supply B.

[0027] The parallel circuit S1 is composed of a circuit in which, for example, a diode 31 and a resistor 32 are connected in series. The diode is preferably a general rectifier diode with an absolute maximum reverse voltage rating of about 400V and an absolute maximum DC forward current rating of about 1A. The resistor 32 is preferably 100Ω with a rated power of about 0.5W.

[0028] The surge protection circuit A configured as described above can effectively prevent failures in the P-channel MOSFET 41 during the period when a surge is applied, thanks to the transfer characteristics of the P-channel MOSFET 41 and the action of the parallel circuit S1. Specifically, in this configuration, the gate-source voltage of the P-channel MOSFET 41 is kept below approximately 5V during the surge application period, thereby preventing failure of the P-channel MOSFET 41.

[0029] Another effect is that, since power is supplied to the regulator 80 via the parallel circuit S1 during the surge application period, fluctuations in the input voltage of the regulator 80 are reduced, improving the overall stability of the circuit.

[0030] Firstly, the surge protection circuit A of this disclosure is A surge protection circuit A is installed in vehicle C and prevents surges from being applied to load circuits 90 and regulators 80 that are powered by power supply B installed in vehicle C, A surge detection circuit D detects surges from power supply B, A switching means S includes a P-channel MOSFET 41 whose drain is connected to the input terminal which is the positive terminal of regulator 80, whose source is connected to power line BAT which is the positive terminal of power supply B, and whose gate is connected to surge detection circuit D (output line Do), Equipped with, Surge detection circuit A is, If no surge is input, the P-channel MOSFET 41 is turned ON. When a surge is input, the P-channel MOSFET 41 is turned off. The switching means S further includes a parallel circuit S1 connected in parallel with the P-channel MOSFET between the drain and the source.

[0031] Secondly, in the surge protection circuit A of this disclosure, the parallel circuit S1 is a series connection circuit in which a diode and a resistor are connected in series.

[0032] (modified version) Although the present invention has been described using the above-described embodiment as an example, the present invention is not limited thereto, and various improvements and design changes are possible in other configurations as long as they do not depart from the spirit of the invention.

[0033] Vehicle display devices are mounted, for example, on automobiles, motorcycles, or mobile vehicles equipped with agricultural or construction machinery. Surge protection circuits can be applied to these types of vehicle display devices.

[0034] Furthermore, surge protection circuits are not limited to vehicle display devices; they only need to be installed between the power supply and the load device mounted on the vehicle. For example, the load device can be a power device, motor device, display device, communication device, etc., but is not limited to these; any electrical device that operates based on power will suffice. [Explanation of symbols]

[0035] C Vehicle B power supply 10 Vehicle display devices A surge protection circuit D Surge Detection Circuit 21 Zener diode 22, 23 resistors 24,25 transistors S Switching Method 41 P-channel MOSFETs 42, 43 resistors 44 transistors 50 Start switch S1 parallel circuit 31 diodes 32 resistors 80 Regulator 90 Load circuit 91 Control Unit 92 Display section GND (Ground) BAT power line

Claims

1. A surge protection circuit mounted on a vehicle, which prevents surges from being applied to a load circuit that is powered by a power source mounted on the vehicle, A surge detection circuit for detecting surges from the aforementioned power supply, A switching means including a P-channel MOSFET, the drain of which is connected to the input terminal which is the positive terminal of the load circuit, the source of which is connected to the output terminal which is the positive terminal of the power supply, and the gate of which is connected to the surge detection circuit, Equipped with, The surge detection circuit described above is If the aforementioned surge is not input, the P-channel MOSFET is turned on. When the aforementioned surge is input, the P-channel MOSFET is turned off. The switching means further includes a parallel circuit connected in parallel with the P-channel MOSFET between the drain and the source. Surge protection circuit.

2. The aforementioned parallel circuit is a series connection circuit in which a diode and a resistor are connected in series. The surge protection circuit according to claim 1.

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